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Publisher: Elsevier   (Total: 3160 journals)

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Showing 1 - 200 of 3160 Journals sorted alphabetically
Academic Pediatrics     Hybrid Journal   (Followers: 37, SJR: 1.655, CiteScore: 2)
Academic Radiology     Hybrid Journal   (Followers: 25, SJR: 1.015, CiteScore: 2)
Accident Analysis & Prevention     Partially Free   (Followers: 97, SJR: 1.462, CiteScore: 3)
Accounting Forum     Hybrid Journal   (Followers: 28, SJR: 0.932, CiteScore: 2)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 37, SJR: 1.771, CiteScore: 3)
Achievements in the Life Sciences     Open Access   (Followers: 5)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 7)
Acta Astronautica     Hybrid Journal   (Followers: 427, SJR: 0.758, CiteScore: 2)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 2)
Acta Biomaterialia     Hybrid Journal   (Followers: 28, SJR: 1.967, CiteScore: 7)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription   (Followers: 3)
Acta de Investigación Psicológica     Open Access   (Followers: 3)
Acta Ecologica Sinica     Open Access   (Followers: 10, SJR: 0.18, CiteScore: 1)
Acta Haematologica Polonica     Free   (Followers: 1, SJR: 0.128, CiteScore: 0)
Acta Histochemica     Hybrid Journal   (Followers: 3, SJR: 0.661, CiteScore: 2)
Acta Materialia     Hybrid Journal   (Followers: 288, SJR: 3.263, CiteScore: 6)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 6, SJR: 0.504, CiteScore: 1)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.542, CiteScore: 1)
Acta Oecologica     Hybrid Journal   (Followers: 12, SJR: 0.834, CiteScore: 2)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription  
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 2, SJR: 0.307, CiteScore: 0)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 1, SJR: 1.793, CiteScore: 6)
Acta Poética     Open Access   (Followers: 4, SJR: 0.101, CiteScore: 0)
Acta Psychologica     Hybrid Journal   (Followers: 27, SJR: 1.331, CiteScore: 2)
Acta Sociológica     Open Access   (Followers: 1)
Acta Tropica     Hybrid Journal   (Followers: 6, SJR: 1.052, CiteScore: 2)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 3, SJR: 0.374, CiteScore: 1)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 2)
Actas Urológicas Españolas     Full-text available via subscription   (Followers: 3, SJR: 0.344, CiteScore: 1)
Actas Urológicas Españolas (English Edition)     Full-text available via subscription   (Followers: 1)
Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 7, SJR: 0.19, CiteScore: 0)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 3)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 8)
Acute Pain     Full-text available via subscription   (Followers: 15, SJR: 2.671, CiteScore: 5)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.53, CiteScore: 4)
Addictive Behaviors     Hybrid Journal   (Followers: 17, SJR: 1.29, CiteScore: 3)
Addictive Behaviors Reports     Open Access   (Followers: 9, SJR: 0.755, CiteScore: 2)
Additive Manufacturing     Hybrid Journal   (Followers: 11, SJR: 2.611, CiteScore: 8)
Additives for Polymers     Full-text available via subscription   (Followers: 23)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 174, SJR: 4.09, CiteScore: 13)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 12, SJR: 1.167, CiteScore: 4)
Advanced Powder Technology     Hybrid Journal   (Followers: 17, SJR: 0.694, CiteScore: 3)
Advances in Accounting     Hybrid Journal   (Followers: 9, SJR: 0.277, CiteScore: 1)
Advances in Agronomy     Full-text available via subscription   (Followers: 16, SJR: 2.384, CiteScore: 5)
Advances in Anesthesia     Full-text available via subscription   (Followers: 28, SJR: 0.126, CiteScore: 0)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 2)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 10, SJR: 0.992, CiteScore: 1)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 11, SJR: 1.551, CiteScore: 4)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 24, SJR: 2.089, CiteScore: 5)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 14, SJR: 0.572, CiteScore: 2)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.61, CiteScore: 7)
Advances in Botanical Research     Full-text available via subscription   (Followers: 2, SJR: 0.686, CiteScore: 2)
Advances in Cancer Research     Full-text available via subscription   (Followers: 32, SJR: 3.043, CiteScore: 6)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 9, SJR: 1.453, CiteScore: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 1.992, CiteScore: 5)
Advances in Cell Aging and Gerontology     Full-text available via subscription   (Followers: 4)
Advances in Cellular and Molecular Biology of Membranes and Organelles     Full-text available via subscription   (Followers: 14)
Advances in Chemical Engineering     Full-text available via subscription   (Followers: 28, SJR: 0.156, CiteScore: 1)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 10, SJR: 0.713, CiteScore: 1)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 10, SJR: 1.316, CiteScore: 2)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 26, SJR: 1.562, CiteScore: 3)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 20, SJR: 1.977, CiteScore: 8)
Advances in Computers     Full-text available via subscription   (Followers: 14, SJR: 0.205, CiteScore: 1)
Advances in Dermatology     Full-text available via subscription   (Followers: 15)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 13)
Advances in Digestive Medicine     Open Access   (Followers: 11)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 7)
Advances in Drug Research     Full-text available via subscription   (Followers: 26)
Advances in Ecological Research     Full-text available via subscription   (Followers: 43, SJR: 2.524, CiteScore: 4)
Advances in Engineering Software     Hybrid Journal   (Followers: 29, SJR: 1.159, CiteScore: 4)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 8)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 49, SJR: 5.39, CiteScore: 8)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 1)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 9)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 61, SJR: 0.591, CiteScore: 2)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 17)
Advances in Genetics     Full-text available via subscription   (Followers: 20, SJR: 1.354, CiteScore: 4)
Advances in Genome Biology     Full-text available via subscription   (Followers: 10, SJR: 12.74, CiteScore: 13)
Advances in Geophysics     Full-text available via subscription   (Followers: 6, SJR: 1.193, CiteScore: 3)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 24, SJR: 0.368, CiteScore: 1)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 12, SJR: 0.749, CiteScore: 3)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 23)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 2, SJR: 0.193, CiteScore: 0)
Advances in Immunology     Full-text available via subscription   (Followers: 36, SJR: 4.433, CiteScore: 6)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 10, SJR: 1.163, CiteScore: 2)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 2, SJR: 1.938, CiteScore: 3)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 6, SJR: 0.176, CiteScore: 0)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 3)
Advances in Life Course Research     Hybrid Journal   (Followers: 8, SJR: 0.682, CiteScore: 2)
Advances in Lipobiology     Full-text available via subscription   (Followers: 1)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 8)
Advances in Marine Biology     Full-text available via subscription   (Followers: 18, SJR: 0.88, CiteScore: 2)
Advances in Mathematics     Full-text available via subscription   (Followers: 11, SJR: 3.027, CiteScore: 2)
Advances in Medical Sciences     Hybrid Journal   (Followers: 7, SJR: 0.694, CiteScore: 2)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 5)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 4, SJR: 1.158, CiteScore: 3)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 23)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 8)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 7, SJR: 0.182, CiteScore: 0)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 4)
Advances in Oncobiology     Full-text available via subscription   (Followers: 2)
Advances in Organ Biology     Full-text available via subscription   (Followers: 2)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 17, SJR: 1.875, CiteScore: 4)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7, SJR: 0.174, CiteScore: 0)
Advances in Parasitology     Full-text available via subscription   (Followers: 5, SJR: 1.579, CiteScore: 4)
Advances in Pediatrics     Full-text available via subscription   (Followers: 25, SJR: 0.461, CiteScore: 1)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 12)
Advances in Pharmacology     Full-text available via subscription   (Followers: 16, SJR: 1.536, CiteScore: 3)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 8, SJR: 0.574, CiteScore: 1)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.109, CiteScore: 1)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 10)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 5)
Advances in Porous Media     Full-text available via subscription   (Followers: 5)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 19)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 20, SJR: 0.791, CiteScore: 2)
Advances in Psychology     Full-text available via subscription   (Followers: 66)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 6, SJR: 0.371, CiteScore: 1)
Advances in Radiation Oncology     Open Access   (Followers: 1, SJR: 0.263, CiteScore: 1)
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 3, SJR: 0.101, CiteScore: 0)
Advances in Space Biology and Medicine     Full-text available via subscription   (Followers: 6)
Advances in Space Research     Full-text available via subscription   (Followers: 413, SJR: 0.569, CiteScore: 2)
Advances in Structural Biology     Full-text available via subscription   (Followers: 5)
Advances in Surgery     Full-text available via subscription   (Followers: 12, SJR: 0.555, CiteScore: 2)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 35, SJR: 2.208, CiteScore: 4)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 19)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 15)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 2.262, CiteScore: 5)
Advances in Water Resources     Hybrid Journal   (Followers: 49, SJR: 1.551, CiteScore: 3)
Aeolian Research     Hybrid Journal   (Followers: 6, SJR: 1.117, CiteScore: 3)
Aerospace Science and Technology     Hybrid Journal   (Followers: 362, SJR: 0.796, CiteScore: 3)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.42, CiteScore: 2)
African J. of Emergency Medicine     Open Access   (Followers: 6, SJR: 0.296, CiteScore: 0)
Ageing Research Reviews     Hybrid Journal   (Followers: 11, SJR: 3.671, CiteScore: 9)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 470, SJR: 1.238, CiteScore: 3)
Agri Gene     Hybrid Journal   (Followers: 1, SJR: 0.13, CiteScore: 0)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 17, SJR: 1.818, CiteScore: 5)
Agricultural Systems     Hybrid Journal   (Followers: 31, SJR: 1.156, CiteScore: 4)
Agricultural Water Management     Hybrid Journal   (Followers: 43, SJR: 1.272, CiteScore: 3)
Agriculture and Agricultural Science Procedia     Open Access   (Followers: 4)
Agriculture and Natural Resources     Open Access   (Followers: 3)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 58, SJR: 1.747, CiteScore: 4)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.589, CiteScore: 3)
Air Medical J.     Hybrid Journal   (Followers: 6, SJR: 0.26, CiteScore: 0)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.19, CiteScore: 0)
Alcohol     Hybrid Journal   (Followers: 12, SJR: 1.153, CiteScore: 3)
Alcoholism and Drug Addiction     Open Access   (Followers: 11)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 2, SJR: 0.604, CiteScore: 3)
Alexandria J. of Medicine     Open Access   (Followers: 1, SJR: 0.191, CiteScore: 1)
Algal Research     Partially Free   (Followers: 11, SJR: 1.142, CiteScore: 4)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 2)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.504, CiteScore: 1)
Allergology Intl.     Open Access   (Followers: 5, SJR: 1.148, CiteScore: 2)
Alpha Omegan     Full-text available via subscription   (SJR: 3.521, CiteScore: 6)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 10, SJR: 0.201, CiteScore: 1)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 52, SJR: 4.66, CiteScore: 10)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 4, SJR: 1.796, CiteScore: 4)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 4, SJR: 1.108, CiteScore: 3)
Ambulatory Pediatrics     Hybrid Journal   (Followers: 6)
American Heart J.     Hybrid Journal   (Followers: 57, SJR: 3.267, CiteScore: 4)
American J. of Cardiology     Hybrid Journal   (Followers: 62, SJR: 1.93, CiteScore: 3)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 44, SJR: 0.604, CiteScore: 1)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 11)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 13, SJR: 1.524, CiteScore: 3)
American J. of Human Genetics     Hybrid Journal   (Followers: 34, SJR: 7.45, CiteScore: 8)
American J. of Infection Control     Hybrid Journal   (Followers: 29, SJR: 1.062, CiteScore: 2)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 35, SJR: 2.973, CiteScore: 4)
American J. of Medicine     Hybrid Journal   (Followers: 48)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3, SJR: 1.967, CiteScore: 2)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 231, SJR: 2.7, CiteScore: 4)
American J. of Ophthalmology     Hybrid Journal   (Followers: 66, SJR: 3.184, CiteScore: 4)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 5, SJR: 0.265, CiteScore: 0)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.289, CiteScore: 1)
American J. of Otolaryngology     Hybrid Journal   (Followers: 25, SJR: 0.59, CiteScore: 1)
American J. of Pathology     Hybrid Journal   (Followers: 29, SJR: 2.139, CiteScore: 4)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 28, SJR: 2.164, CiteScore: 4)
American J. of Surgery     Hybrid Journal   (Followers: 39, SJR: 1.141, CiteScore: 2)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 12, SJR: 0.767, CiteScore: 1)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 7)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.144, CiteScore: 3)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 63, SJR: 0.138, CiteScore: 0)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 20, SJR: 0.411, CiteScore: 1)
Anales de Cirugia Vascular     Full-text available via subscription   (Followers: 1)
Anales de Pediatría     Full-text available via subscription   (Followers: 3, SJR: 0.277, CiteScore: 0)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription  
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 5, SJR: 4.849, CiteScore: 10)
Analytica Chimica Acta     Hybrid Journal   (Followers: 44, SJR: 1.512, CiteScore: 5)
Analytica Chimica Acta : X     Open Access  
Analytical Biochemistry     Hybrid Journal   (Followers: 199, SJR: 0.633, CiteScore: 2)
Analytical Chemistry Research     Open Access   (Followers: 12, SJR: 0.411, CiteScore: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 14)
Anesthésie & Réanimation     Full-text available via subscription   (Followers: 2)
Anesthesiology Clinics     Full-text available via subscription   (Followers: 23, SJR: 0.683, CiteScore: 2)
Angiología     Full-text available via subscription   (SJR: 0.121, CiteScore: 0)
Angiologia e Cirurgia Vascular     Open Access   (Followers: 1, SJR: 0.111, CiteScore: 0)
Animal Behaviour     Hybrid Journal   (Followers: 206, SJR: 1.58, CiteScore: 3)
Animal Feed Science and Technology     Hybrid Journal   (Followers: 6, SJR: 0.937, CiteScore: 2)

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Similar Journals
Journal Cover
Aerospace Science and Technology
Journal Prestige (SJR): 0.796
Citation Impact (citeScore): 3
Number of Followers: 362  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1270-9638
Published by Elsevier Homepage  [3160 journals]
  • AC Plasma Retarded Flame Spread over Thin Solid Fuels in a Simulated
           Microgravity Environment
    • Abstract: Publication date: Available online 24 May 2019Source: Aerospace Science and TechnologyAuthor(s): Zihan Wang, Qi Chen, Xingqian Mao The flame spread over thin solid fuels in a narrow channel by the action of AC plasma was first proposed and reported to show a trade-off between the flame instability produced by ionic wind and the kinetic enhancement stimulated by energetic and chemically active species. The 6mm height narrow channel apparatus has been demonstrated the ability to suppress buoyant flow in horizontally spreading flames, and can successfully simulate a microgravity environment. Plasma acted on flame spread over thin solid fuels led to a confined behavior not typically seen in previous researches, which was investigated by integrated studies of experiment and supporting analysis using BOLSIG+. Four primary variables including flow velocity, reduced electric field, oxygen concentration and electrode length were considered. Among them, the reduced electric field and the oxygen concentration were found the crucial factors affecting the flame spread and further the flammability limit. The experimental results showed the affected field of the flame spread matched the field acted by AC discharge, which suggested a one-to-one correspondence between AC plasma action and flame slowing down or extinguishing. The results also showed that the narrow channel apparatus could capture the essential features of the flame spread in a simulated microgravity, for example the flame-lets phenomenon. The dependence of ionic wind on the reduced electric field was additionally investigated by solving the electron energy deposition into different excited channels and the electron energy distribution function (EEDF), which was essentially in agreement with the experimental observations. This study would develop a new and successful tool with rapid control of spacecraft fire and response to future exploration vehicles.
  • Experimental study on the effects of simulated flight conditions on
           ignition and flame stabilization in a supersonic combustor
    • Abstract: Publication date: Available online 23 May 2019Source: Aerospace Science and TechnologyAuthor(s): Lang Li, Wenyou Qiao Effects of simulated flight conditions on ignition and flame stabilization in a kerosene fueled scramjet combustor were experimentally investigated in the present paper. Simulated flight conditions were Mach 4.5 and Mach 4.0, and the isolator entrance Mach number was 2.0. Wall pressure and flame emission were made during the experiments in an attempt to better understand the combustion characteristics, air throttling was used to enhance the flame stabilization. The results showed that, the kerosene ignition was achieved successfully under the Mach 4.5 flight condition, that of Mach 4.0 flight condition was blowout before the kerosene pressure reached the max pressure. The flame in the combustor without air throttling during Mach 4.0 flight condition only existed in the cavity and near the top wall before it was blown off, that of Mach 4.5 flight condition had spread into the isolator. The flame stabilization was also only achieved under the Mach 4.5 flight condition with the aid of air throttling, the flame in the combustor with air throttling during the Mach 4.0 flight condition was blowout before the throttling air was removed. Ignition and flame stabilization were easy to be achieved under the higher flight condition.
  • Identification of All the Inertial Parameters of a Non-cooperative Object
           in Orbit
    • Abstract: Publication date: Available online 23 May 2019Source: Aerospace Science and TechnologyAuthor(s): Qingliang Meng, Jianxun Liang, Ou Ma Knowing the dynamic properties of a non-cooperative spacecraft is critical for robotic capture and service in orbit. However, using visual observation alone is not sufficient to identify all the inertial parameters (the mass, mass center location, and inertia matrix) of an unknown target object. This paper presents a method to fully identify all the inertial parameters of a non-cooperative object in orbit with data from visual and force-moment sensors. We propose to use a flexible rod to change a target's movement, which is a prerequisite to identify the true values of the target's dynamic properties. A novel algorithm for processing the collected force and torque data is introduced, which reduces the effect of noise on the identification accuracy. Simulation results have shown that for a large target, we only need to apply a very small force to completely identify all the inertial parameters with an acceptable error in the presence of sensor measurement errors as well as a rough initial guess.
  • Integrated thermal protection system based on C/SiC composite corrugated
           core sandwich plane structure
    • Abstract: Publication date: Available online 23 May 2019Source: Aerospace Science and TechnologyAuthor(s): Ying Li, Lu Zhang, Rujie He, Yongbin Ma, Keqiang Zhang, Xuejian Bai, Baosheng Xu, Yanfei Chen A combined theoretical, numerical and experimental investigation of the integrated thermal protection system based on C/SiC composite corrugated core sandwich plane structure was conducted. Corrugated core sandwich plane structure was made from carbon fiber reinforced silicon carbide composite by a hot compression molding combined with precursor infiltration and pyrolysis method. The equivalent thermal conductivity prediction method for the C/SiC composite corrugated core sandwich plane was developed, and its heat transferring behavior was numerical analyzed. Based on the theory and numerical analysis, a novel integrated thermal protection system, which was consisted of three parts: C/SiC composite corrugated core sandwich plane, insulated aerogel filling in the core, and insulated aerogel adhering onto the down surface of the down facesheet, was designed, manufactured and examined by simulated atmospheric re-entry wind tunnel test. It was believe that this novel design of integrated thermal protection system is a potential thermal protection system for the next generation hypersonic flights.
  • On the performance of a body integrated diverterless supersonic inlet
    • Abstract: Publication date: Available online 23 May 2019Source: Aerospace Science and TechnologyAuthor(s): M.R. Soltani, R. Askari Extensive experimental investigations on a body integrated Diverterless Supersonic Inlet (DSI) were conducted. These inlets are implemented for both supersonic flow compression and boundary layer diversion using a three- dimensional bump in combination with a suitable cowl lip. Experiments were performed at a free stream Mach number of 1.65, the design Mach number, and at zero degrees angle of attack and zero degrees sideslip angle. To recreate the operational conditions more accurately and have a realistic performance characteristic, the intake was integrated with a fuselage and a forebody nose with an elliptical cross-section. Wind tunnel tests were conducted at critical, subcritical and supercritical operating conditions where DSI operates in its stable states. The results showed that the present DSI had acceptable performance characteristics in the stable operating conditions and provides the required mass flow and static pressure compression ratio. In addition, it has a wide stable subcritical operating condition. Moreover, a relatively different behavior in the DSI performance curve is evident due to its body integrated geometry and 3D configuration of the bump and cowl lip, especially in the supercritical conditions.
  • Nussbaum gain adaptive control scheme for moving mass reentry hypersonic
           vehicle with actuator saturation
    • Abstract: Publication date: Available online 22 May 2019Source: Aerospace Science and TechnologyAuthor(s): Haolan Chen, Jun Zhou, Min Zhou, Bin Zhao This paper addresses an actuator saturation problem of the moving mass hypersonic vehicles (HSVs) in the reentry phase. The saturation nonlinearity is modeled using a hyperbolic tangent function and the concomitant time-varying coefficients problem is handled via Nussbaum gain technique. Then backstepping technique is applied in control design and the explosion of complexity in traditional backstepping design is avoided by utilizing dynamic surface control. Subsequently, a Nussbaum gain adaptive controller is constructively framed to deal with the actuator saturation. Based on the disturbance observers, the robustness of the proposed controller is enhanced. The semiglobal stability of the closed-loop system is ensured via Lyapunov synthesis. Finally, numerical simulation results are presented to show the effectiveness of the designed control scheme.
  • A comparative study of multi-objective expected improvement for
           aerodynamic design
    • Abstract: Publication date: Available online 22 May 2019Source: Aerospace Science and TechnologyAuthor(s): Lavi Rizki Zuhal, Pramudita Satria Palar, Koji Shimoyama Multi-objective optimization in aerodynamics plays an important role in revealing trade-offs between conflicting objectives in order to discover important knowledge and insight for better future design. Of interest here is the use of Kriging surrogate models incorporated into a sequential Bayesian optimization (BO) strategy. In this paper, we studied four variants of multi-objective BO (MOBO) techniques that are based on expected improvement, that is, Euclidean-based EI (EEI), expected hypervolume improvement (EHVI), ParEGO, and expected inverted penalty boundary intersection improvement (EIPBII) to understand their capabilities on handling multi-objective aerodynamic optimization problems. Numerical tests were performed on a set consisting of six generalized Schaffer problems (GSP), five low-fidelity, and one high-fidelity airfoil design problems. Results suggest that EHVI is the only method which consistently performed well on artificial and aerodynamic problems. EEI yields the worst performance and is not suitable to deal with various problem complexities. ParEGO, although it performs modestly on GSP problem, surprisingly works well on the low- and high-fidelity problems. On the other hand, EIPBII encounters the opposite case, where it is one of the best performer on GSP but yields modest performance on the aerodynamic problems. In light of the results, we suggest that EHVI is a highly potential MOBO method to be applied for multi-objective aerodynamic design optimization.
  • Multi-objective design of optimal higher order sliding mode control for
           robust tracking of 2-DoF helicopter system based on metaheuristics
    • Abstract: Publication date: Available online 22 May 2019Source: Aerospace Science and TechnologyAuthor(s): Wafa Boukadida, Anouar Benamor, Hassani Messaoud, Patrick Siarry This paper deals with the trajectory tracking of a 2 Degrees of Freedom (DoF) helicopter system. The control strategy is designed by the combination of the robust control strategy (Higher Order-Sliding Mode Control (HO-SMC)) and the optimal control technique (Linear Quadratic Regulator (LQR)). Combining these two methods lies in the fact that the robust controllers tackle the uncertainties when the optimal controller performances are unaffected. As the performances of the Sliding Mode Control (SMC) greatly depends on the choice of the sliding surface, a novel method based on the solution of a Sylvester equation is proposed. Furthermore, the problem of deciding the optimal configuration of the LQR controller as well as the gain of the discontinuous control is considered as an optimization problem, which can be solved by the application of an efficient metaheuristic. The adequacy of the specific choice of the discontinuous gain is exhibited through general analysis. The main contribution of this paper is to consider a multi-objective optimization problem. For that, a novel dynamically aggregated objective function is proposed. As a result, a set of non-dominated optimal solutions are provided to the designer and then he selects the most preferable alternative. The proposed control strategy is applied for pitch and yaw axes control of the Quanser helicopter. Experimental results substantiate that the combination of the HO-SMC with the LQR method and metaheuristics results in not only reduced tracking error but also improved tracking response with reduced oscillations.
  • Modelling and control for the mode transition of a novel tilt-wing UAV
    • Abstract: Publication date: Available online 22 May 2019Source: Aerospace Science and TechnologyAuthor(s): Yongchao Wang, Yaoming Zhou, Chenghao Lin This paper mainly presents a multibody dynamics model and a novel control method for the mode transition of a new-style distributed propulsion tilt-wing UAV. Base on the technology of tensor flight dynamics, a multibody attitude dynamics model formulated in an invariant tensor form is developed for the mode transition such that the dynamics induced by the relative movement of the moving parts (wings and rotors) with respect to the fuselage could be formulated explicitly in the model. The control system is decoupled into two parts, namely the position subsystem and the attitude subsystem subject to input perturbation and external aerodynamic disturbances. A novel finite time altitude tracking controller is designed for position subsystem in terms of the existence of the external disturbances and the perturbations acting on the inputs such that the tilt-wing UAV can converge and move along the desired altitude trajectory in a finite time. Besides, a RISE-based attitude tracking controller is developed to control the attitude subsystem, which guaranteeing robustness to the external disturbances. Numerical simulations are carried out to illustrate the performance of the proposed controllers.
  • A passive approach for adjusting the diurnal temperature difference of the
           envelope of stratospheric light aerostat
    • Abstract: Publication date: Available online 21 May 2019Source: Aerospace Science and TechnologyAuthor(s): Jun Liao, Yi Jiang, He Liao, Di-e Xiao, Junjie Yuan, Zechuan Yang, Jun Li, Shibin Luo Stratospheric light aerostat flies relying on the air buoyancy, and has more advantages than other air vehicles. The diurnal temperature difference of the stratospheric light aerostat is important to the long-endurance regional station-keeping performance. In the present paper, a thermal model is proposed, which include the thermal model of the envelope, internal gas, computational model, and adjustment of the diurnal temperature difference. A comparison with related results in the literature is carried out to verify the model. The stratospheric light aerostat temperature distribution and Helium velocity field are simulated. The effects of the envelope radiation properties including emissivity, the absorptivity and the ratio of absorptivity to emissivity on the stratospheric light aerostat thermal performance are discussed. The results show that the envelope radiation properties have great influence on stratospheric light aerostat thermal performance and decreasing the ratio of absorptivity to emissivity of envelope can be a good way to improve thermal performance. The results are conducive to select envelope radiation parameters of the stratospheric aerostat.
  • Elastoplastic postbuckling analysis of moderately thick rectangular plates
           using the variational differential quadrature method
    • Abstract: Publication date: Available online 21 May 2019Source: Aerospace Science and TechnologyAuthor(s): E. Hasrati, R. Ansari, H. Rouhi In this research, the elastoplastic postbuckling response of moderately thick rectangular plates subjected to in-plane loadings is analyzed by a novel numerical approach. The influence of transverse shear deformation is taken into account via the first-order shear deformation theory (FSDT). Also, the elastoplastic behavior is captured based on two theories of plasticity including the incremental theory (IT) (with the Prandtl-Reuss constitutive relations) and the deformation theory (DT) (with the Hencky constitutive relation). Moreover, it is assumed that the material of plate obeys the Ramberg-Osgood (RO) elastoplastic stress-strain relation. First, the matrix formulations of strain rates and constitutive relations are derived. In the next step, according to Hamilton's principle, the weak form of governing equations is derived which is then directly discretized using the variational differential quadrature (VDQ) technique. The discretization process is performed by accurate matrix derivative and integral operators of VDQ. Plates with various boundary conditions under uniaxial and equibiaxial compressions are considered. It is first indicated that the present results are in excellent agreement with the analytical solutions existing in the open literature. Thereafter, the influences of geometrical properties, boundary conditions, elastic modulus-to-nominal yield stress ratio and value of power c in the RO relation on the elastoplastic postbuckling paths of plates are studied. Furthermore, several comparisons are made between the predictions of IT and DT.
  • Simulation of liquid jet primary breakup in a supersonic crossflow under
           adaptive mesh refinement framework
    • Abstract: Publication date: Available online 20 May 2019Source: Aerospace Science and TechnologyAuthor(s): Nan Liu, Zhenguo Wang, Mingbo Sun, Ralf Deiterding, Hongbo Wang Compressible two-phase flows were simulated based on the five-equation model under the Adaptive Mesh Refinement (AMR) framework to balance the requirements between space resolution and computational cost. And the simulation system was established in an open source software AMROC (Adaptive Mesh Refinement Object-oriented C++). A combination of Godunov method and wave propagation method was introduced to integrate numerical methods with the AMR algorithm. High speed and high liquid-gas density ratio are two main challenges in the simulation of liquid jet in a supersonic crossflow. To enhance the robustness of the simulation system, a MOON-type positivity preserving method was adopted in the development of the codes. Based on the system mentioned above, a liquid jet in a Mach 1.5 supersonic crossflow was simulated as the standard case to study the primary breakup process in the near field. The simulation captured the column and surface breakup which were the results of the development of the unstable waves in two directions respectively. The instabilities causing the surface breakup were found to be generated in the transonic region initially. Crossflow of a higher Mach number (Ma 1.8) was found being able to augment the instable waves along the injection direction and increase the number of instabilities responsible for the surface breakup. While there was no obvious enhancement of the penetration in the condition of periodic injection, extra unstable waves were imposed on both of windward and leeward liquid surface. The introduced unstable waves had an improvement on the column and surface breakup.
  • Assessment of a one-dimensional finite element charring ablation material
           response model for phenolic-impregnated carbon ablator
    • Abstract: Publication date: Available online 17 May 2019Source: Aerospace Science and TechnologyAuthor(s): Yeqing Wang, Timothy K. Risch, Joseph H. Koo In this study, mathematical formulations to model charring ablation problems were numerically implemented using finite element analysis (FEA) with ABAQUS, which account for the material decomposition and progressive surface removal in the heat conduction and the surface energy balance equations. FEA was performed for a one-dimensional model to predict the temperature and ablation histories of a phenolic-impregnated carbon ablator sample (i.e., a common heat shield material for hypersonic vehicles and spacecraft) subjected to oxy-acetylene torch flame (i.e., 0.8 SLPM acetylene gas to 2.7 SLPM oxygen gas). The recovery enthalpy and convective heat transfer coefficient for the ablation model were calculated based on gas compositions and two assumed surface conditions (i.e., equilibrium and frozen). Simulations using the calculated recovery enthalpy and convective heat transfer coefficient resulted in a recession rate of 6.38 times (equilibrium) and 14.08 times (frozen) higher than the experimental data, despite fair agreement of the surface temperature. In addition, the effect of the heat transfer coefficient was investigated through a steady-state ablation analysis. The results of the analysis indicate that there is not one single value for the heat transfer coefficient that would allow the prediction to match both measured recession rate and surface temperature. Possible reasons for such an inconsistency are provided and discussed.
  • Civil turbofan engine exhaust aerodynamics: Impact of fan exit flow
    • Abstract: Publication date: Available online 17 May 2019Source: Aerospace Science and TechnologyAuthor(s): Ioannis Goulos, David MacManus, Christopher Sheaf It is envisaged that future civil aero-engines will operate with greater bypass ratios compared to contemporary configurations to lower specific thrust and improve propulsive efficiency. This trend is likely to be accompanied with the implementation of a shorter nacelle and bypass duct for larger engines. However, a short bypass duct may result in an aerodynamic coupling between the exit flow conditions of the fan Outlet Guide Vanes (OGVs) and the exhaust system. Thus, it is imperative that the design of the exhaust is carried out in combination with the fan exit profile. A parabolic definition is used to parameterise and control the circumferentially-averaged radial profiles of stagnation pressure and temperature at the fan OGV exit. The developed formulation is coupled with a parametric exhaust design approach, an automatic computational mesh generator, and a compressible flow solution method. A global optimisation strategy is devised comprising methods for Design of Experiment (DOE), Response Surface Modelling (RSM), and genetic optimisation.A combined Design Space Exploration (DSE) comprising both geometric, as well as fan exit profile variables, is performed to optimise the exhaust geometry in conjunction with the fan exit profile. The developed approach is used to derive optimum exhaust geometries for a tip, mid, and hub-biased fan blade loading distribution. It is shown that the proposed formulation can ameliorate adverse transonic flow characteristics on the core after-body due to a non-uniform bypass inflow. The hub-loaded profile was found to be most penalising in terms of exhaust performance compared to the mid and tip-loaded variants. It is demonstrated that the combined fan exit profile and exhaust geometry optimisation offers significant performance improvement compared to the fixed inflow cases. The predicted performance benefits can reach up to 0.19% in terms of exhaust velocity coefficient, depending on fan loading characteristics. A notable improvement is also noted in terms of bypass nozzle discharge coefficient. This suggests that the combined optimisation can lead to an exhaust design that can satisfy the engine mass-flow rate demand with a reduced geometric throat area, thus potentially offering further exhaust size and weight benefits.
  • On the effectiveness of shimmy dampers in stabilizing nose landing gears
    • Abstract: Publication date: Available online 17 May 2019Source: Aerospace Science and TechnologyAuthor(s): Mohsen Rahmani, Kamran Behdinan The challenge of nose landing gear shimmy vibrations is largely addressed through adding passive shimmy suppression devices to the gear, known as shimmy dampers. Despite the wide treatment of the shimmy modeling in the literature using various approaches, little is known about shimmy dampers' performance and their influence on the dynamics. This article presents a multi degree of freedom nose landing gear model including a two-piece strut, with a generic shimmy damper added in between of the strut parts as it is the case in the actual system. Using linear stability analysis and nonlinear time domain simulations, we identify the required equivalent stiffness and damping to be supplied by the shimmy damper in order to ensure stability of the dynamic system. Furthermore, a parametric study of three shimmy dampers is presented in which effect of design parameters on the equivalent stiffness and damping of shimmy dampers are highlighted and compared. Integrating the learnings from both parts of the study, strategies for arriving at an optimized shimmy damper design are offered.
  • Alcohol and Alkane Fuel Performance for Gas Generator Cycle Air Turbo
           Ramjet Engine
    • Abstract: Publication date: Available online 17 May 2019Source: Aerospace Science and TechnologyAuthor(s): Ryojiro Minato The present study investigates the feasibility of alcohol fuels for a Gas Generator cycle Air Turbo Ramjet (GG-ATR) Engine in comparison with alkane fuels. The alkane and alcohol fuels in the present study range from C1 species (CH4 and CH3OH) to C4 species (n-C4H10 and 1-C4H9OH).The present study analytically evaluates Specific thrust and Specific impulse (Isp) of GG-ATR engine as functions of gas generator combustion temperature. For both alcohols and alkanes, the peak Gas Generator (GG) combustion temperatures exist for specific thrust and ram combustor temperature. Comparing alcohol to alkane in the lower GG combustion temperature, specific thrusts and Isp of alcohol tend to be higher than those of C2H6, C3H8, and 1-C4H10. GG combustion gases for alcohol fuels contain higher mole fractions of H2O and CO2 than those for alkanes. Because of high mole fractions of H2O and CO2, the ratio of GG combustion gas for alcohols to air flow rate is fortunately close to the stoichiometric ratio, resulting in higher ram combustion temperature. The high ram combustion temperature can contribute to the higher specific thrust and Isp. Lower GG combustion temperature is preferable because of a thermal limit of a turbine blade. Thus, alcohols have superiorities to alkanes for the GG-ATR engine application.
  • Rapid design approach for U-bend of a turbine serpentine cooling passage
    • Abstract: Publication date: Available online 16 May 2019Source: Aerospace Science and TechnologyAuthor(s): Changhee Kim, Changmin Son The goal of this study is to propose a rapid design approach for designing a minimum pressure loss U-bend in a turbine internal cooling passage using topology optimization. The total pressure loss for the flow in a bend region is a critical design parameter, as it augments the pressure required at the inlet of the cooling passage, resulting in a lower thermal efficiency. However, no design rules exist for generating a U-bend. The proposed rapid design approach can be applied as a 3D U-bend geometry creation tool. The minimization of the total pressure loss is achieved by means of topology optimization method that uses a continuous adjoint approach with steepest-descent method. The design space is considered as a porous medium with variable porosity. An incompressible steady-state flow (low-fidelity simulation) is considered at a Reynolds number of 100,000 based on the bulk inlet velocity at the domain inlet. 2D and 3D U-bend configurations are produced by the proposed rapid design approach in a few hours. Optimized geometries are automatically achieved around the bend region, leading to a reduced pressure loss.High-fidelity computational simulations are carried out on rapidly designed 2D and 3D U-bend configurations to demonstrate the proposed rapid design approach. The computational studies are performed by solving the compressible, turbulent steady-state Reynolds-averaged Navier-Stokes (RANS) equations with two turbulence models: Spalart-Allmaras model and Shear Stress Transport (SST) model. The high-fidelity simulations predict a relative improvement of 26.8% in total pressure drop with respect to the baseline configuration, mainly due to the reduction of the flow separation region along the inner side of the bend. The results indicate that rapid design approach can come up with design concepts for minimizing pressure loss around U-bend passages in the incompressible flow regime. This approach could be also applied to other fluid systems.
  • Robust tracking control of aero-engine rotor speed based on switched LPV
    • Abstract: Publication date: Available online 16 May 2019Source: Aerospace Science and TechnologyAuthor(s): Tong-Jian Liu, Xian Du, Xi-Ming Sun, Hanz Richter, Fei Zhu Thrust control in aero-engines is achieved indirectly due to the lack of thrust sensing technologies. A related variable must be chosen for the control, typically high or low pressure rotor speeds. In this paper, an H∞ controller is designed for the rotor speed tracking in aero-engines. First, a small deviation linear model at steady state is obtained from the experimental data. Then, sets of small-deviation linear models are used to construct a linear parameter-varying (LPV) model with gain-scheduled parameters that capture the nonlinearity of the aero-engine dynamics. The LPV model is then converted to a switched convex polytopic form with hysteresis switching logic. Next, a theoretical sufficiency criterion is provided to guarantee H∞ performance based on linear matrix inequalities (LMIs). Relevant theoretical results are applied to prove stability when switching between subsystems. Simulation results are given to show the validity of the proposed design method, where the proposed the strategy with hysteresis switching logic can reduce the computational cost and avoid false switching due to disturbances.
  • Spatio–temporal dynamic mode decomposition in a shear layer flow
    • Abstract: Publication date: Available online 16 May 2019Source: Aerospace Science and TechnologyAuthor(s): Lu Weiyu, Huang Guoping, Wang Jinchun, Hong Shuli Dynamic mode decomposition is a useful method for extracting temporal information of coherent structures in unsteady flows. However, this method cannot simultaneously extract temporal and spatial development information, including wave number and spatial growth rate, which is essential in fully developed flows. Thus, using the idea of spatio–temporal dynamic mode decomposition from Le Clainche & Vega, we established an algorithm for spatio–temporal dynamic mode decomposition through element rearrangement, matrix blocking, and re-decomposition techniques, based on the traditional dynamic mode decomposition. This method can calculate the spatio–temporal modes of an unsteady function whose space dimension exceeds two. Each spatio–temporal mode is characterized by temporal growth rate, angular frequency, spatial growth rate, and wave number, thereby expanding the dimension of acquiring information of unsteady flow fields. The feasibility and effectiveness of this method are verified by a function of time and space. The application of spatio–temporal dynamic mode decomposition in a typical unsteady shear layer flow shows that this method can capture the dominant coherent structure in the flow field and accurately acquire its spatio–temporal evolution information.
  • Unsteady Detached-Eddy Simulation (DES) of the Jetstream 31 aircraft in
           One Engine Inoperative (OEI) condition with propeller modelling
    • Abstract: Publication date: Available online 15 May 2019Source: Aerospace Science and TechnologyAuthor(s): Loris Casadei, László Könözsy, Nicholas J. Lawson Numerical results from a three-dimensional (3D) computational fluid dynamics (CFD) model of the Jetstream 31 aircraft in conditions of one engine inoperative are presented. The objective of this work is to analyse the performance of the Jetstream 31 aircraft and provide transient data using an unsteady Detached-Eddy Simulation (DES) CFD approach and a numerical propeller model to compare computational results with a single engine flight test experiment. The propeller modelling approach has been implemented through User-Defined Functions using C programming language to replicate the propeller effect. Different angles of attack and sideslip are studied, based on records from flight test data, both with unsteady (DES) and steady-state Reynolds-Averaged Navier-Stokes (RANS) models. An error analysis on the flight test data provides an error band from 2% to 16% among all cases, high values due to the lack of many data samples. Across the RANS approach, an average deviation of 6.9% and 3.8% for respectively lift and drag coefficients is achieved. By applying the DES turbulence modelling approach, a better lift prediction is achieved (5.4%) despite a slightly worse drag (4.5%). It has also been found that 80% of the numerical results are within the error band defined. A close agreement has been found within moment coefficients, with average percentage deviations from 3.3% to 7.0%. Overall, an analysis has been carried out in the present work, both on the flight test and computational sides to provide reliable numerical results of these aerodynamic properties.
  • Entry trajectory generation with complex constraints based on
           three-dimensional acceleration profile
    • Abstract: Publication date: Available online 15 May 2019Source: Aerospace Science and TechnologyAuthor(s): Zhang Yuan-long, Yu Xie, Shuang-chun Peng, Guo-jian Tang, Wei-min Bao A new entry trajectory generation based on three-dimensional acceleration profile is proposed for hypersonic glide vehicles, meeting range requirement while taking waypoint and no-fly zone constraints into consideration. Firstly, the path constraints, such as maximum dynamic pressure, total overload and peak heating flux at the stagnation-point, are transformed into longitudinal and lateral flight corridors. And the initial lateral and longitudinal sub-profiles are obtained in sequence based on a layered strategy. Secondly, in order to accurately guide the vehicle to reach a target, a method based on Newton's iterative and bisection search is proposed, and the three-dimensional acceleration profile satisfying the mission requirement is quickly obtained. Further, this approach is extended to accommodate the trajectory generation with regarding the waypoint and no-fly zone constraints. Finally, a three-dimensional tracking law is designed to follow the reference trajectory, verifying the feasibility and accuracy of the proposed method.
  • Robust Adaptive Fuzzy Sliding Mode Control of Nonlinear Uncertain MIMO
           Fluttering FGP Plate Based on Feedback Linearization
    • Abstract: Publication date: Available online 15 May 2019Source: Aerospace Science and TechnologyAuthor(s): Mousa Rezaee, Reza Jahangiri, Rasoul Shabani In this study using an adaptive fuzzy sliding mode control (AFSMC) scheme, the robust stabilization of multi-input-multi-output (MIMO) nonlinear aero-elastic fluttering of the Functionally Graded Piezoelectric (FGP) plate in the presence of mismatched time-varying uncertainties have been investigated. It is assumed that the aerodynamic load is modeled by the first order piston theory and the piezoelectric patches are assumed to be bonded to the top and bottom surfaces of the plate in order to produce the controlling bending moment excitations. Using the airy stress function and applying the Hamilton's principle the governing coupled partial differential equations of motion are derived. Then considering the immovable simply supported edges boundary conditions and employing the aero-elastic multi-mode interactions and applying the Galerkin's method, the nonlinear coupled partial differential equations of motion are reduced to nonlinear ordinary differential equations in time. Then using the full state input-output feedback linearization technique, the nonlinear dynamics of the model is linearized and transformed into the multiple decupled single input-single output uncertain subsystems. In order to overcome the chattering phenomenon arises due to the sliding mode control (SMC) discontinuous inputs, a hybrid adaptive fuzzy sliding mode control technique is utilized to approximate the discontinuous synthetic control inputs. It is showed that considering the physical input limitations, the designed AFSMC control system, effectively suppress the fluttering motions in presence of the bounded external inaccuracies and it prevents the unwanted chattering of the subsystems inputs.
  • Adaptive constrained backstepping controller with prescribed performance
           methodology for carrier-based UAV
    • Abstract: Publication date: Available online 15 May 2019Source: Aerospace Science and TechnologyAuthor(s): Yang Zhang, Sheng-hai Wang, Bin Chang, Wen-hai Wu A novel adaptive constrained backstepping control with prescribed performance methodology for carrier-based unmanned aerial vehicle (UAV) in the presence of uncertainties, input constraints and unknown external disturbances is presented in this paper. This controller can guarantee the compensation tracking errors of the carrier-based UAV with prescribed performance including the steady and transient performance. Firstly, A new transformed system based on the compensation tracking errors, not the traditional tracking errors, is designed. Secondly, to deal with the UAV input constraints, the constrained command filters is introduced and the auxiliary dynamic is designed to eliminate the effect of input saturation. Thirdly, the prescribed performance methodology is introduced and the transient performance of the compensation tracking error is analyzed. It is proved that the proposed controller guarantees that all the signals of the closed-loop system are bounded by using Lyapunov method. Finally, the 6-DOF nonlinear carrier-based UAV model is used to demonstrate the effectiveness of the proposed control law. The simulation results show that the proposed controller is able to provide accurate tracking and satisfy the prescribed performance with unknown aerodynamic parameters, input constraints and external disturbances environment.
  • Design optimization of a tri-lobed solar powered stratospheric airship
    • Abstract: Publication date: Available online 14 May 2019Source: Aerospace Science and TechnologyAuthor(s): M. Manikandan, Rajkumar S. Pant The increased interest over multi-lobed hybrid airships which have been recently identified as an ideal platform for high altitude long endurance applications urges to develop a methodology for conceptual design optimization. The sizing methodology estimates the area of solar array required to meet the constraints of energy balance and the weight/lift equilibrium. The methodology involves the coupling of four disciplines (viz., Environment, Geometry, Aerodynamics, and Energy) and accounts for their mutual interactions. Sizing of the airship is carried out in terms of five design variables corresponding to the geometry and layout of the envelope and the solar array. This methodology is coupled to an intelligence-based heuristic algorithm viz., Particle Swarm Optimization (PSO) to obtain the configuration corresponding to a minimum area of solar array for such an airship, meeting the user-specified operating requirements. The effect of wind speed, airship attitude and altitude, geographical location and day of operation on the optimum area are included in this study. The results show the effect of season and operating conditions of deployment on the optimal envelope shapes obtained for deployment on specific days of the year. This study helps in the preliminary design of solar array on an unconventional stratospheric airship.
  • Reconstruction and analysis of non-premixed turbulent swirl flames based
           on kHz-rate multi-angular endoscopic volumetric tomography
    • Abstract: Publication date: Available online 14 May 2019Source: Aerospace Science and TechnologyAuthor(s): Hecong Liu, Jianan Zhao, Chongyuan Shui, Weiwei Cai The development of laser and sensor technologies have provided unprecedented opportunities for the extended applications of volumetric tomography. The recent progresses in computed tomography of chemiluminescence (CTC) have facilitated the understanding of turbulent flows and combustion instability. However, the current demonstrations of CTC can only provide either an instantaneous measurement with a good number of projections to achieve a good spatial resolution or time-resolved measurements (kHz-rate) but with a reduced number of projections which may cause a failure in resolving small details of the flames. In this work, we aim to develop a time-resolved endoscopic CTC system with 17 projections to achieve both good spatial and temporal resolutions. A new method was proposed here to calibrate projections that cover a field of view larger than 180 degrees. The system was then applied to a non-premixed turbulent swirl flame to reconstruct its time-resolved 3D structures. The experimental studies have shown that when only nine projections were used, parts of the flame structures would be lost. To fully recover the flame structures, a minimum of 16 projections should be used. Proper orthogonal decomposition and dynamical mode decomposition were then applied to analyze the time serious of 3D structures of a turbulent swirl flame.
  • Efficient accelerators for PSO in an inverse design of multi-element
    • Abstract: Publication date: Available online 14 May 2019Source: Aerospace Science and TechnologyAuthor(s): Y. Volkan Pehlivanoglu The main object in aerodynamic design is a wing. A high lift (HL) systems are probably the main concern in wing design optimization due to strict regulations. An optimization of high lift systems is difficult because of flow physics and high number of design parameters. Evolutionary algorithms including particle swarm optimization (PSO) are popular methods in HL system optimization. However, the computational burden of PSO may be a serious issue in process. In this article, efficient accelerators are integrated to PSO and applied to an inverse design of multi-element airfoils. The comparative test cases demonstrated that remarkable reductions in computational times have been accomplished.
  • FDOT: A Fast, memory-efficient and automated approach for Discrete adjoint
           sensitivity analysis using the Operator overloading Technique
    • Abstract: Publication date: Available online 14 May 2019Source: Aerospace Science and TechnologyAuthor(s): Reza Djeddi, Kivanc Ekici A new toolbox based on operator overloading is introduced for automatic differentiation of scientific computing codes – and in particular legacy computational fluid dynamics solvers that are developed using Fortran. The method can be readily implemented into existing iterative solvers with minimal changes to the primal code. The integrated toolbox can efficiently calculate the sensitivities of any objective function with respect to all variables (design or intermediate) that can later be used for gradient-based design optimization, uncertainty quantification, error estimation, and mesh adaptation. The underlying definition of the current automatic differentiation is directly related to the discrete adjoint sensitivity analysis. Unlike most traditional operator overloading-based adjoint approaches reported in the literature, the current technique offers huge reductions in the memory footprint. To demonstrate the advantages of the current approach, various solvers/problems are considered. It is shown that the proposed technique can be used as an efficient toolbox for automatic differentiation of scientific solvers requiring only a handful additional lines of coding.
  • Surrogate models for the prediction of the aerodynamic performance of
           exhaust systems
    • Abstract: Publication date: Available online 14 May 2019Source: Aerospace Science and TechnologyAuthor(s): Giorgio Giangaspero, David MacManus, Ioannis Goulos The aerodynamic performance of the exhaust system is becoming more important in the design of engines for civil aircraft applications. To increase propulsive efficiency and reduce specific fuel consumption, it is expected that future engines will operate with higher bypass ratios, lower fan pressure ratios and lower specific thrust. At these operating conditions, the net thrust and the specific fuel consumption are more sensitive to losses in the exhaust. Thus the performance of the exhaust needs to be accurately assessed as early as possible during the design process. This research investigates low-order models for the prediction of the performance of separate-jet exhaust systems, as a function of the free-stream Mach number, the fan nozzle pressure ratio and the extraction ratio (fan to core pressure ratio). In the current practice the two nozzles are typically considered in isolation and the performance is modelled as a function of their pressure ratio. It is shown that the additional degrees of freedom have a substantial impact on the metrics describing the performance of the exhaust system. These models can be employed at a preliminary design stage coupled with engine performance models, which require as input the characteristics of the exhaust system. Two engines, which are representative of current and future large turbofan architectures are studied. The low-order models investigated, generalized Kriging and radial basis functions, are constructed based on data obtained with computational fluid dynamics simulations. The data represents the characteristics of the exhaust of each engine, and they are provided for the first time for a wide operational envelope. The influence on accuracy of the type of surragate model and its settings have been quantified. Furthermore, the trade-off between the accuracy of the model and the number of samples has been identified. It is found that the exhaust performance metrics can be modelled using a low-order model with sufficient accuracy. Recommendations on the best settings of the model are also provided.
  • Turbulence anisotropy analysis in a highly loaded linear compressor
    • Abstract: Publication date: Available online 14 May 2019Source: Aerospace Science and TechnologyAuthor(s): Hao Yan, Yangwei Liu, Lipeng Lu The aerodynamic performance of three-dimensional (3D) corner separation flow in a highly loaded compressor cascade has been investigated using Delayed Detached Eddy Simulation (DDES) based on SST k–ω turbulence model. Turbulence anisotropy of the 3D corner separation has been studied and the relationship between turbulence anisotropy and turbulence kinetic energy budget has been discussed. The Reynolds stress state has been studied, with particular attention in the corner separation region using the Anisotropy Invariant Map (AIM) theory. The analysis revealed that the turbulence anisotropy is high near the wall region initially and then decays gradually as the distance from the wall increases. The shape of Reynolds stress within the corner separation region tends to be rod-like. The anisotropy characteristics of various scale turbulence vortex structures are discussed through Reynolds stress anisotropy tensors (aij) and dissipation rate tensors (dij). Both the large and small scale turbulence vortex structures have shown a return-to-isotropy tendency far from the wall. It is found that the turbulence anisotropy is positively related to the turbulence kinetic energy budget.
  • Investigation of gear walk suppression while maintaining braking
           performance in a main landing gear
    • Abstract: Publication date: Available online 14 May 2019Source: Aerospace Science and TechnologyAuthor(s): Qiaozhi Yin, Jason Zheng Jiang, Simon A. Neild, Hong Nie In this paper, a nonlinear dynamic landing gear model considering the influence of the coupling of the shock absorber stroke variation and the landing gear longitudinal motion with an anti-skid PID braking control system that captures gear walk is established. This gear walk model is verified by comparing with the response from a virtual prototype model. Then a parameter sensitivity analysis is carried out to find out the parameters with greater effects on gear walk and braking performance. The short time Fourier transform is employed to study the transient gear walk amplitude-frequency response, whose results are used to define the optimization constraints. A feedforward controller is proposed as part of the braking control law. Single-objective optimizations are then carried out to improve the gear walk performance while maintaining the braking efficiency. It is shown that the feedforward control, together with the PID feedback controller, can provide 25.68% reduction of the maximum gear walk angle while satisfying other constraints. The stability and robustness of the optimized braking law is verified under different working conditions. Multi-objective optimization is then used to highlight the trade-off between the gear walk vibration and the braking efficiency.
  • Isogeometric analysis of in-plane functionally graded porous microplates
           using modified couple stress theory
    • Abstract: Publication date: Available online 13 May 2019Source: Aerospace Science and TechnologyAuthor(s): Amir Farzam, Behrooz Hassani This paper examines bending, buckling and free vibration behaviors of in-plane functionally graded (FG) porous microplates by means of isogeometric analysis (IGA) and modified couple stress theory (MCST). A hyperbolic shear deformation theory is used, which does not need a shear correction factor. To take into account size-dependent effect, the MCST is employed to analyze functionally graded porous microplates. The IGA meets continuous requirement by using B-Spline or Non-Uniform Rational B-Spline (NURBS) functions. Various types of material distributions are assumed not only through plate thickness, but also in-plane material distributions. The effect of porosity on results is studied, while this parameter has not been paid attention yet for the analysis of in-plane and through-thickness functionally graded (FG) microplates. Furthermore, the effect of other parameters on the behaviors of microplates is investigated by several numerical problems. These parameters include boundary conditions, FG power index and material length scale parameter l.
  • Enhanced bondline thickness analysis for non-rigid airframe structural
    • Abstract: Publication date: Available online 13 May 2019Source: Aerospace Science and TechnologyAuthor(s): Pablo Coladas Mato, Philip Webb, Yigeng Xu, Daniel Graham, Andrew Portsmore, Edward Preston Adhesive bonding is a proven alternative to mechanical fasteners for structural assembly, offering lighter and thus more fuel efficient aircraft and cost-effective manufacturing processes. The effective application of bonded structural assemblies is however limited by the tight fit-up requirement, which is with sub-mm tolerance and can be a challenge for the industry to meet considering the variability of current part manufacturing methods and the conservative nature of the conventional tolerance stack-up analysis method. Such a challenge can discourage effective exploitation of bonding technologies, or lead to development of overengineered solutions for assurance. This paper addresses this challenge by presenting an enhanced bondline thickness variation analysis accounting for part deflection of a bonded skin-stringer assembly representing a typical non-rigid airframe structure. A semi-analytical model accounting for unilateral contact and simplified 1D adhesive flow has been developed to predict bondline thickness variation of the assembly under two typical curing conditions: namely autoclave curing and out-of-autoclave curing. The effects of component stiffness and manufacturing variations on bondline thickness are investigated by incorporating stringers of different stiffness, as well as shims of different thicknesses in-between the skin and stringer, in the stringer-skin assembly. A small-scale bonding demonstrator has been built and the physical results are in good agreement with the model prediction. It has been demonstrated that the part deflections need to be accounted for regarding fit-up requirement of bonded non-rigid structural assembly. The semi-analytical model offers more reliable and realistic prediction of bondline thickness when compared to a rigid tolerance stack-up. The analysis method presented can be a major technology enabler for faster, more economical development of the aircraft of the future, as well as of any analogue structures with high aspect ratios where weight savings and fatigue performance may be key objectives.
  • Soft extreme learning machine for fault detection of aircraft engine
    • Abstract: Publication date: Available online 13 May 2019Source: Aerospace Science and TechnologyAuthor(s): Yong-Ping Zhao, Gong Huang, Qian-Kun Hu, Jian-Feng Tan, Jian-Jun Wang, Zhe Yang When extreme learning machine (ELM) is used to cope with classification problems, the ±1 is commonly used to construct the label vector. Since ELM adopts the square loss function, this means that it tends to force the margins of all the training samples exactly equaling one from the perspective of margin learning theory, which is unreasonable to some extent. To overcome this hard margin flaw, in this paper a soft extreme learning machine (SELM) is proposed, which flexibly sets a soft target margin for each training sample. Through solving a series of regularized ELMs (RELMs), SELM can be computed efficiently. Based on SELM, an improved SELM (ISELM) is proposed to deal with imbalanced classification problems, which can keep the same computational efficiency as SELM via solving a series of weighted RELMs. From the experimental results on benchmark data sets, the effectiveness and feasibility of SELM and ISELM are confirmed. More importantly, when they are applied to fault detection of aircraft engine, they are promising to be developed as the candidate techniques for it, and ISELM is especially in favor.
  • Effect of non-spherical particles on nozzle two-phase flow loss in
           nano-iron powder metal fuel motor
    • Abstract: Publication date: Available online 13 May 2019Source: Aerospace Science and TechnologyAuthor(s): Jin-yun Wang, Zai-lin Yang Metal iron powder is a promising new energy source that is of significant practical and research interest for future automotive power systems. However, the shapes of the particles are typically assumed to be spherical or an equivalent sphere when estimating the specific impulse of motors. Such an assumption lacks objectivity and can result in unreasonable estimations of two-phase flow losses. In order to better optimize the design of an engine, this study focuses on the influence of non-spherical particles (such as ellipsoidal and cuboid particles) on the characteristics of nozzle two-phase flow. Models for the governing equations of nozzle two-phase flow are developed to conduct a theoretical study to analyze the combustion properties of iron oxide particles and flow in the nozzle. In addition, experimental studies involving nanometer iron-powder particle combustion and engine thrust measurements are conducted to validate the results obtained from numerical calculations that are conducted using a fourth order Runge–Kutta–Gill method. The results indicate that particle morphology, size, and coagulation content play a significant role in the motor performance and the two-phase flow losses. Specifically, the hypothesis of the ellipsoidal model is in better agreement with the experimental findings compared to the other particle models.
  • High-Reynolds number transitional flow simulation via parabolized
           stability equations with an adaptive RANS solver
    • Abstract: Publication date: Available online 10 May 2019Source: Aerospace Science and TechnologyAuthor(s): Gustavo L.O. Halila, Guodong Chen, Yayun Shi, Krzysztof J. Fidkowski, Joaquim R.R.A. Martins, Márcio Teixeira de Mendonça The accurate prediction of transition is relevant for aerodynamic analysis and design applications. Extending the laminar flow region over airframes is a potential way to reduce the skin friction drag, which in turn reduces fuel burn and greenhouse gas emissions. This paper introduces a numerical framework that includes the modeling of transition effects for high Reynolds number flows in a high-fidelity, Reynolds–averaged Navier–Stokes (RANS) aerodynamic design framework. The CFD solver uses a discontinuous Galerkin (DG) finite element approach and includes goal-oriented adaptation. The Spalart–Allmaras (SA) turbulence model is used for the closure of the governing equations. In the flow stability analysis, the nonlocal, nonparallel effects that characterize boundary layers are accounted for by using the parabolized stability equations (PSE). Transition onset is obtained through an eN method based on the PSE computations, while a smooth intermittency function includes the transition region length. Numerical results for the NLF(1)-0416 airfoil present good agreement with experimental data, improving the computations when compared to fully-turbulent ones.
  • Linear stability analysis of a non-Newtonian liquid jet in a coaxial
           swirling air
    • Abstract: Publication date: Available online 10 May 2019Source: Aerospace Science and TechnologyAuthor(s): Xin-Tao Wang, Zhi Ning, Ming Lü, Yuan-Xu Li The instability behavior of a power law liquid jet moving in a swirling air is investigated theoretically. The power law model is selected to describe the viscosity of the non-Newtonian jet. The corresponding dispersion relation is obtained by a linear stability analysis. Besides, the effects of air swirl strength, non-axisymmetric mode, liquid Weber number, generalized Reynolds number, power law index and consistency coefficient on the instability of the power law liquid jet surrounded by a swirling gas are studied in the Rayleigh and Taylor modes. The results show that the shear-thickening liquid jet is more unstable than the Newtonian and shear-thinning liquids when the air swirl is introduced. The air swirl is a stabilizing factor on the instability of the power law liquid jet in Rayleigh and Taylor modes. It is also found, when the air swirl is introduced, the maximum growth rate of the power liquid jet decreases as the liquid Weber number increases in Rayleigh mode, while it increases in Taylor mode. Moreover, the viscous forces of the liquid always prevent the jet from breaking up.
  • Critical buckling temperature and force in porous sandwich plates with
           CNT-reinforced nanocomposite layers
    • Abstract: Publication date: Available online 10 May 2019Source: Aerospace Science and TechnologyAuthor(s): Babak Safaei, Rasool Moradi-Dastjerdi, Kamran Behdinan, Fulei Chu This paper presents the thermal and mechanical buckling behaviors of lightweight polymeric nanocomposite sandwich plates containing uniformly dispersed (UD) pores resting on two-parameter elastic foundations. The outer layers of the proposed sandwich plates were assumed to be made of functionally graded (FG) carbon nanotube (CNT)-reinforced polymeric nanocomposite. For nanocomposite layers, the considerable effect of cluster formation of randomly-oriented CNTs was considered and material properties were evaluated through Eshelby-Mori-Tanaka (EMT)'s approach with the definition of cluster state. Furthermore, the first and third order shear deformation theories (FSDT and TSDT) of plates were employed to define the total energy function of sandwich plates. The governed buckling equations were facilitated using a mesh-free method. The effects of porosity, nanofiller characterizations, elastic foundation coefficients, sandwich plate dimensions and boundary conditions on buckling behavior were explored. The obtained results showed that porosity considerably improved thermal buckling behavior; however, it reduced the critical mechanical loads of sandwich plates. Moreover, adding CNTs into outer layers simultaneously improved the mechanical and thermal buckling responses of sandwich plates.
  • Energy optimization and investigation for Z-shaped sun-tracking
           morphing-wing solar-powered UAV
    • Abstract: Publication date: Available online 10 May 2019Source: Aerospace Science and TechnologyAuthor(s): Mingjian Wu, Zhiwei Shi, Tianhang Xiao, Haisong Ang To achieve perpetual flight, solar-powered UAVs (SPUAVs) need to convert sufficient solar energy into electricity during daylight flight. However, perpetual flight at middle and high latitude regions in winter days still poses great challenges for gaining enough solar energy due to the low sun elevation angle and short daylight duration. Among measures for flight endurance enhancement, tracking the sun through changing geometry of wing and orienting flight direction may be an effective design scheme for gaining more solar energy. In this paper, the energy optimization method for Z-shaped sun-tracking morphing-wing SPUAV is developed and used to investigate the advantages on energy performance of the optimal Z-shaped wing over the conventional planar wing. Energy optimization for a whole year's flight shows that the optimal Z-shaped wing is capable of achieving longer flight endurance, improving perpetual flight latitude and extending perpetual flight date efficiently compared with the planar wing, especially for the middle and high latitude regions during winter days. The investigation on implications of conversion efficiency of solar cells indicates that, with higher conversion efficiency of solar cells, the optimal Z-shaped wing is more effective to collect more net energy, retain more energy margin and achieve perpetual flight at higher latitude. The Z-shaped sun-tracking morphing-wing design combined with the energy optimization method proposed is helpful to increase flight endurance and improve perpetual flight latitude for SPUAVs.
  • Safe multi-cluster UAV continuum deformation coordination
    • Abstract: Publication date: Available online 10 May 2019Source: Aerospace Science and TechnologyAuthor(s): Hossein Rastgoftar, Ella M. Atkins This paper proposes a paradigm for coordination of multiple unmanned aerial vehicle (UAV) clusters in a shared motion space. UAVs are arranged in a finite number of teams each bounded by a leading triangle. Collective motion of each UAV cluster is managed by a continuum deformation defined by three leaders at the vertices of a leading triangle and followers contained within this triangle. Each triangular cluster can deform substantially to support maneuverability in constrained spaces. This paper specifies necessary conditions to guarantee obstacle avoidance as well as collision avoidance within and across all clusters operating in a shared motion space. Given initial and target configurations, an existing planner (A*) identifies the shortest coordinated leader UAV paths from initial to final configuration in a manner that satisfies safety constraints. An illustrative simulation case study is presented. Continuum deformation containment offers scalability in collision-free UAV motion planning not previously realized in the detect-and-avoid literature. The proposed multi-cluster coordination protocol also extends previous cooperative control to address detect-and-avoid (DAA) given multiple cooperative teams with different destinations.
  • Dynamic mode decomposition of the acoustic field in radial compressors
    • Abstract: Publication date: Available online 9 May 2019Source: Aerospace Science and TechnologyAuthor(s): A. Broatch, J. García-Tíscar, F. Roig, S. Sharma Widely recognized since the beginning of air travel as a major issue, noise reduction remains nowadays a pressing concern for all stakeholders in the aviation industry. While aeroengine compressors, specially at the approach phase, have been historically identified as a leading source of noise, most of the research has been conducted on compressors of the axial type. However, radial compressors are found in a wide array of applications: smaller business jets, helicopters, unmanned aerial vehicles (UAVs), auxiliary power units (APUs), turbochargers for reciprocating engines, etc. Owing to their geometrical particularities, radial compressors feature flow patterns that differ from their axial counterparts, leading to different acoustic performance but also opening the door for different optimization approaches. Yet, classical modal decomposition techniques focused on duct propagation may fail to reveal the complex interactions between geometry and flow features that act as noise sources. In this paper we apply, in addition to the classical approach, a data-driven Dynamic Mode Decomposition (DMD) to pressure data coming from a Detached Eddy Simulation (DES), in which we have experimentally validated the correct reproduction of the modal behaviour of the compressor, thus obtaining in-depth details of the link between flow phenomena and noise generation and transmission across the inlet and outlet ducts.
  • Buckling and postbuckling of dielectric composite beam reinforced with
           Graphene Platelets (GPLs)
    • Abstract: Publication date: Available online 9 May 2019Source: Aerospace Science and TechnologyAuthor(s): Y. Wang, C. Feng, C. Santiuste, Z. Zhao, J. Yang Buckling and postbuckling behaviours of graphene platelet (GPL) reinforced dielectric composite beams are investigated through theoretical formulation. The effective material properties of the GPL reinforced composite (GPLRC) as required for structural analysis, i.e. tensile modulus, dielectric constant and Poisson's ratio are obtained by using effective medium theory and rule of mixture. Governing differential equations for the composite beam are established through Timoshenko beam theory, von Kármán nonlinear strain-displacement relationship and principle of virtual work. Governing equations are numerically discretized and solved by employing differential quadrature method (DQM), through which several parameters affecting the buckling performances are quantitatively identified. The results demonstrate there exists a critical GPL concentration, above which the electrical field significantly affects the beam's buckling and postbuckling behaviours. The dielectric beam's buckling performances are very sensitive to AC (alternating current) frequency within a certain range. Moreover, it is found the dielectric beam's buckling and postbuckling performances comprehensively depend on the concentration and aspect ratio of GPLs. The present work is envisaged to provide guidelines to develop GPL-based smart composites and structures.
  • Analysis of low-speed height-velocity diagram of a variable-speed-rotor
           helicopter in one-engine-failure
    • Abstract: Publication date: Available online 9 May 2019Source: Aerospace Science and TechnologyAuthor(s): Cheng Chi, Xufei Yan, Renliang Chen, Pan Li This work analyzes the effects of variable operating rotor speed on the helicopter low-speed Height–Velocity (H-V) diagram in one engine inoperative (OEI) situation. Using the UH-60A helicopter as baseline helicopter, a flight dynamics model and the applied optimal control method were validated against the corresponding flight test data. Both low-speed H-V diagram in OEI and landing procedures at corresponding key points (Low hover, Knee and High hover) were investigated. Results indicate that the reduction of operating rotor speed will cause the unsafe area of H-V diagram to shrink gradually at first, and then expand rapidly when the operating rotor speed reduces below a certain value. It is observed that the lower constraint of rotor speed during OEI landing has a significant impact on the H-V diagram. Finally, results also show that a reasonable rotor speed not only effectively reduces the helicopter required power during steady level flight, but also improves the landing performance in the event of OEI.
  • Hub clearance effects of a cantilevered tandem stator on the performance
           and flow behaviors in a small-scale axial flow compressor
    • Abstract: Publication date: Available online 9 May 2019Source: Aerospace Science and TechnologyAuthor(s): Xiaochen Mao, Bo Liu, Botao Zhang The impacts of the increased hub clearance size (HCS) in the cantilevered tandem stator on the overall performance and flow behaviors have been investigated based on numerical simulations in a small-scale axial flow compressor stage. The results indicate that the HCS variation in the front blade of the tandem stator has a more significant effect on the compressor peak efficiency and stall margin. However, there is no obvious change of the compressor performance with the increase of the HCS in the rear blade. Detailed flow analysis shows that the increase of the HCS in the front blade has remarkable impacts on the flow fields in the front blade, while it has an only slight influence on the hub flow fields in the rear blade. It is found that the compressor efficiency penalty is due to the increase of the loss generation near the hub caused by the larger extent of hub leakage flow, while the stall margin improvement is due to the redistribution of the mass flow rate along the spanwise direction. As a result, the inlet flow condition within the upper blade span is improved and the flow blockage is reduced. The resulting influence of the increased HCS in the rear blade is mainly located near the blade leading edge of the rear blade, and there is no remarkable effect on the flow field in the front blade passage.
  • Solar-sail trajectory design for multiple near-Earth asteroid exploration
           based on deep neural networks
    • Abstract: Publication date: Available online 9 May 2019Source: Aerospace Science and TechnologyAuthor(s): Yu Song, Shengping Gong In the preliminary trajectory design of the multi-target rendezvous problem, a model that can quickly estimate the cost of the orbital transfer is essential. The estimation of the transfer time using solar sails between two arbitrary orbits is difficult and usually requires to solve an optimal control problem. Inspired by the successful applications of the deep neural networks in nonlinear regression, this work explores the possibility and effectiveness of mapping the transfer time for solar sails from the orbital characteristics using the deep neural networks. Furthermore, the Monte Carlo Tree Search method is investigated and used to search the optimal sequence considering a multi-asteroid exploration problem. The obtained sequences from preliminary design will be solved and verified by sequentially solving the optimal control problem. Two examples of different application backgrounds validate the effectiveness of the proposed approach.
  • A proposed design method for supersonic inlet to improve performance
    • Abstract: Publication date: Available online 9 May 2019Source: Aerospace Science and TechnologyAuthor(s): M. Farahani, M.M. Mahdavi A new structure for the compression surfaces of a supersonic inlet is proposed which has improved the target performance parameter i.e. total pressure recovery ratio. This idea resulted in development of a new type of supersonic inlet, utilized with four ramps and a cone as the simultaneously compression surfaces. A prototype of the proposed inlet has been designed for a free stream Mach number of 3 and its performance has been evaluated via numerical simulation for both design and off-design conditions. The performance of the newly designed inlet has been compared to the existing experimental data of the inlets equipped with two double-cones. The acquired data are further compared with analytical calculations used for conventional supersonic inlets. The results confirmed the effectiveness of the main idea of the proposed design methodology. The total pressure recovery ratio of the newly designed inlet at its design condition, M∞=3, is calculated to be 76.8%.
  • Advanced numerical prediction of iced airfoil aerodynamics
    • Abstract: Publication date: Available online 9 May 2019Source: Aerospace Science and TechnologyAuthor(s): M. Costes, F. Moens The paper presents a numerical investigation of the flow around a NACA23012 airfoil with two ice shapes, a spanwise ridge and leading edge roughness. RANS and URANS simulations are completed with various 1st and 2nd order turbulence models (Spalart-Allmaras, Menter SST, EARSM, DRSM) for a selected number of points of the airfoil polar. To assess the ability of advanced unsteady hybrid RANS/LES models, one selected flow condition of the spanwise ridge case is also computed with a ZDES hybrid method. The results are compared with experimental data (integrated loads, pressure distribution, velocity field) obtained in the ONERA F1 wind tunnel. The Spalart-Allmaras model is the only RANS model among those assessed in this study converging efficiently towards steady-state whatever the flow condition considered. Together with DRSM, it also provides a reasonable predictive effect on the performance degradation due to ice shape. DRSM is much more expensive as it contains more physics, providing natural unsteady solutions which have to be time-averaged. DRSM first and second-order statistic fields compare well with ZDES ones, both of them indicating that geometrical three-dimensionality of the ice shapes should be taken into account. Furthermore, the unsteady content of the DRSM URANS solution is compared with that of ZDES, showing that the vortex shedding phenomenon can also be captured by DRSM.
  • Numerical investigation of surge prediction in a transonic axial
           compressor with a hybrid BDF/Harmonic Balance Method
    • Abstract: Publication date: Available online 9 May 2019Source: Aerospace Science and TechnologyAuthor(s): Haiou Sun, Meng Wang, Zhongyi Wang, Franco Magagnato This paper aims at evaluating an efficient combination of a hybrid Backward Difference Formula/Harmonic Balance Method and the necessary time dependent exit boundary condition for the prediction of the performance line and ultimately surge line in a transonic one stage axial compressor (Stage 35) designed and measured at NASA Glenn Research Center. The agreement of the total pressure ratio, total temperature ratio as well as the efficiency curve with the experimental findings are encouraging. The results of the proposed methodology compare very well with the URANS predictions of Herrick et al. albeit the calculation is more efficient. While the prediction of the performance line in the stabile regime can be predicted by the classical Harmonic Balance Method (HBM), the investigation of strong off-design conditions, a quasi-periodic extension of the HBM is necessary. In addition, the mass flow rate and the exit pressure are no longer constant in time in this flow field an appropriate boundary condition is required for the successful simulation of this flows. Using this features the prediction of the surge behavior has been computed and a realistic flow pattern has been obtained. The computational time extent over more than 50 revolutions in order to capture the surge frequency of the compressor.
  • Bionic visual close-range navigation control system for the docking stage
           of probe-and-drogue autonomous aerial refueling
    • Abstract: Publication date: Available online 8 May 2019Source: Aerospace Science and TechnologyAuthor(s): Yongbin Sun, Yimin Deng, Haibin Duan, Xiaobin Xu Bionic visual close-range navigation control system and method for the docking stage of probe-and-drogue autonomous aerial refueling (AAR) are developed in this paper. The reasonable bionic visual close-range navigation system is devised to obtain the accurate pose information of drogue which is connected to a flexible hose in the presence of multi-wind disturbances. Correspondingly, the biological eagle-eye-based color detection method is constructed on the basis of the eagle-eye color vision mechanism to detect the drogue region and markers. The different visual navigation methods based on marker matching and ellipse fitting are respectively applied for the two situations: the markers detected normally, and the drogue far away to receiver or the markers blocked partially. Moreover, due to the switch of different control targets and navigation methods (GPS or bionic visual navigation) for controllers in the docking stage, the different relative position precise controllers are designed to control the relative position between the tanker and receiver. The experimental results show that the bionic visual close-range navigation system and method effectively acquire the drogue's pose information in the entire visual docking stage and the designed controllers are suitable to the GPS and bionic visual navigation methods for changing and keeping the relative position between the tanker/receiver or probe/drogue.
  • Neural network-based adaptive sliding mode control design for position and
           attitude control of a quadrotor UAV
    • Abstract: Publication date: Available online 7 May 2019Source: Aerospace Science and TechnologyAuthor(s): Hadi Razmi, Sima Afshinfar In this paper, a novel method is suggested for the position and attitude tracking control of a quadrotor UAV in the presence of parametric uncertainties and external disturbance. The proposed method combines neural network adaptive scheme with sliding mode control, which preserves the advantages of the two methods. Firstly, dynamic model of quadrotor is divided into two fully actuated and under actuated subsystems. Secondly, sliding mode controllers are corresponding designed for each subsystem, and their coefficients in sliding manifolds are adaptively tuned by the neural network method. In each section, using Lyapunov theory, stability of closed loop system is proven.Finally, the method is examined for a square path tracking and a maximum overshoot of 7.5133% and a settling time 5.6648 s are obtained. By comparing the results obtained through different methods, it is concluded that the proposed controller provides the following main advantages: (1) good transient and steady state behaviors, (2) insensitivity to parameter variations, (3) disturbance rejection capability, and (4) remarkable stability and performance robustness. Hence, for operational purposes in which the fast and accurate response are of crucial importance, using the neural network-based adaptive sliding mode control approach is recommended.
  • Investigation on Tones due to Self-excited Oscillation within Leading-edge
           Slat Cove at Different Angles of Attack: Frequency and Intensity
    • Abstract: Publication date: Available online 7 May 2019Source: Aerospace Science and TechnologyAuthor(s): Weishuang Lu, Peiqing Liu, Hao Guo, Tianxiang Hu In an effort to understand the tonal characteristics of high-lift configurations, aero-acoustic experiments are conducted on a two-dimensional, three-element high-lift configuration model, with a stowed flap. As a less expensive aid to experimentation, the numerical simulation method is used to obtain flow parameters possibly related to tones. Experimental results show that the low-mid-frequency band tonal noise generated by the self-excited oscillation in the slat cove is the main far-field noise source. Based on the local flow field information obtained by numerical simulations, an improved empirical formula, as proposed by Terrocal, is adopted to predict the characteristic frequencies of self-excited oscillation within the slat cove, which agrees well with the tonal frequencies observed by wind tunnel testing at varying angles of attack. The intensity of these low to mid frequency band tones is also found to be dependent on the angle of attack, i.e., the primary tone of the self-excited oscillation switches from the second mode to the third mode, with increasing angles of attack. By investigating the local flow around the slat cove, the ratio of the shear layer length over the shear layer momentum thickness is determined, i.e., Lv/θ plays an important role in this transition of tonal intensity. As the angle of attack increases, both Lv and θ monotonous decrease, whereas Lv/θ increases and gives rise to a switch in the main characteristic frequency of the self-excited oscillation and a clear reduction in the overall sound pressure level.
  • A high efficiency aircraft anti-skid brake control with runway
    • Abstract: Publication date: Available online 7 May 2019Source: Aerospace Science and TechnologyAuthor(s): Dong Sun, Yaoxing Shang, Zongxia Jiao, Xiaochao Liu, Shuai Wu Anti-skid brake system is an important aircraft subsystem to ensure safe take-off and landing of aircraft. Accurate runway circumstances identification is the key point to achieve the high efficiency of the anti-skid brake control. Inaccurate identification may cause frequent skidding and longer brake distance, even cause the extremely dangerous wheel lock phenomenon. Moreover, many nonlinear factors such as the variation of the aerodynamic drag can seriously affect the brake efficiency and the aircraft safety. In this paper, we propose an anti-skid brake control algorithm to identify the maximum friction force by analyzing the runway/tire friction characteristics that can only based on the aircraft wheel speed signal. The aerodynamic disturbances are observed and compensated by radical basis function (RBF) neural network, and the brake disc friction coefficient variation is also estimated based on the observation of energy consumption. Software simulations and the inertial test bench experiments are carried out. The result reveals that this method can accurately identify the runway circumstances and greatly improve the braking efficiency.
  • Low-order diving integrated guidance and control for hypersonic vehicles
    • Abstract: Publication date: Available online 7 May 2019Source: Aerospace Science and TechnologyAuthor(s): JianHua Wang, Long Cheng, YuanWen Cai, GuoJian Tang A novel low-order integrated guidance and control (LOIGC) design model is deduced, and an original diving integrated guidance and control design approach is proposed in this paper. An analytical model between three-channel body rates and components of acceleration of the hypersonic vehicle in the ballistic frame is derived, and the commanded body rates can be directly obtained by analytic calculation. The LOIGC design model is conducted based on three dimensional (3D) relative dynamics between the hypersonic vehicle and target, and the direct relation with respect to line-of-sight (LOS) angles and control surface fin deflections of the hypersonic vehicle is established. Based on the LOIGC model, the design of six-degree-of-freedom (6DOF) guidance and control system for diving hypersonic vehicles can be converted into an output tracking problem of a low-order nonlinear system, and the commanded control surface fin deflections can be directly obtained by controlling derivatives of elevation and azimuth angles of line-of-sight between the hypersonic vehicle and target. In this paper, the system order and tuning parameters of the 6DOF guidance and control system are both decreased, and the design procedure of 6DOF guidance and control system is simplified. The process of calculating commands of angle of attack and bank angle based on desired guidance overloads, and the tracking loops with respect to Euler angles and body rates of the rotational system can also be omitted. In addition, the newly proposed method can improve the utilization of velocity measurements in the body frame of the hypersonic vehicle. Finally, the effectiveness and robustness of the newly proposed integrated guidance and control design approach are verified and investigated using a 6DOF generic hypersonic vehicle model.
  • Terminal sliding mode control based impact time and angle constrained
    • Abstract: Publication date: Available online 3 May 2019Source: Aerospace Science and TechnologyAuthor(s): Zhiwei Hou, Ye Yang, Lei Liu, Yongji Wang In this paper, an impact time and angle constrained guidance (ITACG) is proposed based on the nonsingular terminal sliding mode control (NTSMC) theory. First, the guidance law is derived for stationary targets. The proposed ITACG consists of two parts. One part is designed for a missile to intercept a target from the desired impact angle and the other part aims to achieve the desired impact time. Two different terminal sliding mode surfaces are designed so that the missile can satisfy the impact time and angle constraints simultaneously. Corresponding to the designed sliding mode surfaces, two different Lyapunov candidate functions are proposed and analyzed, and stability conditions are obtained. Then, we extend the proposed guidance for constant acceleration targets. The time-to-go estimation method is modified based on the conception of predicted-intercept-point (PIP) with the constant acceleration targets and stability conditions are also revised. Compared with traditional sliding mode control (SMC) based ITACG, the proposed guidance law is a direct online method. It does not need to design the line-of-sight angle curve off-line, nor does it need to switch between impact time constrained guidance and impact angle constrained guidance. In the end, numerical simulation results show that the proposed impact time and angle constrained guidance law has a good performance even though the missile has a constant acceleration. Salvo attack of multi-missiles against one target is shown in the simulation part by applying the proposed guidance law.
  • Formulation and integration of MDAO systems for collaborative design: A
           graph-based methodological approach
    • Abstract: Publication date: Available online 3 May 2019Source: Aerospace Science and TechnologyAuthor(s): Imco van Gent, Gianfranco La Rocca This paper proposes a novel methodology and its software implementation, called KADMOS (Knowledge- and graph-based Agile Design for Multidisciplinary Optimization System), to increase the agility of design teams in collaborative Multidisciplinary Design Analysis and Optimization (MDAO). Agility here refers to the ease and flexibility to assemble, adjust and reconfigure MDAO computational systems. This is a necessary feature to comply with the complex and iterative nature of the (aircraft) design process. KADMOS has been developed on the notion that a formal specification of an MDAO system is required before proceeding with integration of the executable workflow. A thorough formulation of the system becomes essential when such system is built on the many contributions of large, heterogeneous design teams. KADMOS can automate the generation of such formulations through a graph-based methodological approach. The graph syntax and manipulation algorithms form the core content of this paper. First, a simple MDAO benchmark problem is used to illustrate KADMOS's working principles. Second, a wing aerostructural design case is discussed to demonstrate KADMOS's capabilities to enable collaborative MDAO on large problems of industry-representative complexity. Next to its graph-theoretic foundation, KADMOS makes use of two data schemas: one containing the parametric representation of the product being designed and a second to store the achieved formulation of the MDAO system. The latter enables the interchangeable use of different process integration and design optimization platforms to automatically integrate the generated MDAO system formulation as an executable workflow. The proposed approach has been estimated to be capable of halving the time typically required to set up and iteratively reconfigure a complex MDAO system, while allowing discipline experts and system architects to maintain constant oversight and control of the overall system and its components by means of human-readable dynamic visualizations.
  • Effects of boundary layer transition on the aerodynamic analysis of
           high-lift systems
    • Abstract: Publication date: Available online 3 May 2019Source: Aerospace Science and TechnologyAuthor(s): Gustavo Luiz Olichevis Halila, Alexandre Pequeno Antunes, Ricardo Galdino da Silva, João Luiz F. Azevedo Transition to turbulence is known as a factor that impacts the performance of high-lift devices, but only a few numerical results that include transition are available in the literature. We use the Langtry-Menter γ−Reθ transition model to study the influence of transition to turbulence in global aerodynamic coefficients and flow topology in three-dimensional high-lift configurations. The influence of turbulence inflow variables is also addressed. Numerical results are compared with previous results obtained with the Shear Stress Transport (SST) turbulence model, which does not account for transition effects. The numerical simulations are performed using configuration “one” from the 1st AIAA CFD High-Lift Prediction Workshop. Experimental data from the NASA Langley 14 by 22-ft Subsonic Wind Tunnel provide the global aerodynamic information for the verification of our numerical results. It is observed that the inclusion of transition to turbulence impacts the flow topology, as well as the aerodynamic coefficients.
  • Geometrically nonlinear rapid surface heating of temperature-dependent FGM
    • Abstract: Publication date: Available online 3 May 2019Source: Aerospace Science and TechnologyAuthor(s): M. Javani, Y. Kiani, M.R. Eslami Based on the nonlinear dynamic analysis, thermally induced vibrations of the FGM shallow arches subjected to different sudden thermal loads are studied. Temperature and position dependence of the material properties are taken into account. Based on the uncoupled thermoelasticity assumptions, The non-linear one-dimensional transient heat conduction equation is solved numerically by a hybrid iterative GDQ method and Crank-Nicolson time marching scheme. A first order shear deformation arch theory (FSDT) is also combined with the von Kármán type of geometrical non-linearity and the Donnell kinematic assumption to obtain the equations of motion employing the Hamilton principle. Discretization of the highly coupled non-linear equations of motion is done by using the GDQ method in the arch domain. The solution of the system of the ordinary differential equations is established by means of a hybrid iterative Picard-Newmark scheme. Comparison is also made with the existing results for the case of isotropic homogeneous shallow arches, where good agreement is obtained. Also, parametric studies are proposed to show the effects of temperature dependency, geometrical non-linearity, arch thickness, power law index, and the type of thermal-mechanical boundary conditions upon the arch deflection.
  • Aerodynamic characteristics of a tip-jet fan with a large blade pitch
    • Abstract: Publication date: Available online 3 May 2019Source: Aerospace Science and TechnologyAuthor(s): Lei Li, Guoping Huang, Jie Chen This work aims to investigate the availability of a tip-jet on a ducted fan under large blade pitch angle and high solidity conditions. The aerodynamic performance and flow field of a ducted fan in hover are numerically investigated over a range of blade pitch angles at three operating speeds. A numerical experiment is conducted using the shear-stress transport k-omega turbulence model with a refined high-quality structured grid. The maximum thrust, peak efficiency, and stall margin of the ducted fan with tip-jet are the main interests of this investigation. Results indicate a 30% increase in the thrust of the fan with tip-jet near stall margin condition. This aerodynamic improvement seems to increase with the blade pitch angle because the separation flow at the front part of the blade becomes uniform and reattaches to the blade surface due to the entrainment effect of the tip-jet. The nozzle with an angle in downwash direction can improve tip-jet efficiency at a large blade pitch angle. The tip-jet is applicable to a fan with a large pitch angle and high solidity.
  • Dynamics and control of tethered multi-satellites in elliptic orbits
    • Abstract: Publication date: Available online 3 May 2019Source: Aerospace Science and TechnologyAuthor(s): Gefei Shi, Zhanxia Zhu, Zheng H. Zhu This paper studies the dynamics and libration suppression of tethered multi-satellites in elliptic orbits, where the tethered system is subject to periodic excitation resulting from the change of gravity gradient. The tethered system is modeled as a multiple dumbbell model and the relationship between periodical libration and tether length rate is studied. The outcome of study leads to a new tension control law to suppress the libration of tethered multi-satellites in a desired periodic motion by regulating tether length without thrust. The simulation results show that the libration motion of tethered multi-satellites is successfully stabilized to the desired periodic motion with the proposed tension control law. When the orbital eccentricity is small, the analytical solution of time-dependent tether lengths is derived to minimize the magnitudes of tether length rate. Furthermore, the tension control law is modified by including a sliding mode control to suppress initial external perturbations to increase the robustness of control law.
  • Electric Propulsion System Sizing Methodology for an Agriculture
    • Abstract: Publication date: Available online 2 May 2019Source: Aerospace Science and TechnologyAuthor(s): Ngoc Anh Vu, Duy Khang Dang, Tuan Le Dinh Using a suitable propulsion system for Drones capable of obtaining desired performance is one of the primary goals for designing electric multicopters. Choosing the right components for the electric system: Motor, ESC, battery, rotor (propeller) is always challenging because of the diversity of and misleading information on these products on the market. By studying specifications brought by manufacturers and experimental data, the relationship of the components in the propulsion system is given and parameterized. This paper presents a method to size the electric propulsion system for design and manufacturing a multicopter that is able to handle mission requirements. The sensitivity of design parameters to GTOW is given. An Agriculture Quadcopter is built and compared to the results of sizing and the difference stays within ±4% for gross take-off weight. The maximum thrust over weight ratio is introduced, and the cut of payload during operation of pesticide spraying is also accounted in the calculation for improvement of sizing the Quadcopter.
  • Real time estimation of impaired aircraft flight envelope using
           feedforward neural networks
    • Abstract: Publication date: Available online 2 May 2019Source: Aerospace Science and TechnologyAuthor(s): Ramin Norouzi, Amirreza Kosari, Mohammad Hossein Sabour Extensive research in recent years has focused on developing flight envelope estimation methods to improve current loss of control prevention and recovery systems. Such methods are practically efficient only if they are able to evaluate in real time the new flight envelope of damaged aircraft based on the altered dynamics. Due to nonlinear dynamics of aircraft, common approaches to estimate the entire flight envelope of high-fidelity models are numerically intensive and their real time implementation is computationally impossible. So current methods are based on reduced complexity models or flight envelopes are determined locally. This paper presents a novel method to estimate the global flight envelope of impaired aircraft in real-time for any unknown failure degree. In the proposed method, first, numerous flight envelopes are evaluated using a high fidelity model at various failure degrees and different flight conditions and prepared as training data. Then multiple feedforward neural networks are trained offline by a Bayesian regularization backpropagation algorithm. Finally, the trained networks are used to estimate flight envelopes in real time. The method is applied to rudder and aileron failure cases of the NASA Generic Transport Model. Results show that the estimated flight envelopes are good approximations of the high fidelity global flight envelopes.
  • Optimal transition of flapping wing micro-air vehicles from hovering to
           forward flight
    • Abstract: Publication date: Available online 2 May 2019Source: Aerospace Science and TechnologyAuthor(s): Ahmed A. Hussein, Ahmed E. Seleit, Haithem E. Taha, Muhammad R. Hajj In this work, we formulate a minimum-time optimal control problem to steer a FWMAV dynamical system from a hovering condition to forward flight with a prescribed forward speed using time-periodic and averaged dynamics formulations. For the averaged dynamics representation, we optimize the back and forth flapping angle and the up and down-stroke angles of attack of the wing. We represent the flapping angle via a generic periodic function with some parameters that determine the waveform of the flapping angle over the cycle. We formulate the optimal control problem such that the cost functional is the final time, and the slowly time-varying parameters of the flapping angle wave form and the up and down-stroke angles of attack are considered inputs to the averaged dynamics. On the other hand, the instantaneous the flapping speed and wing pitching angle are considered direct inputs to the time periodic system. The problem is then to steer the averaged dynamics from the hovering fixed point (origin) to a prescribed average forward speed, and the time periodic dynamics from the hovering periodic orbit to the orbit of the forward flight condition. We show that the averaging is not suitable for the steering between hovering and forward flight and that time-periodic dynamics are required for the controller to achieve proper transition. Also, we investigated the effect of using the time-averaged stability derivatives obtained using a computational fluid dynamics simulation versus using the time-varying hovering derivatives.
  • A rod-linear cascade model for emulating rotor-stator interaction noise in
           turbofans: A numerical study
    • Abstract: Publication date: Available online 2 May 2019Source: Aerospace Science and TechnologyAuthor(s): Christopher Teruna, Daniele Ragni, Francesco Avallone, Damiano Casalino This manuscript presents a rod-linear cascade model for emulating rotor-stator interaction noise. The model is intended as a test platform for studying noise mitigation techniques for a turbofan fan stage, while it also extends the classical rod-airfoil configuration by considering a row of blades based on realistic geometrical details. The rod-linear cascade model consists of a rod positioned upstream of a 7-blade linear cascade, such that the rod wake impinges onto the central blade. The rod is scaled to obtain a fundamental shedding frequency equal to the first blade passing frequency of the NASA-Glenn Source Diagnostics Test (SDT) fan stage at approach condition. The cascade blade profile is also based on the OGV of the SDT sampled at 90% of the radial span. Subsequently, numerical simulations are performed using lattice-Boltzmann Method on a computational setup comprised of a contraction and a test section enclosing the rod-linear cascade model. The integral length scales of the rod wake and the mean loading of the central blade have been found to be in good agreement with the trends observed in the SDT fan stage. The primary noise sources are localized at the central blade leading edge, although noise propagation to the far-field is influenced by additional diffraction by the other blades. Furthermore, the acoustic-blade row interaction causes intense pressure fluctuation within the inter-blade channels, including in those that are not directly affected by the rod wake.
  • Optimization of aircraft spin recovery maneuvers
    • Abstract: Publication date: Available online 2 May 2019Source: Aerospace Science and TechnologyAuthor(s): D.M.K.K. Venkateswara Rao, Tiauw Hiong Go In this paper, the problem of aircraft spin recovery is solved as a trajectory optimization problem using direct multiple shooting method with time and altitude-loss as cost functions to be minimized. A stable oscillatory spin state is chosen as the initial condition and the optimal control inputs required to transfer the aircraft to a steady level-flight trim state are determined. Optimal spin recovery simulations are carried out with scaled bounds of control inputs to determine their effectiveness and feasibility for recovery in the case of total control failures. It is shown that spin recovery is feasible in the case of aileron failure, and only arresting of yaw-rate is possible in the case of rudder and throttle failures. Optimal spin recovery simulations are also carried out to determine the effects of wind and aerodynamic forces. It is found that spin recovery solutions are sensitive to initial conditions in the presence of wind, and increase of lift and decrease of drag reduce the altitude-loss of the maneuver.
  • In-canopy sensors for state estimation of precision guided airdrop systems
    • Abstract: Publication date: Available online 30 April 2019Source: Aerospace Science and TechnologyAuthor(s): Jacob Wachlin, Michael Ward, Mark Costello Guided airdrop systems have traditionally used position and velocity information from a GPS receiver as their only source of feedback. The use of additional sensors in the guidance units is challenging because sensors in the guidance unit are in close proximity to powerful electric motors. Furthermore, there is a large amount of relative motion between the guidance unit and the parachute as they are coupled by a flexible network of rigging lines. By placing sensors in the parachute itself, it is possible to obtain accurate estimates of the canopy motion and orientation with low-cost sensors requiring minimal calibration. Specialized in-canopy sensor pods were developed to provide distributed sensing throughout a parachute canopy and a sensor fusion algorithm was developed to combine the raw data from these sensor pods into useful canopy state estimates. The effectiveness of this approach is demonstrated first in simulation, and then with flight test results on full-scale airdrop systems. The rich feedback signal available from in-canopy sensors can provide improved datasets for more detailed system identification as well as enabling novel guidance, navigation and control approaches which will lead directly to improved landing accuracy.
  • Finite element analysis of aero-hydroelastic stability of arbitrary shape
    • Abstract: Publication date: Available online 30 April 2019Source: Aerospace Science and TechnologyAuthor(s): Saad A. Ragab, Hassan E. Fayed A fluid-structure model based on Mindlin-Reissner plate theory and linearized incompressible potential flow theory is used to study the aero-hydroelastic stability of panels of arbitrary planforms. A finite-element procedure is developed to reduce the continuous system to a finite flow-structure system, which is solved in the frequency domain. The finite element method is crucial for the study of panels of arbitrary geometry and circumvents difficulties with the assumed mode shape approach. This paper is the first finite-element formulation of a fully coupled fluid-structure model of the aero-hydroelastic panel stability problem for incompressible flow. Circular, square, and triangular panels surrounded by a rigid baffle with different boundary conditions are studied. Eigenvalues of the system are surveyed as a function of the hydrodynamic loading at high and low density ratios. Critical flow velocity at divergence-onset and modal coalescence divergence or flutter are determined and compared for the three planforms. For simply supported or clamped panels of equal area and flexural rigidity, as the fluid velocity increases from zero the circular panel diverges first then the square and equilateral triangle, the later is the most stable. In order to compare the relative stability of the three geometries considered, a velocity ratio that consolidates divergence and flutter conditions for the three panels is introduced. Such a parameter offers a simple formula for the divergence velocity in terms of the panel geometry and flow and material properties, and is very useful to the designer in a wide range of engineering applications.
  • Remotely Piloted Aircraft Systems conceptual design methodology based on
           factor analysis
    • Abstract: Publication date: Available online 26 April 2019Source: Aerospace Science and TechnologyAuthor(s): Álvaro Gómez-Rodríguez, Alejandro Sánchez-Carmona, Luis García-Hernández, Cristina Cuerno-Rejado The rapid expansion of Remotely Piloted Aircraft Systems (RPAS) within the aeronautical industry demands the development of new design methodologies focused on these aircraft. In this paper, a novel rapid-sizing procedure for the initial design phases of H-tail Remotely Piloted Aircraft (RPA) based on the factor analysis technique is proposed. The main concept of this methodology consists in finding the latent design tendencies within the sample of study, that are represented by unobservable factors, which can be employed as specifications in a novel design procedure based on the most prominent design trends of the sample of study. The classical factor analysis procedure has been adapted to the characteristics of the aircraft conceptual design discipline, including a new criterion for the extraction of factors taking into account the desirable accuracy in this phase of design. From the findings of this analysis, a novel conceptual rapid-sizing methodology based on the main design tendencies of H-tail RPA is proposed. This methodology is then tested with a design example case and compared with the results obtained from a conventional approach based purely on regression analysis for the same aircraft in order to validate the procedure. This analysis shows that the results fall within the expected accuracy of the conceptual design phase, with the added novelty of considering the extracted design tendencies as specifications for the initial sizing of the RPA, and constituting a methodology with higher robustness than the contrasting traditional procedure due to the capacity to account simultaneously for the interrelations amongst all the variables and the ability to control a wide range of statistical indicators to augment the confidence in the results.
  • Compressor Surge Based on a One-dimensional-three-dimensional Coupled
           Method—Part 2: Surge Investigation
    • Abstract: Publication date: Available online 26 April 2019Source: Aerospace Science and TechnologyAuthor(s): Qiangqiang Huang, Meijie Zhang, Xinqian Zheng Compressor characteristics and system parameters, which include pipe lengths, plenum volumes, and throttle coefficients, greatly affect compressor surge. The one-dimensional-three-dimensional (1D-3D) coupled method, is established in Part 1, combines a 3D solver for compressor internal flows and a 1D solver for pipe, plenum, and throttle flows to simulate compressor surge in a compression system. In this paper, the capability of the method to reflect changes of compressor characteristics and system parameters will be demonstrated. Given a centrifugal compressor, variable inlet prewhirl and variable diffuser vanes are employed to adjust compressor characteristics; based on the setup of a datum test rig, the pipe length, plenum volume and throttle coefficient in the 1D solver are modified to get different system setups. Thus, the compressor system can be numerically configured with various compressor characteristics and system parameters, and the 1D-3D coupled method is applied to simulate compressor surge in various configurations. Simulation results show that compressor surge flow rates decrease, and surge periods prolong in the case of positive inlet prewhirl, which is consistent with known results concerning inlet prewhirl; if the diffuser vanes are closed by 5 degrees, the compressor would get out of surge and operate stably, which aligns with expectations. In terms of system parameters, simulation results indicate that the surge period is shortened and the trajectory of surge cycle on the performance map shrinks if the pipe length or plenum volume reduces. Mild surge, mixed surge, and deep surge are captured while the throttle is set with big, moderate and small openings, respectively. Thus, the 1D-3D coupled method is proved being sensitive to changes of compressor characteristics and system parameters, justifying using the 1D-3D coupled method to explore several research topics concerning compressor characteristics and system parameters in compressor surge. This paper lays a foundation of using the 1D-3D coupled method to investigate the relation between compressor surge and stall, compressor surge in a dynamic compression system, structures and dynamics during compressor surge, and the flow instability boundary.
  • Study on flight dynamics of flexible projectiles based on closed-loop
           feedback control
    • Abstract: Publication date: Available online 26 April 2019Source: Aerospace Science and TechnologyAuthor(s): Ruhao Hua, Xianxu Yuan, Zhigong Tang, Zhengyin Ye Since projectiles with large slenderness ratio are prone to elastic deformation, the effect of structural deformation is necessary to be taken into consideration for dynamic modeling. In order to obtain the precise aerodynamic performance and flight dynamic characteristics of flexible projectiles, a new numerical flight simulation system is developed based on computational fluid dynamics and generalized dynamic-mesh technique. Furthermore, flight dynamic stability of a typical flexible projectile is carried out in detail by introducing PID controller. By means of installing the sensors at various locations, the effect of different mode shapes on the characteristics of the closed-loop flight dynamic system is researched. Numerical results indicate that, when the disturbance due to elastic vibration is added into the mixed signals gained from the angular velocity/acceleration sensors, the feedback response of the closed-loop system becomes adversely divergent. In contrast, the stability of the closed-loop system is not sensitive to the elastic disturbance added to the centroid velocity and acceleration. Moreover, the stability of closed-loop system is much less affected by the unsteady aerodynamic loading due to elastic vibration than the interference of the elastic vibration on the dynamic signals detected by the sensors. The phenomenon can be explained by the requirement on the stability of the long and short period modes of flight dynamics, which can provide some guidance for the layout of the sensor and the design of control system of the projectiles with large slenderness ratio.
  • Compressor surge based on a one-dimensional-three-dimensional coupled
           method—Part 1: Method establishment
    • Abstract: Publication date: Available online 26 April 2019Source: Aerospace Science and TechnologyAuthor(s): Qiangqiang Huang, Meijie Zhang, Xinqian Zheng Compressors are core components in gas turbines and turbocharged engines to feed air. No matter in axial compressors and centrifugal compressors, a fatal issue which can happen in the system is compressor surge, a violent flow oscillation throughout a compression system. Understanding internal flows of compressors in compressor surge is crucial to investigate surge precursors and post-surge behaviors. Aerodynamic behaviors of compressor surge are not only affected by compressors but also other parts in the system primarily including pipes, a plenum, and a throttle valve. It is necessary to look at compressor surge internal flows in the context of compressions systems. The purpose of this study is to establish a one-dimensional and three-dimensional (1D-3D) coupled method for simulating compressor surge in a compression system. The method can jointly solve one-dimensional flows through the piping, plenum, and valve and three-dimensional flows in the compressor. Compared with fully lumped parameter models, the 1D-3D coupled method can simulate overall responses of compressor surge without inputting compressor performance maps; furthermore, 3D flows can be obtained to reveal more details concerning compressor surge. In contrast with fully 3D simulations, the 1D-3D coupled method saves computational cost on the piping, plenum, and valve, which take large space of the system but are just dominated by 1D flows. Therefore, via the 1D-3D coupled method, compressor surge behaviors of a newly designed compressor can be evaluated swiftly once geometry models are given. The method is based on a combination of unsteady Reynolds-averaged Navier-Stokes simulations, the method of characteristics, and lumped parameter models. Boundary conditions and domain interfaces are carefully treated to reach a closed-form solution. A shock tube problem is modeled and simulated by the method to validate its implementation. 1D-3D coupled simulations are performed on the compression system of a centrifugal compressor, and the results are compared with experimental data. Typical phases of compressor surge are captured by the 1D-3D coupled simulation, and leading mode responses in spectrums are well reproduced by the method; however, the method fails to capture high-frequency modes and a quiet zone during a surge cycle, which are respectively attributed to rough temporal and turbulent resolutions and rotational speed variations during compressor surge. Improved identification of system parameters, finer temporal resolutions and the implementation of variable rotational speed are recommended for future developments of the method.
  • Adaptive fault-tolerant boundary control for a flexible aircraft wing with
           input constraints
    • Abstract: Publication date: Available online 25 April 2019Source: Aerospace Science and TechnologyAuthor(s): Shiqi Gao, Yuanyuan Zhang, Jinkun Liu This paper discusses the boundary control problem of actuator input constraints for a flexible aircraft wing in the presence of unknown external disturbances and unknown actuator failure. Based on the application of smooth hyperbolic function and a projection algorithm, an innovative adaptive boundary controller with an external disturbance estimator is designed to suppress the bending and twist deformations of the flexible aircraft wing. The flexible aircraft wing is modeled as a coupled twist-bending system, the dynamics of which are described by several partial differential equations (PDEs) and ordinary differential equations (ODEs). The proposed boundary control scheme is shown to satisfy the input restrictions and physical conditions. The elastic vibration and vibration rate of the flexible aircraft wing system is also eliminated successfully even after the actuator failure. Both theoretical analysis and numerical simulations are provided which demonstrate the effectiveness of the proposed scheme.
  • Added Masses of generic shape bodies interacting with external walls
    • Abstract: Publication date: Available online 25 April 2019Source: Aerospace Science and TechnologyAuthor(s): Giovanni Carbone, Guillaume Martinat, Dominique Farcy, Jean-Luc Harion The aim of this paper is to propose an efficient method to evaluate the Added Masses of generic shape bodies in infinite fluid or in the proximity of external walls. The Added Masses (AM) are the result of the inertial reaction of the fluid in response to an accelerated movement of a body immersed in it. The AM effects are more evident when the body density is similar to that of the surrounding fluid, as in the case of airships. In the take-off or landing phases, the proximity to the ground causes an increase in the Added Masses that must be correctly estimated to properly size the airship controls. In our method, the calculation of the Added Masses matrix is carried out by the Boundary Element Method (BEM). To verify the accuracy of the results, the study cases are based on simple shapes, whose Added Masses are well known. The analyses in infinite fluid and in the presence of a flat wall are carried out. Numerical results are compared to the theoretical values found in literature. The calculated Added Masses are intrinsically dependent on the mesh definition and the relative error, referred to the theoretical values, depends on the surface and volume discretization. In the case of interaction between geometries with complex shapes, the influence on the Added Masses is very difficult to predict without a numerical approach. The method proposed gives a good compromise in terms of quality of results and computational cost.
  • Nonlinear buckling and post-buckling of eccentrically oblique stiffened
           sandwich functionally graded double curved shallow shells
    • Abstract: Publication date: Available online 25 April 2019Source: Aerospace Science and TechnologyAuthor(s): Tran Quoc Quan, Nguyen Huy Cuong, Nguyen Dinh Duc This paper aims to investigate the nonlinear buckling and post-buckling of eccentrically oblique stiffened sandwich functionally graded double curved shallow shells resting on elastic foundations in thermal environment. The shells are reinforced by functionally graded eccentrically oblique stiffeners with deviation angles. Two types of sandwich functionally graded double curved shallow shells with the differences of distribution of functionally graded face sheets and homogenous core are considered. Material properties of the sandwich shells and stiffeners are assumed to vary continuously and smoothly in the thickness direction according to Sigmoid power law. The formula of force and moment resultants and the nonlinear equilibrium equations are established based on the improved Donnell theory and Lekhnitskii's smeared stiffeners technique. The analytical displacement solutions are chosen based on the trigonometric forms satisfying the boundary conditions. The value of critical buckling loads and the load – deflection curves of the shells are obtained by using the Bubnov – Galerkin method. In numerical results; effect of geometrical parameters, elastic foundations, temperature increment, compressive load and oblique stiffeners on the critical buckling loads and post-buckling load – deflection curves of the shells are studied specifically. The obtained results are also compared with others from literature to validate the accuracy of the present method and approach.
  • Aeroelastic tailoring of nonlinear typical section using the method of
           multiple scales to predict post-flutter stable LCOs
    • Abstract: Publication date: Available online 25 April 2019Source: Aerospace Science and TechnologyAuthor(s): Leonardo Sanches, Thiago A.M. Guimarães, Flávio D. Marques Most aeroelastic systems suffer from nonlinear behavior. The characterization of nonlinear response in aeroelastic systems is, therefore, a relevant issue. When designing for best performance, for instance, to expand the flutter boundaries, the nonlinear aeroelastic behavior is also a formidable challenge. Towards optimal aeroelastic tailoring, an alternative approach may be admitting acceptable levels when nonlinearities are present to the problem. To do this post-flutter behavior can be added to the optimization reasoning, along with the traditional flutter boundaries expansion. The current work proposes an investigation on the aeroelastic tailoring of a typical section with hardening nonlinearity in pitching stiffness seeking to expand the flutter onset boundary and minimum stable LCO amplitudes in post-flutter. This investigation uses the traditional typical section model to develop a reduced order model based on the multiple scales method viewing fast evaluations of the flutter onset and values of LCO amplitudes at some post-flutter airspeeds. Aeroelastic tailoring is based on the differential evolution algorithm to yield Pareto frontiers for the two selected objectives. An analysis of the design variables is presented, and the optimization results reveal that adequate compromise solutions can be assessed. Therefore, possible optimal post-flutter conditions for minimum LCO amplitudes can also be achieved.
  • Flying qualities evaluation criteria design for scaled-model aircraft
           based on similarity theory
    • Abstract: Publication date: Available online 24 April 2019Source: Aerospace Science and TechnologyAuthor(s): Lixin Wang, Xianshuai Zuo, Hailiang Liu, Xiaopeng Jia, Junbin You, Ting Yue In the preliminary design phase of aircraft, evaluating the flying qualities characteristics of full-size aircraft preliminarily through scaled-model flight test helps to shorten cycle times and reduce the technical risks of aircraft development. In this paper, the flying qualities evaluation criteria for scaled-model flight test are designed. In order to make full-size aircraft and scaled-model dynamically similar, the similarity relations between their configuration parameters, control law parameters, and flight condition parameters are analyzed. In addition, the change rules of four different flying qualities parameters with the scale factor of aircraft size are analyzed, including time-domain, frequency-domain, low order equivalent system (LOES) and pilot compensation. According to the obtained change rules, the flying qualities evaluation criteria applicable for scaled-model are designed by modifying the evaluation criteria for full-size aircraft. Finally, the flying qualities evaluations of a sample full-size aircraft and its 1/4 scaled-model are conducted, and the results show that the flying qualities evaluation of scaled-model can reflect the flying quality characteristics of the full-size aircraft accurately.
  • Planform Dependency of Optimum Cross-sectional Geometric Distributions for
           Supersonic Wing
    • Abstract: Publication date: Available online 24 April 2019Source: Aerospace Science and TechnologyAuthor(s): Yuki Kishi, Shinya Kitazaki, Atthaphon Ariyarit, Yoshikazu Makino, Masahiro Kanazaki The difference in the supersonic aerodynamic characteristic of different wing planforms is evaluated to determine the optimum parameters for the cross-sectional geometry of a supersonic wing. The supersonic performance of wing with integrated engine intakes was evaluated for a quadruple-tapered wing with a large sweep angle and for a single-tapered wing with a small sweep angle. To reduce the required computation time, the design problems were solved using a multi-fidelity approach consisting of a hybrid surrogate model assisted by evolutionary computation. To evaluate aerodynamic performance, the compressible Euler equation and the linearized compressible potential equation were employed as high- and low- level fidelity solvers, respectively. Through design optimizations, the contributions of different cross-sectional parameters to drag reduction were determined. It was found that the shape of the forward camber and the twist angle around the middle of the wing had the most noteworthy influence on the drag reduction for both wing planforms, because most of the aerodynamic force was generated near the wing mid-span. For a wing with a large sweep angle, a cross-sectional geometry involving a small positive camber at the leading edge, and a small twisted angle was optimum. For a wing with a small sweep angle, a cross-sectional geometry involving a negative camber at the leading edge, and a thinner leading edge, and higher twisted angle than those for a large swept-back wing was optimum because of the ready generation of a shock wave at the leading edge.
  • Performance impact of flow and geometric variations for a turbine blade
           using an adaptive NIPC method
    • Abstract: Publication date: Available online 23 April 2019Source: Aerospace Science and TechnologyAuthor(s): Zhiheng Xia, Jiaqi Luo, Feng Liu Geometric variations of the realistic blades due to the limited machining precision and flow variations at the outlet boundary due to the operational condition changes for turbomachinery blades cannot be totally eliminated, the significant effects of which require to be taken into account in the aerodynamic shape design and optimization. The present paper investigates the performance impact of flow and geometric variations by using the polynomial chaos. The adaptive non-intrusive polynomial chaos (NIPC) model based on an adaptive sparse grid technique is firstly introduced, the response performance of which is validated through function experiments and uncertainty quantification of performance change for a three-dimensional turbine blade. Then the adaptive NIPC is used to statistically evaluate the adiabatic efficiency change of the turbine blade due to the geometric and back pressure variations separately. The performance change exhibits nonlinear dependence on the geometric and back pressure variations. Moreover, the geometric variations induce more performance deteriorations to the turbine blade in the present study. Finally, the simultaneous performance impact of geometric and back pressure variations are investigated. The results are presented in detail and compared with those obtained from the uncoupled studies, demonstrating that these two kinds of uncertain effects to the performance change are nonlinearly dependent.
  • Three-dimensional flow structures and droplet-gas mixing process of a
           liquid jet in supersonic crossflow
    • Abstract: Publication date: Available online 19 April 2019Source: Aerospace Science and TechnologyAuthor(s): Peibo Lia, Zhenguo Wang, Xue-song Bai, Hongbo Wang, Mingbo Sun, Liyin Wu, Chaoyang Liu The mixing process of a liquid jet in supersonic crossflow with a Mach number of 2.1 was investigated numerically using large eddy simulation (LES) based on the Eulerian-Lagrangian method. The gas phase was described using the Navier-Stokes equations and the liquid phase was represented using discrete droplets, which were injected and tracked in the computational domain individually according to Newton's second law of motion. The KH (Kelvin-Helmholtz) breakup model was used to calculate the droplet stripping process, and the secondary breakup process was simulated by coupling the RT (Rayleigh-Taylor) breakup model and the TAB (Taylor Analogy Breakup) model. Two-way coupling was enforced to consider the momentum and energy exchange between the gas and the droplets. It was found that the LES predicted spray characteristics, including spray penetration and cross-sectional distribution, agree reasonably well with the experiment. The major gas flow structures such as the bow shock, the large-scale vortices, and the recirculation zones were replicated successfully in the simulations. It was found that the gas flow structures have a significant effect on the mixing process of the droplets. The simulation results revealed that two sets of counter-rotating vortex pair (CVP) exist in the gas-liquid mixing region. Under the influence of CVP, part droplets were transported to the near wall region and subsequently to both sides of the core spray region. The formation mechanism of the CVP was analyzed by comparing the pressure gradient and the source term of droplets in the Navier-Stokes equations. Differences of the mixing process of a liquid jet in supersonic crossflow, gas jet in supersonic crossflow and liquid jet in incompressible crossflow were identified.
  • An optimization study for rotorcraft avionics bay cooling
    • Abstract: Publication date: Available online 19 April 2019Source: Aerospace Science and TechnologyAuthor(s): Altug Akin, Harika S. Kahveci In this paper, a computational investigation of a rotorcraft avionics-bay cooling system is carried out. The introduced avionics cooling system utilizes a forced-convection method in which the ambient air is supplied to the avionics bay by a fan and then exhausted back into the ambient after cooling the equipment inside. The aim of this system is to keep the air temperature in the vicinity of the avionics equipment below the operational temperature limits. Depending on the locations of the fan and exhaust, local hot zones may form near some of the equipment. In order to overcome this issue, the fan capacity must be designed to provide a sufficiently high mass flow rate so that the temperature limits are not exceeded, while an excessive amount of cooling should be avoided to reduce power consumption. In this study, the effects of the fan and the exhaust locations on the amount of required mass flow rate are investigated. A prediction function is built by using Gaussian Process Regression method to predict the avionics surface temperatures. The Gaussian Process Regression method is trained by the results obtained from a large number of computational fluid dynamics (CFD) analyses. The prediction function is later used to determine the required mass flow rate depending on the fan and the exhaust locations. It is found out that the required mass flow rate changes significantly as the fan location changes. On the other hand, the exhaust location has a relatively lessened effect on the required mass flow rate. It is observed that depending on the locations of the fan and the exhaust, the required mass flow rate could be reduced to around half of its value. The amount of decrease in the electrical power consumption is even more significant.
  • Simultaneous interface position and bulk velocity measurements in
           cryogenic sloshing
    • Abstract: Publication date: Available online 19 April 2019Source: Aerospace Science and TechnologyAuthor(s): A. Simonini, L. Peveroni, M.R. Vetrano Cryogenic sloshing is of primary importance in aerospace propulsion since it can affect the dynamic stability and the propellant management during each phase of spacecraft missions. We show in this work, for the first time, that cryogenic sloshing can be investigated by means of tracer-based laser techniques, such as Particle Image Velocimetry (PIV), to obtain the liquid/gas interface and the bulk velocity both in the unsteady and steady regime. The fluid heating due to the laser interaction with the tracer particles and the possible effect on the particle-fluid slip velocity is evaluated. An experimental campaign is conducted, and both the liquid/gas interface position and the velocity maps of the bulk are obtained in time-resolved conditions. Finally, the logarithmic damping at the liquid/gas interface and in the bulk are evaluated and compared with satisfactory results to the models available in the literature.
  • Slew path planning of agile-satellite antenna pointing mechanism with
           optimal real-time data transmission performance
    • Abstract: Publication date: Available online 19 April 2019Source: Aerospace Science and TechnologyAuthor(s): Yuchen She, Shuang Li, Yinkang Li, Liu Zhang, Shuyi Wang This paper investigates the mission planning problem of an agile satellite equipped with a two-dimensional antenna pointing mechanism. Multiple relay satellites and ground stations are included into the scenario to ensure the real-time data downlink. Therefore, to achieve the optimal real-time data transmission performance, two optimization modes are proposed in this paper to generate the slew path for both the satellite base and the antenna pointing mechanism. First, a baseline attitude coordinate system is introduced to efficiently handle the constraint of the problem. Second, the decoupled method is presented based on the two-level optimization strategy, which combines the genetic algorithm and the artificial potential method. Third, the dynamic programming concept is introduced to generate the optimal slew path by multi-body control approach. Simulation results show that the proposed algorithms can properly circumvent the complex mission planning problem, and that the maximum real-time data downlink can be established while ensuring the complete coverage of the target area.
  • Multi-objective design optimization of blunt body with spike and aerodisk
           in hypersonic flow
    • Abstract: Publication date: Available online 19 April 2019Source: Aerospace Science and TechnologyAuthor(s): Jie Huang, Wei-Xing Yao In order to reduce the aerodynamic drag and aerodynamic heating of the hypersonic blunt body, the aerodisk and spike are installed on the blunt body. In this paper, the influences of the aerodisk on the aerodynamic drag and aerodynamic heating of the hypersonic blunt body are studied by numerical method. The results show that the drag coefficient and maximum heat flux of the blunt body for the configuration with the aerodisk are reduced by 34.09% and 51.06% respectively compared with the configuration without the aerodisk, and the two configurations achieve the drag and heat reduction by reconstructing the flow field. On this basis, multi-objective design optimization of the hypersonic blunt body with the aerodisk and spike is performed by the weighting method and NSGA-II method. The results show that increasing the length of the spike and radius of the aerodisk can reduce total heat flux of the blunt body. The drag coefficient decreases with the increase of the length of the spike. However, with the increase of the radius of the aerodisk, the drag coefficient decreases first and then increases. In addition, the drag coefficient and total heat flux of the blunt body of typical Pareto optimal solution are reduced by 35.90% and 46.97% respectively compared with original design, and adjusting the weighting coefficient of the weighting method can obtain the Pareto frontier calculated by NSGA-II method.
  • A study on the similarity method for helium compressors
    • Abstract: Publication date: Available online 18 April 2019Source: Aerospace Science and TechnologyAuthor(s): Yiming Chen, Zhengping Zou, Chao Fu As the helium compressor is a key component of a hypersonic precooled engine, obtaining accurate performance characteristics of the helium compressor under different working conditions is the basis of the engine system matching. In order to obtain performance characteristics of the helium compressor through compressor performance experiments with air, it is essential to study the similarity method for helium compressors. Based on the dimensional analysis and velocity triangle analysis, a similarity method, which consists of a similarity criterion and translation methods for performance parameters, is proposed in this paper. In order to validate this method, a similar transformation between a centrifugal helium compressor and an identical compressor using air as the substitute working medium and another similar transformation between a centrifugal helium compressor and a geometrically similar compressor using air as the substitute working medium are performed. The performance map of the helium compressor obtained by the similarity method is compared with the one obtained by the numerical simulation. Results show that the proposed similarity method is of high accuracy and can be used to obtain performance characteristics of helium compressors through compressor performance experiments with air.
  • Multi-objective coordinated control of regeneratively-cooled scramjet
           engine with two-stage kerosene injection
    • Abstract: Publication date: Available online 18 April 2019Source: Aerospace Science and TechnologyAuthor(s): Jicheng Ma, Juntao Chang, QingPing Huang, Wen Bao, Daren Yu Aimed at diversity of hypersonic flight mission, multi-objective coordinated control of regeneratively-cooled scramjet engine with two-stage kerosene injection is discussed for guaranteeing a safe, steady and high-efficient operation. Firstly, characteristics analyses and system identification are conducted under the situation of flight Mach number 5 using unsteady 1-D model for regeneratively-cooled scramjet engine. Based on transfer functions obtained from system identification, corresponding proportional integral (PI) controllers are designed for different control objectives such as thrust, steady margin and kerosene temperature at cooling channels outlet. Secondly, different control strategies where flow rates of two stage kerosene injections are adjusted are created in different single control loops, including thrust regulation, steady margin protection, restart recovery, temperature protection and overtemperature recovery control loop. Optimal control strategy is determined ultimately in respective single control loop by analyzing merits and demerits from the perspectives of response speed and engine performance. Lastly, multi-loop coordinated control system is designed on the basis of switch rules and algorithm. Simulation results indicate that rapid responses of control system, smooth and steady switch between different loops are realized. Engine can operate steadily with high performance and recover to a safe operation state rapidly during unstart and overtemperature.
  • Deep learning based short-term air traffic flow prediction considering
           temporal–spatial correlation
    • Abstract: Publication date: Available online 17 April 2019Source: Aerospace Science and TechnologyAuthor(s): Yi Lin, Jian-wei Zhang, Hong Liu In order to improve the accuracy and stability of air traffic flow prediction, an end-to-end deep learning-based model is proposed in this paper. By analyzing spatial correlations of adjacent areas and temporal correlations of historical traffic on given area, we firstly apply the gridded map method (including the flight levels) to encode the whole air traffic flow situation into a new data representation, i.e., traffic flow matrix (TFM). By the proposed data representation, inherent features of air traffic flow and their transition patterns on different cells and flight levels can be represented comprehensively. Learning from the powerful ability of convolutional neural network and recurrent neural network on modeling spatial and temporal correlations, the ConvLSTM module is proposed to build a trainable model for air traffic flow prediction. Since the output of the proposed model is also the TFM and shows the overall air traffic situation of studied regions, we call the proposed model as an end-to-end one. Experimental results on real data show the superior performance over existing approaches on prediction accuracy and stability. Furthermore, the proposed model can also predict the flow distribution on different flight levels in our application, which promotes the level of air traffic management. By analyzing the distribution of prediction errors on different cells, flight levels and predicting instants, we can draw the conclusion that spatial and temporal transition patterns of flight flow in air traffic system are fully learned by the proposed model. With the proposed model, more efficient air traffic flow measures are expected to be fulfilled to improve the operation efficiency.
  • Numerical study of a fully confined supersonic slot impinging jet from
           bleed system
    • Abstract: Publication date: Available online 16 April 2019Source: Aerospace Science and TechnologyAuthor(s): Tinglong Huang, Lianjie Yue, Xinyu Chang A supersonic slot jet issuing from a bleed system and impinging into a plenum is numerically investigated to deepen our understanding of the flow field and heat transfer of a fully confined impinging jet. The air of the slot jet is forced to exhaust from a plenum in unidirection, resulting in a fully confined configuration. It is of significant practical interest because of its presence in the bleed systems of a scramjet or other related applications. Three primary factors are surveyed, i.e., impingement angle, impingement distance, and back pressure at the plenum exit. The results show that the supersonic slot jet spontaneously generates a plate shock standing on the impingement wall and a strong jet shock on the right side of the jet core. On the left side, the jet shear layer can directly impinge the wall because of the pressure self-adaption effect of a recirculation region. The jet shock and jet shear layer result in two peaks of Stanton number. As the impingement angle increases, the jet shock weakens gradually and moves toward the impingement region of the shear layer until the shock disappears. And thus a single heat peak occurs in place of the previous two peaks. When the downstream flow of the plenum is choked, a wall jet pattern is exhibited because of the formation of a large scale recirculation region. The walls suffer severe aerodynamic heating as the plenum back pressure increases. In particular, the impingement wall endures the maximum thermal load at a certain back pressure at which the jet reduces to the sound speed. The plenum should be controlled to keep the back pressure below this threshold so that the slot walls Stanton number won't increase further. And the plenum should be designed as high as possible to relieve its thermal load.
  • Stability analysis of spinning missiles induced by seeker disturbance
           rejection rate parasitical loop
    • Abstract: Publication date: Available online 16 April 2019Source: Aerospace Science and TechnologyAuthor(s): Wei Li, Qiuqiu Wen, Yu Yang This paper focuses on the dynamic stability of spinning missiles equipped with two-loop autopilot considering the seeker disturbance rejection rate parasitical loop (DRRPL) effect induced by attitude disturbance of projectile. The representative mathematical model of spinning missiles in the non-spinning coordinate system is established, and the cross-coupling effect between the pitch and yaw induced by the rotation motion of missile body is analyzed and decoupled. The two-loop acceleration autopilot for each channel is designed with the conventional design method, and the relationship between the autopilot gains and the expected design indexes is deduced. A proportional navigation guidance (PNG) system model with consideration for the seeker DRRPL is further proposed in the form of complex summation. After strict mathematic deduction, the sufficient and necessary condition of the dynamic stability for spinning missiles is obtained. Numerical simulations and discussions under different cases are conducted to demonstrate the validity of stability condition. The results indicate that the stability of a spinning missile is closely related to the amplitude of the seeker DRR, the rolling rate, and the autopilot design indices. The stable region of the autopilot design frequency is obtained by solving the dynamic stability condition. To meet the requirement of stable controlling at a constant spinning rate, it was found to be effective to decrease the amplitude of the seeker DRR for spinning missiles, employ the lead angle decoupling approach to the commands for the servo system, and guarantee that the autopilot design frequency is lower than the critical value. The dynamic stability condition derived in this paper is useful for evaluating the stability of a spinning missile with consideration for the seeker DRRPL, and the conclusions obtained can provide guidance for the autopilot design of spinning missiles.
  • Experimental and numerical investigation of high velocity soft impact
           loading on aircraft materials
    • Abstract: Publication date: Available online 12 April 2019Source: Aerospace Science and TechnologyAuthor(s): J. Zhou, J. Liu, X. Zhang, Y. Yan, L. Jiang, I. Mohagheghian, J.P. Dear, M.N. Charalambides Bird strike on aircraft remains a serious threat to flight safety. Experimental investigations employing real birds are associated with high cost and low reproducibility. Therefore, physical substitute materials are often used instead of real birds. This study investigates the soft impact loading on aluminium and laminated glass targets from ballistic gelatine and rubber projectiles. The two targets simulate strike on the aircrafts' fuselage and windshield respectively. The full field out of plane displacements of the targets were recorded for velocities 110 to 170 m s−1 using digital image correlation during gas gun experiments. A simulation model based on Smoothed Particle Hydrodynamics was developed and validated against the experimental data from all four projectile-target material combinations. It was shown that for the same momentum, a rubber projectile exerts a higher pressure on a target as compared to gelatine, even though the out of plane displacements and in-plane strains are similar. This led to fractures in the impacted laminated glass when rubber was used. The study offers new experimental data as well as efficient design modelling tools to mitigate damage imposed during bird strike. The models provide a way towards enabling the optimisation of real, large scale aircraft structures and components.
  • Task scheduling and attitude planning for agile earth observation
           satellite with intensive tasks
    • Abstract: Publication date: Available online 11 April 2019Source: Aerospace Science and TechnologyAuthor(s): Shuo Wang, Lin Zhao, Jianhua Cheng, Junfeng Zhou, Yipeng Wang This paper investigates the task scheduling and attitude planning of single agile earth observation satellite for intensive tasks. We aim to obtain the execution strategy and corresponding attitude path at the same time by the maximization of the total number of imaged tasks together with minimization of the energy cost, where the rectangle strip observation tasks are considered. Denoting the ground task as a time-varying attitude path, the whole collaborative task scheduling and attitude planning problem is modeled in the attitude apace. To prepare for the final solution, we first design a time-dependent mechanism to determinate the start working time, based on which an energy-dependent mechanism is designed to determine the attitude path corresponding for each possible execution strategy. Using the results produced by the mechanisms to construct the evaluation process, we propose a novel pseudospectral cooperative genetic algorithm (PCGA) to obtain the effective execution strategy and attitude path simultaneously. In PCGA, the genetic algorithm is employed to search the optimal solution, while the pseudospectral procedure and cooperative concept are combined into the genetic algorithm framework to further eliminate the uncertainty and obtain a compromise solution between two objectives, respectively. Simulation results demonstrate the effectiveness of proposed model and algorithm.
  • Adaptive modeling strategy for constrained global optimization with
           application to aerodynamic wing design
    • Abstract: Publication date: Available online 9 April 2019Source: Aerospace Science and TechnologyAuthor(s): N. Bartoli, T. Lefebvre, S. Dubreuil, R. Olivanti, R. Priem, N. Bons, J.R.R.A. Martins, J. Morlier Surrogate models are often used to reduce the cost of design optimization problems that involve computationally costly models, such as computational fluid dynamics simulations. However, the number of evaluations required by surrogate models usually scales poorly with the number of design variables, and there is a need for both better constraint formulations and multimodal function handling. To address this issue, we developed a surrogate-based gradient-free optimization algorithm that can handle cases where the function evaluations are expensive, the computational budget is limited, the functions are multimodal, and the optimization problem includes nonlinear equality or inequality constraints. The proposed algorithm—super efficient global optimization coupled with mixture of experts (SEGOMOE)—can tackle complex constrained design optimization problems through the use of an enrichment strategy based on a mixture of experts coupled with adaptive surrogate models. The performance of this approach was evaluated for analytic constrained and unconstrained problems, as well as for a multimodal aerodynamic shape optimization problem with 17 design variables and an equality constraint. Our results showed that the method is efficient and that the optimum is much less dependent on the starting point than the conventional gradient-based optimization.
  • An intelligent design method for actuation system architecture
           optimization for more electrical aircraft
    • Abstract: Publication date: Available online 9 April 2019Source: Aerospace Science and TechnologyAuthor(s): Zongxia Jiao, Bo Yu, Shuai Wu, Yaoxing Shang, Haishan Huang, Zhewen Tang, Renlei Wei, Chunfang Li The design of flight control actuation system is facing major challenge due to the development of more electrical aircraft. The task is to find the combinations of power sources, actuators and computers, which becomes more complex because of the new power sources and actuator types of more electrical aircraft. It is impossible to determine optimal architecture by traditional trial-and-error method within acceptable time. Therefore, the need for new methodology for actuation system architecture design emerges. This study proposes an intelligent design method which has steps of design space exploration of actuation system architectures by constraint satisfaction problem (CSP) method, safety assessment process to exclude unsafety solution, multi-objectives optimization to get Pareto optimal front and comprehensive decision for final architecture via analytic hierarchy process. And the design method is implemented in python and a software platform is developed. Furthermore, within the paper a case study for A350 flight control actuation system is presented to testify the application of this methodology. Compared to the traditional hydraulic architecture, the optimal architecture is more competitive in weight, power and cost. At the same time, the optimal architecture is found in less than 30 minutes among 1075 candidates, which greatly reduces the design cycle. This method deals with the problem in the design of flight control actuation system.
  • Multi-objective optimisation of short nacelles for high bypass ratio
    • Abstract: Publication date: Available online 19 February 2019Source: Aerospace Science and TechnologyAuthor(s): Fernando Tejero, Matthew Robinson, David G. MacManus, Christopher Sheaf Future turbo-fan engines are expected to operate at low specific thrust with high bypass ratios to improve propulsive efficiency. Typically, this can result in an increase in fan diameter and nacelle size with the associated drag and weight penalties. Therefore, relative to current designs, there is a need to develop more compact, shorter nacelles to reduce drag and weight. These designs are inherently more challenging and a system is required to explore and define the viable design space. Due to the range of operating conditions, nacelle aerodynamic design poses a significant challenge. This work presents a multi-objective optimisation approach using an evolutionary genetic algorithm for the design of new aero-engine nacelles. The novel framework includes a set of geometry definitions using Class Shape Transformations, automated aerodynamic simulation and analysis, a genetic algorithm, evaluations at various nacelle operating conditions and the inclusion of additional aerodynamic constraints. This framework has been applied to investigate the design space of nacelles for high bypass ratio aero-engines. The multi-objective optimisation was successfully demonstrated for the new nacelle design challenge and the overall system was shown to enable the identification of the viable nacelle design space.
  • Numerical simulation on thermal and mass diffusion of MMH–NTO
           bipropellant thruster plume flow using global kinetic reaction model
    • Abstract: Publication date: Available online 3 December 2018Source: Aerospace Science and TechnologyAuthor(s): Kyun Ho Lee A space propulsion system has a crucial role to perform several mission operations of a spacecraft successfully in an orbit. When a thruster is fired, the exhaust plume gas can have effects on the performance of a spacecraft because the expanded plume gas molecules directly collide with the spacecraft surfaces in the vacuum environment. Thus, the present study investigated more realistic plume flow behaviors using a global kinetic reaction model for an actual combustion process of a fuel and an oxidizer. To achieve this, the 4-step global combustion model of monomethylhydrazine and nitrogen tetroxide was incorporated for the first time in the plume flow analysis to reflect a more practical firing condition of a bipropellant thruster. Then, thermal and mass diffusion predictions of the plume flow were compared with the chemical equilibrium condition to examine the distinct differences between the proposed and conventional approach. For efficient numerical calculations, the Navier–Stokes equations and the DSMC method were combined to deal with a continuum flowfield inside the thruster and a rarefied plume gas flow outside the nozzle together. With the present analysis results, major differences in the thermal and mass behaviors of the plume gases were compared between the two reaction models, and their influences are also discussed.
  • Mechanism/structure/aerodynamic multidisciplinary optimization of flexible
           high-lift devices for transport aircraft
    • Abstract: Publication date: Available online 24 October 2018Source: Aerospace Science and TechnologyAuthor(s): Yun Tian, Jianchong Quan, Peiqing Liu, Doudou Li, Chuihuan Kong Mission adaptive variable camber wing in both chord-wise and span-wise directions that can improve the aerodynamic performance during takeoff, landing and cruising flight, will be the state-of-the-art high-lift system for next generation airliners. Based on NASA TrapWing model released on the 1st AIAA CFD High-lift Prediction Workshop, a smart high-lift system with “Flexible Droop Nose & Single Slotted Hinge Flap combined with spoiler deflection & Flexible Trailing Edge Flap” is proposed in this paper. The Flexible Droop Nose is actuated by kinematic chains mechanism, the Single Slotted Hinge Flap is actuated by simple hinge mechanism and the Flexible Trailing Edge Flap is actuated by link/track mechanism.A mechanism/structure/aerodynamic multidisciplinary optimization platform based on iSIGHT software is constructed for this smart high-lift system. This platform consists of stress analysis, high-lift configuration generation, high-lift configuration structure grid generation, computational fluid dynamics and optimization algorithm modules. The optimal takeoff and landing configurations with comprehensive performance of mechanism, aerodynamic and structure is then obtained after multidisciplinary optimization. Finally, the CFD results show that the aerodynamics performance of this smart high-lift system is more effective than the original NASA TrapWing model.
  • Structural Health Monitoring for Long-Term Aircraft Storage Tanks under
           Cryogenic Temperature
    • Abstract: Publication date: Available online 4 March 2019Source: Aerospace Science and TechnologyAuthor(s): Dongyue Gao, Zhanjun Wu, Lei Yang, Yuebin Zheng, Wan Yin In order to monitor the structural conditions, an SHM technology is necessary for long-term aircraft storage tanks under cryogenic conditions. In this paper, a PZT- based Lamb waves SHM technology is developed for such storage tanks. In order to determine the survivability, durability of different PZT-epoxy sensor systems and functionality of the damage diagnosis method under cryogenic conditions of long-term storage tanks, a series of tests have been conducted. First, the durability of PZT-epoxy sensor systems under cryogenic environment was considered by cryogenic durability tests. Simultaneously, performance tests of different PZT-epoxy sensor systems were performed, include high strain performance test and Lamb waves propagation tests under different temperature environments. The high strain performance of different epoxy adhesives under cryogenic environments was investigated by lap shear strength tests. The functionality of different PZT-epoxy sensor systems was investigated by Lamb waves propagation tests. At last, the damage diagnosis ability of the SHM technology was evaluated in a composite damage diagnosis experiment under cryogenic temperature. Experimental results demonstrated that the developed SHM technology can withstand operational levels of high strain and long-term under cryogenic/room temperature on cryogenic storage tanks, and is functional in the cryogenic environment.
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Heriot-Watt University
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