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Aerospace Science and Technology
Journal Prestige (SJR): 0.796
Citation Impact (citeScore): 3
Number of Followers: 345  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1270-9638
Published by Elsevier Homepage  [3155 journals]
  • Preliminary aeroelastic design of composite wings subjected to critical
           gust loads
    • Abstract: Publication date: February 2019Source: Aerospace Science and Technology, Volume 85Author(s): D. Rajpal, E. Gillebaart, R. De Breuker Including a gust analysis in an optimization framework is computationally expensive as the critical load cases are not known a priori and hence a large number of points within the flight envelope have to be analyzed. Model order reduction techniques can provide significant improvement in computational efficiency of an aeroelastic analysis. In this paper, after thorough analysis of 4 commonly used model order reduction methods, balanced proper orthogonal decomposition is selected to reduce the aerodynamic system which is based on potential flow theory. The reduced aerodynamic system is coupled to a structural solver to obtain a reduced-order aeroelastic model. It is demonstrated that the dominant modes of the aerodynamic model can be assumed to be constant for varying equivalent airspeed and Mach number, enabling the use of a single reduced model for the entire flight envelope. A dynamic aeroelastic optimization method is then formulated using the reduced-order aeroelastic model. Results show that both dynamic and static loads play a role in optimization of the wing structure. Furthermore, the worst case gust loads change during the optimization process and it is important to identify the critical loads at every iteration in the optimization.
       
  • Adaptive control of underactuated flight vehicles with moving mass
    • Abstract: Publication date: February 2019Source: Aerospace Science and Technology, Volume 85Author(s): Jianqing Li, Sai Chen, Chaoyong Li, Changsheng Gao, Wuxing Jing The configuration of internal moving masses is a key challenge for applying moving mass control technology to flight vehicle control. A novel configuration with a large mass ratio moving mass and reaction jets is proposed for bank-to-turn control. The control system of the proposed configuration consists of the attitude dynamics and the moving mass dynamics, which are coupled by the additional inertia moment of moving mass. To deal with the coupling, the integrated control of an attitude-servo system and a lateral underactuated control based on immersion and invariance theory is presented. To overcome the uncertainties in the flight vehicle model, immersion and invariance theory is employed to design an estimator for the unknown aerodynamic parameters. The estimator has an additional nonlinear term which adjusts the performance of the estimation error. The simulation results show that the proposed attitude-servo controller for the longitudinal subsystem can enhance the response of the system and the underactuated controller of the lateral subsystem can reduce fuel consumption.
       
  • Dynamic response of axially functionally graded beam with
           longitudinal–transverse coupling effect
    • Abstract: Publication date: February 2019Source: Aerospace Science and Technology, Volume 85Author(s): Ke Xie, Yuewu Wang, Tairan Fu This study investigates the dynamic response of an axially functionally graded (AFG) beam with longitudinal–transverse coupling effect. The beam is acted by a moving transverse harmonic load and a moving longitudinal harmonic load simultaneously. Both the classical beam theory (CBT) and the Timoshenko beam theory (TBT) are employed and written in a unified form. The system of equations of motion is obtained using Lagrange's equations. The nonlinear formulations of the longitudinal–transverse coupling AFG beams are presented. These formulations are solved using the Newmark method in conjunction with a direct iteration procedure; subsequently, the free and forced dynamic behavior characteristics of the AFG beams are investigated. A comparison of the results obtained using the TBT and CBT is performed. The nonlinear effects caused by different excitation frequencies and amplitudes both in the transverse and longitudinal directions of the moving loads on the dynamic responses of the AFG beam are discussed. Further, different nonlinear dynamic behaviors of the AFG beam caused by different longitudinal–transverse coupling coefficients are revealed. The numerical results indicate that the longitudinal–transverse coupling effect plays an important role in the dynamic behavior of the AFG beam.
       
  • Optimization and control application of sensor placement in
           aeroservoelastic of UAV
    • Abstract: Publication date: February 2019Source: Aerospace Science and Technology, Volume 85Author(s): Weiqi Yang, Hui Yang, Shuo Tang In order to suppress aeroservoelastic in high-aspect-ratio flexible UAV, in the present work an advanced sensor placement criterion is developed using Cuckoo search algorithm in combination with an enhanced active control method. The advanced sensor placement criterion basically combines the vibration energy based observability measurement as well as further information on evaluating sensor influence in terms of H2 norm to balance the low and high frequency modes. By eliminating several nests with worst fitness values in each generation and using self-adaptive feedback scaling factor, the proposed elimination mechanism Cuckoo search (EMCS) algorithm is almost three times faster than the standard one. Subsequently, an enhanced active disturbance rejection control (ADRC) method is proposed for the first time in the active vibration control and wind load alleviation of flexible UAV. It is demonstrated that the enhanced ADRC/PID approach with obtained sensor locations can result in a 45.83% reduction in generalized vibrations energy and about 52.16% reduction in wind load alleviation when compared with designs where the sensor locations are not optimum. Finally, the simulation results show that the optimization algorithm can effectively find the optimal location of sensors. Meanwhile, the suppression of aeroservoelastic can be realized with the utilization of the active control.
       
  • A new continuous adaptive finite time guidance law against highly
           maneuvering targets
    • Abstract: Publication date: February 2019Source: Aerospace Science and Technology, Volume 85Author(s): Jianguo Guo, Yifei Li, Jun Zhou A novel continuous adaptive finite time guidance (CAFTG) law is proposed for homing missiles. Firstly, three-dimensional nonlinear dynamics describing the pursuit situation of the missile and the target are introduced to obtain the mathematical model of engagement. Secondly, in order to improve the accuracy of interception, a nonlinear disturbance observer with finite time convergence is employed to estimate the acceleration of a target and compensate the guidance law. A continuous guidance scheme with robustness is constructed via sliding mode control theory, which guarantees finite time convergence by Lyapunov stability theory. Finally, simulations are conducted on the nonlinear dynamic models and results demonstrate the effectiveness of proposed guidance method.
       
  • Flow simulation and drag decomposition study of N3-X hybrid wing-body
           configuration
    • Abstract: Publication date: February 2019Source: Aerospace Science and Technology, Volume 85Author(s): Hyoungjin Kim, May-Fun Liou Flow simulation and drag decomposition study was conducted for the flow field around the clean airframe of the N3-X hybrid wing body configuration at a cruise flight condition. Adopted flow solver was GO-flow; an unstructured hybrid mesh cell-vertex finite volume RANS solver. The OVERFLOW code was also used to cross check the results. We have found that the major flow features such as surface pressure distributions and shock waves from the two flow solvers were almost identical to each other. Evaluation of drag force using near- and mid-field approaches was also conducted. Comparisons of various drag components between two tested CFD codes are examined with various grid resolutions for angle of attack sweep at the cruise condition. From the results, it is recommended for the computational mesh of the unstructured CFD code to have anisotropic (stretched) meshes near the leading and trailing edges and enough resolution in wake regions for accurate estimation of the drag coefficient. Nacelle installation effects were also tested using inviscid simulations by flow-through single-passage nacelle and mail slot nacelle, and it was found that fan suction effects should be properly considered for the accurate modeling of the nacelle installation effects. Lessons learned in this study enhance confidence in using CFD based integrative approach to encompass design of future hybrid wing body aircraft.
       
  • Control of corner separation via dimpled surface for a highly loaded
           compressor cascade under different inlet Mach number
    • Abstract: Publication date: February 2019Source: Aerospace Science and Technology, Volume 85Author(s): Huawei Lu, Yi Yang, Shuang Guo, Wenxuan Pang, Fan Yang, Jingjun Zhong In this paper, flow characteristics of dimpled compressor cascades are numerically discerned by solving the compressible Reynolds-averaged Navier–Stokes equations on structured grids over the inlet Mach number ranging from 0.3 to 0.8. Four rows of parallel, spherical dimples with a depth of 0.2 mm and a depth-to-diameter ratio of 0.25 are embedded along 10%–32% and 38%–60% chord of suction surface respectively. Results showed that two dimple configurations can both reduce the total pressure loss in all researched Mach number except that of 0.8. The suppression of three-dimensional separation near the hub-corner region is the primary cause of loss reduction. What's more, the separation bubble on the suction surface can be also eliminated or depressed due to the disturbance and higher level of turbulence kinetic energy within boundary layer. According to the distribution of axial vorticity in flow passage, the dimpled vortex can also suppress the migration of secondary flow along spanwise direction under a relative higher cross pressure gradient.
       
  • Fuzzy logic based equivalent consumption optimization of a hybrid electric
           propulsion system for unmanned aerial vehicles
    • Abstract: Publication date: February 2019Source: Aerospace Science and Technology, Volume 85Author(s): Ye Xie, Al Savvaris, Antonios Tsourdos This paper presents an energy management strategy for a hybrid electric propulsion system designed for unmanned aerial vehicles. The proposed method combines the Equivalent Consumption Minimization Strategy (ECMS) and fuzzy logic control, thereby being named Fuzzy based ECMS (F-ECMS). F-ECMS can solve the issue that the conventional ECMS cannot sustain the battery state-of-charge for on-line applications. Furthermore, F-ECMS considers the aircraft safety and guarantees the aircraft landing using the remaining electrical energy if the engine fails. The main contribution of the paper is to solve the deficiencies of ECMS and take into consideration the aircraft safely landing, by implementing F-ECMS. Compared with the combustion propulsion system, the hybrid propulsion system with F-ECMS at least reduces 11% fuel consumption for designed flight missions. The advantages of F-ECMS are further investigated by comparison with the conventional ECMS, dynamic programming and adaptive ECMS. In contrast with ECMS and dynamic programming, F-ECMS can accomplish a balance between sustaining the battery state-of-charge and electric energy consumption. F-ECMS is also superior to the adaptive ECMS because there are less fuel consumption and lower computational cost.
       
  • Recurrence network analysis for uncovering dynamic transition of
           thermo-acoustic instability of supercritical hydrocarbon fuel flow
    • Abstract: Publication date: February 2019Source: Aerospace Science and Technology, Volume 85Author(s): Hao Zan, Weixing Zhou, Xuefeng Xiao, Long Lin, Junlong Zhang, Haowei Li Characterizing the transition of thermo-acoustic instability of supercritical hydrocarbon fuel flow is a fundamental problem eliciting a great deal of attention from different disciplines. We experimentally and theoretically investigate the transition process between thermo-acoustic stability and instability. The method of recurrence network is applied to analyze the pressure time series of supercritical hydrocarbon fuel flow. As a result, we can distinguish a thermo-acoustic transition process from normal signals by real-time detecting the complexity variation of pressure signals of fuel in cooling channels with the recurrence network method. Then, we construct the recurrence network from experimental data under the stable, transition and unstable states, and investigate the degree distribution and motifs distribution. We find that the degree distribution and motifs distribution allow quantitatively uncovering the complexity dynamic process. We investigate the during time of transition process, and find that the mass flow rate and the inlet pressure will make an influence on the transition time. These findings present a first step towards an improved understanding on the transition of thermo-acoustic instability from a complex network perspective. Moreover, the investigation on the transition of thermo-acoustic instability under supercritical pressure condition offers guidance on the control of scramjet fuel supply, which can secure stable fuel flowing in regenerative cooling system.
       
  • Dynamic modelling and control of a Tendon-Actuated Lightweight Space
           Manipulator
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Kai Li, Yao Zhang, Quan Hu The Tendon-Actuated Lightweight Space Manipulator has advantages such as a large range of motion and lightweight when compared with conventional space manipulators. In this paper, dynamic modelling and controller design of a tendon-actuated manipulator are investigated. First, nonlinear coupling dynamic equations of the central body spacecraft and a four-degree-of-freedom tendon-actuated manipulator mounted on it are derived based on Kane's equation, and their controllers are then designed while considering the dynamic coupling. In addition, a tension analysis method is proposed that is subject to the tension constraints, and the actuators of the tendon-actuated manipulator are analysed. Numerical simulations indicate that the designed controller can achieve attitude stability of the central body spacecraft and endpoint trajectory tracking of the tendon-actuated manipulator. A feature of the tendon-actuated manipulator is its enlargement of the joint actuated torque, and a long link, tendon-actuated manipulator has more benefits relative to a conventional space manipulator.
       
  • Human-in-the-loop control of guided airdrop systems
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Martin R. Cacan, Mark Costello, Michael Ward, Edward Scheuermann, Michael Shurtliff Advances in guided airdrop technology including guidance, navigation, and control algorithms, novel control mechanisms and wind sensing algorithms have led to significant improvements over unguided airdrop systems. Guided systems are autonomously controlled with an embedded microprocessor using position and velocity feedback. While capable of highly accurate landing, these systems struggle to overcome deviations from expected flight dynamics due to canopy damage or cargo imbalance, complex terrain at the drop zone, and loss of sensor feedback. Human operators are intelligent, highly adaptive, and can innately judge the flight vehicle and environment to steer the vehicle to the desired impact point provided sufficient information. This work experimentally explores operators' abilities to accurately land an airdrop system using different sensing modalities. Human operator landing results are compared with a state of the art fully autonomous airdrop system. Across the methods analyzed, human operators attained up to a 40% increase in landing accuracy over the fully autonomous control algorithm.
       
  • Unsteady characteristics of S-duct intake flow distortion
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Daniel Gil-Prieto, Pavlos K. Zachos, David G. MacManus, Grant McLelland The unsteady distorted flow fields generated within convoluted intakes can have a detrimental effect on the stability of an aero-engine. The frequency signature in the distorted flow field is of key importance to the engine's response. In this work, time-resolved particle image velocimetry is used to obtain the three-component velocity field at the outlet plane of two S-duct intake configurations for a range of inlet Mach numbers. Proper orthogonal decomposition of the time-resolved velocity data allows the identification of the main frequencies and coherent structures in the flow. The most energetic unsteady structures comprise an in-plane vortex switching mode, associated with a lateral oscillation of the main loss region, and a vertical oscillation of the main loss region. The switching structure occurs at a frequency of St=0.42 and 0.32 for the high and low offset ducts, respectively. The vertical perturbation is associated with a more broadband spectrum between approximately St=0.6–1.0 and St=0.26–1.0 for the high and low offset configurations, respectively. The determined frequencies for these main unsteady flow structures are within the range, which is expected to be detrimental to the operating stability of an aero-engine. The results provide a novel, time-resolved dataset of synchronous velocity measurements of high spatial resolution that enables analysis of the unsteady flows at the exit of complex aero-engine intakes.
       
  • A novel aspect of composite sandwich fairing structure optimization of a
           two-stage launch vehicle (Safir) using multidisciplinary design
           optimization independent subspace approach
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Foozieh Morovat, Ali Mozaffari, Jafar Roshanian, Hadi Zare In this article, a novel composite sandwich structure analysis of launch vehicle fairing is considered by a new multidisciplinary design optimization methodology. Among the most important roles of this method, in addition to the convergence of optimization process, is tackling with complicated composite structure discipline. The bidirectional coupling existing between composite structure and trajectory disciplines is one of the complex problems of this multidisciplinary design optimization method. Accordingly, multidisciplinary design optimization based on independent subspaces is employed using the fixed point iteration method to achieve the best convergence at system level and segregate the disciplines. Therefore, the two proposed subspaces overcome the difficulties of common mentioned multidisciplinary design optimization of launch vehicles as the main novelty of this study. The first subspace is a multidisciplinary design optimization which includes propulsion, aerodynamics, weight and trajectory disciplines. The second one includes the novel composite fairing structure optimization as the other single discipline optimization which is analytically and numerically considered as a compact problem and is regarded as the other novelty of this work. In a case study, by applying the proposed architecture on Safir launch vehicle and considering propulsion, trajectory and also composite sandwich fairing structure design as the variables and then performing an optimization process, the Safir fairing mass is reduced from 100 kg to 57.8 kg. This causes the launch vehicle gross mass to decrease from 26 tons to 25.2 tons due to the payload nature of fairing. This 3% mass decrease of an operational launch vehicle, despite the preservation of mission performance, can be called an industrial novelty which leads to the cost reduction of space transportation. The proposed system engineering demonstrates the great importance of using multidisciplinary design optimization in complicated designs using independent subspaces to be employed for the design of future launch vehicles. It can also be a road map for future designers of space vehicles, especially those who want to consider structure optimization in the design loop of launch vehicles.
       
  • A study of coaxial rotor aerodynamic interaction mechanism in hover with
           high-efficient trim model
    • Abstract: Publication date: Available online 29 November 2018Source: Aerospace Science and TechnologyAuthor(s): Haotian Qi, Guohua Xu, Congling Lu, Yongjie Shi A numerical method based on Reynolds Averaged Navier–Stokes (RANS) equations and moving overset mesh technique is developed to simulate the aerodynamics of Harrington rotor-2. A high-efficient trim model for hover is presented and coupled into the numerical method and the “delta trim arithmetic” is implemented to simplify the calculation of Jacobian matrix. Validation cases are computed, showing reasonably coincident with the available experimental data. Hover cases of different thrust coefficients with torque-balanced are conducted. Specially, zero-lift and one-rotor-stay cases are set for a better understanding of the interaction mechanism. Results indicate that the temporal thrusts of the coaxial rotor show a variation of gradually increasing and sharply decreasing. Different from the previous work, the fluctuation features are mainly explained by strong-weak “induction effect” and impulsive “overlap effect” caused by the interaction of wakes and bound vortexes of coaxial rotor. At a positive attack angle, the induction and overlap effects are more evident for the upper rotor because the induced flow is stronger above the blade than that below it. The first impulse of thrust caused by overlap effect takes place at about 3° azimuth after the alignment of the blades for present cases, as the upper and lower blades meet in a rotating way.
       
  • Dynamic coupling on the design of space structures
    • Abstract: Publication date: Available online 28 November 2018Source: Aerospace Science and TechnologyAuthor(s): Andrés García-Pérez, Ángel Sanz-Andrés, Gustavo Alonso, Marcos Chimeno Manguán For the design of space structures, the dynamic coupling between equipment and the satellite (or between a satellite and the launcher) is usually avoided due to negative effects like high stresses produced by structural resonance. The usual procedure to assure the dynamic decoupling is by limiting the minimum value of natural frequency of the secondary structure to a value high enough above the main natural frequencies of the main structure. However, in some spacecraft configurations, it is unavoidable that some parts or equipment present natural frequencies close to the main natural frequencies of the spacecraft because these parts may be massive or may have a special interface design with low stiffness. This dynamic coupling provokes modifications on the modal behavior of the satellite, which can lead to a significant decrease in the first natural frequency of the entire satellite. To analyze this phenomenon, a representative but simple mathematical model is studied to evaluate the influence of the design parameters of space structures. Analytical expressions are obtained that can help to highlight the influence of the parameters. The results are demonstrated with the example of the UPMSat-2 satellite design.
       
  • Ignition and heterogeneous combustion of aluminum boride and
           boron–aluminum blend
    • Abstract: Publication date: Available online 28 November 2018Source: Aerospace Science and TechnologyAuthor(s): Daolun Liang, Rui Xiao, Jianzhong Liu, Yang Wang Adding other metals is an efficient method of breaking through the energy release efficiency limitation of boron-based fuels. A laser ignition testing system was used for investigating the ignition and heterogeneous combustion characteristics of aluminum boride and boron–aluminum blend. The emission spectra and combustion flames of the samples during combustion were recorded by a fiber optic spectrometer and a high-speed camera, respectively. The component, morphology, and distribution features of the condensed combustion products (CCPs) were then analyzed using an X-ray diffractometer, a scanning electron microscope, and an X-ray energy dispersive spectrometer. The emission spectral intensity curves show that the boron–aluminum blend has better ignition feature than aluminum boride (the ignition delay time was 45% shorter). However, the combustion intensity and self-sustaining combustion time of boron–aluminum blend are both inferior to those of aluminum boride. In full wave emission spectra of the samples, the characteristic peaks of combustion intermediate products like BO2, AlO, and AlO2 were found. The combustion flames of the two samples were both yellow green and tapered. The variation trend of the flame size corresponded to that of the emission spectral intensity curves. During the first half of the combustion, large amounts of sparks were ejected from the combustion flame of boron–aluminum blend, which caused the acute fluctuation of combustion intensity. B, Al, B2O3, Al2O3, AlN, and Al5O6N were detected in the CCPs of both samples. In addition, the CCPs of aluminum boride contained unburned AlB2, and those of boron–aluminum blend contained Al4B2O9. Webbed AlN fibers were observed only in the CCPs of boron–aluminum blend, while AlN and Al5O6N whiskers were found in those of both samples. The observed bulks were partially oxidized AlB2 in the CCPs of aluminum boride, or partially oxidized B in those of boron–aluminum blend. As both diffusion and melt-dispersion reactions of aluminum were proceeded during the combustion of boron–aluminum blend, oxidation products of aluminum with different morphology were found in the CCPs of boron–aluminum blend as follows: smooth aluminum spheres with low oxidation degree, rough aluminum oxide spheres with high oxidation degree, empty aluminum oxide shells with hollows or cracks, and fine aluminum oxide particles adhered on the surface of boron bulks.
       
  • Ablative thermal protection system under uncertainties including pyrolysis
           gas composition
    • Abstract: Publication date: Available online 28 November 2018Source: Aerospace Science and TechnologyAuthor(s): M. Rivier, J. Lachaud, P.M. Congedo Spacecrafts such as Stardust (NASA, 2006) are protected by an ablative Thermal Protection System (TPS) for their hypersonic atmospheric entry. A new generation of TPS material, called Phenolic Impregnated Carbon Ablator (PICA), has been introduced with the Stardust mission. This new generation of low density carbon-phenolic composites is now widely used in the aerospace industry. Complex heat and mass transfer phenomena coupled to phenolic pyrolysis and pyrolysis gas chemistry occur in the material during atmospheric entry. Computer programs, as the Porous material Analysis Toolbox based on OpenFoam (PATO) released open source by NASA, allow to study the material response. In this study, a non-intrusive Anchored Analysis of Variance (Anchored-ANOVA) method has been interfaced with PATO to perform low-cost sensitivity analysis on this problem featuring a large number of uncertain parameters. Then, a Polynomial-Chaos method has been employed in order to compute the statistics of some quantities of interest for the atmospheric entry of the Stardust capsule, by taking into account uncertainties on effective material properties and pyrolysis gas composition. This first study including pyrolysis gas composition uncertainties shows their key contribution to the variability of the quantities of interest.
       
  • Vibration reduction of the blisk by damping hard coating and its
           intentional mistuning design
    • Abstract: Publication date: Available online 28 November 2018Source: Aerospace Science and TechnologyAuthor(s): Yugang Chen, Hongchun Wu, Jingyu Zhai, Hui Chen, Qingyu Zhu, Qingkai Han This paper presents a vibration reduction approach of the blisk by using of the damping hard coating and its intentional mistuning design. Firstly the amplified forced vibration responses of mistuned blisk were studied based on the reduced order finite element model (FEM) established by component mode synthesis (CMS) method, by using the actual mistuning value of a blisk specimen. Then the effects of damping hard coating on forced vibration responses of the tuned and mistuned blisk were investigated. Further, intentional mistuning design by depositing hard coating with different thickness on blades was researched, after comparing several mistuning patterns. At last, experiment research was conducted by using a blisk specimen with random mistuning. NiCrAlY coating was deposited on blades with designed thickness, in accordance with the simulation results. It reveals to be an effective approach for reducing the vibration level of mistuned blisk, judging from the observed lower vibration response level after the intentional mistuning design by hard coating. The results of this paper can help to decrease the fatigue failure induced by mistuned vibration and improve the structure integrity and security of the blisk in aero-engine.
       
  • Data-driven fault diagnosis of satellite power system using fuzzy Bayes
           risk and SVM
    • Abstract: Publication date: Available online 28 November 2018Source: Aerospace Science and TechnologyAuthor(s): Baolong Zhu, Mingliang Suo, Ruoming An, Huimin Sun, Shengzhong Xu, Zhenhua Yu Data-driven fault diagnosis is more suitable than model-based methods for diagnosing the complicated spacecraft systems, e.g., the satellite power system, because of its simplicity and convenience. Nevertheless, some redundant and irrelevant features in monitoring data are usually not conducive to identify fault state but significantly reduce the correct rate of diagnosis and increase the computational complexity and memory storage space. The existing filter feature selection approaches usually need to provide the number of selected features in advance, which brings an extra burden to decision makers. To make up for this deficiency, this paper proposes a feature selection method based on fuzzy Bayes risk (FBR) to generate an optimal feature subset automatically without having to preset the feature number. A heuristic forward greedy feature selection algorithm based on the proposed fuzzy Bayes risk theory is designed. Subsequently, a data-driven fault diagnosis strategy is designed by employing FBR and Support Vector Machine (SVM). Finally, numerical experiments on UCI data and the fault diagnoses of satellite power system are carried out to illustrate the superiority and applicability of the proposed method. The results of comparison experiments show that both classification accuracy of UCI data and diagnosis effect of satellite power system are better than the other state-of-the-art methods.
       
  • Investigation on magnetic-based attitude de-tumbling algorithm
    • Abstract: Publication date: Available online 27 November 2018Source: Aerospace Science and TechnologyAuthor(s): Xiwang Xia, Chongbin Guo, Guoshan Xie Most of the low-cost NanoSats, which run on the low-earth orbits and have no severe pointing requirement, usually adopt magnetic-based attitude control scheme as an important or even the dominant attitude control strategy to de-tumble and stabilize themselves. The attitude control components regularly equipped include magnetic torquers and magnetometer, and sometimes even a miniaturized momentum wheel. The primary task of the attitude control system of the NanoSats is to achieve rate damping and the famous B-dot control algorithm is widely adopted to de-tumble the satellites. However, when the initial angular velocity is significantly fast and an obvious lag exists in the control system, the wide-spread B-dot control algorithm would fail to de-tumble the satellite. Oppositely, the angular velocity would be controlled to a large-scale one. In this paper, one novel rate damping algorithm is proposed to deal with this case. For momentum satellites, during de-tumbling control process based on B-dot algorithm, their attitude motion is analyzed in detail. Analysis indicates that the roll-yaw control channel is stable and the pitch angle tumbles from 180 deg down to −180 deg in about one orbit period. In addition, the optional range of the bias moment has been specified. Simulation results indicate that the proposed novel damping algorithm is effective and the momentum satellite's attitude motion during B-dot damping process is coincided with the resulted attitude motion characteristics, which is benefit for the satellites, which are running in dawn-dusk orbits, to obtain solar energy for the positive/negative Y-body axis is always pointing at the negative normal direction of the orbital plane.
       
  • Autonomous relative navigation around uncooperative spacecraft based on a
           single camera
    • Abstract: Publication date: Available online 27 November 2018Source: Aerospace Science and TechnologyAuthor(s): Vincenzo Pesce, Roberto Opromolla, Salvatore Sarno, Michèle Lavagna, Michele Grassi The interest of the space community toward missions like On-Orbit Servicing of functional satellite to extend their operative life, or Active Debris Removal to reduce the risk of collision among artificial objects in the most crowded orbital belts, is significantly increasing for both economical and safety aspects. These activities present significant technical challenges and, thus, can be enabled only by increasing the level of autonomy and robustness of space systems in terms of guidance, navigation and control functionalities. Clearly this goal requires the design and development of ad-hoc technologies and algorithms. In this framework, this paper presents an original architecture for relative navigation based on a single passive camera able to fully reconstruct the relative state between a chaser spacecraft and a non-cooperative, known target. The proposed architecture is loosely coupled, meaning that pose determination and full relative state estimation are entrusted to separate, but rigidly interconnected processing blocks. Innovative aspects are relevant to both the pose determination algorithms and the filtering scheme. Preliminary performance assessment is carried out by means of numerical simulations considering multiple realistic target/chaser relative dynamics and target geometries. Results allow demonstrating robustness against measurement error sources caused possibly by image processing as well as fast rotational dynamics.
       
  • A novel quasi-one-dimensional model for performance estimation of a
           Vaporizing Liquid Microthruster
    • Abstract: Publication date: Available online 26 November 2018Source: Aerospace Science and TechnologyAuthor(s): M.G. De Giorgi, D. Fontanarosa The present work aims to propose a novel quasi-one-dimensional model for the performance estimation of a Vaporizing Liquid Microthruster (VLM). The analytical model was applied to the analysis of a MEMS-based VLM composed of a rectangular inlet chamber, a set of parallel microchannels as heating chamber, and a planar convergent-divergent micronozzle. It combines a steady-state boiling model for the analysis of the heater with a real nozzle flow model for the evaluation of actual thrust force and specific impulse, based on iterative procedure aiming at the convergence of the actual mass flow rate and the heat flux. For the purpose, a set of semi-empirical formulas found among both theoretical and experimental scientific works have been introduced for the estimation of the critical heat flux condition and the local heat transfer coefficient. In addition, the real nozzle flow model predicts the performance and the viscous losses due to the boundary layer growth inside the micronozzle. The last ones are estimated by introducing analytical expressions for the discharge coefficient and the Isp-efficiency into the isentropic nozzle flow theory. The resulting performance predictions of the 1D model referred to the on-design operating conditions. They well agreed with the experimental data, with a maximum estimated error of 7.3% on the thrust and the specific impulse. Furthermore, the analytical model of the micronozzle predicted a reduction of the mass flow rate up to about 8%, as well as thrust losses up to 15% due to the contraction of the cross sectional area.In addition, 2D and 3D computational fluid dynamics (CFD) simulations were performed in order to enforce the analysis of the viscous effects. Predictions of 2D computations overestimated the performances of the microthruster with respect to experiments, up to about 19% of the thrust and 20% of the specific impulse. On the other hand, the 3D predicted thrust approached to the experimental one with an error of about 9.2% below. In addition, a severe reduction of jet thrust in favor of the pressure thrust was observed at the nozzle exit. Furthermore, 3D computations pointed out the influence of the micronozzle depth on the boundary layer growth and the viscous losses. In particular, they revealed the establishment of the nozzle blockage and the thermal chocking of the supersonic flow owing to the subsequent viscous heating.
       
  • Nonlinear stability of moderately thick functionally graded sandwich
           shells with double curvature in thermal environment
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Minh-Chien Trinh, Seung-Eock Kim Theoretical closed-form solutions and numerical results for nonlinear stability of the moderately thick functionally graded sandwich shells subjected to thermomechanical loadings are presented in this study. Two proposed material distribution models supported by elastic foundations are examined. The nonlinear strain field is deduced from the first-order shear deformation theory taking the stretching, bending and shear effects into consideration. The Bubnov–Galerkin procedure and harmonic balance principle are utilized to bring about the explicit algebraic expression for the shell static behaviors from governing equations derived from Hamilton's principle. Mechanical buckling loads and critical thermal rises for the shells in spherical, cylindrical, and hyperbolic paraboloid forms are obtained. The effect of geometry, elastic foundations, volume fraction index, material distribution models, buckling modes, and imperfections on the shell stability behaviors are considered in parametric studies. The yielding plateau in the thermal analysis of the spherical shells in case of temperature dependent characteristics is recognized for the first time. Verification studies are also conducted.
       
  • Aircraft engine degradation prognostics based on logistic regression and
           novel OS-ELM algorithm
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Feng Lu, Jindong Wu, Jinquan Huang, Xiaojie Qiu Online sequential extreme learning machine (OS-ELM) learns data one-by-one or chunk-by-chunk, and the recursive least square (RLS) algorithm is commonly employed to train the topological parameters of OS-ELM. Since it is hard to guarantee the smallest estimation error of the state variable by the RLS, the regression performance of the OS-ELM easily fluctuates in practical applications. To address this gap, a new training approach of the OS-ELM using Kalman filter called KFOS-ELM is proposed, and state propagation is combined into extreme learning process to obtain the OS-ELM's topological parameters. Besides, an adaptive-weighted ensemble mechanism is developed and used to dynamically tune the weight coefficients of each KFOS-ELM in the learning network. The regression performance of the proposed methodology is evaluated using benchmark datasets. The simulation results show that proposed methods are superior to the OS-ELM and EOS-ELM in terms of the regression accuracy and stability without additional computational efforts. Furthermore, an enhanced multi-sensor prognostic model based on KFOS-ELM and logistic regression (LR) model is designed for remaining useful life (RUL) prediction of aircraft engine. The experimental results confirm our viewpoints.
       
  • Roles and mechanisms of casing treatment on different scales of flow
           instability in high pressure ratio centrifugal compressors
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Xiao He, Xinqian Zheng The development of single-stage high pressure ratio centrifugal compressors for small gas turbine engines is hindered by compressor flow instabilities with various temporal and spatial scales. In this paper, the effect of a self-recirculation casing treatment device for suppressing various scales of flow instability has been discussed. Rig tests of a high pressure ratio centrifugal compressor with and without a casing treatment device are performed, and transient pressure signals are measured at endwalls by fast response pressure transducers. By analyzing measured pressure signals in both time and frequency domain, the casing treatment device is found effective in eliminating rotating instability and stall at the impeller inlet at low speeds, as well as suppressing surge of the compression system at middle and high speeds. The flow recirculation process generated inside the casing treatment device removes the vortical structures at the impeller inlet tip section, therefore eliminating the regional rotating instability and stall. Besides, the casing treatment device turns the pressure rise characteristics of the impeller more negative by enhancing the impeller work input, but turns that of the vaned diffuser more positive by increasing the incidence at the vaned diffuser inlet. Combining both effects, mild surge and the deep surge are suppressed.
       
  • Repeated low-velocity impact response and damage mechanism of glass fiber
           aluminium laminates
    • Abstract: Publication date: Available online 23 November 2018Source: Aerospace Science and TechnologyAuthor(s): Lijun Li, Lingyu Sun, Taikun Wang, Ning Kang, Wan Cao Glass fiber aluminium laminate (GLARE) is a kind of fiber metal laminates widely applied in aircraft structures, frequently subjected to low-velocity impact incidents. The purpose of this paper is to investigate the dynamic response and damage mechanism characterization of GLARE under single and repeated low-velocity impacts. Firstly, a progressive degradation finite element (FE) model was developed and validated. Three different failure criteria were compared to analyze the damage behavior of composites of GLARE in terms of accuracy and efficiency, wherein a user defined material subroutine VUMAT was introduced. Then, the validated model was used to study the influence of the impact angle. Four different impact angles including 30°, 45°, 60° and 90° were analyzed in terms of plastic deformation, impact contact force, energy absorption and internal damage. Finally, the simulation of GLARE subjected to repeated impacts was carried out, in which the cumulative damage effects were considered. The detailed dynamic response and damage evolution of aluminium layers and composite layers as well as their interfaces with the number of impacts increasing were revealed.
       
  • Numerical investigation of the porpoising motion of a seaplane planing on
           water with high speeds
    • Abstract: Publication date: Available online 23 November 2018Source: Aerospace Science and TechnologyAuthor(s): Xupeng Duan, Weiping Sun, Cheng Chen, Meng Wei, Yong Yang During the taking-off and landing processes on water, a seaplane will begin to porpoise under a certain set of conditions, which is a threat to the flying safety. Porpoising motion is an unstable oscillation about the gravity center in the vertical direction. In this paper, the porpoising phenomenon is studied by a modified two-phase flow solver in OpenFOAM through the simulation of a large seaplane with four turbines during take-off. In order to study the porposing motion under real conditions, complex effects are fully considered such as the hydrodynamic forces, aerodynamic forces, ground effect and slipstream. Firstly, an actuator disk method is added to the interDyMFoam solver, and the sixDoFRigidBodyMotion solver is also modified to make the actuator disk move together with the aircraft. By doing this, the efficiency of computation is greatly improved in the unsteady multi-phase calculation. Secondly, verification and validation (V&V) studies are carried out by comparing the results herein to those of the benchmark towing tank experiments of Fridsma and a single propeller wind tunnel test. Stable high speed planing is studied in advance, and the triggering conditions and dynamic characteristics of porpoising are investigated subsequently. The free surface together with pressure and velocity fields are analyzed and discussed in detail. The result shows that slipstream offers a nose down pitching moment, which increases the aerodynamic lift significantly, and the center of hydrodynamic force moves to the front of gravity center, leading to the continuous amplification of the unstable oscillation in porpoising. As a result the heaving and pitching oscillations are mainly determined by hydrodynamic force, while the aerodynamic force only plays an auxiliary role.
       
  • Attitude estimation for cooperating UAVs based on tight integration of
           GNSS and vision measurements
    • Abstract: Publication date: Available online 22 November 2018Source: Aerospace Science and TechnologyAuthor(s): Amedeo Rodi Vetrella, Giancarmine Fasano, Domenico Accardo This paper presents a cooperative navigation approach for Unmanned Aerial Vehicles (UAVs) that allows robust and accurate attitude determination for a chief vehicle flying in formation with other deputy UAVs. The proposed method is based on a tightly coupled Extended Kalman Filter (EKF) that exploits the spatial diversity of measurements coming from Global Navigation Satellite Systems (GNSS) receivers and a vision system, which are integrated with inertial and magnetic sensor data. The focus is set on outdoor environments and the innovative idea is to extend attitude estimation approaches based on multiple GNSS antennas, to a multi-vehicle system where differential-GNSS and vision-based UAV-to-UAV tracking are exploited to build a virtual additional navigation sensor. Concept and processing architecture are described with emphasis on the EKF measurement update phase which is applicable for any number of cooperating deputies, and for different GNSS processing architectures. Performance of the proposed method is assessed through experimental tests involving two multi-rotors and two fixed ground antennas, one of which is used as Ground Control Point for pointing accuracy analysis. Results show the potential of the developed approach in terms of accuracy and capability to provide drift-free estimates, in real time or in post processing scenarios.
       
  • vOn-board passive-image based non-cooperative space object capture window
           estimation
    • Abstract: Publication date: Available online 22 November 2018Source: Aerospace Science and TechnologyAuthor(s): Meng Yu, Shuang Li, Shu Leng This paper proposes a novel capture window estimation framework for non-cooperative space object capture mission. The proposed approach is developed by taking into account the following facts: 1) only one monocular camera onboard the capturer satellite is available; 2) the a-priori knowledge of resident space objects (RSOs) is strictly limited; 3) the capture window estimation framework is independent from the capture modes. The relative state between the observed space object and capturer is formulated in a probabilistic manner through solving the admissible region from passive-images. Then, the probability and probability rate of a target entering the capture zone are efficiently characterized, leading to a complete RSO capture window estimation architecture. Finally, the entire algorithm is validated by a Monte Carlo simulation and an experimental trial, results from which demonstrate the effectiveness of the proposed approach in terms of estimation accuracy and reliability.
       
  • Conflict-risk assessment model for continuous climb operations
    • Abstract: Publication date: Available online 22 November 2018Source: Aerospace Science and TechnologyAuthor(s): Javier A. Pérez-Castán, Fernando Gómez Comendador, Álvaro Rodríguez-Sanz, Rosa M. Arnaldo Valdés Continuous Climb Operations (CCO) enable aircraft to execute optimal departing trajectories. However, current airspace design may not allow the integration of CCO due to incompatibility with air traffic flow. This paper lays out a new conflict risk model and assesses the impact of CCO in complex airspace. In this document, conflict risk is defined as the combination of conflict probability between an aircraft pair (CCO and arrivals) and estimated air traffic flows. The authors set out a new approach to determining the probability of vertical conflicts. This approach is based on the altitude distributions at conflict points, which are estimated using simulations (CCO) and real data (arrivals). Using altitude distributions, it is possible to statistically determine the probability of two aircraft infringing the vertical separation minimum. This methodology is applied to Palma airport (Spain). Results show that it is feasible to integrate CCO except for one conflict point where air traffic flows need to be redesigned. Therefore, this new conflict risk model can form the basis of a future decision-making process to validate new flight procedures or modify existing ones.
       
  • Smooth-switching LPV control for vibration suppression of a flexible
           airplane wing
    • Abstract: Publication date: Available online 22 November 2018Source: Aerospace Science and TechnologyAuthor(s): Tianyi He, Guoming G. Zhu, Sean S.-M. Swei, Weihua Su In this paper, active vibration suppression of a Blended-Wing-Body flexible airplane wing is studied by utilizing a smooth-switching linear parameter-varying (LPV) dynamic output-feedback control. For the reduced-order LPV models, developed for each divided flight envelop subregion, a family of mixed Input Covariance Constraint and H∞ LPV controllers are designed to robustly suppress the wing bending displacement using hard-constrained control surfaces, while achieving smooth-switching between adjacent controllers. The proposed LPV controllers are developed by minimizing a combination of weighted H2 output performance and smoothness index, subject to a set of Parametric Linear Matrix Inequalities derived from stability and performance conditions. In addition, the weighting coefficient in the cost function is tuned to balance between H2 performance and switching smoothness by iteratively solving convex optimization problems. Simulation results demonstrate that simultaneous smooth-switching and improved performance can be achieved by the proposed LPV control.
       
  • Coulomb tether double-pyramid formation, a potential configuration for
           geostationary satellite collocation
    • Abstract: Publication date: Available online 22 November 2018Source: Aerospace Science and TechnologyAuthor(s): Rui Qi, Anrui Shi, Arun K. Misra, Krishna D. Kumar, Jingrui Zhang This paper proposes the Coulomb tether double-pyramid satellite formation, which includes a cluster of charged satellites repelling each other by Debye-shielded Coulomb forces and two counterweights connecting to each satellite via elastic massless tethers. The center of mass of the formation is prescribed to move along the geostationary orbit. The equations of motion of the formation are obtained by using Lagrange's equation. Analytical individual satellite charges are derived for the spinning and non-spinning three-satellite configurations, respectively. When the number of satellites is more than three, approximate analytical charges are obtained. Numerical simulations indicate that the proposed formation may be successfully applied to the geostationary satellite collocation in the future.
       
  • Integrated form finding method for mesh reflector antennas considering the
           flexible truss and hinges
    • Abstract: Publication date: Available online 22 November 2018Source: Aerospace Science and TechnologyAuthor(s): Rui Nie, Baiyan He, Dewey H. Hodges, Xiaofei Ma Form finding plays an essential role in the design of deployable mesh reflectors (DMRs), and it concerns their electromagnetic performance. However, classic form finding methods ignore the compatible deformation between cable networks and supporting structures. Even though the finite element method can be adopted to compensate the deviations caused by the compatible deformation, many iterations have to be involved and the effects are usually not satisfied. In this paper, an integrated form finding method considering the flexibility of the truss and hinges is proposed. Firstly, the rod of the truss is modeled by Euler–Bernoulli beam and the hinge is described by the flexible joint with six degree of freedoms (DOFs) to form the integrated element. These elements are assembled according to the topology of the truss to obtain the equilibrium equation of the truss. Secondly, the boundary conditions are applied to condense the DOFs of beam nodes, so that the rods, hinges and cable networks can be combined by adopting the corresponding consistency conditions, and then the equilibrium equation of the coupled model is established. Finally, the integrated form finding method is formed by incorporating the gradient based optimization method into the coupled model. This method is further applied to the form finding of the ring truss DMR, and the corresponding case studies are provided. The stiffness coefficients of three kinds of hinges in six DOFs are measured and utilized. The obtained design parameters are imported into ABAQUS to calculate the actually formed reflective surface, so as to verify the result. The form finding results are also compared with those in previous literature. The proposed method is proved to be effective in the form finding of DMRs, and the deviations of the form and force distribution of reflective surfaces caused by the compatible deformation are totally avoided.
       
  • Self-organizing control for satellite clusters using artificial potential
           function in terms of relative orbital elements
    • Abstract: Publication date: Available online 22 November 2018Source: Aerospace Science and TechnologyAuthor(s): Zhaokui Wang, Yun Xu, Chao Jiang, Yulin Zhang Self-organizing control for satellite clusters is a challenging and promising problem which has drawn considerable attention in the recent past. The artificial potential function method has been widely used for self-organizing control due to its elegant mathematical analysis and simplicity. This paper proposes a set of self-organizing control rules for satellite clusters described by artificial potential functions, so that the reconfiguration, uniform distribution and collision avoidance operations can be achieved spontaneously. It may work regardless of the failure of satellites, attendance of new members or existence of space debris, and the corresponding communication and control system are completely distributed. Particularly, the artificial potential functions are written in terms of relative orbital elements derived from T–H equations, so that the self-organizing control can reflect relative motion dynamics, and guide the satellite along a fuel-efficient trajectory. The proposed method is especially suitable for highly distributed micro-satellite clusters and large-scale clusters to track moving targets, with few fuel cost and relatively high control accuracy, and it is applicable to clusters in either deep space or near-earth space. The stability of the control was proved by Lyapunov second method, and verified by Monte Carlo simulation. Finally, the comparison between self-organizing control and fuel-optimal control was made to demonstrate the performance properties.
       
  • Trajectory clustering of air traffic flows around airports
    • Abstract: Publication date: Available online 22 November 2018Source: Aerospace Science and TechnologyAuthor(s): Xavier Olive, Jérôme Morio We present a new approach to separate air traffic trajectories in an area constrained by operational procedures. This technique is applied on a set of real trajectories in Toulouse terminal manoeuvring area (TMA). The resulting clusters foster good understanding of the structure of traffic and of how controllers schedule landings at Toulouse–Blagnac airport; on the other hand, a group of peculiar trajectories emerge with useful information calling for further analysis and paving the way for a probabilistic approach to risk assessment in air traffic safety.
       
  • Parameters estimation methodology for the nonlinear rolling motion of
           finned cylindrical body
    • Abstract: Publication date: Available online 22 November 2018Source: Aerospace Science and TechnologyAuthor(s): Momtaz Abadir, Sezsy Yusuf, Alessandro Pontillo, Mudassir Lone Identification of nonlinear roll dynamics of finned cylindrical bodies is a critical step when assessing free motion stability and trajectories of aerially dispensed munitions or decoys. In this paper the authors present a parameter estimation process that focuses on identifying nonlinear aerodynamic models that characterize the roll dynamics of a cylindrical body with wrap around fins using data from a series of dynamic wind tunnel tests. This is a three step approach that combines ordinary least squares, stepwise regression and the augmented output-error method, and it is initially tested using simulation data corrupted by white Gaussian noise and then applied to the wind tunnel data. Roll and roll rate dynamics were captured through a series of high angle of attack free-to-roll tests carried out at an airspeed of 35m/s corresponding to a Reynolds number of 800,000. The results and discussion in this paper demonstrate how simulation can be used to develop and mature a system identification routine followed by its assessment through wind tunnel test data. It is shown that high order nonlinear models with up to 14 terms can be parameterized to provide high levels of agreement with roll and roll rate dynamics observed in the dynamic wind tunnel tests.
       
  • Entry trajectory planning with terminal full states constraints and
           multiple geographic constraints
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Xiao Wang, Jie Guo, Shengjing Tang, Shuai Qi, Ziyao Wang This paper proposes an online entry trajectory planning algorithm satisfying terminal full states constraints, path constraints and multiple geographic constraints for lifting-body entry vehicles. The vehicle is considered as a 3DOF point mass. The entry trajectory is divided into the initial descent phase, gliding phase and terminal guidance phase. In the gliding phase, a piecewise polynomial in the altitude-versus-velocity plane is used to plan the longitudinal trajectory and a new heading angle corridor based bank angle reversal logic is designed to satisfy all geographic constraints simultaneously. In the terminal guidance phase, an optimal guidance law with terminal angle constraints is adopted to generate the trajectory. Finally, the terminal full states constraints including terminal velocity direction constraints are implemented by iterating over the altitude in the gliding phase. Then the highly constrained entry trajectory planning problem is converted into a one-parameter search problem. The key of this planning algorithm is the use of terminal guidance phase, through which the terminal velocity direction is constrained strictly rather than kept around the line-of-sight angle and the range error caused by great arc assumption is also avoided. Simulation results with the CAV-H model show that this algorithm can generate entry trajectories satisfying complex constraints rapidly and is suitable for various missions.
       
  • Benchmark aerodynamic shape optimization with the POD-based CST airfoil
           parametric method
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Xiaojing Wu, Weiwei Zhang, Xuhao Peng, Ziyi Wang This paper conducts a benchmark aerodynamic shape optimization with the developed POD-based CST airfoil parametric method. The POD analysis transforms the basis functions of the CST parametric method into reduced orthogonal POD basis functions which are used to describe the geometric variation of the aerodynamic shape. A benchmark aerodynamic shape optimization for drag minimization of RAE2822 airfoil in transonic viscous flow provided by AIAA aerodynamic design optimization discussion group is used to verify the optimization effect of the developed parametric method. The optimized results indicate that developed parametric method can maintain almost the same ability to cover potential airfoils with much fewer parameters as the original high-dimensional CST method does, which can overcome the contradiction of high-dimensionality of design parameters and increase of optimization difficulty well. Moreover, the benchmark optimized results verify the optimization effect of the developed method by comparing with benchmark results optimized by other international counterparts in the field of aerodynamic shape optimization.
       
  • Instantaneous observable degree modeling based on movement measurement for
           airborne POS
    • Abstract: Publication date: Available online 20 November 2018Source: Aerospace Science and TechnologyAuthor(s): Jianli Li, Yun Wang, Zhaoxing Lu, Yiqi Li The observable degree is significant for the airborne Position and Orientation System (POS), and is a key parameter that reflects accuracy and rapidity of filter. The conventional mathematical method based on singular value decomposition cannot analyze the impact mechanism of movement on observable degree, and is impracticable to determine the movement of observable degree improvement. To solve the problem, an instantaneous observable degree model based on movement measurement for airborne POS is proposed to demonstrate the relationship between instantaneous movement and observable degree. The instantaneous observability matrix in the model is established to reduce analytical complexity. Experiment results show that the proposed model is valid to determine how to improve observable degree.
       
  • A Hybrid Reduced-Order Framework for Complex Aeroelastic Simulations
    • Abstract: Publication date: Available online 20 November 2018Source: Aerospace Science and TechnologyAuthor(s): Jiaqing Kou, Weiwei Zhang This paper develops a hybrid and parallel-structured reduced-order framework for modeling unsteady aerodynamics, which incorporates both linear and nonlinear system identification methods. To reflect unsteady flow physics, the hybrid model introduces time-delayed output feedback to both linear and nonlinear subsystems. The linear output and nonlinear residual are identified by the autoregressive with exogenous input model and the multi-kernel neural network, respectively. The proposed approach is illustrated here with the reduction of computational-fluid-dynamics-based aeroelastic analysis of a NACA0012 airfoil oscillating in transonic and viscous flows. In particular, we exploit the potential of this model in analyzing complex aeroelastic phenomena including limit-cycle oscillations, the beat phenomenon at high reduced velocities, and nodal-shaped oscillations induced by the interaction between buffet and flutter. Results demonstrate that the proposed approach approximates the dynamically linear and nonlinear aerodynamic characteristics obtained from high-fidelity time-marching methods with a high level of accuracy. This framework can be used as a general reduced-order modeling strategy to represent dynamic systems exhibiting both linear and nonlinear characteristics.
       
  • Trajectory planning and tracking control for towed carrier aircraft system
    • Abstract: Publication date: Available online 20 November 2018Source: Aerospace Science and TechnologyAuthor(s): Jie Liu, Wei Han, Haijun Peng, Xinwei Wang As an efficient and safe dispatching scheme is of great importance to ensure the effectiveness and safety of personnel on the Aircraft Carrier, and the towed aircraft system without bar is a common means of dispatching, the dispatching of the system is a significance and interesting question. In this paper, the towed carrier aircraft system without bar is transformed into a tractor-trailer system, and the nonlinear motion constraint is proposed. In order to improve the efficiency and safety of dispatching, the trajectory-planning and tracking of the system are studied, respectively. Obstacles in the environment and the nonlinear motion constraints are taken into consideration, the trajectory-planning is transformed into the optimal control problem, and combined with the symplecticity and pseudospectral method, an offline optimal control algorithm with high efficiency is proposed firstly. In order to accurately track the obtained trajectory, an online tracking method is proposed based on the receding horizon control (RHC) theory and the offline optimal control algorithm. Finally, the offline trajectory-planning algorithm has been proved by simulation experiment, it shows that the algorithm has high computational efficiency and good applicability. And the system can track the standard trajectory, even though there are disturbances in the environment, with high precision using the online tracking method, the calculation efficiency is also verified, and real-time tracking can be achieved.
       
  • Effects of Vibration Characteristics on Improvement of Deployment
           Repeatability by Vibration
    • Abstract: Publication date: Available online 19 November 2018Source: Aerospace Science and TechnologyAuthor(s): Hiroaki Tanaka, Ryotaro Sakamoto A method of improving the positioning accuracy of deployable space structures using vibrations was developed, and its effectiveness was demonstrated. The effects of vibration characteristics on improvements to shape repeatability were investigated via experiments and numerical simulations. An experimental model consisting of a beam, spring, and ball joint was developed, and it was used to simulate a portion of a deployable structure. Macro-fiber composite actuators were attached to the beam to generate vibrations. Experiments were conducted while changing the vibration characteristics, including the applied voltage for the actuator, the actuator position, and the frequency and duration. Positions of the beam, after applying vibrations, were measured using a laser displacement sensor, and the results were compared. A corresponding numerical simulation model was developed, and shape repeatability was investigated. The results indicated that the shape repeatability was improved by applying vibrations using an actuator at the natural frequency. The applied voltage had a large impact on shape repeatability, and the effective actuator position was investigated by considering the model force.
       
  • A new approach of orbit determination for LEO satellites based on optical
           tracking of GEO satellites
    • Abstract: Publication date: Available online 19 November 2018Source: Aerospace Science and TechnologyAuthor(s): Yunpeng Hu, Xianzong Bai, Lei Chen, Hongtao Yan Ability of autonomous orbit determination (OD) for a satellite is receiving increasing interests due to its considerable value in engineering application. A new OD approach for low earth orbit (LEO) satellites based on tracking geosynchronous orbit (GEO) satellites using space-based optical tracking approach is proposed which can improve the autonomy of LEO satellites and reduce their dependence on ground facilities. Based on the information support of Space Surveillance Network (SSN), several GEO satellites are selected as guidance and calibration functions like beacons for LEO satellites equipped with space-based optical (SBO) sensors, as they are called beacon GEO satellites in this paper. LEO satellites can determine their own orbits by tracking these GEO objects without measures of ground facilities, which only need to provide necessary information of beacon objects for them. Unlike traditional space-based observation, long arcs and high-frequency measurements, which are more beneficial to determine orbit precisely, are possibly obtained. This paper focuses on demonstrating the feasibility and performance of proposed approach. To determine orbits, batch least-squares (LS) estimator with Tschauner-Hempel (T-H) equation state-transition matrix to estimate the propagation of initial errors is used. Different scenarios are simulated and results show that tracklet length, measurement frequency, and measurement errors are the main factors that influence the accuracy of OD.
       
  • Barrier Lyapunov function-based integrated guidance and control with input
           saturation and state constraints
    • Abstract: Publication date: Available online 19 November 2018Source: Aerospace Science and TechnologyAuthor(s): Wangkui Liu, Yiyin Wei, Guangren Duan In this paper, input saturation and constraints of attack angle, sideslip angle and velocity deflection angle are taken into consideration in integrated guidance and control (IGC) design for skid-to-turn missile. The novel adaptive IGC scheme is proposed by combing dynamic surface control with barrier Lyapunov function (BLF). The BLF and modified saturation function are incorporated to prevent the constrained states from overstepping the constraints. To handle input saturation, auxiliary system is constructed. According to the stability analysis, all signals in closed-loop system are uniformly ultimately bounded while the constrained states remain in the constraint sets. The performance of the proposed adaptive IGC scheme is demonstrated by nonlinear numerical simulation results.
       
  • Numerical study of tip leakage flow control in turbine cascades using the
           DBD plasma model improved by the parameter identification method
    • Abstract: Publication date: Available online 15 November 2018Source: Aerospace Science and TechnologyAuthor(s): Jianyang Yu, Jianing Yu, Fu Chen, Cong Wang In the present work, an improved dielectric barrier discharge (DBD) plasma model is applied to a highly-loaded turbine cascade to numerically study its effect on suppressing tip leakage flow. First, a parameter identification system is established using the Kriging model and genetic algorithm. The simplified model is then improved based on this parameter identification system so that it is more consistent with the published experimental results. Expressions of maximum electric field strength and the outline of the plasma active region are rebuilt in this improved model. It is then integrated into the blade tip with a tip clearance of 1% of the blade height on the suction side. This design is used to suppress the tip leakage flow. This would lead to a decrease in the leakage by 40.5% when the plasma device is applied to the blade tip.
       
  • Accurate flight path tracking control for powered parafoil aerial vehicle
           using ADRC-based wind feedforward compensation
    • Abstract: Publication date: Available online 15 November 2018Source: Aerospace Science and TechnologyAuthor(s): Shuzhen Luo, Qinglin Sun, Wannan Wu, Mingwei Sun, Zengqiang Chen, Yingping He Winds are the major contributors to the tracking error in the control process of the powered parafoil, making it difficult to achieve better control performance. To address this problem, an accurate flight path tracking control approach for the powered parafoil combining active disturbance rejection control (ADRC) and wind feedforward compensation is proposed. The wind impacts on the lateral heading and longitudinal altitude dynamics of the powered parafoil are analyzed firstly. Moreover, the wind feedforward compensation control, the lateral heading and longitudinal altitude tracking controller are designed to directly compensate the wind disturbance in the control process, such that the tracking precision and disturbance-rejection capacity can be enhanced simultaneously. Eventually, the mathematical simulation, robustness test, and experimental results demonstrate that the proposed control approach achieve better tracking performance and robustness against the variable wind disturbance than the conventional ADRC and PID.
       
  • Optimized layout methods based on optimization algorithms for DPOS
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Xiaolin Gong, Xiaorui Zheng, Jiancheng Fang, Gang Liu Attention has been devoted to distributed position and orientation system (DPOS) which can provide high precision spatial and temporal information for all remote sensing loads for airborne multi-task synthetical earth observation system in recent years. Since there are restrictions of space, weight and cost of the DPOS, it is unrealistic to install an IMU of DPOS at the location of each load, and the optimized layout of DPOS has become an urgent problem should be solved. However, there is no report on the optimized layout method for airborne DPOS yet. In this paper, the optimized layout of DPOS is classified as the optimization problem, and two classical optimization algorithms, the genetic algorithm (GA) and particle swarm optimization (PSO), and two novel optimization algorithms, the particle swarm optimization with mutation (PSOM) and hybrid of PSO and GA (HPSOGA), are used and compared for the first time to determine the optimal layout of DPOS. The mathematical simulation shows that the novel method named HPSOGA is superior to the other three methods. In order to accelerate the convergence rate of this layout method, further mathematical simulation and semi-physical simulation based on flight experiment is carried out and the results show that the calculation amount of this method can be reduced by adjusting the individual number calculated by PSO. The work of this paper can provide new ideas and make a good start for the optimized layout study of DPOS.
       
  • UAV aerodynamic design involving genetic algorithm and artificial neural
           network for wing preliminary computation
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Abdelwahid Boutemedjet, Marija Samardžić, Lamine Rebhi, Zoran Rajić, Takieddine Mouada In this paper, the aerodynamic design procedure of a mini unmanned aerial vehicle, intended to perform aerial reconnaissance at low altitude and low Reynolds number, was summarized. Design process was divided into two major parts: conceptual design phase and preliminary design phase. During the conceptual design, classical procedures and data from similar unmanned aerial vehicles already designed were employed to define the requirements related to unmanned aerial vehicle design. The preliminary design was performed using panel method where the emphasis was given on the design of the UAV wing, fuselage design and empennage. The wing planform parameters were determined through an aerodynamic optimization process using both genetic algorithms and artificial neural networks. Finally an aerodynamic analysis using panel method, Computational Fluid Dynamic simulations and wind tunnel testing was carried out. Unmanned aerial vehicle full configuration design process was consistent, where a comparison between the final obtained results was carried out and showed an agreement in terms of lift, drag and pitch moment coefficients.
       
  • Experimental study on flame development and stabilization in a kerosene
           fueled supersonic combustor
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Ye Tian, Xuejun Zeng, Shunhua Yang, Baoguo Xiao, Fuyu Zhong, Jialing Le Flame development and stabilization in a kerosene fueled supersonic combustor with air throttling were experimentally investigated in the present paper. Stagnation conditions were 1100 K and 1.0 MPa and Mach number at the isolator entrance was 2.0. Various measurements included schlieren, shadow, interferometry, flame emission and PLIF were made during the experiments in an attempt to better understand the combustion flow field. The flow structure of non-reacting flow with and without air throttling was investigated firstly, the results showed a shock train was generated due to the increased back pressure by the throttling air, shock waves of the two cases oscillated with the flow. The flame development of pilot hydrogen was studied secondly, the ER (Equivalence Ratio) of pilot hydrogen should be 0.1, because a stable flame was beneficial to ignition transient. Finally, the effects of air throttling on flame stabilization were investigated, time for ignition of the case with air throttling was nearly a third of the case without air throttling, the pilot flame was blown off by the room temperature kerosene. But the kerosene was ignited successfully by the pilot hydrogen with the aid of air throttling, and even when the throttling air was removed, the flame was still stable.
       
  • Investigations on flame liftoff characteristics in liquid-kerosene fueled
           supersonic combustor equipped with thin strut
    • Abstract: Publication date: Available online 14 November 2018Source: Aerospace Science and TechnologyAuthor(s): Junlong Zhang, Juntao Chang, Jicheng Ma, Youyin Wang, Wen Bao The flame characteristics of liftoff and attachment in supersonic combustor fueled with liquid kerosene were investigated by the methods of numerical simulation and experiment. A thin strut was equipped in the center of the combustor acting as the flame holder, and the function of fuel injection was also achieved by the thin strut. In the experimental and numerical conditions, the Mach number in the inlet of the combustor is 2.8, with the stagnation state of Tt=1680 K, Pt=1.87 MPa. The flame images during the experiment process are captured by high speed camera, with the camera parameter of 8000 frames per second, and the pressure distributions in the combustor are also recorded by the pressure sensors. Results show that the flame structure could be divided into two statuses, namely flame liftoff status and flame attachment status, and both the equivalence ratio and the plasma jet ignitor could make an influence on the flame status. By analyzing the flow field characteristics obtained by numerical simulation, the formation mechanism of the flame liftoff phenomenon is discussed, and the flame status depends on both the fuel premixed process and flame propagation characteristics. Further, to investigate the influence of equivalence ratio on the flame liftoff characteristic, an experiment with a linearly increasing equivalence ratio from 0.3 to 0.76 is conducted. The hysteresis of flame liftoff distance is found in different equivalence ratio changing paths, and the path response characteristics are probed. The conclusions of this article is helpful for having an understanding of propagation process and revealing the combustion stabilization mechanism in the thin strut-equipped scramjet combustor.
       
  • Buzz Evolution Process Investigation of a Two-ramp Inlet with Translating
           Cowl
    • Abstract: Publication date: Available online 14 November 2018Source: Aerospace Science and TechnologyAuthor(s): Wen Shi, Juntao Chang, Youyin Wang, Wen Bao, Xiaoyong Liu In order to satisfy the requirement of high integration, the inlet equipped with translating cowl, which is able to adjust the geometries of combustor and inlet simultaneously, is proposed and studied. Numerical investigations are conducted to obtain hysteresis loop, stability boundary and buzz evolution process with various internal contraction ratios in wide range of flight Mach numbers. The dynamic mesh method is utilized to simulate the geometric adjustment. The results reveal that the buzz evolution process has obvious hysteretic characteristics under the change of translating direction. Meanwhile, the mechanism of inlet buzz mode transition is provided. Then, the effects that the translating velocities have on the oscillatory frequency, position of separation leading edge and dynamic drag are given. The higher velocity is able to restrain the intension of separation oscillation and enlarge the stable region, but has insignificant effect on the reduction of oscillatory frequency and dynamic drag. For specific velocities, there is no oscillation. Therefore, the appropriate velocity can be selected for the improvement of inlet stability. This research gives a full insight into the dynamic performance of a hypersonic variable-geometry inlet.
       
  • Vibration analysis of functionally graded plates using the eight-unknown
           higher order shear deformation theory in thermal environments
    • Abstract: Publication date: Available online 13 November 2018Source: Aerospace Science and TechnologyAuthor(s): Tran Minh Tu, Tran Huu Quoc, Nguyen Van Long This paper deals with free vibration of functionally graded material plates using eight-unknown higher order shear deformation theory in thermal environments. The theory is based on full twelve-unknown higher order shear deformation theory, simultaneously satisfies zero transverse shear stress at the top and bottom surfaces of the FG plate. Heat conduction and temperature-dependent material properties are both taken into account. The temperature field considered is assumed to be a uniform distribution over the plate surface and varied in the thickness direction only. Material properties are assumed to be temperature-dependent, and graded in the thickness direction according to a simple power law distribution in terms of the volume power laws of the constituents. Equations of motion are derived from Hamilton's principle. The accuracy of present analytical solution is confirmed by comparing the present results with those available in existing literature. The effects of the temperature field, volume fraction index of functionally graded material, side-to-thickness ratio on free vibration responses of the functionally graded plates are investigated.
       
  • An Experimental Study on Transonic Swept Convex-Corner Flows
    • Abstract: Publication date: Available online 13 November 2018Source: Aerospace Science and TechnologyAuthor(s): K.M. Chung, Kao-Chun Su An experimental study was conducted to investigate the effect of swept angle on a compressible convex-corner flow. The freestream Mach number and the convex-corner angle were 0.64–0.89 and 10°–17°, respectively. The swept angle was 5°–15°. The characteristics of a swept convex-corner flow were evaluated from the distributions of both mean and fluctuating pressures. Surface oil flow visualization was also performed to determine the length of shock-induced separated boundary layer. Shock excursion phenomenon was detected by pressure trace and the shock zero-crossing frequency was evaluated using a two-threshold method. A delay in transition from subsonic to transonic expansion flow for a swept case is observed. The effect of swept angle on peak pressure fluctuations and shock Strouhal number is evident.
       
  • Effects of the aerothermoelastic deformation on the performance of the
           three-dimensional hypersonic inlet
    • Abstract: Publication date: Available online 13 November 2018Source: Aerospace Science and TechnologyAuthor(s): Kun Ye, Zhengyin Ye, Chunna Li, Jie Wu The hypersonic inlet is more prone to deform when simultaneously subjected to aerodynamic load and harsh aerothermodynamic load. Moreover, the flow field of the hypersonic inlet is sensitive to configuration. Therefore, it is necessary to investigate the effects of the aerothermoelastic deformation on the flow structure and the performance of the hypersonic inlet. This study develops a loose coupling static aerothermoelastic analysis framework based on the CFD/CSD coupling method, and the one-way and the two-way aerothermal-aeroelastic coupling are both used in the analysis. Furthermore, the effects of the aerothermoelastic deformation on the flow structure and the performance of a three-dimensional hypersonic inlet are studied in detail. The reliabilities of the CFD method and the CFD/CSD coupling method are verified by the validation cases of DLR hypersonic inlet experimental model and the HIRENASD experimental model. The results obtained by the coupling methods are similar. However, the aerothermoelastic deformation obtained through the two-way coupling method is relatively larger, and the effects of the deformation on the inlet performance are more obvious. The maximum of the aerothermoelastic deformation exists at the leading edge of the inlet lip. The deformation changes the shock wave structure near the lip, strengthens the shock wave intensity inside the inlet, increases the length of the separated region and the temperature of the external wall, and changes the flow field of the exit. The aerothermoelastic deformation will lead to the increasing of the mass flow coefficient and the pressure rise ratio; however, it will decrease the total pressure recovery coefficient.
       
  • Numerical investigation and optimization on the micro-ramp vortex
           generator within scramjet combustors with the transverse hydrogen jet
    • Abstract: Publication date: Available online 13 November 2018Source: Aerospace Science and TechnologyAuthor(s): Lang-quan Li, Wei Huang, Li Yan, Zhao-bo Du, Ming Fang An effective fuel supply strategy with high mixing efficiency, large penetration depth and low stagnation pressure losses determines the overall performance of the scramjet (supersonic combustion ramjet) engine. In this paper, the transverse hydrogen injection flow field with a micro-ramp located upstream of the wall orifice has been investigated numerically based on the code validation. There are four design variables considered in the current study, namely the width, length, and height of the micro-ramp and the distance between the center of the wall orifice and the trailing point of the micro-ramp. Nine cases predicted by the three-dimensional Reynolds-averaged Navier–Stokes (RANS) equations coupled with the two equation k–ω shear stress transport (SST) turbulence model are used for parametric analysis, and the parametric analysis has been carried out by the extreme difference analysis approach. Three optimization cases are obtained, and they have different objectives, namely the minimization of the mixing length, the maximization of the penetration depth and the minimization of the stagnation pressure losses. The flow structures of all cases have been discussed and compared. The quantitative evaluation results of three optimization cases show that the extreme difference analysis approach is an efficient parametric analysis method, and it can obtain the optimal strategy for the micro-ramp within scramjet combustors with the transverse hydrogen jet.
       
  • Rapid planning for aerocapture trajectory via convex optimization
    • Abstract: Publication date: Available online 12 November 2018Source: Aerospace Science and TechnologyAuthor(s): Hongwei Han, Dong Qiao, Hongbo Chen, Xiangyu Li Aerocapture, which usually refers to delivering a vehicle from hyperbolic orbit to planetary orbit using the aerodynamic force, can potentially lower fuel consumption. By controlling the direction and magnitude of the aerodynamic force, the vehicle can be accurately transferred to the target orbit. This paper mainly focuses on developing a convex algorithm for the constrained trajectory planning of aerocapture. For nonlinear aerocapture problem, the main task is to convert this problem into a convex sub-problem, and then the solution of the original problem can be efficiently obtained by solving a sequence of such sub-problems with convex optimization. In order to formulate a highly constrained aerocapture trajectory-planning problem into a convex-form one, all non-convex items in aerocapture problem are turned into convex functions by successive linearization, variable equivalent replacement and control variable relaxation. The simulation results of the optimal aerocapture, represented by minimum impulse, flight time and heat load, indicate that the proposed method is highly efficient and can be potentially applied for on-board trajectory planning method.
       
  • Parametric modeling and aerodynamic optimization of EXPERT configuration
           at hypersonic speeds
    • Abstract: Publication date: Available online 12 November 2018Source: Aerospace Science and TechnologyAuthor(s): Yang Shen, Wei Huang, Tian-tian Zhang, Li Yan With the rapid development of aviation and space industry, hypersonic vehicles with high lift-to-drag ratio have attracted an increasing attention. The aerodynamic performance of the aircraft plays a dominant role in the conceptual design of flight vehicles. Based on the sketch of the European EXPERT re-entry vehicle, this investigation provides readers with detailed instructions for the Free Form Deformation (FFD) parametric modeling and aerodynamic optimization of the design of hypersonic vehicles. The aerodynamic characteristics of the vehicle are numerically investigated by the panel method. The Multi-Island Genetic Algorithm (MIGA) is utilized to optimize the aerodynamic shape. The obtained results show that the value of the objective function (L/D)max increases from 0.7141 to 1.4133, and the optimum angle of attack decreases from 21° to 12°. The further analysis digs out the potential effects of the upper and lower surfaces to the vehicle. The impact of the upper surface is greatly diminished. The influence of the body flap, as well as the other objective functions, would be taken into consideration in the oncoming work.
       
  • Optimal control based guidance law to control both impact time and impact
           angle
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Xiaotian Chen, Jinzhi Wang A new guidance law with both impact time and impact angle constraints is proposed in this paper. We first simplify missile dynamics under small heading error approximation, and derive an optimal guidance law with impact angle constraint against a stationary target. By adding a feedback controller to the obtained optimal guidance law, both impact time and angle requirements are achieved and the singularity problem is tackled. The proposed guidance law can be used to perform a simultaneous formation cooperative attack. Numerical simulations are demonstrated to illustrate the effectiveness of the proposed method.
       
  • A hybrid reduced-order modeling technique for nonlinear structural dynamic
           simulation
    • Abstract: Publication date: Available online 10 November 2018Source: Aerospace Science and TechnologyAuthor(s): Chen Yang, Ke Liang, Yufei Rong, Qin Sun Thin-walled structures are always subjected to a large range of extreme loading cases leading to obvious geometric nonlinearities in structural dynamic response, such as vibration with large amplitudes in aeronautics and astronautics field. Various dynamic reduced-order models have been investigated from detailed finite element models, to largely reduce the computational burden of the structural dynamic responses. However, to construct these low-order models,applying a series of nonlinear static simulations to the full-order model is necessary. This paper aims to develop a hybrid reduced-order modeling method by combining the dynamic and static reduced-order models together, to estimate the dynamic transient response caused by geometrically nonlinear finite element models. A few free-vibration modes of interest are selected to reduce basis vectors of dynamic reduced-order model. Based on Koiter asymptotic expansion theory, the constructed static reduced-order model is applied to the nonlinear static analyses. Therefore, not only does the proposed method make it possible to calculate the nonlinear dynamic response far more efficiently than full-order modeling methods, but computational burdens in construction of dynamic reduced-order model are also largely reduced compared to existing approaches. Various engineering numerical examples with hardening and/or softening nonlinearities are carefully tested to validate the good quality and efficiency of the proposed method.
       
  • Large-eddy simulation of shock-wave/boundary-layer interaction control
           using a backward facing step
    • Abstract: Publication date: Available online 9 November 2018Source: Aerospace Science and TechnologyAuthor(s): Weipeng Li, Hong Liu A new passive flow control method, putting a backward facing step ahead of the shock interaction position, is numerically investigated, aiming to control the shock-wave/boundary-layer interaction in a rocket-based combined-cycle scramjet engine. The height of the step is designed to be smaller than the boundary layer thickness. Implicit large-eddy simulations of an oblique shock wave impinging on a supersonic turbulent boundary layer are performed to examine the efficiency of this flow control method. Results show that with the flow control the length of shock-induced separation bubble is increased, but its height is reduced. The upstream extending of the reflected shock is suppressed, which indicates that the flow control method is able to relieve or avoid the adverse effects caused by the inner going of the reflected shock into the air-intake of the engine. The mechanism and the influence of the applied control method on instantaneous, mean and statistical flow-fields are discussed.
       
  • Numerical investigation of the effects of different parameters on the
           thrust performance of three dimensional flapping wings
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Chunlin Gong, Jiakun Han, Zongjing Yuan, Zhe Fang, Gang Chen After billions of years of evolution, many creatures employing flapping wing in nature tend to have excellent flight capabilities. To understand the bionic wings flow mechanism will be helpful to design high performance underwater vehicles and new conception aircrafts. The geometric parameters, kinematic parameters and flow parameters have great effects on the bionic wings thrust performance. Facing the diverse parameters, it's very difficult to explore the three-dimensional (3D) bionic flapping wing flow mechanism with traditional numerical simulation method. In this paper, a general large-scale parallel solver using Immersed Boundary-Lattice Boltzmann Method (IB-LBM) was developed. The evolution procedures of the 3D flapping wing leading edge vortex and wake flow vortex structures were analyzed in detail. Our study explained the 3D flapping wing thrust performance variation with different wing shapes, aspect ratios and pitch-bias angles of attack. Using Chinese supercomputer TianHe-II presents a wide range of possibilities for the further development of parallel IB-LBM, employing tens of millions grids will help us to obtain more complete and accurate 3D flapping wing flow field information. It's indicated that the obtuse wing has the best thrust performance compared with other sharp wing shapes. With the increase of the aspect ratio, the thrust coefficient of flapping wing increases firstly and then decreases, and with pitch-bias angles of attack increases, the thrust coefficient decreases quickly or even shown resistance phenomenon at the large pitch-bias angel of attack. The discussion of these parameters will provide a theoretical basis for improving flapping-like vehicles propulsive performance.
       
  • Time-optimal trajectory generation for aerial coverage of urban building
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Peng Yao, Yangguang Cai, Qian Zhu This paper presents a hierarchical architecture for generating the cooperative trajectories of multiple unmanned aerial vehicles (UAVs) attached with camera sensors, which aim to cover buildings with optimal time in 3D urban environment. It incorporates the centralized high-level layer performing the mission analysis and task allocation functions yielding instructions that are transmitted to the UAVs, as well as the decentralized low-level fashion that the UAVs perform the trajectory generation function in turn. First, the mission features especially the theoretical coverage time of building envelope are extracted quantitatively, and the buildings are then allocated to the UAVs in order to convert the cooperative control problem into multiple single-vehicle control problems. Then, each UAV visits and scans its allocated buildings sequentially, and the corresponding coverage trajectories are obtained by the parallel circle strategy (PCS) and the time-optimal guidance vector field (TOGVF) transition method, as well as the interfered fluid dynamic system (IFDS) method for obstacle avoidance. Finally, our proposed method is verified in various scenarios, and the simulation results show its high efficiency with least time to solve the cooperative coverage problem.
       
  • Surrogate model of complex non-linear data for preliminary nacelle design
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Alexander Heidebrecht, David G. MacManus Most response surface methods typically work on isotropically sampled data to predict a single variable and fitted with the aim of minimizing overall error. This study develops a metamodel for application in preliminary design of aircraft engine nacelles which is fitted to full-factorial data on two of the eight independent variables, and a Latin hypercube sampling on the other six. The specific set of accuracy requirements for the key nacelle aerodynamic performance metrics demand faithful reproduction of parts of the data to allow accurate prediction of gradients of the dependent variable, but permit less accuracy on other parts. The model is used to predict not just the independent variable but also its derivatives, and the Mach number, an independent variable, at which a certain condition is met. A simple Gaussian process model is shown to be unsuitable for this task. The new response surface method meets the requirements by normalizing the input data to exploit self-similarities in the data. It then decomposes the input data to interpolate orthogonal aerodynamic properties of nacelles independently of each other, and uses a set of filters and transformations to focus accuracy on predictions at relevant operating conditions. The new method meets all the requirements and presents a marked improvement over published preliminary nacelle design methods.
       
  • Numerical analysis of transonic buffet flow around a hammerhead payload
           fairing
    • Abstract: Publication date: Available online 7 November 2018Source: Aerospace Science and TechnologyAuthor(s): Yi Liu, Gang Wang, Hongyu Zhu, Zhengyin Ye During ascent of launcher, the unsteady aerodynamic loads associated with transonic buffet flow have become of considerable concern. To study the unsteady dynamics of buffet flow, delayed detached-eddy simulations of a hammerhead configuration have been conducted at transonic Mach numbers. The results, including mean Cp, Cprms, PSD and Schlieren visualizations, were validated by the measurements obtained from the wind-tunnel experiments. Nevertheless, to perform a good validation for unsteady loads, the numerical data needed to be filtered according to the data acquisition used in the experiments. The studies were performed by means of instantaneous, statistical, spectral and cross-spectral analysis of the numerical data, which identify the fluid dynamic mechanism that produces a relatively strong buffet environment. The mechanism involves a sequence of vortex, which is shed downstream, merges together, and ultimately impinges on the wall leading to large fluctuations. Besides, the cross-spectral analysis also revealed that the subsequent large scale and low frequency vortex shedding of the developed shear layer provides a strong influence on the flows around cone-cylinder conjunction. The fluctuations in this area are highly sensitive to Mach numbers, and the peak of Cprms appears at Ma ≈ 0.81.
       
  • A spline ROM of blade aerodynamic force to upstream wake
    • Abstract: Publication date: Available online 7 November 2018Source: Aerospace Science and TechnologyAuthor(s): Li Li-zhou, Yang Minglei, Luo Xiao, Zhang Jun, Yuan Mei-ni All related research nowadays are devoted to build ROM of aerodynamic forces induced by vibration of blades or wings. There is no discussion of ROMs of the aerodynamic forces of the blades corresponding to upstream wakes, which is more important to turbine machines' safety. In this paper, a spline Volterra ROM method is proposed to predict the blades' aerodynamic forces induced by the upstream wakes to fasten the blade-wake interaction analysis in turbine machine design. Traveling wave method is applied to simplify the inputs representing the upstream wakes. The kernels of the Volterra ROM are expressed in spline to reduce the number of parameters to be identified. The coefficients of the spline kernels are identified by minimizing the difference between ROM results and CFD data. The ROM method is used to predict a blade's aerodynamic forces under an actual wake. The results show that the ROM can capture most information of the aerodynamic forces due to the wake.
       
  • Solution-Based Adaptive Mesh Redistribution Applied to Harmonic Balance
           Solvers
    • Abstract: Publication date: Available online 7 November 2018Source: Aerospace Science and TechnologyAuthor(s): Reza Djeddi, Kivanc Ekici A primary source of inaccuracy in numerical simulations is due to errors that are introduced into the solution via the discretization of the continuous governing equations over the computational domain. By increasing the grid resolution in regions with high flow gradients and large curvatures using a solution-adaptive approach, these discretization errors can be reduced. In this paper, an adaptive mesh technique is presented that can efficiently cluster the grid nodes in sensitive regions by redistribution and relocation of the grid nodes. This adaptive technique is specifically important to unsteady periodic flow cases where the length scales of the flow features (such as shocks, boundary layer, and separation zones) can differ between time instances. The proposed technique is developed – for the first time in the literature – for a harmonic balance method to efficiently model unsteady periodic flows. To study the performance of the proposed technique in improving the accuracy of the flow solver, steady and unsteady flow cases are studied. Numerical results show that the adaptive mesh redistribution technique is capable of efficiently increasing the accuracy of the numerical solver with a relatively low computational overhead.
       
  • Skin Friction Drag Reduction over Staggered Three Dimensional Cavities
    • Abstract: Publication date: Available online 6 November 2018Source: Aerospace Science and TechnologyAuthor(s): Erwin R. Gowree, Chetan Jagadeesh, Christopher J. Atkin The effect of three-dimensional staggered circular cavities on a zero-pressure gradient incompressible turbulent boundary layer was studied. Two key parameters were varied, being the ratio of the diameter, d, to the depth, h, of the cavity, d/h and the Reynolds number based on the diameter of the cavity, Rd. Velocity profile measurements showed that for the cases of d/h>1 an increase in skin friction drag was experienced with respect to a smooth surface, but for d/h≤1 the drag increment was almost negligible and in some cases it was lower than that of a smooth surface by up to 10%. Measurements along the spanwise plane showed the presence of organised transverse velocity components which bear some resemblance with the flow over riblets. The skin friction drag appears to be a strong function of Rd, where for Rd>5500 a drag increment is experienced which could potentially be due to shear layer breakdown and more production of turbulence.
       
  • Parametric study of a VLS based on 2-D FSI analysis
    • Abstract: Publication date: Available online 6 November 2018Source: Aerospace Science and TechnologyAuthor(s): HyunShig Joo, Haeseong Cho, Younghun Lee, SangJoon Shin, Jack J. Yoh, Jae-Cheol Shin Vertical launching system(VLS) is useful in operating and sheltering high-speed rockets. The aft closure in the plenum plays a significant role in protecting the interiors from the exhaust gas induced by the ignition of adjacent or in-positioned canisters. During the aft opening/closing event, a complex flow is propagated into the VLS . By presence of such structural components, it is necessary to analyze the interaction between the deforming aft closure and a highly pressurized plume.This paper presents a two-dimensional fluid-structure interaction(FSI) simulation under high pressure loading condition for preliminary design of VLS. A quadrilateral 9-node element based on co-rotational (CR) framework is used to predict the geometrically/materially nonlinear deformation of the aft closure while supersonic impinging jet plume is predicted by fully Eulerian modeling. A contact mechanism is also utilized to apply reaction forces between the structures and inclined plenum using a penalty term. The interface and boundary conditions are obtained by the hybrid particle level-set method via the Ghost framework. Furthermore, a parametric study is conducted by changing the thickness of the aft closure and the inclined angle of the plenum. It is expected that the magnitudes of pressure and temperature can be decreased by the introduction of appropriate thickness of the aft closure and inclined angle in the plenum.
       
  • Barrier Lyapunov function-based robust flight control for the ultra-low
           altitude airdrop under airflow disturbances
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Zikang Su, Chuntao Li, Honglun Wang This paper investigates the anti-disturbance constrained trajectory flight control for the ultra-low altitude airdrop under airflow disturbances, by innovatively integrating the finite time convergent high-order sliding mode observer and barrier Lyapunov function-based back-stepping technique. The dynamics of transport aircraft during the airdrop are established based on the fixed-wing aircraft's 6 DOF nonlinear model and are transformed into the affine nonlinear form for the convenient control design. These dynamics include the complex influence of the flow disturbances, the ground effect, the consecutive movement and abrupt extraction of the heavy cargo. Then, the flight controller is divided into several cascade subsystems via back-stepping technique. The items reflect the disturbances during the drop in each subsystem, as well as the items which are independent of the predefined virtual control variables, are taken as components of the “lumped disturbances” which are estimated and compensated by the specially designed finite time convergent high order sliding mode observer. On this basis, a barrier Lyapunov function-based back-stepping flight controller is proposed for the robust and safe flight control of the ultra-low altitude airdrop. And the closed-loop stability is discussed via the Lyapunov stability theorem. Simulation comparisons are conducted to verify the robustness and effectiveness of the proposed airdrop flight control method.
       
  • Model reference adaptive state-dependent Riccati equation control of
           nonlinear uncertain systems: Regulation and tracking of free-floating
           space manipulators
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Saeed Rafee Nekoo This work proposes a model reference adaptive state-dependent Riccati equation (SDRE) controller for nonlinear time-invariant systems considering uncertainty in the plant. The SDRE is vulnerable to uncertainty of nonlinear model, hence the adaptive structure is to compensate for the difference between a reference model and a real uncertain system. The application of the proposed method is dedicated to controlling a free-floating space manipulator (FFSM), a robotics system with a base in two modes: an inactive (no actuation or thrust) state, and a base reaction torque mode. A non-actuated heavy base FFSM probably performs a regulation or a tracking task precisely though that might not be a good solution. A new design is proposed for FFSM control: a heavy base is selected for base of a reference model and the uncertain system with proper weight of base will follow the reference system; and considering three motors for rotating back the base when it reorients from initial position. The new design has improved the precision of the FFSM and reduced the weight of the robot. A planar two degree-of-freedom and a 3D Stanford arm were modeled, simulated and analyzed to assess the performance of the proposed structure and adaptive SDRE controller; that successfully confirmed the claimed expectations.
       
  • Adaptive super-twisting sliding mode control of 6-DOF nonlinear and
           uncertain air vehicle
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Ali-Reza Babaei, Maryam Malekzadeh, Davood Madhkhan In this paper, to control the six degree-of-freedom non-linear unmanned aerial vehicle, two strategies are implemented using adaptive super-twisting sliding mode control approach. The first one is a single-channel controller that is designed on the basis of decoupled equations of motion. The other one is a three-channel controller that is designed based on the coupling equations of motion along with an adaptive super-twisting observer. The stability of the closed loop system of the controller-observer is proven. The comparison between the single-channel controller and the three-channel could lead us to select between a little lower efficiency and less complexity versus efficiency and more complexity. To examine the performance and robustness of these two control loops, their performances are analyzed in the presence of combined uncertainties, including aerodynamics, mass, inertial moment, sensor, and actuator disturbances and parametric uncertainties in the stage separation phase. The explosive bolt separation mechanism is assumed to perform the stage separation, and its forces, moments and disturbances are modeled as needed. Finally, the responses are compared with the classic PID controller.
       
  • Characteristics of entropy layer for cones and cylinders in supersonic
           flows
    • Abstract: Publication date: Available online 5 November 2018Source: Aerospace Science and TechnologyAuthor(s): Wang Gang, Zhang Wen-xi, Xie Zhu-xuan, Yang Yan-guang An analytic method is presented to study the distribution of vorticity downstream the shock wave and the characteristics of the entropy layer for various cones and cylinders in supersonic flows. The relations of shock-shape, the distribution character of various parameters within the shock layer, and the entropy increment were combined to obtain the characteristics of vorticity and the entropy gradient. Numerical simulation are performed at the Mach number of 3, 5 and 10. The results indicate that the distribution of entropy and vorticity is connected with shock shape directly. Due to the differences of the shape of shock, the vorticity and the extreme value of entropy gradient for blunt-nosed cylinders are both larger than the cases for flat cylinders. As the shock-shape of flat-nosed cylinders is more liable to be affected than blunt-nosed cylinders with increasing Mach number, the position of the extreme value moves to the surface as the Mach number increases for flat-nosed cylinders, while it remains the identical value for blunt-nosed cylinders. The vorticity is regarded as the criterion of the edge of entropy layer in the normal direction, and two methods are proposed and discussed to estimate the edge.
       
  • Near time-optimal controller based on analytical trajectory planning
           algorithm for satellite attitude maneuver
    • Abstract: Publication date: Available online 5 November 2018Source: Aerospace Science and TechnologyAuthor(s): Li You, Ye Dong Near time-optimal controller based on analytical trajectory planning algorithm for satellite attitude maneuver is proposed in this paper. The attitude maneuver issue is constructed as three successive attitude maneuvers and the desired trajectory is derived by calculating the minimum rotate angle, meanwhile each maneuver process is optimized by Bang-Bang control logic so that the system could have near time optimal character. The constraint on control torque is discussed and the relationship between system upper bound and control parameters is given. A special case of attitude maneuver is discussed and system acceleration and deceleration process is optimized inspired by Hohmann transfer of orbit control. The analytical solution of desired trajectory is given hence the computation is largely reduced. The attitude tracking controller is designed so that system could maneuver along the designed trajectory. System stability is proved by Lyapunov method and system performance is demonstrated by numerical simulation.
       
  • Principles of non-intrusive diagnostic techniques and their applications
           for fundamental studies of combustion instabilities in gas turbine
           combustors: A brief review
    • Abstract: Publication date: Available online 3 November 2018Source: Aerospace Science and TechnologyAuthor(s): Can Ruan, Feier Chen, Weiwei Cai, Yong Qian, Liang Yu, Xingcai Lu Combustion instabilities are often manifested in modern fuel-lean gas turbine combustors. Investigating the mechanisms and developing control strategies for combustion instabilities in such systems are of practical importance and give rise to interesting scientific issues as large-amplitude pressure and heat release perturbations can lead to catastrophic and irreversible consequences on costly gas turbine hardware. In recent years, tremendous efforts have been made to achieve a deeper understanding of the periodic combustion oscillations in gas turbine engines with both advanced numerical simulations and experimental diagnostics. In the latter case, state-of-the-art, non-intrusive diagnostic techniques have been well adopted to conduct fundamental studies on combustion instabilities in gas turbine model combustors. For example, simultaneous time-resolved measurements with planar laser-induced fluorescence (PLIF) for characterizing flame structure and particle image velocimetry (PIV) for imaging flow field significantly contribute to the understanding of the role of flame-flow-acoustics coupling in the events of combustion instabilities, and to the development and validation of advanced numerical models. However, planar measurements can be restrictive when flames are not axisymmetric or exhibit complex large-scale three-dimensional (3D) dynamics, which are commonly encountered in practical combustion system when combustion instabilities occur. Therefore, more recently, new volumetric imaging techniques for combustion diagnostics have attracted considerable research efforts. This paper categorizes different advanced non-intrusive combustion diagnostic techniques, including their basic principles and especially applications for the study of combustion instability. Some of the recent progresses in the diagnostic techniques, such as computed tomography of chemiluminescence (CTC), volumetric laser induced fluorescence (VLIF), rainbow-PIV, etc., are also discussed. These volumetric combustion diagnostic techniques offer the advantage to measure both spatial and temporal characteristics of the flame/flow of interest, which will enable deeper insights into the nature of unsteady combustion in the future. This brief review is intended to be useful for both researchers and engineers to design and conduct further fundamental experiments on combustion instabilities in gas turbine engines.
       
  • Modeling and vibration control of aero two-blade propeller with input
           magnitude and rate saturations
    • Abstract: Publication date: Available online 30 October 2018Source: Aerospace Science and TechnologyAuthor(s): Xueyan Xing, Jinkun Liu, Lijun Wang In this paper, the dynamic modeling and vibration control of a two-blade propeller system of an aircraft are investigated in the presence of input magnitude and rate constraints and external disturbances. To avoid discretizing the original system, a partial differential equation (PDE) model preserving all system modes is developed. Based on the proposed PDE model, boundary control laws are derived to restrict the bending and twist deformations of the two-blade propeller under disturbances. To meet the input magnitude and rate constraints, a backstepping controller is designed. The closed-loop system stability is proved by using the Lyapunov's direct method. Numerical simulations are presented to demonstrate the effectiveness of the proposed control method.
       
  • Comparison of Filtering Techniques For Relative Attitude Estimation of
           Uncooperative Space Objects
    • Abstract: Publication date: Available online 29 October 2018Source: Aerospace Science and TechnologyAuthor(s): Vincenzo Pesce, Muhammad Farooq Haydar, Michèle Lavagna, Marco Lovera Nowadays, one of the most active research fields in space engineering is autonomous relative navigation around uncooperative objects. A common approach used to tackle this problem is through vision-based pose determination techniques. This paper investigates the possibility of using non-linear filtering techniques to improve the attitude estimation performance of vision-based methods. Furthermore, a simulation study is presented to compare the proposed nonlinear techniques with the multiplicative extended Kalman filter for attitude estimation. First-order and second-order nonlinear filters are adapted, implemented and tested for relative attitude estimation. Finally, the consequences of uncertainty in the knowledge of the target inertia matrix are investigated.
       
  • Least squares support vector machine for class imbalance learning and
           their applications to fault detection of aircraft engine
    • Abstract: Publication date: Available online 24 October 2018Source: Aerospace Science and TechnologyAuthor(s): Peng-Peng Xi, Yong-Ping Zhao, Pei-Xiao Wang, Zhi-Qiang Li, Ying-Ting Pan, Fang-Quan Song Imbalanced problems often occur when the size of majority class is bigger than that of the minority one. The Least squares support vector machine (LSSVM) is an effective method for solving classification problem on balanced datasets. However, LSSVM has bad performance on minority class facing with class imbalance learning for the classification boundary skewing toward the majority class. In order to overcome the drawback, LSSVM for class imbalance learning (LSSVM-CIL) is proposed. LSSVM-CIL utilizes two different regularization parameters C+ and C− that evaluate different misclassification costs. Furthermore, a method of combining reduced technique and recursive strategy is proposed to reduce the size of support vectors and retain representative samples. In addition, decomposition of the matrices via Cholesky factorization is employed as a solution to enhance the computational stability. Furthermore, the effectiveness of the two algorithms presented in this paper is confirmed with experimental results on various real-world imbalanced datasets. Fault detection of aircraft engine can be regarded as a CIL problem and has the demand for the real time. Finally, experiments on aircraft engine indicate that the two algorithms can be selected as candidate techniques for fault detection of aircraft engine.
       
  • Integrated strapdown missile guidance and control based on neural network
           disturbance observer
    • Abstract: Publication date: Available online 24 October 2018Source: Aerospace Science and TechnologyAuthor(s): Bin Zhao, Siyong Xu, Jianguo Guo, Ruimin Jiang, Jun Zhou This paper investigates one integrated guidance and control (IGC) method for missiles with strapdown seeker. The IGC model considering the field-of-view (FOV) constraint is built by employing the strapdown decoupling method, based on which the strict feedback state equation with unmatched uncertainties is derived. The system uncertainties are tackled by neural network (NN) disturbance observer. To handle state constrain issue, the integral Barrier Lyapunov function (iBLF) is employed with the dynamic surface control (DSC) method to deal with the unmatched uncertainties. Then, the uniform ultimately boundedness of the system is proved and the FOV constraint is also guaranteed. Numerical simulation results demonstrate the effectiveness of the proposed control scheme.
       
  • Application of endwall contouring in a high-subsonic tandem cascade with
           endwall boundary layer suction
    • Abstract: Publication date: Available online 24 October 2018Source: Aerospace Science and TechnologyAuthor(s): Longxin Zhang, Songtao Wang, Wei Zhu A proper combination of active and passive flow control methods would be a promising way to further enhance the compressor performance. This numerical investigation presents a new attempt of application of endwall contouring in a high subsonic tandem cascade with the endwall boundary layer suction implemented in the forward blade. The study aims to further improve the corner flow in the rear blade at design and lower incidences. The planar endwall is redesigned using the optimization method. Nonuniform rational B-spline surface is employed to parameterize the endwall surface. A multi-points optimization strategy is selected to minimize the aerodynamic loss generated in the cascade. In the optimization, the suction strategy remains unchanged. To clarify the impacts of endwall contouring on the cascade performance, flow details in both mainflow passage and suction flow path at design and off-design incidences are analyzed.As a result, the total loss decreases by 8.4% at the design incidence via the endwall contouring. Furthermore, a more prominent loss reduction can be achieved at lower incidences. However, the control effects of endwall contouring is weakened towards higher positive incidences. Worse still, even a deterioration in the cascade performance can be detected at I = 5° due to the presence of a small-scale corner stall in the forward blade. The results indicate that, as the gap flow is not strong enough to counteract the endwall secondary flow, the endwall contouring could be employed to further enhance the flow control ability of the previous proposed compound flow control method, while its negative impact on the cascade performance at higher positive incidences still remains to be addressed.
       
  • Modeling for solar array drive assembly system and compensating for the
           rotating speed fluctuation
    • Abstract: Publication date: Available online 24 October 2018Source: Aerospace Science and TechnologyAuthor(s): Yuteng Cao, Dengqing Cao, Jin Wei, Wenhu Huang A dynamic model of the solar array drive assembly (SADA) system consisting of a stepper motor and two flexible solar arrays is investigated. The fluctuation compensation of the rotating speed and vibration suppression is studied by integrating the sliding mode control (SMC) method and input shaping (IS) technique. The dynamic equations of the system are derived by the Hamiltonian Principle. The linearized form of the nonlinear dynamic equations with boundaries conditions is adopted to obtain the natural frequencies and global modes of the solar arrays. Based on the electromechanical dynamics model of the stepper motor, a cooperative compensation scheme is designed to achieve the stability of solar arrays and the suppression of system vibration. Numerical results show that the driving speed is significantly influenced by the harmonic torque and the structural vibration of payload. The SMC method compensates for the rotating speed fluctuation much better than the pure feed-forward operation used in the traditional stepper motor. The system with SMC method and IS technique performs much better than the case without vibration suppression.
       
  • Trajectory optimization for a TBCC-powered supersonic vehicle with
           transition thrust pinch
    • Abstract: Publication date: Available online 24 October 2018Source: Aerospace Science and TechnologyAuthor(s): Jialin Zheng, Juntao Chang, Shengbo Yang, Xinyue Hao, Daren Yu Transition thrust pinch is a critical issue of Turbine-Based-Combined Cycle engines when vehicles operate at trajectories with constant dynamic pressures. The insufficiency of the net thrust might cause that the vehicle fails to accelerate over mode transition from a turbine engine to a scramjet engine and then lead to mission abortion. Existed solutions to this problem mainly focus on increasing thrust of propulsion systems by using auxiliary power units when transition thrust pinch occurs. Without bothering to develop new propulsion systems, this paper turns to trajectory optimization to change the thrust and drag status of the vehicle to gain an additional net thrust. Additionally, the gravity-assist strategy is also used to make up for the thrust pinch in optimized trajectories. The transition thrust pinch issue is abstracted into an optimal control problem with the maximum terminal speed as the cost function, which is then solved via the Gauss pseudospectral method. Firstly, the effectiveness of this strategy is demonstrated by several cases with transition thrust pinch issues. Then, the upper-limit of this method is analyzed. Finally, this study indicates that the limited capacity can be broaden by loosening the constraint on the minimum dynamic pressure.
       
  • Cooperative load transportation using multiple UAVs
    • Abstract: Publication date: Available online 24 October 2018Source: Aerospace Science and TechnologyAuthor(s): Behzad Shirani, Majdeddin Najafi, Iman Izadi The aim of this paper is cooperative task assignment to multiple unmanned aerial vehicles (UAV) for load transportation. The main goal is to transport a slung load safely with minimal swing. To this end, for each UAV, which is regarded as an agent, a distributed controller is proposed. The proposed controller guarantees a fixed formation, which in turn achieves the main objective. A model of the system is obtained using the Udwadia–Kalaba method for an arbitrary number of UAVs and one slung load with ropes. This method leads to a novel multi-agent system model with interactions between neighbor and non-neighbor agents. The control law is then proposed based on sub-optimal LQR-PID for the extended system. Simulation results are presented to verify the ability of the proposed method to keep the formation of the agents, and to guide the load in the desired direction.
       
  • An aerothermodynamic design optimization framework for hypersonic vehicles
    • Abstract: Publication date: Available online 24 October 2018Source: Aerospace Science and TechnologyAuthor(s): Simone Di Giorgio, Domenico Quagliarella, Giuseppe Pezzella, Sergio Pirozzoli In the aviation field great interest is growing in passengers transportation at hypersonic speed. This requires, however, careful study of the enabling technologies necessary for the optimal design of hypersonic vehicles. In this framework, the present work reports on a highly integrated design environment that has been developed in order to provide an optimization loop for vehicle aerothermodynamic design. It includes modules for geometrical parametrization, automated data transfer between tools, automated execution of computational analysis codes, and design optimization methods. This optimization environment is exploited for the aerodynamic design of an unmanned hypersonic cruiser flying at M∞=8 and 30 km altitude. The original contribution of this work is mainly found in the capability of the developed optimization environment of working simultaneously on shape and topology of the aircraft. The results reported and discussed highlight interesting design capabilities, and promise extension to more challenging and realistic integrated aerothermodynamic design problems.
       
  • Nonlinear filtering in unknown measurement noise and target tracking
           system by variational Bayesian inference
    • Abstract: Publication date: Available online 24 October 2018Source: Aerospace Science and TechnologyAuthor(s): Xingkai Yu, Jianxun Li, Jian Xu This paper considers a class of nonlinear filtering algorithms based on variational Bayesian (VB) theory to settle the unknown measurement noise problem in target tracking system. When the unknown measurement noise is conditionally independent of states, based on the variational idea, estimate of probability density function of state is converted into approximation two probability density functions for both unknown noise and nonlinear states. Then, an iterative algorithm is established to jointly estimate the state and the unknown measurement noise using variational Bayesian inference. Thus, the unknown measurement noise could be estimated as hidden state. The convergence result of the proposed nonlinear probability density function approximation algorithm is also given. The simulation results of typical examples show that the proposed VB based methods have superior performance to these classic algorithms in target tracking problems.
       
  • Nonlinear Supersonic Flutter for the Viscoelastic Orthotropic Cylindrical
           Shells in Supersonic Flow
    • Abstract: Publication date: Available online 23 October 2018Source: Aerospace Science and TechnologyAuthor(s): B.A. Khudayarov, F.J. Turaev On the example of an orthotropic shell, the problems of the dynamics of thin-walled structures under aerodynamic loading are studied, taking into account the viscoelastic properties of material and geometric nonlinearity. The aerodynamic pressure is determined using the AA. Ilyushin's piston theory. Equations of motion relative to displacements are described by a system of integro-differential equations in partial derivatives. Using the Bubnov–Galerkin method, based on the polynomial approximation of deflections, the problem is reduced to a system of ordinary integro-differential equations, where time is an independent variable. Solutions of integro-differential equations are determined by a numerical method based on the elimination of the singularity in the relaxation kernel of the integral operator. Computational algorithms and applied programs have been developed to solve the problems on the nonlinear flutter for viscoelastic elements of an aircraft. The critical flutter speed for the viscoelastic orthotropic cylindrical shells is determined. It is established that an account of viscoelastic properties of shell material leads to a decrease in the critical flutter.
       
  • Flexible all-plastic aircraft models built by additive manufacturing for
           transonic wind tunnel tests
    • Abstract: Publication date: Available online 23 October 2018Source: Aerospace Science and TechnologyAuthor(s): Weijun Zhu, Xiaoyu Zhang, Dichen Li Wind tunnel testing is considered as a reliable tool, especially for the high-order non-linear aerodynamic problems of large aircraft with high-aspect-ratio wings at transonic speeds. Thanks to its capacity to manufacture complex structures quickly, the introduction of the additive manufacturing (AM) technique into the design and fabrication of testing models can improve the testing performance significantly. However, these AM-built models so far are limited to low-speed testing due to the low strength and modulus of non-metal materials, epoxy resins mostly, used in popular AM processes for aircraft models. The easy-deformation properties are usually considered as the major weakness and many methods are adopted to strengthen the plastic models for high speed tests. Taking advantage of the properties, however, this paper proposes a plastic flexible testing model with a specific pre-deformation that can be deformed into the desired state during wind tunnel tests. To obtain the pre-deformation quantitatively, an optimization formulation was developed based on the coupling of computational fluid dynamics (CFD) and computational structural dynamics (CSD). As a case study, testing models with the DLR (German Aerospace Center) F4 configuration were designed and fabricated by stereolithography (SL), a popular AM process. After the strength calibration, the plastic models were tested in a transonic wind tunnel. All the models performed normally in the harsh condition when the Mach number reached 0.85, and the resulting lift coefficients (CL) obtained by the plastic models showed good consistence with their metallic counterparts. This indicates that the plastic models of large aircraft made by SL could be used in wind tunnel tests at transonic speeds. However, the all plastic models can only be used in a single combination of testing condition. Further studies should be conduct to extend the scope of application of the models. In conclusion, due to AM's capacity to manufacture complex structures with low-modulus materials, flexible models could be designed and built quickly in an economic way. The method could be used in the conceptual design for configuration screening of high-aspect-ratio aircraft, and the paper would provide a new test scheme that is fast and reliable for aircraft design.
       
  • RANS investigation of the effect of pulsed fuel injection on scramjet
           HyShot II engine
    • Abstract: Publication date: Available online 22 October 2018Source: Aerospace Science and TechnologyAuthor(s): Song Chen, Dan Zhao Effective and efficient fuel–air mixing plays a critical role in the successful operation of scramjet engines. To enhance the fuel–air mixing in supersonic combustion systems with a short flow residence time, the pulsed fuel injection strategy in a realistic scramjet combustor flow condition provided by the HyShot II is numerically studied in this work. For this, 2D and 3D simulations of the hydrogen fueled HyShot II scramjet with pulsed fuel injections are performed. Emphasis is placed on the cold flow field characteristics and fuel–air mixing performance in the combustor. Reynolds-Averaged Navier–Stokes equations are solved with the implementation of the two equation k–ω SST turbulence model via using the ANSYS FLUENT v17.1. The pulsed fuel injection is numerically achieved by implementing a time-dependent total pressure pulse with the shape of a square wave. The total pressure peak is maintained as same as the one that chokes the fuel injector in steady operations. The numerical model is validated first by comparing the results with the experimental data available in the literature. It is then used to study the effect of the pulse injection with different frequencies. It is found that complicated waves structures are formed inside the fuel injector in pulsed fuel injections due to the total pressure pulse. These waves transport outside the fuel injector and lead to the fuel streams with wavy patterns and the unsteady shock structures in the combustion chamber. Fuel penetration depths are not found to be increased for pulsed injections in this study, but much high turbulent kinetic energy (TKE) levels are observed especially inside the fuel injector. With the help of increased TKE, mixing efficiency is found to be improved for all of the pulsed fuel injection by up to 30%. This mixing improvement also strongly depends on the frequency applied.
       
  • Assessment of S-76 rotor hover performance in ground effect using an
           unstructured mixed mesh method
    • Abstract: Publication date: Available online 22 October 2018Source: Aerospace Science and TechnologyAuthor(s): Je Young Hwang, Oh Joon Kwon In the present study, the aerodynamic performance of an S-76 rotor in hover was numerically investigated by using an unstructured mixed mesh flow solver. The study was made for the rotor for both OGE (out-of-ground-effect) and IGE (in-ground-effect) conditions, and the results are compared against each other. In the present mixed mesh methodology, body-fitted prismatic/tetrahedral mesh was adopted in the near-body flow domain to treat complex geometries easily and to capture the viscous layer on the solid surface more accurately, while in the off-body region away from the blades Cartesian mesh was used. To better resolve the flow characteristics and to prevent excessive numerical dissipation, a high-order accurate weighted essentially non-oscillatory (WENO) scheme was employed in the off-body flow region. An overset mesh topology was adopted to handle blade rotation and to exchange the flow variables between the two different mesh regions. The calculations were made for three different blade configurations, having swept-tapered, rectangular, and swept-tapered-anhedral tip shapes, and the results are compared with experimental rotor performance data in terms of thrust, torque and figure of merit. The predictions were obtained for a collective pitch angle sweep from 5 to 10 degrees at a tip Mach number of 0.60 for both with and without ground effects. The detailed flow characteristics, such as vorticity contours and tip-vortex trajectory, were also investigated.
       
  • Multiphysics modeling and experimental validation of low temperature
           accumulator for cryogenic space propulsion systems
    • Abstract: Publication date: Available online 17 October 2018Source: Aerospace Science and TechnologyAuthor(s): S. Torras, J. Castro, J. Rigola, S. Morales-Ruiz, J. Riccius, J. Leiner Within the framework of Low Thrust Cryogenic Propulsion (LTCP) systems, a low-temperature accumulator acting as thermal energy storage tank is an interesting option for cyclical processes under intermittent firings avoiding the use of turbopumps in the cryogenic stages. Thus, liquid propellant (oxygen, hydrogen or methane) can be gasified under a fast transient evaporation process cooling the accumulator. On the other hand, the same accumulator can be heated by solar collectors, electrical heaters or by means of evaporated propellants recovering heat losses from fuel cells. To obtain a very high thermal energy storage density, the thermal energy stored in the accumulator is performed using a Phase Change Material (PCM) rounding the different fluid flow tubes which heat or cool the storage tank during periodical cycles. The energy management due to the mismatch between intermittent firings, together with optimum design based on minimum weight with maximum heat transfer capacity has led to developing a numerical simulation model. Thermal and fluid dynamic behavior of multi-physics phenomena in the accumulator is based on coupling the two-phase flow inside tubes working under cryogenic conditions with sensible and latent heat transfer through the tank. The numerical model is divided into: 1) a one-dimensional and transient resolution of the governing equations (conservation of mass, momentum, and energy) for the fluid flow inside ducts; 2) a multi-dimensional and transient resolution of the governing equations in the region occupied by the PCM, incorporating a turbulence model to solve the convection phenomena involved; and 3) a multidimensional and transient treatment of the thermal conduction equation for the solid tubes. The numerical results are validated by means of an experimental cylindrical accumulator test facility, instrumented with 25 thermocouples around the vertical tube which goes through the tank and four multilevel thermocouples columns at different distances radially far from the vertical tube located at the center. The comparative analysis shows a good agreement between both numerical results and experimental data for a wide range of different working conditions showing detailed phenomena analysis, together with the possibilities of this model for design optimization purposes.
       
  • A novel distributed extended Kalman filter for aircraft engine gas-path
           health estimation with sensor fusion uncertainty
    • Abstract: Publication date: Available online 17 October 2018Source: Aerospace Science and TechnologyAuthor(s): Feng Lu, Tianyangyi Gao, Jinquan Huang, Xiaojie Qiu This paper is concerned with state estimation approach to track aircraft engine gas-path health condition in an advanced distributed architecture. The sensor measurements are divided into several subsets by installation position along gas path, and they are integrated to estimate engine health state changes with sensor fusion uncertainty. The uncertain sensor fusion is characterized by time delay and packet dropout in the fusion behavior of sensor measurements, and the delay steps occur randomly. A novel distributed extended Kalman filter with the data buffer bank (DEKF) is developed, and self-tuning buffer strategy of recursive fusion estimation is combined to the DEKF to form the self-tuning DEKF (SDEKF) algorithm for improving state estimation performance. The lengths of data buffer bank related to the local filters of SDEKF are different, and they are independently adaptive to the information loss level and local estimation accuracy. Local states are calculated using the measurements collected at the latest steps in self-tuning buffer banks, and then sent to master filter to yield global state and covariance by fusion estimation. The contribution of this study is to propose a novel EKF algorithm for state estimation in the distributed framework with sensor fusion uncertainty, and it achieves better trade-off between the estimation accuracy and computational efforts. The systematical comparisons of basic EKF, constant buffer DEKF and SDEKF algorithms are carried out for aircraft engine gas-path health estimation with sensor fusion uncertainty. The simulation results show the superiority of the SDEKF, and it confirms our viewpoints in this paper.
       
  • Research on control-oriented coupling modeling for air-breathing
           hypersonic propulsion systems
    • Abstract: Publication date: Available online 16 October 2018Source: Aerospace Science and TechnologyAuthor(s): Dong Zhang, Shuo Tang, Lin Cao, Feng Cheng, Fan Deng A control-oriented coupling hypersonic propulsion system model is proposed to enable the rapid development of a propulsion model for air-breathing hypersonic flight vehicles (ABHV) in early stages of the design process and facilitate design control and analysis. An airframe/propulsion coupling hypersonic inlet model was established based on oblique shock wave theory. An isolator model in which the effects of the back pressure of the combustion chamber were adjusted by the static pressure ratio of the isolator was established. A hypersonic combustion model was also established, taking into account the fuel flow, cross-sectional area, wall friction, combustion efficiency, and exothermic reactions based on quasi-1D flow theories. Nozzle/afterbody modeling was established based on identification of the free boundary (i.e., the location of the shear layer) by Newton collision theory, and flow parameters were determined according to the influence coefficient method. The mass flow rates of air in the design state and two typical non-design states were determined geometrically based on the application of oblique shock wave theory. A propulsion coupling model that reflects the coupling of propulsion system and aerodynamics, as well as the physical mechanisms of the propulsion mechanism, was then established based on air flow rates obtained and the momentum theorem. Simulation results of airframe/propulsion integrated module air-breathing hypersonic flight vehicles (ABHVs) by the proposed model were compared to results achieved by numerical 3D Computational Fluid Dynamics (CFD) models. Results indicated that the efficacy and accuracy of the proposed models met the established requirements of control-oriented modeling, thus facilitating dynamic modeling and control in the early stage of the design process.
       
  • Adaptive control for hypersonic vehicle with input saturation and state
           constraints
    • Abstract: Publication date: Available online 16 October 2018Source: Aerospace Science and TechnologyAuthor(s): Hai-Yan Qiao, Hao Meng, Meng-Jun Wang, Wei Ke, Jing-Guang Sun The tracing control problem of hypersonic vehicle subject to external disturbances, parametric uncertainties, input saturation and state constraints. Firstly, the longitudinal model of the hypersonic vehicle is converted to the velocity subsystem and altitude subsystem based on the functional decomposition. Secondly, two adaptive anti-saturation controllers are proposed for the velocity subsystem and altitude subsystem with the unknown upper bound of external disturbances. By using the asymmetric barrier Lyapunov function, the two controllers can make flight path angle, angle of attack and pitch angle rate keep within the certain ranges. Meanwhile, the auxiliary system is introduced to deal with the problem of input saturation and a low-pass filter is designed to avoid the “explosion of terms” in traditional backstepping control caused by the complicated differentiations of the virtual control signals. Finally, the effectiveness of the presented control strategy is verified by the Lyapunov stability theory and numerical simulations results.
       
  • Method and numerical simulation for evaluating the effects of water film
           on the performance of low-speed axial compressor
    • Abstract: Publication date: Available online 15 October 2018Source: Aerospace Science and TechnologyAuthor(s): Lu Yang, Jie Zhou, Shuangming Fan, Qun Zheng, Hai Zhang Numerical simulations for a low-speed axial compressor under water ingestion are performed to evaluate the aerodynamic performance degradation due to the formation of water film. The water film thickness on a blade surface is calculated by a self-compiled program developed by the authors. In addition, the blade surface is divided into several regions, which can be roughened separately, to elucidate the characteristics of the nonuniform water film. The equivalent sand roughness corresponding to the root-mean-square water film thickness are specified for the blade surface to simulate the aerodynamic losses of the blade row caused by water deposition. The results show that the water film thickness is positively correlated with the water content, and negatively correlated with the compressor outlet pressure. The overall compression performance presents a downtrend after water ingestion. When the water content increased from 0.37% to 4.02%, the compression efficiency deteriorated by 1%–3% compared with the dry condition. The distribution of the static pressure coefficient on the blade surface is also changed, wherein the deviation degree at the tip region is greater than that at the hub region. Unfortunately, considering the limitations of the current water film models and computational methods, the water film formed on the tip region cannot be simulated. Therefore, the calculated results near the stall point are different from the experimental results. However, rough surface treatment can still be considered as a feasible method for evaluating the effects of water film on compressor performance.
       
  • Fuzzy multiobjective cooperative surveillance of multiple UAVs based on
           distributed predictive control for unknown ground moving target in urban
           environment
    • Abstract: Publication date: Available online 13 October 2018Source: Aerospace Science and TechnologyAuthor(s): Chaofang Hu, Zelong Zhang, Na Yang, Hyo S. Shin, Antonios Tsourdos In this paper, a fuzzy multiobjective path planning method based on distributed predictive control is proposed to deal with the problem of cooperative searching and tracking of unknown ground moving target by multiple unmanned aerial vehicles (UAVs) in urban environment. Firstly, extended Kalman filter (EKF) is combined with probability estimation to predict the states of the unknown target. Secondly, the line of sight occlusion of buildings, and energy consumptions of UAVs and sensors are considered in path planning. The objective functions are designed as target coverage degree, control input cost of UAV and sensor energy consumption respectively. The cooperative surveillance path planning problem is transformed into multiobjective optimization with different importance levels. Thirdly, distributed predictive control is used to obtain the local optimal path of each UAV. The predictive states of UAVs in finite horizon are exchanged to build the collision avoidance constraint, and the minimum turning radius constraint is also addressed. Then, all the objectives are fuzzified to handle the different importance level requirement. The sensor energy consumption function with switch value is equivalently converted using Sigmoid function and sign function. According to the principle that the objective with higher priority has higher satisfactory degree, preemptive priorities are transformed into the relaxed order of satisfactory degrees. The best path satisfying the requirement of multiobjective optimization and importance levels can be obtained. Finally, the simulation results show the effectiveness of the proposed method by comparing with traditional multiobjective weighted algorithm.
       
  • Persistent standoff tracking guidance using constrained particle filter
           for multiple UAVs
    • Abstract: Publication date: Available online 12 October 2018Source: Aerospace Science and TechnologyAuthor(s): Hyondong Oh, Seungkeun Kim This paper presents a new standoff tracking framework of a moving ground target using UAVs with limited sensing capabilities and motion constraints. To maintain persistent track of the target even in case of target loss for a certain period, this study predicts the target existence area using the particle filter and produces control commands that ensure that all predicted particles can stay within the field-of-view of the UAV sensor at all times. To improve target position prediction and estimation accuracy, the road information is incorporated into the constrained particle filter where the road boundaries are modelled as inequality constraints. Both Lyapunov vector field guidance and nonlinear model predictive control-based methods are applied, and the characteristics of them are compared using numerical simulations.
       
  • Two-time-scale control of a multirotor aircraft for suspended load
           transportation
    • Abstract: Publication date: Available online 11 October 2018Source: Aerospace Science and TechnologyAuthor(s): Emanuele L. de Angelis, Fabrizio Giulietti, Goele Pipeleers This paper presents a trajectory control strategy for a multirotor aircraft carrying a suspended load. The load is modeled as a pendulum connected by a rigid link to the center of gravity of the vehicle. Starting from the dynamic equations describing the motion of the coupled vehicle slung-load systems, a nonlinear controller is proposed that simultaneously performs trajectory tracking and payload swing damping. Controller gains are chosen so that the system exhibits a two-time-scale behavior, with fast dynamics for the pendulum and slow dynamics for the positioning task. Under these conditions, the basic results of singular perturbation theory are evoked for both the proof of stability and the preliminary design of control gains. Results of numerical simulations are provided in order to assess the stability and performance of the considered approach.
       
  • Analytical entry guidance for coordinated flight with multiple no-fly-zone
           constraints
    • Abstract: Publication date: Available online 11 October 2018Source: Aerospace Science and TechnologyAuthor(s): Wenbin Yu, Wanchun Chen, Zhiguo Jiang, Wanqing Zhang, Penglei Zhao This paper addresses the problem of coordinating a group of Hypersonic Glide Vehicles (HGVs) for the goal of simultaneous arrival in the presence of multiple No-Fly Zones (NFZs). Firstly, a high-precision analytical solution of flight time is derived from the nonlinear entry dynamics model built over a spherical and rotating Earth. Next, an entry guidance considering multi-NFZs and flight-time constraints is designed based on the new analytical flight-time formula as well as the existing 3-D analytical gliding-trajectory formulae. In the longitudinal part of the guidance, the flight-time and downrange formulae are used jointly to plan the longitudinal reference profile by considering both energy-management and flight-time requirements. In the lateral part, the downrange and crossrange formulae are used to plan the bank-reversal sequence according to the NFZ constraints. Additionally, in order to improve the accuracy of terminal time, speed, and altitude, a multi-objective iterative planning scheme employing onboard trajectory simulation is put forward and enabled at a time between the last two bank reversals to fine-tune the remaining short trajectory. In this scheme, the quasi-Newton method is improved by the use of directional derivatives such that the number of the trajectory simulations required to calculate the Jacobian matrix is reduced from 3 to 2 in each iteration, which greatly reduced the amount of calculation. Finally, a flight-time coordination scheme is developed for multiple HGVs to determine the starting times of entry flight, which can further determine the launch times once the boost guidance is specified. The superior performance of the guidance is demonstrated by Monte-Carlo simulations in stochastic disturbed circumstances.
       
  • Optimum attitude planning of near-space solar powered airship
    • Abstract: Publication date: Available online 9 October 2018Source: Aerospace Science and TechnologyAuthor(s): Weiyu Zhu, Jun Li, Yuanming Xu The attitude of Near-space airship including yaw, roll and pitch angle is important to the output performance of airship solar array. The yaw angle of airship can be controlled without affecting airship mission execution in the quasi-zero wind layer of near-space. This paper aims to improve solar energy system of near-space airship by optimizing airship yaw angle. Based on the solar radiation model and solar array energy model, a MATLAB program is established to calculate the output power. For model validation, solar radiation and output power are simulated and compared with experimental results. The optimum yaw angle for a whole year is obtained with optimization model based on genetic algorithm. The effect of airship shape parameters including the slenderness ratio and the ratio of forebody length to total length (L1/L) is elaborated. The results show that the effect of yaw angle on output power is greater at higher latitude than that at lower latitude and the solar array output energy can be remarkable increased after adjusting yaw angle of airship according to the optimization result. Although the optimal yaw angle is different with the change of working date and latitude, the optimum values mainly lie in 0° and 180°. Moreover, the optimal yaw angle is barely changed, when the slenderness ratio and L1/L of airship are greater than 0.3 and 0.25, respectively. The result has great valuable engineering reference in attitude planning of near-space airship and other aerospace vehicle for energy improvement.
       
  • Continuous finite-time extended state observer based fault tolerant
           control for attitude stabilization
    • Abstract: Publication date: Available online 9 October 2018Source: Aerospace Science and TechnologyAuthor(s): Bo Li, Qinglei Hu, Yongsheng Yang This work investigates the challenging problem of fast robust fault tolerant attitude control for spacecraft to handle external disturbances, actuator failures and misalignments. More specially, a novel nonsingular terminal sliding mode based finite-time extended state observer is first designed to estimate and compensate for the lumped system faults or uncertainties. And the proposed extended state observer is analysed and proved to be stable in the sense of fast finite-time uniformly ultimately bounded stability. Then, utilizing the techniques of super-twisting and terminal sliding mode control synthetically, a novel continuous attitude control algorithm is developed. The finite-time stability of the closed-loop attitude control system is proved by using a continuously-differentiable, homogeneous and strict Lyapunov function. And also the proposed control scheme is continuous with the property of chattering restraining. Finally, some numerical simulation results are shown to verify the effectiveness and superior performances of the spacecraft attitude stabilization control system driven by the proposed fast robust fault tolerant attitude control scheme.
       
  • Bird-striking damage of rotating laminates using SPH-CDM method
    • Abstract: Publication date: Available online 9 October 2018Source: Aerospace Science and TechnologyAuthor(s): Yadong Zhou, Youchao Sun, Wenchao Cai Bird strike represents a major hazard to civil aviation. In this paper, impact damage under high velocity is numerically investigated by means of non-linear explicit finite element analysis. We mainly focus the influence of rotational speeds on damage modes and energy variations of bird impact on a circular laminated plate. The Smoothed Particle Hydrodynamics method and an equation of state were employed for the bird projectile. A Continuum Damage Mechanics approach has been applied to simulate failure initiation and damage evolution in unidirectional composite laminates. Hashin's failure initiation criteria have been employed to be able to distinct lamina failure modes. Two damage regimes are identified with respect to the rotational speeds, i.e. impact-dominated damage and rotation-dominated damage. A threshold rotational speed exists for the rotating thin plate in terms of damage regimes. The results can serve as design guidelines in future full-scale or part-scale study of rotating laminated structures.
       
 
 
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