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CIVIL ENGINEERING (203 journals)                  1 2 | Last

Showing 1 - 200 of 203 Journals sorted alphabetically
ACI Structural Journal     Full-text available via subscription   (Followers: 20)
Acta Polytechnica : Journal of Advanced Engineering     Open Access   (Followers: 3)
Acta Structilia : Journal for the Physical and Development Sciences     Open Access   (Followers: 2)
Advances in Civil Engineering     Open Access   (Followers: 39)
Advances in Structural Engineering     Full-text available via subscription   (Followers: 32)
Agregat     Open Access   (Followers: 1)
Ambiente Construído     Open Access   (Followers: 1)
American Journal of Civil Engineering and Architecture     Open Access   (Followers: 34)
Architectural Engineering     Open Access   (Followers: 5)
Archives of Civil and Mechanical Engineering     Full-text available via subscription   (Followers: 3)
Archives of Civil Engineering     Open Access   (Followers: 12)
Archives of Hydro-Engineering and Environmental Mechanics     Open Access   (Followers: 2)
ATBU Journal of Environmental Technology     Open Access   (Followers: 4)
Australian Journal of Structural Engineering     Full-text available via subscription   (Followers: 6)
Baltic Journal of Road and Bridge Engineering     Open Access   (Followers: 1)
BER : Building and Construction : Full Survey     Full-text available via subscription   (Followers: 10)
BER : Building Contractors' Survey     Full-text available via subscription   (Followers: 2)
BER : Building Sub-Contractors' Survey     Full-text available via subscription   (Followers: 2)
BER : Survey of Business Conditions in Building and Construction : An Executive Summary     Full-text available via subscription   (Followers: 3)
Bioinspired Materials     Open Access   (Followers: 5)
Bridge Structures : Assessment, Design and Construction     Hybrid Journal   (Followers: 14)
Building & Management     Open Access   (Followers: 1)
Building and Environment     Hybrid Journal   (Followers: 15)
Building Women     Full-text available via subscription  
Built Environment Project and Asset Management     Hybrid Journal   (Followers: 14)
Bulletin of Pridniprovsk State Academy of Civil Engineering and Architecture     Open Access   (Followers: 6)
Canadian Journal of Civil Engineering     Hybrid Journal   (Followers: 13)
Case Studies in Engineering Failure Analysis     Open Access   (Followers: 6)
Case Studies in Nondestructive Testing and Evaluation     Open Access   (Followers: 11)
Case Studies in Structural Engineering     Open Access   (Followers: 9)
Cement and Concrete Composites     Hybrid Journal   (Followers: 20)
Challenge Journal of Concrete Research Letters     Open Access   (Followers: 3)
Challenge Journal of Structural Mechanics     Open Access   (Followers: 6)
Change Over Time     Full-text available via subscription   (Followers: 2)
Civil and Environmental Engineering     Open Access   (Followers: 8)
Civil And Environmental Engineering Reports     Open Access   (Followers: 7)
Civil and Environmental Research     Open Access   (Followers: 17)
Civil Engineering = Siviele Ingenieurswese     Full-text available via subscription   (Followers: 4)
Civil Engineering and Architecture     Open Access   (Followers: 22)
Civil Engineering and Environmental Systems     Hybrid Journal   (Followers: 3)
Civil Engineering and Technology     Open Access   (Followers: 12)
Civil Engineering Dimension     Open Access   (Followers: 10)
Civil Engineering Infrastructures Journal     Open Access   (Followers: 1)
Cohesion and Structure     Full-text available via subscription   (Followers: 2)
Composite Structures     Hybrid Journal   (Followers: 282)
Computer-aided Civil and Infrastructure Engineering     Hybrid Journal   (Followers: 11)
Computers & Structures     Hybrid Journal   (Followers: 38)
Concrete Research Letters     Open Access   (Followers: 7)
Construction Economics and Building     Open Access   (Followers: 4)
Construction Engineering     Open Access   (Followers: 11)
Construction Management and Economics     Hybrid Journal   (Followers: 21)
Construction Science     Open Access   (Followers: 5)
Constructive Approximation     Hybrid Journal  
Curved and Layered Structures     Open Access   (Followers: 3)
DFI Journal : The Journal of the Deep Foundations Institute     Hybrid Journal   (Followers: 1)
Earthquake Engineering and Structural Dynamics     Hybrid Journal   (Followers: 17)
Enfoque UTE     Open Access   (Followers: 4)
Engineering Project Organization Journal     Hybrid Journal   (Followers: 7)
Engineering Structures     Hybrid Journal   (Followers: 13)
Engineering Structures and Technologies     Open Access   (Followers: 2)
Engineering, Construction and Architectural Management     Hybrid Journal   (Followers: 10)
Environmental Geotechnics     Hybrid Journal   (Followers: 5)
European Journal of Environmental and Civil Engineering     Hybrid Journal   (Followers: 9)
Fatigue & Fracture of Engineering Materials and Structures     Hybrid Journal   (Followers: 18)
Frontiers in Built Environment     Open Access  
Frontiers of Structural and Civil Engineering     Hybrid Journal   (Followers: 6)
Geomaterials     Open Access   (Followers: 3)
Geosystem Engineering     Hybrid Journal   (Followers: 1)
Geotechnik     Hybrid Journal   (Followers: 3)
Géotechnique Letters     Hybrid Journal   (Followers: 7)
GISAP : Technical Sciences, Construction and Architecture     Open Access  
HBRC Journal     Open Access   (Followers: 2)
Hormigón y Acero     Full-text available via subscription  
HVAC&R Research     Hybrid Journal  
Indonesian Journal of Urban and Environmental Technology     Open Access  
Indoor and Built Environment     Hybrid Journal   (Followers: 2)
Infrastructure Asset Management     Hybrid Journal   (Followers: 3)
Infrastructures     Open Access  
Ingenio Magno     Open Access   (Followers: 1)
Insight - Non-Destructive Testing and Condition Monitoring     Full-text available via subscription   (Followers: 30)
International Journal for Service Learning in Engineering     Open Access  
International Journal of 3-D Information Modeling     Full-text available via subscription   (Followers: 3)
International Journal of Advanced Structural Engineering     Open Access   (Followers: 17)
International Journal of Civil, Mechanical and Energy Science     Open Access   (Followers: 2)
International Journal of Concrete Structures and Materials     Open Access   (Followers: 15)
International Journal of Condition Monitoring     Full-text available via subscription   (Followers: 2)
International Journal of Construction Engineering and Management     Open Access   (Followers: 10)
International Journal of Geo-Engineering     Open Access   (Followers: 3)
International Journal of Geosynthetics and Ground Engineering     Full-text available via subscription   (Followers: 4)
International Journal of Masonry Research and Innovation     Hybrid Journal   (Followers: 1)
International Journal of Pavement Research and Technology     Open Access   (Followers: 6)
International Journal of Protective Structures     Hybrid Journal   (Followers: 6)
International Journal of Steel Structures     Hybrid Journal   (Followers: 2)
International Journal of Structural Engineering     Hybrid Journal   (Followers: 8)
International Journal of Structural Integrity     Hybrid Journal   (Followers: 2)
International Journal of Structural Stability and Dynamics     Hybrid Journal   (Followers: 7)
International Journal of Sustainable Built Environment     Open Access   (Followers: 5)
International Journal of Sustainable Construction Engineering and Technology     Open Access   (Followers: 8)
International Journal on Pavement Engineering & Asphalt Technology     Open Access   (Followers: 7)
International Journal Sustainable Construction & Design     Open Access   (Followers: 1)
Journal of Applied Research in Water and Wastewater     Open Access  
Journal of Bridge Engineering     Full-text available via subscription   (Followers: 14)
Journal of Building Engineering     Hybrid Journal   (Followers: 1)
Journal of Building Materials and Structures     Open Access   (Followers: 2)
Journal of Building Performance Simulation     Hybrid Journal   (Followers: 6)
Journal of Civil Engineering     Open Access  
Journal of Civil Engineering and Construction Technology     Open Access   (Followers: 15)
Journal of Civil Engineering and Management     Open Access   (Followers: 7)
Journal of Civil Engineering and Science     Open Access   (Followers: 9)
Journal of Civil Engineering Research     Open Access   (Followers: 7)
Journal of Civil Engineering, Science and Technology     Open Access   (Followers: 1)
Journal of Civil Society     Hybrid Journal   (Followers: 5)
Journal of Civil Structural Health Monitoring     Hybrid Journal   (Followers: 4)
Journal of Composites     Open Access   (Followers: 78)
Journal of Composites for Construction     Full-text available via subscription   (Followers: 13)
Journal of Computing in Civil Engineering     Full-text available via subscription   (Followers: 23)
Journal of Construction Engineering     Open Access   (Followers: 9)
Journal of Construction Engineering and Management     Full-text available via subscription   (Followers: 18)
Journal of Constructional Steel Research     Hybrid Journal   (Followers: 6)
Journal of Earth Sciences and Geotechnical Engineering     Open Access   (Followers: 4)
Journal of Fluids and Structures     Hybrid Journal   (Followers: 6)
Journal of Frontiers in Construction Engineering     Open Access   (Followers: 2)
Journal of Green Building     Full-text available via subscription   (Followers: 10)
Journal of Highway and Transportation Research and Development (English Edition)     Full-text available via subscription   (Followers: 14)
Journal of Infrastructure Systems     Full-text available via subscription   (Followers: 19)
Journal of Legal Affairs and Dispute Resolution in Engineering and Construction     Full-text available via subscription   (Followers: 5)
Journal of Marine Science and Engineering     Open Access   (Followers: 1)
Journal of Materials and Engineering Structures     Open Access   (Followers: 5)
Journal of Materials in Civil Engineering     Full-text available via subscription   (Followers: 8)
Journal of Nondestructive Evaluation     Hybrid Journal   (Followers: 9)
Journal of Performance of Constructed Facilities     Full-text available via subscription   (Followers: 3)
Journal of Pipeline Systems Engineering and Practice     Full-text available via subscription   (Followers: 6)
Journal of Rehabilitation in Civil Engineering     Open Access   (Followers: 3)
Journal of Solid Waste Technology and Management     Full-text available via subscription   (Followers: 1)
Journal of Structural Engineering     Full-text available via subscription   (Followers: 36)
Journal of Structural Fire Engineering     Full-text available via subscription   (Followers: 6)
Journal of Structural Mechanics     Open Access  
Journal of Structures     Open Access   (Followers: 4)
Journal of Sustainable Design and Applied Research in Innovative Engineering of the Built Environment     Open Access   (Followers: 1)
Journal of the Civil Engineering Forum     Open Access  
Journal of the South African Institution of Civil Engineering     Open Access   (Followers: 2)
Journal of Water and Environmental Nanotechnology     Open Access  
Journal of Water and Wastewater / Ab va Fazilab     Open Access  
Jurnal Spektran     Open Access   (Followers: 1)
Jurnal Teknik Sipil     Open Access  
Jurnal Teknik Sipil dan Perencanaan     Open Access   (Followers: 1)
Konstruksia     Open Access  
KSCE Journal of Civil Engineering     Hybrid Journal   (Followers: 2)
Latin American Journal of Solids and Structures     Open Access   (Followers: 4)
Materiales de Construcción     Open Access   (Followers: 1)
Mathematical Modelling in Civil Engineering     Open Access   (Followers: 4)
Media Komunikasi Teknik Sipil     Open Access  
Mokslas – Lietuvos ateitis / Science – Future of Lithuania     Open Access  
Nondestructive Testing And Evaluation     Hybrid Journal   (Followers: 15)
npj Materials Degradation     Open Access  
Obras y Proyectos     Open Access   (Followers: 1)
Open Journal of Civil Engineering     Open Access   (Followers: 9)
Photonics and Nanostructures - Fundamentals and Applications     Hybrid Journal   (Followers: 3)
Practice Periodical on Structural Design and Construction     Full-text available via subscription   (Followers: 3)
Proceedings of the Institution of Civil Engineers - Bridge Engineering     Hybrid Journal   (Followers: 8)
Proceedings of the Institution of Civil Engineers - Civil Engineering     Hybrid Journal   (Followers: 14)
Proceedings of the Institution of Civil Engineers - Management, Procurement and Law     Hybrid Journal   (Followers: 9)
Proceedings of the Institution of Civil Engineers - Municipal Engineer     Hybrid Journal   (Followers: 2)
Proceedings of the Institution of Civil Engineers - Structures and Buildings     Hybrid Journal   (Followers: 3)
Promet : Traffic &Transportation     Open Access  
Random Structures and Algorithms     Hybrid Journal   (Followers: 5)
Recent Trends In Civil Engineering & Technology     Full-text available via subscription   (Followers: 5)
Research in Nondestructive Evaluation     Hybrid Journal   (Followers: 6)
Resilience     Open Access   (Followers: 1)
Revista IBRACON de Estruturas e Materiais     Open Access   (Followers: 1)
Road Materials and Pavement Design     Hybrid Journal   (Followers: 11)
Russian Journal of Nondestructive Testing     Hybrid Journal   (Followers: 5)
Science and Engineering of Composite Materials     Hybrid Journal   (Followers: 61)
Selected Scientific Papers - Journal of Civil Engineering     Open Access   (Followers: 3)
Slovak Journal of Civil Engineering     Open Access   (Followers: 2)
Soils and foundations     Full-text available via subscription   (Followers: 5)
Steel Construction - Design and Research     Hybrid Journal   (Followers: 3)
Structural and Multidisciplinary Optimization     Hybrid Journal   (Followers: 11)
Structural Concrete     Hybrid Journal   (Followers: 11)
Structural Control and Health Monitoring     Hybrid Journal   (Followers: 8)
Structural Engineering International     Full-text available via subscription   (Followers: 11)
Structural Mechanics of Engineering Constructions and Buildings     Open Access   (Followers: 1)
Structural Safety     Hybrid Journal   (Followers: 6)
Structural Survey     Hybrid Journal  
Structure     Full-text available via subscription   (Followers: 24)
Structure and Infrastructure Engineering: Maintenance, Management, Life-Cycle Design and Performance     Hybrid Journal   (Followers: 12)
Structures     Hybrid Journal   (Followers: 1)
Study of Civil Engineering and Architecture     Open Access   (Followers: 10)
Superlattices and Microstructures     Hybrid Journal   (Followers: 2)
Surface Innovations     Hybrid Journal  
Technical Report Civil and Architectural Engineering     Open Access   (Followers: 1)
Teknik     Open Access  
Territorium : Revista Portuguesa de riscos, prevenção e segurança     Open Access  
The IES Journal Part A: Civil & Structural Engineering     Hybrid Journal   (Followers: 6)
The Structural Design of Tall and Special Buildings     Hybrid Journal   (Followers: 5)
Thin Films and Nanostructures     Full-text available via subscription   (Followers: 2)
Thin-Walled Structures     Hybrid Journal   (Followers: 4)
Transactions of the VŠB - Technical University of Ostrava. Construction Series     Open Access   (Followers: 1)
Transportation Geotechnics     Full-text available via subscription   (Followers: 1)
Transportation Infrastructure Geotechnology     Hybrid Journal   (Followers: 8)

        1 2 | Last

Journal Cover
Journal of Fluids and Structures
Journal Prestige (SJR): 1.481
Citation Impact (citeScore): 3
Number of Followers: 6  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0889-9746 - ISSN (Online) 1095-8622
Published by Elsevier Homepage  [3162 journals]
  • Control design in cyber-physical fluid–structure interaction
    • Abstract: Publication date: October 2018Source: Journal of Fluids and Structures, Volume 82Author(s): R. Waghela, M. Bryant, F. Wu Cyber-physical fluid dynamics is a hybrid experimental–computational approach to study fluid–structure interaction (FSI). It enables on-the-fly changes to structure inertia, damping, stiffness, and even kinematic constraints by replacing traditional elastically-mounted structures with actuators and a controller. The control design plays a central role in matching the closed-loop dynamics of the cyber-physical structure (CPS) to those of the desired structure. Control designs based on traditional proportional–integral–derivative (PID) and post-modern H∞ control are presented. The controllers are synthesized to match the linearized desired structural dynamics (or the input–output response) but no assumption of linearity is levied on the fluid behavior. To quantify the matching of input–output response, a CPS deviation index is defined based on H∞ norms. To evaluate and compare the performance of the control designs, two well-known FSI instabilities are considered, galloping and aeroelastic flutter. These FSI instabilities represent convenient test cases because they can be analyzed with linear aerodynamic models. Comparing the critical instability flow velocity and oscillation frequency of the CPS with different control designs and the desired mechanical structure demonstrates that the internal structure of the controller is crucial to fully matching the response of the desired structure. H∞ model-matching control with admittance causality is found to be the most adept control design for the CPS.
  • A synergistic study of a CFD and semi-analytical models for aeroelastic
           analysis of bridges in turbulent wind conditions
    • Abstract: Publication date: October 2018Source: Journal of Fluids and Structures, Volume 82Author(s): Igor Kavrakov, Guido Morgenthal Long-span bridges are prone to wind-induced vibrations. Therefore, a reliable representation of the aerodynamic forces acting on a bridge deck is of a major significance for the design of such structures. This paper presents a systematic study of the two-dimensional (2D) fluid–structure interaction of a bridge deck under smooth and turbulent wind conditions. Aerodynamic forces are modeled by two approaches: a computational fluid dynamics (CFD) model and six semi-analytical models. The vortex particle method is utilized for the CFD model and the free-stream turbulence is introduced by seeding vortex particles upstream of the deck with prescribed spectral characteristics. The employed semi-analytical models are based on the quasi-steady and linear unsteady assumptions and aerodynamic coefficients obtained from CFD analyses.The underlying assumptions of the semi-analytical aerodynamic models are used to interpret the results of buffeting forces and aeroelastic response due to a free-stream turbulence in comparison with the CFD model. Extensive discussions are provided to analyze the effect of linear fluid memory and quasi-steady nonlinearity from a CFD perspective. The outcome of the analyses indicates that the fluid memory is a governing effect in the buffeting forces and aeroelastic response, while the effect of the nonlinearity is overestimated by the quasi-steady models. Finally, flutter analyses are performed and the obtained critical velocities are further compared with wind tunnel results, followed by a brief examination of the post-flutter behavior. The results of this study provide a deeper understanding of the extent of which the applied models are able to replicate the physical processes for fluid–structure interaction phenomena in bridge aerodynamics and aeroelasticity.
  • Fluid–structure interaction simulation of slam-induced bending in large
           high-speed wave-piercing catamarans
    • Abstract: Publication date: October 2018Source: Journal of Fluids and Structures, Volume 82Author(s): Jason McVicar, Jason Lavroff, Michael R. Davis, Giles Thomas A ship in waves may experience a water impact event known as a slam. In this paper, slam-induced bending of wave-piercing catamarans in head seas is predicted by way of fluid–structure interaction simulations. The flow field during slamming of a wave-piercing catamaran is highly non-linear and cannot be accurately captured using potential flow methods as a result of the interactions between the flow fields produced by water entry of the separate demihulls and centre bow. Thus, the Reynolds-Averaged Navier–Stokes (RANS) equations are solved for rigid body motion of a vessel at model-scale. Verification and validation is conducted using model-scale data from a Hydroelastic Segmented Model (HSM). One-way and two-way interactions are computed considering vibration of the hull girder. In the case of one-way interactions, the computed fluid loads affect the structure, but the structural response does not affect the fluid domain solution whereas for the two-way interactions the structural response affects the fluid solution. A new method for capturing the non-linear time variation in added mass is developed and deemed necessary when computing one-way interactions, primarily as a result of the large changes in forward wetted area present for a wave-piercing catamaran. It is shown that two-way interaction simulation is not needed for predicting the slam induced hull girder loads. One-way interaction simulation can therefore be used allowing reduced computational effort.
  • Breaking wave impact on a floating body with air bubble effect
    • Abstract: Publication date: October 2018Source: Journal of Fluids and Structures, Volume 82Author(s): Shiyan Sun, Guoxiong Wu, Gang Xu The hydrodynamic problem of a breaking wave impacting on a floating body with air bubble effect is modelled based on the incompressible velocity potential theory, which is solved using the boundary element method in the time domain. To avoid the numerical inaccuracies due to the sharp temporal and spatial variations of velocity and pressure at the initial stage of impact, a dual system is adopted. The simulation close to the impact zone is conducted in a stretched coordinate system, while away from the impact zone the deformation and propagation of incoming overturning wave is simulated in the physical coordinate system. The continuities of both pressure and velocity are enforced at the interface of two zones. When the impact zone is no longer small, the dual systems will be merged and the simulation will be undertaken in one single domain. The air bubble trapped between the breaking wave and the solid surface is taken into account based on the assumption that the trapped air undergoes an adiabatic process. An auxiliary function method is used to decouple the nonlinear mutual dependence of fluid loading, body motion and bubble deformation. Simulations are undertaken for cases related to breaking wave impact in various engineering problems, including a solid coastal wall, a freely floating ship cross section, a floating breakwater and a tension leg platform. Detailed results for pressure, free surface profile, bubble deformation and body motion are provided, and their physical implications are discussed.
  • Passive locomotion of freely movable flexible fins near the ground
    • Abstract: Publication date: October 2018Source: Journal of Fluids and Structures, Volume 82Author(s): Young Dal Jeong, Jae Hwa Lee We numerically examine the hydrodynamic interaction between a flexible fin and surrounding fluid near the ground when four relevant parameters of initial position, bending rigidity, mass ratio and Reynolds number are varied. The leading edge of the fin is fixed in the streamwise direction, whereas the lateral motion is freely movable by the fluid–flexible body interaction near the ground. When the fin is initially positioned far from the ground, the fin passively migrates toward another wall-normal position near the ground for an equilibrium state due to larger positive deflection angle for the fin than the negative angle by the effects of vorticity generated by the lateral velocity gradient near the ground. In addition, as the flapping amplitude of the fin is small for large bending rigidity and small mass ratio, the great asymmetry between the positive and negative deflection angles reduces the transient time of the fin to reach the equilibrium position near the ground, and thus the fins can quickly take the hydrodynamic benefits with low drag at an equilibrium state without any energy consumption for lift force due to local balance between the flapping motion and the ground. The most important observation is that the equilibrium position of the fin is invariant to the initial position, bending rigidity and mass ratio of the fin. However, the equilibrium position of the fin is dramatically affected by the Reynolds number. The present results provide new insights into the functional role of the relevant parameters in passively flapping-based locomotion near the ground.
  • Flow control around a circular cylinder with swinging thin plates
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Babak Bagherzadeh Chehreh, Khodayar Javadi Flow around a 2D circular cylinder with attached swinging thin splitter plates is numerically investigated. The ratio of the plates’ length to the cylinder diameter is 1 (LD=1) where L is the Plates’ length and D is the cylinder diameter. The plates are attached at ±55 degrees (trigonometric angle) downstream and are forced to oscillate at different ratios of the natural vortex shedding frequencies with magnitudes of FR=0.75,1,1.25,1.5 and 2. The oscillation amplitude “α” as the other main variable ranges from 10 to 18 degrees. Two-dimensional simulations are carried out at the Reynolds number 100, and then extended to higher Reynolds number of 200. The results show that in certain configurations, an in-phase vortex-shedding pattern is dominant and the oscillatory nature of the lift force completely vanishes. Different flow patterns are observed and classified as well. The effects of the splitter plates’ oscillation on the lift and drag forces, flow patterns and vortex shedding frequencies are also discussed to develop a link between different flow patterns and the acting lift force on the cylinder.
  • Modal decomposition of fluid–structure interaction with application
           to flag flapping
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Andres Goza, Tim Colonius Modal decompositions such as proper orthogonal decomposition (POD), dynamic mode decomposition (DMD) and their variants are regularly used to educe physical mechanisms of nonlinear flow phenomena that cannot be easily understood through direct inspection. In fluid–structure interaction (FSI) systems, fluid motion is coupled to vibration and/or deformation of an immersed structure. Despite this coupling, data analysis is often performed using only fluid or structure variables, rather than incorporating both. This approach does not provide information about the manner in which fluid and structure modes are correlated. We present a framework for performing POD and DMD where the fluid and structure are treated together. As part of this framework, we introduce a physically meaningful norm for FSI systems. We first use this combined fluid–structure formulation to identify correlated flow features and structural motions in limit-cycle flag flapping. We then investigate the transition from limit-cycle flapping to chaotic flapping, which can be initiated by increasing the flag mass. Our modal decomposition reveals that at the onset of chaos, the dominant flapping motion increases in amplitude and leads to a bluff-body wake instability. This new bluff-body mode interacts triadically with the dominant flapping motion to produce flapping at the non-integer harmonic frequencies previously reported by Connell and Yue (2007). While our formulation is presented for POD and DMD, there are natural extensions to other data-analysis techniques.
  • Flow-induced loading on and unsteady flow structure in the wake of bluff
           perforated plates at zero incidence
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Mostafa Rahimpour, Filippo Carlo Bossi, Oleksandr Barannyk, Stefano Malavasi, Peter Oshkai Flow over rectangular plates positioned at zero incidence can result in high-amplitude forces on the plates. In this study, we apply particle image velocimetry (PIV) and direct force measurements to investigate the effect of transverse perforations on the flow-induced loading on and the flow structure in the near-wake of the plates. We compare plates with different characteristic diameter of the perforations, as well as a reference configuration without perforations, in terms of the spectra of the flow-induced forces, frequencies of the trailing edge vortex shedding and boundary layer profiles at the trailing edge at different planes across the perforation patterns for a range of inflow velocities. The three-dimensionality of the near-wake of the perforated plate is related to the proximity of the individual perforations to the trailing edge of the plate. In the vicinity of the perforations, transverse oscillations of the flow velocity in the wake become suppressed as the diameter of the perforations increases.
  • Computational fluid–structure interaction analysis of blood flow on
           patient-specific reconstructed aortic anatomy and aneurysm treatment with
           Dacron graft
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Raja Jayendiran, Bakr Nour, Annie Ruimi We use the fluid–structure interaction (FSI) capability in Abaqus to evaluate radial displacements, von Mises stresses and wall shear stresses (WSS) on the human aorta in response to the blood flowing through it. Complications arise when aneurysm is detected and causes the wall to thinner so much that rupture may result. We use the Materialise suite, a specialty software to reconstruct a three-dimensional geometry of the aorta from two-dimensional computerized axial tomography (CAT) images. Results are compared to those obtained on a healthy individual. Blood is assumed to be a Newtonian and incompressible medium and the blood flow is taken as pulsatile, fully developed and turbulent. The model used for aorta is Holzapfel–Gasser–Ogden (HGO), a sophisticated hyperelastic model that can describe biological tissues. We also study the behavior of Dacron, a polyester fabric used as graft in aortic surgical repair. Here, Dacron is represented by a neo-Hookean (isotropic) hyperelastic model. Time-dependent pressure conditions are assumed at the inlet and outlet of the resulting structure. Results indicate that using a patient-specific geometry for the aorta yields additional insight on the state of the stresses applied on the aortic walls. In addition, stress contours on the Dacron are comparable to those obtained on a healthy patient and stresses evaluated at the interface of the biological tissues and the fabric, provide useful information regarding the suture strength needed during surgery. In the case of aneurysm, our simulation results agree well with experimental data taken from the literature particularly with regard to WSS which can be used to assess the seriousness of the aneurysm condition. If an idealized cylindrical shell is used in place of the reconstructed anatomy, the von Mises stress values do not differ much but it underestimates the values of WSS which could interpreted as the presence of an aneurysm when there is not. Among the novel contributions, the present FSI model has the ability to predict the Dacron’s response to realistic hemodynamic loading conditions.
  • Interaction of surface waves with an actuated submerged flexible plate:
           Optimization for wave energy extraction
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): N. Desmars, J. Tchoufag, D. Younesian, M.-R. Alam We investigate the interaction of linear surface waves with a submerged wave energy converter which consists of a submerged flexible plate actuated by one (or more) units of power take off (PTO), each modeled as a combination of a linear spring and a linear damper. We develop a wave-flexible structure interaction model through modal decomposition of the structure deformations, and use Boundary Element Method to find hydrodynamic coefficients of each deformation mode of the structure. We validate our methodology with existing analytical results of hydro-elasticity. We then perform a case study and obtain the maximum efficiency (or Capture Width Ratio (CWR)) of our wave energy converter when excited by monochromatic waves through a comprehensive parametric study of the device parameters (e.g. rigidity of the plate, and location and characteristics of the PTO units). In the absence of viscous effects, the device can reach an efficiency as high as 80%. We find that the efficiency is more sensitive to the location of the PTOs than to their damping coefficients. For a range of plate length to wavelength ratios (close to unity) and with a single PTO unit, the optimal PTO location is past the middle of the plate (along the incident wave direction). This location is nearly independent of the rigidity of the plate although the resulting CWR depends on the rigidity. When two PTO units are used the optimal configuration of PTOs depends on the plate’s aspect ratio and its placement with respect to the incident wave: the two PTOs may need to be at the same location, lined up along the direction of wave propagation, or placed side-by-side perpendicular to the direction of the wave propagation.
  • Numerical study of the wind loads on a cooling tower by a stationary
           tornado-like vortex through LES
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Zhenqing Liu, Chong Zhang, Takeshi Ishihara A tornado simulator is built and large eddy simulations are carried out to model the swirling flow fields in a tornado-like vortex and the tornado-induced wind loads on a cooling tower. When the cooling tower is close to the tornado core, the mean and fluctuating loads exerted by the tornado tend to be much larger than those applied by a straight-line wind. However, when the cooling tower is sufficiently far from the center of the tornado, r>3.0rc, the aerodynamic force coefficients show almost the same value as those induced by the straight-line wind. In the tornado core, the forces show the maximum fluctuations. To explain these large force fluctuations, spectrum analyses are carried out and two peaks are identified. These two peaks are found to be the result of two factors, i.e., the sub-vortices in the tornado and the vortex shedding in the wake of the cooling tower. This is the most important finding in this study, and it clarifies the dynamic response of a cooling tower exposed to a tornado.
  • Dynamic analysis of a cantilevered pipe conveying fluid with density
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Yuchuan Bai, Wude Xie, Xifeng Gao, Wanhai Xu The fluid flow conveyed by a cantilevered pipe might be a multi-phase flow, the density of which can fluctuate with time and space. In this paper, variable density fluid is simulated by a new mathematical model that satisfies the continuity of the fluid flow. The fluid forces acting on the pipe are derived from Newton’s second law. Combined with a Bernoulli–Euler beam model, a new dynamic model for a cantilevered pipe conveying a variable density fluid is established. The numerical results of the present model can be obtained by utilizing finite difference methods and agree with the classical theoretical results. The influences of the fluctuating amplitude, wave number and initial phase angle of the fluid density on the stability and dynamics of the cantilevered pipe system are analysed in detail. It can be found that when the fluid density varies with a large amplitude, the cantilevered pipe system is prone to losing its stability, which consequently leads to flutter. A small wave number of the fluid density has a notable influence on the system’s stability. Moreover, the stability of this system is seldom affected by the initial phase angle of the fluid density. Based on the current research work, an improved stability criterion is proposed with which the stability of the present system can be more precisely determined.
  • Numerical investigation of virtual control surfaces for aeroelastic
           control on compressor blades
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): V. Motta, L. Malzacher, D. Peitsch Virtual control surfaces are assessed numerically as a means to enhance the aeroelastic response of a compressor cascade. Virtual surfaces are realized with plasma actuators placed on the pressure and on the suction side of the blade trailing edge. The plasma-induced flow is meant to be against the direction of the freestream. This allows for generating controlled recirculating flow areas and in turn modifying the effective blade camber and enlarging the actual chord. Computational fluid dynamic analyses with the blades at constant angle of attack show that the effects of pressure side actuation on flow field, pressure distribution and integral loads are comparable to those of flap-like devices. On the contrary suction side actuation yields effects which are analogous to those of wing spoilers. Traveling wave simulations for the torsion mode show that properly triggering an alternate pressure/suction side actuation during the blade pitching cycle improves significantly the blade aeroelastic stability. At the same time an effective reduction in the peaks of the oscillating airloads normal to the freestream direction is achieved, with potential benefits for the alleviation of fatigue phenomena.
  • Hydrodynamic force investigation of a rigid cylinder under the coupling CF
           and IL motion
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Kunpeng Wang, Chunyan Ji, Qinghai Chi, Hairong Wu Extensive researches have been conducted to simulate the two-degree-of-freedom (2DOF) vortex induced vibration (VIV) of a cylinder during the past few decades. However, there are still very few publications in terms of the hydrodynamic force of a cylinder with 2DOF motion in cross-flow (CF) and in-line (IL) directions. This study employs the Reynolds-Average-Navier–Stokes (RANS) equations and shear stress transport (SST) k-ω turbulence model to investigate the hydrodynamic force characteristics. The numerical model is firstly validated based on the 2DOF VIV experiment of an elastically supported cylinder in the literature. The results indicate that the predicted displacement and hydrodynamic force are approximately harmonic, and are in reasonable agreement with the experimental data. By imposing harmonic motion on the cylinder in CF and IL directions with period ratio of 2, parametric analyses are carried out to simply broaden the understanding of the sensitivity of the hydrodynamic coefficients including force coefficient, excitation coefficient and added mass coefficient, to the motion-related parameters, such as the motion phase angle, non-dimensional amplitude and frequency. There would be a sudden change for the excitation coefficient and added mass coefficient at a certain motion phase angle approximately corresponding to the peak of the force coefficient. The varying trend of the hydrodynamic coefficient with non-dimensional amplitude is different from that obtained from one-degree-of-freedom (1DOF) forced vibration test in literatures, and is significantly related with the motion phase angle and non-dimensional frequency. The non-dimensional frequency seems to mainly affect the excitation coefficient, added mass coefficient and mean drag coefficient in the lock-in range.
  • Influence of aerodynamic nonlinearity due to static panel-curvature on
           flutter of panels at transonic and low supersonic Mach numbers
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Manav Bhatia, Philip Beran This study focuses on assessing the influence of aerodynamic nonlinearity due to a static panel curvature on the flutter characteristics of a semi-infinite panel at transonic and low supersonic Mach numbers. The fluid flow is modeled with compressible Euler equations and discretized using density-based streamline-upwind Petrov Galerkin finite element variational form. The structure is analyzed using finite element discretization of a linear Timoshenko beam model. The curved shape of the panel is defined by a half-sine bump with increasing amplitude. Steady-state flow is calculated for this shape and a linearization about this state is used to solve for the flutter mode using a small-disturbance stability eigenvalue formulation. The flutter characteristics are studied for increasing height of the panel curve at several Mach numbers between 0.7 and 2.0. At subsonic Mach numbers flow over the curved panel creates a supersonic bubble and at a sufficiently large height changes the instability mode from zero-frequency divergence to oscillatory flutter. At low supersonic Mach numbers the increasing curve height creates a subsonic region over the panel with a change in the composition of the resulting flutter mode. While the flutter speed is seen to monotonically increase at Mach 1.1, large reductions are observed at Mach 1.5 and 2.0.
  • Active control of composite fuselage type structures with enclosed
           acoustic cavity
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): C. Hesse An active structural–acoustic control system for a composite fuselage type structure is developed in this paper. The focus of the active control system is the global reduction of the sound field in an enclosed acoustic cavity using structure-integrated sensors and actuators. Active structural–acoustic control systems are commonly designed based on the acoustic radiation modes which diagonalize a radiation operator. In the case of interior sound radiation, this radiation operator is derived in this paper from the coupled acoustic modes, which take into account the boundary conditions of the coupled velocity from the fuselage type structure. This results in frequency-independent radiation modes which do not rely on the validity of the modal interaction approach. The latter one violates the continuity condition of the velocity along the coupling surface. Parameter studies regarding active control implementations are conducted in order to evaluate how many radiation modes need to be considered for achieving a global sound attenuation.
  • Experimental analysis of a strong fluid–structure interaction on a soft
           membrane—Application to the flapping of a yacht downwind sail
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Julien Deparday, Benoit Augier, Patrick Bot In the present study we investigate the flapping instability of a light, soft, highly cambered membrane subject to wind loading. An original in-situ experiment is developed where time-resolved pressures and forces are measured on a full-scale yacht downwind sail called a spinnaker. Particular features of this aero-elastic problem are that the membrane is weakly constrained – held only at three corners –, has a free leading edge, and has no proper shape in the absence of wind loading. In usual operating conditions, the soft structure is subject to a flapping instability giving rise to almost periodic folding and unfolding of the fore part of the sail, associated to strong variations of pressures and forces. This dynamic behavior is analyzed in detail and the space–time evolution of pressures on the membrane is linked to the flapping phenomenon. A peak in forces is observed when the membrane recovers its full shape. Thanks to the Bi-Orthogonal Decomposition (BOD) applied to the pressure fields, the dynamic behavior is reasonably well represented by the two first modes where mode 1 mostly carries the global aerodynamic force behavior and mode 2 mostly represents the effects of the membrane flapping. A physical mechanism of the flapping process is proposed based on the discussion of aerodynamic pressures and strains in the membrane.
  • Added mass evaluation with a finite-volume solver for applications in
           fluid–structure interaction problems solved with co-simulation
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): C. Yvin, A. Leroyer, M. Visonneau, P. Queutey This work is devoted to the implementation and analysis of an efficient fluid–structure interaction coupling algorithm used in a cooperative simulation context for rigid bodies. This framework makes possible the study of complex fluid–structure configurations, through the coupling between CFD and dedicated multibody dynamics solvers.A specific focus is here laid on the characterisation of the numerical properties of the proposed coupling algorithm in terms of convergence speed and stability. In order to stabilise the segregated algorithm while keeping non-intrusive in the structure solver, a relaxation operator based on an artificial added mass technique is used. To compute an efficient relaxation operator, an original resolution of the added mass effect is implemented into the fluid finite-volume solver. Good convergence properties are observed for rigid bodies with six degrees of freedom even in case of strong destabilising added mass effects.
  • On the Morison hydrodynamic forces on perforated flat plates in combined
           steady, low frequency and high frequency motion
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): H. Santo, P.H. Taylor, C.H.K. Williamson This paper aims to model the hydrodynamic forces on grids of perforated flat plates undergoing forced motions at three scales, namely steady (current), and combined low (wave) frequency and high (structural) frequency oscillatory motion. The intended application is the design and re-assessment of dynamically-responding offshore platforms. A recent set of experimental results by Santo et al. (2018c) is taken as the reference for comparison with the numerical predictions. A block of porous cells is used as a proxy to the grids of perforated plates in the numerical simulation, but with comparable resistance and added mass represented by equivalent Morison drag and inertia stresses both uniformly distributed over the porous cells. Both stresses are characterised by empirical force coefficients, F and Cm′, which correspond to Morison drag, Cd and inertia, Cm coefficients, respectively. Using these two adjustable empirical parameters, the simulated forces compare reasonably well with the measured hydrodynamic forces on the grids, both in terms of peak forces as well as the complete force–time histories for most of the flow conditions tested in the experiments. This is particularly true when the amplitude of wave velocity is larger than that of current velocity, a representation of large waves in a small current which is realistic for the harsh ocean environment. The porous block model is capable of capturing the global large-scale wake structures, which are responsible for the reduction in fluid flow velocity and associated forces on a structure. The simulated forces however only exhibit slight force asymmetry, unlike the measured forces, because the local fine-scale wake structures are not represented in the numerical modelling. For the scale of the experiments used for the comparison, the contribution from these small-scale wake structures to the global hydrodynamic forces can be quite significant, in particular when the amplitude of wave velocity is comparable to that of current velocity. Overall, this paper demonstrates the versatility of the porous block modelling approach in capturing most of the dominant flow physics and reproducing almost all the experimental results. The generality of the approach allows straightforward extension to wider range of flow conditions including three-dimensional flow.
  • A new modeling approach for transversely oscillating square-section
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Y.Z. Liu, C.M. Ma, Q.S. Li, B.W. Yan, H.L. Liao This paper proposes a new generalized semi-empirical model to simulate fluid–structure interaction forces experienced by a transversely oscillating square-section cylinder by a more comprehensive approach. The total fluctuating transverse aerodynamic forces determined by this new modeling approach are composed of three main unsteady excitation modules. The first component relates to the conventional fluid inertia effect; the second component represents the varying incidence angle effect, including the wavelength-changing effect of downstream wake undulation by introducing a circulation lag function; and the last one denotes the excitation effect due to the strong resonant interaction between wake undulation and Kármán vortex shedding. In addition, the new model establishment process follows the “simple-to-use” principle, so it can be applicable even when few experimental data are available. Good agreements are observed between the predictions by this model and unsteady force coefficient results taken from harmonically forced vibration experiments. Moreover, the new model developed in this study can not only simulate the interaction effects between the vortex-induced vibration (VIV) and galloping, but also retain the predictive capability for the cases of pure vortex resonance and pure galloping phenomena. Finally, some significant findings are also presented in the context of the aeroelastic instability phenomena.
  • Suppression of vortex-induced vibrations using flexible shrouding—An
           experimental study
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Narendran Kumar, Vinay Kumar Varma Kolahalam, Murali Kantharaj, Siddharth Manda A number of offshore compliant structures such as risers, mono-columns, tension leg platforms (TLPs), spars, etc., which are deployed in the offshore field are subjected to vortex-induced vibration (VIV). The harsh environmental conditions often lead to failure of these structures well before their design life period resulting in fatal accidents. To minimize VIV, several investigations were conducted by other researchers. The present study focuses on the experimental investigations of an elastically mounted circular cylinder shrouded with net substructure called as Ventilated Net (VN) to suppress VIV. The VN is an omnidirectional, economical, customizablenet substructure comprising of flexible hollow tubes in a systematic arrangement. This device could be retrofitted to the offshore structures/risers, to attenuate VIV, thereby preventing the structure from fatigue failure. Experimental investigations are conducted to address the reduction of VIV and drag forces acting on the oscillating cylinder shrouded with VN of various configurations. The experiments are performed in towing tank facility in Department of Ocean Engineering, IIT Madras, India. The primary objective of the present investigation is to quantify the VIV amplitudes by employing VN shrouding the cylinder, at high Re regime, ranging from (0.22–2.50) × 105. The effect of spaces between the flexible hollow tubes and shrouding radii of VN around the cylinder are also addressed in this article. From the measurements, it is observed that cylinder with VN of dense mesh at a radial spacing of twice the diameter of the bare cylinder, suppresses VIV by 98% and drag force by 40% at Re of 1.2 × 105.
  • Synthetic jet Reynolds number based on reaction force measurement
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Paweł Gil The paper presents a new method for calculating Reynolds number and dimensionless stroke length based on synthetic jet actuator reaction force measurement. The new method was validated for axisymmetric synthetic jet and classical Reynolds number from about 2000 to 25000 and dimensionless stroke length from 0.5 to about 100, obtaining the coefficient of determination R2=0.90 for Reynolds number and R2=0.94 for dimensionless stroke length. New method is simple, time and cost effective, allows measuring the Reynolds number for orifices of any shape and multi orifices configuration.
  • Multi-disciplinary simulations of stores in weapon bays using scale
           adaptive simulation
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): G.J.M. Loupy, G.N. Barakos, N.J. Taylor This paper presents cavity flow calculations using the scale-adaptive simulation method involving door opening, store release and aeroelasticity. For established bay flows, the structural excitation showed a directional dependence, and the structures were responding to the flow frequency content. Maximum store deformations were of about 2% of the store diameter during store release. This is the first time where such effects are quantified for stores released from within bays. The store deformation, the role of the shear layer, and the store trajectory variability are also quantified.
  • Interval analysis for uncertain aerodynamic loads with
           uncertain-but-bounded parameters
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Jingjing Zhu, Zhiping Qiu In this paper, we make the first effort to apply the interval method to aerodynamic loads analysis considering uncertainty in the case of insufficient sample data, and the effectiveness of this method is validated. The interval perturbation method and subinterval perturbation method are extended to evaluate the uncertain aerodynamic loads region with uncertain-but-bounded parameters. The uncertain parameters with insufficient information are quantified as interval variables. By combining the vortex lattice method and the interval theory, the interval aerodynamic model which is applicable to the subsonic regime is constructed. The first-order Taylor expansion and first-order Neumann series are employed to calculate the response intervals of lift coefficients. Based on the subinterval theory, the subinterval perturbation method for the interval aerodynamic model is developed to solve the aerodynamic problems with large uncertainty level. Two numerical examples for wing models, which consider uncertainty in incoming flow conditions and geometry, are given to validate the feasibility and effectiveness of the proposed methods by comparing the results with Monte Carlo simulations. Moreover, the present methods are extended to evaluate the uncertainty propagation in the pitching moment coefficient and induced drag coefficient.
  • Observed mode shape effects on the vortex-induced vibration of bending
           dominated flexible cylinders simply supported at both ends
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Ersegun D. Gedikli, David Chelidze, Jason M. Dahl The effect of varying the structural mode excitation on bending-dominated flexible cylinders undergoing vortex-induced vibrations was investigated. The response of the bending-dominated cylinders was compared with the response of a tension-dominated cylinder using multivariate analysis techniques. Experiments were conducted in a recirculating flow channel with a uniform free stream with Reynolds numbers between 650 and 5500. Three bending-dominated cylinders were tested with varying stiffness in the cross-flow and in-line directions of the cylinder in order to produce varying structural mode shapes associated with a fixed 2:1 (in-line:cross-flow) natural frequency ratio. A fourth cylinder with natural frequency characteristics determined through applied axial tension was also tested for comparison. The spanwise in-line and cross-flow responses of the flexible cylinders were measured through motion tracking with high-speed cameras. Global smooth-orthogonal decomposition was applied to the spatio-temporal response for empirical mode identification. The experimental observations show that for excitation of low mode numbers, the cylinder is unlikely to oscillate with an even mode shape in the in-line direction due to symmetric drag loading, even when the system is tuned to have an even mode at the expected frequency of vortex shedding. In addition, no mode shape changes were observed in the in-line direction unless a mode change occurs in the cross-flow direction, implying that the in-line response is a forced response dependent on the cross-flow response. The results confirm observations from previous field and laboratory experiments, while demonstrating how structural mode shape can affect vortex-induced vibrations.
  • Time-domain numerical simulations of a loosely supported tube subjected to
           frequency-dependent fluid–elastic forces
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Philippe Piteau, Laurent Borsoi, Xavier Delaune, Jose Antunes Flow-induced vibrations of heat-exchanger tubes are extensively studied in the nuclear industry for safety reasons. Adequate designs, such as anti-vibration bars in PWR steam generators, prevent excessive vibrations provided the tubes are well supported. Nevertheless, degraded situations where the tube/support gaps would widen, must also be considered. In such a case, the tubes become loosely supported and may exhibit vibro-impacting responses due to both turbulence and fluid–elastic coupling forces induced by the cross-flow. This paper deals with the predictive analysis of such a nonlinear situation, given the necessity of taking into account both the strong impact nonlinearity due to the gap and the linearized fluid–elastic forces. In time-domain numerical simulations, computation of flow-coupling forces defined in the frequency-domain is a delicate problem. We recently developed an approach based on a hybrid time–frequency method. In the present paper a more straightforward and effective technique, based on the convolution of a flow impulse response pre-computed from the frequency-domain coefficients, is developed. Illustrative results are presented and discussed, in connection with the previous hybrid method and with experiments. All results agree in a satisfactory manner, validating both computational methods, however the convolutional technique is faster than the hybrid method by two orders of magnitude. Finally, to highlight the subtle self-regulating frequency effect on the stabilization of such system, additional demonstrative computations are presented.
  • Experimental FSI study of adaptive shock control bumps
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Michela Gramola, Paul J.K. Bruce, Matthew Santer The shock stabilisation and wave drag reduction potential of a two-dimensional adaptive shock control bump has been studied in the Imperial College supersonic wind tunnel. The bump was modelled as a flexible aluminium alloy plate deformed through spanwise actuation, and several bump heights were tested beneath a Mach 1.4 transonic shock wave. Schlieren images and static pressure readings along the flexible plate allowed the study of the λ-shock structure generated by the bifurcation of the normal shock for a range of shock positions. All bumps tested were found to increase shock stability, but wave drag reduction was only observed for shocks close to the leading edge of the flexible plate. Positive deformations of the flexible plate for downstream shocks are believed to reduce supersonic flow reacceleration, and hence the strength of the rear leg of the λ-shock and wave drag, in comparison to a solid bump with the same shape. The position of the rear leg of the λ-shock was found to exhibit a bistable behaviour, and this is hypothesised to be caused by a complex coupling of aerodynamic and structural instabilities.
  • Enhanced particle method with stress point integration for simulation of
           incompressible fluid-nonlinear elastic structure interaction
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Hosein Falahaty, Abbas Khayyer, Hitoshi Gotoh A fully-Lagrangian particle-based computational method is developed for simulation of incompressible Fluid, non-linear Structure Interaction (FSI) with incorporation of stress point integration (Randles and Libersky, 2005) to resolve instabilities related to zero-energy modes. Structural dynamics is founded on discretization of the divergence of stress according to Moving Least Squares (MLS) method. The stress point integration is incorporated in calculation of structural dynamics, resulting in a Dual Particle Dynamics (DPD) structure model (Randles and Libersky, 2005). A structure model based on nodal integration is also considered for comparison and simply referred to as MLS. The DPD and MLS structure models are coupled with an enhanced projection-based Moving Particle Semi-implicit (MPS) method as the fluid model, resulting in DPD–MPS and MLS–MPS FSI solvers, respectively. The enhanced performance of DPD with respect to MLS is first shown through a set of tests for structure model. Then the superior performance of DPD–MPS FSI solver with respect to MLS–MPS one is demonstrated through a set of FSI benchmark tests. The present study also presents a new algorithm for fluid–structure coupling via components of stress tensors in surface boundary stress points.Graphical abstractGraphical abstract for this article
  • Experimental investigation of wake-induced aeroelastic limit cycle
           oscillations in tandem wings
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Benjamin Kirschmeier, Matthew Bryant This paper aims to experimentally investigate multi-body aeroelastic wing–wake interactions to quantify how structural properties dictate vortex energy transfer. The paper examines three different components needed to study this phenomenon; first, single wing aeroelastic response and wake characteristics; second, flutter boundary characteristics of tandem aeroelastic wings with wing–wake interactions; third, limit cycle behavior and wake frequency content in tandem oscillating wings. Single wing and tandem wing–wake studies conducted through hot-wire anemometer sweeps downstream of the trailing edge find dominant frequency content and wake velocity profiles. Pitch stiffness on the downstream wing is varied to be less than or equal to that of the upstream wing. It is hypothesized that pitch stiffness modulates the sensitivity of the wing to incoming vortex disturbances thus changing vortex energy transfer to the wing. The experimental results showed that the limit cycle and transient response of the downstream wing in tandem configuration are dependent on its pitch stiffness, while the aeroelastic stability and flutter point of the downstream wing is dictated by the upstream wing. In addition, the wake frequency content in tandem configuration demonstrates strong dependence on downstream wing pitch stiffness. The results show that highest wake energy transfer occurs when the downstream wing pitch stiffness is less than pitch stiffness of the upstream wing.
  • Damping effects on vortex-induced vibration of a circular cylinder and
           implications for power extraction
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Atul Kumar Soti, Jisheng Zhao, Mark C. Thompson, John Sheridan, Rajneesh Bhardwaj The effect of damping on vortex-induced vibration (VIV) of a circular cylinder with a fixed mass ratio (m∗=3.0) was studied through water-channel experiments. An eddy-current-based damping mechanism was constructed to provide controlled and adjustable damping values. It consisted of a permanent magnet connected to the cylinder that moves parallel to a copper plate at some predetermined gap, which determines the damping in the system. Increased damping was found to reduce the reduced-velocity range of the upper and lower branches, thus reducing the synchronization region. As the damping is increased, the lower branch remains easy to identify from the amplitude response curves, but the boundary between the initial and upper branch becomes less clear. However, the frequency response under higher damping shows similarities to that at the lowest damping and these similarities, for the first time, were used to delimit the different response branches. The existence of the upper branch was found to continue down to A∗≈0.2D. The experimental data was assembled to plot the peak amplitude response as a function of the mass–damping parameter in a “Griffin plot”. Due to a restricted variation in Reynolds number in the experiments, the measured data shows negligible scatter compared to the assembled literature data. Three sets of experiments using different sets of springs were conducted to quantify the Reynolds number effect previously established by Govardhan and Williamson (2006). An exponential fitting function was then used to successfully fit the data on the Griffin plot. Under higher damping, it was found that the total and vortex phases are no longer at either 0°or 180°, and take intermediate values throughout the response branches. The power extracted by the damping mechanism was also calculated. Maximum power extraction occurs for a combination of optimal damping and reduced velocity. The power was also found to increase with Reynolds number, correlated with the increase in vibration amplitude. At the highest Reynolds number examined, the dimensionless energy conversion ratio is 0.2, indicating that approximately 20% of the flow energy approaching the cylinder frontal cross-section can be converted to useful electrical energy. This factor increased substantially with Reynolds number from approximately 15 to 20% over the Reynolds number range considered (Re∼1700–5900). The fit devised for the peak vibration amplitude was extended for expressing the average extracted power as a function of mass–damping and Reynolds number.
  • Characteristics of force coefficients and energy transfer for vortex
           shedding modes of a square cylinder subjected to inline excitation
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Hrisheekesh Krishnan, Amit Agrawal, Atul Sharma, Mark Thompson, John Sheridan The nature of the circulation regions around a bluff body in a cross flow can vary considerably from the normal von Kármán vortex-shedding mode when subjected to external excitations. The dynamics of the circulation regions around the bluff body has a direct impact on the force coefficients of the bluff body. In the present work, we correlate the spectral content and characteristics of the force coefficients of different vortex-shedding modes, observed for a square cylinder that is subjected to external excitation in the form of inline sinusoidal pulsation, to the near body vortical events. The strengths of various circulation regions around the bluff body and its location of formation are used to assess the impact of the vortical events on the force coefficient characteristics. In addition, the implication of relative timing of vortical events with respect to the inline excitation on the energy transfer is also discussed.
  • Influence of flexibility on the steady aeroelastic behavior of a swept
           wing in transonic flow
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Günter Schewe, Holger Mai The development in the last decades generally shows that large aircraft wings have become more light and flexible, thus the investigation of the effects of elasticity is suggested. If for example the flexible wing is also backward swept, then the situation becomes even more complex — the kinematic coupling between bending and torsion leads to a structural washout effect.In order to investigate the influence of flexibility, in the project “Aerostabil” an aeroelastically scaled half-model was tested compared to its rigid equivalent. The flexible model was equipped with pressure transducers in three wing sections and accelerometers, while the rigid model had a reduced number of sensors. The experiments were performed in the adaptive test section of a transonic wind tunnel. Steady and unsteady pressure-, and force measurements were conducted for fixed and oscillating wings. Already Dietz et al. (2003) have reported about the special features of the wing models, their structural properties and preliminary results. The present paper is focused on the analysis of the global forces and pressure distributions for the range 0.5 ≤Ma≤ 0.88. The angle of attack was varied from −4° to 4° and also the quasistatic aeroelastic derivatives for lift and moment were obtained.When the model is rigid in the transonic regime and at moderate angles of incidence the pressure distribution exhibits a single shock system, in contrast for the flexible wing there is a double shock system. For the flexible wing up to about Ma=0.82 the curves of global lift, moment and their derivatives are rather smooth and are remaining on nearly the same level. Beyond there are moderate deviations up to the end of the transonic regime. However examining the corresponding curves of the rigid wing the changes are drastic, particularly in the transonic range. Obviously the structural wash-out, particularly of the outer wing leads to an attenuation of the transonic effects.
  • Numerical methods for hydraulic transients in visco-elastic pipes
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Giulia Bertaglia, Matteo Ioriatti, Alessandro Valiani, Michael Dumbser, Valerio Caleffi In technical applications involving transient fluid flows in pipes, the convective terms of the corresponding governing equations are generally negligible. Typically, under this condition, these governing equations are efficiently discretized by the Method of Characteristics. Only in the last years the availability of very efficient and robust numerical schemes for the complete system of equations, such as recent Finite Volume Methods, has encouraged the simulation of transient fluid flows with numerical schemes different from the Method of Characteristics, allowing a better representation of the physics of the phenomena.In this work, a wide and critical comparison of the capability of Method of Characteristics, Explicit Path-Conservative (DOT solver) Finite Volume Method and Semi-Implicit Staggered Finite Volume Method is presented and discussed, in terms of accuracy and efficiency. To perform the analysis in a framework that properly represents real-world engineering applications, the visco-elastic behaviour of the pipe wall, the effects of the unsteadiness of the flow on the friction losses, cavitation and cross-sectional changes are taken into account. Analyses are performed comparing numerical solutions obtained using the three models against experimental data and analytical solutions. In particular, water hammer studies in high density polyethylene pipes, for which laboratory data have been provided, are used as test cases. Considering the visco-elastic mechanical behaviour of plastic materials, 3-parameter and multi-parameter linear visco-elastic rheological models are adopted and implemented in each numerical scheme. Original extensions of existing techniques for the numerical treatment of such visco-elastic models are introduced in this work for the first time. After a focused calibration of the visco-elastic parameters, the different performance of the numerical models is investigated. A comparison of the results is presented taking into account the unsteady wall-shear stress, with a new approach proposed for turbulent flows, or simply considering a quasi-steady friction model. A predominance of the damping effect due to visco-elasticity with respect to the damping effect related to the unsteady friction is confirmed in these contexts. Moreover, all the numerical methods show a good agreement with the experimental data and a high efficiency of the Method of Characteristics in standard configuration is observed. Finally, three Riemann Problems are chosen and run to stress the numerical methods, taking into account cross-sectional changes, more flexible materials and cavitation cases. In these demanding scenarios, the weak spots of the Method of Characteristics are depicted.
  • Full-scale measurements of slamming loads and responses on high-speed
           planing craft in waves
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): J. Camilleri, D.J. Taunton, P. Temarel Full-scale trials on a high-speed planing craft in waves were conducted to investigate the characteristics of slamming impacts and related rigid body and structural response. Measurements of acceleration, pressure, strain and global hull deflection were made in different sea conditions and at different speeds and headings. Low pass filtering is used to remove unwanted noise from the acceleration signals and extract the rigid body response. Methods for removing trends from the strain signals and identifying the peaks in the pressure and strain signals are established. Characteristic results including time series, distributions of peak values, averages of the largest 1/3rd and 1/10th peak values and individual impact events, are presented and discussed. The Weibull and Generalized Pareto models are used to describe the pressure and strain peak values and for estimating extreme loads and responses. Automated algorithms for fitting the statistical models to the peak value distributions are developed and the goodness-of-fit of the models to the data is examined.
  • Boundary Layer Impedance model to analyse the visco-thermal
           acousto-elastic interactions in centrifugal compressors
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Jithin Jith, Sunetra Sarkar Conventional acousto-elastic interaction studies on centrifugal compressors generally ignore the dissipative effects of visco-thermal phenomena present in all acoustic fluids. This work presents a numerically efficient framework for solving acousto-elastic problems, while taking visco-thermal effects into consideration, in centrifugal compressor-like geometries in the frequency domain. Compared to conventional acousto-elastic analyses, the framework enables the computation of a more realistic estimate of the frequency response of a centrifugal compressor. The acoustic fluid is modelled using Boundary Layer Impedance (BLI) model which accounts for dissipative visco-thermal effects through an impedance-like boundary condition. An improved finite element implementation is presented which reduces the computational time of the BLI acousto-elastic model to almost half, while not compromising on accuracy. To further reduce the computational cost, a Krylov subspace based reduced order model (ROM) is developed and implemented in the analysis. The ROM is specifically designed to handle frequency dependent system matrices encountered in the BLI acousto-elastic analysis.
  • Blockage and relative velocity Morison forces on a dynamically-responding
           jacket in large waves and current
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): H. Santo, P.H. Taylor, A.H. Day, E. Nixon, Y.S. Choo This paper documents large laboratory-scale measurements of hydrodynamic force time histories on a realistic 1:80 scale space-frame jacket structure, which is allowed to respond dynamically when exposed to combined waves and in-line current. This is a follow-on paper to Santo, Taylor, Day, Nixon and Choo (2018a) which used the same jacket structure but very stiffly supported. The aim is to investigate the validity of the Morison equation with a relative velocity formulation when applied to a complete space-frame structure, and to examine the fluid flow (and the associated hydrodynamic force) reduction relative to ambient flow due to the presence of the jacket structure as an obstacle array as well as the dynamic structural motion, interpreted as wave–current-structure blockage. Springs with different stiffness are used to allow the jacket to respond freely in the incident wavefield, with the emphasis on high frequency modes of structural vibration relative to the dominant wave frequency. Transient focussed wave groups, and embedded wave groups in a smaller regular wave background are generated in a towing tank. The jacket is towed under different speeds opposite to the wave direction to simulate wave loading with different in-line uniform currents. The measurements are compared with numerical predictions using Computational Fluid Dynamics (CFD), with the actual jacket represented in a three-dimensional numerical wave tank as a porous tower and modelled as a uniformly distributed Morison stress field derived from the relative velocity form. A time-domain ordinary differential equation solver is coupled internally with the CFD solver to account for feedback from the structural motion into the Morison distributed stress field. An approximate expanded form of the Morison relative-velocity is also tested and is recommended for practical industrial applications. Reasonably good agreement is achieved in terms of incident surface elevation, dynamic model displacement as well as total hydrodynamic force time histories, all using a single set of Morison drag (Cd) and inertia (Cm) coefficients, although the numerical results tend to slightly overpredict the total forces. The good agreement between measurements and numerical predictions and the generality of the results shows that the Morison relative-velocity formulation is appropriate for a wide range of space-frame structures. In these tests, this gives rise to additional damping of the dynamic system which is equivalent to 8% of critical damping. This is significantly larger than both the structural and hydrodynamic damping combined (which is about 1%) as quantified through free vibration (push test) in otherwise stationary water.
  • Non-linear limit cycle flutter of a plate with Hertzian contact in axial
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Peng Li, Zhaowen Li, Sheng Liu, Yiren Yang This paper is aimed at the nonlinear flutter of a cantilevered plate with Hertzian contact in axial flow. The contact effect is modeled as a nonlinear spring force with both square and cubic nonlinearity. The fluid force is considered as the sum of two parts, one is the reactive fluid force due to plate motion and the other is the resistive fluid force independent on plate motion. The reactive fluid force is derived by solving the bound and wake vorticity with the help of Glauert’s expansions, and the resistive force is evaluated in terms of drag coefficient. The governing nonlinear partial differential equation of the system is discretized in space and time domains by using the Galerkin method. Results show that the plate loses its stability by flutter and then undergoes limit cycle motions due to the contact nonlinearity after instability. The present fluid model is reliable and shows good agreement with other theories archived. A heuristic analysis scheme based on the equivalent linearization method is developed for the analysis of bifurcations and limit cycles. The Hopf bifurcation is either supercritical or subcritical, which is closely dependent on the contact location. For some special cases the bifurcations are, interestingly, both supercritical and subcritical. When the plate experiences limit cycles, with the increasing dynamic pressure there firstly appear the lock-in motions; and then the quasi-periodic motions show up as a breaking of limit cycle by inclusion of a secondary significant frequency with an irrational value of 14π of the dominant limit cycle frequency. Finally the plate undergoes dynamic buckling characterized by quasi-periodic divergence when the dynamic pressure is relatively large.
  • Hydroelastic analysis of two degree of freedom hydrofoil using a
           reduced-order hydrodynamic model considering unsteady partial sheet cavity
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): S.M. Alavi, H. Haddadpour, R.D. Firouz-Abadi In the present study a new, fast, precise algorithm for studying hydroelastic stability of a typical section with two degrees of freedom (2DOF) is proposed based on the finite element method (FEM), while the partial sheet cavitation effects are considered. For this means, the steady cavity boundary is calculated by some conventional iterative procedures, developed based on the potential flow simulation. Thereafter, assuming that the amplitude and the frequency of the body oscillations are altered so that the cavity length in unsteady flow remains unchanged, the simulation of the unsteady hydrodynamic flow is performed by imposing some velocity fluctuations over the rigid cavity boundary. For the next step, according to the modal analysis of this model, the hydrodynamic eigen modes, which are employed to construct governing hydrodynamic system of equations, are calculated. Using this model along with the structural model the governing hydroelastic set of equations are introduced. According to this simulation approach, numerous calculations are preformed over the considered hydrofoil and the effects of various parameters including the cavitation number, initial angle of attack and structural parameters such as the elastic axis location, radius of gyration, static unbalance, structure to fluid density ratio, and the frequency ratio, over the stability range are surveyed and some conclusions are outlined.
  • Shake table testing of an open rectangular water tank with water sloshing
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Jure Radnić, Nikola Grgić, Marina Sunara Kusić, Alen Harapin Liquid storage tanks are widely used structures in industry. Their safety during an earthquake is important because damage to or the collapse of these structures can cause substantial material damage and human losses. In this paper, the behaviour of small-scale open rectangular water tanks with water sloshing during dynamic excitation was experimentally investigated. The effects of several parameters were studied using a shake table (tank wall stiffness; tank water level; dynamic excitation type; and period, amplitude and duration of the harmonic ground excitation). The most important conclusions of the investigated effects are presented. It is expected that the experimental database can be useful for the verification and calibration of numerical models used to simulation liquid–structure coupled problems.
  • Effects of flexibility on the hovering performance of flapping wings with
           different shapes and aspect ratios
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Aamer Shahzad, Fang-Bao Tian, John Young, Joseph C.S. Lai The effects of isotropic homogeneous flexibility on the aerodynamic performance of flapping wings with different shapes and aspect ratios in hover at a Reynolds number of 400 have been studied numerically with a 3-D Navier–Stokes solver coupled with a structure solver. Three wing shapes, defined by the radius of the first moment of wing area, r1¯ (=0.43, 0.53 and 0.63), with four aspect ratios, AR (=1.5, 2.96, 4.5 and 6.0) are considered. We used a set of moderately flexible wings with an effective stiffness of 14 and 2.31 (for the mass ratio, m∗=4.0 and 0.66 respectively) and a set of more flexible wings with an effective stiffness of 6.12 and 1.01 (for m∗=4.0 and 0.66 respectively). The wings have a limited spanwise twist and a dominant chordwise flexibility because the leading edge is modeled as rigid. The results show that although the prescribed kinematics is advanced pitch rotation, it becomes symmetric or delayed pitch rotation depending on the value of r1¯, the degree of flexibility and the mass ratio. This change in pitch angle kinematics causes variations in the time histories of lift and power with flexibility including the timings and magnitudes of lift and power peaks. Flexible wings with high AR such as 4.5 and 6.0 produce less lift than rigid wings for both mass ratios because of lower pitch angles during the mid-stroke, but they are more efficient in terms of power economy; for example, 11% less lift but 33% higher power economy at AR = 6.0, r¯1=0.63 and m∗=0.66. At m∗=4.0, the low r1¯ and high AR wings maximize PE for a given lift. However, at m∗=0.66, there is a limited range of lift for which low r1¯ and high AR wings are efficient, as r1¯=0.63 wing at higher AR (=6.0) consumes lesser aerodynamic power than r1¯=0.
  • Vibrations of micron-sized fluid membranes induced via pulsed laser
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): A. Vega-Flick, N.W. Pech-May, F. Cervantes-Alvarez, J.J. Alvarado-Gil We study the acoustic vibrations of three different micron-sized square fluid membranes induced by means of a nanosecond pulsed laser. Several vibration modes in the kHz range are excited when the metallic frame, on which the fluid membrane is suspended, undergoes rapid thermal expansion after absorption of the pulsed laser light. The vibration frequencies detected are compared with a model based on bending vibrations of the fluid film similar to those in a solid membrane. Finite element method based simulations are employed to calculate the membrane deformation for different excitation cases of light absorption, as well as the highest excited modes. In addition we explore the effect on the film vibrations due to the inclusion of carbon nanofibers in the fluid membrane. The carbon nanofibers affect the surface tension in a way that couples bending modes to Marangoni waves in the membrane.
  • Nonlinear dynamics of a sliding pipe conveying fluid
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Hao Yan, Huliang Dai, Qiao Ni, Lin Wang, Yikun Wang In this study, nonlinear analysis on dynamic responses of a sliding fluid conveying pipe with length time-varying is performed in detail. An extended Hamilton’s principle is utilized to derive the nonlinear governing equation of motion for the pipe system. Subsequently, effects of flow velocity, sliding rate and two key parameters, e.g. mass ratio and gravity, on dynamic behavior of the pipe are elaborately addressed. The obtained results indicate that the dynamics and stabilities of the pipe system are quite sensitive to the flow velocity, which is dependent on different values of the sliding rate. As the flow velocity is beyond the critical value, flutter occurs and this flutter amplitude of pipe changes with time going on. In addition, it is shown that the pipe becomes easier to lose stability with the increase of the sliding rate, while increasing the mass ratio and gravity of the pipe can enhance its stability.
  • Numerical investigation of the stability of armour units in low-crested
           breakwaters using combined SPH–Polyhedral DEM method
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): Mohammad Sarfaraz, Ali Pak Low-crested breakwaters have become more attractive because they do not hinder the beautiful coastal landscape and are more environmentally friendly comparing to traditional breakwaters. The available formulae for design of these types of structures mainly focus on wave transmission, reflection and dissipation aspects. However, stability of the armour blocks are not directly taken into account in the design process. In this study the Lagrangian meshfree method of SPH along with a discrete element method i.e. Polyhedral DEM are used to simulate the interaction between the sea water waves with different characteristics and low-crested breakwaters constructed using cubic armour blocks. SPH is used for computing the wave forces and moments applied to each armour unit subjected to sea wave action under various conditions. The fluid velocity and pressure time series near the armour units are calculated and based on those, the applied forces and moments are determined. Stability analysis for armour units are conducted by employing DEM which can determine whether the armour units can be displaced by wave action, a phenomenon that causes failure of the whole breakwater over time. Based on the results of a large number of numerical simulations, a practical non-dimensional relationship is proposed for calculating the required dimension of the cubic armour units that can be used for preliminary design of low-crested breakwaters. The newly proposed relationship can fill the gap that currently exists in the literature regarding using cubic armour units for this type of marine structures.
  • Propulsive performance of a pair of pitching foils in staggered
    • Abstract: Publication date: August 2018Source: Journal of Fluids and Structures, Volume 81Author(s): F.J. Huera-Huarte The propulsive performance and the wake interactions between a pair of pitching foils in several staggered configurations are studied experimentally. Results are limited to cases with in-phase and out-of-phase kinematics. Measurements include thrust forces, input torques and the quantification of the flow field around the flapping system.The side-by-side configurations have been found to be beneficial in terms of efficiency when compared to the case of solitary foils. If one of the foils is staggered, efficiency is decreased because of the existence of wake asymmetry.
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