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Study of flexible fin and compliant joint stiffness on propulsive performance: theory and experiments

BIOINSPIRATION & BIOMIMETICS 2014年第3期9卷 036011-36010页

作者： Kancharala, A. K. Philen, M. K. Virginia Polytech Inst & State Univ Blacksburg VA 24061 USA

The caudal fin is a major source of thrust generation in fish locomotion. Along with the fin stiffness, the stiffness of the joint connecting the fish body to the tail plays a major role in the generation of thrust. This paper investigates the combined effect of fin and joint flexibility on propulsive performance using theoretical and experimental studies. For this study, fluid-structure interaction of the fin has been modeled using the 2D unsteady panel method coupled with nonlinear Euler-Bernoulli beam theory. The compliant joint has been modeled as a torsional spring at the leading edge of the fin. A comparison of self-propelled speed and efficiency with parameters such as heaving and pitching amplitude, oscillation frequency, flexibility of the fin and the compliant joint is reported. The model also predicts the optimized stiffnesses of the compliant joint and the fin for maximum efficiency. Experiments have been carried out to determine the effect of fin and joint stiffness on propulsive performance. Digital image correlation has been used to measure the deformation of the fins and the measured deformation is coupled with the hydrodynamic model to predict the performance. The predicted theoretical performance behavior closely matches the experimental values.

关键词： flexible foil propulsion compliant joint stiffness caudal fin and peduncle self-propelled speed digital image correlation unsteady panel method fluid-structure interaction

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ALE Formulation and WEB-Method Approximation for a fluid structure interaction Problem on Carotids

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International Conference on Advancements of Medicine and Health Care Through Technology

作者： Maierean, A. M. I. Tech Univ Cluj Napoca Romania

ISBN: (纸本)9783642042911

Treating fluid-structure interaction problems on carotids, implies taking into account that when blood is pumped by the heart through arteries, large nonlinear deformation of the domain occur. This paper reviews the experimental use of the Arbitrary Lagrangian Eulerian technique over the complex geometry of the carotids, which allows the construction of a mobile mesh chosen independently from the material motion in order to minimize the mesh distortion. In a new approach weighted extended B splines are used as basis functions on the tensor product grid.

关键词： fluid-structure interaction ALE method web FEM

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Flexible propulsors in ground effect

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BIOINSPIRATION & BIOMIMETICS 2014年第3期9卷 036008-36007页

作者： Quinn, Daniel B. Lauder, George V. Smits, Alexander J. Princeton Univ Dept Mech & Aerosp Engn Princeton NJ 08544 USA Harvard Univ Dept Organismal & Evolutionary Biol Cambridge MA 02138 USA Monash Univ Clayton Vic 3800 Australia

We present experimental evidence for the hydrodynamic benefits of swimming 'in ground effect', that is, near a solid boundary. This situation is common to fish that swim near the substrate, especially those that are dorsoventrally compressed, such as batoids and flatfishes. To investigate flexible propulsors in ground effect, we conduct force measurements and particle image velocimetry on flexible rectangular panels actuated at their leading edge near the wall of a water channel. For a given actuation mode, the panels swim faster near the channel wall while maintaining the same propulsive economy. In conditions producing net thrust, panels produce more thrust near the ground. When operating in resonance, swimming near the ground can also increase propulsive efficiency. Finally, the ground can act to suppress three-dimensional modes, thereby increasing thrust and propulsive efficiency. The planform considered here is non-biological, but the hydrodynamic benefits are likely to apply to more complex geometries, especially those where broad flexible propulsors are involved such as fish bodies and fins. Such fish could produce more thrust by swimming near the ground, and in some cases do so more efficiently.

关键词： fluid dynamics ground effect fluid-structure interaction biolocomotion benthic fish

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Numerical Study of Slat Screen Pattern Effect on Design Parameters of Tuned Liquid Dampers

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JOURNAL OF fluidS ENGINEERING-TRANSACTIONS OF THE ASME 2014年第6期136卷 061201-061201页

作者： Marivani, Morteza Hamed, M. S. McMaster Univ Dept Mech Engn Thermal Proc Lab Hamilton ON L8S 4L7 Canada

Tuned liquid dampers (TLDs) are considered economical and effective dynamic vibration absorbers. They are increasingly being used to mitigate the dynamic resonant response of tall buildings and it is often designed to reduce the structure's acceleration at a serviceability limit state. Slat screens can increase the inherent damping factor of TLDs. They have been used as a common flow damping device in TLDs because of the simplicity of using them and also the ability to control their effects on the performance of a TLD. Two slat screens with the same solidity ratio and different patterns could have different effects on the TLD's performance. Many former numerical researches used the potential and linear theory as a base to describe the fluid flow behavior inside the TLD. The applicability of the linearized flow models was for the condition of the low amplitude of excitations. Under large excitation events such as high return period wind storms or earthquakes, the assumptions of linear theory are no longer valid. Moreover, in the linearized model, screens were modeled as a hydraulic resistance point as a function of the screen solidity ratio without the ability to consider the effect of screen pattern. In the present study, a numerical algorithm has been developed which can handle both the small and large amplitude of excitations. In this algorithm, the fluid flow through the screen is fully resolved and it can take into account the effect of the screen pattern on the TLD's performance. The major focus of this paper is to use this developed algorithm and conduct a numerical investigation to study the effects of the slat screen pattern on the inherent damping and natural frequency of the TLD, as the design parameters of the TLD. In this numerical investigation a selected TLD outfitted by different slat screens and interacted with the structure is exposed by both harmonic and random external excitations. The numerical results have been validated against experimental wor

关键词： numerical fluid flow fluid-structure interaction tuned liquid damper slat screen screen pattern

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Analysis of Supersonic and Transonic Panel Flutter Using a fluid-structure Coupling Algorithm

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JOURNAL OF VIBRATION AND ACOUSTICS-TRANSACTIONS OF THE ASME 2014年第3期136卷 031013-031013页

作者： Mei, Guanhua Zhang, Jiazhong Xi, Guang Sun, Xu Chen, Jiahui Xi An Jiao Tong Univ Sch Energy & Power Engn Xian 710049 Shaanxi Peoples R China

In order to analyze the supersonic and transonic panel flutter behaviors quantitatively and accurately, a fluid-structure coupling algorithm based on the finite element method (FEM) is proposed to study the two-dimensional panel flutter problem. First, the Von Karman's large deformation is used to model the panel, and the high speed airflow is approached by the Euler equations. Then, the equation of panel is discretized spatially by the standard Galerkin FEM, and the equations of fluid are discretized by the characteristic-based split finite element method (CBS-FEM) with dual time stepping;thus, the numerical oscillation encountered frequently in the numerical simulation of flow field could be removed efficiently. Further, a staggered algorithm is used to transfer the information on the interface between the fluid and the structure. Finally, the aeroelastic behaviors of the panel in both the supersonic and transonic airflows are studied in details. And the results show that the system can present the flat and stable, simple harmonic oscillation, buckling, and inharmonic oscillation states at Mach 2, considering the effect of the pretightening force;at Mach 1.2, as the panel loses stability, the ensuing limit cycle oscillation is born;at Mach 0.8 and 0.9, positive and negative bucklings are the typical states of the panel as it loses its stability. Further, the transonic stability boundary is obtained and the transonic bucket is precisely captured. More, this algorithm can be applied to the numerical analysis of other complicated problems related to aeroelasticity.

关键词： transonic and supersonic panel flutter fluid-structure interaction characteristic-based split finite element method aeroelasticity

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An experimental and three-dimensional computational study on the aerodynamic contribution to the passive pitching motion of flapping wings in hovering flies

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BIOINSPIRATION & BIOMIMETICS 2014年第4期9卷 046009-046009页

作者： Ishihara, D. Horie, T. Niho, T. Kyushu Inst Technol Iizuka Fukuoka Japan

The relative importance of the wing's inertial and aerodynamic forces is the key to revealing how the kinematical characteristics of the passive pitching motion of insect flapping wings are generated, which is still unclear irrespective of its importance in the design of insect-like micro air vehicles. Therefore, we investigate three species of flies in order to reveal this, using a novel fluid-structure interaction analysis that consists of a dynamically scaled experiment and a three-dimensional finite element analysis. In the experiment, the dynamic similarity between the lumped torsional flexibility model as a first approximation of the dipteran wing and the actual insect is measured by the Reynolds number Re, the Strouhal number St, the mass ratio M, and the Cauchy number Ch. In the computation, the three-dimension is important in order to simulate the stable leading edge vortex and lift force in the present Re regime over 254. The drawback of the present experiment is the difficulty in satisfying the condition of M due to the limitation of available solid materials. The novelty of the present analysis is to complement this drawback using the computation. We analyze the following two cases: (a) The equilibrium between the wing's elastic and fluid forces is dynamically similar to that of the actual insect, while the wing's inertial force can be ignored. (b) All forces are dynamically similar to those of the actual insect. From the comparison between the results of cases (a) and (b), we evaluate the contributions of the equilibrium between the aerodynamic and the wing's elastic forces and the wing's inertial force to the passive pitching motion as 80-90% and 10-20%, respectively. It follows from these results that the dipteran passive pitching motion will be based on the equilibrium between the wing's elastic and aerodynamic forces, while it will be enhanced by the wing's inertial force.

关键词： insect flight fluid-structure interaction passive pitching motion dynamically scaled experiment finite element analysis

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Stability and Dynamics of Axially Moving Unidirectional Plates Partially Immersed in a Liquid

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INTERNATIONAL JOURNAL OF STRUCTURAL STABILITY AND DYNAMICS 2014年第4期14卷 1450010-1-1450010-23页

作者： Wang, Yan Qing Guo, Xing Hui Sun, Zhen Li, Jian Northeastern Univ Inst Appl Mech Shenyang 110819 Peoples R China

The stability and dynamics of an axially moving unidirectional plate partially immersed in a liquid and subjected to a nonlinear aerodynamic excitation are investigated. The method of singular functions is adopted to study the dynamic characteristics of the unidirectional plates with discontinuous characteristics. Nonlinearities due to large-amplitude plate motions are considered by using the classical nonlinear thin plate theory, with allowance for the effect of viscous structural damping. The velocity potential and Bernoulli's equation are used to describe the fluid pressure acting on the unidirectional plate. The effect of fluid on the vibrations of the plate may be equivalent to added mass of the plate. The formulation of added mass is obtained from kinematic boundary conditions of the plate-fluid interfaces. The system is discretized by Galerkin's method while a model involving two degrees of freedom, is adopted. Attention is focused on the behavior of the system in the region of dynamic instability, and several motions are found by numerical simulations. The effects of the moving speed and some other parameters on the dynamics of the system are also investigated. It is shown that chaotic motions can occur in this system in several certain regions of parameter space.

关键词： Axially moving unidirectional plate method of singular functions discontinuous characteristics nonlinear fluid-structure interaction chaos

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Vibration of Elastic Beams in the Presence of an Inviscid fluid Medium

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INTERNATIONAL JOURNAL OF STRUCTURAL STABILITY AND DYNAMICS 2014年第6期14卷 1450022-1450022页

作者： Soltani, Helnaz Payette, Gregory S. Reddy, J. N. Texas A&M Univ Dept Mech Engn College Stn TX 77843 USA

The physical interaction of fluids and solids is of practical significance in engineering (e.g. utter of aerodynamic structures, vortex induced vibrations of sub-sea pipelines and risers, inflatable dams, parachute dynamics and blood flow through arteries). In this paper, a finite element formulation is developed for determining the vibration characteristics of beams in contact with inviscid incompressible fluid. The classical, first-order and third-order shear deformation beam theories are used to model the structural response. Numerical results for vibration frequencies are presented showing the parametric effect of thickness and immersion depth on the frequency response. The results indicate that the presence of fluid interaction has significant effect on the dynamic response. The formulation presented herein is also applicable to a vast number of vibration problems related to beams under a variety of excitations.

关键词： Classical beam theory fluid-structure interaction finite element analysis Reddy third-order beam theory timoshenko beam theory

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Elasto-Dynamic Behavior of a Two-Dimensional Square Lattice With Entrained fluid II: Microstructural and Homogenized Models

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JOURNAL OF VIBRATION AND ACOUSTICS-TRANSACTIONS OF THE ASME 2014年第3期136卷 031005-031005页

作者： Dorodnitsyn, Vladimir Spadoni, Alessandro Ecole Polytech Fed Lausanne Inst Engn Mech CH-1015 Lausanne Switzerland

This paper presents a detailed study of the pressure waves and effective mechanical properties of a closed-cell cellular solid with entrained fluid. Plane-harmonic-waves are analyzed in a periodic square with a finite-element model of a representative-volume element, which explicitly considers fluid-structure interactions, structural deformations, and the fluid dynamics of entrained fluid. The wall, cavity, and coupled-system resonance frequencies are identified as key parameters that describe the propagation characteristics. A tube-piston model based on computed microstructural deformations allows us to determine the effective stiffness tensor of an equivalent continuum at the macroscale. The analysis of dispersion surfaces indicates a single isotropic pressure mode for frequencies below resonance of the lattice walls, unlike Biot's theory which predicts two pressure modes. Shear modes are instead strongly anisotropic for all values of relative density rho* describing both cellular rho* < 0: 3 and porous solids rho* >= 0.3. The dependence of the pressure wave phase velocity on the relative density is analyzed for varying properties of the entrained fluid. Depending on the relative density and mass coupling of the solid and fluid phases, the microstructural deformations can be of three types: bending, through-the-thickness, and the combination of the two. For heavy and stiff entrained fluid, the bending regime is confined to extremely small values of relative density, whereas for light fluid such as a gas, deformations are of the bending-type for rho* < 0.1. Through-the-thickness deformations appear only for the heavy entrained fluid for large values of rho*.

关键词： wave propagation Biot's theory poroelasticity cellular solids band structure fluid-structure interaction

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Integral equation model for warm and hot dense mixtures

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Physical Review E 2014年第3期90卷 033110-033110页

作者： C. E. Starrett D. Saumon J. Daligault S. Hamel Lawrence Livermore National Laboratory Livermore California 94550 USA

In a previous work [C. E. Starrett and D. Saumon, Phys. Rev. E 87, 013104 (2013)] a model for the calculation of electronic and ionic structures of warm and hot dense matter was described and validated. In that model the electronic structure of one atom in a plasma is determined using a density-functional-theory-based average-atom (AA) model and the ionic structure is determined by coupling the AA model to integral equations governing the fluid structure. That model was for plasmas with one nuclear species only. Here we extend it to treat plasmas with many nuclear species, i.e., mixtures, and apply it to a carbon-hydrogen mixture relevant to inertial confinement fusion experiments. Comparison of the predicted electronic and ionic structures with orbital-free and Kohn-Sham molecular dynamics simulations reveals excellent agreement wherever chemical bonding is not significant.

关键词： INTEGRAL equations DENSITY functional theory fluid-structure interaction IONIC structure ELECTRONIC structure MOLECULAR simulation methods CHEMICAL bonds

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