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Stability of a flexible insert in one wall of an inviscid channel flow

JOURNAL OF fluidS AND structureS 2014年 48卷 435-450页

作者： Burke, Meagan A. Lucey, Anthony D. Howell, Richard M. Elliott, Novak S. J. Curtin Univ Dept Mech Engn Fluid Dynam Res Grp Perth WA 6845 Australia

A hybrid of computational and theoretical methods is extended and used to investigate the instabilities of a flexible surface inserted into one wall of an otherwise rigid channel conveying an inviscid flow. The computational aspects of the modelling combine finite-difference and boundary-element methods for structural and fluid elements respectively. The resulting equations are coupled in state-space form to yield an eigenvalue problem for the fluid-structure system. In tandem, the governing equations are solved to yield an analytical solution applicable to inserts of infinite length as an approximation for modes of deformation that are very much shorter than the overall length of the insert. A comprehensive investigation of different types of inserts - elastic plate, damped flexible plate, tensioned membrane and spring-backed flexible plate - is conducted and the effect of the proximity of the upper channel wall on stability characteristics is quantified. Results show that the presence of the upper-channel wall does not significantly modify the solution morphology that characterises the corresponding open-flow configuration, i.e. in the absence of the rigid upper channel wall. However, decreasing the channel height is shown to have a very significant effect on instability-onset flow speeds and flutter frequencies, both of which are reduced. The channel height above which channel-confinement effects are negligible is shown to be of the order of the wavelength of the critical mode at instability onset. For spring-backed flexible plates the wavelength of the critical mode is much shorter than the insert length and we show very good agreement between the predictions of the analytical and the state-space solutions developed in this paper. The small discrepancies that do exist are shown to be caused by an amplitude modulation of the critical mode on an insert of finite length that is unaccounted for in the travelling-wave assumption of the analytical model. Overall, the

关键词： fluid-structure interaction Boundary-element method Finite-difference method Eigen-analysis Divergence Flutter

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A mixed modal-differential quadrature method for free and forced vibration of beams in contact with fluid

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MECCANICA 2014年第3期49卷 535-564页

作者： Eftekhari, S. A. Jafari, A. A. KN Toosi Univ Technol Dept Mech Engn Tehran Iran

A simple and accurate mixed modal-differential quadrature formulation is proposed to study the dynamic behavior of beams in contact with fluid. Both free and forced vibration problems are considered. The proposed mixed methodology uses the modal technique for the structural domain while it applies the differential quadrature method (DQM) to the fluid domain. Thus, the governing partial differential equations of the beam and fluid are reduced to a set of ordinary differential equations in time. In the case of forced vibration, the Newmark time integration scheme is employed to solve the resulting system of ordinary differential equations. The proposed formulation, in general, combines the simplicity of the modal method and high accuracy and efficiency of the DQM. Its application is shown by solving some beam-fluid interaction problems. Comparisons with analytical solutions show that the present method is very accurate and reliable. To demonstrate its efficiency, the test problems are also solved using the finite element method (FEM). It is found that the proposed method can produce better accuracy than the FEM using less computational time. The technique presented in this investigation is general and can be used to solve various fluid-structure interaction problems.

关键词： Mixed modal-differential quadrature formulation Integral quadrature rule fluid-structure interaction Beams in contact with fluid Free and force vibration analysis Analytical solution

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Boundary conditions for flow simulations of abdominal aortic aneurysms

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INTERNATIONAL JOURNAL OF HEAT AND fluid FLOW 2014年 50卷 342-351页

作者： Jozsa, Tunas Istvan Paal, Gyoergy Budapest Univ Technol & Econ Fac Mech Engn Dept Hydrodynam Syst H-1111 Budapest Hungary

Boundary conditions for abdominal aortic aneurysm simulations are problematic both on the fluid and the solid side. In this paper improvements are suggested on existing methodology in both respects. First, a derivation of a hyperelastic wall model is given, taking into account the wall stresses at the diastolic instant. It is demonstrated that this model can be approximated with a simplified linear wall model in the physiologically interesting range. Then a new method for inlet and outlet boundary condition generation is introduced on the fluid side, based on a one-dimensional transient simulator. Finally, the effect of spine support on the intra-aneurysmal flow is studied. Good agreement was found between rigid wall flow simulations on the "systolic" geometry and the fluid-structure interaction simulations. Other authors found much larger differences because earlier the "diastolic" geometry had been used for comparisons and the stresses in the diastolic state were neglected. It was concluded that the spine support does not have a great impact on the flow field. Significant differences were found between the flow behaviour of artificially generated and real aneurysm geometries. (C) 2014 Elsevier Inc. All rights reserved.

关键词： Aortic aneurysm fluid-structure interaction Boundary conditions Hemodynamic simulations

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The influence of computational assumptions on analysing abdominal aortic aneurysm haemodynamics

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PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART H-JOURNAL OF ENGINEERING IN MEDICINE 2014年第8期228卷 768-780页

作者： Ene, Florentina Delassus, Patrick Morris, Liam Galway Mayo Inst Technol Dept Mech & Ind Engn Galway Med Technol Ctr GMedTech Galway Ireland

The variation in computational assumptions for analysing abdominal aortic aneurysm haemodynamics can influence the desired output results and computational cost. Such assumptions for abdominal aortic aneurysm modelling include static/transient pressures, steady/transient flows and rigid/compliant walls. Six computational methods and these various assumptions were simulated and compared within a realistic abdominal aortic aneurysm model with and without intraluminal thrombus. A full transient fluid-structure interaction was required to analyse the flow patterns within the compliant abdominal aortic aneurysms models. Rigid wall computational fluid dynamics overestimates the velocity magnitude by as much as 40%-65% and the wall shear stress by 30%-50%. These differences were attributed to the deforming walls which reduced the outlet volumetric flow rate for the transient fluid-structure interaction during the majority of the systolic phase. Static finite element analysis accurately approximates the deformations and von Mises stresses when compared with transient fluid-structure interaction. Simplifying the modelling complexity reduces the computational cost significantly. In conclusion, the deformation and von Mises stress can be approximately found by static finite element analysis, while for compliant models a full transient fluid-structure interaction analysis is required for acquiring the fluid flow phenomenon.

关键词： Abdominal aortic aneurysms haemodynamics finite element method computational fluid dynamics fluid-structure interaction von Mises stresses computational cost

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Level set immersed boundary method for coupled simulation of air/water interaction with complex floating structures

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JOURNAL OF COMPUTATIONAL PHYSICS 2014年 277卷 201-227页

作者： Calderer, Antoni Kang, Seokkoo Sotiropoulos, Fotis Univ Minnesota St Anthony Falls Lab Minneapolis MN 55414 USA Univ Minnesota Dept Civil Engn Minneapolis MN 55414 USA Hanyang Univ Seoul 133791 South Korea

We propose a new computational approach for simulating the coupled interaction between air-water flows and arbitrarily complex floating rigid bodies. The numerical method integrates the fluid-structure interaction (FSI) curvilinear immersed boundary (CURVIB) method of Borazjani et al. (2008) [21] with a level set approach for simulating free surface flows in arbitrarily complex domains. We show that when applying the CURVIB method to simulate two-phase flow FSI problems the approach used to calculate the force imparted on the body is critical for determining the overall accuracy of the method. We develop and demonstrate the accuracy of a new approach for calculating the force, namely the pressure projection boundary condition (PPBC), which is based on projecting the pressure on the surface of the body using the momentum equation along the local normal to the body direction. Extensive numerical tests show that the new approach greatly improves the ability of the method to correctly predict the dynamics of the floating structure motion. To demonstrate the predictive capabilities of the method and its ability to simulate non-linear free surface phenomena, such as breaking waves, we apply it to various two-and three-dimensional problems involving complex rigid bodies interacting with a free surface both with prescribed body motion and coupled FSI. We show that for all cases the proposed method yields results in very good accuracy with benchmark numerical data and available experiments. The simulations also reveal the onset of dynamically rich, energetic coherent structures in the air phase induced by the waves generated as the rigid body interacts with the free surface. (C) 2014 Elsevier Inc. All rights reserved.

关键词： fluid-structure interaction Two-phase free surface flow Large eddy simulation Level set method Immersed boundary method Floating structures Falling wedge

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Dynamics of a nonlinear elastic plate interacting with a linearized compressible viscous fluid

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NONLINEAR ANALYSIS-THEORY METHODS & APPLICATIONS 2014年 95卷 650-665页

作者： Chueshov, Igor Kharkov Natl Univ Dept Mech & Math UA-61022 Kharkov Ukraine

We study well-posedness and long time dynamics of a coupled model consisting of the compressible isothermal linearized Navier-Stokes fluid in some 3D domain and a nonlinear elastic plate placed on a part of the boundary. We first prove the existence and uniqueness of solutions of the corresponding initial-boundary value problem in a finite energy space. Our main result states the existence of a global finite-dimensional attractor even in the absence of a mechanical damping applied to the plate. (C) 2013 Elsevier Ltd. All rights reserved.

关键词： fluid-structure interaction Linearized isothermal viscous fluid Nonlinear plate Well-posedness Global finite-dimensional attractor

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Numerical study on hydrodynamic effect of flexibility in a self-propelled plunging foil

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COMPUTERS & fluidS 2014年 97卷 1-20页

作者： Zhu, Xiaojue He, Guowei Zhang, Xing Chinese Acad Sci Inst Mech State Key Lab Nonlinear Mech LNM Beijing 100190 Peoples R China

The present study is a numerical investigation of the hydrodynamic effects of passive flexibility on a self-propelled plunging foil. In the model problem, the flow is two-dimensional, incompressible and laminar, while the flexible foil is treated as an inextensible filament. The leading-edge of the foil undergoes a prescribed harmonic oscillation in the vertical direction. In the horizontal direction, the foil is free to move and no constraint is imposed. The simulations are performed by using a solver which couples the immersed boundary method for the flow and the finite difference method for the structure. A systematic parametric study has been conducted to investigate the effects of flexibility on important physical quantities such as the cruising speed, swimming power and propulsive efficiency. It is found that optimal cruising speed is always achieved in foils with some passive flexibility and not the rigid ones. Another important finding is that optimum performance is always achieved at a forcing frequency much lower than the resonance point. Based on the simulation results, three dynamical states of a self-propelled foil have been identified with the increase of bending rigidity, i.e., non-periodic movement, periodic backward-movement and periodic forward-movement. For a flexible foil in forward movement, depending on the range of bending rigidity, either a deflected or a symmetric vortex street arises as the characteristic wake structure. It is found that moderate flexibility is beneficial to symmetry preservation in the wake, while excessive flexibility can trigger symmetry-breaking. The results obtained in the current work shed some light on the role of flexibility in flapping-based biolocomotion. (c) 2014 Elsevier Ltd. All rights reserved.

关键词： fluid-structure interaction Passive flexibility Self-propulsion Plunging foil Immersed boundary method Vortex street

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Nondimensional frequency scaling of aerodynamically-tensioned membranes

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JOURNAL OF fluidS AND structureS 2014年 48卷 14-26页

作者： Zhang, Zheng Hopper, Logan Wrist, Andrew Hubner, James P. Ukeiley, Lawrence Univ Alabama Dept Aerosp Engn & Mech Tuscaloosa AL 35487 USA Univ Florida Dept Mech & Aerosp Engn Gainesville FL 32611 USA

Membrane wings have applications that involve low Reynolds number flyers such as micro air vehicles. The time-averaged and time-dependent deformations of the membrane affect the aerodynamic characteristics of the wing, primarily in the region beyond the maximum aerodynamic efficiency of the wing. This paper investigates an appropriate nondimensional vibration frequency scaling of a spanwise tensioned membrane with free (unattached) leading and trailing edges at low Reynolds numbers relative to nondimensional aeroelastic parameters. Silicone rubber membranes with varying spanwise pre-tension, aerodynamic tension (due to wing angle-of-attack and flow dynamic pressure), modulus of elasticity, span, and thickness are studied. Experimental results are compared to a proposed scaling that simplifies the aerodynamic loading as a uniform pressure distribution acting on the membrane. Data is further compared and discussed relative to previous published results of membrane wings with finite wing spans (three-dimensional flow) and fixed (rigid) leading edges. (C) 2014 Elsevier Ltd. All rights reserved.

关键词： Membrane wings fluid-structure interaction Frequency scaling Aeroelastic scaling Low Reynolds number flow

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Seismic response analysis of residual heat removal pump considering transient fluid excitation force in 1000-MW nuclear power plants

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JOURNAL OF VIBROENGINEERING 2014年第2期16卷 965-976页

作者： Deng, Xin Yuan, Shouqi Si, Qiaorui Li, Yalin Pei, Ji Yuan, Jianping Jiangsu Univ Natl Res Ctr Pumps Zhenjiang 212013 Peoples R China

To prevent nuclear leakage accidents at nuclear power plants because of earthquakes, a new method for seismic response analysis that considers the transient fluid excitation force was used. The inherent modal analysis was based on a newly developed three-dimensional residual heat removal pump model. The equivalent static method and response spectrum method were used to analyze the seismic response at half of the safe shutdown earthquake (SSE) seismic load according to the square root of the sum of the squares algorithm;the actions of gravity, the operation load, the piping load under accident conditions, the SSE seismic load, and the fluid excitation force were considered simultaneously. The fluid excitation force was applied to the rotor system by the fluid-structure interaction method. The seismic response of the rotor with and without the fluid excitation force was analyzed. The deformations caused by the seismic load and fluid excitation force of the impeller surface fitted with a wear ring and the trailing edge of the impeller were analyzed. This study revealed that the primary vibration mode of the residual heat removal pump was translational vibration in the horizontal direction. The total deformation of the trailing edge of the impeller was far below the unilateral clearance between the impeller and diffuser, and the total deformation of the impeller surface fitted with the wear ring met the requirements for seismic response analysis. There was no rub and disturbance between the rotor and stator. The requirements for pump operation under a seismic load were guaranteed to be met. The deformation of the trailing edge of the impeller on the shroud was larger than that on the hub. At different positions of the impeller passage, the deformations of the trailing edge of the impeller on the shroud and hub were basically the same;only the phase of the deformation changed. The results proved that the residual heat removal pump sufficiently meets the RCC-M 2000 standa

关键词： seismic response analysis residual heat removal pump fluid-structure interaction transient fluid excitation force

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A Coupled Finite Difference Material Point Method and Its Application in Explosion Simulation

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CMES-COMPUTER MODELING IN ENGINEERING & SCIENCES 2014年第6期98卷 565-599页

作者： Cui, X. X. Zhang, X. Zhou, X. Liu, Y. Zhang, F. Tsinghua Univ Sch Aerosp Beijing 100084 Peoples R China Beijing Inst Special Engn Design & Res Beijing 100028 Peoples R China

The material point method (MPM) discretizes the material domain by a set of particles, and has showed advantages over the mesh-based methods for many challenging problems associated with large deformation. However, at the same time, it requires more computational resource and has difficulties to construct high order scheme when simulating the fluid in high explosive (HE) explosion problems. A coupled finite difference material point (CFDMP) method is proposed through a bridge region to combine the advantages of the finite difference method (FDM) and MPM. It solves a 3D RE explosion and its interaction with the surrounding structures by dividing the problem domain into FDM region and MPM region in space. FDM is employed to simulate the region where the detonation products disperse into the surrounding air, while the FSI region is simulated by MPM. A bridging region is employed to exchange the information. In the bridge region, MPM provides the boundary condition for FDM region by mapping the variables from MPM background grid nodes to FDM fictitious points, while FDM provides the boundary condition for MPM region by mapping the variables from FDM cell-centre points to MPM interface grid nodes. The transportation between the two computational regions is implemented by moving particles in the bridge region. Numerical results are in good agreement with those of theoretical solutions, empirical formula and experiments. No obvious interface effect are observed in the bridge region in numerical tests.

关键词： Material point method finite difference method bridge region high explosive explosion fluid-structure interaction

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