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Numerical simulation of flow-induced bi-directional oscillations

JOURNAL OF fluidS AND structureS 2013年 37卷 220-231页

作者： Lee, Hyun-Boo Lee, Tae-Rin Chang, Yoon-Suk Sungkyunkwan Univ Sch Mech Engn Suwon South Korea Northwestern Univ Dept Mech Engn Evanston IL 60208 USA Kyung Hee Univ Dept Nucl Engn Yongin South Korea

Flow-induced vibration (FIV) by vortex shedding behind a submerged cylinder can lead to damage of nuclear components. With respect to such a serious scenario, various experiments and numerical simulations have been conducted to predict the vibration phenomena. Especially in simulation, the immersed finite element method (IFEM) is a promising approach to solve fluid-structure interaction problems because it needs less computational resources. In this paper, two-dimensional motions of cylinders are simulated by using IFEM to obtain their vibration characteristics. Three benchmark tests such as flow past a fixed circular cylinder, in-line oscillation of a circular cylinder and flow-induced vibration with uni-directional motion are performed to verify the proposed numerical method. Furthermore, bi-directional motions of two horizontally and vertically arranged cylinders as well as that of a single cylinder in fluid flow are analyzed, and then key findings are fully discussed. (c) 2012 Elsevier Ltd. All rights reserved.

关键词： Bi-directional motions Directly coupled Euler-Lagrange method Flow-induced vibration fluid-structure interaction Immersed finite element method

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Difference in hemodynamic and wall stress of ascending thoracic aortic aneurysms with bicuspid and tricuspid aortic valve

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JOURNAL OF BIOMECHANICS 2013年第10期46卷 1729-1738页

作者： Pasta, Salvatore Rinaudo, Antonino Luca, Angelo Pilato, Michele Scardulla, Cesare Gleason, Thomas G. Vorp, David A. Fdn Ri MED I-90133 Palermo Italy Univ Palermo Dipartimento Ingn Chim Gest Informat & Meccan I-90128 Palermo Italy Mediterranean Inst Transplantat & Adv Specialized I-90127 Palermo Italy Univ Pittsburgh Dept Cardiothorac Surg Pittsburgh PA 15213 USA Univ Pittsburgh Dept Bioengn Pittsburgh PA 15213 USA

The aortic dissection (AoD) of an ascending thoracic aortic aneurysm (ATAA) initiates when the hemodynamic loads exerted on the aneurysmal wall overcome the adhesive forces holding the elastic layers together. Parallel coupled, two-way fluid structure interaction (FSI) analyses were performed on patient-specific ATAAs obtained from patients with either bicuspid aortic valve (BAV) or tricuspid aortic valve (TAV) to evaluate hemodynamic predictors and wall stresses imparting aneurysm enlargement and AoD. Results showed a left-handed circumferential flow with slower-moving helical pattern in the aneurysm's center for BAV ATAAs whereas a slight deviation of the blood flow toward the anterolateral region of the ascending aorta was observed for TAV ATAAs. Blood pressure and wall shear stress were found key hemodynamic predictors of aneurysm dilatation, and their dissimilarities are likely associated to the morphological anatomy of the aortic valve. We also observed discontinues, wall stresses on aneurysmal aorta, which was modeled as a composite with two elastic layers (i.e., inhomogeneity of vessel structural organization). This stress distribution was caused by differences on elastic material properties of aortic layers. Wall stress distribution suggests AoD just above sinotubular junction. Moreover, abnormal flow and lower elastic material properties that are likely intrinsic in BAV individuals render the aneurysm susceptible to the initiation of AoD. (C) 2013 Elsevier Ltd. All rights reserved.

关键词： fluid-structure interaction Aortic dissection Ascending thoracic aortic aneurysm Bicuspid aortic valve

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Force production and asymmetric deformation of a flexible flapping wing in forward flight

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JOURNAL OF fluidS AND structureS 2013年 36卷 149-161页

作者： Tian, Fang-Bao Luo, Haoxiang Song, Jialei Lu, Xi-Yun Vanderbilt Univ Dept Mech Engn Nashville TN 37235 USA Univ Sci & Technol China Dept Modern Mech Hefei 230026 Anhui Peoples R China

Insect wings usually are flexible and deform significantly under the combined inertial and aerodynamic load. To study the effect of wing flexibility on both lift and thrust production in forward flight, a two-dimensional numerical simulation is employed to compute the fluid-structure interaction of an elastic wing section translating in an inclined stroke plane while pitching around its leading ledge. The effects of the wing stiffness, mass ratio, stroke plane angle, and flight speed are considered. The results show that the passive pitching due to wing deformation can significantly increase thrust while either maintaining lift at the same level or increasing it simultaneously. Another important finding is that even though the wing structure and actuation kinematics are symmetric, chordwise deformation of the wing shows a larger magnitude during upstroke than during downstroke. The asymmetry is more pronounced when the wing has a low mass ratio so that the fluid-induced deformation is significant. Such an aerodynamic cause may serve as an additional mechanism for the asymmetric deformation pattern observed in real insects. (C) 2012 Elsevier Ltd. All rights reserved.

关键词： Insect flight Forward flight fluid-structure interaction Immersed-boundary method

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An unsteady adaptive stochastic finite elements formulation for rigid-body fluid-structure interaction

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COMPUTERS & structureS 2008年第23-24期86卷 2123-2140页

作者： Witteveen, Jeroen A. S. Bijl, Hester Delft Univ Technol Fac Aerosp Engn NL-2629 HS Delft Netherlands

An adaptive stochastic finite elements approach for unsteady problems is developed. Time-dependent solutions of dynamical systems are known to be sensitive to small input variations. Stochastic finite elements methods usually require a fast increasing number of elements with time to capture the effect of random input parameters in these unsteady problems. The resulting large number of samples required for resolving the asymptotic stochastic behavior, results for computationally intensive fluid-structure interaction simulations in impractically high computational costs. The unsteady adaptive stochastic finite elements (UASFE) formulation proposed in this paper maintains a constant interpolation accuracy in time with a constant number of samples. The approach is based on a time-independent parametrization of the sampled time series in terms of frequency, phase, amplitude, reference value, damping, and higher-period shape function. This parametrization is interpolated using a robust adaptive stochastic finite elements method based on Newton-Cotes quadrature in simplex elements. The effectiveness of the UASFE approach is illustrated by applications to a mass-spring-damper system, the Duffing equation, and a rigid-airfoil fluid-structure interaction problem with multiple random input parameters. The results are verified by comparison to those of Monte Carlo simulations. (C) 2008 Elsevier Ltd. All rights reserved.

关键词： Stochastic finite elements fluid-structure interaction Unsteady problems Random parameters

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Wake modes of a cylinder undergoing free streamwise vortex-induced vibrations

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JOURNAL OF fluidS AND structureS 2013年 38卷 127-145页

作者： Cagney, N. Balabani, S. UCL Dept Mech Engn London WC1E 7JE England

Simultaneous measurements of the response of a circular cylinder experiencing vortex-induced vibrations (VIVs) in the streamwise direction and the resulting wake field were performed for a range of reduced velocities using time-resolved Particle-Image Velocimetry in the Reynolds number range 450-3700. The dominant vortex shedding mode was identified using phase-averaged vorticity fields. The cylinder response amplitude was characterised by two response branches, separated by a low amplitude region at resonance, as has been previously reported in the literature. During the first response branch the wake exhibited not only the symmetric S-I mode, but also the alternate A-II mode at slightly higher reduced velocities. For both modes, the vortices were observed to be shed at the cylinder response frequency, but rearranged downstream into a more stable structure in which the velocity fluctuations were no longer synchronised to the cylinder motion. A special case of the A-II mode, referred to as the SA mode, was found to dominate in the second response branch and the low amplitude region, while the far wake and the cylinder motion were synchronised (lock-in). A change in the timing of the vortex shedding with respect to the cylinder motion was observed between the low amplitude region and the second response branch. This is likely to correspond to a change in the fluid forcing and levels of excitation, and may explain the variation in the cylinder amplitude observed in this region. Lock-in and the second response branch were found to coincide with a contraction of the wake and an increase in strength of the shed vortices. This work reveals the inherent differences between the extensively studied case of transverse-only VIV and the streamwise-only case, which is crucial if the wealth of information available on transverse VIV is to be extended to the more practical two degree-of-freedom case. (C) 2012 Elsevier Ltd. All rights reserved.

关键词： Vortex-induced vibrations Vortex flows fluid-structure interaction Wake modes

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The enriched space-time finite element method (EST) for simultaneous solution of fluid-structure interaction

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INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING 2008年第3期75卷 305-334页

作者： Zilian, A. Legay, A. Tech Univ Carolo Wilhelmina Braunschweig Inst Stat D-38106 Braunschweig Germany Conservatoire Natl Arts & Metiers Struct Mech & Coupled Syst Lab F-75003 Paris France

The paper introduces a weighted residual-based approach for the numerical investigation of the interaction of fluid flow and thin flexible structures. The presented method enables one to treat strongly coupled systems involving large structural motion and deformation of multiple-flow-immersed solid objects. The fluid flow is described by the incompressible Navier-Stokes equations. The current configuration of the thin structure of linear elastic material with non-linear kinematics is mapped to the flow using the zero iso-contour of an updated level set function. The formulation of fluid, structure and coupling conditions uniformly uses velocities as unknowns. The integration of the weak form is performed on a space-time finite element discretization of the domain. Interfacial constraints of the multi-field problem are ensured by distributed Lagrange multipliers. The proposed formulation and discretization techniques lead to a monolithic algebraic system, well suited for strongly coupled fluid-structure systems. Embedding a thin structure into a flow results in non-smooth fields for the fluid. Based on the concept of the extended finite element method, the space-time approximations of fluid pressure and velocity are properly enriched to capture weakly and strongly discontinuous solutions. This leads to the present enriched space-time (EST) method. Numerical examples of fluid-structure interaction show the eligibility of the developed numerical approach in order to describe the behavior of such coupled systems. The test cases demonstrate the application of the proposed technique to problems where mesh moving strategies often fail. Copyright (C) 2007 John Wiley & Sons, Ltd.

关键词： fluid-structure interaction enriched space-time finite elements EST method level set method

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Vortex-induced vibrations of a diamond cross-section: Sensitivity to corner sharpness

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JOURNAL OF fluidS AND structureS 2013年 39卷 371-390页

作者： Leontini, Justin S. Thompson, Mark C. Monash Univ FLAIR Dept Mech & Aerosp Engn Melbourne Vic 3800 Australia

This paper studies the fluid-structure interaction of an elastically mounted square cross-section cylinder immersed in a free stream. The cross-section is mounted such that its sides are at 45 to the free stream direction, in a "diamond" configuration, and its motion is constrained to the transverse direction relative to the flow direction. Apart from the cross-section, this setup is the same as the majority of single-degree-of-freedom vortex-induced vibration studies of cylinders. Two-dimensional direct numerical simulations of this system have been performed. The Reynolds number based on the point-to-point distance of the cross-section has been fixed at Re=200). Simulations at this Reynolds number allow a direct comparison with previous results from circular cylinders, and therefore focus directly on the impact of the geometry. The sensitivity of the flow, and therefore the motion of the cylinder, to geometrical effects is considered. This is done by rounding the two side corners (those pointing across the flow) at a given radius. For well-rounded corners, the flow behaviour resembles that of a circular cylinder undergoing vortex-induced vibration. However, below a critical radius, the dynamics are considerably altered. Highly disordered and irregular wakes and body motions are observed, as well as a synchronized, periodic P+S wake mode (Williamson and Roshko, 1988), which consists of a pair of vortices on one side, and a single vortex on the other side, shed per oscillation cycle, which results in a non-zero mean lift force. A period-doubled version of this P+S wake is also presented. The spatial structure, and the spatio-temporal symmetries of each of these modes is reported. The results show that even though the spatio-temporal symmetry of the flow is unaffected by the geometry when the body is rigidly mounted (the flow always saturating to a Karman vortex street) geometric features such as sharp corners can induce a number of spontaneous symmetry breaking bifu

关键词： Vortex-induced vibration fluid-structure interaction Symmetry breaking

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Incompressible smoothed particle hydrodynamics (SPH) with reduced temporal noise and generalised Fickian smoothing applied to body-water slam and efficient wave-body interaction

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COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING 2013年第Oct.1期265卷 163-173页

作者： Skillen, Alex Lind, Steven Stansby, Peter K. Rogers, Benedict D. Univ Manchester Sch MACE Modelling & Simulat Ctr Manchester M13 9PL Lancs England Manchester Metropolitan Univ Sch Comp Math & Digital Technol Manchester M15 6BH Lancs England

Incompressible smoothed particle hydrodynamics generally requires particle distribution smoothing to give stable and accurate simulations with noise-free pressures. The diffusion-based smoothing algorithm of Lind et al. (J. Comp. Phys. 231 (2012) 1499-1523) has proved effective for a range of impulsive flows and propagating waves. Here we apply this to body-water slam and wave-body impact problems and discover that temporal pressure noise can occur for these applications (while spatial noise is effectively eliminated). This is due to the free-surface treatment as a discontinuous boundary. Treating this as a continuous very thin boundary within the pressure solver is shown to effectively cure this problem. The particle smoothing algorithm is further generalised so that a non-dimensional diffusion coefficient is applied which suits a given time step and particle spacing. We model the particular problems of cylinder and wedge slam into still water. We also model wave-body impact by setting up undisturbed wave propagation within a periodic domain several wavelengths long and inserting the body. In this case, the loads become cyclic after one wave period and are in good agreement with experiment. This approach is more efficient than the conventional wave flume approach with a wavemaker which requires many wavelengths and a beach absorber. Results are accurate and virtually noise-free, spatially and temporally. Convergence is demonstrated. Although these test cases are two-dimensional with simple geometries, the approach is quite general and may be readily extended to three dimensions. (C) 2013 Elsevier B.V. All rights reserved.

关键词： Incompressible SPH Free-surface flow simulation fluid-structure interaction

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Two-dimensional water entry and exit of a body whose shape varies in time

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JOURNAL OF fluidS AND structureS 2013年 40卷 317-336页

作者： Tassin, A. Piro, D. J. Korobkin, A. A. Maki, K. J. Cooker, M. J. Univ E Anglia Sch Math Norwich NR4 7TJ Norfolk England Univ Michigan Dept Naval Architecture & Marine Engn Ann Arbor MI 48109 USA

The two-dimensional water entry and exit of a body whose shape varies in time in a prescribed way is investigated through analytical and numerical modelling. For this purpose, an analytical model has been developed which extends the modified Logvinovich model of water impact to bodies with time-varying shape. A modified von Karman approach has been developed to describe the exit stage, and a rational derivation of the water exit model which is in use in offshore engineering is presented. CFD simulations are used to assess the accuracy of the analytical model. Several case studies of water entry and exit are presented. The analytical model provides very good force predictions during the entry stage in all cases, but the accuracy of the model in the exit stage depends on the maximum penetration depth. In particular, the appearance of high fluid forces on the body directed downward in both the entry and exit stages is remarkable. (C) 2013 Elsevier Ltd. All rights reserved.

关键词： Water entry Water exit fluid-structure interaction Wagner theory Modified Logvinovich model CFD

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Vibrations and stability of a periodically supported rectangular plate immersed in axial flow

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JOURNAL OF fluidS AND structureS 2013年 39卷 391-407页

作者： Tubaldi, E. Amabili, M. McGill Univ Montreal PQ H3A 0C3 Canada Ecole Polythecn Montreal Montreal PQ Canada

Vibrations and stability of a thin rectangular plate, infinitely long and wide, periodically supported in both directions (so that it is composed by an infinite number of supported rectangular plates with slope continuity at the edges) and immersed in axial liquid flow on its upper side is studied theoretically. The flow is bounded by a rigid wall and the model is based on potential flow theory. The Galerkin method is applied to determine the expression of the flow perturbation potential. Then the Rayleigh-Ritz method is used to discretize the system. The stability of the coupled system is analyzed by solving the eigenvalue problem as a function of the flow velocity;divergence instability is detected. The convergence analysis is presented to determine the accuracy of the computed eigenfrequencies and stability limits. Finally, the effects of the plate aspect ratio and of the channel height ratio on the critical velocity giving divergence instability and vibration frequencies are investigated. (C) 2013 Elsevier Ltd. All rights reserved.

关键词： fluid-structure interaction Plate Static instability

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