This paper introduces a topology optimization approach that combines an explicit level set method (LSM) and the extended finite element method (XFEM) for designing the internal structural layout of fluid-structure int...
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This paper introduces a topology optimization approach that combines an explicit level set method (LSM) and the extended finite element method (XFEM) for designing the internal structural layout of fluid-structure interaction (FSI) problems. The FSI response is predicted by a monolithic solver that couples an incompressible Navier-Stokes flow model with a small-deformation solid model. The fluid mesh is modeled as an elastic continuum that deforms with the structure. The fluid model is discretized with stabilized finite elements and the structural model by a generalized formulation of the XFEM. The nodal parameters of the discretized level set field are defined as explicit functions of the optimization variables. The optimization problem is solved by a nonlinear programming method. The LSM-XFEM approach is studied for two- and three-dimensional FSI problems at steady-state and compared against a density topology optimization approach. The numerical examples illustrate that the LSM-XFEM approach convergences to well-defined geometries even on coarse meshes, regardless of the choice of objective and constraints. In contrast, the density method requires refined grids and a mass penalization to yield smooth and crisp designs. The numerical studies show that the LSM-XFEM approach can suffer from a discontinuous evolution of the design in the optimization process as thin structural members disconnect. This issue is caused by the interpolation of the level set field and the inability to represent particular geometric configurations in the XFEM model. While this deficiency is generic to the LSM-XFEM approach used here, it is pronounced by the nonlinear response of FSI problems.
fluidstructureinteraction (FSI) analyses of cerebral aneurysm using patient-specific geometry with uniform and pathological aneurysmal wall thickness models are carried out. The objective is to assess the influence ...
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fluidstructureinteraction (FSI) analyses of cerebral aneurysm using patient-specific geometry with uniform and pathological aneurysmal wall thickness models are carried out. The objective is to assess the influence of the wall thickness on the FSI and hemodynamics in aneurysms. Two aneurysm models that were reconstructured based on CT images are used. The arterial wall thickness is set to 0.3 mm for the non-aneurysmal artery and to 0.05 mm for the aneurysmal wall based on experimental findings. Another set of aneurysm models with a uniform wall thickness of 0.3 mm for the entire model is used for comparison. The FSI simulations are carried out using the deforming-spatial-domain/stabilized space time method with physiological inflow and pressure profiles. Computations with different aneurysmal wall thicknesses depict considerable differences in displacement, flow velocity and wall shear stress (WSS). The wall displacement for the pathological wall model is 61% larger than that of the uniform wall model. Consequently, the flow velocities in the aneurysm with the pathological wall model are lower, and that results in a 51% reduction in WSS on the aneurismal wall. Because low WSS on the aneurymal wall is linked to growth and rupture risk of aneurysm, the results suggest that using uniform wall thickness for the aneurysmal wall could underestimate risk in aneurysms. Copyright (C) 2009 John Wiley & Sons, Ltd.
A simplified fluid-structure interaction model is presented, consisting of a cylinder tethered by a spring system interacting dynamically with the two-dimensional and incompressible lid-driven cavity flow. The fluid-s...
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A simplified fluid-structure interaction model is presented, consisting of a cylinder tethered by a spring system interacting dynamically with the two-dimensional and incompressible lid-driven cavity flow. The fluid-structure interaction was solved in a partitioned way, having separate solvers for the fluid flow equations and the structural equations. The influence of the Reynolds number and spring constants on the cylinder motion and fluid flow was analyzed. Results show that as the Reynolds number increases, the secondary eddies grow in size and the primary eddy adapts to this change, shifting toward the center of the cavity. When the values of the spring constants are small (k = 0.01N/m), such that the spring forces are weaker than the fluid drag force, the springs stretch freely and the cylinder motion is the direct result of the fluid dynamics action. For higher values of spring constants (k > 0.01N/m), the cylinder motion reaches a maximum displacement, and the spring forces induce the cylinder to an oscillatory movement damped by the viscous fluid force;subsequently, the amplitude of the displacements decreases. As the Reynolds number increases, the cylinder motion is restricted within the mainstream fluid flow (considered the more energized region), having smaller displacements.
The ionic liquid compressor is promising for hydrogen refuelling stations, where the dynamic characteristics of the free piston are crucial for adjusting the compressor performance. This paper presents an investigatio...
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The ionic liquid compressor is promising for hydrogen refuelling stations, where the dynamic characteristics of the free piston are crucial for adjusting the compressor performance. This paper presents an investigation of the dynamic characteristics of the free piston in the ionic liquid compressor through a fluid-structure interaction modelling in three typical conditions. The results show that in the typical condition with no impact, phenomenons of buffering, oil charging, and oil overflow are observed in the oil pressure variation. Three features are found in the motion curve: asymmetric motion with a delay of reversal due to the buffering effect, variable location of the dead centre, and fluctuation in the piston velocity. When the impact occurs at the TDC, an opposite variation trend is observed in the gas and oil pressure curve. In the typical condition with impact at the BDC, the oil pressure drops below the atmospheric pressure.& COPY;2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
The importance of the aortic root compliance in the aortic valve performance has most frequently been ignored in computational valve modeling, although it has a significant contribution to the functionality of the val...
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The importance of the aortic root compliance in the aortic valve performance has most frequently been ignored in computational valve modeling, although it has a significant contribution to the functionality of the valve. Aortic root aneurysm or (calcific) stiffening severely affects the aortic valve behavior and, consequently, the cardiovascular regulation. The compromised mechanical and hemodynamical performance of the valve are difficult to study both 'in vivo' and 'in vitro'. Computational analysis of the valve enables a study on system responses that are difficult to obtain otherwise. In this paper a numerical model of a fiber-reinforced stentless aortic valve is presented. In the computational evaluation of its clinical functioning the interaction of the valve with the blood is essential. Hence, the blood-tissue interaction is incorporated in the model using a combined fictitious domain/arbitrary Lagrange-Euler formulation, which is integrated within the Galerkin finite element method. The model can serve as a diagnostic tool for clinical purposes and as a design tool for improving existing valve prostheses or developing new concepts. Structural mechanical and fluid dynamical aspects are analyzed during the systolic course of the cardiac cycle. Results show that aortic root compliance largely influences the valve opening and closing configurations. Stresses in the delicate parts of the leaflets are substantially reduced if fiber-reinforcement is applied and the aortic root is able to expand. (C) 2003 Elsevier Science Ltd. All rights reserved.
A simple and efficient computational framework is presented for the simulation of fluid-structure interaction problems involving rigid body and multiphase flows in the context of hydrodynamics. Unlike existing publica...
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A simple and efficient computational framework is presented for the simulation of fluid-structure interaction problems involving rigid body and multiphase flows in the context of hydrodynamics. Unlike existing publications, this method does not solve the general motion of rigid bodies in the Lagrangian form of Newton's law. Derived from the distributed Lagrange multiplier treatment of the rigid body, a new set of governing equations is presented on the fully Eulerian one-fluid formulation. To solve the problem numerically, the complex problem is separated into three parts: balance of the momentum and mass (dynamic problem), evolving of the Heaviside function by the external velocity (geometric problem) and rigid motion projection (kinematic problem). The conservation of mass and momentum is guaranteed by the multiphase fluid solver. The water, air and structure coupling is accomplished by the smeared interface. A new way of initialisation and convection of the rigid Heaviside function is designed for an arbitrary shape. To deal with rigid velocity vector, a linear least square method is proposed. The excellent agreement between the numerical experiment and the reference data from experiments demonstrate the validity and applicability of the new methodology (C) 2017 Elsevier B.V. All rights reserved.
In this paper we present a full Eulerian model for a dynamic fluid-structure interaction (FSI) problem in terms of phase field approach, and design its full Eulerian finite element discretization and effective iterati...
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In this paper we present a full Eulerian model for a dynamic fluid-structure interaction (FSI) problem in terms of phase field approach, and design its full Eulerian finite element discretization and effective iterative method. The present full Eulerian FSI model effectively demonstrates the interaction between fluid flow and solid structure in terms of a uniform system of governing equations defined in a single domain, thus the computational grid is fixed, and the re-meshing and interpolation techniques which are always required by other FSI modeling approaches are no longer needed here. We develop a new stable scheme to discretize the Euler equation of an incompressible hyperelastic structure in Eulerian description, and employ Galerkin/least-square (GLS) stabilization scheme, streamline-upwind/Petrov-Galerkin (SUPG) method, and the second-order backward difference formula (BDF) to solve the derived transient nonlinear system of Navier-Stokes equations and transport equations. Numerical experiment is carried out for a cross spinning around its rotation of axis due to the passing flow field, and the numerical results dramatically show the spinning motion of the cross due to the interaction with the fluid, showing that our model and numerical methods are effective to simulate the dynamic fluid-structure interaction phenomena. (C) 2013 Elsevier Ltd. All rights reserved.
The effects of the uniform and spatially varying ground motions on the stochastic response of fluid-structure interaction system during an earthquake are investigated by using the displacement based fluid finite eleme...
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The effects of the uniform and spatially varying ground motions on the stochastic response of fluid-structure interaction system during an earthquake are investigated by using the displacement based fluid finite elements in this paper. For this purpose, variable-number-nodes two-dimensional fluid finite elements based on the Lagrangian approach is programmed in FORTRAN language and incorporated into a general-purpose computer program SVEM, which is used for stochastic dynamic analysis of solid systems under spatially varying earthquake ground motion. The spatially varying earthquake ground motion model includes wave-passage, incoherence and site-response effects. The effect of the wave-passage is considered by using various wave velocities. The incoherence effect is examined by considering the Harichandran-Vanmarcke and Luco-Wong coherency models. Homogeneous medium and firm soil types are selected for considering the site-response effect where the foundation supports are constructed. A concrete gravity dam is selected for numerical example. The S16E component recorded at Pacoima dam during the San Fernando Earthquake in 1971 is used as a ground motion. Three different analysis cases are considered for spatially varying ground motion. Displacements, stresses and hydrodynamic pressures occurring on the upstream face of the dam are calculated for each case and compare with those of uniform ground motion. It is concluded that spatially varying earthquake ground motions have important effects on the stochastic response of fluid-structure interaction systems.
In fluid-structure interaction (FSI) problems, accuracy of the data transfer between fluid-structure interfaces is mainly attributed to the element type and discretization density of grids in both fluid and structure ...
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In fluid-structure interaction (FSI) problems, accuracy of the data transfer between fluid-structure interfaces is mainly attributed to the element type and discretization density of grids in both fluid and structure domains. To remedy the inaccuracy caused by the prevalently applied solo elemental node interpolation strategy, a novel interpolation method is proposed in the present study. The approach is based on the radial basis function and introduces a weight coefficient through which the centroid and nodes of an element are joined. This way, the interpolation will be conducted in accordance to a weighted summation of both terms. Before it is applied to practice relevant engineering examples, the validity of the formulated approach is first examined by simple 2D and further 3D case studies. Studies have clearly illustrated that, compared to pure element centroid or nodes based interpolation schemes, the established approach is insensitive to the pressure distribution. Meanwhile, in these cases the influence of selected basis functions and mesh densities have been examined in detail. Based on the knowledge gained from these case studies, it further investigated a problem emerged from high-speed trains in which the CFD simulation is validated by the field experiment and the task is to transfer data from the fluid domain to the structure domain. Result of the study shows that for the high speed train model considered which has complicated non-matching grids, the accuracy of data transfer in fluid-structure interaction is highly improved and the maximum of global relative error achieves 2.62%.
This paper studies the dynamic properties of aqueduct-water coupling system in bent-type aqueduct structures using the Arbitrary Lagrangian-Eulerian (ALE) method. A three-dimensional fluid-structure interaction model ...
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This paper studies the dynamic properties of aqueduct-water coupling system in bent-type aqueduct structures using the Arbitrary Lagrangian-Eulerian (ALE) method. A three-dimensional fluid-structure interaction model was established, with plate rubber supports. The speed-time sequence of fluctuating wind acting on the aqueduct was simulated by the Auto-regressive Moving Average (ARMA) model. The natural vibration characteristics, seismic responses, and wind responses of the aqueduct structure were calculated and comparatively analyzed in different conditions of water depth. The simulation results show that the application of isolation technology can reduce aqueduct stiffness and change the vibration characteristics of an aqueduct structure. The application of isolated technique is able to elevate the earthquake resistance performance of aqueduct structure. However, the isolation remarkably increases the wind stress response and reduces wind resistance performance of the aqueduct bridge. (C) 2012 Elsevier Ltd. All rights reserved.
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