In this paper, we describe a three-dimensional simulation of the fluid-structure interaction (FSI) of the aortic valve using a direct-forcing immersed-boundary method. The geometry of the valve is taken from a biopros...
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In this paper, we describe a three-dimensional simulation of the fluid-structure interaction (FSI) of the aortic valve using a direct-forcing immersed-boundary method. The geometry of the valve is taken from a bioprosthetic valve, and the computational framework is based on a previous partitioned approach that is versatile for handling a range of biological FSI problems involving large deformations. When applying the approach in the heart valve simulation, we implemented an efficient parallel algorithm based on domain decomposition to handle the costly flow simulation. As compared with previous simulations of the aortic valve, our simulation was able to capture both realistic deformation of the leaflets and vortex structures in the flow, thus providing a balanced modeling approach for the flow and the valve. The results show that the pressure distribution on the leaflet surface is highly nonuniform and the jet flow contains a sequence of vortices during the opening process. After the valve is fully opened, both the three leaflets and the jet still experience significant oscillations. The drag resistance of the valve is also characterized, and it is found that the resistance is approximately equivalent to the inertial force of accelerating the fluid column of three diameter length. These details could be potentially used to characterize FSI of the aortic valve. (C) 2018 Elsevier Ltd. All rights reserved.
In this paper, we develop a novel phase-field model for fluid-structure interaction (FSI), that is capable to handle very large deformations as well as topology changes like contact of the solid to a wall. The model i...
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In this paper, we develop a novel phase-field model for fluid-structure interaction (FSI), that is capable to handle very large deformations as well as topology changes like contact of the solid to a wall. The model is based on a fully Eulerian description of the velocity field in both, the fluid and the elastic domain. Viscous and elastic stresses in the Navier-Stokes equations are restricted to the corresponding domains by multiplication with their characteristic functions. The solid is described as a hyperelastic neo-Hookean material and the elastic stress is obtained by solving an additional Oldroyd-B - like equation. Thermodynamically consistent forces are derived by energy variation. The convergence of the derived equations to the traditional sharp interface formulation of fluid-structure interaction is shown by matched asymptotic analysis. The model is evaluated in a challenging benchmark scenario of an elastic body traversing a fluid channel. A comparison to reference values from Arbitrary Lagrangian Eulerian (ALE) simulations shows very good agreement. We highlight some distinct advantages of the new model, like the avoidance of re-triangulations and the stable inclusion of surface tension. Further, we demonstrate how simple it is to include contact dynamics into the model, by simulating a ball bouncing off a wall. We extend this scenario to include adhesion of the ball, which to our knowledge, cannot be simulated with any other FSI model. While we have restricted simulations to fluid-structure interaction, the model is capable to simulate any combination of viscous fluids, visco-elastic fluids and elastic solids. (C) 2018 Elsevier Inc. All rights reserved.
This paper presents a comprehensive analysis on a super-tall structure where a numerical approach is used to measure its structural response when subjected to turbulent wind. The aim of this study is to provide a feas...
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This paper presents a comprehensive analysis on a super-tall structure where a numerical approach is used to measure its structural response when subjected to turbulent wind. The aim of this study is to provide a feasible alternate approach, to the experimental multi-degree of freedom (MDOF) aeroelastic wind tunnel tests, which are commonly used in industry to estimate structural responses of super-tall structures. An innovative and time-efficient uncoupled one-way fluid-structure interaction (FSI) simulation technique was used to measure the structural response. This novel method was evaluated against a commercially available two-way FSI analysis technique and validated with an experimental MDOF aeroelastic model. It is shown that the uncoupled one-way FSI analysis is capable of estimating structural responses and provides similar numerical accuracy to that of the experimental response. This performance was achieved in a total of 74 clock hours which accounts for the CFD simulation and transient structural analysis calculated for eighteen different structural configurations. In comparison, the two-way FSI analysis, which uses a commercial code, took 4800 clock hours to calculate for six configurations. The uncoupled one-way FSI technique also provided good correlations with experimentally observed trends such as vortex-induced resonance. In comparison the two-way FSI simulation was not as accurate due to the practical limitations (such as mesh size) that needed to be introduced in order to obtain results within a feasible time frame. Finally through validation, it is demonstrated that the proposed uncoupled one-way FSI analysis technique can provide accurate results at a feasible cost.
In this paper the cell-based smoothed finite element method (CS-FEM) is introduced into two mainstream aspects of computational fluid dynamics: incompressible flows and fluid-structure interaction (FSI). The emphasis ...
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In this paper the cell-based smoothed finite element method (CS-FEM) is introduced into two mainstream aspects of computational fluid dynamics: incompressible flows and fluid-structure interaction (FSI). The emphasis is placed on the fluid gradient smoothing which simply requires equal numbers of Gaussian points and smoothing cells in each four-node quadrilateral element. The second-order, smoothed characteristic-based split scheme in conjunction with a pressure stabilization is then presented to settle the incompressible Navier-Stokes equations. As for FSI, CS-FEM is applied to the geometrically nonlinear solid as usual. Following an efficient mesh deformation strategy, block-Gauss-Seidel procedure is adopted to couple all individual fields under the arbitrary Lagriangian-Eulerian description. The proposed solvers are carefully validated against the previously published data for several benchmarks, revealing visible improvements in computed results.
In this work, we propose both a theoretical framework and a numerical method to tackle shape optimization problems related with fluid dynamics applications in presence of fluid-structure interactions. We present a gen...
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In this work, we propose both a theoretical framework and a numerical method to tackle shape optimization problems related with fluid dynamics applications in presence of fluid-structure interactions. We present a general framework relying on the solution to a suitable adjoint problem and the characterization of the shape gradient of the cost functional to be minimized. We show how to derive a system of (first-order) optimality conditions combining several tools from shape analysis and how to exploit them in order to set a numerical iterative procedure to approximate the optimal solution. We also show how to deal efficiently with shape deformations (resulting from both the fluid-structure interaction and the optimization process). As benchmark case, we consider an unsteady Stokes flow in an elastic channel with compliant walls, whose motion under the effect of the flow is described through a linear Koiter shell model. Potential applications are related e.g. to design of cardiovascular prostheses in physiological flows or design of components in aerodynamics.
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 cons...
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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-infinity, 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-infinity 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-infinity model-matching control with admittance causality is found to be the most adept control design for the CPS. (C) 2018 Elsevier Ltd. All rights reserved.
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. Comp...
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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 hyperelas tic 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
Based on the coupled problem of time-dependent fluid-structure interaction, equations for an appropriate adjoint problem are derived by the consequent use of the formal Lagrange calculus. Solutions of both primal and ...
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Based on the coupled problem of time-dependent fluid-structure interaction, equations for an appropriate adjoint problem are derived by the consequent use of the formal Lagrange calculus. Solutions of both primal and adjoint equations are computed in a partitioned fashion and enable the formulation of a surface sensitivity. This sensitivity is used in the context of a steepest descent algorithm for the computation of the required gradient of an appropriate cost functional. The efficiency of the developed optimization approach is demonstrated by minimization of the pressure drop in a simple two-dimensional channel flow and in a three-dimensional ducted flow surrounded by a thin-walled structure.
Pulse wave imaging (PWI) is an ultrasound-based method that allows spatiotemporal mapping of the arterial pulse wave propagation, from which the local pulse wave velocity (PWV) can be derived. Recent reports indicate ...
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Pulse wave imaging (PWI) is an ultrasound-based method that allows spatiotemporal mapping of the arterial pulse wave propagation, from which the local pulse wave velocity (PWV) can be derived. Recent reports indicate that PWI can help the assessment of atherosclerotic plaque composition and mechanical properties. However, the effect of the atherosclerotic plaque's geometry and mechanics on the arterial wall distension and local PWV remains unclear. In this study, we investigated the accuracy of a finite element (FE) fluid-structure interaction (FSI) approach to predict the velocity of a pulse wave propagating through a stenotic artery with an asymmetrical plaque, as quantified with PWI method. Experiments were designed to compare FE-FSI modeling of the pulse wave propagation through a stenotic artery against PWI obtained with manufactured phantom arteries made of polyvinyl alcohol (PVA) material. FSI-generated spatiotemporal maps were used to estimate PWV at the plaque region and compared it to the experimental results. Velocity of the pulse wave propagation and magnitude of the wall distension were correctly predicted with the FE analysis. In addition, findings indicate that a plaque with a high degree of stenosis (>70%) attenuates the propagation of the pulse pressure wave. Results of this study support the validity of the FE-FSI methods to investigate the effect of arterial wall structural and mechanical properties on the pulse wave propagation. This modeling method can help to guide the optimization of PWI to characterize plaque properties and substantiate clinical findings.
Many important engineering applications involve the interaction of free-moving objects with dispersed multi-phase flows, however due to the challenge and complexity of modelling these systems, modelling approaches rem...
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Many important engineering applications involve the interaction of free-moving objects with dispersed multi-phase flows, however due to the challenge and complexity of modelling these systems, modelling approaches remain very limited and very few studies have been reported. This work presents a new method capable of addressing these problems. It integrates a dynamic meshing approach, used to explicitly capture the flow induced by free-moving large object(s), with a conventional CFD-DEM method to capture the behaviour of small particles in particle-fluid flow. The force and torque acting on the large object due to the fluid flow are explicitly calculated by integrating pressure and viscous stress acting on the object's surface and the forces due to collisions with both the smaller particles and other structures are calculated using a soft-sphere DEM approach. The developed model has been fully implemented on the ANSYS/Fluent platform due to its efficient handling of dynamic meshing and complex and/or free-moving boundaries, thus it can be applied to a wide range of industrial applications. Validation tests have been carried out for two typical gas-solid fluidization cases, they show good qualitative and quantitative agreement with reported experimental literature data. The developed model was then successfully applied to gas fluidization with a large immersed tube which was either fixed or free moving. The predicted interacting dynamics of the gas, particle and tube were highly complex and highlighted the value of fully resolving the flow around the large object. The results demonstrated that the capability of a conventional CFD-DEM approach could be enhanced to address free-body fluid-structure interaction problems encountered in particle-fluid systems. (C) 2017 The Authors. Published by Elsevier B.V.
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