We propose a numerical method for modeling the interaction of a Stokes fluid and a linear elastic solid. The model problem is expressed in the stress-displacement formulation for the linear elastodynamics in the solid...
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We propose a numerical method for modeling the interaction of a Stokes fluid and a linear elastic solid. The model problem is expressed in the stress-displacement formulation for the linear elastodynamics in the solid region and the stress-velocity formulation for the Stokes equations in the fluid region. These two systems are coupled in such a way that the interface conditions are imposed naturally in the resulting weak formulation, which is based on the Hellinger-Reissner variational principle. For the time discretization, we use a three-level scheme for each time step, with an exception at the first time step. We provide a priori error analysis for fully-discrete, nonconforming mixed finite element methods and show some numerical results to confirm our theoretical results. (C) 2019 Elsevier Inc. All rights reserved.
We present a coupled left atrium-mitral valve model based on computed tomography scans with fibre-reinforced hyperelastic materials. fluid-structure interaction is realised by using an immersed boundary-finite element...
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We present a coupled left atrium-mitral valve model based on computed tomography scans with fibre-reinforced hyperelastic materials. fluid-structure interaction is realised by using an immersed boundary-finite element framework. Effects of pathological conditions, eg, mitral valve regurgitation and atrial fibrillation, and geometric and structural variations, namely, uniform vs non-uniform atrial wall thickness and rule-based vs atlas-based fibre architectures, on the system are investigated. We show that in the case of atrial fibrillation, pulmonary venous flow reversal at late diastole disappears, and the filling waves at the left atrial appendage orifice during systole have reduced magnitude. In the case of mitral regurgitation, a higher atrial pressure and disturbed flows are seen, especially during systole, when a large regurgitant jet can be found with the suppressed pulmonary venous flow. We also show that both the rule-based and atlas-based fibre defining methods lead to similar flow fields and atrial wall deformations. However, the changes in wall thickness from non-uniform to uniform tend to underestimate the atrial deformation. Using a uniform but thickened wall also lowers the overall strain level. The flow velocity within the left atrial appendage, which is important in terms of appendage thrombosis, increases with the thickness of the left atrial wall. Energy analysis shows that the kinetic and dissipation energies of the flow within the left atrium are altered differently by atrial fibrillation and mitral valve regurgitation, providing a useful indication of the atrial performance in pathological situations.
Computational fluid dynamics (CFD) is increasingly used to study blood flows in patient-specific arteries for understanding certain cardiovascular diseases. The techniques work quite well for relatively simple problem...
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Computational fluid dynamics (CFD) is increasingly used to study blood flows in patient-specific arteries for understanding certain cardiovascular diseases. The techniques work quite well for relatively simple problems but need improvements when the problems become harder when (a) the geometry becomes complex (eg, a few branches to a full pulmonary artery), (b) the model becomes more complex (eg, fluid-only to coupled fluid-structure interaction), (c) both the fluid and wall models become highly nonlinear, and (d) the computer on which we run the simulation is a supercomputer with tens of thousands of processor cores. To push the limit of CFD in all four fronts, in this paper, we develop and study a highly parallel algorithm for solving a monolithically coupled fluid-structure system for the modeling of the interaction of the blood flow and the arterial wall. As a case study, we consider a patient-specific, full size pulmonary artery obtained from computed tomography (CT) images, with an artificially added layer of wall with a fixed thickness. The fluid is modeled with a system of incompressible Navier-Stokes equations, and the wall is modeled by a geometrically nonlinear elasticity equation. As far as we know, this is the first time the unsteady blood flow in a full pulmonary artery is simulated without assuming a rigid wall. The proposed numerical algorithm and software scale well beyond 10 000 processor cores on a supercomputer for solving the fluid-structure interaction problem discretized with a stabilized finite element method in space and an implicit scheme in time involving hundreds of millions of unknowns.
作者:
Cho, HaeseongShin, SangJoonLee, NamhunLee, SeungsooSeoul Natl Univ
Inst Adv Machines & Design BK21 Plus Transformat Training Program Creat Mech Seoul 08826 South Korea Seoul Natl Univ
Inst Adv Aerosp Technol Dept Mech & Aerosp Engn Seoul 08826 South Korea Hanwha Def Syst
R&D Strategy Team Vehicle & Launcher Syst R&D Div Changwon Si 51561 Gyeongsangnam D South Korea Inha Univ
Dept Aerosp Engn Incheon 22212 South Korea
During the past few decades, various fluid-structure interaction (FSI) analysis approaches have been developed and applied to understand the physical processes related to a flexible flapping wing. In this paper, a dyn...
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During the past few decades, various fluid-structure interaction (FSI) analysis approaches have been developed and applied to understand the physical processes related to a flexible flapping wing. In this paper, a dynamic shell analysis based on a corotational (CR) formulation is developed. Geometrically nonlinear dynamic shell formulation based on the CR framework is derived from Lagrange's equation of motion. This brand new shell formulation is implicitly combined with a preconditioned Navier-Stokes solution for a relevant FSI analysis. Specifically, the shell analysis is extended to a multibody dynamic approach to facilitate the passive pitching motion of a flapping wing. The present analysis is validated by a comparison with the results from either previous analyses or experiments. The effect of a passive pitching motion on a flapping wing is also investigated. Finally, it is found that the presented dynamic shell analysis can enable accurate predictions, and the relevant passive pitching motion of a spanwise flexible wing may be advantageous for generating several aerodynamic loads that are applicable for the control forces of a micro aerial vehicle.
Obstructive sleep apnea is one of the most common breathing disorders. Undiagnosed sleep apnea is a hidden health crisis to the patient and it could raise the risk of heart diseases, high blood pressure, depression an...
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Obstructive sleep apnea is one of the most common breathing disorders. Undiagnosed sleep apnea is a hidden health crisis to the patient and it could raise the risk of heart diseases, high blood pressure, depression and diabetes. The throat muscle (i.e., tongue and soft palate) relax narrows the airway and causes the blockage of the airway in breathing. To understand this phenomenon computational fluid dynamics method has emerged as a handy tool to conduct the modeling and analysis of airflow characteristics. The comprehensive fluid-structure interaction method provides the realistic visualization of the airflow and interaction with the throat muscle. Thus, this paper reviews the scientific work related to the fluid-structure interaction (FSI) for the evaluation of obstructive sleep apnea, using computational techniques. In total 102 articles were analyzed, each article was evaluated based on the elements related with fluid-structure interaction of sleep apnea via computational techniques. In this review, the significance of FSI for the evaluation of obstructive sleep apnea has been critically examined. Then the flow properties, boundary conditions and validation of the model are given due consideration to present a broad perspective of CFD being applied to study sleep apnea. Finally, the challenges of FSI simulation methods are also highlighted in this article. (C) 2019 Published by Elsevier B.V.
A two-dimensional (2D) partitioned solver is extended for large-displacement fluid-structure interaction (FSI) simulations of thin plate systems, particularly to investigate their potential of aeroelastic energy harve...
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A two-dimensional (2D) partitioned solver is extended for large-displacement fluid-structure interaction (FSI) simulations of thin plate systems, particularly to investigate their potential of aeroelastic energy harvesting. The 2D vortex particle method with immersed interface technique and adaptive solution strategy is used for analyzing flow around deformable bodies;three-dimensional edge effects are ignored. The geometrically nonlinear plate motion is analyzed using 2D corotational beam element. The coupled solver is validated on benchmark large-displacement FSI problems such as flag-type flapping of cantilever plates in axial flow and Karman vortex street. The validated solver is used further to perform a comparative study on different cantilever systems to obtain guidelines for the design of experimental set-ups of prototype harvesters. The changes in aerodynamic behavior and flapping pattern of inverted and T-shaped cantilevers with/without tip mass are investigated. The simulations are performed for increasing wind speeds until the permanent deflection mode occurs. The influences of damping ratios are analyzed as preliminary studies to investigate the electrical damping effects of harvesters. The influential parameters such as response amplitude and oscillating frequency are compared to identify not only efficient cantilever harvesters but also an appropriate combination of physical and electrical parameters depending on target wind speeds. (C) 2019 Elsevier Ltd. All rights reserved.
Abdominal aortic aneurysms (AAAs) occur because of dilation of the infra-renal aorta to more than 150% of its initial diameter. Progression to rupture is aided by several pathophysiological and biomechanical factors. ...
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Abdominal aortic aneurysms (AAAs) occur because of dilation of the infra-renal aorta to more than 150% of its initial diameter. Progression to rupture is aided by several pathophysiological and biomechanical factors. Surgical intervention is recommended when the aneurysm maximum transverse diameter (DAAA) exceeds 55mm. A system model that incorporates biomechanical parameters will improve prognosis and establish a relationship between AAA geometry and rupture risk. Two Asian patient-specific AAA geometries were obtained from an IRB-approved vascular database. A biomechanical model based on the fluid-structure interaction (FSI) method was developed for a small aneurysm with DAAA of 35mm and a large aneurysm with a corresponding diameter of 75mm. The small aneurysm (patient 1) developed a maximum principal stress (PS1) of 3.16e5Pa and the large aneurysm (patient 2) developed a PS1 of 2.32e5Pa. Maximum deformation of arterial wall was 0.0020m and 0.0022m for patients 1 and 2 respectively. Location of maximum integral wall shear stress (WSS) (fluid) was different from that of PS1. Induced WSS was also higher in patient 1 (18.74Pa vs 12.88Pa). An FSI model incorporating the effect of both the structural and fluid domains aids in better understanding of the mechanics of AAA rupture. Patient 1, having a lower DAAA than patient 2, developed a larger PS1 and WSS. It may be concluded that DAAA may not be the sole determinant of AAA rupture risk.
fluid-structure interaction (FSI) plays a significant role in the deformation of flapping insect wings. However, many current FSI models are high-order and rely on direct computational methods, thereby limiting parame...
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fluid-structure interaction (FSI) plays a significant role in the deformation of flapping insect wings. However, many current FSI models are high-order and rely on direct computational methods, thereby limiting parametric studies as well as insights into the physics governing wing dynamics. We develop a novel flapping wing FSI framework that accommodates general wing geometry and fluid loading. We use this framework to study the unilaterally coupled FSI of an idealized hawkmoth forewing considering two fluid models: Reynolds-averaged Navier-Stokes computational fluid dynamics (RANS CFD) and blade element theory (BET). We first compare aerodynamic modal forces estimated by the low-order BET model to those calculated via high fidelity RANS CFD. We find that for realistic flapping kinematics, BET estimates modal forces five orders of magnitude faster than CFD within reasonable accuracy. Over the range flapping kinematics considered, BET and CFD estimated modal forces vary maximally by 350% in magnitude and approximately pi/2 radians in phase. The large reduction in computational time offered by BET facilitates high-dimensional parametric design of flapping-wing-based technologies. Next, we compare the contributions of aerodynamic and inertial forces to wing deformation. Under the unilateral coupling assumption, aerodynamic and inertial-elastic forces are on the same order of magnitude-however, inertial-elastic forces primarily excite the wing's bending mode whereas aerodynamic forces primarily excite the wing's torsional mode. This suggests that, via conscientious sensor placement and orientation, biological wings may be able to sense independently inertial and aerodynamic forces.
The main stream of blunt trauma injuries has been reported to be related to the automobile crashes, sporting activities, and military operations. Glass shards, which can be induced due to car accident, earthquake, gun...
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The main stream of blunt trauma injuries has been reported to be related to the automobile crashes, sporting activities, and military operations. Glass shards, which can be induced due to car accident, earthquake, gunshot, etc., might collide with the eye and trigger substantial scarring and, consequently, permanently affect the vision. The complications as a result of the collision with the eye and its following injuries on each component of the eye are difficult to be diagnosed. The objective of this study was to employ a Three-Dimensional (3D) computational fluid-structure interaction (FSI) model of the human eye to assess the results of the glass shards collision with the eye. To do this, a rigid steel-based object hit a Smoothed-Particle Hydrodynamics (SPH) glass wall at the velocities of 100, 150, and 200 m/s and, subsequently, the resultant glass shards moved toward the eye. The amount of injury, then, quantified in terms of the stresses and strains. The results revealed the highest amount of stress in the cornea while the lowest one was observed in the vitreous body. It was also found that increasing the speed of the glass shards amplifies the amount of the stress in the components which are located in the central anterior zone of the eye, such as the cornea, aqueous body, and iris. However, regarding those components located in the peripheral/posterior side of the eye, especially the optic nerve, by increasing the amount of velocity a reduction in the stresses was observed and the optic nerve is hardly damaged. These findings have associations not only for understanding the amount of stresses/strains in the eye components at three different velocities, but also for providing preliminary information for the ophthalmologists to have a better diagnosis after glass shards (small objects impact) injuries to the eye.
This paper presents a multi-objective optimization methodology that applies the Non-dominated Sorting Genetic Algorithm-II(NSGA-II) to propeller design, and realizes fluid-structure interaction (FSI) weak-coupling bas...
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This paper presents a multi-objective optimization methodology that applies the Non-dominated Sorting Genetic Algorithm-II(NSGA-II) to propeller design, and realizes fluid-structure interaction (FSI) weak-coupling based on Panel Method (PM) and the Finite Element Method (FEM). The FSI iterative process and the convergent pressure coefficient distribution and pressure fluctuation of HSP (a propeller installed on a Japanese bulk freighter - Seiun-Maru) are numerical calculated. The FSI results turn out to have higher precision than those without FSI. The appropriate optimization parameters are chosen after studying five cases. The Sobol method, a global Sensitivity Analysis (SA) algorithm, is used to quantify the dependence of objectives and constraints on the input parameters. In the multi-objective optimization methodology, efficiency, unsteady force, and mass are chosen as optimum objectives under certain constraints. Effectiveness and robustness of the methodology are validated by running the program starting from four different random values, which all improve the objectives and converge to the similar results. The proposed multi-objective optimization methodology could be a promising tool for propeller design to help improve design efficiency and ability in the future.
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