Fluid-structure Interaction Finite Element Analysis Research Articles

Combined residual stresses and fluid-structure interaction finite element analysis on bent pipes

ABSTRACT The combined inherent residual stress (RS) from manufacturing and in-service loading acted on a bent pipe which could be exerted from the fluid flow and/or thermal loading, a common situation faced by main steam pipes in high temperature plants, needs to be considered to understand their overall impact on the integrity of the pipe. The geometrical influence on a bent pipe’s stress distribution was investigated using a combined RS – Fluid-Structure Interaction (FSI) finite element analysis approach. The reduced stresses along the pipe derived from the room temperature RS-FSI simulation and analysis demonstrated the impact of the fluid and structure interaction, particularly at the locations where geometry varied. A substantial reduction in the stress level observed, especially at the extrados where wall thinning was detected. The combined RS-FSI analysis therefore offers a more realistic approach in predicting a safe allowable stress, thus the integrity or life of bent pipes.

Fluid-Structure Interaction Analysis of Perfusion Process of Vascularized Channels within Hydrogel Matrix Based on Three-Dimensional Printing.

The rise of three-dimensional bioprinting technology provides a new way to fabricate in tissue engineering in vitro, but how to provide sufficient nutrition for the internal region of the engineered printed tissue has become the main obstacle. In vitro perfusion culture can not only provide nutrients for the growth of internal cells but also take away the metabolic wastes in time, which is an effective method to solve the problem of tissue engineering culture in vitro. Aiming at user-defined tissue engineering with internal vascularized channels obtained by three-dimensional printing experiment in the early stage, a simulation model was established and the in vitro fluid–structure interaction finite element analysis of tissue engineering perfusion process was carried out. Through fluid–structure interaction simulation, the hydrodynamic behavior and mechanical properties of vascularized channels in the perfusion process was discussed when the perfusion pressure, hydrogel concentration, and crosslinking density changed. The effects of perfusion pressure, hydrogel concentration, and crosslinking density on the flow velocity, pressure on the vascularized channels, and deformation of vascularized channels were analyzed. The simulation results provide a method to optimize the perfusion parameters of tissue engineering, avoiding the perfusion failure caused by unreasonable perfusion pressure and hydrogel concentration and promoting the development of tissue engineering culture in vitro.

Identification of the Lumped Parameters for Hydraulic Bushing Based on FSI Finite Element Simulation

Radial damping hydraulic bushing is the object of this study, which is widely used as vibration isolator in the vehicle chassis system. The lumped parameter (LP) model for hydro-bushing is usually applied to the dynamic characteristic analyses. Two-way fluid-structure interaction FEA (nonlinear finite element analysis) technique is used to identify the main parameters of the LP model. The method proposed in this paper can ensure high quality and low cost in hydraulic bushing development.

Discordance of the Areas of Peak Wall Shear Stress and Tissue Stress in Coronary Artery Plaques as Revealed by Fluid-Structure Interaction Finite Element Analysis

Simulation studies have been performed in attempts to elucidate the signifi cance of shear and tissue stresses in the progression and rupture of coronary artery plaques, but few studies have analyzed both stresses simultaneously. We analyzed the distributions of shear stress and tissue stress in a model of coronary artery plaque based on intravascular ultrasound data by fluid-structure interaction finite element analysis under physiological pressure and flow. As shown in previous studies, the region of peak shear stress was observed at the proximal side of the plaque where flow velocity was high but its value was at most 10 Pa. On the other hand, 1000-10,000 times greater tissue stress was located in the stenotic region but the location of peak tissue stress was different from that of shear stress. We also found that stenting not only stabilizes the stented segment but also reduces the stress in the adjacent region. Fluid-structure interaction analysis revealed discordance in the distribution of shear and tissue stresses. These two stresses exert distinct influences on the coronary plaque, rupture of which may occur where tissue stress exceeds the plaque strength, which is weakened by pathological processes triggered by shear stress.

Bicuspid aortic valves undergo excessive strain during opening: A simulation study

The objective of this study was to examine the influence of the morphologic characteristics of the bicuspid aortic valve on its disease progression by comparing the motion, stress/strain distribution, and blood flow of normal and stenotic tricuspid valves using simulation models. Bicuspid, stenotic tricuspid with commissural fusion or thickened leaflet, and normal aortic valves were modeled with internal blood flow. Blood flow and the motion of aortic valve leaflets were studied using fluid-structure interaction finite element analysis, and stress/strain (curvature) distributions were calculated during the cardiac cycle. To mimic disease progression, we modified the local thickness of the leaflet where the bending stress was above a threshold. Transvalvular pressure gradient was greater in the bicuspid valve compared with the stenotic tricuspid valve with a similar valvular area. The bending strain (curvature) increased in both stenotic tricuspid and bicuspid valves, but a greater increase was observed in the bicuspid valve, and this was concentrated on the midline of the fused leaflets. During disease progression analysis, severity of the stenosis increased only in the bicuspid aortic valve model in terms of valvular area and pressure gradient. The characteristic morphology of the bicuspid valve creates excessive bending strain on the leaflets during ventricular ejection. Such mechanical stress may be responsible for the rapid progression of this disease.

The sinus of Valsalva relieves abnormal stress on aortic valve leaflets by facilitating smooth closure

Recently, various modifications have been made to aortic root replacement procedures to include the pseudosinus in the synthetic graft, but its effect on valve function still remains to be elucidated. The purpose of this study was to compare the flow dynamics and its influence on the stress/strain in the valve leaflet in two types of aortic root, either with or without the pseudosinus, with a simulation model. The proximal portions of the ascending aorta and aortic valves were modeled with blood flowing inside. Blood flow and the motion of aortic valve leaflets were studied while applying a physiologic pressure waveform using fluid-structure interaction finite element analysis. Waveforms were varied to simulate the change in cardiac contractility. In the aorta without the sinus, the time during which the valve was open was longer and the rapid valve closing velocity was faster under all conditions studied. In the pseudosinus model, we could clearly observe vortex formation from the early phase of ejection, which seemed to facilitate the gradual but smooth closure of the valve. Valve leaflets without the sinus were subject to greater stress and underwent bending deformation in the longitudinal direction. Sinuses of Valsalva facilitate the smooth closure of the aortic valve, thereby avoiding the building up of abnormal stress in the leaflet. Such an effect may assure the durability of valve leaflets in aortic grafts with a pseudosinus.

Fluid-Structure Interaction Analysis of a Two-Dimensional Flag-in-Wind Problem by the ALE Finite Element Method

In a recent experiment, Zhang and co-workers found that a flexible filament in a flowing soap film can exhibit three states; stretched-straight, flapping, and bistability. When this experimental model is regarded as a one-dimensional flag in a two-dimensional fluid flow, their findings contradict the common idea that flags always flap in a wind. In this paper, the flag-in-wind problem is simulated by fluid-structure interaction finite element analysis where Navier-Stokes equations based on the ALE method are strongly coupled with Lagrangian equilibrium equations of the structure. In the simulation the three states are successfully reproduced, and the effects of some representative parameters on the amplitude and frequency of the oscillations are investigated to reveal the underlying mechanism involved in flag flapping.

Fluid-Structure Interaction Analysis of a Two-Dimensional Flag-in-Wind Problem by the ALE Finite Element Method

In a recent experiment, Zhang and co-workers found that a flexible filament in a flowing soap film can exhibit three states; stretched-straight, flapping, and bistability. When this experimental model is regarded as a one-dimensional flag in a two-dimensional fluid flow, their findings contradict the common idea that flags always flap in a wind. In this paper, the flag-in-wind problem is simulated by fluid-structure interaction finite element analysis where Navier-Stokes equations based on the ALE method are strongly coupled with Lagrangian equilibrium equations of the structure. In the simulation the three states are successfully reproduced, and the effects of some representative parameters on the amplitude and frequency of the oscillations are investigated to reveal the underlying mechanism involved in flag flapping.

Experimental study and simulation of a hydraulic engine mount with fully coupled fluid–structure interaction finite element analysis model

Non-linear properties of a generic hydraulic engine mount (HEM) are identified and characterized by experiment and simulation approaches. The experimental methods for obtaining static and dynamic performances of the HEM are presented. The characteristics of two configurations of the take-apart HEMs (one is with an inertia track and a free decoupler and the other one is only with an inertia track) and their rubber springs are studied. The relations between static stiffness of an HEM and its rubber springs in three orthogonal directions are investigated. The influences of preload, excitation amplitudes and frequencies on the dynamic stiffness of an HEM are verified. The effects of the free decoupler on dynamic characteristics of the HEM are studied by comparisons of the test results of the two HEMs. The dynamic fluid pressure and the temperature in the upper chamber of an HEM are measured under different excitation conditions. A fully coupled fluid–structure interaction (FSI) and finite element analysis (FEA) model for simulation of HEMs is developed in this paper, which can be used to simulate the static and dynamic performances of the HEMs with only stress versus strain relations of the rubber materials, the fluid physical parameters and the HEMs sizes. The simulated results of one HEM with the proposed model are given, and the results match well with the measured data, or in coincidence with the working mechanisms of HEMs.

Modelling of a hydraulic engine mount with fluid–structure interaction finite element analysis

Hydraulic engine mount (HEM) is now widely used as a highly effective vibration isolator in automotive powertrain. A lumped parameter (LP) model is a traditional model for modelling the dynamic characteristics of HEM, in which the system parameters are usually obtained by experiments. In this paper, a fluid–structure interaction (FSI) finite element analysis (FEA) method and a non-linear FEA technology are used to determine the system parameters, and a fully coupled FSI model is developed for modelling the static and lower-frequency performance of an HEM. A FSI FEA technique is used to estimate the parameters of volumetric compliances, equivalent piston area, inertia and resistance of the fluid in the inertia track and the decoupler of an HEM. A non-linear FEA method is applied to determine the dynamic stiffness of rubber spring of the HEM. The system parameters predicated by FEA are compared favorably with experimental data and/or analytical solutions. A numerical simulation for an HEM with an inertia track and a free decoupler is performed based on the FSI model and the LP model along with the estimated system parameters, and again the simulation results are compared with experimental data. The calculated time histories of some variables in the model, such as the pressure in the upper chamber, the displacement of the free decoupler and the volume flow through the inertia track and the decoupler, under different excitations, elucidate the working mechanism of the HEM. The pressure distribution calculated with the FSI model in the chambers of the HEM validates the assumption that the pressure distribution in the upper and lower chamber is uniform in the LP model. The work conducted in the paper demonstrates that the methods for estimating the system parameters in the LP model and the FSI model for modelling HEM are effective, with which the dynamic characteristic analysis and design optimization of an HEM can be performed before its prototype development, and this can ensure its low cost and high quality for development.