Coupled Fluid Structure Interaction Model Research Articles

Fluid-structure interaction characteristics of inflatable reentry aeroshell at subsonic speed

Inflatable aeroshells, made of flexible membranes and pressurized inflatable torus, experience significant aerodynamic loads during atmospheric entry. The aerodynamic forces deform the lightweight, flexible membrane, and such deformation changes the flow field, changing the aerodynamic characteristics and increasing the deformation even further. Thus, fluid-structure coupled modeling of these problems is crucial for the reliable performance prediction of such reentry vehicles. This study provides wind tunnel experimental results on subsonic fluid-structure interaction (FSI), focusing on the aeroshell deformation and oscillatory behavior designed to validate coupled simulations. Wind tunnel experiments were conducted using a scaled membrane aeroshell model for subsonic speed. Aerodynamic coefficients, pressures at the rear of the model, and structural vibrations were measured for freestream Mach number of 0.3. A two-way coupled FSI model was set up in a partitioned manner for analyzing detailed distributions of the flow field properties, which was validated by the experimental data. The model was based on the open-source fluid solver OpenFOAM, computational structural solver CalculiX and coupling library preCICE. The present FSI analysis model well reproduced fundamental features such as swing motion, membrane deformation, and the wake in the flow field simulation, which were observed in the experiment. The results indicated that the membrane surface deforms elastically by aerodynamic force caused by the large pressure difference between the front and rear sides of the vehicle. The continuous generation and shedding of the wake vortex caused unsteady behavior in the flow field, followed by the small amplitude oscillation of the aeroshell. An external aerodynamic force caused the oscillation because the frequency of this oscillation did not correspond to that of natural frequencies.

A two-way coupled FSI model for the rapid evaluation of accidental loads following ship hard grounding

The assessment of structural crashworthiness following ship grounding events should consider the influence of multi-physics on dynamic response. To date, this has been achieved by computationally expensive approaches combining explicit 3D FEA with hydrodynamic solvers (e.g. Conti et al. (2021); Kim et al. (2021)). To offer an alternative, this paper presents a rapid six degree of freedom (6-DoF) two-way coupled fluid–structure interaction (FSI) model that could be used for the rapid evaluation of ship dynamic response and structural crashworthiness during hard grounding events. The time domain solution is based on a simplified contact analysis model that combines the external dynamics idealization of Taimuri et al. (2020) with an extended version of the internal mechanics analytical formulation of Simonsen (1997a) and Sun et al. (2017). The plate cutting angle is calibrated based on the rock geometry and hull indentation. A ray-tracing algorithm that utilizes panels and the tip of a conical rock is implemented to idealize hull penetration. The model is numerically validated by comparing results against LS-DYNA simulations for a box-shaped barge of double bottom configuration and a passenger vessel. Parametric studies demonstrate that longitudinal and vertical forces produced by different models compare well. However, the lateral forces for the study case of a passenger ship progressing along a straight path are shown to be underestimated. This is because the proposed method (i) does not allow for the influence of lateral loading on longitudinal hull members and (ii) overestimates the forces in regions of extreme curvature (e.g. fore shoulder, bow and boundaries of the hull).

Liposome destruction by a collapsing cavitation microbubble: A numerical study

Hydrodynamic cavitation poses as a promising new method for wastewater treatment as it has been shown to be able to eradicate bacteria, inactivate viruses, and destroy other biological structures, such as liposomes. Although engineers are already commercializing devices that employ cavitation, we are still not able to answer the fundamental question: What exactly are the damaging mechanisms of hydrodynamic cavitation in various applications? In this light, the present paper numerically addresses the interaction between a single cavitation microbubble and a nearby lipid vesicle of a similar size. A coupled fluid–structure interaction model is employed, from which three critical modes of vesicle deformation are identified and temporally placed in relation to their corresponding driving mechanisms: (a) unilateral stretching at the waist of the liposome during the first bubble collapse and subsequent shock wave propagation, (b) local wrinkling at the tip until the bubble rebounds, and (c) bilateral stretching at the tip of the liposome during the phase of a second bubble contraction. Here, unilateral and bilateral stretching refer to the local in-plane extension of the bilayer in one and both principal directions, respectively. Results are discussed with respect to critical dimensionless distance for vesicle poration and rupture. Liposomes with initially equilibrated envelopes are not expected to be structurally compromised in cases with δ>1.0, when a nearby collapsing bubble is not in their direct contact. However, the critical dimensionless distance for the case of an envelope with pre-existing pores is identified at δ=1.9. Additionally, the influence of liposome-bubble size ratio is addressed, from which a higher potential of larger bubbles for causing stretching-induced liposome destruction can be identified.

Fluid-structure interaction computational analysis and experiments of tsunami bore forces on coastal bridges

PurposeTwo disastrous Tsunamis, one on the west coast of Sumatra Island, Indonesia, in 2004 and another in North East Japan in 2011, had seriously destroyed a large number of bridges. Thus, experimental tests in a wave flume and a fluid structure interaction (FSI) analysis were constructed to gain insight into tsunami bore force on coastal bridges.Design/methodology/approachVarious wave heights and shallow water were used in the experiments and computational process. A 1:40 scaled concrete bridge model was placed in mild beach profile similar to a 24 × 1.5 × 2 m wave flume for the experimental investigation. An Arbitrary Lagrange Euler formulation for the propagation of tsunami solitary and bore waves by an FSI package of LS-DYNA on high-performance computing system was used to evaluate the experimental results.FindingsThe excellent agreement between experiments and computational simulation is shown in results. The results showed that the fully coupled FSI models could capture the tsunami wave force accurately for all ranges of wave heights and shallow depths. The effects of the overturning moment, horizontal, uplift and impact forces on a pier and deck of the bridge were evaluated in this research.Originality/valuePhotos and videos captured during the Indian Ocean tsunami in 2004 and the 2011 Japan tsunami showed solitary tsunami waves breaking offshore, along with an extremely turbulent tsunami-induced bore propagating toward shore with significantly higher velocity. Consequently, the outcomes of this current experimental and numerical study are highly relevant to the evaluation of tsunami bore forces on the coastal, over sea or river bridges. These experiments assessed tsunami wave forces on deck pier showing the complete response of the coastal bridge over water.

Numerical investigation of a bio-inspired underwater robot with skeleton-reinforced undulating fins

In this paper, the propulsion performance of a bio-inspired underwater robot with a pair of ray-supported undulating pectoral fins is numerically investigated with a fully coupled fluid–structure interaction model. In this model, the flexible fin rays are represented by nonlinear Euler–Bernoulli beams while the surrounding flow is simulated via solving the Navier–Stokes equations. Kinematically, each pectoral fin is activated independently via individually distributed time-varying forces along each fin ray, which imitate effects of tendons that can actively curve the fin rays. We find that the propulsion performance of the bio-inspired robot is closely associated with the phase difference between the leading edge ray and the trailing edge ray of the pectoral fin. The results show that with a symmetrical kinematics, the highest thrust is created when the phase difference is 90 degree while the point maximizing the propulsion efficiency varies with the motion frequency. It is also found that there is a minimum frequency of generating net thrust for a specific parameter setup, which rises as the increase of phase difference. Compared with the symmetrical kinematics, the non-symmetrical kinematics generates more complicated hydrodynamic forces and moments which may be beneficial for the turning maneuver.

Reduced-Order Modeling and Experimental Studies of Bilaterally Coupled Fluid–Structure Interaction in Single-Degree-of-Freedom Flapping Wings

AbstractFlapping wings deform under both aerodynamic and inertial forces. However, many flapping wing fluid–structure interaction (FSI) models require significant computational resources which limit their effectiveness for high-dimensional parametric studies. Here, we present a simple bilaterally coupled FSI model for a wing subject to single-degree-of-freedom (SDOF) flapping. The model is reduced-order and can be solved several orders of magnitude faster than direct computational methods. To verify the model experimentally, we construct a SDOF rotation stage and measure basal strain of a flapping wing in-air and in-vacuum. Overall, the derived model estimates wing strain with good accuracy. In-vacuum, the wing has a large 3ω response when flapping at approximately one-third of its natural frequency due to a superharmonic resonance, where the superharmonic occurs due to the interaction of inertial forces and time-varying centrifugal softening. In-air, this 3ω response is attenuated significantly as a result of aerodynamic damping, whereas the primary ω response is increased due to aerodynamic loading. These results highlight the importance of (1) bilateral coupling between the fluid and structure, since unilaterally coupled approaches do not adequately describe deformation-induced aerodynamic damping and (2) time-varying stiffness, which generates superharmonics of the flapping frequency in the wing’s dynamic response. The simple SDOF model and experimental study presented in this work demonstrate the potential for a reduced-order FSI model that considers both bilateral fluid–structure coupling and realistic multi-degrees-of-freedom flapping kinematics moving forward.

The transient characteristics of cloud cavitating flow over a flexible hydrofoil

The objective of this paper is to investigate the two-phase flow structure of cloud cavitation over a flexible hydrofoil with particular emphasis on cavitating flow-induced vibration and the cavity shedding dynamics via combined experimental and numerical studies. The experimental studies are conducted in a closed-loop cavitation tunnel using a simultaneous sampling technique and the numerical investigations are performed using a hybrid coupled fluid structure interaction model. Results are presented for a modified NACA66 hydrofoil made of POM Polyacetate and good agreement can be obtained between the numerical and experimental results. The predicted cavitation behaviors, including the cavity growth, break-off and collapse, agree fairly well with the experiment. The vibration velocity goes up with the growth of the attached cavity and the break off of the cloud cavity induces some fluctuations of the vibration velocity. For the cavity shedding dynamics, the cavity partially collapses with the vibration and breaks into several medium-scale cloud cavities accompanied with complex interaction between the counter-rotating vortexes. Good agreement can be obtained between the predicted and measured vibration amplitudes, with the dominant flow-induced vibration frequency in accordance with the cavity shedding frequency and other two vibration frequencies corresponding to the natural frequencies of the first bending and twisting mode respectively. The one-dimensional analytical model is applied to better illustrate the physical mechanism of the cavitating flow induced pressure pulsation. The results show that the transient cavitating behaviors lead to the periodic pressure fluctuation on the hydrofoil. The one-dimensional model can track the main features of the pressure fluctuations, which are mainly derived from the cavity volume acceleration.

Numerical study of mean drift force on stationary flexible barge

In this study, a fully coupled fluid–structure interaction model was used to compute the mean drift force on a flexible barge under various wave conditions. The fluid domain was solved using a time domain B-spline 3-D Rankine panel method. The structural domain was modeled using a shell-element-based 3-D finite element model. The fluid model was coupled with the 3-D FE model via eigenvectors. Seakeeping analysis of the flexible body was performed by the fully coupled model. In the computation of drift force, two approaches were employed: a near-field method and a far-field method. The near-field method included an extension of the rigid body formula in the flexible body formula. The far-field method used the same formula for the rigid body and the flexible body. To the knowledge of the authors, it was not easy to find validation data for the mean drift force on a flexible barge. Therefore, an indirect validation was conducted by comparison of numerical results using a different approach. As a test model, a virtual barge model was used. The motion and mean drift force on the rigid barge were compared with the results of a commercial software, WADAM. The mean drift force on the flexible barge was compared to the results of the near-field and far-field methods.

Numerical simulations of aeroelastic instabilities to optimize the performance of flutter-based electromagnetic energy harvesters

The article presents a two-dimensional fully coupled fluid–structure interaction model for simulating aeroelastic instabilities to evaluate and optimize the performance of flutter-based electromagnetic energy harvesters. The flutter-type unstable vibration of T-shaped cantilever systems is investigated as a driving mechanism for small-scale energy conversion. A flow solver based on the vortex particle method and a structural solver based on a corotational finite element formulation are coupled in order to accurately account for the geometrically nonlinear effects of such very flexible elements. A reference harvester is simulated considering the damping effects arising from the electromagnetic transducer. The estimated flutter wind speed and the predicted energy outputs under different electrical resistances are found to agree reasonably well with reference wind tunnel experiments. The influence of physical parameters such as length, thickness, and cantilever tip height on the performance of the harvester is investigated up to an envelope volume of 42 cm3. The maximum power output is found to be 5.3 mW at 8 m/s. The optimized harvester shows a better performance under low wind speeds by producing 0.65 mW at 4 m/s where the reference harvester produced no power.

Simulating low frequency sound transmission through walls and windows by a two-way coupled fluid structure interaction model

Aircraft, supersonic flights, blasts, and explosions emit sound with substantial energy below 100Hz. When the low frequency sound is transmitted inside a building, it generates vibration and rattling that may lead to annoyance. Our understanding of these low frequency phenomena is presently limited. In this paper, we attempt to improve our computational capabilities related to the low frequency sound transmission. For this purpose, a finite element methodology that incorporates a two-way coupled fluid-structure interaction, has been developed. Results from a broad experimental investigation of low frequency sound transmission are compared with the numerical finite element simulations. Plain walls, and walls with windows are studied. Close agreement between the simulations and the laboratory measurement data is obtained in the frequency range investigated (10–100Hz). It was found that structural connections were of large importance for modeling the vibration and sound transmission. The windows control the low frequency transmission from 15 to 30Hz, whereas the walls control the sound transmission from 30 to 100Hz. Mitigation of vibrations and rattling induced by low frequency sound therefore needs to consider both wall and window construction.

Physical and numerical investigation of the flow induced vibration of the hydrofoil

The objective of this paper is to investigate the flow induced vibration of a flexible hydrofoil in cavitating flows via combined experimental and numerical studies. The experiments are presented for the modified NACA66 hydrofoil made of POM Polyacetate in the closed-loop cavitation tunnel at Beijing Institute of Technology. The high-speed camera and the single point Laser Doppler Vibrometer are applied to analyze the transient flow structures and the corresponding structural vibration characteristics. The hybrid coupled fluid structure interaction model is conducted to couple the incompressible and unsteady Reynolds Averaged Navier-Stokes solver with a simplified two-degree-of-freedom structural model. The k-ω SST turbulence model with the turbulence viscosity correction and the Zwart cavitation model are introduced to the present simulations. The results showed that with the decreasing of the cavitation number, the cavitating flows display incipient cavitation, sheet cavitation, cloud cavitation and supercavitation. The vibration magnitude increases dramatically for the cloud cavitation and decline for the supercavitation. The cloud cavitation development strongly affects the vibration response, which is corresponding to the periodically developing and shedding of the large-scale cloud cavity. The main frequency of the vibration amplitude is accordance with the cavity shedding frequency and other two frequencies of the vibration amplitude are corresponding to the natural frequencies of the bending and twisting modes.

A Fully Coupled Fluid–Structure Interaction Model for Foil Gas Bearings

Foil gas bearings are self-acting, compliant-surface hydrodynamic bearings that usually use air or other process gas as their working fluid or lubricant. Foil gas bearings are made of one or more bump foils, which are compliant surfaces of corrugated metal, and one or more layers of top foil. Because foil gas bearing performance parameters, such as load capacity, are dominated by foil material and foil geometric designs, numerical models have been developed to predict the bearing's performance based on these characteristics. However, previous models often simplify bump foil as elastic foundation with constant stiffness and neglect top foil altogether. Further, they typically use the Reynolds equation to simplify the fluid solution. In this study, ansys software is used to build a 3D, fully coupled, fluid–structure interaction (FSI) model for a foil gas bearing to predict the key performance parameters such as load capacity and journal attitude angle. The model's results show good agreement with previously published test data. This not only demonstrates the feasibility of 3D fully coupled fluid–structure interaction model for a conventional foil bearing using commercial codes, but also shows modeling capability for future generations of foil gas bearing.

Fracture propagation control in CO2 pipelines: Validation of a coupled fluid–structure model

Existing engineering methods to ensure fracture propagation control in natural-gas transmission pipelines have been shown to be non-applicable when dense-phase CO2 is transported. To overcome this, a coupled fluid–structure interaction model has been developed. It consists of a homogeneous equilibrium flow model, coupled with the Span–Wagner equation of state and including solid-phase formation, and a finite-element model of the pipe taking into account large deformations and fracture propagation through a local fracture criterion.Model predictions are compared with data from two medium-scale crack-arrest experiments with dense-phase CO2. Good agreement is observed in fracture length, fracture-propagation velocity and pressure. Simulations show that, compared to natural-gas pipelines, the pressure level at the opening fracture flaps is sustained at a much higher level and at a much longer distance behind the moving fracture tip. This may be one important reason why the existing engineering methods do not work for dense-phase CO2.

Fluid–structure interaction for nonlinear response of shells conveying pulsatile flow

Circular cylindrical shells with flexible boundary conditions conveying pulsatile flow and subjected to pulsatile pressure are investigated. The equations of motion are obtained based on the nonlinear Novozhilov shell theory via Lagrangian approach. The flow is set in motion by a pulsatile pressure gradient. The fluid is modeled as a Newtonian pulsatile flow and it is formulated using a hybrid model that contains the unsteady effects obtained from the linear potential flow theory and the pulsatile viscous effects obtained from the unsteady time-averaged Navier–Stokes equations. A numerical bifurcation analysis employs a refined reduced order model to investigate the dynamic behavior. The case of shells containing quiescent fluid subjected to the action of a pulsatile transmural pressure is also addressed. Geometrically nonlinear vibration response to pulsatile flow and transmural pressure are here presented via frequency-response curves and time histories. The vibrations involving both a driven mode and a companion mode, which appear due to the axial symmetry, are also investigated. This theoretical framework represents a pioneering study that could be of great interest for biomedical applications. In particular, in the future, a more refined model of the one here presented will possibly be applied to reproduce the dynamic behavior of vascular prostheses used for repairing and replacing damaged and diseased thoracic aorta in cases of aneurysm, dissection or coarctation. For this purpose, a pulsatile time-dependent blood flow model is here considered by applying physiological waveforms of velocity and pressure during the heart beating period. This study provides, for the first time in literature, a fully coupled fluid–structure interaction model with deep insights in the nonlinear vibrations of circular cylindrical shells subjected to pulsatile pressure and pulsatile flow.

Uniform stabilization to equilibrium of a nonlinear fluid–structure interaction model

We consider uniform stability to a nontrivial equilibrium of a nonlinear fluid–structure interaction (FSI) defined on a two or three dimensional bounded domain. Stabilization is achieved via boundary and/or interior feedback controls implemented on both the fluid and the structure. The interior damping on the fluid combining with the viscosity effect stabilizes the dynamics of fluid. However, this dissipation propagated from the fluid alone is not sufficient to drive uniformly to equilibrium the entire coupled system. Therefore, additional interior damping on the wave component or boundary porous like damping on the interface is considered. A geometric condition on the interface is needed if only boundary damping on the wave is active. The main technical difficulty is the mismatch of regularity of hyperbolic and parabolic component of the coupled system. This is overcome by considering special multipliers constructed from Stokes solvers. The uniform stabilization result obtained in this article is global for the fully coupled FSI model.

Rigid-Object Water-Entry Impact Dynamics: Finite-Element/Smoothed Particle Hydrodynamics Modeling and Experimental Validation

A numerical study on the dynamic response of a generic rigid water-landing object (WLO) during water impact is presented in this paper. The effect of this impact is often prominent in the design phase of the re-entry project to determine the maximum force for material strength determination to ensure structural and equipment integrity, human safety and comfort. The predictive capability of the explicit finite-element (FE) arbitrary Lagrangian-Eulerian (ALE) and smoothed particle hydrodynamics (SPH) methods of a state-of-the-art nonlinear dynamic finite-element code for simulation of coupled dynamic fluid structure interaction (FSI) responses of the splashdown event of a WLO were evaluated. The numerical predictions are first validated with experimental data for maximum impact accelerations and then used to supplement experimental drop tests to establish trends over a wide range of conditions including variations in vertical velocity, entry angle, and object weight. The numerical results show that the fully coupled FSI models can capture the water-impact response accurately for all range of drop tests considered, and the impact acceleration varies practically linearly with increase in drop height. In view of the good comparison between the experimental and numerical simulations, both models can readily be employed for parametric studies and for studying the prototype splashdown under more realistic field conditions in the oceans.

Innovative coupled fluid–structure interaction model for carbon nano-tubes conveying fluid by considering the size effects of nano-flow and nano-structure

In this article, we reappraise the well-known equation of motion for a pipe conveying viscous fluid. We utilize prominent principles of fluid mechanics such as Navier–Stokes’ equation as well as several benchmark references in the field of fluid–structure interaction (FSI) to reveal that the viscosity of the fluid flow should not appear explicitly in the equation of motion of pipe conveying fluid. Based on this result, we could develop an innovative model for one dimensional coupled vibrations of carbon nano-tubes (CNTs) conveying fluid using slip velocity of the fluid flow on the CNT walls as well as utilizing size-dependent continuum theories to consider the size effects of nano-flow and nano-structure. Therefore, this innovative coupled FSI equation suggests that CNTs conveying nano-flow remain stable for higher velocities. In the other words, the critical average velocity of the fluid flow at which the divergence instability occurs, should be greater in comparison with the critical velocity predicted by the models used plug flow and classical continuum theories.

Fully coupled fluid–structure interaction model of congenital bicuspid aortic valves: effect of asymmetry on hemodynamics

A bicuspid aortic valve (BAV) is a congenital cardiac disorder where the valve consists of only two cusps instead of three, as in a normal tricuspid valve (TAV). Although 97% of BAVs include asymmetric cusps, little or no prior studies have investigated the blood flow through a three-dimensional BAV and root. The aim of the present study was to characterize the effect of asymmetric BAV on the blood flow using fully coupled fluid-structure interaction (FSI) models with improved boundary conditions and tissue properties. This study presents four FSI models, including a native TAV, asymmetric BAVs with or without a raphe, and an almost symmetric BAV. Cusp tissue is composed of hyperelastic finite elements with collagen fibres embedded in the elastin matrix. A full cardiac cycle is simulated by imposing the same physiological blood pressures for all the TAV and BAV models. The latter have significantly smaller opening areas compared with the TAV. Larger stress values were found in the cusps of BAVs with fused cusps, at both the systolic and diastolic phases. The asymmetric geometry caused asymmetric vortices and much larger flow shear stress on the cusps which could be a potential initiator for early valvular calcification of BAVs.

A Novel Left Heart Simulator for the Multi-modality Characterization of Native Mitral Valve Geometry and Fluid Mechanics

Numerical models of the mitral valve have been used to elucidate mitral valve function and mechanics. These models have evolved from simple two-dimensional approximations to complex three-dimensional fully coupled fluid structure interaction models. However, to date these models lack direct one-to-one experimental validation. As computational solvers vary considerably, experimental benchmark data are critically important to ensure model accuracy. In this study, a novel left heart simulator was designed specifically for the validation of numerical mitral valve models. Several distinct experimental techniques were collectively performed to resolve mitral valve geometry and hemodynamics. In particular, micro-computed tomography was used to obtain accurate and high-resolution (39μm voxel) native valvular anatomy, which included the mitral leaflets, chordae tendinae, and papillary muscles. Three-dimensional echocardiography was used to obtain systolic leaflet geometry. Stereoscopic digital particle image velocimetry provided all three components of fluid velocity through the mitral valve, resolved every 25ms in the cardiac cycle. A strong central filling jet (V~0.6m/s) was observed during peak systole with minimal out-of-plane velocities. In addition, physiologic hemodynamic boundary conditions were defined and all data were synchronously acquired through a central trigger. Finally, the simulator is a precisely controlled environment, in which flow conditions and geometry can be systematically prescribed and resultant valvular function and hemodynamics assessed. Thus, this work represents the first comprehensive database of high fidelity experimental data, critical for extensive validation of mitral valve fluid structure interaction simulations.

Numerical simulation of transonic limit cycle oscillations using high-order low-diffusion schemes

This paper simulates the NLR7301 airfoil limit cycle oscillation (LCO) caused by fluid–structure interaction (FSI) using Reynolds averaged Navier–Stokes equations (RANS) coupled with Spalart–Allmaras (S–A) one-equation turbulence model. A low diffusion E-CUSP (LDE) scheme with 5th order weighted essentially nonoscillatory scheme (WENO) is employed to calculate the inviscid fluxes. A fully conservative 4th order central differencing is used for the viscous terms. A fully coupled fluid–structural interaction model is employed. For the case computed in this paper, the predicted LCO frequency, amplitudes, averaged lift and moment, all agree excellently with the experiment performed by Schewe et al. The solutions appear to have bifurcation and are dependent on the initial fields or initial perturbation. The developed computational fluid dynamics (CFD)/computational structure dynamics (CSD) simulation is able to capture the LCO with very small amplitudes measured in the experiment. This is attributed to the high order low diffusion schemes, fully coupled FSI model, and the turbulence model used. This research appears to be the first time that a numerical simulation of LCO matches the experiment. The simulation confirms several observations of the experiment.