Two-dimensional Fluid-structure Interaction Research Articles

Aeroacoustic simulation of human phonation based on the flow-induced vocal fold vibrations including their contact

This paper deals with the numerical simulation of the flow induced sound as generated in the human phonation process including vocal folds (VF) contact. The hybrid approach is used allowing to separate the acoustic and the biomechanical description of the considered problem. The two-dimensional fluid–structure interaction (FSI) problem is modelled by a simplified linear elastic model coupled to the incompressible Navier–Stokes equations in the arbitrary Lagrangian–Eulerian form and special attention is paid to the treatment of the contact problem in the FSI context. Following approach of [Sváček and Horáček, 2021] the incompressible flow model is modified by an addition of fictitious porosity term and the penalization inlet boundary condition is used. Further, the Lighthill acoustic analogy is applied for calculation of sound sources and their propagation through a vocal tract model. All partial differential equations, describing the elastic body vibration, the fluid flow and the acoustics, are approximated by finite element method. Numerical results of one-sided vocal fold paralysis are presented.

Attenuation of Tollmien–Schlichting waves using resonating surface-embedded phononic crystals

A novel method for control of convective boundary layer instabilities using metamaterial concepts is investigated. Attenuation of Tollmien–Schlichting (TS) waves with surface-embedded one-dimensional phononic crystals (PCs) is theoretically and numerically modeled, capitalizing on the inherent frequency band stop of PCs. The PC is tuned to the targeted TS wave characteristics through the use of analytical models derived from transfer matrix and interface response theories, verified using a finite elements analysis. The interaction between TS waves and a single PC is investigated using coupled two-dimensional fluid structure interaction simulations in the frequency domain. It is shown that TS waves are either amplified or attenuated depending on whether the PC free-face surface displacement and unsteady perturbation pressure at the wall are in-phase or out-of-phase, respectively. The perturbation pressure acts solely as the driver for the mechanical oscillation of the PC. The emerging hydrodynamic coupling between TS waves and the PC is found to be governed by a combination of the Orr mechanism and wall-normal velocity linear superposition near the wall. Finally, a metasurface comprised of an array of streamwise-distributed PCs is evaluated, resulting in an amplitude growth delay of 11.3% of the TS wavelength along the metasurface extent.

On aerodynamic force computation in fluid–structure interaction problems — Comparison of different approaches

This paper is interested in the numerical approximation of a two-dimensional fluid–structure interaction problem. A special attention is paid to the numerical realization of aerodynamic force (AF) calculations. Three different AF computations within finite element method framework are described and compared. First, the extrapolation of fluid stress tensor components from the interior of the fluid domain is the most straightforward method; however, this approach is of lower theoretical accuracy due to the explicit computation of velocity gradient. Second, the local reconstruction method applied on the velocity gradient is based idea of the least square fit of the gradients evaluated at finite element centroids from local patch. Third, the weak reformulation technique using the weak formulation of the fluid flow problem leads to the expression of AF in an integral form. As it avoids direct velocity gradient computation it is of higher accuracy compared to previous methods.The experimental convergence of all mentioned methods for the drag and lift coefficients is tested on the benchmark of a static cylinder in a cross-flow and further extended to the case with prescribed motion of the cylinder. Further, two FSI simulations compare the transferred energy from the fluid to the structure for the case of structure vibrations submerged in the viscous fluid and also for the flow-induced structural vibrations. The critical inlet velocity of flutter instability is determined and it is shown that for a given numerical setting the choice of AF computation can lead to the different FSI behavior.

Galloping of two-dimensional section of a marine riser attached with fairing under different inflow angles

Fairing is one of the most effective and popular devices for suppressing vortex-induced vibration (VIV) of marine risers. However, when the fairing is stuck and cannot rotate due to biological contamination and other reasons, it may cause serious galloping oscillation and endanger the safety of the riser. In this paper, a reliable two-dimensional fluid-structure interaction (FSI) model with two degrees of freedom (DOF) was established based on computational fluid dynamics (CFD) and finite element method (FEM). The steady flow fields and galloping characteristics of a faired riser under different inflow attack angles were studied by numerical method. The results showed that when the structure is stationary, there is a critical attack angle αc ∈ (25°, 30°), which divides the vortex shedding state and the variation law of the hydrodynamic coefficient. This is because when the inflow attack angle α > αc, a reattachment of the shear layer occurs on one side of the fairing. In the 2 DOF FSI analysis, typical cross-flow (CF) direction galloping was observed in the region of α < αc. When α > αc, the oscillation was relatively weak, and the amplitudes in the in-line (IL) and CF directions were similar. When the α was near αc, the vibration was smallest. According to the structure of the wake vortex, the stable reattachment of the separated shear layer generated on one side of the fairing affected by the inflow attack angle is not easy to cause galloping. Only when the periodic reattachment occurs, it will trigger a strong galloping.

The internal substructure method for shock wave input in 2D fluid-structure interaction analysis with unbounded domain using doubly-asymptotic ABC

Interaction between underwater shock waves and structures has attracted significant interest of many researchers. This study aims to develop a method to solve two-dimensional (2 D) fluid-structure interaction problems during far-field underwater explosion (UNDEX). The acoustic domain which can undergo small pressure variations is considered to describe the fluid-structure interaction during UNDEX. First, the empirical formula of the incident shock waves is considered as free wave motion of the fluid, and the fluid domain is Discretized by the finite element method. Based on the scaled boundary finite element method (SBFEM) and continued fraction solution, an artificial boundary condition (ABC) with high accuracy in time domain is adopted to simulate the truncated infinite domain, which can be placed very close to the radiating field is adopted to simulate the truncated infinite domain. Third, an internal substructure method (ISM) to calculate the equivalent input shock wave loads is proposed. Finally, the proposed method is used to study the scattered waves on a rigid circular structure due to the shock wave, and the effect of the radiation wave due to the motion of the structure on the dynamic responses of the circular structure during UNDEX is studied.

A CFD-FEM based partitioned fluid structure interaction model to investigate surface cracks in elastohydrodynamic lubricated line contacts

This paper presents a partitioned, two-dimensional fluid structure interaction (FSI) model developed to investigate the effects of surface cracks in rolling/sliding line contacts operating under elastohydrodynamic lubrication (EHL). The lubricant behavior as it flows over and through the crack is determined by solving the Navier-Stokes equations using the Ansys Fluent computational fluid dynamics (CFD) solver. The structural response of the solid body is governed via an elastic-plastic constitutive relationship and solved using the Ansys Mechanical finite element solver. The exchange of (i) forces due to fluid pressure, and (ii) displacements due to solid deformation across the fluid-solid interface (including the crack faces) is facilitated by an iterative implicit coupling scheme. A smoothing based dynamic meshing technique is utilized to capture the deformation of the fluid region. The FSI model developed for this investigation is capable of modeling surface cracks with inclined geometries, overcoming the limitations of the classical Reynolds based approach. The fluid pressure results are presented for different loads, speeds and slide-to-roll ratios. The effects of crack geometry (i.e. location, dimension, inclination, crack tip radius, etc.) on fluid pressure and structural response are investigated. The FSI model presents the details of pressure distribution, fluid streamlines and stress concentration in the solid simultaneously. The model results can be used to provide accurate boundary conditions on the crack faces for crack propagation modeling in rolling contact fatigue. The results of this investigation identify the crack geometries that affect fatigue life of rolling elements in EHL contact by predicting the location and severity of stress concentrations in the material.

A numerical approach for coupled analysis of the seismic response of a cable-moored submerged floating tunnel

A submerged floating tunnel (SFT) is propounded as an efficacious alternative to conventional bridges and underground/submerged tunnels for crossing deep waterways. SFT designers must ensure safe margins and develop approaches to prevail a wide range of plausible situations related to transport, wave, natural vibrations etc. to evaluate the structural stability. To date, only limited researches on this field have been performed to illustrate the significance of seaquake analyses and their effects have been underlined. The present paper intends at numerically simulating a two-dimensional (2D) fluid-structure interaction (FSI) problem in order to scrutinize the dynamic response of an SFT system under bidirectional earthquake actions. Hydrodynamic Pressure due to seismic base excitation is considered as independent nodal variables to represent the gravity influenced inviscid, compressible and irrotational fluid flow effects and the tunnel shell is considered as flexible. This work exposes the importance of the input seismic excitation characteristics that governs the distribution of the induced internal acceleration/force around the lining of the tunnel. Numerical results indicate that the increment rate of the internal acceleration in high SFT caused by vertical ground motion is nearly by 200% when compared to the low-laying tunnel. It is confirmed that long-period record may amplify the overall response of the SFT (up to 80%) when the tunnel approaches the ocean surface, as well as the mooring tensile force to a lesser extent. Finally the proposed coupled numerical procedure suggests that earthquake response spectrum in various intensity levels has an influential role in the response of long-span SFTs and special attention should be paid to the seismic design of such structures.

Alignment of a flexible platelike particle in shear flow: Effect of surface slip and edges

Rigid plate-like particles displaying interfacial slip can attain a constant orientation in a shear flow when the slip length is sufficiently large. But actual thin particles such as single-layer graphene are prone to bending deformations when exposed to shear stress. To study the effect of bending deformation on the particle's stable orientation, we develop a two-dimensional fluid-structure interaction model. We find that (i) a stable alignment occurs even for relatively flexible particles, and that (ii) edges effects on the shape of the plate are important for values of the length-to-thickness aspect ratio as large as 100.

Partitioned MPS-FEM method for free-surface flows interacting with deformable structures

In this paper, the partitioned MPS-FEM method is employed for two-dimensional and three-dimensional free surface flow interacting with deformable structures. The discretization of fluid and structure govern equations relies independently on the Moving Particle Semi-implicit method (MPS) and Finite Element Method (FEM). Two types of interpolation techniques, including the Shape Function Based Interpolation Technique (SFBI) and Kernel Function Based Interpolation Technique (KFBI) are proposed on the fluid-structure isomerous interface. The performance of MPS-FEM coupled method is validated by a series of two-dimensional Fluid-Structure Interaction (FSI) tests, including precision test and convergence validation. The results obtained show good agreements with published experimental result as well as referenced numerical results. At last, an extension of aforementioned coupled method to three-dimensional model is performed to investigate characteristics of three-dimensional FSI phenomena. It indicates that partitioned MPS-FEM method is effective and stable for the simulation of free-surface flow interacting with deformable structures.

Study on Fluid-Structure Interaction of Flexible Membrane Structures in Wind-Induced Vibration

A strongly coupled monolithic method was previously proposed for the computation of wind-induced fluid-structure interaction of flexible membranous structures by the authors. How to obtain the accurate solution is a key issue for the strongly coupled monolithic method. Projection methods are among the commonly used methods for the coupled solution. In the work here, to impose initial pressure boundary conditions implicitly defined in the original momentum equations in classical projection methods when dealing with large-displacement of membranous structures, a modified factor is introduced in corrector step of classical projection methods and a new modified projection method is obtained. The solution procedures of the modified projection method aimed at strongly coupled monolithic equations are given, and the related equations are derived. The proposed method is applied to the computation of a two-dimensional fluid-structure interaction benchmark case and wind-induced fluid-structure interaction of a three-dimensional flexible membranous structure. The performance and efficiency of the modified projection method are evaluated. The results show that the modified projection methods are valid in the computation of wind-induced fluid-structure interaction of flexible membranous structures, with higher accuracy and efficiency compared with traditional methods. The modified value has little effects on the computation results whereas iteration times has significant effects. Computation accuracy can be improved greatly by increasing iteration times with less increase in computation time and little effects on stability with the modified projection method.

Novel Thrust Foil Bearing With Pocket Grooves for Enhanced Static Performance

Abstract The integration of foil bearing technology into high-speed oil-free machines has been slow in progress, in part, due to the low load-carrying capacity of the foil thrust bearing. It is crucial this issue is addressed through innovative solutions without overcomplicating the bearing design because simplicity is one of the attractive features of the foil bearing. This work presents novel thrust foil bearing with taper-flat configuration and pocket grooves on the bearing top foil as a secondary pressure boosting mechanism. Parametric study of the pocket dimensions on a rigid bearing reveals that the bearing static performance is the most sensitive to the pocket angular span. Further two-dimensional fluid–structure interaction analyses on foil thrust bearing predict a reduction of power loss by 10% with increased average film thickness. Minimum film thickness also increases when the bearing is lightly loaded but it is reduced 20% at the taper-flat transition area under high loading condition. This issue can be overcome by using stiffer bump foil; however, this is not implemented in this work due to other design constraints. Test results at 90,000 rpm and 140,000 rpm show, by adding the pocket groove pattern on the top foil, the power loss is reduced by 16% compared to the traditional taper-flat configuration.

Wake dynamics and flow-induced vibration of a freely rolling cylinder

Abstract

A coupled numerical approach to simulate the effect of earthquake frequency content on seismic behavior of submarine tunnel

Roughly 90% of all natural vibrations have epicenters in offshore zones and may cause destruction of submarine and floating structures. Such excitations can influence the safe performance of facilities set up on the seabed, like tunnels, jacket legs and subsea oil pipelines. Some researches on this theme have been carried out to demonstrate the importance of seaquake analyses and their effects have been underlined. The present study intends to numerically simulate a two-dimensional fluid-structure interaction (FSI) problem in order to examine the dynamic response of submarine tunnel under real horizontal earthquakes. Pressure is considered as independent nodal variables to represent the fluid flow effects and the induced time-dependent acceleration in porous medium equation is incorporated in the analysis and the tunnel shell is considered as flexible. This work highlights the importance of the input ground motion frequency content that governs the development of the induced seismic stress/strain around the lining of the tunnel. The results demonstrate that for deep sea the increment rate of the circumferential stress caused by surface gravity waves is below 7% when compared to the no-wave interface condition. Moreover, it is confirmed that long-period record may amplify the overall response of the system (up to 60%) specially the lateral and vertical displacements, as well as the principal stress to a lesser extent. The developed numerical model can attend to further analysis of tunnels embedded in a half-space in conjunction with fluid undergoing the severe long-period earthquakes.

An investigation of the effect of elastic membrane on liquid sloshing in partially filled tank vehicles

Roll plane fluid slosh within a partly-filled tank with an elastic membrane restraining the free surface is investigated through development of a two-dimensional computational fluid dynamic and fluid-structure interaction (CFD-FSI) model. The air-membrane-liquid interaction analysis is performed to investigate effect of the membrane on the liquid cargo movement. Laboratory experiments were conducted on a circular tank with an elastic membrane-like restraint under harmonic lateral acceleration excitations. The validity of the CFD-FSI model is demonstrated on the basis of the laboratory-measured responses. The effectiveness of the membrane in limiting the fluid slosh is illustrated by comparing simulation results obtained for a circular tank with and without the membrane. It is shown that addition of the membrane could yield substantial reduction in the fluid cargo motion and thus roll moment, while increasing the fundamental slosh frequency by more than two times that obtained for the cleanbore tank.

Fully Coupled Smoothed Particle Hydrodynamics-Finite Element Method Approach for Fluid–Structure Interaction Problems With Large Deflections

Abstract In this study, a combination of the smoothed particle hydrodynamics (SPH) and finite element method (FEM) solving the complex problem of interaction between fluid with free surface and an elastic structure is studied. A brief description of SPH and FEM is presented. Contact mechanics is used for the coupling between fluid and structure, which are simulated with SPH and FEM, respectively. In the proposed method, to couple mesh-free and mesh-based methods, fluid and structure are solved together by a complete stiffness matrix instead of iterative predictive–corrective or master–slave methods. In addition, fully dynamic large-deformation analysis is carried out in FEM by taking into account mass and damping of the elastic structure. Accordingly, a two-dimensional fluid–structure interaction (FSI) code is developed and validated with two different experiments available in the literature. The results of the numerical method are in good agreement with the experiments. In addition, a novel laboratory experiment on a dam break problem with elastic gate in which the length of the initial water column is larger than its height is conducted. The main difference between the previous experiments and the one conducted in this study is that an upward water motion parallel to the elastic gate is observed at the upstream side of the gate. This motion is captured with the numerical method.

English

We are interested in the numerical solution of a two-dimensional fluid-structure interaction problem. A special attention is paid to the choice of physically relevant inlet boundary conditions for the case of channel closing. Three types of the inlet boundary conditions are considered. Beside the classical Dirichlet and the do-nothing boundary conditions also a generalized boundary condition motivated by the penalization prescription of the Dirichlet boundary condition is applied. The fluid flow is described by the incompressible Navier-Stokes equations in the arbitrary Lagrangian-Eulerian (ALE) form and the elastic body creating a part of the channel wall is modelled with the aid of linear elasticity. Both models are coupled with the boundary conditions prescribed at the common interface. The elastic and the fluid flow problems are approximated by the finite element method. The detailed derivation of the weak formulation including the boundary conditions is presented. The pseudo-elastic approach for construction of the ALE mapping is used. Results of numerical simulations for three considered inlet boundary conditions are compared. The flutter velocity is determined for a specific model problem and it is shown that the boundary condition with the penalization approach is suitable for the case of the fluid flow in a channel with vibrating walls.

A monolithic algorithm for the flow simulation of flexible flapping wings

It has been a challenge to simulate flexible flapping wings or other three-dimensional problems involving strong fluid–structure interactions. Solving a unified fluid–solid system in a monolithic manner improves both numerical stability and efficiency. The current algorithm considered a three-dimensional extension of an earlier work which formulated two-dimensional fluid–structure interaction monolithically under a unified framework for both fluids and solids. As the approach is extended from a two-dimensional to a three-dimensional configuration, a cell division technique and the associated projection process become necessary and are illustrated here. Two benchmark cases, a floppy viscoelastic particle in shear flow and a flow passing a rigid sphere, are simulated for validation. Finally, the three-dimensional monolithic algorithm is applied to study a micro-air vehicle with flexible flapping wings in a forward flight at different angles of attack. The simulation shows the impact from the angle of attack on wing deformation, wake vortex structures, and the overall aerodynamic performance.

Feedback Stabilization of a Two-Dimensional Fluid-Structure Interaction System with Mixed Boundary Conditions

We study the stabilization of a fluid-structure interaction system around an unstable stationary solution. The system consists of coupling the incompressible Navier-Stokes equations, in a two dimensional polygonal domain with mixed boundary conditions, and a damped Euler-Bernoulli beam equations located at the boundary of the fluid domain. The control acts only in the beam equations. The feedback is determined by stabilizing the projection of the linearized model onto a finite dimensional invariant subspace. Here we have resolved two important challenges for applications in this field. One is the fact that we prove a stabilization result around a non zero stationary solution, which is new for such fluid-structure interaction systems. The other one is that the feedback laws that we determine do not depend on the Leray projector used to get rid of the algebraic constraints of partial differential equations. This is essential for numerical aspects

Parametric study of a VLS based on 2-D FSI analysis

Vertical launching system (VLS) is useful in operating and sheltering high-speed rockets. The aft closure in the plenum plays a significant role in protecting the interiors from the exhaust gas induced by the ignition of adjacent or in-positioned canisters. During the aft opening/closing event, a complex flow is propagated into the VLS. By presence of such structural components, it is necessary to analyze the interaction between the deforming aft closure and a highly pressurized plume.This paper presents a two-dimensional fluid–structure interaction (FSI) simulation under high pressure loading condition for preliminary design of VLS. A quadrilateral 9-node element based on co-rotational (CR) framework is used to predict the geometrically/materially nonlinear deformation of the aft closure while supersonic impinging jet plume is predicted by fully Eulerian modeling. A contact mechanism is also utilized to apply reaction forces between the structures and inclined plenum using a penalty term. The interface and boundary conditions are obtained by the hybrid particle level-set method via the Ghost framework. Furthermore, a parametric study is conducted by changing the thickness of the aft closure and the inclined angle of the plenum. It is expected that the magnitudes of pressure and temperature can be decreased by the introduction of appropriate thickness of the aft closure and inclined angle in the plenum.

On the Application of Acoustic Analogies in the Numerical Simulation of Human Phonation Process

This paper deals with the numerical simulation of the flow induced sound as generated in the human phonation process. The two-dimensional fluid-structure interaction problem is modeled with the aid of linear elastic problem coupled to the incompressible Navier-Stokes equations in the arbitrary Lagrangian-Eulerian form. For calculation of sound sources and its propagation the Lighthill acoustic analogy is used. This approach is compared to the Perturbed Convective Wave Equation method. All partial differential equations, describing the elastic body motion, the fluid flow and the acoustics, are solved by applying the finite element method. In order to overcome numerical instabilities in the Navier-Stokes equations arising due to high Reynolds numbers, the modified streamline-upwind/Petrov-Galerkin stabilization is used. The implemented iterative coupling procedure is described. Numerical results are presented.