Fluid-structure Interaction Interface Research Articles

A localized subdomain smoothing MMALE particle method for efficient modeling FSI problems

Fluid–structure-interaction (FSI) phenomena with multi-phase flow dynamics and structural damage commonly exist in engineering practice, which however bring great challenges to nowadays numerical FSI algorithms. A novel localized subdomain smoothing MMALE particle method (ls-ALEPM) is proposed in this paper for efficient and accurate simulations of large scale FSI problems. The MMALE method and the MPM are strongly coupled by immersing the MPM particles into the MMALE grid. In order to avoid the spurious strain induced by the mixed FSI velocity field, a decoupled stress updating scheme is proposed to update the stress of solid particles by introducing a virtual velocity field in the vicinity of FSI interface. And specifically, the highly accurate polyhedron intersection based method is employed for its remapping phase, which however is time-consuming. Thus, the localized subdomain smoothing method (LSSM) is put forward to accelerate the remapping phase which only involves the distorted regions of computational grid. The LSSM is composed of a distorted subdomain determination step and a combinated mesh smoothing step. Each iteration of the combinated mesh smoothing step consists of the modified GETMe and the weighted average method, and the transfinite interpolation method is adopted if the quality criteria is still not satisfied after prescribed maximum number of iterations. The validity and efficiency of ls-ALEPM is verified by several benchmark numerical examples and practical engineering simulations.

A hybrid Lagrangian–Eulerian particle finite element method for free‐surface and fluid–structure interaction problems

AbstractThe dynamics of fluid flows with free surfaces and interacting with highly deformable structures is a complex problem, attracting considerable attention. The Particle Finite Element Method (PFEM) is one of the various numerical methods recently proposed in the literature to simulate this type of problems. It is a mesh‐based Lagrangian approach, particularly suited for problems with fast changes in the domain topology, since the fluid boundaries and the Fluid–Structure Interaction (FSI) interface are naturally tracked by the position of the mesh nodes. However, when nonhomogeneous boundary conditions are imposed on velocities or when there are regions where the topology varies moderately, for example, in confined portions of the fluid domain characterized by fixed boundaries, an Eulerian formulation turns out to be more convenient. To exploit the advantages of both formulations, an adaptive hybrid Lagrangian–Eulerian approach is presented in this work. According to the proposed method, nodes on the fluid free‐surface and on the FSI interface are treated as Lagrangian, while the remaining nodes can be either Eulerian or Lagrangian. Furthermore, to increase the efficiency of the method, an algorithm to automatically detect runtime the transition zone between the two kinematic descriptions is devised. To validate the proposed approach, several numerical examples are developed and their results are compared to those available in the literature.

Dynamic Effect of Fluid–Structure Interaction and Modal Analysis of Crude–Pipeline Interaction System Considering the Fluctuating Pressure of Medium

This work explored the fluid–structure interaction (FSI) effect of crude oil and pipeline and the vibration characteristics of the pipe–crude oil structural system. A finite element computational analysis theory and corresponding simulation method were proposed for crude oil pipelines considering the FSI effect. Meanwhile, the spring model of the FSI interface between crude oil and pipeline was proposed. The experimental simulation and neural network were adopted to obtain the flow-excited pulsation pressure (FEPP), and the kinetic equations of the pipe–crude oil FSI were analyzed. The finite element computation (FEC) model for pipe–crude oil bi-directional FSI dynamics was established, which was composed of five support span lengths and four pipe liquid levels and can provide five different crude oil fluid velocities. One hundred orthogonal simulation test conditions were designed. In addition, the displacement response and acceleration response under FSI of the pipe wall were calculated, and the first six orders of inherent frequencies and main vibration patterns of the FEC model were analyzed. The results revealed that the dynamic effect of FSI between the crude oil transport medium and pipeline was complex and was influenced by the length of the pipeline crossing section, medium flow velocity, difference of liquid surface height, and displacement response. The acceleration response possessed prominent vibration decay characteristics, and the response peak in the same condition was about 8.2 times larger than that of the steady-flow state response. Therefore, the effect changed the inherent frequency and vibration pattern of the pipeline, to which the engineering design should pay sufficient attention.

An integrated model for offshore wind turbine monopile in porous seabed under multi-directional seismic excitations

This study proposes an integrated three-dimensional time-domain finite element model for offshore wind turbine (OWT) monopile in porous seabed under multi-directional seismic excitations. Biot's u-p formulation is used to describe the dynamic interaction between the soil skeleton and pore water. Potential-based fluid elements are used for seawater to accurately model fluid–structure interaction (FSI). Moreover, FSI interface elements are applied to the interface of seawater and pile and to the interface of seawater and mud line. To analyze the response of the OWT-monopile-seabed-seawater system to multi-directional seismic excitations, a viscous-spring artificial boundary is implemented in the finite element model. The integrated model was sufficiently verified in terms of the vibration characteristics of OWTs, the displacement and the excess pore water pressure using implemented viscoelastic artificial boundary, and the FSI interaction under both horizontal and vertical excitation. The results indicated that: (1) The hydrodynamic pressure and the excess pore water pressure varied with different positions along the OWT and the pile; (2) Adding the excitation of the EW component ground motion caused the change of the distribution of transient liquefaction with respect to that under the excitation of only NS component ground motion; (3) The vertical ground motion caused a substantial fluctuation of the vertical displacement of the OWT and larger area of transient liquefaction near the surface of the seabed and near the tip of the pile; (4) resonance occurred when the frequency of input motion was approaching to the first natural frequency of OWT, leading to extremely large acceleration and displacement of OWT.

Fluid-Structure Interaction Study of the Serpentine Nozzle for Turbofan

Serpentine nozzle can effectively suppress the infrared radiation signatures of the aero-engine exhaust system. However, it experiences the remarkable fluid-structure interaction (FSI) process at the work condition. In this paper, the deformation behavior of the serpentine nozzle and its flow characteristic were investigated numerically. Then, the influences of the wall thickness and the geometric configuration on the FSI effect were also explored. The results show that, the mechanism of the fluid-structure interaction is formed through the data transfer of the force and the displacement at the FSI interface. Under the FSI effect, there occur the ballon-like swellings at the second S passage, and the linear section bends upward along the Y direction. They induce the special flow features including the flow separation, the shock wave and the plume vector angle. As the value of the wall thickness increases from 3mm to 6mm, the maximum of the deformation displacement of the serpentine nozzle decreases 68.5mm. As compared to the uncoupled state, the variation of the axial thrust decreases from 2.70% to 0.70% at the coupled state. The circular-to-rectangular profile and the S-shaped passage enlarge the deformation behavior of the nozzle structure. The value of the axial thrust of the serpentine nozzle with 5mm wall thickness for the coupled state is lower 1.92% than these for the uncoupled state.

An immersed boundary-material point method for shock-structure interaction and dynamic fracture

As a class of extreme fluid-structure interaction (FSI), shock-structure interaction problems are always accompanied with dynamic fracture phenomena in solid structure. During the dynamic fracture process, small fragments of thin geometry and fresh FSI interfaces will be generated, which makes the FSI interface difficult to be reconstructed. An immersed boundary-material point method (IBMPM) is proposed in this paper for simultaneous simulations of shock-structure interaction and accompanied dynamic fracture. The finite volume method (FVM) is employed as fluid solver and specifically a TVD Riemann solver is adopted for shock simulation, while the material point method (MPM) is employed as solid solver for simulation of extreme deformation problem. The FVM and MPM are then coupled by our improved immersed boundary method (IBM) which is named as Lagrangian continuous-forcing IBM (lg-CFIBM). The lg-CFIBM is proposed in the frame of continuous forcing approach with a compact support area for the immersed boundary conditions. It can guarantee the boundary velocity conditions strictly at each time step and has no need to reconstruct FSI interfaces. Several numerical examples, including shock-cylinder obstacle interaction, flexible panel deformation induced by shock wave and fragmentation driven by detonation, are studied to verify and validate the proposed method, and numerical results are in good agreement with experiments.

An isogeometric b-rep mortar-based mapping method for non-matching grids in fluid-structure interaction

In this study the isogeometric B-Rep mortar-based mapping method for geometry models stemming directly from Computer-Aided Design (CAD) is systematically augmented and applied to partitioned Fluid-Structure Interaction (FSI) simulations. Thus, the newly proposed methodology is applied to geometries described by their Boundary Representation (B-Rep) in terms of trimmed multipatch Non-Uniform Rational B-Spline (NURBS) discretizations as standard in modern CAD. The proposed isogeometric B-Rep mortar-based mapping method is herein extended for the transformation of fields between a B-Rep model and a low order discrete surface representation of the geometry which typically results when the Finite Volume Method (FVM) or the Finite Element Method (FEM) are employed. This enables the transformation of such fields as tractions and displacements along the FSI interface when Isogeometric B-Rep Analysis (IBRA) is used for the structural discretization and the FVM is used for the fluid discretization. The latter allows for diverse discretization schemes between the structural and the fluid Boundary Value Problem (BVP), taking into consideration the special properties of each BVP separately while the constraints along the FSI interface are satisfied in an iterative manner within partitioned FSI. The proposed methodology can be exploited in FSI problems with an IBRA structural discretization or to FSI problems with a standard FEM structural discretization in the frame of the Exact Coupling Layer (ECL) where the interface fields are smoothed using the underlying B-Rep parametrization, thus taking advantage of the smoothness that the NURBS basis functions offer. All new developments are systematically investigated and demonstrated by FSI problems with lightweight structures whereby the underlying geometric parametrizations are directly taken from real-world CAD models, thus extending IBRA into coupled problems of the FSI type.

A partitioned solution approach for the fluid–structure interaction of thin-walled structures and high-Reynolds number flows using RANS and hybrid RANS–LES turbulence models

In this work the partitioned solution approach for the fluid–structure interaction (FSI) of thin-walled structures and high-Reynolds number (Re) flows modeled using Reynolds–Averaged Navier–Stokes (RANS) and hybrid Reynolds–Averaged Navier–Stokes – Large Eddy Simulation (RANS–LES) turbulence models are described. The advanced turbulence modeling is needed to capture very complex fluid phenomena which triggers instabilities of thin–walled structures present in supersonic flow regimes. The finite element (FE) updated Lagrangian formulation (ULF) for the nonlinear elastic solids is used to predict its dynamical behavior. The main contribution addresses to the linear stress–strain relation Laplacian members, which are solved implicitly, on that way decreasing required memory resources and improving solution stability in the same time. The structures of the interest include the vast variety of membranes, curved shells and plates. The instabilities encountering these structures include limit cycle oscillations (LCO), flutter and buckling of the panels. The phenomena appear in everyday engineering practice and a need for the powerful tools to handle such problems is a common goal. Utilization of the unstructured non-regular meshes allows the precise distribution of computational nodes at the physical boundaries of the fluid and solid domains. It is naturally allowing application of the common approach for the fluid–solid interface coupling, as well as classical data interpolation schemes between fluid and solid on the FSI interface. High-Re flows, both 2D (benchmark) and 3D turbulent FSI case are chosen for the validation. Two numerical methods are coupled via a moving boundary treatment, in a staggered way. The proposed coupling method showed a good agreement with the reference test cases. The current FSI framework is developed to serve as a tool for the liquid rocket engine development.

On the linear global stability analysis of rigid-body motion fluid–structure-interaction problems

Abstract

An Eulerian-Lagrangian-Lagrangian method for solving fluid-structure interaction problems with bulk solids

This paper presents an Eulerian-Lagrangian-Lagrangian (ELL) method to solve the fluid-structure interaction (FSI) problem, in which a bulk solid is immersed in the fluid. The ELL approach uses a small portion of the Lagrangian fluid to wrap the solid body, and they are treated as an enlarged “composite solid”. Then the conventional immersed finite element method (IFEM) is implemented. The velocity condition of the moving interface is explicitly imposed within the unified Lagrangian grids of the composite solid domain, and then smoothly transferred onto the Eulerian fluid nodes nearby the FSI interaction zone. The inaccurate numerical FSI interface in IFEM is hence significantly improved. The idea of warping Lagrangian fluid makes ELL a combination of the body-conforming method and the immersed type method. It is straightforward but offers an excellent physical explanation that makes ELL more realistic. Several numerical examples are computed to demonstrate the superior performance of the proposed approach for solving FSI problems with bulk solids, in comparison with the conventional IFEM.

Systematic evaluation of the interface description for fluid–structure interaction simulations using the isogeometric mortar-based mapping

Within this study the influence of the interface description for partitioned Fluid–Structure Interaction (FSI) simulations is systematically evaluated. In particular, a Non-Uniform Rational B-Spline (NURBS)-based isogeometric mortar method is elaborated which enables the transfer of fields defined on low-order and isogeometric representations of the interface along which the FSI constraints are defined. Moreover, the concept of the Exact Coupling Layer (ECL) using the proposed isogeometric mortar-based mapping method is presented. It allows for smoothing fields that are transferred between two standard low-order surface discretizations applying the exact interface description in terms of NURBS. This is especially important for highly turbulent flows, where the artificial roughness of the low-order faceted FSI interfaces results in spurious flow fields leading to inaccurate FSI solutions. The approach proposed is subsequently compared to the standard mortar-based mapping method for transferring fields between two low-order surface representations (finite volume method for the fluid and finite element method for the structure) and validated on a simple lid-driven cavity FSI benchmark. Then, the physically motivated 3D example of the turbulent flow around a membranous hemisphere (Wood et al., 2016) is considered. Its behavior is predicted by combining the large-eddy simulation technique with the isogeometric analysis to demonstrate the usefulness of the isogeometric mortar-based mapping method for real-world FSI applications. Additionally, the test case of a bluff body significantly deformed in an eigenmode shape of the aforementioned hemisphere is used. For this purpose, both “standard” low-order finite element discretizations and a smooth IGA-based description of the structural surface are considered. This deformation is transferred to the fluid FSI interface and the influence of the interface description on the fluid flow is analyzed. Finally, the computational costs related to the presented methodology are evaluated. The results suggest that the proposed methodology can effectively improve the overall FSI behavior with minimal effort by considering the exact geometry description based on the Computer-Aided Design (CAD) model of the FSI interface.

A CFD/CSD coupled method with high order and its applications in flow induced vibrations of tube arrays in cross flow

Wear and tear are the most common failures of tubes in cross-flow during long time operation of a steam generator due to the fluid induced vibrations. A fluid-elastic approach with high order was developed by coupling the CFD method and the CSD method. In the method, fluid forces were predicted by the CFD method followed by structural response calculations, and data were transferred via fluid-structure interaction interface. The unsteady flow through normal triangular cylinder arrays with one single tube undergoing self-excited oscillations was simulated by the proposed method. Lifts, displacement and velocity of the particular cylinder were obtained followed by calculations of the corresponding frequency spectrums. Results showed that the proposed method can predict the flow induced vibrations with high accuracy. When the natural frequency of the cylinder increased to the dominant frequency of the flow, an abrupt increment of vibrational velocity was observed.

A fully partitioned Lagrangian framework for FSI problems characterized by free surfaces, large solid deformations and displacements, and strong added-mass effects

In this work a fully partitioned Lagrangian framework for the solution of fluid–structure interaction (FSI) problems involving free surfaces, large solid displacements and deformations, and strong added mass effects is presented. The fluid is simulated using the Particle Finite Element Method (PFEM), while Metafor, a large deformations nonlinear Finite Element code, is employed to simulate the solid part. The fully partitioned coupling is ensured through an Interface Quasi-Newton Inverse Least Squares (IQN-ILS) (Degroote et al., 2009) strategy to avoid added mass effects. The Lagrangian particle nature of the PFEM allows the simulation of problems involving free surfaces and very large solid displacements, usually difficult to achieve with traditional body-fitted CFD techniques. We show that owing to the generality of its formulation the PFEM can be used as is in the framework of fully partitioned FSI coupling schemes, where minimal information (i.e. loads and displacements at the FSI interface) is exchanged between the fluid and the solid solvers. More importantly, we demonstrate that a fully partitioned PFEM–FEM coupling based on the IQN-ILS strategy allows the simulation of a very large spectrum of FSI problems without incurring added-mass instabilities. The performance of the IQN-ILS coupling strategy in a fully Lagrangian framework is also assessed and compared to more traditional approaches such as Block-Gauss–Seidel (BGS) iterations with Aitken relaxation. An extensive work of verification and benchmarking is proposed, aiming to encompass all the combinations of physical and numerical parameters possibly leading to added-mass instabilities, and testing the IQN-ILS strategy on different benchmarks beyond those already proposed in the literature. The coupling is performed through CUPyDO (Thomas et al., 2019), a general Python framework for partitioned FSI coupling.

Preliminary Study on Mesh Stiffness Models for Fluid-structure Interaction Problems

One of the challenges in modern computational engineering is the simulation of fluid-structure interaction (FSI) phenomena where one of the crucial issues in the multi-physics simulation is the choice of stiffness model for mesh deformation. This paper focuses on the application of iteratively implicit coupling procedure on two transient FSI cases of vortex induced-vibration (VIV) that manifest oscillating flexible structures. The aim is to study various mesh stiffness models in the Laplace equation of diffusion employed within the arbitrary Lagrangian-Eulerian (ALE) methodology to handle the moving mesh. In the first case where a laminar flow interacted with a flexible splitter, it was demonstrated that a near FSI boundaries increased-stiffness model prevails to manage a large deformation of the moving structure as compared to a near volume increased-stiffness model. However, the potential technique could not be exploited to the second FSI configuration, where the effect of the turbulence of flow was included. It was found that the mesh topology near the FSI interface was collapsed. Instead of utilizing the same approach, a mesh stiffness based on a wall distance was found to be auspicious. Thus, the mesh stiffness model in the FSI simulation is case-dependent.

Fluid-Structure Interaction Vibration Response Analysis of the Hydrocyclone Under Periodic Excitation

Considering that the hydrocyclone will be affected by internal and external fluid forces in practical work, the numerical simulation method of fluid-structure interaction(FSI) of the hydrocyclone is proposed, and the finite volume method is used in the fluid domain and the finite element method is used in the solid domain. According to the numerical simulation of the flow around a circular cylinder, the magnitude and frequency of fluid flow around the hydrocyclone are obtained. On this basis, the numerical simulation and experimental research of the hydrocyclone are carried out, and the vibration characteristic of the hydrocyclone under the FSI condition is discussed, which the modal frequencies and modes of the hydrocyclone, the structural displacement and stress distribution characteristics of the FSI interface under periodic excitation are obtained. The results of numerical simulation and measured are compared and analyzed. The distribution trend and position of the maximum acceleration values are in good agreement between the measured and numerical simulation. The maximum deformation and the maximum acceleration values position of the hydrocyclone structure which is near the intersection between small conical section and tail pipe, and the structural deformation and maximum acceleration values of the hydrocyclone increase with the increase of inlet velocity. The analysis shows that the FSI model of the hydrocyclone is reasonable. Moreover, the influencing factors of fluid flow around the hydrocyclone should be considered in the future design and application of the hydrocyclone.

An Eulerian–Lagrangian–Lagrangian method for solving thin moving rigid body immersed in the fluid

It is convention in computational mechanics to use Eulerian grids for fluids and Lagrangian grids for solids. In this paper, a novel method called ELL using both Lagrangian and Eulerian grids for fluids is presented in a carefully designed manner to handle complex fluid–structure interaction (FSI) problems with moving thin rigid body. The key idea is to use a small portion of the fluid to wrap the thin body. This wrapping fluid is described in Lagrangian coordinate, the same way the solid is described. They are treated as one “composite solid” thus the immersed domain method (IDM) can be implemented. In this way, the moving interface boundary conditions can be explicitly imposed with the help of the unified Lagrangian grids in the interaction zone. The initial fluid domain can still be treated as usual Eulerian grids based on IDM theory by introducing a fictitious fluid. The FSI interface can be accurately modeled since the wrapping fluid and the solid are always attached together. This effectively solves the major “blur interface” problem in the conventional immersed boundary method (IBM). To demonstrate this ELL idea, a number of benchmark examples have been studied in comparison with the results in the open literature. Finally, a 2D flapping wing is simulated to show the potential of ELL in engineering application. It is observed that ELL method proves to be good in performance.

A Topology-alterative Algorithm for Transient Dynamic Hydraulic Response Investigation

In this paper, a hexahedra-based topology-alterative algorithm is proposed to simulate dynamic boundary issues of the gate opening motions in water conservancy projects. The algorithm, which cooperates with the two-phase, incompressible solver of OpenFOAM platform, enables researchers to investigate transient hydraulic characteristic variations comprehensively. Two benchmark experiments were performed to validate the numerical results under the working conditions of moving sluice gates and unsteady weir head. The time history response of water level and pressure on specified monitoring points, flow pattern scenario near moving gate, furthermore, the development of antisymmetric-revolving vertical vortices around gate piers were recorded to assess the accuracy of the proposed model. The cross-contrasting results show that the relative error of weir flow time is less than 5.00 %. Moreover, good agreement has been obtained about time history curves of free surface elevation and pressure between numerical and experiment solutions. The vivid flow pattern shows the simulating capability of the current model and indicates an inspiring way to numerically investigate generation mechanism of vertical vortex inside gate grooves. The proposed algorithm is believed to be a useful utility on the further investigation on flow variation in real hydraulic engineering applications, such as improvement of semi-empirical discharge formulas, reduction of cavitation damage, elimination of pipe hammer pressure even spectral analysis of sluice gates with a fluid structure interaction interface.

Unified fractional step method for Lagrangian analysis of quasi‐incompressible fluid and nonlinear structure interaction using the PFEM

SummaryThe fractional step method (FSM) is an efficient solution technique for the particle finite element method, a Lagrangian‐based approach to simulate fluid–structure interaction (FSI). Despite various refinements, the applicability of the FSM has been limited to low viscosity flow and FSI simulations with a small number of equations along the fluid–structure interface. To overcome these limitations, while incorporating nonlinear response in the structural domain, an FSM that unifies structural and fluid response in the discrete governing equations is developed using the quasi‐incompressible formulation. With this approach, fluid and structural particles do not need to be treated separately, and both domains are unified in the same system of equations. Thus, the equations along the fluid–structure interface do not need to be segregated from the fluid and structural domains. Numerical examples compare the unified FSM with the non‐unified FSM and show that the computational cost of the proposed method overcomes the slow convergence of the non‐unified FSM for high values of viscosity. As opposed to the non‐unified FSM, the number of iterations required for convergence with the unified FSM becomes independent of viscosity and time step, and the simulation run time does not depend on the size of the FSI interface. Copyright © 2016 John Wiley & Sons, Ltd.

INTEGRATED 3D MULTI-PHYSICAL SIMULATION OF A MICROFLUIDIC SYSTEM USING FINITE ELEMENT ANALYSIS

Microfluidics technology has emerged as an attractive approach in physics, chemistry and biomedical science by providing increased analytical accuracy, sensitivity and efficiency in minimized systems. Numerical simulation can improve theoretical understanding, reduce prototyping consumption, and speed up development. In this paper, we setup a 3D model of an integrated microfluidic system and study the multi-physical dynamics of the system via the finite element method (FEM). The fluid–structure interaction (FSI) of fluid and an immobilized single cell within the cell trapping component, and the on-chip thermodynamics have been analyzed. The velocity magnitude and streamline of flow field, the distribution of von Mises stress and Tresca stress on the FSI interface have been studied. In addition, the on-chip heat transfer performance and temperature distribution in the heating zone have been evaluated and analyzed respectively. The presented approach is capable of optimizing microfluidic design, and revealing the complicated mechanism of multi-physical fields. Therefore, it holds the potential for improving microfluidics application in fundamental research and clinical settings.

An unconditionally stable semi-implicit FSI finite element method

Abstract The paper addresses the numerical solution of fluid–structure interaction (FSI) problems involving incompressible viscous Newtonian fluid and hyperelastic material. A well known challenge in computing FSI systems is to provide an effective time-marching algorithm, which avoids numerical instabilities due to the loose coupling of fluid and structure motion on the FSI interface. In this work, we introduce a semi-implicit finite element scheme for an Arbitrary Lagrangian–Eulerian formulation of the fluid–structure interaction problem. The approach strongly enforces the coupling conditions on the fluid–structure interface, but requires only a linear problem to be solved on each time step. Further, we prove that the numerical solution to the fully discrete problem satisfies the correct energy balance, and the stability estimate follows without any extra model simplifications or assumptions on the time step. The analysis covers the cases of Saint Venant–Kirchhoff compressible and incompressible neo-Hookean materials. Results of several numerical experiments are included to illustrate the properties of the method and its applicability for the simulation of certain hemodynamic flows. We also experiment with the enforcement of material incompressibility condition in the finite element method via an integral constraint or alternatively letting the Poisson ratio in the compressible model to be close to 1 2 . From these experiments conclusions are drawn concerning the accuracy of flow statistics prediction for incompressible vs. nearly incompressible structure models.