Coupled Fluid Structure Problem Research Articles

Numerical Simulation of a Submerged Floating Tunnel: Validation and Analysis

The dynamic response analysis of submerged floating tunnels (SFTs) under seismic action is a complex two-way fluid–structure coupling problem that requires expertise in structural dynamics, fluid mechanics, and advanced computational methods. The coupled Eulerian–Lagrangian (CEL) method is a promising method for solving fluid–structure interaction problems, but its application to SFTs is not well established. Therefore, it is crucial to verify the accuracy and reliability of the CEL method in fluid–structure coupling simulations. This study verified the applicability of the CEL method for simulating one-way and two-way fluid–structure coupling cylindrical flow problems, and then applied the CEL method for the analysis of a shaking table test of a model SFT. A comparison of results obtained with the CEL method with those obtained in a previous indoor model test of an SFT demonstrates the agreement between the results of the CEL method and the overall trend of the experimental results, indicating the reliability of the method for the seismic analysis of SFTs. Moreover, the analysis of the dynamic response characteristics of SFTs under seismic conditions provides data support and a technological means for the seismic design of SFTs.

Numerical investigation of skipping stones using a hybrid volume of fluids and boundary data immersion method

Water skipping is a common physical phenomenon that represents a complex multiphase fluid–structure coupling problem involving a gas, liquid, and solid. This phenomenon is observed in various scenarios, such as seaplane landings, the entry and exit of amphibious aircraft on water surfaces, and even the slamming of a ship bow, all of which involve intricate water skipping dynamics. Therefore, skipping dynamics hold significant research value and offer broad practical applications. In this paper, a numerical method involving the volume of fluid method and boundary data immersion method is presented to study the fluid–structure interaction of a disk undergoing water skipping. Moreover, the six degrees of freedom motion of the rigid disk is described by unit quaternions. We validated the accuracy of our numerical method through comparisons with the experimental data. The results show good agreement on the disk's trajectory and cavity evolution. Furthermore, we studied the influence of the rotational angular velocity on the disk's trajectory, velocity, acceleration, hydrodynamic force, and cavity dynamics. As the angular velocity increases, the disk undergoes shorter collision durations with the water, diminished alterations in the azimuth angles, faster exit velocities, and faster velocity attenuations.

The Effect of Spanwise Folding on the Aerodynamic Performance of a Passively Deformed Flapping Wing.

The wings of birds exhibit multi-degree-of-freedom motions during flight. Among them, the flapping folding motion and chordwise passive deformation of the wings are prominent features of large birds in flight, contributing to their exceptional flight capabilities. This article presents a method for the fast and accurate calculation of folding passive torsional flapping wings in the early design stage. The method utilizes the unsteady three-dimensional panel method to solve the aerodynamic force and the linear beam element model to analyze the fluid-structure coupling problem. Performance comparisons of folding flapping wings with different kinematics are conducted, and the effects of various kinematic parameters on folding flapping wings are analyzed. The results indicate that kinematic parameters significantly influence the lift coefficient, thrust coefficient, and propulsion efficiency. Selecting the appropriate kinematic and geometric parameters is crucial for enhancing the efficiency of the folding flapping wing.

The Effect of Torsional and Bending Stiffness on the Aerodynamic Performance of Flapping Wing

For large bird-like flapping wing aircraft, the fluid–structure coupling problem is very important. Through the passive torsional deformation of the wing, sufficient thrust is generated and propulsion efficiency is ensured. Moreover, spanwise bending deformation will affect lift and thrust. The flow field on the surface of the wing and the geometric nonlinearity caused by the large deformation of the wing should be considered during the design process. Existing research methods do not solve this problem accurately and efficiently. This paper provides a method to analyze the fluid–structure coupling problem of the flapping wing which adopts the three-dimensional unsteady panel method to solve the aerodynamic force, and adopts the linear beam element model combined with the corotational formulation method to consider the geometric nonlinear deformation of the wing beam. This article compares the performance of the flapping wing with different torsional and bending stiffness, and analyzes the airfoil surface pressure coefficients at different portions of the wing during the period. The results show that torsional stiffness has a large influence on the lift coefficient, thrust coefficient and propulsion efficiency. Meanwhile, the torsional stiffness of the wing beam and the initial geometric twist angle of the wing need to be well coordinated to achieve high efficiency. Moreover, appropriate bending stiffness of the wing is conducive to improving propulsion efficiency.

Three-dimensional analytical solution of free vibrations of a simply supported composite plate in contact with a fluid

Background:The quantification of fluid–structure interactions is critical for the design and optimization of marine structures. As composite materials gain more traction in naval construction, there is a dire need of modeling tools to detail the dynamic response of composites in contact with fluids. Current structural theories and finite-element simulations offer promising pathways, but their strong hypotheses on through-the-thickness deformations and high computational cost challenge their practical feasibility. Methods:We propose an analytical three-dimensional solution to the free vibration of a bidirectional composite, separating a fluid column from vacuum. We leverage Pagano’s method to describe the three-dimensional displacement field in each ply of the composite plate and the fluid potential in the form of a Fourier series. Results:An analytical solution to the coupled fluid–structure problem is derived by imposing the continuity of displacement and stress at the ply interfaces, as well as boundary conditions on dry and wetted plies. We specialize the solution to sandwich structures of naval interest, offering insight on how the interactions with water can dramatically affect mode shapes and through-the-thickness profiles of displacement and stress. Discussion:The proposed approach provides the foundations for the design of thick composite plates for use in marine structures.

A GPU-accelerated adaptive particle refinement for multi-phase flow and fluid-structure coupling SPH

In this paper, a graphical processing unit (GPU) implementation of adaptive particle refinement (APR) in the Smoothed Particle Hydrodynamics (SPH) framework is used to simulate the multi-phase flow and fluid-structure coupling problems. The multi-phase flow and fluid-structure coupling SPH models based on the Riemann solver are presented and the local particle refinement technique based on the axis-aligned square refinement pattern is adopted to split particles. A particle shifting technique constructing virtual fine particles (VFP-PST) is proposed to regularize the particle distribution for numrical accuracy and stability. To facilitate the device memory throughput efficiently, a dynamic resource management algorithm is used to implement GPU-accelerated adaptive particle refinement. Precision analysis shows the effect of the smooth length ratio of fine and coarse particles on numerical accuracy. Different tests have demonstrated that the proposed GPU-accelerated IAPR is accurate and stable and provides a promising approach to simulate the multi-phase flow and fluid-structure problems with low computational cost and comparable precision when compared with uniform particles.

Nonlinear wave energy dissipator with wave attenuation and energy harvesting at low frequencies

It is important to determine how to reduce the wave load and utilize the ocean energy through the hybrid wave attenuation and energy harvesting structure (WAAEHS) as it is the basic scientific problem in the field of ocean engineering. The existing linear hybrid devices have poor performance due to the mismatch between the natural frequency and the excitation frequency in the low frequency region. The method of increasing the mass is unreliable and low economic, and the introduction of nonlinear mechanism to reduce the stiffness has complex fluid-structure coupling problem between waves and structures. In this paper, a new type of negative stiffness mechanism with a simple structure and good stability has been proposed and applied to a hybrid WAAEHS, and a nonlinear frequency domain method combining eigenfunction expansion matching method(EEMM)and multi-harmonic balance method(MHBM) has been proposed to solve the nonlinear wave–structure interaction dynamic model. The influence of the key parameters of the mechanism on the wave attenuation and energy harvesting performance is examined, and the “phase control” mechanism of the negative stiffness mechanism is revealed to improve the low-frequency wave attenuation and energy harvesting performance.

Impact characteristics and strength evaluation of a slender body obliquely entering water at high speed

Based on Coupled Eulerian-Lagrangian method, the impact characteristics and strength evaluation of high speed multi-angle oblique water entry of slender body were studied. In order to solve the complex fluid-structure coupling problem and large deformation problem, the Lagrangian grid is used to divide the slender body structure grid, and the Euler grid is used to divide the fluid grid, the effectiveness of the method is verified by comparing with the experimental results. Furthermore, by simulating the impact process of multi-angle water entry, the time-history curves of acceleration, stress and strain at the head position of the slender body were analyzed, and the strength evaluation was carried out to verify the structural safety combined with the residual strength formula. The results show that there is a positive correlation between the impact load and the water inlet angle, and the larger the water inlet angle, the greater the impact load; the residual strength factor of the slender body is positive at 15° and 20°, and the structure is safe, at 30°, the residual strength factor is -0.203, and the structure is unsafe.

FLUID–STRUCTURE COUPLING SIMULATION OF EXPLOSIVE FLOW FIELD IN HETEROGENEOUS POROUS MEDIA BASED ON FRACTAL THEORY

In this paper, through finite difference and finite element coupling algorithms with structured grid, the fluid–structure coupling problems of the pressure of the fluid as well as stress and strain of the heterogeneous porous medium under the initial pressure of MPa magnitude are calculated, respectively. The porous medium is a cavity cylinder with fractal characteristics. The parameters of porosity, elastic modulus and Poisson’s ratio of porous media with different fractal dimensions ([Formula: see text], 2.4 and 2.5) are obtained by theoretical calculation. Through theoretical derivation, the amplitude of WM function is expressed by the fractal parameter porosity, which can predict the uneven characteristics caused by the nonuniformity of pore size distribution after explosion. The results show that with the increase of fractal dimensions, the porosity increases, and both the elastic modulus and the Poisson’s ratio decrease. The Poisson’s ratio has a linear relationship with porosity, which is well consistent with the modified formula in the literature. Under the same initial pressure, the stress and strain values of the material without fractal characteristics are much larger than those of the material with fractal feature which has an obvious fluctuation by extracting the average values. It indicates that the fractal porous media with rough surface can effectively reduce the pressure wave peak at the wall surface, and reduce the size of the stress and strain concentrations to prevent the vibration of the cylinder. As expected, if the initial pressure increases with an equal fractal dimension, the stress and strain values of the fluid–structure coupling will increase too. When the initial pressure is equal, the peak value of pressure in wall decreases gradually with the increase of fractal dimension, and the stress and strain values also decrease.

A Scalable Moving Boundary Treatment in the Lattice Boltzmann Method

Based on the lattice Boltzmann Method (LBM), a new moving boundary treatment is proposed by studying the influence of the moving boundary in a low-speed incompressible fluid. Simulating flow past a static cylinder, flow past a moving cylinder, and flow in a curved moving pipe shows that the LBM has high reliability and stability with moving boundary conditions. In order to reduce parallel computing time and take full advantage of the characteristics of the model, the solid grids are allocated according to the number of computing cores. Two parallel speedup ratios were tested, keeping the overall task volume unchanged to increase the number of cores and keeping the single-core task volume unchanged. In the first speedup ratio, the efficiency of the flow field calculation at 112 cores reached more than 80%. The second speedup ratio indicated that the proportion of communication in the program was tiny and suitable for large-scale parallel computing. The study of the moving boundary problem can effectively help solve the fluid-structure coupling problem. Due to the particularity of the model, it can be used to simulate the fluid-structure coupling problem of blood vessel flow effectively.

1D/3D Finite-Volume coupling in conjunction with beam/shell elements coupling for fast transients in pipelines with fluid–structure interaction

A 1D/3D Finite-Volume coupling is proposed for the Euler/Homogeneous Equilibrium Model equations. The present approach is based on the Finite-Volume framework making it possible to tackle general equations of state. A special attention is given to the conservation of mass, momentum and energy at the common 1D/3D interface. For fluid–structure interaction induced by fast-transient phenomena occurring in pipelines, the present 1D/3D fluid coupling is also associated with a beam/shell elements coupling to deal with the mechanical pipe behavior. A series of test-cases involving both purely fluid, purely structural and coupled fluid–structure problems with available analytical or experimental references is considered to demonstrate the performance of the present 1D/3D coupling.

FEA design and analysis of flow sensor

In this research article a resonating tube was designed for Coriolis mass flow Sensor (CMFS) and sensor locations was varied. Resonant tube was designed to withstand maximum pressure with governing equations of coupled fluid structure problems. What is the result of sensor location on phase shift is the main goal of this research study. For omega type resonant tube from the base of vertical omega tube, the sensor locations have been varied from 60 mm to 120 mm in the present research article. CMFS is based on Coriolis Effect principle. For modelling of tube design, pro-E was used, and for analysis purpose Ansys 14.5 was used. Sensor locations and phase shift simulation results have been validated with experimental results. With the help of experimental results validation of sensor locations and phase shift simulations has been done. Omega type test configuration having L = 300 and D = 400 mm was used for experimentation for tube materials. The maximum values of phase shift was observed around 120 mm sensor location for 0.1 and 0.2 kg/s mass flow rate. It was observed from result that phase shift values are linearly varying with all range of mass flow rates. The resonant frequency is 24 Hz obtained from modal analysis for copper omega resonating tube.

Experimental study of cavity evolution and deformation during water entering into hyperelastic sphere

Hyperelastic materials, which have strong nonlinear mechanical properties, are commonly used in the engineering field. The application of hyperelastic materials to the water entry problem is a new interdisciplinary research topic. Unlike the water entering into a traditional rigid sphere, the hyperelastic sphere is very easy to deform during water entry. In order to explore the fluid-structure coupling problem with large deformations during water entry, a high-speed camera is used to study the problem of vertical water entering into hyperelastic sphere in this paper. Based on the experimental results, the effects of the material properties and impacting conditions on the cavity flow and sphere deformation behaviors during water entry are compared and analyzed. The experimental results show that the formation of the nested cavity after impacting a free surface of the hyperelastic sphere needs large enough impact conditions and small material shear modulus. The time for the nested cavity to be formed and retained during water entry is related to the material shear modulus and sphere diameter. The sphere displacement and length of cavity formed by the hyperelastic sphere increase with the increase of the impact velocity and material shear modulus, but decrease with the increase of the diameter of the sphere. The increase of the impacting velocity can only aggravate the deformation behaviors of the hyperelastic sphere, but does not affect the formation moment of the nested cavity. In addition, the characteristics for the deformation behaviors of the hyperelastic sphere to vary with the Froude number and the dimensionless ratio of material shear modulus to impacting hydrodynamic pressure are described and studied.

A revised numerical model for parachute inflation based on ALE method

The parachute inflation process is a typical time-varying, non-linear and fluid-structure coupling problem, especially inairdrop condition. For its complexity, numerical model of the inflation process is a big challenge, and most of the modelsestablished before still have room for improvement. There were two common problems that the first one was ignoranceof inertia force of canopy and line, and the second was that took stretch speed as the initial airdrop speed in modelling.Thus, a modified finite element model for canopy inflation process based on ALE (Arbitrary Lagrange Euler) method wasestablished that the inertia force of canopy and line was taken into consideration and the initial airdrop speed wasestimated and adjusted. The opening load in finite mass situation during deployment-inflation process of C-9 typeparachute was calculated. The result was compared to experimental data and calculated data of unmodified models. Itwas indicated that the opening load and peak time of modified model was the closest to experiment and the snatch loadwas also calculated and confirmed, so that the correctness and rationality of the model was verified. Then the factorinfluence of inertia force and initial airdrop speed was analysed, which provided a reference for parachute numericalmodelling.

A revised numerical model for parachute inflation based on ALE method

The parachute inflation process is a typical time-varying, non-linear and fluid-structure coupling problem, especially inairdrop condition. For its complexity, numerical model of the inflation process is a big challenge, and most of the modelsestablished before still have room for improvement. There were two common problems that the first one was ignoranceof inertia force of canopy and line, and the second was that took stretch speed as the initial airdrop speed in modelling.Thus, a modified finite element model for canopy inflation process based on ALE (Arbitrary Lagrange Euler) method wasestablished that the inertia force of canopy and line was taken into consideration and the initial airdrop speed wasestimated and adjusted. The opening load in finite mass situation during deployment-inflation process of C-9 typeparachute was calculated. The result was compared to experimental data and calculated data of unmodified models. Itwas indicated that the opening load and peak time of modified model was the closest to experiment and the snatch loadwas also calculated and confirmed, so that the correctness and rationality of the model was verified. Then the factorinfluence of inertia force and initial airdrop speed was analysed, which provided a reference for parachute numericalmodelling.

A GPU-accelerated fluid–structure-interaction solver developed by coupling finite element and lattice Boltzmann methods

This study focuses on finding high-performance numerical solutions to fluid–structure coupling problems encountered in biomechanical engineering. A numerical framework for simulating fluid–structure interaction (FSI) is proposed by strongly coupling the finite element and lattice Boltzmann methods. The lattice Boltzmann method is efficient for solving weakly compressible fluid flows. The explicit finite element method (FEM) is used to solve solid structure deformation. A partitioned iterative solution is adopted to couple these two methods together. A fixed point iteration method is used with the Aitken dynamic relaxation algorithm to improve numerical stability. A multi-direct forcing immersed boundary method with a sub-iteration scheme is adopted to represent the interaction between fluid and structure. Validation of the proposed coupling method was conducted on a vortex induced vibration problem. The numerical results are in good agreement with the reference results (Li and Favier, 2017). The proposed method does not have to solve large systems of linear equations, so it is suited to parallel computation. Therefore, we then present a parallel implementation of our method on a graphics processing unit, which increases the computation speed more than 18-fold. Our developed FSI solver is very efficient, which makes it possible to provide more accurate results with finer meshes. Finally, our method is applied to the simulation of complicated motions of a bileaflet heart valve caused by blood flow.

Two-phase SPH model based on an improved Riemann solver for water entry problems

There are challenges in simulating two-phase flows with large density ratios using traditional SPH. Taking full advantages of Riemann solver in dealing with contact discontinuity problems and combining two-phase flow SPH method with Riemann solver, a new model of two-phase flow coupling with structure based on an improved Riemann solver is described for the water entry problems with the effect of air. The flow momentum equation of the Riemann form is improved to decrease the Riemann dissipation and simulate the two-phase flows with different viscosity ratios. One-sided Riemann problem considering the free-slip and no-slip conditions at a wall is used to deal with the fluid-body interaction. A switch-function-based Riemann solver dissipation is used to improve the instability of interface owing to the strong impact. In order to test the accuracy of the model in fluid-structure coupling problems, five cases, including dam break, sinking of a rectangle body, water entry of a wedge, flat plate slamming on water and water entry of a catamaran, are numerically simulated. The agreements between the present results and other reference results demonstrate that the proposed method is robust and stable to simulate the water entry problems with the air.

Numerical simulation of entropy generation due to natural convection heat transfer using Kernel Derivative-Free (KDF) Incompressible Smoothed Particle Hydrodynamics (ISPH) model

This paper develops and applies a Kernel Derivative-Free (KDF) Incompressible Smoothed Particle Hydrodynamics (ISPH) model for analysis of entropy generation and heat transfer in fluid-structure coupling problems. A modified high order Laplacian operator is applied for the treatment of pressure-velocity coupling (Poisson's equation), while an explicit third-order TVD Runge-Kutta scheme is used for time integration of the momentum, energy and displacement equations. To improve the consistency and stability of the model, a new particle regularization technique based on the particle shifting is also introduced for simulating free-surface flows. The developed KDF-ISPH model is validated and evaluated for a series of challenging benchmark cases, including, dam break, stretching water drop, rotating square patch of fluid, and natural convection in square cavity. Accuracy and applicability of the method are further validated by analyzing entropy generation due to the natural convection heat transfer in three well-known geometries including: square cavity with hot obstacle inside, C-shaped enclosure, and square enclosure containing a pair of hot and cold horizontal pipes (heat exchanger). The results are found to be in good agreement with available numerical and experimental data. The accuracy of the developed KDF-ISPH with new Laplacian operator, for use in prediction of fluid flow and heat transfer characteristics is also proven. Finally, by combining the cosine and signal functions, a new high order smoothing kernel is constructed. The evaluation of this new kernel for the propagation of shock wave in 1D tube demonstrates better global stability and consistency properties compared to two frequently used SPH kernels (i.e. cubic and quintic spline functions).

Linear stability analysis of strongly coupled fluid–structure problems with the Arbitrary-Lagrangian–Eulerian method

The stability analysis of elastic structures strongly coupled to incompressible viscous flows is investigated in this paper, based on a linearization of the governing equations formulated with the Arbitrary-Lagrangian–Eulerian method. The exact linearized formulation, previously derived to solve the unsteady non-linear equations with implicit temporal schemes, is used here to determine the physical linear stability of steady states. Once discretized with a standard finite-element method based on Lagrange elements, the leading eigenvalues/eigenmodes of the linearized operator are computed for three configurations representative for classical fluid–structure interaction instabilities: the vortex-induced vibrations of an elastic plate clamped to the rear of a rigid cylinder, the flutter instability of a flag immersed in a channel flow and the vortex shedding behind a three-dimensional plate bent by the steady flow. The results are in good agreement with instability thresholds reported in the literature and obtained with time-marching simulations, at a much lower computational cost. To further decrease this computational cost, the equations governing the solid perturbations are projected onto a reduced basis of free-vibration modes. This projection allows to eliminate the extension perturbation, a non-physical variable introduced in the ALE formalism to propagate the infinitesimal displacement of the fluid–solid interface into the fluid domain.

Shock response of electrostatically coupled microbeams under the squeeze-film damping effect

This paper presents a theoretical investigation of the dynamic response of electrostatically coupled microcantilever beams under the combined effect of squeeze-film damping and mechanical shock for MEMS applications. We consider two different microsystem designs, namely single and dual beams, operating at varying conditions to explore their possible use based on the application of interest. The single-beam system is actuated via a fixed electrode (uncoupled actuation), while the electric actuation of the dual-beam system, comprising two movable microbeams, is achieved by applying a DC voltage among them (coupled actuation). We develop a multi-physics model to simulate the dynamic response of single and dual microbeams while accounting for the fringing field effect, the squeeze-film damping resulting from the interactions between the vibrating microbeams and the surrounding fluid, and the mechanical shock. The squeeze-film damping is incorporated using a nonlinear analytical expression rather than solving the fully coupled fluid–structure problem. Numerous studies have shown the validity of this analytical approach under the assumption of long beams and neglecting the fluid compressibility. Some benchmark cases are considered to verify the predictive capability of the numerical model. The simulation results are in good qualitative and quantitative agreements with those reported in the literature. A parametric study is then conducted to investigate the effects of the initial gap distance, the fluid viscosity, and the beam geometry on the shock response of the microsystem. The squeeze-film damping enables the protection of the vibrating microbeams from hitting the substrate under mechanical shock and can be exploited to enhance the reliability of MEMS devices. However, this protection can be significantly reduced by increasing the gap distance or decreasing the operating pressure. The numerical study shows that the dual-beam systems withstand better to a mechanical shock. Breaking the symmetry of the dual-beam system in terms of the beams’ geometry is found to reduce significantly the resistance to shocks. On the other hand, given their high sensitivity to a mechanical shock, single-beam systems are observed to be more attractive for deployment as microswitches.