Parallelization strategies for resolved simulations of fluid-structure-particle interactions

Fluid-structure-particle interactions in three spatial dimensions happen in many environmental and engineering flows.This paper presents the parallel algorithms for the hybrid diffuse and sharp interface immersed boundary(IB)method developed in our previous work.For the moving structure modeled using the sharp interface IB method,a recursive box method is developed for efficiently classifying the background grid nodes.For the particles modeled using the diffuse interface IB method,a‘master-slave’approach is adopted.For the particle-particle interaction(PPI)and particle-structure interaction(PSI),a fast algorithm for classifying the active and inactive Lagrangian points,which discretize the particle surface,is developed for the‘dry’contact approach.The results show that the proposed recursive box method can reduce the classifying time from 52seconds to 0.3 seconds.Acceptable parallel efficiency is obtained for cases with different particle concentrations.Furthermore,the lubrication model is utilized when a particle approaches a wall,enabling an accurate simulation of the rebounding phenomena in the benchmark particle-wall collision problem.At last,the capability of the proposed computational framework is demonstrated by simulating particle-laden turbulent channel flows with rough walls.

Numerical Simulation of Aerodynamic Interaction Effects in Coaxial Compound Helicopters

The so-called coaxial compound helicopter features two rigid coaxial rotors,and possesses high-speed capabilities.Nevertheless,the small separation of the coaxial rotors causes severe aerodynamic interactions,which require careful analysis.In the present work,the aerodynamic interaction between the various helicopter components is investigated by means of a numerical method considering both hover and forward flight conditions.While a sliding mesh method is used to deal with the rotating coaxial rotors,the Reynolds-Averaged Navier-Stokes(RANS)equations are solved for the flow field.The Caradonna&Tung(CT)rotor and Harrington-2 coaxial rotor are considered to validate the numerical method.The results show that the aerodynamic interaction of the two rigid coaxial rotors significantly influences hover’s induced velocity and pressure distribution.In addition,the average thrust of an isolated coaxial rotor is smaller than that of the corresponding isolated single rotor.Compared with the isolated coaxial rotor,the existence of the fuselage results in an increment in the thrust of the rotors.Furthermore,these interactions between the components of the considered coaxial compound helicopter decay with an increase in the advance ratio.

Numerical simulation of soft palate movement and airflow in human upper airway by fluid-structure interaction method

In this paper, the authors present airflow field characteristics of human upper airway and soft palate movement attitude during breathing. On the basis of the data taken from the spiral computerized tomography images of a healthy person and a patient with Obstructive Sleep Apnea-Hypopnea Syndrome （OSAHS）, three-dimensional models of upper airway cavity and soft palate are reconstructed by the method of surface rendering. Numerical simulation is performed for airflow in the upper airway and displacement of soft palate by fluid-structure interaction analysis. The reconstructed threedimensional models precisely preserve the original configuration of upper airways and soft palate. The results of the pressure and velocity distributions in the airflow field are quantitatively determined, and the displacement of soft palate is presented. Pressure gradients of airway are lower for the healthy person and the airflow distribution is quite uniform in the case of free breathing. However, the OSAHS patient remarkably escalates both the pressure and velocity in the upper airway, and causes higher displacement of the soft palate. The present study is useful in revealing pathogenesis and quantitative mutual relationship between configuration and function of the upper airway as well as in diagnosingdiseases related to anatomical structure and function of the upper airway.

Simulation of Underground Reservoir Stability of Pumped Storage Power Station Based on Fluid-Structure Coupling

Based on global initiatives such as the clean energy transition and the development of renewable energy,the pumped storage power station has become a new and significant way of energy storage and regulation,and its construction environment is more complex than that of a traditional reservoir.In particular,the stability of the rock strata in the underground reservoirs is affected by the seepage pressure and rock stress,which presents some challenges in achieving engineering safety and stability.Using the advantages of the numerical simulation method in dealing deal with nonlinear problems in engineering stability,in this study,the stability of the underground reservoir of the Shidangshan(SDS)pumped storage power station was numerically calculated and quantitatively analyzed based on fluid-structure coupling theory,providing an important reference for the safe operation and management of the underground reservoir.First,using the COMSOL software,a suitablemechanicalmodel was created in accordance with the geological structure and project characteristics of the underground reservoir.Next,the characteristics of the stress field,displacement field,and seepage field after excavation of the underground reservoir were simulated in light of the seepage effect of groundwater on the nearby rock of the underground reservoir.Finally,based on the construction specifications and Molar-Coulomb criterion,a thorough evaluation of the stability of the underground reservoir was performed through simulation of the filling and discharge conditions and anti-seepage strengthening measures.The findings demonstrate that the numerical simulation results have a certain level of reliability and are in accordance with the stress measured in the project area.The underground reservoir excavation resulted in a maximum displacement value of the rock mass around the caverns of 3.56 mm in a typical section,and the safety coefficient of the parts,as determined using the Molar-Coulomb criterion,was higher than 1,indicating that the project as a whole is in a stable state.

Numerical Simulation of the Slit-Trap Dam Based on Fluid-Structure Interaction

Debris flow can cause serious damage,and it is a part of the study of fluid-structure interaction(FSI).FSI analysis was established on the interaction between unsteady flow and the slit-trap dam's vibration,with a coupling bench which can transfer fluid pressure and structure displacement.Debris flow can be seen as the Bingham body of incompressible.Based on ANSYS and CFX softwares,unidirectional and bidirectional coupling methods were used to study the transient interaction between debris flow and dam.The comparison between lateral fluid pressure states under different velocities and the equivalent stresses of the dam under different coupling conditions was made.The result shows that fluid-structure coupling becomes stronger with the increase of flow velocity.The maximum equivalent stress appears at the dam foundation,while the minimum equivalent stress appears at the dam abutment.With the increase of height,the fluid pressure decreases.The fluid pressure based on unidirectional FSI analysis is larger than that based on bidirectional FSI analysis and the maximum appears on the joint of the dam foundation and channel.The maximum equivalent stress of the dam based on the former is less than that based on the latter.

Numerical Simulation of Two-Dimensional Shock/Boundary-Layer Interaction between a Rocket and Booster

A two-dimensional Reynolds-averaged Navier-Stokes solver is applied to analyze the aerodynamic behavior of the Shock/Boundary-Layer interaction of rocket with a boosted The K-ε turbulence model and a finite volume method in a unstructured body-fitted curvilinear coordinates have been used. The results indicate that the separation and the reattachment occur in the Boundary-Layer of the main rocket because of the shock interaction. The shape of the booster nose effects the flow field obviously. In the case of the hemisphere booster nose the pressure has complicate distributions and the separation is very clear. The distance between the booster and main rocket has the evident effect on the flow field. If the distance is smaller the pressure coefficient is bigger the separation zone even the separation bubble occurs.

Numerical Simulation of Interaction Between Laminar Flow and Elastic Sheet

A numerical simulation of the interaction between laminar flow with low Reynolds number and a highly flexible elastic sheet is presented. The mathematical model for the simulation includes a three-dimensional finitevolume based fluid solver for incompressible viscous flow and a combined finite-discrete element method for the three-dimensional deformation of solid. An immersed boundary method is used to couple the simulation of fluid and solid. It is implemented through a set of immersed boundary points scattered on the solid surface. These points provide a deformable solid wall boundary for the fluid by adding body force to Navier-Stokes equations. The force from the fluid is also obtained for each point and then applied on the boundary nodes of the solid. The vortex-induced vibration of the highly flexible elastic sheet is simulated with the established mathematical model. The simulated results for both swing pattern and oscillation frequency of the elastic sheet in low Reynolds number flow agree well with experimental data.

AN ANALYSIS OF SUBGRID-RESOLVED SCALE INTERACTIONS WITH USE OF RESULTS FROM DIRECT NUMERICAL SIMULATIONS

Subgrid nonlinear interaction and energy transfer are analyzed using direct numerical simulations of isotropic turbulence. Influences of cutoff wave number at different ranges of scale on the energetics and dynamics have been investigated. It is observed that subgrid-subgrid interaction dominates the turbulent dynamics when cut-off wave number locates in the energy-containing range while resolved-subgrid interaction dominates if it is in the dissipation range. By decomposing the subgrid energy transfer and nonlinear interaction into ‘forward’ and ‘backward’ groups according to the sign of triadic interaction, we find that individually each group has very large contribution, but the net of them is much smaller, implying that tremendous cancellation happens between these two groups.

DYNAMIC SIMULATION OF FLUID-STRUCTURE INTERACTION PROBLEMS INVOLVING LARGE-AMPLITUDE SLOSHING

An effective computational method is developed for dynamic analysis offluid-structure interaction problems involving large-amplitude sloshing of the fluid andlarge-displacement motion of the structure. The structure is modeled as a rigid container supportedby a system consisting of springs and dashpots. The motion of the fluid is decomposed into twoparts: the large-displacement motion with the container and the large-amplitude sloshing relative tothe container. The former is conveniently dealt with by defining a container-fixed noninertiallocal frame, while the latter is easily handled by adopting an ALE kinematical description. Thisleads to an easy and accurate treatment of both the fluid-structure interface and the fluid freesurface without producing excessive distortion of the computational mesh. The coupling between thefluid and the structure is accomplished through the coupling matrices that can be easilyestablished. Two numerical examples, including a TLD-structure system and a simplified liquid-loadedvehicle system, are presented to demonstrate the effectiveness and reliability of the proposedmethod. The present work can also be applied to simulate fluid-structure problems incorporatingmultibody systems and several fluid domains.

Experiment and numerical simulation on the characteristics of fluid–structure interactions of non-rigid airships

Fluid-structure interaction is an important issue for non-rigid airships with inflated envelopes. In this study, a wind tunnel test is conducted, and a loosely coupled procedure is correspondingly established for numerical simulation based on computational fluid dynamics and nonlinear finite element analysis methods. The typical results of the numerical simulation and wind tunnel experiment, including the overall lift and deformation, are in good agreement with each other. The results obtained indicate that the effect of fluid-structure interaction is noticeable and should be considered for non-rigid airships. Flow- induced deformation can further intensify the upward lift force and pitching moment, which can lead to a large deformation. Under a wind speed of 15 m/s, the lift force of the non-rigid model is increased to approximatelv 60% compared with that of the rigid model under a high angle of attack.

TWO-DIMENSIONAL NONLINEAR DYNAMIC SYSTEM MODEL OF INTERSPECIFIC INTERACTION AND NUMERICAL SIMULATION RESEARCH ON IT

The mechanism and the course of two_dimensional nonlinear dynamic system of interspecific interaction were dealt with systematically. By extending the Lotka_Volterra model from the viewpoint of biomechanics, it developed new models of two_dimensional nonlinear autonomous and nonautonomous dynamic systems, with its equilibrium point's stability and the existence and stability of its periodical solutions analyzed, and did numerical simulation experiments on its dynamics course. The results show that efficiency of interaction between two populations, time_varying effort, and change direction of action coefficient and reaction coefficient have important influences on the stability of dynamic system, that too large or too small interspecific interaction efficiency and contrary change direction of action coefficient and reaction coefficient may result in the nonstability of the system, and thus it is difficult for two populations to coexist, and that time_varying active force contributes to system stability.

A Fluid-Structure Interaction Simulation of Coal and Gas Outbursts Based on the Interaction between the Gas Pressure and Deformation of a Coal-Rock Mass

Based on the theories of the gas seepage in coal seams and the deformation of the coal-rock medium,the gas seepage field in coal-rock mass is coupled with the deformation field of the coal-rock mass to establish a fluidstructure interaction model for the interaction between coal gas and coal-rock masses.The outburst process in coal-rock masses under the joint action of gas pressure and crustal stress is simulated using the material point method.The simulation results show the changes in gas pressure,velocity distribution,maximum principal stress distribution,and damage distribution during the process of the coal and gas outburst,as well as themovement and accumulation of coal-rock masses after the occurrence of the outburst.It was found that the gas pressure gradient was greatest at theworking face after the occurrence of the outburst,the gas pressures and pressure gradients at each location within the coal seamgradually decreased with time,and the damage distribution was essentially the same as the minimum principal stress distribution.The simulation further revealed that the outburst first occurred in themiddle of the tunnel excavation face and that the speed at which particles of coal mass were ejected was highest at the center and decreased toward the upper and lower sides.The study provides a scientific basis for enhancing our understanding of the mechanism behind coal and gas outbursts,as well as their prevention and control.

Numerical Simulation of Lateral Jet Interaction

Jet interaction effects on aerodynamic characteristics of aircraft in subsonic/transonic compressible crossflow are investigated numerically. The high reliable CFD method is established and compared with existing experimental results. The lateral jet interaction characteristics of lateral jet in subsonic/ transonic compressible crossflow on an ogive-cylinder configuration are simulated numerically. Variation characteristics of normal force amplification factor, pitching moment and amplification factor are analyzed and compared with the results at supersonic condition. Research results and some useful conclusions can be provided for the design of RCS aircraft control system as basis and reference in subsonic/transonic compressible crossflow.

Numerical Simulation of Shock Bubble Interaction with Different Mach Numbers

The interaction of a shock wave with a spherical helium bubble is investigated numerically by using the high- resolution piecewise parabolic method （PPM）, in which the viscous and turbulence effects are both considered. The bubble is of the same size and is accelerated by a planar shock of different Mach numbers （Ma）. The re- suits of low Ma cases agree quantitatively with those of experiments [G. Layes, O. Le M4tayer. Phys. Fluids 19 （2007） 042105]. With the increase of Ma, the final geometry of the bubble becomes quite different, the com- pression ratio is highly raised, and the time-dependent mean bubble velocity is also influenced. The compression ratios measured can be well normalized when Ma is low, while less agreement has been achieved for high Ma cases. In addition, the mixedness between two fluids is enhanced greatly as Ma increases. Some existed scaling laws of these quantities for the shock wave strength cannot be directly applied to high Ma cases.

Numerical Simulation Study of Vibration Characteristics of Cantilever Traffic Signal Support Structure under Wind Environment

Computational fluid dynamics(CFD)and the finite element method(FEM)are used to investigate the wind-driven dynamic response of cantilever traffic signal support structures as a whole.By building a finite element model with the same scale as the actual structure and performing modal analysis,a preliminary understanding of the dynamic properties of the structure is obtained.Based on the two-way fluid-structure coupling calculation method,the wind vibration response of the structure under different incoming flow conditions is calculated,and the vibration characteristics of the structure are analyzed through the displacement time course data of the structure in the crosswind direction and along-wind direction.The results show that the maximum response of the structure increases gradually with the increase of wind speed under 90°wind direction angle,showing a vibration dispersion state,and the vibration response characteristics are following the vibration phenomenon of galloping;under 270°wind direction angle,the maximum displacement response of the structure occurs at the lower wind speed of 5 and 6m/s,and the vibration generated by the structure is vortex vibration at this time;the displacement response of the structure in along-wind direction increaseswith the increase of wind speed.The along-wind displacement response of the structure will increase with increasing wind speed,and the effective wind area and shape characteristics of the structurewill also affect the vibration response of the structure.

Analysis of the Influence of the Blade Deformation on Wind Turbine Output Power in the Framework of a Bidirectional Fluid-Structure Interaction Model

The blades of large-scale wind turbines can obviously deform during operation,and such a deformation can affect the wind turbine’s output power to a certain extent.In order to shed some light on this phenomenon,for which limited information is available in the literature,a bidirectional fluid-structure interaction(FSI)numerical model is employed in this work.In particular,a 5 MW large-scale wind turbine designed by the National Renewable Energy Laboratory(NREL)of the United States is considered as a testbed.The research results show that blades’deformation can increase the wind turbine’s output power by 135 kW at rated working conditions.Compared with the outcomes of the simulations conducted using the model with no blade deformation,the results obtained with the FSI model are closer to the experimental data.It is concluded that the bidirectional FSI model can replicate the working conditions of wind turbines with great fidelity,thereby providing an effective method for wind turbine design and optimization.

A NUMERICAL METHOD FOR SIMULATING NONLINEAR FLUID-RIGID STRUCTURE INTERACTION PROBLEMS

A numerical method for simulating nonlinear fluid-rigid structure interaction problems is developed. The structure is assumed to undergo large rigid body motions and the fluid flow is governed by nonlinear, viscous or non-viscous, field equations with nonlinear boundary conditions applied to the free surface and fluid-solid interaction interfaces. An Arbitrary-LagrangianEulerian (ALE) mesh system is used to construct the numerical model. A multi-block numerical scheme of study is adopted allowing for the relative motion between moving overset grids, which are independent of one another. This provides a convenient method to overcome the difficulties in matching fluid meshes with large solid motions. Nonlinear numerical equations describing nonlinear fluid-solid interaction dynamics are derived through a numerical discretization scheme of study. A coupling iteration process is used to solve these numerical equations. Numerical examples are presented to demonstrate applications of the model developed.

A hybrid contact approach for modeling soil-structure interaction using the material point method

The grid-based multi-velocity field technique has become increasingly popular for simulating the Material Point Method(MPM)in contact problems.However,this traditional technique has some shortcomings,such as(1)early contact and contact penetration can occur when the contact conditions are unsuitable,and(2)the method is not available for contact problems involving rigid-nonrigid materials,which can cause numerical instability.This study presents a new hybrid contact approach for the MPM to address these limitations to simulate the soil and structure interactions.The approach combines the advantages of point-point and point-segment contacts to implement contact detection,satisfying the impenetrability condition and smoothing the corner contact problem.The proposed approach is first validated through a disk test on an inclined slope.Then,several typical cases,such as granular collapse,bearing capacity,and deformation of a flexible retaining wall,are simulated to demonstrate the robustness of the proposed approach compared with FEM or analytical solutions.Finally,the proposed method is used to simulate the impact of sand flow on a deformable structure.The results show that the proposed contact approach can well describe the phenomenon of soil-structure interaction problems.

Direct numerical simulation of shock wave/boundary layer interaction controlled by steady microjet in a compression ramp

Shock wave/boundary layer interaction in a 24°turning angle of the compression ramp at Mach number 2.9 controlled by steady microjet is investigated using direct numerical simulation.Three different jet spacings which are termed as sparse,moderate and dense are considered,and the induced vortex system and shock structures are compared.A moderate jet spacing configuration is found to generate counter-rotating vortex pairs that transport high-momentum fluid towards the vicinity of wall and strengthen the boundary layer to resist separation,reducing the separation region.The dense jet spacing configuration creates a larger momentum deficit region,reducing the friction downstream of the corner.Analysis of pressure and pressure gradient reveals that dense jet spacing configuration reduces the intensity of separation shock.The impact of varying jet spacings on the turbulent kinetic energy transport mechanism is also investigated by decomposing the budget terms in the transport equation.Furthermore,the spectral characteristics of the separation region are studied using power spectral density and dynamic mode decomposition methods,revealing that moderate jet spacing configuration suppresses low-frequency fluctuations in the separation region.

Full Dynamic Model for Liquid Sloshing Simulation in Cylindrical Tank Shape

This study presents a comprehensive full dynamic model designed for simulating liquid sloshing behavior within cylindrical tank structures. The model employs a discretization approach, representing the liquid as a network of interconnected spring-damper-mass systems. Key aspects include the adaptation of liquid discretization techniques to cylindrical lateral cross-sections and the calculation of stiffness and damping coefficients. External forces, simulating various vehicle maneuvers, are also integrated into the model. The resulting system of equations is solved using Maple Software with the Runge-Kutta-Fehlberg method. This model enables accurate prediction of liquid displacement and pressure forces, offering valuable insights for tank design and fluid dynamics applications. Ongoing refinement aims to broaden its applicability across different liquid types and tank geometries.