Numerical Investigation on Fluid Structure Interaction Considering Rotor Deformation for a Centrifugal Pump

The existing research for unsteady flow field and the corresponding flow induced vibration analysis of centrifugal pump are mainly carried out respectively without considering the interaction between fluid and structure. The ignorance of fluid structure interaction （FSI） means that the energy transfer between fluid and structure is neglected. To some extent, the accuracy and reliability of unsteady flow and rotor deflection analysis should be affected by this interaction mechanism. In this paper, a combined calculation between two executables for turbulent flow and vibrating structure was established using two-way coupling method to study the effect of FSI. Pressure distributions, radial forces, rotor deflection and equivalent stress are analyzed. The results show that the FSI effect to pressure distribution in flow field is complex. The pressure distribution is affected not only around impeller outlet where different variation trends of pressure values with and without FSI appear according to different relative positions between blade and cutwater, but also in the diffusion section of volute. Variation trends of peak values of radial force amplitude calculated with and without FSI are nearly same under high flow rate and designed conditions while the peak value with FSI is slightly smaller, and differently, the peak value with FSI is larger with low flow rate. In addition, the effect of FSI on the angle of radial force is quite complex, especially under 0.5Q condition. Fluctuation of radial deflection of the rotor has obvious four periods, of which the extent is relatively small under design condition and is relatively large under off-design condition. Finally, fluctuations of equivalent stress with time are obvious under different conditions, and stress value is small. The proposed research establishes the FSI calculation method for centrifugal pump analysis, and ensures the existing affect by fluid structure interaction.

Resonance mechanism of flapping wing based on fluid structure interaction simulation

Certain insect species have been observed to exploit the resonance mechanism of their wings.In order to achieve resonance and optimize aerodynamic performance,the conventional approach is to set the flapping frequency of flexible wings based on the Traditional Structural Modal(TSM)analysis.However,there exists controversy among researchers regarding the relationship between frequency and aerodynamic performance.Recognizing that the structural response of wings can be influenced by the surrounding air vibrations,an analysis known as Acoustic Structure Interaction Modal(ASIM)is introduced to calculate the resonant frequency.In this study,Fluid Structure Interaction(FSI)simulations are employed to investigate the aerodynamic performance of flapping wings at modal frequencies derived from both TSM and ASIM analyses.The performance is evaluated for various mass ratios and frequency ratios,and the findings indicate that the deformation and changes in vortex structure exhibit similarities at mass ratios that yield the highest aerodynamic performance.Notably,the flapping frequency associated with the maximum time-averaged vertical force coefficient at each mass ratio closely aligns with the ASIM frequency,as does the frequency corresponding to maximum efficiency.Thus,the ASIM analysis can provide an effective means for predicting the optimal flapping frequency for flexible wings.Furthermore,it enables the prediction that flexible wings with varying mass ratios will exhibit similar deformation and vortex structure changes.This paper offers a fresh perspective on the ongoing debate concerning the resonance mechanism of Flexible Flapping Wings(FFWs)and proposes an effective methodology for predicting their aerodynamic performance.

Fluid structure interaction of supersonic parachute with material failure

The material damage of parachute may occur in parachutes at high speeds,and the growth of tearing may finally lead to failure of aerospace mission.In order to study the damage mechanism of parachute,a material failure model is proposed to simulate the failure of canopy fabric.The inflation process of supersonic parachute is studied numerically based on Arbitrary Lagrange Euler(ALE)method.The ALE method with material failure can predict the transient parachute shape with damage propagation as well as the flow characteristics in the parachute inflation process,and the simulated dynamic opening load is consistent with the flight test.The damage propagation mechanism of parachute is then investigated,and the effect of parachute velocity on the damage process is discussed.The results show that the canopy tears apart by the fast flow from the initial damaged area and the damaged canopy shape leads to the asymmetric change of the flow structure.With the increase of Mach number,the canopy tearing speed increases,and the tearing directions become uncertain at high Mach numbers.The dynamic load when damage occurs increases with the Mach number,and is proportional to the dynamic pressure above the critical Mach number.

Dynamic Analysis of Tension Leg Platform for Offshore Wind Turbine Support as Fluid-Structure Interaction

Tension leg platform （TLP） for offshore wind turbine support is a new type structure in wind energy utilization. The strong-interaction method is used in analyzing the coupled model, and the dynamic characteristics of the TLP for offshore wind turbine support are recognized. As shown by the calculated results： for the lower modes, the shapes are water＇s vibration, and the vibration of water induces the structure＇s swing; the mode shapes of the structure are complex, and can largely change among different members; the mode shapes of the platform are related to the tower＇s. The frequencies of the structure do not change much after adjusting the length of the tension cables and the depth of the platform; the TLP has good adaptability for the water depths and the environment loads. The change of the size and parameters of TLP can improve the dynamic characteristics, which can reduce the vibration of the TLP caused by the loads. Through the vibration analysis, the natural vibration frequencies of TLP can be distinguished from the frequencies of condition loads, and thus the resonance vibration can be avoided, therefore the offshore wind turbine can work normally in the complex conditions.

Fluid structure interaction simulation of supersonic parachute inflation by an interface tracking method

An Arbitrary Lagrangian-Eulerian(ALE)approach with interface tracking is developed in this paper to simulate the supersonic parachute inflation.A two-way interaction between a nonlinear finite element method and a finite volume method is accomplished.In order to apply this interface tracking method to problems with instantaneous large deformation and self-contact,a new virtual structure contact method is proposed to leave room for the body-fitted mesh between the contact structural surfaces.In addition,the breakpoint due to the fluid mesh with negative volume is losslessly restarted by the conservative interpolation method.Based on this method,fluid and structural dynamic behaviors of a highly folded disk-gap-band parachute are obtained.Numerical results such as maximum Root Mean Square(RMS)drag,general canopy shape and the smallest canopy projected areas in the terminal descent state are in accordance with the wind tunnel test results.This analysis reveals the inflation law of the disk-gap-band parachute and provides a new numerical method for supersonic parachute design.

Hydro-elastic computational analysis of a marine propeller using two-way fluid structure interaction

Marine propellers have complex geometry and their performance is determined by costly and time consuming open water experiments.Use of numerical techniques helps researchers in effective design of propellers.Several approaches are used that predicted either hydrodynamic and acoustic response or structural response.Two-way fluid-structure interaction(FSI)analysis is a very useful approach providing all three responses which helps in the design,analysis and optimization of a propeller.The objective of this paper is to predict the hydro-elastic response of a propeller using two-way FSI on a 0.2m diameter,DTMB-4119 propeller using ANSYS software.Two-way FSI analysis is carried out using system coupling approach that transfers the data between the structural and fluid solvers.The turbulence effects are captured using the large-eddy simulation(LES)model and the Ffowcs Williams Hawkings(FWH)acoustic model is used for evaluating the sound pressure level(SPL)generated by propeller.Analysis is extended to evaluate the hydro-elastic and acoustic response of the propeller after validating the hydrodynamic performance with the experimental result in the literature.The results from Two-way FSI analysis are in close agreement when compared with the one-way FSI analysis.Two-way FSI can accommodate the peak value of stress and deformation developed during the initial part of the transient solution which is important in the design of propeller.This study reveals that metallic(NAB)propeller can be replaced by a composite propeller.The acoustic response from two-way FSI analysis will be more realistic due to the consideration of hydro-elastic effect of propeller.

The deformation characteristics and flow field around knotless polyethylene netting based on fluid structure interaction(FSI)one-way coupling

Knotless polyethylene(PE)netting is widely used in fisheries because of its excellent hydrodynamic performance and low cost.Netting deformation and the surrounding flow field distribution play an important role in determining the hydrodynamic characteristics of netting in moving water.In order to investigate the effect of solidity ratio and attack angle on drag,netting deformation,and flow field distribution through the netting,a fluid-structure interaction(FSI)model based on a one-way coupling combining the shear stress turbulent(SST)k-omega model and the large deformation nonlinear structural finite element model was evaluated.Our results showed the difference between the parallel and normal drag forces found in the present numerical model and experimental flume tank data were 9.17%and 11.58%,respectively.The mean relative error in the inclined hydrodynamic drag for different flow velocities and attack angles was 8.35%,6.69%,and 5.37%for the nettings 1,2,and 3,respectively.These results show that the present numerical simulation based on FSI one-way coupling can be used to examine hydrodynamic forces on netting.The flow simulation results show that there is a noticeable flow velocity decrease through the netting and a rather large velocity reduction region downstream from the netting for different attack angles.These results reveal the existence of turbulent flow due to the netting wake.It was found that the equivalent stress and total deformation increase as the flow velocity increases and solidity ratio decreases.

Fluid Structure Interaction Problems:the Necessity of a Well Posed,Stable and Accurate Formulation

We investigate problems of fluid structure interaction type and aim for a formulation that leads to a well posed problem and a stable numerical procedure.Our first objective is to investigate if the generally accepted formulations of the fluid structure interaction problem are the only possible ones.Our second objective is to derive a stable numerical coupling.To accomplish that we will use a weak coupling procedure and employ summation-by-parts operators and penalty terms.We compare the weak coupling with other common procedures.We also study the effect of high order accurate schemes.In multiple dimensions this is a formidable task and we start by investigating the simplest possible model problem available.As a flow model we use the linearized Euler equations in one dimension and as the structure model we consider a spring.

Fluid-Structure Interaction Analysis for Drug Transport in a Curved Stenotic Right Coronary Artery

A blockage of blood vessels resulting from thrombus or plaque deposit causes serious cardiovascular diseases. This study developed a computational model of blood flow and drug transport to investigate the effectiveness of drug delivery to the stenotic sites. A three-dimensional (3D) model of the curved stenotic right coronary artery (RCA) was reconstructed based on the clinical angiogram image. Then, blood flow and drug transport with the flexible RCA wall were simulated using the fluid structure interaction (FSI) analysis and compared with the rigid RCA wall. Results showed that the maximal total displacement and von Mises stress of the flexible RCA model are 2.14 mm and 92.06 kPa. In addition, the effective injecting time point for the best performance of drug delivery was found to be between 0 s and 0.15 s (i.e., the fluid acceleration region) for both rigid and flexible RCA models. However, there was no notable difference in the ratio of particle deposition to the stenotic areas between the rigid and flexible RCA models. This study will be significantly useful to the design of a drug delivery system for the treatment of the stenotic arteries by targeting drugs selectively to the stenotic sites.

Fluid−Structure Interaction of Two-Phase Flow Passing Through 90° Pipe Bend Under Slug Pattern Conditions

Numerical simulations of evolution characteristics of slug flow across a 90°pipe bend have been carried out to study the fluid−structure interaction response induced by internal slug flow.The two-phase flow patterns and turbulence were modelled by using the volume of fluid(VOF)model and the Realizable k−εturbulence model respectively.Firstly,validation of the CFD model was carried out and the desirable results were obtained.The different flow patterns and the time-average mean void fraction was coincident with the reported experimental data.Simulations of different cases of slug flow have been carried out to show the effects of superficial gas and liquid velocity on the evolution characteristics of slug flow.Then,a one-way coupled fluid-structure interaction framework was established to investigate the slug flow interaction with a 90°pipe bend under various superficial liquid and gas velocities.It was found that the maximum total deformation and equivalent stress increased with the increasing superficial gas velocity,while decreased with the increasing superficial liquid velocity.In addition,the total deformation and equivalent stress has obvious periodic fluctuation.Furthermore,the distribution position of maximum deformation and stress was related to the evolution of slug flow.With the increasing superficial gas velocity,the maximum total deformation was mainly located at the 90°pipe bend.But as the superficial liquid velocity increases,the maximum total deformation was mainly located in the horizontal pipe section.Consequently,the slug flow with higher superficial gas velocity will induce more serious cyclical impact on the 90°pipe bend.

Impact Dynamics of Supercavitating Projectile with Fluid/Structure Interaction

As supercavitating projectiles move at high speed, the periodic impacts ("tail-slap") on the interior surface of the cavity generally occur due to disturbances. The interactions between the projectile and the water/cavity interface are the sources of structural vibrations, which affect the guidance of the vehicle and undermine the structural reliability. The Fluid/Structure Interaction calculation procedure of the tail-slaps of supercavitating projectile is established, and the dynamic behaviours of the projectile operating in tail-slap conditions with and without considering Fluid/Structure Interaction are obtained and compared. The responses of the projectile riding a reducing cavity are studied, and the effect of Fluid/Structure Interaction is also analyzed. The results show that the angular velocity of projectile increases as the body slowing down, and the amplitude of the elastic displacement response decreases at the beginning and increases when the cavity size is close to the diameter of the tail of projectile. The effect of Fluid/Structure Interaction reduces the amplitudes and frequencies of the impact loads and the vibration responses of the body, and when the speed is higher, the effect is more apparent.

A transient fiuid–structure interaction analysis strategy and validation of a pressurized reactor with regard to loss-ofcoolant accidents

A loss-of-coolant accident(LOCA)is one of the basic design considerations for nuclear reactor safety analysis.A LOCA induces propagation of a depressurization wave in the coolant,exerting hydrodynamic forces on structures viafiuid–structure interaction(FSI).The analysis of hydrodynamic forces on the core structures during a LOCA process is indispensable.We describe the implementation of a numerical strategy for prestressed structures.It consists of an initialization and a restarted transient analysis process,all implemented via the ANSYS Workbench by system coupling of ANSYS and Fluent.Our strategy is validated by making extensive comparisons of the pressures,displacements,and strains on various locations between the simulation and reported measurements.The approach is appealing for dynamic analysis of other prestressed structures,owing to the good popularity and acknowledgement of ANSYS and Fluent in both academia and industry.

人工神经网络与遗传算法预测液体晃荡参数的比较

This paper develops a numerical code for modelling liquid sloshing.The coupled boundary element-finite element method was used to solve the Laplace equation for inviscid fluid and nonlinear free surface boundary conditions.Using Nakayama and Washizu’s results,the code performance was validated.Using the developed numerical mode,we proposed artificial neural network(ANN)and genetic algorithm(GA)methods for evaluating sloshing loads and comparing them.To compare the efficiency of the suggested methods,the maximum free surface displacement and the maximum horizontal force exerted on a rectangular tank’s perimeter are examined.It can be seen from the results that both ANNs and GAs can accurately predict η_(max) and F_(max).

Effect of coronary artery dynamics on the wall shear stress vector field topological skeleton in fluid–structure interaction analyses

In this paper,we investigate the impact of coronary artery dynamics on the wall shear stress(WSS)vector field topology by comparing fluid–structure interaction(FSI)and computational fluid dynamics(CFD)techniques.As one of the most common causes of death globally,coronary artery disease(CAD)is a significant economic burden;however,novel approaches are still needed to improve our ability to predict its progression.FSI can include the unique dynamical factors present in the coronary vasculature.To investigate the impact of these dynamical factors,we study an idealized artery model with sequential stenosis.The transient simulations made use of the hyperelastic artery and lipid constitutive equations,non‐Newtonian blood viscosity,and the characteristic out‐of‐phase pressure and velocity distribution of the left anterior descending coronary artery.We compare changes to established metrics of time‐averaged WSS(TAWSS)and the oscillatory shear index(OSI)to changes in the emerging WSS divergence,calculated here in a modified version to handle the deforming mesh of FSI simulations.Results suggest that the motion of the artery can impact downstream patterns in both divergence and OSI.WSS magnitude is also decreased by up to 57%due to motion in some regions.WSS divergence patterns varied most significantly between simulations over the systolic period,the time of the largest displacements.This investigation highlights that coronary dynamics could impact markers of potential CAD progression and warrants further detailed investigations in more diverse geometries and patient cases.

Dynamic Response Analysis of Interaction System of R.C. Gravity Single-Leg Platform

In this paper, the responses of the interaction system of R.C. gravity single-leg platform to seismic excitation are mainly analysed. A set of nonlinear equations for the interaction system are established by using the wave, one is the soil-structure interaction and the other is the fluid-structure interaction. The seismic response of the interaction system is analysed for the influence of the asymmetric structure, fluid action, etc. with the input of seismic SH waves in any direction. The numerical results are given for a simple example.

SECOND ORDER STEADY DRIFT FORCES ON OFFSHORE STRUCTURES

In this paper, the second order steady drift forces on the ships and other floating offshore structures are calculated by the far field method. The amplitudes of diffracted waves and radiated waves at infinity are obtained by the two-dimensional source distribution and strip-theory method. For the twin hull structure, the hydrodynamic interaction between the two hulls is taken into account. The drift forces on cross sections of Lewis type as well as on the semi-submersibles are computed. The theoretical results obtained by the present method agree fairly well with experimental results.

Towards development of enhanced fully-Lagrangian mesh-free computational methods for fluid-structure interaction

Simulation of incompressible fluid flow-elastic structure interactions is targeted by using fully-Lagrangian mesh-free computational methods. A projection-based fluid model（moving particle semi-implicit（MPS）） is coupled with either a Newtonian or a Hamiltonian Lagrangian structure model（MPS or HMPS） in a mathematically-physically consistent manner. The fluid model is founded on the solution of Navier-Stokes and continuity equations. The structure models are configured either in the framework of Newtonian mechanics on the basis of conservation of linear and angular momenta, or Hamiltonian mechanics on the basis of variational principle for incompressible elastodynamics. A set of enhanced schemes are incorporated for projection-based fluid model（Enhanced MPS）, thus, the developed coupled solvers for fluid structure interaction（FSI） are referred to as Enhanced MPS-MPS and Enhanced MPS-HMPS. Besides, two smoothed particle hydrodynamics（SPH）-based FSI solvers, being developed by the authors, are considered and their potential applicability and comparable performance are briefly discussed in comparison with MPS-based FSI solvers. The SPH-based FSI solvers are established through coupling of projection-based incompressible SPH（ISPH） fluid model and SPH-based Newtonian/Hamiltonian structure models, leading to Enhanced ISPH-SPH and Enhanced ISPH-HSPH. A comparative study is carried out on the performances of the FSI solvers through a set of benchmark tests, including hydrostatic water column on an elastic plate,high speed impact of an elastic aluminum beam, hydroelastic slamming of a marine panel and dam break with elastic gate.

Hydrodynamic modeling of cochlea and numerical simulation for cochlear traveling wave with consideration of fluid-structure interaction

The cochlea is an important structure in the hearing system of humanity. Its unique structure enables the sensibility to the sound waves of varied frequencies. The widely accepted model of the cochlea is expressed as a long tube longitudinally divided by a membrane named the Basilar Membrane （BM）, into two fluid-filled channels. Based on various assumptions for the cochlear fluid and structure, simplified mathematical and mechanical cochlear models were developed to help to understand the mechanism of the complex coupled system in the past decades. This paper proposes a hydrodynamic numerical cochlear model with consideration of the Fluid-Structure Interaction （FSI）. In this model, the cochlear lymph is considered as in a Newtonian viscous fluid, and the basilar membrane is modeled as a composite structure. The traveling wave is simulated. Also focusing on the pressure in the fluid field, the results are compared with studies of Peterson and Bogert, where it was assumed that the slow compressive waves are traveling along the BM. Furthermore, the transmitting time of the cochlear traveling wave is also discussed.

Partitioned and Monolithic Algorithms for the Numerical Solution of Cardiac Fluid-Structure Interaction

We reviewand compare different fluid-structure interaction(FSI)numerical methods in the context of heart modeling,aiming at assessing their computational efficiency for cardiac numerical simulations and selecting the most appropriate method for heart FSI.Blood dynamics within the human heart is characterized by active muscular action,during both contraction and relaxation phases of the heartbeat.The efficient solution of the FSI problem in this context is challenging,due to the added-mass effect(caused by the comparable densities of fluid and solid,typical of biomechanics)and to the complexity,nonlinearity and anisotropy of cardiac consitutive laws.In this work,we review existing numerical coupling schemes for FSI in the two classes of strongly-coupled partitioned and monolithic schemes.The schemes are compared on numerical tests that mimic the flow regime characterizing the heartbeat in a human ventricle,during both systole and diastole.Active mechanics is treated in both the active stress and active strain frameworks.Computational costs suggest the use of a monolithic method.We employ it to simulate a full heartbeat of a human ventricle,showing how it allows to efficiently obtain physiologically meaningful results.

Simulation of 3D parachute fluid–structure interaction based on nonlinear finite element method and preconditioning finite volume method

A fluid–structure interaction method combining a nonlinear finite element algorithm with a preconditioning finite volume method is proposed in this paper to simulate parachute transient dynamics. This method uses a three-dimensional membrane–cable fabric model to represent a parachute system at a highly folded configuration. The large shape change during parachute inflation is computed by the nonlinear Newton–Raphson iteration and the linear system equation is solved by the generalized minimal residual（GMRES） method. A membrane wrinkling algorithm is also utilized to evaluate the special uniaxial tension state of membrane elements on the parachute canopy. In order to avoid large time expenses during structural nonlinear iteration, the implicit Hilber–Hughes–Taylor（HHT） time integration method is employed. For the fluid dynamic simulations, the Roe and HLLC（Harten–Lax–van Leer contact） scheme has been modified and extended to compute flow problems at all speeds. The lower–upper symmetric Gauss–Seidel（LUSGS） approximate factorization is applied to accelerate the numerical convergence speed. Finally,the test model of a highly folded C-9 parachute is simulated at a prescribed speed and the results show similar characteristics compared with experimental results and previous literature.