Fluid-structure Interaction Effects Research Articles

내부 유체에 의한 고유진동수 분리 효과를 고려한 배관계의 적절한 시간이력 해석 방법론

In this study, the natural frequency separation phenomena found in the dynamic analysis of piping systems with internal fluids were identified, and methods for efficient seismic time history analysis were studied. We conducted a dynamic analysis of a piping system with consideration for the effect of its internal fluids using the coupled model, which incorporates the fluid-structure interaction effect. Owing to the mode separation effect, modes were divided into the fluid mass added (FMA) mode, generated by the added mass effect of the fluid, and coupled mode, which is created by the resonance of the internal fluid. The response contribution of the FMA and coupled modes was confirmed to be effective for efficient seismic time history analysis.

An isogeometric FE-BE method and experimental investigation for the hydroelastic analysis of a horizontal circular cylindrical shell partially filled with fluid

Abstract In this study, the dynamic characteristics (i.e. natural frequencies and associated mode shapes) of a partially filled horizontal cylindrical shell are investigated experimentally and by an isogeometric finite element-boundary element method. The proposed numerical procedure is divided into two parts. In the first part, the dynamic characteristics of the cylindrical shell under in-vacuo conditions are obtained by the isogeometric finite element method (IGAFEM) based on a linear Kirchhoff-Love shell formulation. In the second part, the fluid-structure interaction effects are calculated in terms of generalized added mass coefficients by using the isogeometric boundary element method (IGABEM), assuming that the structure vibrates in its in-vacuo principle mode shapes. By adopting the linear hydroelasticity theory, it is assumed that the fluid flow is ideal, i.e., an incompressible flow and inviscid fluid. In order to show the versatility of the numerical method, the results are compared with those obtained by the conducted experiments. Relevant numerical challenges in the hydroelastic vibration analysis are highlighted and it is shown that the numerical predictions and experimental results are in good agreement.

Dynamic and fluid-structure interaction simulations of a ceramic matrix composite plate

This study presents numerical simulations of a unidirectional ceramic matrix composite (CMC) plate under different loads considering the effect of fluid-structure interaction (FSI). The two-scale method was used in the dynamic simulation of CMC plate. The shear-lag model considering the damage modes of CMCs was used to simulate the constitutive behavior in the micro-scale. The explicit dynamic finite element method was used to simulate the dynamic response in the macro-scale. The dynamic responses of CMC plate under impulse and harmonic load were simulated. The incompressible Navier-Stokes equations were employed in the simulation of fluid. The dynamic response of CMC plate with FSI was solved based on the staggered method. The effect of fluid on the dynamic response of CMC plate was discussed.

A simulation model of Gerotor pumps considering fluid–structure interaction effects: Formulation and validation

Gerotors are compact, inexpensive and robust pumps generally used in hydraulic systems. Owing to their characteristic operation at low pressure (up to 30 bar), these units can be modelled using relatively simple tools considering only their fluid dynamics aspects. However, some commercially available Gerotors operate at higher pressures so that material deformation effects cannot be neglected under such conditions. This paper presents an omni-comprehensive simulation approach for Gerotor units that considers the fluid–structure interaction effects at the lateral lubricating gaps and related to the contacts between the rotors. The numerical tool consists of different submodels which allow the evaluation of the fluid dynamic features of the flow through the pump considering micro-motion effects of the rotors. This paper particularly details the novel aspects of the simulation approach, which is the introduction of submodels that account for fluid–structure interaction effects: the lateral lubricating gap models and the rotor contact models, both based on the solution of the Reynolds equation considering the deformation of the solid parts.For the model validation, a commercially available pump able to operate above 100 bar was tested at the authors’ research center. The comparison between the simulation results and the experimental data clearly show the good accuracy of the model, in terms of volumetric flow and port pressure pulsation. In particular, the model allows predicting both the volumetric and the torque efficiency of the unit. Furthermore, the simulation results permit to interpret the reasons for instances of wear present in the unit.

Fluid-Structure Interaction in Transient-Based Extended Defect Detection of Pipe Walls

AbstractThis paper investigates the effect of fluid-structure interaction (FSI) on the efficiency of transient-based reflections analysis (TBRA) applied to the detection of extended deteriorations ...

Investigation on the formation mechanism and controlling method of machined surface topography of ultra-precision flycutting machining

The three-dimensional topography of machined surface induced by machine tool vibration has a great impact on the optical performance of ultra-precision optical components. This paper aims to explain the formation mechanism of the wavy topography of the machined surface of ultra-precision flycutting. Firstly, a dynamic model of the machine tool was built based on finite element method (FEM) considering the fluid-structure interaction (FSI) effect. Then, a mathematic model for simulating the machined surface topography was built based on the FEM model of the machine tool. The machined surface topography was simulated, and the spatial periods of waviness errors were analyzed based on power spectral density (PSD) method. The reason of waviness errors on machined surface was revealed by investigating the internal relationship between the spatial period of waviness error and the dynamic performance of the machine tool. Moreover, the method for controlling the spatial period of waviness error was discussed, which provides guidance for improving the optical performance of large size optical component.

Research on Seismic Response of Base‐Isolated Nuclear Island Building considering FSI Effect of PCS Water Tank

Base isolation can be used to reduce seismic response of structure and protect the structure from damage subjected to earthquake. To study the isolation effect of new PWR nuclear power plant with a base isolation system, considering FSI (fluid‐structure interaction) effect by the simplified model, two 3D numerical models (one nonisolated model and one isolated model) were established. After natural frequency analysis, one artificial ground motion was chosen to analyze isolation effect qualitatively. Based on the results, the accelerations and relative displacements of nuclear island building under ten natural ground motions were statistically analyzed to evaluate the isolation effect quantitatively. The results show that the base isolation system can reduce the natural frequencies of nuclear island building. Horizontal accelerations can be reduced effectively, but the isolation effect is not obvious in vertical direction. The acceleration reduction ratio of the top is about 70%–90%, and the acceleration reduction ratio of the lower part is about 20%–60%. Horizontal displacement of the isolated model is far larger than that of the nonisolated model, and horizontal displacement will become larger considering FSI effect. These conclusions could provide some references for studies on the isolation system of nuclear island building.

Shock vibration characteristics of fluid-structure interaction phononic crystal pipeline

<sec>Fluid-structure interaction pipeline systems are extensively adopted to transfer matter, energy and momentum, which are widely used in various fields. Due to the fluid-structure interaction effect, the pipe wall proves to produce strong vibration and noise under fluid action, which has a serious influence on the safety and concealment of the equipment, even leading to serious damages. Therefore, it is of great significance to study the vibration characteristics of fluid-structure interaction pipeline and methods to reduce the vibration of pipeline both in theory and in practice. </sec><sec>Phononic crystal can suppress the propagation of elastic waves in a specific frequency range by their special band-gap characteristics, which have wide application prospects in the field of vibration and noise reduction. Especially, the band gap characteristics of phononic crystal pipeline used to design fluid-structure interaction pipeline system have been widely studied, thus providing a new technical approach to reducing the vibration and noise of the pipeline. </sec><sec>In this paper, based on the theory of phononic crystal, the vibration transfer characteristics of the Bragg phononic crystal pipeline under fluid-structure interaction are studied. Combining the transfer matrix method and the finite element method, the band structure and band gap characteristics are calculated. Using the finite element method, the vibration characteristics of the phononic crystal pipeline under fluid-structure interaction effect, the shock excitation of pipe wall and the shock excitation of the fluid are considered. The influence of the fluid-structure interaction on the vibration transmission characteristics of the phononic crystal pipeline is also analyzed. </sec><sec>The research results indicate that when the fluid velocity in the fluid-structure interaction pipeline system is small the Bragg phononic crystal pipeline has a good attenuation effect on the shock excitation of pipe wall in the band gap range, and that when the fluid velocity increases the fluid-structure interaction effect becomes significant, the attenuation effect becoming weaker. Bragg phononic crystal pipeline has a certain attenuation effect on the pipe wall vibration caused by the fluid shock excitation near the band gap. The research results are expected to be able to provide a technical reference for the vibration control of pipeline systems under fluid-structure interaction conditions. </sec>

Seismic fragility analysis of AP1000 SB considering fluid-structure interaction effects

AP1000 nuclear power plant has an advanced passive cooling system with a vast water tank located above the shield building, which may affect the seismic performance of the structure. This paper conducts a fragility assessment of shield building and considers the fluid-structure interaction (FSI) effect on the damage of the shield building. Arbitrary Lagrangian Eulerian algorithm is applied to calculate the FSI and eight cases of water levels are considered. Three different fragility analysis methods, namely linear regression, quadratic regression and truncated maximum likelihood estimation, are adopted for assessing the seismic vulnerability of shield building. It is indicated from the results that the regression and the truncated maximum likelihood estimation are close to each other. The maximum likelihood estimation not only can effectively save the computational cost, but also can assure the reasonable calculated results. It is observed that different water levels have the individual probabilities of failure, and case 6 has the smallest probability of failure with a more considerable seismic reduction, whereas the case 1 and case 2 have the higher failure probabilities. The fragility analysis framework can thus be applied for evaluating the vulnerability of shield building under earthquakes considering the FSI effect.

Investigation of underwater explosion near composite structures using a combined RKDG-FEM approach

A combined RKDG-FEM approach, using the Runge-Kutta discontinuous Galerkin (RKDG) method [1,2] for fluid simulating and the finite element method (FEM) [3,4] for structure simulating, is developed to study the complex interactions between compressible multiphase flows and deformable steel and composite structures in near-field early-time underwater explosion (UNDEX). The level set method (LSM) [5,6] and the real ghost fluid method (RGFM) [7,8] are applied to capture and treat the moving gas-water interface, respectively. A GFM-based interface treating scheme [9,10] is adopted to treat the fluid-structure interface, achieving the coupling by solving simultaneously the fluid characteristic equation and the structure equation of motion at the material interface to satisfy the kinematic compatibility and pressure equilibrium conditions. The isentropic one-fluid cavitation model in [11] is employed to capture the transient flow cavitation. Accuracy and effectiveness of the combined RKDG-FEM approach are validated by five benchmark cases, and then it is applied to simulate early-time UNDEX problems near a submerged aluminum foam-cored sandwich plate and a monolithic steel plate of equivalent mass. Numerical results show that the sandwich plate has a higher underwater explosion load resistance through absorbing plastic energy by the foam core than the monolithic steel plate of equivalent mass, and that the foam core plays an important role in the fluid-structure interaction (FSI) and flow cavitation effects, which can be exploited to improve the UNDEX mitigation capability of composite sandwich structures.

Analytical treatment for vibration analysis of partially cracked orthotropic and FGM submerged cylindrical shell with consideration of fluid-structure interaction

Analytical solution for vibration analysis of orthotropic and FGM submerged cylindrical shell containing a surface crack of variable angular orientation is presented in this work. The governing equations in terms of transverse deflection of cracked-submerged shell have been derived using classical shell theory. The fluid forces associated with its inertial effects are added in the governing differential equation to incorporate the fluid–structure interaction effect. The line spring model (LSM) is used to formulate the crack coefficients to accommodate the effect of crack in the governing equation. Furthermore, the governing equation is solved using Donell–Mushtari–Vlasov (DMV) theory to get the fundamental frequency. The results are presented for frequency by giving the input parameters as crack length, crack orientation, and shell’s physical properties such as radius, thickness, and length of the shell. Communicated by Wei-Chau Xie

The effects of stenting on hemorheological parameters: An in vitro investigation under various blood flow conditions.

Despite their wide clinical usage, stent functionality may be compromised by complications at the site of implantation, including early/late stent thrombosis and occlusion. Although several studies have described the effect of fluid-structure interaction on local haemodynamics, there is yet limited information on the effect of the stent presence on specific hemorheological parameters. The current work investigates the red blood cell (RBC) mechanical behavior and physiological changes as a result of flow through stented vessels. Blood samples from healthy volunteers were prepared as RBC suspensions in plasma and in phosphate buffer saline at 45% haematocrit. Self-expanding nitinol stents were inserted in clear perfluoroalkoxy alkane tubing which was connected to a syringe, and integrated in a syringe pump. The samples were tested at flow rates of 17.5, 35 and 70 ml/min, and control tests were performed in non-stented vessels. For each flow rate, the sample viscosity, RBC aggregation and deformability, and RBC lysis were estimated. The results indicate that the presence of a stent in a vessel has an influence on the hemorheological characteristics of blood. The viscosity of all samples increases slightly with the increase of the flow rate and exposure. RBC aggregation and elongation index (EI) decrease as the flow rate and exposure increases. RBC lysis for the extreme cases is evident. The results indicate that the stresses developed in the stent area for the extreme conditions could be sufficiently high to influence the integrity of the RBC membrane.

Experimental study on the interaction between water and cylindrical structure under earthquake action

Generally, the fluid-structure interaction effect needs to be considered when studying the seismic response of the coastal and offshore engineering structures located in the earthquake region. Morison equation has been widely used to calculate the hydrodynamic pressure on the structures. Many researchers have investigated the inertial and drag coefficients in Morison equation for wave force. However, there is hardly study on the coefficients in Morison equation for earthquake induced hydrodynamic pressure. To examine the hydrodynamic added mass and the inertial coefficient in Morison equation, a series of dynamic tests are conducted. The hydrodynamic pressure and acceleration of four steel tubes with different diameters are measured. The changing rule of hydrodynamic added mass with tube diameter, water depth, action frequency, and action amplitude is studied. The inertial coefficient under different conditions is investigated, and a formula is fitted to calculating it under sinusoidal ground motions. A method to calculate the hydrodynamic added mass under the real earthquake was proposed. Finally, a series of underwater shaking table tests were conducted to validate the proposed formula and the method. The results show that the proposed formula and method can be used to estimate the earthquake induced hydrodynamic added mass of cylindrical structures.

Numerical Investigation Into the Influence on Hydrofoil Vibrations of Water Tunnel Test Section Acoustic Modes

High-speed water tunnels are typically used to investigate the single-phase and two-phase flows around hydrofoils for hydraulic machinery applications but their dynamic behavior is not usually evaluated. The modal analysis of an NACA0009 hydrofoil inside the test section was calculated with a coupled acoustic fluid–structure model, which shows a good agreement with the experimental results. This numerical model has been used to study the influence on the hydrofoil modes of vibration of the acoustic properties of the surrounding fluid and of the tunnel test section dimensions. It has been found that the natural frequencies of the acoustic domain are inversely proportional to the test section dimensions. Moreover, these acoustic frequencies decrease linearly with the reduction of the speed of sound in the fluid medium. However, the hydrofoil frequencies are not affected by the change of the speed of sound except when they match an acoustic frequency. If both mode shapes are similar, a strong coupling occurs and the hydrofoil vibration follows the linear reduction of natural frequency induced by the acoustic mode. If both mode shapes are dissimilar, a new mode appears whose frequency decreases linearly with speed of sound while keeping the acoustic mode of vibration. This new fluid–structure mode of vibration appears in between two hydrofoil structure modes and its evolution with sound speed reduction has been called “mode transition.” Overall, these findings reinforce the idea that fluid–structure interaction effects must be taken into account when studying the induced vibrations on hydrofoils inside water tunnels.

Study of integrated calculation method of fluid-structure coupling vibrations, acoustic radiation, and propagation for axisymmetric structures in ocean acoustic environment

Based on a combination of the finite element method and wave superposition method (FEM-WSM), an integrated calculation method of fluid-structure coupling vibrations, acoustic radiation, and propagation for axisymmetric structures in ocean acoustic environments is proposed. The FEM was applied to study the dry mode of axisymmetric structures in a vacuum, and WSM was used to consider the fluid-structure interaction effects and calculate the acoustic radiation field in ocean acoustic environments. The method proposed combines the advantages of FEM and WSM. This method is suited for complex or large axisymmetric structures. Furthermore, it is more efficient than FEM, and the calculation range of the water is not limited. To simplify the calculation, the Green's functions corresponding to the propagation of specific ocean environments were calculated differently in the near and far fields. Using spherical and elliptical axisymmetric shells as examples, the results from the method proposed and COMSOL were compared to verify the correctness of the proposed model. In the calculation of the acoustic radiation field, the numerical errors from matrices, including partial derivatives of the Green's function with huge condition numbers, required the use Tikhonov regularization, and the efficiency was not influenced.

Effect of Fluid–Structure Interaction on Vibration and Deflection Analysis of Generally Orthotropic Submerged Micro-plate with Crack Under Thermal Environment: An Analytical Approach

To develop a new analytical model for vibration analysis of cracked-submerged orthotropic micro-plate affected by fibre orientation and thermal environment. The proposed analytical model is based on Kirchhoff’s classical thin plate theory and the size effect is introduced using the modified couple stress theory. Effect of crack is deduced using appropriate crack compliance coefficients based on line spring model while the effect of thermal environment is introduced in terms of thermal in-plane moments and forces. The coupling of shear and normal stresses for fibre orientation is represented using the coefficient of mutual influence. The fluid forces associated with its inertial effects are added in the governing differential equation to incorporate the fluid–structure interaction effect. The results are presented for frequency response as affected by different fibre orientation, crack length, crack location, level of submergence, temperature variation and material length-scale parameter for simply supported boundary condition. Furthermore, to study the phenomenon of shifting of primary resonance in a cracked micro-plate, the classical relations for central deflection of plate is also proposed. The results show that the fundamental frequency of micro-plate decreases by the presence of crack and thermal environment and this decrease in frequency is further intensified by the presence of surrounding fluid medium in present study. Another important conclusion is that with increase in temperature variation the reduction in frequency at 45° of fibre orientation is less when compared to 0 and 90° for both intact and cracked orthotropic plates.

Fluid–Structure Interaction Effects on Free Vibration of Containerships

The interaction between fluid and structure affects the vibration response of the structure due to the additional hydrodynamic pressure. These effects are accounted for by incorporating the so-called added mass into the vibration equation of the structure. In this paper, a containership was used to study the impact of the added mass on its free vibration response. The natural frequencies of the ship decrease after including the added mass in the vibration analysis. It is shown that the frequency-ascending sequence of the wet mode shapes, for which the added mass is accounted for, may differ from that obtained for the dry state of the ship. Also, the effects of different draft levels on the mode shapes of the ship are reported. These results provide a better insight for designing ships based on their wet-state frequencies and mode shapes, which is the typical operation condition when sailing in the open seas.

Numerical investigation of entrapped air pockets on pressure surges and flow structure in a pipe

This research presents a numerical investigation of two-phase flow during the expulsion of entrapped air in a non-confined pipe. A modified version of the volume of fluid (VOF) approach is employed considering the effect of compressibility in the liquid. A modification is introduced to the original approach relating the density changes in the liquid to the pressure changes using the fluid bulk modulus. The bulk modulus is also modified to consider the pipe elasticity, the air bubble entrainment and the two-phase flow regime in a pipe. Fluid–structure interaction (FSI) code is developed and used to calculate the motion of the downstream orifice wall during the impact of the water column on the pipe end wall. The numerical results of the pressure variation agree well with experimental data. The two-phase flow structure and physics behind the pressure waves are investigated. The numerical results show that to capture the amplitude and time interval of the pressure surges, the effect of FSI should be considered during the expulsion of the entrapped air. Additionally, the effects of initial air pocket size, supply pressure and orifice size on the pressure increase are investigated. The developed VOF-FSI approach can be employed as a numerical tool to investigate the transient flow during pipe filling.

Pressure wave propagation in pressurized thin-walled circular tubes under axial impact

The pressurized thin-walled tubes are called as a member of adaptive energy absorbers of which energy absorbing performance can be controlled by variation of internal pressure. In this context, this study numerically investigates the axial impact performance of pressurized thin-walled circular tubes. For the realistic modeling of the compressed air, the ALE model was developed in LS-DYNA, which enabled an opportunity to investigate both pressure wave propagation in pressurized air and fluid-structure interaction effects between tube-wall and air. In addition, the models were run by taking into account both states, whether pressure regulator, which is an adjustable valve to control internal pressure value, was active. To validate the numerical models, the axial impact tests on Aluminum Aerosol cans were carried out using a light gas gun set-up. The results showed that at the onset of impact, a radial pressure wave, as well as an axial pressure one, simultaneously emerged. Whereas a radial pressure wave propagated towards the center from the tube-wall, the other one propagated along the centerline of the tube. Therefore, a complex pressure distribution and wave propagation occurred in the pressurized tubes. The pressure distribution obtained in the model with a pressure regulator revealed different behavior from the corresponding one obtained without pressure regulator. Also, the results showed that there is no distinct interaction between strain energy absorbed by tube-wall and pressure wave propagation although the total absorbed energy of pressurized tubes increases to some extent with the effects of wave propagation in the pressurized medium.

Numerical Characterization of the Mass Added to a Submerged Plate with the Fluid Structure Interaction Effect

This article focuses on the effect of the fluid on the dynamic behavior (natural frequencies, added mass ... etc.) of a vibrating plate structure in contact with a non-compressible fluid. The relationship between the eigenfrequency in the fluid and the natural frequencies of the structure in the air is an adimensionnel factor of the added mass, which reflects the increase in inertia due to the presence of fluid. In this work, this dimensionless mass factor of a square flexible plate having simply free and fixed edges is characterized by using a modal analysis pre-constraints of an ANSYS code and taking into account the effect of the bidirectional fluid-structure interaction (IFS). The results of plate vibration in air are compared with those obtained by considering the IFS for various modes.