Fluid-structure Model Research Articles

Numerical Study about Damping Effect of Liquid Damper on Tall Buildings

Based on the finite element method, three models are built: classical solid model, potential flow model and a combination of fluid-structure coupling model. Based on the above model the damping mechanism of tuned liquid damper has been investigated. Study focused on classical solid model and the boundary constrained potential fluid model respectively. After the completion of the above calculation, the analysis of bidirectional fluid-structure interaction model being carried out with the implicit dynamics algorithm. The results shows the contrast of the dynamic response of structure in the hydrated and anhydrous state. The calculations show that: the additional water mass can effectively reduce the natural vibration frequency of the structure, and it also can effectively reduce the displacement and velocity response of structure under vibration loads.

A computational model of blast loading on the human eye

Ocular injuries from blast have increased in recent wars, but the injury mechanism associated with the primary blast wave is unknown. We employ a three-dimensional fluid-structure interaction computational model to understand the stresses and deformations incurred by the globe due to blast overpressure. Our numerical results demonstrate that the blast wave reflections off the facial features around the eye increase the pressure loading on and around the eye. The blast wave produces asymmetric loading on the eye, which causes globe distortion. The deformation response of the globe under blast loading was evaluated, and regions of high stresses and strains inside the globe were identified. Our numerical results show that the blast loading results in globe distortion and large deviatoric stresses in the sclera. These large deviatoric stresses may be indicator for the risk of interfacial failure between the tissues of the sclera and the orbit.

Reliability Analysis of Vibro-Acoustic Problem

The comprehension of the interactions between a fluid and an elastic solid has a capital importance in several industrial applications. When a structure vibrates in the presence of a fluid, there is interaction between the natural waves of each media: the fluid flow generates a structural deformation and/or the movement of a solid causes the displacement of the fluid. These applications require an effective coupling. In addition, the dynamic analysis of the industrial systems is often expensive from the numerical point of view. For the coupling fluid-structure finite elements models, the importance of the size reduction becomes obvious because the fluid's freedom degrees will be added to those of the structure. A method of condensation will be used to reduce the matrixes size. One of the principal hypothesis in the use of component mode synthesis method is that the model is deterministic; it is to say that parameters used in the model have a defined and fixed values. Furthermore, the knowledge of variation response of a structure involving uncertain materials, geometrical parameters, boundary conditions, tolerances of manufactures and loading conditions is essential in global process of conception. In order to do that, the modal condensation method is extended to reliability analysis for the coupled fluid-structure finite elements models. A numerical vibratory study is leaded on a plate in the air and in immersion in water taking into account the acoustic aspect. The results of the reliability analysis tend to show the effectiveness of the proposed approach based on the condensation techniques.

Fluid–structure interactions in micro-interlocked regions of the cement–bone interface

Experimental tests and computational modelling were used to explore the fluid dynamics at the trabeculae–cement interlock regions found in the tibial component of total knee replacements. A cement–bone construct of the proximal tibia was created to simulate the immediate post-operative condition. Gap distributions along nine trabeculae–cement regions ranged from 0 to 50.4 μm (mean = 12 μm). Micro-motions ranged from 0.56 to 4.7 μm with a 1 MPa compressive load to the cement. Fluid–structure analysis between the trabeculae and the cement used idealised models with parametric evaluation of loading direction, gap closing fraction (GCF), gap thickness, loading frequency and fluid viscosity. The highest fluid shear stresses (926 Pa) along the trabecular surface were found for conditions with very thin and large GCFs, much larger than reported physiological levels (∼1–5 Pa). A second fluid–structure model was created with a provision for bone resorption using a constitutive model with resorption velocity proportional to fluid shear rate. A lower cut-off was used, below which bone resorption would not occur (50 s− 1). Results showed that there was initially high shear rates (>1000 s− 1) that diminished after initial trabecular resorption. Resorption continued in high shear rate regions, resulting in a final shape with bone left deep in the cement layer, and is consistent with morphology found in post-mortem retrievals. Small gaps between the trabecular surface and the cement in the immediate post-operative state produce fluid flow conditions that appear to be supra-physiologic; these may cause fluid-induced lysis of trabeculae in the micro-interlock regions.

Numerical modeling of arterial pulse wave propagation to characterize aortic hemodynamic: Validation using magnetic resonance data

ObjectivesArterial stiffness, which is caused by aging and other cardiovascular risk factors and primarily affects the aorta, is associated with cardiac and cerebral morbidity and mortality. The objective of our study was to non-invasively estimate local biomechanical and hemodynamic biomarkers related to proximal aortic stiffness, by combining cardiovascular magnetic resonance (CMR) data and numerical simulations. Materials and methodsTo achieve this aim, we used a numerical 1D fluid-structure model to simulate blood flow in the descending aorta, and we combined this model with clinical data (areas and velocities in three levels of the descending aorta, carotid pressures) acquired in two healthy subjects using CMR and applanation tonometry. ResultsFirst, we studied the sensibility of our model on an idealized aorta and showed that our model was able to characterize age-related arterial alterations, when compared to established physiological knowledge. Furthermore, while comparisons of simulations against clinical data revealed low errors (<20%) in terms of aortic areas and velocities for the two subjects, more important errors were found for pulse pressures (up to 20%). Importantly, errors in terms of velocity and area were lower than their variations occurring with aging. ConclusionsThus, our fast method could enable the non-invasive estimation of aortic functional parameters and a more realistic version of our numerical model could also provide a reliable estimation of central pressure.

Development of Numerical Evaluation Methods for Multi-Physics Phenomena under Tube Failure Accident in Steam Generator of Sodium-Cooled Fast Reactor

Multi-physics analysis system for a heat transfer tube failure event in a steam generator of sodium-cooled fast reactors has been developed. The analysis system consists of the multiple computer codes. In this study, applicability of the newly constructed numerical models in the analysis system was investigated. The droplet entrainment / transport model which was incorporated into the SERAPHIM code was verified through the analysis of the related experiment. The experimental data about the pressure variation when the droplet entrainment occurs was reproduced by our model successfully. The TACT code is integrated by the numerical models of fluid-structure thermal coupling, stress evaluation and failure judgment of the structure. The fluid-structure thermal coupling model could predict the temperature distribution formed by the flow around the circular cylinder. About the failure judgment model, the predicted time of failure occurrence showed good agreement with the results of the tube rupture simulation experiment.

Longitudinal displacement in viscoelastic arteries:A novel fluid-structure interaction computational model, and experimental validation

Recent in vivo studies, utilizing ultrasound contour and speckle tracking methods, have identified significant longitudinal displacements of the intima-media complex, and viscoelastic arterial wall properties over a cardiac cycle. Existing computational models that use thin structure approximations of arterial walls have so far been limited to models that capture only radial wall displacements. The purpose of this work is to present a simple fluid-struture interaction (FSI) model and a stable, partitioned numerical scheme, which capture both longitudinal and radial displacements, as well as viscoelastic arterial wall properties. To test the computational model, longitudinal displacement of the common carotid artery and of the stenosed coronary arteries were compared with experimental data found in literature, showing excellent agreement. We found that, unlike radial displacement, longitudinal displacement in stenotic lesions is highly dependent on the stenotic geometry. We also showed that longitudinal displacement in atherosclerotic arteries is smaller than in healthy arteries, which is in line with the recent in vivo measurements that associate plaque burden with reduced total longitudinal wall displacement. This work presents a first step in understanding the role of longitudinal displacement in physiology and pathophysiology of arterial wall mechanics using computer simulations.

Numerical aspects and controllability of a one dimensional fluid-structure model

In this paper we summarize some recent results from Cîndea et al. (2013) concerning the controllability of a one dimensional fluid-structure model. These results are confirmed by numerical experiments in some particular cases. More precisely, we consider a simplified model for a point swimmer moving, according to Newton's law, in an one dimensional fluid which is modeled by the viscous Burgers equation. The control variable is the relative velocity of the swimmer with respect to the fluid. The main result of the paper gives the conditions in which we can drive the fluid and the velocity of the point mass to zero. A set of reachable positions of the point mass is also obtained. From the numerical point of view, we compute the L2-minimal norm control for a linearized and simplified model. The method we used combine a finite elements discretization in space, a finite-difference centered scheme in time and the conjugate gradient method.

CO2 Pipeline Integrity: A Coupled Fluid-structure Model Using a Reference Equation of State for CO2

We present a coupled fluid-structure model to study crack propagation and crack arrest in pipelines. Numerical calculations of crack arrest, crack velocity and pressure profiles have been performed for steel pipes with an outer diameter of 267mm and a wall thickness of 6mm. The pipe material and fracture propagation have been modelled using the finite-element method with a local ductile fracture criterion and an explicit time-integration scheme. An in-house finite-volume method has been employed to simulate the fluid dynamics inside the pipe, and the resulting pressure profile was for each time step applied as a load in the finite-element model. Choked-flow theory was used for calculating the flow through the pipe opening as the crack propagated. Simulations were performed with both methane and CO2, pressurized at 75, 120 and 150bar. Initial results indicate that crack arrest does not necessarily occur with CO2 under circumstances where it would occur with methane.

On well-posedness for a free boundary fluid-structure model

We address a fluid-structure interaction model describing the motion of an elastic body immersed in an incompressible fluid. We establish a prioriestimates for the local existence of solutions for a class of initial data which also guarantees uniqueness.

Development of low frequency, insulating thick diaphragms for power MEMS applications

Major challenges of micro thermal machines are the thermal insulation and mechanical tolerance in the case of sliding piston. Replacing piston by membrane in microengines can alleviate the latter and lead to planar architectures. However, the thermal isolation would call for very thick structures which are associated to too high resonant frequencies which are detrimental to the engine performances. A thermal and mechanical compromise is to be made. On the contrary, based on fluid structure interaction, using an incompressible fluid contained in a cavity sealed by deformable diaphragm it would be possible to design a thick, low frequency insulating diaphragm. The design involves a simple planar geometry that is easy to manufacture with standard microelectronics methods. An analytical fluid-structure model is proposed and theoretically validated. Experimental structures are realized and tested. The model is in agreement with the experimental results. A dimensionless model is proposed to design hybrid fluid structures for micromachines.

Sequential identification of boundary support parameters in a fluid-structure vascular model using patient image data

Viscoelastic support has been previously established as a valuable modeling ingredient to represent the effect of surrounding tissues and organs in a fluid-structure vascular model. In this paper, we propose a complete methodological chain for the identification of the corresponding boundary support parameters, using patient image data. We consider distance maps of model to image contours as the discrepancy driving the data assimilation approach, which then relies on a combination of (1) state estimation based on the so-called SDF filtering method, designed within the realm of Luenberger observers and well adapted to handling measurements provided by image sequences, and (2) parameter estimation based on a reduced-order UKF filtering method which has no need for tangent operator computations and features natural parallelism to a high degree. Implementation issues are discussed, and we show that the resulting computational effectiveness of the complete estimation chain is comparable to that of a direct simulation. Furthermore, we demonstrate the use of this framework in a realistic application case involving hemodynamics in the thoracic aorta. The estimation of the boundary support parameters proves successful, in particular in that direct modeling simulations based on the estimated parameters are more accurate than with a previous manual expert calibration. This paves the way for complete patient-specific fluid-structure vascular modeling in which all types of available measurements could be used to estimate additional uncertain parameters of biophysical and clinical relevance.

ON THE INSTABILITY OF SPINNING CYLINDRICAL SHELLS PARTIALLY FILLED WITH LIQUID

The dynamics and stability of rotating circular cylindrical shells partially filled with ideal liquid is analyzed. The structural dynamics of the shell is modeled by using the first-order shear deformable shell theory and the flow inside the cylinder is simulated by a quasi 2D model based on the Navier–Stokes equations for ideal liquid. The fluid and structural models are combined using the nonpenetration condition of the flow on the wetted surface of the cylinder and the fluid pressure on the flexible shell. The obtained fluid–structure model is employed for the determination of the stable regions of the spinning frequency of the cylinder. A series of case studies are performed on the governing parameters of the instability of the cylinder and some conclusions are outlined.

Influence of Diameter and Number of Orifice on Static Characteristics of Radial-Thrust Aerostatic Bearing

The working performance of the spindle system is the most important factor to embody the overall performance of the machine tool. To ensure the advanced capabilities, besides the high-precision manufacturing technologies, it is mainly depending on the bearing module and the forces on the spindle. In this paper, a new strategy of the vertical spindle supporting system is presented to meet the high stiffness requirement for the aerostatic bearing. Based on the computational fluid dynamics and finite volume method, a fluid dynamic model and structure model of the large diameter incorporate radial-thrust aerostatic bearing is developed and simulated to find out the pressure distribution laws of the spindle supporting system. The grid subdivision in the direction of film thickness is paid more attentions when establishing the grid of the whole gas film. Simulation results show that this special structure of bearing module can supply enough load capacity and stiffness for the machine tool. The results also indicate that the static characteristics of the bearing are improved as the supply pressure increases and as the supply orifice diameter decreases.

Shock attenuation of PMMA sandwich panels filled with soda-lime glass beads: A fluid-structure interaction continuum model simulation

The dramatic increase of Improvised Explosive Device (IED) related injuries has stimulated many studies to reconsider the design of the current state-of-the-art vehicle and body protective equipment. Materials now need to be chosen not only to stop solid projectiles such as shrapnel or bullets but also to attenuate the injurious effects of incoming blast waves. New advanced computational models of such events have been proved to facilitate the access to information currently inaccessible to experiments. To this end, we developed a fluid–structure interaction computational continuum model to investigate the attenuation properties of foam specimens containing filler materials under shock loading. Three test specimens were examined: a solid foam sample, and two other foam samples incorporating an intermediate layer of filler material: SiO2 aerogel and soda-lime glass beads. The model was then calibrated and the results compared to the corresponding shock tube experimental results [M.D. Alley, S.F. Son, G. Christou, R. Goel, L. Young, 2009]. In conclusion, the model shows good agreement with experiment values for the peak pressure of the transmitted wave as well as its propagation time. Complementing the existing experimental results, high density soda-lime glass beads filler material is shown to substantially decrease the peak magnitude of the transmitted wave and to decrease the spatial gradient of the pressure compared to the other lower density filler samples. However, the history of the sample reaction force suggests that the frame constraining the test specimen is being subjected to a higher impulse using the high density filler. Such a model paves the road to a new series of complex numerical models designed to accompany experimental testing by providing new insights on the mechanisms of fluid–structure interaction.

A new coupled fluid–structure modeling methodology for running ductile fracture

A coupled fluid–structure modeling methodology for running ductile fracture in pressurized pipelines has been developed. The pipe material and fracture propagation have been modeled using the finite-element method with a ductile fracture criterion. The finite-volume method has been employed to simulate the fluid flow inside the pipe, and the resulting pressure profile was applied as a load in the finite-element model. Choked-flow theory was used for calculating the flow through the pipe crack. A comparison to full-scale tests of running ductile fracture in steel pipelines pressurized with hydrogen and with methane has been done, and very promising results have been obtained.

Pipeline Flow Modelling with Source Terms Due to Leakage: The Straw Method

A numerical method for calculating the leakage flow rate through a crack in a pressurized pipeline is presented. Calculations of the flow inside, and leakage from, a pipeline with a running crack are performed. For the case of single-phase flow, the flow through the crack can also be calculated using choked-flow theory. The two methods are compared and identical results obtained. The advantage of the present method is that it does not rely on analytical expressions for the flow through the crack, and it is therefore thought to be applicable for two-phase flow, including phase transition. Hence it may be of use in the development of coupled fluid-structure models for the assessment of running ductile fracture in carbon dioxide transport pipelines.

Dynamics of the aortic arch submitted to a shock loading: Parametric study with fluid-structure models.

This work aims to present some fluid-structure models for analyzing the dynamics of the aorta during a brusque loading. Indeed, various lesions may appear at the aortic arch during car crash or other accident such as brusque falling. Aortic stresses evolution are simulated during the shock at the cross section and along the aorta. One hot question was that if a brusque deceleration can generate tissue tearing, or a shock is necessary to provoke such a damage. Different constitutive laws of blood are then tested whereas the aorta is assumed linear and elastic. The overall shock model is inspired from an experimental jig. We show that the viscosity has strong influence on the stress and parietal moments and forces. The nonlinear viscosity has no significant additional effects for healthy aorta, but modifies the stress and parietal loadings for the stenotic aorta.

Investigations for a model reduction technique of fluid–structure coupled systems

In this paper, a methodology for coupled fluid–structure model reduction is proposed. The overall objective of the method is to reduce the numerical computational costs without affecting the accuracy level of the prediction. This methodology is organized according to the three following steps. In the first step, this method uses a reliable criterion for selecting the number of the kept modes for the fluid and the structure in vacuo subsystems. In the second step, this basis will be enriched through static residual responses taking into account the fluid–structure coupling effects. These responses are selected according to an energetic criterion. Finally, the enriched basis is extended by introducing some residual static responses due to the error forces considered as structural modifications forces. In the context of the finite element method (FEM), the performances of the proposed method are established through a comparative study with other strategies that are proposed in the literature. Thus, the computational cost (CPU time) and the accuracies of the different methods are discussed and compared with a reference method. The validation of the proposed method and the comparative study are performed through two numerical simulation examples. The first one concerns a parallelepiped acoustic cavity with a simply supported plate. The method can handle both weak and strong couplings; as illustrated in the examples. The second one consists of a pipe with a strong coupling and a larger model size.

Detached-eddy simulation of transonic limit cycle oscillations using high order schemes

This paper is to investigate the NLR7301 airfoil limit cycle oscillation (LCO) caused by the flow nonlinearity of the fluid-structural interaction using detached eddy simulation (DES) of turbulence. A low diffusion E-CUSP (LDE) scheme with 5th order WENO scheme is employed to calculate the inviscid fluxes. A fully conservative 4th order central differencing is used for the viscous terms. A fully coupled fluid-structural model is employed. The limited cycle oscillation (LCO) of the NLR7301 airfoil is simulated using DES method developed by Spalart et al. For the case computed in this paper, the predicted LCO agrees excellently with the experiment performed by Schewe et al. The solutions also show bifurcation and are dependent on the initial fields or initial perturbation. The developed computational fluid dynamics (CFD)/computational structure dynamics (CSD) simulation is able to capture the LCO with very small amplitudes measured in the experiment under the same conditions except that the computation is conducted in an unbounded field. This is attributed to the high order low diffusion schemes, fully coupled FSI model, and the DES method used.