Fluid-structure Phenomena Research Articles

Fluid-Structure Interaction Analysis of a Competitive Car during Brake-in-Turn Manoeuvre

The relationship between the presented work and energy conservation is direct and indirect. Most of the literature related to energy-saving focuses on reducing the aerodynamic drag of cars, which typically leads to the appearance of vehicle motion instabilities at high speeds. Typically, this instability is compensated for by moving aerodynamic body components activated above a certain speed and left in that position until the vehicle speed drops. This change in vehicle configuration results in a significant increase in drag at high velocities. The presented study shows a fully coupled approach to fluid–structure interaction analyses of a car during a high-speed braking-in-turn manoeuvre. The results show how the aerodynamic configuration of a vehicle affects its dynamic behaviour. In this work, we used a novel approach, combining Computational Fluid Dynamics (CFD) analysis with the Multibody Dynamic System. The utilisation of an overset technique allows for car movement in the computational domain. Adding Moving Reference Frame (MRF) to this motion removes all restrictions regarding car trajectory and allows for velocity changes over time. We performed a comparative analysis for two aerodynamic configurations. In the first one, a stationary rear airfoil was in a base position parallel to a trunk generating low drag. No action of the driver was assumed. In the second scenario, brake activation initiates the rotation of the rear airfoil reaching in 0.1 s final position corresponding to maximum aerodynamic downforce generation. Also, no action of the driver was assumed. In the second scenario, the airfoil was moving from the base position up to the point when the whole system approached its maximum downforce. To determine this position, we ran a separated quasi-steady analysis in which the airfoil was rotating slowly to avoid transient effects. The obtained results show the importance of the downforce and load balance on car stability during break-in-turn manoeuvres. They also confirm that the proposed methodology of combining two independent solvers to analyse fluid–structure phenomena is efficient and robust. We captured the aerodynamic details caused by the car’s unsteady movement.

MHD Flow around Circular Cylinder UnderControl through three Different magnetic Permeability Status

Through the current work, the flow around an insulating cylinder of various magnetic permeability, submitted to a flow of an incompressible electrically conducting fluid has been investigated. The homogeneous fluid flow and the homogeneous applied magnetic field are aligned at infinity. When the cylinder has the similar magnetic permeability as the fluid, the applied field is not influenced by the cylinder. However, when the cylinder has a different magnetic permeability than that of the fluid, the applied field is agitated by the cylinder and then the flow structures will become different from those of the previous case. Consequently, two cases can be distinguished following the last state whereas the cylinder magnetic permeability may have less or greater value than the fluid one’s. The best agreed results that have been obtained following the comparison to the literature magnetic field behaviors were selected .The event has been occurred, where the convergence and divergence of the magnetic stream lines were realized to the previous both cases of magnetic permeability situations, respectively. In fact, an important influence of magnetic field on the fluid has been occurred. Consequently, it can be concluded that the fluid has significant influences on the cylinder structure, through the impact of the fluid structure phenomenon, the shedding vortex process and its suppression. Accordingly, good results of drag aerodynamic coefficient evolution were obtained at the fixed value of the Reynolds number Re=550, for different Stuart numbers, greater than and lessen than a critical value adopting at N=0.8.

Experimental study of the liquid damping effects on a SDOF vertical sloshing tank

The analysis of violent sloshing is of great interest for European aeroplane manufacturers. It has been widely reported that aircraft fuel sloshing significantly damps wing vibrations, but the complexity of the fluid–structure phenomena still demands further research. The aim of this work is to define an experimental methodology to quantify the sloshing force acting on a vertical Single Degree Of Freedom (SDOF) tank when the accelerations are similar to the ones found in a real wing. In this work, two different methodologies are presented for the calculation of the sloshing force involved in the SDOF tests, finding a very good level of agreement between them.A Froude scaled SDOF experiment has been devised for sloshing study, confirming first that the fluid presence increases the damping of the system notably, and second that the slosh-induced damping force is composed of an inertial term and a dissipative term.The sloshing force study also shows that this force is shifted with respect to position measurements, and this phase-shift is a key element in fluid-induced energy dissipation. A global energy study connecting the sources of energy dissipation with the forces involved in the dynamics of the system is performed, obtaining a quantitative contribution of the fluid’s role in the system. Finally, a numerical model has been tested using the experimentally obtained sloshing forces as an input exhibiting good agreement with the previously obtained experimental results.

Two-way coupled simulation of the Francis-99 hydrofoil using model order reduction

The Francis-99 hydrofoil is simulated using a quasi two-way Fluid-Structure Interaction procedure. The structural domain is reduced by the use of modal decomposition, and solved for inside the commercial fluid solver ANSYS CFX. Both the first order Backward Euler and second order Crank-Nicolson time discretization scheme is used in the structural equations, with significantly different results. Several coupled fluid-structure phenomena is observed that would be unobtainable in a normal one-way approach. The most interesting is an “added stiffness” effect, where the eigenfrequency of the foil increases when the flow velocity is increased. This trend corresponds well with available experimental results. The same phenomenon is observed in the hydrodynamic damping on the foil. Self-induced vibration due to vortex shedding is also simulated with good results.The implemented two-way approach allows the different forcing terms to be tracked individually, due to the discretization of the second order structural system. This provides insight into the underlying physics behind the different FSI phenomena seen, and helps us explain why the damping and eigenfrequency characteristics change as the flow velocity passes the lock-in region.

Updated results on hydrodynamic mass and damping estimations in tube bundles under two-phase crossflow

Flow-Induced Vibration (FIV) is the most critical dynamic issue in the design of shell-and-tube heat exchangers. This fluid-structure phenomenon may generate high amplitude vibration of tubes or structural parts, which leads to fretting wear between the tubes and supports, noise or even fatigue failure of internal components. The study of this phenomenon is more challenging if considered that two-phase crossflow exists in many shell-and-tube heat exchangers. In this framework, the analysis of the influence of void fraction and flow patterns on FIV is of particular interest. In fact, void fraction and flow patterns do affect the dynamic parameters involved in tube vibration and, hence, the current vibration mechanism. However, in spite of the importance of devices subjected to two-phase flow, FIV under these conditions have not been entirely understood. In this paper, the results of an extensive experimental campaign, aiming at validating the flow pattern maps found in open literature, are presented. For this purpose, a normal triangular (transversal pitch per diameter ratio of 1.26) tube bundle subjected to two-phase air - water vertical upward crossflow is used. Structural sensors are used to measure the tube dynamic responses and estimate parameters such as hydrodynamic mass and damping ratios, which are strongly dependent on flow conditions. Theoretical models and data previously published are compared with the present experimental results, showing good agreement.

Dynamic analysis of a nuclear reactor with fluid–structure interaction: Part I: Seismic loading, fluid added mass and added stiffness effects

The present paper is related to the dynamic (seismic) analysis of a naval propulsion ground prototype (land-based) nuclear reactor with fluid–structure interaction modelling. Many numerical methods have been proposed over the past years to take fluid–structure phenomenon into account in various engineering domains, among which nuclear engineering in seismic analysis. The purpose of the present paper is to make a comparative study of these methods on an industrial case, namely the pressure vessel and internals of a nuclear reactor. A simplified model of the pressure vessel and the internal structure is presented; fluid–structure interaction is characterised by added mass, added stiffness and coupling effects. The basic principles of the mathematical techniques for fluid–structure modelling and dynamic methods used in the analysis are first presented and then applied to compute the eigenmodes and the dynamic response of the fluid–structure coupled system with various numerical procedures (quasi-static, spectral and temporal approaches). Numerical results are presented and discussed; fluid–structure interaction effects are highlighted. As a main conclusion, added mass effects are proved to have a significant influence on the dynamic response of the nuclear reactor.

Biofluid Mechanics of the Pulmonary System

Presents an overview of leading areas of discovery in bio-fluid mechanics related to the pulmonary system, with particular reference to the airways. Areas briefly reviewed include airway gas dynamics, impedance studies, collapsible-tube studies, and airway liquid studies. Emphasis is placed on promising further directions, such as analysis of interacting fluid-mechanical or fluid-structure phenomena, multi-scale modeling across widely varying length and time scales, and integration of advanced simulations into respiratory investigation and pulmonary medicine.

Finite element procedures for fluid-structure interactions and application to liquid storage tanks

Most of the failures of large tanks after severe earthquakes are suspected to have resulted from the dynamic buckling caused by overturning moments of seismically induced liquid inertia and surface slosh waves. In this paper, a nonlinear finite element method is presented which can treated the structural behavior of the tanks in conjunction with fluid, including the dynamics and buckling. Both the formulation and computer implementation aspects are presented. The areas upon which attention is focused are: the mixed Lagrangian-Eulerian kinematical description for modeling fluid subdomains in fluid-structure interaction problems, the finite rotation effects in numerical integration of rate constitutive equations arising in large-deformation analysis and the implicit-explicit finite element techniques for transient analysis. All these nonlinear methodologies have been integrated into a finite element computer code [47]. A number of physically important buckling and dynamic analyses of tanks are being investigated. Various other fluid structure phenomena such as the stability of off-shore structures can be analyzed with this computer program. The proposed nonlinear finite-element procedures can serve as a basis for future developments of various other fluid-structure phenomena such as the transient motion of submerged or partially submerged structures.

Simulation of ship-ice collision dynamics: ice interface modeling considerations

A time-domain simulation of collisions between icebreaking ships and multiyear ice is described. The model, ITHACA SHIP, considers the transient shipice interaction and fluid-structure phenomena as strongly coupled through ship dynamics. The present paper discusses the modeling of ice forces. It examines the requirement for exactly satisfying the kinematic boundary conditions on the ice interface; including progressively more detailed representations of the interaction. Results are compared with MV Arctic physical model tests and full scale trials' data. Hullgirder stresses at open water impact speeds are predicted.