Fluid-structure problems

In physics, fluid dynamics is a sub-discipline of fluid mechanics that deals with fluid flow —the natural science of fluids (liquids and gases) in motion. It has several subdisciplines itself, including aerodynamics (the study of air and other gases in motion) and hydrodynamics (the study of liquids in motion). Fluid dynamics offers a systematic structure that underlies these practical disciplines, that embraces empirical and semi-empirical laws derived from flow measurement and used to solve practical problems. The solution to a fluid dynamics problem typically involves calculating various properties of the fluid, such as velocity, pressure, density, viscosity and temperature, as functions of space and time. 

This problem falls into a category of strongly coupled fluid-structure interaction (FSI) problems due to comparable stiffnesses of the container and its liquid content. Hence, accurate prediction of containers behaviour requires a liquid-container interaction model. Here, a two-system FSI model based on the Finite Volume Method is employed, and a good agreement is found between measured and predicted pressure and strain histories. 

This paper presents the combined experimental/numerical investigation of the behaviour of fluid-filled plastic containers subjected to drop impact. Drop Impact experiments were conducted on original and modified bottles. During the test, strain and pressure histories were recorded at various positions. Tests were simulated numerically using the two-system FSI model. Both solid and fluid domains remain fixed during the calculations, i.e. a small-strain analysis was performed for the solid while an Eulerian fi-ame of reference was used for the fluid. This procedure was found to be simple, stable and efficient. Numerical results agreed well with experimental data, demonstrating the capability of the code to cope with this complex fluid-structure interaction problem. 

A. Karac, A. Ivankovic, Drop Impact of Fluid-Filled Plastic Containers Finite Volume Method for Coupled Fluid-Structure-Fracture Problems, in Proc. Fifth World Congress on Computational Mechanics WCCM V, Vienna, Austria (2002). 

Experience has shown structured fluids to be more difficult to manufacture, due to the complexity of their rheological profiles. In addition to elasticity, dilatancy, and rheopexy, certain structured fluid compositions may exhibit solid-like properties in the quiescent state and other flow anomalies under specific flow conditions. For emulsions and solid particulate dispersions, near the maximum packing volume fraction of the dispersed phase, for example, yield stresses may be excessive, severely limiting or prohibiting flow under gravity, demanding special consideration in nearly all unit operations. Such fluids pose problems in... 

Sullivan et al. and Thompson et al. have studied the structure of hard diatomic fluids in contact with a hard wall and Lennard-Jones 12-6 diatomic fluids interacting with a wall via the Lennard-Jones 9-3 potential. Computer simulations were carried out via the Monte Carlo method for the hard diatomic system and via molecular dynamics for the 12-6 diatomic system. In each case, the simulation results were compared with the results from solutions of the RISM or SSOZ-PY theory adapted to the fluid-wall problem. This adaptation can be achieved by noting that the site density profile for a diatomic fluid in contact with a plane surface can be related to... 

All calculations were performed using the Geocrack2D finite element code, which was developed to solve coupled structure / fluid / thermal problems. Summary and basic equations of the code are given in Swenson et al. (1995). A simulation consists of arbitrarily shaped rock blocks with linear / non-linear contact and discrete fluid paths between the blocks. Heat transfer occurs by conduction in the rock blocks and conduction and transport in the fluid. 

If more than one force is acting, the F in Eq. 7.11 must be replaced with a sum of forces. Usually several forces act in fluid flow problems, so we write the momentum balance with a S F. The forces acting on the system shown in Fig. 7.1 are the external pressure on all parts of its exterior and the force of gravity. Other forces which we might consider are electrostatic or magnetic forces. If we had chosen our system such that the boundary passed through the foundations in Fig. 7.1, then there would be a compressive force in the structural members of the foundation, which would have to be taken into account. 

Evidently the MI method is less objectionable than cutoff from the standpoint of studying fluid structure. If one wants to add a tail correction to the results, however, a spherical cutoff truncation is much more convenient. One way around this difficulty might be to carry out a Markov chain based on the MI method, but simultaneously to keep track of the energy contributions from pairs within some cutoff distance, and finally to add a tail correction to the latter. A very attractive approach to approximating long-range effects in fluids is the reaction field (RF) method described above, which seems to be free of some of the faults of the Ewald method. It is, however, most convenient to use a spherical cavity in the continuum. If this is done one evidently does not entirely escape these problems associated with a spherical cutoff, however, and some way around them should be sought. 

Under the hypothesis of rigid tank, the impulsive and convective part of hydrodynamic pressure can be easily evaluated. On the contrary, the p>art, which depends on the deformability of the tank wall, can be determined solving a fluid-structure interaction problem, whose solution depends on the geometrical and mechanical characteristics of the tank radius R, liquid level H, thickness s, liquid density p and elastic modulus of steel E. The problem can be uncoupled in infinite vibration modes, but only few of them have a significant mass. Thus, the impulsive mass is distributed among the first vibration modes of the wall. 

Pulsatile flow in an elastic vessel is very complex, since the tube is able to undergo local deformations in both longitudinal and circumferential directions. The unsteady component of the pulsatile flow is assumed to be induced by propagation of small waves in a pressurized elastic tube. The mathematical approach is based on the classical model for the fluid-structure interaction problem, which describes the dynamic equilibrium between the fluid and the tube thin wall (Womersley, 1955b Atabek and Lew, 1966). The dynamic equilibrium is expressed by the hydrodynamic equations (Navier-Stokes) for the incompressible fluid flow and the equations of motion for the wall of an elastic tube, which are coupled together by the boundary conditions at the fluid-wall interface. The motion of the liquid is described in a fixed laboratory coordinate system (f , 6, f), and the dynamic... 

Chelghoum,A., Dowling, P.J., An Updated Lagrangian Finite element Approach to Non-linear Fluid Structure Interaction Problems . 

In recent years, the SPH methods in particular have gone through major improvements and their application was expanded into a wider range of engineering problems. These include both more advanced physical models and more advanced engineering processes. For example, SPH was successfully used to simulate non-Newtonian fluid flows and viscoelastic materials. It has been also used for the analysis of fluid-structure interaction problems, fluid flow in porous media and fractures, heat transfer and reacting flow problems. 

For a systematic study of the random structural fluid interaction problem,... 

The behaviour of the reactor block was on the whole in line with estimates. The main problem was the appearance of oscillations in the internal structures during the first build-up in speed of the pumps this gave feedback for further theoretical knowledge on the questions of fluid-structure coupling. 

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