Dynamic response analysis of a liquid-filled cylindrical tank with annular baffle
ABSTRACT Baffles are generally used as damping devices in liquid storage tanks. The focus of the present paper is to study the influence of a baffle on the dynamic response of a partially liquid-filled cylindrical tank. A baffle is assumed here to have the shape of a thin annular circular plate. The natural frequencies of an inviscid and incompressible liquid are determined for varying positions and dimensions of a baffle attached normal to the tank wall. The flexibility of both the baffle and the tank are considered in studying the effects of liquid–baffle and liquid–tank interactions on the sloshing mode frequencies. Finite element codes are developed and are then used to analyze both the liquid domain and the structural domain (i.e., the tank and the baffle). The coupled vibration frequencies of the tank–baffle system are computed considering the effect of sloshing of liquid. The results obtained for a liquid-filled elastic tank without a baffle and a rigid tank with a rigid baffle are in good agreement with the available results. The slosh amplitude of liquid in a rigid tank with and without a rigid baffle is studied under translational base excitation. The effects of the tank wall and baffle flexibility on the slosh response are also investigated.
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ABSTRACT: Dissertation Acoustoelasticity is the study of the dynamic interaction between elastic structures and acoustic enclosures. In this dissertation, acoustoelasticity is considered in the context of liquid rocket engine design. The techniques presented here can be used to determine which forcing frequencies are important in acoustoelastic systems. With a knowledge of these frequencies, an analyst can either find ways to attenuate the excitation at these frequencies or alter the system in such a way that the prescribed excitations do result in a resonant condition. The end result is a structural component that is less susceptible to failure. The research scope is divided into three parts. In the first part, the dynamics of cylindrical shells submerged in liquid hydrogen (LH<sub>2</sub>) and liquid oxygen (LOX) are considered. The shells are bounded by rigid outer cylinders. This configuration gives rise to two fluid-filled cavities: an inner cylindrical cavity and an outer annular cavity. Such geometries are common in rocket engine design. The natural frequencies and modes of the fluid-structure system are computed by combining the rigid wall acoustic cavity modes and the in vacuo structural modes into a system of coupled ordinary differential equations. Eigenvalue veering is observed near the intersections of the curves representing natural frequencies of the rigid wall acoustic and the in vacuo structural modes. In the case of a shell submerged in LH<sub>2</sub>, system frequencies near these intersections are as much as 30% lower than the corresponding in vacuo structural frequencies. Due to its high density, the frequency reductions in the presence of LOX are even more dramatic. The forced responses of a shell submerged in LH<sub>2</sub> and LOX while subject to a harmonic point excitation are also presented. The responses in the presence of fluid are found to be quite distinct from those of the structure in vacuo . In the second part, coupled mode theory is used to explore the fundamental features of acoustoelastic systems. The result is the development of relatively simple techniques that allow analysts to make informed decisions concerning the importance of acoustic-structure coupling without resorting to more time consuming and complex methods. In this part, a new nondimensional parameter is derived to quantify the fundamental strength of a particular acoustic-structure interaction irrespective of material and fluid properties or cavity size. It is be shown that, in some cases, reasonable approximations of the coupled acoustic-structure frequencies can be calculated without explicit knowledge of the uncoupled component mode shapes. Monte Carlo simulations are performed to determine the parameter values over which the approximate coupled frequency expressions are accurate. General observations concerning the forced response of acoustoelastic systems are then made by investigating the response of a simplified two mode system. The third part of this research discusses the implementation of a component mode synthesis (CMS) technique for use with geometrically complex acoustoelastic systems. The feasibility of conceptually similar techniques was first demonstrated over 30 years ago. Since that time there have been remarkable advancements in computational methods. It is therefore reasonable to question the extent to which CMS remains a computationally advantageous approach for acoustoelastic systems of practical interest. This work demonstrates that relative to the most recent release of the popular finite element software package, ANSYS, CMS techniques have a significant computational advantage when the forced response of an acoustoelastic system is of interest. However, recent improvements to the unsymmetric eigensolver available in ANSYS have rendered CMS a less efficient option when calculating system frequencies and modes. The CMS technique is then used to generate new results related to geometrically complex acoustoelastic systems.01/2008;
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ABSTRACT: We consider the finite element approximations of an optimal control problem consisting in the suppression of slosh arising in fluid–structure interaction problems with free surface. The vibration of a plate in contact with an incompressible fluid is considered as state equations in the optimization problem, and distributed controls on the plate are calculated to suppress the slosh.Locking‐free finite elements are used to discretize the plate, which is modeled by Reissner–Mindlin equations. The effect of the fluid is taken into account by means of an added mass formulation, discretized by standard piecewise linear tetrahedral finite elements, and the gravity waves on the free surface of the liquid are considered in the model. The control variable is the amplitude of a secondary force actuating on the structure.Implementation issues are discussed, and numerical experiments are presented. Copyright © 2012 John Wiley & Sons, Ltd.International Journal for Numerical Methods in Engineering 08/2012; 91(6):604-621. · 2.06 Impact Factor
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ABSTRACT: In the present paper a method is proposed to investigate the effects of a rigid internal body on the coupled vibration of a partially fluid-filled cylindrical container. The internal body is a thin-walled and open-ended cylindrical shell. The internal body is concentrically and partially submerged inside a container. The radial and axial distances between the internal body and the container are filled with fluid. Along the contact surface between the container and the fluid, the compatibility requirement for the fluid–structure interactions is applied and the Rayleigh–Ritz method is used to calculate the natural frequencies and modes of a partially fluid-filled cylindrical container. The fluid domain is continuous, simply connected, and non-convex. The fluid is assumed to be incompressible and inviscid. The velocity potential for fluid motion is formulated in terms of eigenfunction expansions for two distinct fluid regions. The resulting equations are solved by using the Galerkin method. The results from the proposed method are in good agreement with experimental and numerical solutions available in the literature for the partially water-filled cylindrical container without internal body. A finite element analysis is also used to check the validity of the present method for the partially water-filled cylindrical container with internal body. The effects of the fluid level, internal body radius, and internal body length on the natural frequencies of the coupled system are also investigated.Journal of Fluids and Structures 01/2009; 25(2):389-405. · 2.05 Impact Factor