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Sloshing in reservoirs with multi-degrees-of-freedom base motions Premasiri, Sundaralingam

Abstract

This thesis describes an investigation of the influence of multiple base motion components and hydrodynamic damping on the hydrodynamic loads and fluid surface elevation in a fluid filled reservoir subjected to base excitation. The investigation is carried out for two configurations: rectangular and circular cylindrical reservoirs. The multiple motions are horizontal and rocking excitations and the hydrodynamic damping is due to boundary layers along the reservoir walls and baffles in the reservoir. Initially, the boundary value problem for the case of an inviscid fluid and a harmonic base motion is solved on the basis of linearized potential flow theory. The case of energy dissipation of a real fluid is then treated by a extension to this, which involves an assumption of dissipation at the free surface and a corresponding modification to the free surface boundary condition. In order to treat earthquake-induced motions, this solution is then extended to a simplified method of estimating maximum forces using a modal analysis and involving earthquake response spectra. The estimation of hydrodynamic damping is also discussed. The combined effect of the two component excitations on the overall fluid elevation and hydrodynamic forces are calculated using superposition. An experimental investigation for liquid filled rectangular tanks has been carried out. The tanks were subjected to component motions (horizontal and rocking) and combined motions, both for harmonic and earthquake motions. The important parameters are the size of the tank, depth of fluid, frequency of excitation, and amplitude of the base motion. The resulting parameters of interest include the maximum fluid surface elevation, the maximum horizontal force and the maximum overturning moment at the base of the tank. The experiments were extended to investigate the effects of damping, whereby the experiments were repeated with baffles in the rectangular reservoir. The theoretical results are compared with existing solutions and experimental results. The effects of additional degrees of freedom motions and of hydrodynamic damping on the hydrodynamic loading and fluid elevations are discussed in detail. The effects of damping on hydrodynamic loading and the fluid surface elevation are also discussed. Finally, conclusions are given including the effect of multi-degree-of-freedom base motion, the effect of hydrodynamic damping and the effectiveness of various baffle configurations.

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