Numerical simulation of nonlinear interaction between structures and steep waves

摘要

Responding to great concerns about the interaction between steep waves andudstructures in naval architecture and offshore engineering, a methodology andudcorresponding numerical algorithm for computing three-dimensional inviscid flow with audfree surface are developed based on a fully nonlinear theory in this thesis. The associatedudboundary value problem is solved using a finite element method. In order to chose anudefficient solver for algebraic equations, a direct method and an iterative method withudtwo different preconditioners are compared to each other, which leads to the suggestionudthat the conjugate gradient method with an SSOR preconditioner is the most suitable forudthe problem of concern. Furthermore, the radiation condition at a truncated boundary isudimposed with an associated damping coefficient optimised to reduce the reflection ofudwaves. In addition, an analytical solution for transient standing waves in a circular tankudis derived using second order theory, which provides a tool to validate the numericaludmethod.udThe developed numerical method is first utilised in simulating the sloshing wave in audtank generated by initial disturbance on the free surface and by the translational motionudof the tank. Numerical results are compared with analytical solutions in several cases,udwhich show that the numerical method can be very accurate. The features of the steepudsloshing waves are then examined.udIn the second application, the interaction between vertical cylinders and wavesudgenerated by a wave maker is investigated. The motion of the wavemaker can beudspecified accordingly, in order to generate monochromatic, bichromatic or irregularudprogressive waves. The forces on one and two cylinders are obtained and comparedudwith published data. The steep waves and their effects on hydrodynamic loads areudanalysed.udIt is concluded that the developed methodology based on the finite element method isuda good alternative to the existing techniques for the simulation of steep waves. Itsudaccuracy, flexibility and efficiency demonstrated by various numerical examples appear toudbe quite favourable.