Numerical Simulation Of Freak Wave And The Interactions Between Freak Wave And Offshore Structures

The freak wave is extremely dangerous to offshore structures due to itsunexpected high wave height, strong nonlinearity. Although increasingly moreattentions are paid to the investigations of freak wave, the principle of its generationmechanism and the factors that contribute to its occurrence still remain unclear. Alsofew efforts were exerted to investigate the interactions between offshore structuresand freak wave such as wave run-up and slamming force.First of all, different freak wave generation models were put forward bychanging the energy distributions patterns of the classical Longuet-Higgins wavemodel. A two dimensional (2-D) and three dimensional (3-D) numerical wave tankwere established by the commercial computational fluid dynamics software FLUENT.The simulations of the freak waves based on different models were carried out and thecomparisons between these models in simulating the freak wave were conducted.Then the numerical simulation and model test were performed to investigate thewave run-up and slamming force on cylinder due to freak wave. The influences ofdifferent parameters such as the significant period, peak value of wave height, focusposition and the water depth on wave run-up and slamming force were alsoinvestigated. Also the experimental results were used to validate the effectiveness ofdifferent empirical formulae in predicting the wave run-up and slamming force.Finally, Hydrodynamic performance of a semisubmersible platform in the waterdepth of500m was studied using time-domain fully coupled analysis method. Thehydrodynamics performances of the platform under two kinds of predeterminedextreme wave sequences were compared. Moreover, the effects of the waveparameters (e.g. focus points, significant wave period, peak value of wave height) onplatform motions were investigated.