Influence Of Island And Reef Topography On Motion Response Of Semi-submersible Offshore Platform

With the introduction of building China into a maritime power and the deep blue strategy,there will be a wide variety of new and old marine structures appeared in the South China Sea.However,the average depth of the South China Sea is 1200 meters and the topography around islands and reefs in the South China Sea is complex which leads to the drastic change of water depth.In such peculiar environment,offshore structures may be exposed to the mutual influence of waves and topography which result in a distinctive structural load or motion response other from uniform water depth or deep water.Therefore,it is necessary to conduct research on the motion response of structure to find suitable locations for installing marine structures(such as launch platforms,nuclear power platforms,large ships,etc.)and water-break.With the property site selection and the coverage of water-break,we may witness a great progress on the reliability and safety of these structures.Based on ANSYS FLUENT CFD model,this paper studies the motion response of semi-submersible offshore platform under the influence of breakwater and topography.The main work of this paper is followed:(1)After Generalizing and summarizing the literature of related issues in this paper,author concentrates on the regions mentioned afterwards: the research status of numerical wave tank,the interaction between wave and structure,the motion response and hydrodynamic performance analysis of offshore platform,the influence of island and reef topography on platform hydrodynamic performance are studied.(2)In the second part,author establishes a three-dimensional numerical wave tank,then conducts convergence analysis on its space step,time step and length of wave absorbing region.So as to formulate the numerical tank model that meets the requirements of subsequent tests.In the verification part,the simulated experimental value and theoretical value were compared to prove the availability of the numerical tank,which laid a good foundation for the subsequent numerical experimental research.(3)The models of the semi-submersible offshore platform and its surrounding waters are established to study the motion response of the platform with or without breakwater protection.Firstly,the effects of wave period and wave steepness parameters on the platform motion response under unprotected conditions are discussed.Then,the shielding effect of the breakwater is verified.Also,the shielding effect of the breakwater against waves with different period are analyzed.Finally,the influence of the layout position,shielding area and layout form of the breakwater on the shielding effect is studied.(4)On the basis of the above research,the wave propagation and platform motion response are further studied with attachment of several typical topography.Firstly,the effects of topography and slope of reef front on wave propagation are analyzed.Then,the paper focuses on the influence of several kinds of raised and sunken topography,as well as the slope of the reef front on the motion response of the platform,and verifies the conclusions of the influence of topography on wave propagation.