Numerial Investigation On Wave Run-up Of Semi-submersible Platform

It poses a severe challenge to platform security，with the frequent worsening ofeep-sea environment and the appearance of super typhoon. Air-gap performance hasbeen key issue in the design of semi-submersible platform.The air-gap is defined asthe ertical distance between the lower deck of platform and the wave surface， whichis a mportant parameter to judge whether some nonlinear phenomena such asslamming and reen water happen or not.Traditional design concept is that the initialair-gap is large enough to ensure wave ould not impact the deck. However，the heightof deck is constrained by its own weight nd stability. In addition，with the continuousdeterioration of ocean environment，it is ifficult to avoid wave impacts and greenwater by simply increasing the height of reeboard of platform.It is a hot topic of the research on wave run-up and air-gap response in oceanengineering field， and becoming an important issue in oil and gas exploitationstrategy of the South China Sea. The mechanism of wave diffraction and run-upeffects， the cross-sectional shape of column， the directions of incident wave，nonlinear coupling between wave and current， hydrodynamic interference ofmulti-columns structure.Wave run-up and wave disturbance around a fixed truncated column isinvestigated based on model test and CFD method. The wave run-up effect accordingto different incident wave parameters is investigated. The edge wave effects andnon-linear harmonic frequency components during wave scatters around column isalso discussed. Data from model test verifies the accuracy of the numerical simulation.The flow distributions and vertex shedding characteristics are analyzed deeply.Considering the multi-direction of ocean wave in actual sea conditions， whichwill lead to a change of projection surface，wave run-up around column in different direction of incident wave is studied. Wave run-up effects and the mechanism ofvortex shedding on free surface are discussed from some factors such as wave run-upamplitude along circumferential direction，curve fluctuations，projection shape，equivalent diameter of column.The hydrodynamics interaction among columns is pretty strong forsemi-submersible， which will induce large wave run-up and local surfaceamplification. A detailed analysis of wave non-linear effects in different kinds ofcolumn combinations according to incident wave parameters，column spacing and thedirections of incident wave is presented. In addition，the interactions of edge wave，wave run-up round columns， wave superposition effects and forces are alsoinvestigated. The free surface characteristics and the mechanism of amplification asthe near trapping phenomenon occurs，are studied in detail.Based on the work of each column-type， numerical wave tank used forinvestigating the interaction between waves and semi-submersible platform isestablished. The wave run-up and non-linear slamming around the platform accordingto incident wave frequency and steepness are investigated. Many factors which affectimpact pressure，movement characteristics of wave tongue are also presented. Inaddition，relative wave run-up and air-gap distributions，the non-linear harmoniccomponents and shape of wave time series around platform in motion conditions areobtained. In order to verify the accuracy of numerical simulation，model test isconducted.The thesis launches on several factors such as incident wave steepness，scatteringparameters，cross-section geometry，the direction of incident wave，wave-current coupling condition，hydrodynamic interfere among multi-columns， thearrangement of multi-columns，column spacing，pontoon，platform motion etc， inorder to investigate wave run-up，air-gap response and non-linear slamming effects.More systematic and innovative conclusions are drawn，which provides a theoreticalbasis and technical support for prediction of wave run-up and air-gap response when multi-column types of platforms are design ed for deep water.