The Study Of Local Scour Around Column Feet Of Offshore Platform

When a column stands in the flow, the presence of it will change the state of flow in its neighborhood, resulting in the following phenomena: the contraction of the flow, the formation of a horseshoe vortex in front of the pile and lee-wake vortices behind it and so on. These changes will break the original balance state of sediment, which start into exciting movement, leading to local scour. The scour will influence the steady of the offshore platform, threatening the safety of the platform. The text will make research around local scour of column feet of platform, make numerical simulation of the flow field near the column which is up against local scour by use of the finite element software, pointing out the direction of future research.The major research work and harvest as follows:(1)After summarizing and consulting lots of papers and researches existing currently, according to be in different wave and currents surroundings, the main cause which arouses local scour is different, the paper depicts the mechanism of scour around column in different conditions, compares and discusses the research methods and depth formulae existing recently, and analyses kinds of factors that influence depth of scour hole, providing a firm theoretic base to the continuing research.(2)The depth of scour hole is the key point of the problems of scour, which is waiting to be resolved. The depth formulae of small diameter pile have been studied extensively, but of large diameter not. Therefore, the paper summarizes the depth formulae of different D/L range and makes program of them using JAVA, intelligence the course of calculation of the formulae.(3)The paper makes numerical simulation of the flow field near a column by use of the finite element software ANSYS CFX. The pre-disposing module of which, ICEM CFD, has special function of plotting hexahedron girdding through mapping technology, building slippery and close-fitting girdding. The result displays the velocity and pressure distributing around the column and presence of vortices. At the same time, the paper discusses multiphase flow, a research method in ANSYS CFXwhich can simulate the whole scour properly, offering a direction to the future research.(4)Since local scour brings great danger to platform, scour prevention techniques should be taken into account in the course of designing and working. The paper enumerates some scour-prevence methods, which are proved resultful in practical coastal engineer.