Research On Semi-submersible Offshore Platform Structural Response Under The Tender Collision

The collision of offshore platform is a kind of complicated dynamic response process,take place when the structure suffers from a huge impact load in a short period and shows very obvious nonlinear dynamic characteristics.Considering the complexity of the problem and the serious consequences caused by collision damage,this study focuses on the specific research of semi-submersible offshore platform and the tender stern collision,which is of great significance in strengthening the intensity of offshore platform structure,preventing the happening of the platform collision accident and giving advices on offshore platform structure design and anti-collision system design.The research object is the deepwater semi-submersible offshore platform,with the maximum operating depth of 3000 meters and the maximum drilling depth of 10000 meters in the South China Sea.On the basis of a systematic analysis and summary of offshore structures’ mutual collision mechanism,this research mainly uses the additional quality standard to solve the problem of dynamic response of semi-submersible offshore platform under the tender stern collision,and applies the finite element software ANSYS/LS-DYNA numerical simulation calculation.The specific research presented in this paper include:1.Expound the research status of impact dynamics home and abroad,and introduce the basic theory of numerical simulation collision in this paper.It summarizes the surrounding fluid processing method in the process of collision,and determines the mechanics model of the offshore platform and tender material.2.Establish the finite element model of semi-submersible offshore platform and the tender based on ANSYS software,and detail the offshore platform and ship collision area of the grid.It carries on the numerical simulation aiming at the most typical collision situation,when the tender stern collides with the offshore platform column at a speed of 4m/s.3.Research the impact of the collision response of different collision parameters(impact velocity,impact angle and the collision position)on offshore platform in order to obtain the collision force,energy distribution,temporal results of damage deformation and strain.It ensures the degree of damage for the offshore platform,and presents a relative dangerous collision situation of the offshore platform.4.Process the simulation results by using equivalent force-displacement and energy equivalent principle of simplified algorithm.It amends the stiffness coefficient by change the thickness of pillar collision area,so as to obtain the general expression of stiffness coefficient k.Finally,it contrast analysis the collision results when the tender collides with offshore platform at a speed of 4m/s by using the fluid-solid coupling method.This paper focuses on the numerical simulation in the collision of half submerged structure response of offshore platform column under the tender stern collision,by changing the impact velocity,impact angle and the collision position.The basic conclusions are as follows:1.The overall movement of offshore platform has a certain lag quality,and the collision force presents obvious nonlinear characteristics.In the process of column structures’ collision,the shell absorbs internal energy the most,followed by the transverse frame,vertical wall plate,shell T profile and deck of the internal structure.The column structure destroys it mainly through extrusion,bending,stretching and crushing.2.In the process of energy conversion,the tender has a "play" back to the process by offshore platform.When the impact velocity is slow,the platform shell structure unit generates vibration phenomenon,in addition,the cell stress and energy fluctuate during a short period.3.From the results of the two kinds of simplified algorithms,it can be concluded that the result is more precise when adopting the method of energy equivalence theory.The result is consistent by using attaching quality standard and fluid-structure coupling method computation,and usually recommended of the additional quality standard for the finite element calculation.