Prediction Of Wave Slamming Load Of Semi-submersible Offshore Platform Brace Under Towing Condition

With the development of the exploitation of Marine resources from shallow water to deep water,semi-submersible platforms have gradually been selected as the preferred tool for exploring Marine resources due to its good adaptability and ability to resist harsh environments.During this towing process,the semi-submersible platform will be subjected to the wave slamming.Slender structures such as bracing rods are more vulnerable to the wave slamming.The wave slamming caused severe structural damage to the platform and more seriously threatened the life safety of operators.Therefore,it is necessary to study and forecast the wave slamming pressure law of semi-submersible offshore platforms.This means that the wave slamming loads should be fully considered in the platform structure design stage to achieve the improvement of its structural strength.In this paper,the direction and problems of the research on wave slamming of semi-submersible offshore platforms at home and abroad are summarized.CFD(computational fluid dynamics)method is used to predict the wave slamming under the conditions of wind,wave and current.The mechanism and sensitivity of the effects of wave steepness,velocity and wave direction angle on the wave slamming of semi-submersible offshore platform under towing condition are studied.As extremely dangerous sea conditions,freak wave not only generate in bad weather with strong winds and waves,but also often generate in calm sea conditions.This will cause great damage to the semi-submersible platform.Therefore,the problem of the semi-submersible platform under the towing condition is studied.The pressure change characteristics of the platform are obtained when it is hit by the freak wave.Finally,the towing model test of semi-submersible offshore platform is explored and compared with the numerical simulation results to verify the reliability of the numerical simulation method.The main research content includes:(1)Firstly,this paper summarizes the research status and numerical simulation methods of wave slamming on offshore platforms in recent years.The research hotspot and problem of wave slamming are studied.The research methods to solve the above problems are given.(2)In this paper,the VOF(fluid volume function)method and the overlapping grid method are used to study the unsteady movement of viscous fluid with time,which can more accurately simulate the wave surface change of waves.It can accurately simulate the motion response of the semi-submersible offshore platform under the action offluid-structure coupling.The parameters of the wave making grid of the numerical wave tank are optimized and analyzed.The numerical simulation results of the wave are compared with the theoretical values.Obtained more accurate numerical simulation results of waves,and verified the accuracy of the wave formation in the numerical tank.(3)The wave slamming of semi-submersible platform braces and the influence mechanism and sensitivity of parameters were studied in the created numerical tank by using the above simulation method.The wave slamming of the semi-submersible platform brace under towing conditions is predicted.The effect rules of wave steepness,flow velocity,wave direction angle and other parameters on the wave slamming of the semi-submersible offshore platform brace are obtained.At the same time,the slamming pressure distribution area on the surface of the strut is studied,and the slamming pressure distribution characteristics on the strut surface are obtained,which provided theoretical support for the design of the offshore platform.(4)The experimental physical model is designed based on froude similarity criterion.The tank model test scheme was completed and the semi-submersible platform wave slamming towing test is finished.The distribution characteristics and variation rules of the wave slamming pressure of semi-submersible offshore platform braces and columns under towing conditions are obtained by experiments.At the same time,the accuracy of the above CFD research method is verified.(5)The wave slamming of freak wave on semi-submersible platform brace is studied based on CFD method.Longuet-Higgins model was used to generate freak waves by MATLAB programming.A numerical tank of freak waves is created based on the generated freak waves.The wave slamming characteristics of semi-submersible platform under the action of freak wave are studied.This paper focuses on the analysis of the slamming law of different parts of the platform under the slamming pressure of freak wave,which provides theoretical support for the structural design of semi-submersible offshore platform.