Analysis And Optimization Design Of Hydrodynamic Performance Of SEMI

With the development of world industry, the demand for oil and gas of human is increasing, and the decrease of onshore and offshore oil causes human to pay more attention to the exploration and exploitation of resources in deep water. With the increase of water depth, the jacket platform and gravity platform are not suitable because of their cost, and platform suitable for operating in deep water is becoming a hot spot of research. At present, there are several types of platform suitable in deep water, such as SPAR, TLP and SEMI. The semi-submersible (SEMI) platform has larger deck area and scope of operating depth, and stronger ability of drilling and lower cost, so it is the most suitable platform working in the South China Sea. In this paper, the hydrodynamic analysis and multi-objective optimization design of a semi-submersible are studied.Based on the three dimensional potential theory, the paper computed the hydrodynamics of a semi-submersible platform. Firstly, the hydrodynamic model is established and some relevant parameters, such as added mass, damping and RAO, are obtained. Then the motion of the platform in frequency domain and time domain is analyzed under the sea condition of10year return period in the South China Sea. The comparison of the results show that that the heaving, rolling and pitching response of the two methods are similar, and the surging and swaying response are different, because of the influence of wave force of low frequency.In order to reduce the heaving response and construction cost of the semi-submersible platform, the paper determines the range of the principle dimensions of the semi-submersible platform according to the data of existing platforms. Based on20groups of sample points produced by LHT method, the surrogate models of the heaving response, rolling response, air gap and stability of the semi-submersible platform are established by the RBF agent modal. The principle dimensions of the semi-submersible platform are optimized by Isight to reduce its heaving response and construction cost with its air gap, rolling response and stability as constraints, and the Pareto results of this multi-objective optimization problem are obtained.The results of the hydrodynamic analysis and optimization design of a semi-submersible platform in this paper are helpful to the preliminary design of the semi-submersible platform.