Study On Characteristic Wave Cases In Global Strength Analysis Of A Semi-submersible Platform

Deepwater semi-submersible drilling platform subjects to complexwave loads. It is very important for the safety assessment of structures toconsider the critical wave cases comprehensively during the whole life ofa semi-submersible platform.The three-dimensional potential flow diffraction theory is applied forthe wave loads calculation of semi-submersible platform and design wavemethod is generally used for statistical forecasting of wave loads. Somecharacteristic wave cases in the global strength analysis of the aimedplatform are concluded according to the rules and the analysis of thestructural properties. The stochastic design wave method and long termresponse method are adapted for the hydrodynamic calculations and FEMare for the structure responses of aimed platform. The dangerous wavestates of platform are found by considering the section loads and structurestress level in each wave cases.The main research work of this paper is as follows:1．The principle and application of two wave calculation theories for the semi-submersible platform are introduced at first. The calculationprocess of stochastic design wave method and long term response methodis illustrated. Then the design loads, wave cases and the analysis flowbased on SESAM for the global strength assessment are elaborated.2．The wave cases proposed for the global strength analysis accordingto the rules and the structure properties of the aimed platform.Three-dimensional potential flow theory is applied for the hydrodynamiccalculation and the design wave parameters of survival and operationconditions are gotten. Stress level of platform and section loads areobtained after the calculation of wave load and structure responses.3. The stress level of main structures, the distribution of section loadsand the loads of target sections are analyzing comprehensively to foundthe dangerous wave states of semi-submersible for the global strength.Some critical wave cases are concluded and then discuss the differencesof two design wave methods.