| It is necessary to study the ultimate strength of Semi-submersible platform in order to ensure the safety of the structure. The key is how to analyze the ultimate strength for the complex offshore engineering structure who usually works in the tough environment. Based on the nonlinear finite element method, a quasi-static method is used in this thesis to study the ultimate strength of the Semi-submersible platform from the local and whole points of view. The major works are as follows:1. The origin of the nonlinearity is introduced. And two methods of NFEM for evaluation of ship structure, the static method and the quasi-static method are compared.2. The four ultimate states of the semi-submersible platform are introduced; choose two typical local models of the dangerous structures under one ultimate state as an example.3. A complete method of analyzing the local ultimate strength of semi-submersible platform with NFEM is established. Through a lot of calculation, we get a series of significative conclusions.4. Use the NFEM to analyze the ultimate strength of the longitudinal pontoon, deck and the total structure of the semi-submersible platform, calculate the ultimate hogging and sagging bending moment of them. Analyze and compare the calculation, obtain a series of significative conclusions, and the wave parameters under the ultimate states can be derived. |
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