Offshore Platforms Wave Load Calculation And Transient Dynamic Response Sensitivity Analysis Of The Adjoint Method

In this paper the search was carried out from the solution of the wave load in analysis of fixed offshore platform structures. Based on the finite element analysis and structural optimization design software system JIFEX, the algorism for solving the linear wave, Stokes wave and isolated wave are realized. And it also studied the adjoint method of the sensitivity analysis for structural transient dynamic responses.In the part of the analysis and calculation for the wave load of fixed offshore platform, firstly, the solution of the wave load in analysis of the fixed offshore platform structures and the algorism of the application of several wave theories was discussed. And then, based on the finite element analysis and structural optimization design software system JIFEX, the algorism for solving the linear wave, Stokes wave and isolated wave are realized. A pre-processing subsystem for environmental load that mainly deals with the wave load was designed. With Morison function, the wave load act on beams of structures can be calculated, and the result of distributed wave load can be dispersed to centralized load for beam element which is convenient for finite element analysis, then the wave load data that is caused by multifarious wave environmental factor is created. The research and realization of the pre-processing subsystem for wave load is also a part of the dynamic analysis system of JIFEX. It founded the foundation not only for the calculation of regular wave and the simulation of stochastic wave, but also for the calculation of dynamic water load considering the reciprocity of structure-liquid in the wave dynamic analysis for platform structure.In the part of the adjoint method for sensitivity analysis, based on the summary of the analysis method for structural dynamic responses and sensitivity, the adjoint method for the sensitivity of structural dynamic responses was researched and the formula was derivatived. Because of being independent of design variable, using adjoint method is more effective when dealing with problems with more constraint functions and less design variables. The dynamic responses on critical time can be worked out using Newmark method, and the adjoint vector can be worked out using direct method (the solving of responsesand adjoint vector is separate), then we can get the sensitivity on critical time. In this paper, the analysis system for adjoint method based on JIFEX was realized. Conclusion was made that satisfying result can be worked out by choosing appropriate step length.