Robust Design Optimization Of Fixed Support Structure Of Offshore Wind Turbine

The support structure is the key assembly of the offshore wind turbine, which faces harsh marine environment. With the fast development of offshore wind power exploitation and the increasing enlargement of installed capacity, the fixed support structure of offshore wind turbine confronts great challenges in design, manufacturing and operation.Firstly, the safety requirement and cost requirement of the fixed support structure of offshore wind turbine need to be deeply investigated. The support structure undertakes the nonlinear loads during the operation of the turbine at the tower top, and the stochastic loads of wind, waves and streams. The safety requirement is considerably important due to the damage of the support structure, which may lead to the fall of the rotor and cabin. Such accident will cause huge economic loss. Meanwhile, the cost of manufacturing, transportation and installation of the support structure of offshore wind turbine is several times higher than the onshore one. So it needs to use the design optimization method to decrease the cost of the support structure and to fulfill the safety requirement at the same time.Secondly, the uncertainties of material properties, structural geometries and marine environmental loads will make the dynamic responses of supporting structure deviate from the original design expectation, which may lead to structure failure and economic loss. So the robust design optimization considering the uncertain factors needs to be utilized.In the light of the challenges mentioned above, the robust dynamic optimization of the fixed support structure of offshore wind turbine concerning the uncertainties is investigated. The main jobs are as follows:1) The dynamic response analysis of tripod-type support structure in time domain under different control modes of turbine is conducted. The nonlinear time domain loads of turbine at the tower top are simulated and calculated using several control strategies including fault conditions. The dynamic loads due to yaw fault condition with the control mode of the turbine can cause the largest dynamic responses of support structure.2) The optimization of time domain simulations of tripod-type support structure is carried out. Via establishing the approximate model, the time consumed finite element model is replaced and the dynamic response analysis in time domain is simplified. When controlling the accuracy, the approximate model built by Kriging method utilizing design of experiment of Optimal Latin proves to having the minimal error.3) The robust design optimization of tripod-type support structure is realized. Firstly the sensitivity analysis is used for selecting the best structural design variables. Then the combination of optimization algorithms is introduced for global and efficient searching through design space. Compared with traditional deterministic optimization, the robust optimization considering the uncertainties can promote the structural reliability, minimize the economic cost and improve its robustness at the same time.It can be concluded that the robust optimization of the fixed support structure of offshore wind turbine takes the uncertainties into consideration. And the optimized results give consideration to both the safety and cost of tripod-type support structure of offshore wind turbine. The approximate model technology can decrease the simulations of dynamic response analysis, which improves the efficiency of iterative process of optimization. The whole framework of robust optimization can be applied to other similar marine structures, which has certain engineering significance.