Risk-based multi-objective optimisation of a monopile offshore wind turbine support structure

The present work carries out a multi-objective design optimization of a monopile offshore wind turbine support structure. Three objective functions are created related to the minimization of the total construction cost of the monopile support structure, fatigue damage, and permissible stress ratio. The construction cost takes into account the costs associated with welding and labor. The constructional limitations in the offshore industry take into consideration in the selection of the upper boundaries of the design variables. The reliability index is employed to identify the topology of the structure as a part of the Pareto frontier solution in reducing the failure probability for the critical limit states and satisfying the target reliability level. A risk-based assessment of the optimal designs is performed and the output is used to update the life-cycle cost assessment. The ultimate optimization target is deemed to be the minimization of the levelised cost of energy, which is estimated based on the discounted cash-flow method considering the life-cycle costs constituting CAPEX and OPEX.