Although mostly used in wind turbine market, single rotor wind turbines have problems with transportation and installation costs due to their large size. In order to solve such problems, multi-rotor wind turbine research has been performed. This study proposes the structural design method of multi-rotor wind turbine using a topology optimization scheme. Wind turbines operate under various load conditions and must have a certain level of static and dynamic stiffness in order to withstand the forces. Therefore, both static and dynamic behaviors are simultaneously considered in the design process.

The structure of a multi rotor wind turbine is optimized to minimize the compliance of structure while satisfying the stress and the volume constraint for 3D structural design. The density method [1] combined with the method of moving asymptotes [2] is employed for topology optimization. Since the resultant shape by topology optimization is hard to realize in manufacturing, the obtained structure in branch parts is changed to have shell structures and modified through parametric design using the design of experiments (DOE) and the response surface method (RSM) for their thicknesses and radii. The structure, which acts as a reinforcement around the joint, where stress concentrations occur, is optimized by the topology optimization method. To reduce the weight, the solid structures obtained at joint parts is modified to have shell structures. Then, the applicability of the resultant structure is determined through static and dynamic analysis. For the finite element analysis and regression analysis, commercial packages COMSOL and Minitab are used.