Substructure topology optimization of an electric machine: Master's thesis

In the thesis a structural optimization method called topology optimization is applied to redesign a substructure of an electric machine. The objective is to increase the stiffness of this structure with a prescribed volume constraint. Topology optimization is performed with commercial software OptiStruct. The software utilizes the so called SIMP method. The initial substructure of the electric machine is welded from steel plates. The optimization result consists of base material, thus no welds are found in the optimized structure. The influence of this to the fatigue life of the structure is briefly studied. Topology optimization theory is outlined and the software is validated with three optimal benchmark cases from the literature. The implementation of topology optimization in a product design process is discussed and examples of the procedure are provided. According to the software validation, OptiStruct delivers optimized and near optimal topologies. The software is recommended to be used in the thesis. Topology optimization with linear element models revealed known features of the SIMP method, like the formation of the so called checkerboarding in the optimization solution. In the optimization of the substructure various load cases, with prescribed static displacements, are used. These are extracted from a separate FEA and they represent loadings of the substructure in its operating environment. The topology optimization is initially performed in individual load cases with linear element models. No additional constraints of the software are used in this optimization. Defining features and differences of the resulting structures are studied. Finally a combined optimization of multiple load cases is performed with parabolic element models with symmetry and minimum member size constraints. The new substructure consists of topology optimization results, with modified features by the author. The stiffness of the structure was multiplied in specific load cases, with around 8% added weight, when compared to the original substructure. The fatigue strength of the structure was increased, as no welds are found in highly stressed regions of the structure. The implementation of the topology optimization method was recommended in the concept phase of product development, but it can be also used in cases where the initial structure is strictly defined.