Scientific Events

The development of energy efficient electrical machines requires accurate knowledge of the magnetic material behavior, i.e., iron loss components  and magnetizability, already in the design stage. In addition, knowledge on the magnetic property deterioration due to induced  residual  stresses occurring during the manufacturing as well as due to applied mechanical  stresses during the operation of the electrical machine is indispensable for the contemporary machine-design.In general, the modeling can be approached at different length scales, i.e., from quantum mechanics at the atomic level and micromagnetics at the sub-micrometer length scale to continuum modeling at the ultra-millimeter scale. The difficulty to apply micromag- netic approaches in the numerical simulation of electrical machines is given both, by the tremendous  need of computational effort as well as the difficulty to consider the inter- action with effects present at the macroscale such as, e.g., residual  stresses or non-local eddy currents.A more modern view of such aspects is to regard materials  as multilevel structures, where structural features at all length scales play a significant role. Multiscale modeling is the field of solving such problems that have important features at multiple spatial and/or temporal scales.  It allows calculating material properties on one level using information or models from other levels. In the light of this, this presentation will give an overview on the current modeling  approaches applied at the Institute of Electrical Machines (IEM) for soft magnetic materials in the simulation of rotating electrical machines.  Particular attention will be paid to the effect of residual  as well as applied  mechanical stress on the magnetic behavior occurring at the various steps of machine manufacturing and during machine operation.Selected References[1] N. Leuning, S. Steentjes, M. Schulte, W. Bleck, and K. Hameyer, ”Effect of elastic and plastic tensile mechanical loading on the magnetic properties of NGO elec- trical steel,” Journal of Magnetism and Magnetic Materials, vol.  417, pp.  42-48, November 2016.[2] S. Elfgen,  S. Steentjes, S. B¨ohmer, D. Franck, and K. Hameyer, ”Continuous Local Material Model for Cut Edge Effects in Soft Magnetic Materials,” IEEE Transac- tions on Magnetics, vol. 52, no. 5, pp. 1-4, May 2016.[3] N. Leuning, S. Steentjes, M. Schulte, W. Bleck, and K. Hameyer, ”Effect of Mate- rial Processing and Imposed Mechanical  Stress on the Magnetic, Mechanical, and Microstructural Properties of High-Silicon Electrical Steel,” steel research interna-tional, to appear, 2016.  [more]

Two-scale simulations of components classically  rely upon finite element simulations  on boundary- and interface-fitted  meshes on both the macro and the micro scale. For complex microstructures fast and memory-efficient  solvers posed on regular voxels grids, in particular the FFT-based homogenization method [1], provide a powerful  alternative to FE simulations on unstructured  meshes and can be used to replace the micro-solver [2, 3]. Since representative volume elements of the microstructure  consist of up to 80003  voxels, even this micro-solver reaches its limits for nonlinear elastic computations.This talk focuses on the composite voxel technique [4], where sub-voxels  are merged into bigger voxels to which an effective material law based on laminates is assigned. Due to the down-sampled grid, both the memory requirements and the computational effort are severely reduced. We discuss the extensions of linear elastic ideas [4, 5] to the physically non-linear setting  and assess the accuracy  of reconstructed solution fields by comparing them to direct full-resolution computations.References[1] H. Moulinec and P. Suquet. A numerical method for computing the overall response of nonlinear composites with complex microstructure.Computer Methods in Applied Mechanics and Engineering, 157(1-2):69–94, 1998. [2] J. Spahn, H. Andra, M. Kabel, and R. Mueller.A multiscale approach for modeling pro- gressive damage of composite materials using fast Fourier transforms. Computer Methods in Applied Mechanics and Engineering, 268(0):871 – 883, 2014. [3] J. Kochmann,  S. Wulfinghoff, S. Reese, J. R. Mianroodi,  and B. Svendsen.  Two-scale FEFFT- and phase-field-based computational modeling of bulk microstructural evolution and macroscopic material behavior. Computer Methods in Applied Mechanics and Engi- neering, 305:89 – 110, 2016. [4] M. Kabel, D. Merkert, and M. Schneider. Use of composite voxels in FFT-based homog- enization. Computer Methods in Applied Mechanics and Engineering, 294(0):168–188,2015. [5] L. Gelebart and F. Ouaki. Filtering Material Properties to Improve FFT-based Methodsfor Numerical Homogenization.  J. Comput. Phys., 294(C):90–95, 2015. [more]