arXiv subjects

Karl Hollaus

Publications and source records attributed to Karl Hollaus.

4 recordsLinked to original sources

arXiv2026

An Iterative Method for Transient Finite Element Simulations of Non-Linear Eddy Current Problems

A method is presented to carry out a transient simulation of eddy current problems with nonlinear materials. Coils are voltage-driven. The magnetic field due to currents in coils are considered by their Biot-Savart-fields. The magnetic vector potential is used in the finite element formulation. The time stepping method is based on implicit Euler. The arising nonlinear equation system is split into two parts, the common finite element system and a circuit equation. Each part is solved separately by Newton's method. Additionally, a line search is used to solve the nonlinear field equations. Inrush currents and average magnetic flux densities through cross sections of laminates of a nonlinear benchmark problem consisting of a laminated iron core inserted in a cylindrical coil are studied. All details of the numerical benchmark are given to evaluate the presented results. Numerical data describing the performance of the presented method are provided.

math.NA↗

arXiv2023

Multiscale Finite Element Formulations for 2D/1D Problems

Multiscale finite element methods for 2D/1D problems have been studied in this work to demonstrate their excellent ability to solve real-world problems. These methods are much more efficient than conventional 3D finite element methods and just as accurate. The 2D/1D multiscale finite element methods are based on a magnetic vector potential or a current vector potential. Known currents for excitation can be replaced by the Biot-Savart-field. Boundary conditions allow to integrate planes of symmetry. All presented approaches consider eddy currents, an insulation layer and preserve the edge effect. A segment of a fictitious electrical machine has been studied to demonstrate all above options, the accuracy and the low computational costs of the 2D/1D multiscale finite element methods.

math.NA↗

arXiv2023

An Equilibrated Error Estimator for the 2D/1D MSFEM T-Formulation of the Eddy Current Problem

The 2D/1D multiscale finite element method (MSFEM) is an efficient way to simulate rotating machines in which each iron sheet is exposed to the same field. It allows the reduction of the three dimensional sheet to a two dimensional cross-section by resolving the dependence along the thickness of the sheet with a polynomial expansion. This work presents an equilibrated error estimator based on flux equilibration and the theorem of Prager and Synge for the T-formulation of the eddy current problem in a 2D/1D MSFEM setting. The estimator is shown to give both a good approximation of the total error and to allow for adaptive mesh refinement by correctly estimating the local error distribution.

math.NA↗

arXiv2020

Effective Medium Transformation: the Case of Stratified Magnetic Structures

Effective medium theory replaces a given fine-scale heterostructure with a homogeneous one in such a way that the physically measurable quantities, e.g. reaction fields and losses, remain approximately the same. This Letter shows that the very nature of the physical problem may change upon homogenization. A specific example is a stratified nonlinear magnetic and conducting medium, where a low frequency excitation induces eddy currents. It is shown that the appropriate coarse-scale (homogeneous) model is, counter intuitively, magnetostatic, with an effective complex valued BH curve whose real and imaginary parts represent active and reactive losses in the sample. Similar situations may arise in other physical and engineering applications, notably, in diffusion problems with boundary layers.

physics.comp-ph↗