T. Weiland

Technical University Darmstadt, Darmstadt, Hesse, Germany

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Publications (601)582.7 Total impact

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    ABSTRACT: We consider the discretization of electromagnetic wave propagation problems by a discontinuous Galerkin Method based on Trefftz polynomials. This method fits into an abstract framework for space-time discontinuous Galerkin methods for which we can prove consistency, stability, and energy dissipation without the need to completely specify the approximation spaces in detail. Any method of such a general form results in an implicit time-stepping scheme with some basic stability properties. For the local approximation on each space-time element, we then consider Trefftz polynomials, i.e., the subspace of polynomials that satisfy Maxwell's equations exactly on the respective element. We present an explicit construction of a basis for the local Trefftz spaces in two and three dimensions and summarize some of their basic properties. Using local properties of the Trefftz polynomials, we can establish the well-posedness of the resulting discontinuous Galerkin Trefftz method. Consistency, stability, and energy dissipation then follow immediately from the results about the abstract framework. The method proposed in this paper therefore shares many of the advantages of more standard discontinuous Galerkin methods, while at the same time, it yields a substantial reduction in the number of degrees of freedom and the cost for assembling. These benefits and the spectral convergence of the scheme are demonstrated in numerical tests.
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    ABSTRACT: The modeling and simulation of electromagnetic wave propagations is often acompanied by a restriction to bounded domains and the introduction of artificial boundary conditions which should be chosen in order to minimize parasitic reflections. In this paper, we investigate a new type of transparent boundary condition and its implementation in a Discontinuous Galerkin Trefftz Finite Element Method. The choice of a particular set of basis functions allows us to split the electromagnetic field into components with a specified direction of propagation. The reflections at the artificial boundaries are then reduced by penalizing components of the field incoming into the space-time domain of interest. We formally introduce this concept, discuss its realization within the discontinuous Galerkin framework, and demonstrate the performance of the resulting approximations in comparison with commonly used absorbing boundary conditions. In our numerical tests, we observe spectral convergence in the L2 norm and a dissipative behaviour for which we provide a theoretical explanation.
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    ABSTRACT: Quadrupolar or beam envelope oscillations give valuable information about the injection matching and the incoherent space charge tune shift. An asymmetric capacitive pick-up was installed at GSI SIS-18 to measure these oscillations. In this contribution, we present the simulations performed to es-timate the sensitivity of the quadrupolar pick-up to the beam quadrupolar moment and compare it with respect to other pick-up types installed at SIS-18. Further, dedicated beam measurements are performed to interpret the quadrupolar signal under high intensity conditions.
    IBIC 2014; 09/2014
  • Irene Woyna, Erion Gjonaj, Thomas Weiland
    COMPEL International Journal of Computations and Mathematics in Electrical 07/2014; 33(4):1082-1096. · 0.44 Impact Factor
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    ABSTRACT: In this paper, we address a fast approach for an accurate eigenfrequency determination, based on a finite-element computation of electromagnetic fields for a superconducting cavity and further employment of the Lanczos method for the eigenvalue determination. The major challenges posed by this paper are: 1) the ability of the approach to tackle the large-scale eigenvalue problem and 2) the capability to extract many, i.e., order of thousands, eigenfrequencies for the considered problem. In addition to the need to ensure high precision of the calculated eigenfrequencies, we compare them side by side with the reference data available from analytical expressions and CEM3D eigenmode solver. Furthermore, the simulations have shown high accuracy of this technique and good agreement with the reference data. Finally, all of the results show that the suggested technique can be used for precise determination of many eigenfrequencies.
    IEEE Transactions on Magnetics 02/2014; 50(2):481-484. · 1.21 Impact Factor
  • Ulrich Römer, Sebastian Schöps, Thomas Weiland
    IEEE Transactions on Magnetics 01/2014; · 1.21 Impact Factor
  • T. Weiland, E. Gjonaj, H. Jorks
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    ABSTRACT: Pulse width modulation is known to cause high frequency (HF) common mode (CM) currents in speed controlled motors. In this paper, two aspects of transmission line (TL) motor modelling are discussed. Firstly, the effect of lamination is analysed with regard to the assumption of transverse electromagnetic fields. A TL model is validated against a full-wave simulation. Secondly, a frequency domain (FD) method is presented, which accounts for core saturation effects. The method is applied to a HF CM analysis of a 240 kW induction motor.
    9th IET International Conference on Computation in Electromagnetics (CEM 2014); 01/2014
  • Annette Fröhlcke, Erion Gjonaj, Thomas Weiland
    International Journal of Computational Science and Engineering 01/2014; 9(5):478-483.
  • Jens Trommler, Stephan Koch, Thomas Weiland
    International Journal of Computational Science and Engineering 01/2014; 9(5/6):538-548.
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    ABSTRACT: Purpose ‐ The purpose of this paper is to review the mutual coupling of electromagnetic fields in the magnetic vector potential formulation with electric circuits in terms of (modified) nodal and loop analyses. It aims for an unified and generic notation. Design/methodology/approach ‐ The coupled formulation is derived rigorously using the concept of winding functions. Strong and weak coupling approaches are proposed and examples are given. Discretization methods of the partial differential equations and in particular the winding functions are discussed. Reasons for instabilities in the numerical time domain simulation of the coupled formulation are presented using results from differential-algebraic-index analysis. Findings ‐ This paper establishes a unified notation for different conductor models, e.g. solid, stranded and foil conductors and shows their structural equivalence. The structural information explains numerical instabilities in the case of current excitation. Originality/value ‐ The presentation of winding functions allows to generically describe the coupling, embed the circuit equations into the de Rham complex and visualize them by Tonti diagrams. This is of value for scientists interested in differential geometry and engineers that work in the field of numerical simulation of field-circuit coupled problems.
    COMPEL International Journal of Computations and Mathematics in Electrical 11/2013; 32(6):2063-2083. · 0.44 Impact Factor
  • Hai Van Jorks, Erion Gjonaj, Thomas Weiland
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    ABSTRACT: Purpose ‐ The purpose of this paper is to propose a transmission line model for induction machines, which serves to compute the common mode input impedance in the frequency range 10?Hz-1?MHz. Design/methodology/approach ‐ Special diligence is attributed to the modelling of eddy currents inside the core lamination. In order to determine the transmission line parameters accurately, two modelling approaches are compared. The first is a two-dimensional simulation approach where iron core lamination effects are included by means of an equivalent material approximation. The second approach consists in fully three-dimensional analysis taking into account explicitly the eddy currents induced in the laminations. Findings ‐ It is shown that homogenised equivalent material models may lead to large errors in the calculation of machine inductances, especially at high frequencies. However, the common mode input impedance, which is the final parameter of interest, seems to be less affected by the lamination modelling. Originality/value ‐ The paper compares different analytical and numerical approaches in the frequency range 10?Hz-1?MHz and tries to give benchmarks for errors which occur due to a number of commonly used model simplifications.
    COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering. 09/2013; 32(5):1609-1619.
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    ILASS-Europe, 25th European Conference on Liquid Atomization and Spray Systems, Chania, Greece; 09/2013
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    ABSTRACT: 1. Introduction. Electrical machine design is typically based on finite element (FE) simulations of steady-state working conditions. Motional eddy current effects are commonly resolved by transient simulation, which may be too expensive if only steady-state behaviour has to be simulated. This paper offers a time-harmonic FE approach for machines operating at steady-state, incorporating motional eddy current effects. The formulation incorporates interface conditions connecting the boundary of one stator model to the boundaries of several rotor models based on Fast Fourier Transforms and restriction operations. The matrix- free discretisation of the interface conditions excludes the use of algebraic iterative solution techniques. Instead, techniques related to iterative substructuring are proposed to solve the model. 2. Finite element machine models. Two common approaches for simulating electrical machines are the transient approach and the time-harmonic approach. The tran- sient approach accounts for motional eddy currents by the Lagrange technique: between two successive time steps, the previous solution is azimuthally moved together with the rotor part. Accordingly, the interface conditions between stator and rotor are updated. The rela- tive motion of both motor parts can be modelled by a moving band technique (5), a hybrid FE, boundary-element approach (8), discontinuous finite elements (1) or a sliding surface tech- nique, possibly resolved by mortar finite elements (2). Transient methods are however too expensive when only stationary operations have to be simulated. For electrical machines excited by alternating current sources and rotating at constant velocities, formulations in frequency domain are preferred. The simplest case is when only one frequency f is present in the excitating voltages. Then, one can adopt the time-harmonic formulation
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    ABSTRACT: A finite element method for the solution of the time-dependent Maxwell equations in mixed form is presented. The method allows for local $hp$-refinement in space and in time. To this end, a space-time Galerkin approach is employed. In contrast to the space-time DG method introduced in \cite{vegt_space_2002} test and trial space do not coincide. This allows for obtaining a non-dissipative method. In order to obtain an efficient implementation, a hierarchical tensor product basis in space and time is proposed. In particular it allows to evaluate the local residual with a complexity of $\mathcal{O}(p^4)$ and $\mathcal{O}(p^5)$ for affine and non-affine elements, respectively.
    Journal of Computational Physics 07/2013; 275. · 2.49 Impact Factor
  • T. Banova, W. Ackermann, T. Weiland
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    ABSTRACT: In this paper we address a fast approach for an accurate eigenfrequency extraction, taken into consideration the evaluated electric field computations in time domain of a superconducting resonant structure. Upon excitation of the cavity, the electric field intensity is recorded at different detection probes inside the cavity. Thereafter, we perform Fourier analysis of the recorded signals and by means of fitting techniques with the theoretical cavity response model (in support of the applied excitation) we extract the requested eigenfrequencies by finding the optimal model parameters in least square sense. The major challenges posed by our work are: first, the ability of the approach to tackle the large scale eigenvalue problem and second, the capability to extract many, i.e. order of thousands, eigenfrequencies for the considered cavity. At this point, we demonstrate that the proposed approach is able to extract many eigenfrequencies of a closed resonator in a relatively short time. In addition to the need to ensure a high precision of the calculated eigenfrequencies, we compare them side by side with the reference data available from CEM3D eigenmode solver. Furthermore, the simulations have shown high accuracy of this technique and good agreement with the reference data. Finally, all of the results indicate that the suggested technique can be used for precise extraction of many eigenfrequencies based on time domain field computations.
    Advances in Radio Science 07/2013;
  • M. Vuchkovikj, I. Munteanu, T. Weiland
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    ABSTRACT: In the last two decades, the increasing number of electronic devices used in day-to-day life led to a growing interest in the study of the electromagnetic field interaction with biological tissues. The design of medical devices and wireless communication devices such as mobile phones benefits a lot from the bio-electromagnetic simulations in which digital human models are used. The digital human models currently available have an upright position which limits the research activities in realistic scenarios, where postured human bodies must be considered. For this reason, a software application called "BodyFlex for CST STUDIO SUITE" was developed. In its current version, this application can deform the voxel-based human model named HUGO (Dipp GmbH, 2010) to allow the generation of common postures that people use in normal life, ensuring the continuity of tissues and conserving the mass to an acceptable level. This paper describes the enhancement of the "BodyFlex" application, which is related to the movements of the forearm and the wrist of a digital human model. One of the electromagnetic applications in which the forearm and the wrist movement of a voxel based human model has a significant meaning is the measurement of the specific absorption rate (SAR) when a model is exposed to a radio frequency electromagnetic field produced by a mobile phone. Current SAR measurements of the exposure from mobile phones are performed with the SAM (Specific Anthropomorphic Mannequin) phantom which is filled with a dispersive but homogeneous material. We are interested what happens with the SAR values if a realistic inhomogeneous human model is used. To this aim, two human models, a homogeneous and an inhomogeneous one, in two simulation scenarios are used, in order to examine and observe the differences in the results for the SAR values.
    Advances in Radio Science 07/2013;
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    ABSTRACT: The Super-FRS (superconducting fragment separator) will be constructed in the frame of the Facility for Antiproton and Ion Research project at GSI (Darmstadt, Germany). This work presents quench calculations done on the Super-FRS main dipole magnet. Two quench programs were used. One developed at CIEMAT (Madrid, Spain), and the other developed at GSI. Both quench programs use finite-difference method. For the GSI quench program the mesh size influence was investigated. A protection system for Super-FRS dipoles is presented as well. Optimum energy extraction resistors for the Super-FRS dipoles were calculated. Quench calculations are compared to measurements done on the first dipole prototype.
    IEEE Transactions on Applied Superconductivity 06/2013; 23(3):4701704-4701704. · 1.32 Impact Factor
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    ABSTRACT: A challenge in accelerator magnet design is the strong nonlinear behavior due to magnetic saturation. In practice, the underlying nonlinear saturation curve is modeled according to measurement data that typically contain uncertainties. The electromagnetic fields and in particular the multipole coefficients that heavily affect the particle beam dynamics inherit this uncertainty. In this paper, we propose a stochastic model to describe the uncertainties and we demonstrate the use of generalized polynomial chaos for the uncertainty quantification of the multipole coefficients. In contrast to previous works we propose to start the stochastic analysis from uncertain measurement data instead of uncertain material properties and we propose to determine the sensitivities by a Sobol decomposition.
    IEEE Transactions on Magnetics 05/2013; 49(5). · 1.21 Impact Factor
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    ABSTRACT: Two different tune measurement systems have been installed in the GSI Helmholtzzentrum für Schwerionenforschung heavy-ion synchrotron SIS-18. Tune spectra are obtained with high accuracy using these fast and sensitive systems. Besides the machine tune, the spectra contain information about the intensity dependent coherent tune shift and the incoherent space charge tune shift. The space charge tune shift is derived from a fit of the observed shifted positions of the synchrotron satellites to an analytic expression for the head-tail eigenmodes with space charge. Furthermore, the chromaticity is extracted from the measured head-tail mode structure. The results of the measurements provide experimental evidence of the importance of space charge effects and head-tail modes for the interpretation of transverse beam signals at high intensity.
    Physical Review Special Topics - Accelerators and Beams 03/2013; · 1.52 Impact Factor

Publication Stats

3k Citations
582.70 Total Impact Points


  • 1994–2013
    • Technical University Darmstadt
      • • Insitute of Computational Electromagnetics
      • • Institut für Kernphysik
      Darmstadt, Hesse, Germany
  • 2008–2009
    • Southeast University (China)
      Nan-ching-hsü, Jiangxi Sheng, China
  • 2007–2009
    • University of Leuven
      Louvain, Flanders, Belgium
  • 2006–2008
    • Universität Paderborn
      Paderborn, North Rhine-Westphalia, Germany
    • Vienna University of Technology
      • Institute of Energy Systems and Electrical Drives (ESEA)
      Vienna, Vienna, Austria
    • Hokkaido University
      • Graduate School of Engineering
      Sapporo-shi, Hokkaido, Japan
  • 1985–2007
    • Deutsches Elektronen-Synchrotron
      Hamburg, Hamburg, Germany
  • 2005–2006
    • Helmut-Schmidt University
      Hamburg, Hamburg, Germany
    • University of Wisconsin, Madison
      • Department of Electrical and Computer Engineering
      Madison, MS, United States
  • 1982–2006
    • Darmstadt University of Applied Sciences
      Darmstadt, Hesse, Germany
  • 2002
    • Warsaw University of Technology
      Warszawa, Masovian Voivodeship, Poland
  • 2000
    • Universität Kassel
      Cassel, Hesse, Germany
  • 1996–1997
    • Stanford University
      • Stanford Linear Accelerator Center
      Stanford, CA, United States
  • 1981
    • CERN
      Genève, Geneva, Switzerland