T. Weiland

Technical University Darmstadt, Darmstadt, Hesse, Germany

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Publications (612)555.26 Total impact

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    ABSTRACT: An evaluation of the cone-shaped pickup performance as a part of the high bandwidth bunch arrival-time monitors (BAMs) for a low charge sub-10 fs arrival-time measurements is presented. Three sets of pickups are installed at the free electron laser FLASH at Deutsches Elektronen-Synchrotron, the quasi-cw SRF accelerator ELBE at the Helmholtz-Zentrum Dresden-Rossendorf and the SwissFEL injector test facility at Paul Scherrer Institute. Measurements and simulations are in good agreement and the pickups fulfill the design specifications. Utilizing the high bandwidth BAM with the cone-shaped pickups, an improvement of the signal slope by a factor of 10 is demonstrated at ELBE compared to the BAM with a low bandwidth.
    Physical Review Special Topics - Accelerators and Beams 01/2015; DOI:10.1103/PhysRevSTAB.18.012801 · 1.52 Impact Factor
  • Hideki Kawaguchi, Seiya Itasaka, Thomas Weiland
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    ABSTRACT: A time-domain boundary element method (TDBEM) provides one more possibility of potential numerical schemes for a time domain microwave simulation in addition to the finite difference time domain method. However, it is known that the TDBEM requires very large memory of order of 100 GB. As one of the solutions to effective memory reduction, this paper presents a 4-D domain decomposition method for the TDBEM. It is shown that the 4-D domain decomposition method of the TDBEM works well for the effective memory reduction in a particle accelerator wake field analysis.
    IEEE Transactions on Magnetics 01/2015; 51(3):1-4. DOI:10.1109/TMAG.2014.2361613 · 1.21 Impact Factor
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    ABSTRACT: Explicit expressions for the permittivity and inverse permeability tensor for gyrotropic materials are derived for the finite integration technique (FIT) in frequency domain. In contrast to the standard FIT, the material matrices exhibit nondiagonal elements. The obtained expressions are fully consistent with the standard FIT when applied to nongyrotropic materials. Furthermore, the manifestly Hermitian matrix structure in the lossless case enables numerically stable simulations. Since the gyrotropic characteristics notably depend on the bias magnetic field and on the frequency of the superimposed field, a dedicated solver to determine the field distributions in practical applications has been developed. In particular, emphasis has been put on the implementation to enable efficient computing. Finally, the extended formulation is applied to the computation of eigenmodes of biased cavity resonators of cylindrical and rectangular shape, which are filled with material exhibiting both gyromagnetic and gyroelectric characteristics. For the latter resonator, material losses are included. The validity of numerically obtained results is confirmed by comparison with semianalytical calculations.
    IEEE Transactions on Magnetics 01/2015; 51(1):1-7. DOI:10.1109/TMAG.2014.2338275 · 1.21 Impact Factor
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    ABSTRACT: This paper proposes the extraction of surrogate field models from 3-D electromagnetic simulation results, for use in a Vlasov beam-dynamics code. Each accelerator component is represented by a dedicated surrogate field model based on a series expansion of its 3-D field distribution. The obtained beam-dynamics simulation results are validated against a particle-in-cell tracking code that integrates a 3-D field distribution of the corresponding accelerator component.
    IEEE Transactions on Magnetics 01/2015; 51(3):1-4. DOI:10.1109/TMAG.2014.2357027 · 1.21 Impact Factor
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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
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    ABSTRACT: Purpose - The purpose of this paper is to present a time domain discontinuous Galerkin (DG) approach for modeling wideband frequency dependent surface impedance boundary conditions. Design/methodology/approach - The paper solves the Maxwellian initial value problem in a computational domain, which is spatially discretized by the higher order DG method. On the boundary of the computational domain the paper applies a suitable impedance boundary condition (IBC). The frequency dependency of the impedance function is modeled by auxiliary differential equations (ADE). Findings - The authors will study the resonance frequency and the Q factor of different types of cavity resonators including lossy materials. The lossy materials are modeled by means of IBCs. The authors will compare the results with analytical results, as well as numerical results obtained by direct calculations where lossy materials are included explicitly into the numerical model. Several convergence studies are performed which demonstrate the accuracy of the approach. Originality/value - Modeling of frequency dependent boundary conditions in time domain with finite difference time domain method (FDTD) method is considered in numerous papers, as well as in frequency domain finite element method (FEM), and in a few papers also time domain FEM. However, FDTD method is only first order accurate and fails in modeling of complicated surfaces. FEM allows for high order accuracy, but time domain modeling is numerically extremely expensive. In frequency domain, broadband modeling of frequency dependent boundary conditions requires several simulations as opposed to the time domain, where a single simulation is needed. The time domain DG method proposed in this paper allows to overcome the difficulties. The authors introduce a broadband surface impedance formulation based on the ADE approach for the higher order DG method.
    COMPEL International Journal of Computations and Mathematics in Electrical 07/2014; 33(4):1082-1096. DOI:10.1108/COMPEL-08-2013-0260 · 0.44 Impact Factor
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  • Hideki Kawaguchi, Seiya Itasaka, Thomas Weiland
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    ABSTRACT: A time domain boundary element method (TDBEM) gives us another possibility of time domain microwave simulations in addition to a finite difference time domain (FDTD) method. In particular, the TDBEM has good advantages in analysis of coupling problems with charged particle motion such as in a particle accelerator. However, it is known that time domain microwave simulations in the particle accelerator by the conventional TDBEM often encounter numerical instability and inaccuracy because of its bad matrix property. To avoid the numerical instability and inaccuracy caused by the conventional open boundary problem formulation of the TDBEM, an initial value problem formulation of 3-D TDBEM is presented in this paper.
    IEEE Transactions on Magnetics 02/2014; 50(2):593-596. DOI:10.1109/TMAG.2013.2281057 · 1.21 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. DOI:10.1109/TMAG.2013.2283917 · 1.21 Impact Factor
  • Annette Fröhlcke, Erion Gjonaj, Thomas Weiland
    International Journal of Computational Science and Engineering 01/2014; 9(5):478-483. DOI:10.1504/IJCSE.2014.064533
  • Ulrich Römer, Sebastian Schöps, Thomas Weiland
    IEEE Transactions on Magnetics 01/2014; · 1.21 Impact Factor
  • Jens Trommler, Stephan Koch, Thomas Weiland
    International Journal of Computational Science and Engineering 01/2014; 9(5/6):538-548. DOI:10.1504/IJCSE.2014.064538
  • 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
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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(6-6):2063-2083. DOI:10.1108/COMPEL-01-2013-0004 · 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.
    09/2013; 32(5-5):1609-1619. DOI:10.1108/COMPEL-04-2013-0128
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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. DOI:10.1016/j.jcp.2014.07.015 · 2.49 Impact Factor

Publication Stats

4k Citations
555.26 Total Impact Points

Institutions

  • 1994–2014
    • Technical University Darmstadt
      • • Insitute of Computational Electromagnetics
      • • Institute of Nuclear Physics
      Darmstadt, Hesse, Germany
  • 2010
    • GSI Helmholtzzentrum für Schwerionenforschung
      • ExtreMe Matter Institute EMMI and Research Division
      Darmstadt, Hesse, Germany
  • 2008
    • Argonne National Laboratory
      Lemont, Illinois, United States
  • 2007
    • University of Leuven
      Louvain, Flanders, Belgium
  • 1982–2006
    • Darmstadt University of Applied Sciences
      Darmstadt, Hesse, Germany
  • 2005
    • University of Wisconsin, Madison
      • Department of Electrical and Computer Engineering
      Madison, MS, United States
  • 1985–2005
    • Deutsches Elektronen-Synchrotron
      Hamburg, Hamburg, Germany
  • 1998
    • University of Rostock
      Rostock, Mecklenburg-Vorpommern, Germany
  • 1996
    • Stanford University
      Palo Alto, California, United States
  • 1981
    • CERN
      Genève, Geneva, Switzerland