Thermoelectric simulation of electric machines with permanent magnets

The objective of this work is to describe some numerical tools developed to perform the thermoelectric simulation of electric machines. From the electromagnetic point of view, we will focus on the computation of nonlinear 2D transient magnetic fields where the data concerning the electric current sources involve potential drops excitations. From the thermal point of view, once the electromagnetic losses are known, we will show an application of a Galerkin lumped parameter method (GLPM) to simulate the thermal behavior of an electric motor. The proposed methods are applied to the simulation of a permanent magnet synchronous electric motor

A novel numerical method for accelerating the computation of the steady-state in induction machines

This paper presents a novel and efficient methodology to reduce the time needed to reach the steady-state in the finite element simulation of induction machines. More precisely, the work focuses on induction motors with squirrel cage rotor, where sources in the stator coil sides are given in terms of periodic currents. Essentially, the procedure consists in computing suitable initial conditions for the currents in the rotor bars, thus allowing to obtain the steady-state fields of the machine by solving a transient magnetic model in just a few revolutions. Firstly, the mathematical model that simulates the behavior of the machine is introduced. Then, an approximation of this model is developed, from which suitable initial currents are derived by computing the solution in the least-square sense to an overdetermined problem with only two unknowns. Finally, the method is applied to a particular induction machine working under different operating conditions. The results show important computational savings to reach the motor steady-state in comparison with assuming zero initial conditions, which validate the efficiency of the procedure.This work has been partially supported by Robert Bosch GmbH, Spain under contract ITMATI-C31-2015, by FEDER and Xunta de Galicia (Spain) under grant GI-1563 ED431C 2017/60, by FEDER/Ministerio de Ciencia, Innovación y Universidades-Agencia Estatal de Investigación, Spain under the research project MTM2017-86459-R, and by Ministerio de Educación, Cultura y Deporte (Spain) under grant FPU13/03409. The authors express their gratitude to Dr Marcus Alexander and Dr Stefan Kurz from Robert Bosch GmbH for useful discussions about induction machines and for providing us with the data for the numerical experiments.S

A New Parareal Algorithm for Time-Periodic Problems with Discontinuous Inputs

The Parareal algorithm, which is related to multiple shooting, was introduced for solving evolution problems in a time-parallel manner. The algorithm was then extended to solve time-periodic problems. We are interested here in time-periodic systems which are forced with quickly-switching discontinuous inputs. Such situations occur, e.g., in power engineering when electric devices are excited with a pulse-width-modulated signal. In order to solve those problems numerically we consider a recently introduced modified Parareal method with reduced coarse dynamics. Its main idea is to use a low-frequency smooth input for the coarse problem, which can be obtained, e.g., from Fourier analysis. Based on this approach, we present and analyze a new Parareal algorithm for time-periodic problems with highly-oscillatory discontinuous sources. We illustrate the performance of the method via its application to the simulation of an induction machine

Mathematical and numerical analysis of a transient magnetic model with voltage drop excitations

This paper deals with the mathematical and numerical analysis of a nonlinear 2D transient magnetic model when the source data are given in terms of the voltage drop excitations in conductors and the remanent magnetic flux for permanent magnets. The formulation consists of a distributed nonlinear magnetostatic model with time appearing as a parameter, and a circuit equation linking currents and voltage drops. This last equation is used to express the problem as an implicit ODE system whose operator involves the resolution of the distributed model. The model is spatially discretized using a finite element method and an implicit Euler scheme is employed for time discretization. We perform the mathematical analysis of the problem at both the continuous and discrete levels and obtain an error estimate that is illustrated with some numerical results.Work partially supported by FEDER and Xunta de Galicia (Spain) under grant GRC2013–014, by Ministerio de Economía y Competitividad (Spain) under the research project ENE2013–47867–C2–1–R, and by Ministerio de Educación, Cultura y Deporte (Spain) under grant FPU13/03409.S

Physics of Neutron Star Crusts

The physics of neutron star crusts is vast, involving many different research fields, from nuclear and condensed matter physics to general relativity. This review summarizes the progress, which has been achieved over the last few years, in modeling neutron star crusts, both at the microscopic and macroscopic levels. The confrontation of these theoretical models with observations is also briefly discussed.Comment: 182 pages, published version available at <http://www.livingreviews.org/lrr-2008-10

Cold atoms in cavity-generated dynamical optical potentials

We review state-of-the-art theory and experiment of the motion of cold and ultracold atoms coupled to the radiation field within a high-finesse optical resonator in the dispersive regime of the atom-field interaction with small internal excitation. The optical dipole force on the atoms together with the back-action of atomic motion onto the light field gives rise to a complex nonlinear coupled dynamics. As the resonator constitutes an open driven and damped system, the dynamics is non-conservative and in general enables cooling and confining the motion of polarizable particles. In addition, the emitted cavity field allows for real-time monitoring of the particle's position with minimal perturbation up to sub-wavelength accuracy. For many-body systems, the resonator field mediates controllable long-range atom-atom interactions, which set the stage for collective phenomena. Besides correlated motion of distant particles, one finds critical behavior and non-equilibrium phase transitions between states of different atomic order in conjunction with superradiant light scattering. Quantum degenerate gases inside optical resonators can be used to emulate opto-mechanics as well as novel quantum phases like supersolids and spin glasses. Non-equilibrium quantum phase transitions, as predicted by e.g. the Dicke Hamiltonian, can be controlled and explored in real-time via monitoring the cavity field. In combination with optical lattices, the cavity field can be utilized for non-destructive probing Hubbard physics and tailoring long-range interactions for ultracold quantum systems.Comment: 55 page review pape

Linear and nonlinear optical excitations in spatially-inhomogeneous semiconductor systems

Gegenstand der vorliegenden Arbeit ist die Licht-Materie-Wechselwirkung in raeumlich inhomogenen Halbleiterstrukturen. In den Kapiteln 2, 3 und 4 werden grundlegende Eigenschaften herausgearbeitet, die dadurch entstehen, dass die untersuchten Systeme von dreidimensionaler raeumlicher Homogenitaet abweichen. Darunter ist zu verstehen, dass sowohl das (anregende) Lichtfeld inhomogen verteilt (Kap 2 und 3) als auch die intrinsischen Materialeigenschaften des Halbleiters raeumlich strukturiert sein koennen (Kap. 2 und 4). In Kapitel 2 wird eine Theorie entwickelt, die es ermoeglicht, Halbleiterstrukturen zu beschreiben, die sich in der Naehe eines photonischen Kristalls befinden. Lineare und nichtlineare optische Eigenschaften von verschiedenen Silizium-Halbleiteroberflaechen werden in Kapitel 4 behandelt