Accelerated Steady-State Torque Computation for Induction Machines using Parallel-In-Time Algorithms

This paper focuses on efficient steady-state computations of induction machines. In particular, the periodic Parareal algorithm with initial-value coarse problem (PP-IC) is considered for acceleration of classical time-stepping simulations via non-intrusive parallelization in time domain, i.e., existing implementations can be reused. Superiority of this parallel-in-time method is in its direct applicability to time-periodic problems, compared to, e.g, the standard Parareal method, which only solves an initial-value problem, starting from a prescribed initial value. PP-IC is exploited here to obtain the steady state of several operating points of an induction motor, developed by Robert Bosch GmbH. Numerical experiments show that acceleration up to several dozens of times can be obtained, depending on availability of parallel processing units. Comparison of PP-IC with existing time-periodic explicit error correction method highlights better robustness and efficiency of the considered time-parallel approach

Uncertainty Quantification For A Permanent Magnet Synchronous Machine With Dynamic Rotor Eccentricity

The influence of dynamic eccentricity on the harmonic spectrum of the torque of a permanent magnet synchronous machine is studied. The spectrum is calculated by an energy balance method. Uncertainty quantification is applied by using generalized Polynomial Chaos and Monte Carlo. It is found that the displacement of the rotor impacts the spectrum of the torque the most

How to Build the Optimal Magnet Assembly for Magnetocaloric Cooling: Structural Optimization with Isogeometric Analysis

In the search for more efficient and less environmentally harmful cooling technologies, the field of magnetocalorics is considered a promising alternative. To generate cooling spans, rotating permanent magnet assemblies are used to cyclically magnetize and demagnetize magnetocaloric materials, which change their temperature under the application of a magnetic field. In this work, an axial rotary permanent magnet assembly, aimed for commercialization, is computationally designed using topology and shape optimization. This is efficiently facilitated in an isogeometric analysis framework, where harmonic mortaring is applied to couple the rotating rotor-stator system of the multipatch model. Inner, outer and co-rotating assemblies are compared and optimized designs for different magnet masses are determined. These simulations are used to homogenize the magnetic flux density in the magnetocaloric material. The resulting torque is analyzed for different geometric parameters. Additionally, the influence of anisotropy in the active magnetic regenerators is studied in order to guide the magnetic flux. Different examples are analyzed and classified to find an optimal magnet assembly for magnetocaloric cooling

Temperature dependent radiative and non-radiative recombination dynamics in CdSe-CdTe and CdTe-CdSe type II hetero nanoplatelets

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.We investigate the temperature-dependent decay kinetics of type II CdSe-CdTe and CdTe-CdSe core-lateral shell nanoplatelets. From a kinetic analysis of the photoluminescence (PL) decay and a measurement of the temperature dependent quantum yield we deduce the temperature dependence of the non-radiative and radiative lifetimes of hetero nanoplates. In line with the predictions of the giant oscillator strength effect in 2D we observe a strong increase of the radiative lifetime with temperature. This is attributed to an increase of the homogeneous transition linewidth with temperature. Comparing core only and hetero platelets we observe a significant prolongation of the radiative lifetime in type II platelets by two orders in magnitude while the quantum yield is barely affected. In a careful analysis of the PL decay transients we compare different recombination models, including electron hole pairs and exciton decay, being relevant for the applicability of those structures in photonic applications like solar cells or lasers. We conclude that the observed biexponential PL decay behavior in hetero platelets is predominately due to spatially indirect excitons being present at the hetero junction and not ionized e-h pair recombination

Time-resolved amplified spontaneous emission in quantum dots

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 97, 251106 (2010) and may be found at https://doi.org/10.1063/1.3529447.In time-resolved experiments at InGaAs/GaAs quantum-dots-in-a-well (DWELL) semiconductor optical amplifiers, pump-probe of the ground state (GS) population, and complementary measurement of the amplified spontaneous emission of the excited state (ES) population, we are able to separate the early subpicosecond dephasing dynamics from the later picosecond population relaxation dynamics. We observe a 10 ps delay between the nonlinear GS pulse amplification and the subsequent ES population drop-off that supports the dominance of a direct two dimensional reservoir-GS capture relaxation path in electrically pumped quantum-dot-DWELL structures.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement