Stefan Böhmer

Protocols for a wireless-ATM multihop network

A medium access control protocol for a wireless multihop network is described and evaluated. The network is able to guarantee the bandwidth contracted to a connection in a hidden station environment and to most efficiently use the spectrum capacity by providing a mechanism for dynamic channel allocation to services. Both channel and packet switched services are supported, based on real channel connections. Ad-hoc networks without a central control node can be realized due to the ability of any station to route connections according to the current meshing of the network. Channels are established and used for the duration of a so called train of data packets, released when the train ends and reestablished when the next train arrives. To guarantee available capacity of the network for the reestablishment of a connection, connection admission control is applied and new connections are accepted only if spare capacity is available. The traffic performance of the proposed protocol is given by means of a simulation study in an example scenario.

Influences of material degradation due to laser cutting on the operating behaviour of PMSM using a continuous local material model

During manufacturing of electrical machines, shape giving production steps such as punching and cutting introduce plastic deformations and residual stress to the soft magnetic material. As a result the magnetic properties of the material decreases and locally both, static and dynamic hysteresis losses increase in the vicinity of the cut surfaces. For consideration of local permeability deteriorations, different models have been published. These are capable to describe the changing local magnetisation and loss behaviour. Current approaches subdivide the magnetic core into slices of different magnetic properties, thereby discretising the continuous deterioration. This paper analyses the effects of material degradation due to cutting on the performance and machine parameters of a Permanent Magnet Synchronous Machine (PMSM) using a continuous material model for efficient numerical modelling of the local magnetisation behaviour. By replacing inefficient sliced models, the continuous model is independent of the discretisation and converges in case of coarse meshes to the sliced model. Influences on the machine behaviour are studied in terms of local flux density distributions, iron losses, efficiency, torque and inductances on the operating map and an exemplary working point.

Mesh Decomposition for Efficient Parallel Computing of Electrical Machines by Means of FEM Accounting for Motion

The relative motion between stator and rotor in electrical machines requires a flexible representation in 2-D and 3-D finite element (FE) models. Numerous approaches to incorporate the relative motion are available. Due to increasing problem size and accuracy, parallel computing becomes more desirable. The parallel simulation of sufficiently large problems often involves domain decomposition algorithms, especially if distributed memory systems are used for the parallelisation. Accounting for motion usually requires explicit domain decomposition at each simulation step. This paper proposes an approach avoiding the computationally expensive domain decomposition at each step by properly choosing an initial decomposition, which can be applied to all steps throughout the simulation.

Continuous Local Material Model for Cut Edge Effects in Soft Magnetic Materials

Shape-giving production steps in the manufacturing of electrical machines often introduce plastic deformation and residual stress into the soft magnetic material, thus decreasing the magnetic quality and locally increasing both the static and dynamic hysteresis losses near the cut edges. Different models have been published, aiming to describe the changing local magnetization and loss behavior. Current approaches often consider permeability deteriorations by subdividing the soft magnetic material into the slices of different material properties. Three cut edge models are discussed here, where two describe the changed local polarization and the third estimates the resulting global iron losses. This paper presents a continuous material model for an efficient numerical model of the local magnetization. By replacing effortful sliced models, the continuous model is independent of the discretization and converges in the case of coarse meshes to the sliced model.

A new approach to performance evaluation of formally specified protocols

This report proposes enhanced methods for performance evaluation of formally specified communication protocols. A concept as well as an implementation is shortly described which combines the techniques of formal specification and stochastic simulation. A main focus is on semi-automatic generation of a program for stochastic simulation directly from a given protocol specification in SDL. Further, a new method is introduced to estimate the hardware performance requirements to run a given communication protocol properly. By means of an appropriate hardware emulation system that has been implemented, it becomes as well possible to compare different protocol implementations with regard to the efficiency of hardware utilization.

Performance analysis of the GSM signalling protocol LAPD/sub m/

The increasing user demands on mobile networks with regard to the integration of services and availability of supplementary services lead to an increasing importance and complexity of signalling protocols. Especially the efficiency and robustness of signalling protocols at the (GSM) air interface must be seen as one of the critical parts in the process carrying out user requests within an acceptable time space and have to be improved simultaneously with data transfer protocols. This paper describes the impact of LAPD/sub m/ protocol on the chronological sequence, duration and successful implementation of the signalling phase. A simulative performance evaluation based on a formal protocol specification in SDL has beers carried out for different radio conditions. Especially the influence of modified protocol parameters and different channel allocation strategies have been examined, compared and evaluated.<<ETX>>

Transientes Simulationsmodell für lokale Kraftanregungen elektrischer Antriebe

ZusammenfassungFür die Simulation von transienten lokalen Kraftanregungen innerhalb einer elektrischen Maschine wird eine Simulationsumgebung vorgestellt. Damit ist es möglich, drehzahl- und drehmomentdynamische Vorgänge zu bewerten. Es werden sowohl das Simulationsmodell als auch die Methode zur Kraftberechnung beschrieben und ein Simulationsergebnis als Abschluss gezeigt.AbstractA simulation environment for the transient simulation of local force excitations of electrical machines is presented. The model enables the evaluation of dynamic speed and torque situations. The simulation model as well as the method of the force determination are shown and a simulation result is given.

Eddy Currents and Non-Conforming Sliding Interfaces for Motion in 3-D Finite Element Analysis of Electrical Machines

This paper presents non-conforming sliding interfaces for motion in 3-D finite element simulations. Sliding interfaces are favorable, especially for field circuit coupling in comparison to other approaches such as the Lockstep method because an arbitrary position of the rotor is possible. A previously presented approach by the authors is extended to take eddy-currents into account. The sliding interfaces approach utilizes specific Lagrange multiplier to handle the relative motion between stator and rotor which require a magnetic scalar potential formulation. The formulation is presented as well as methods to compute the mandatory cohomology basis functions.

Transientes Simulationsmodell für die akustische Bewertung elektrischer Antriebe

ZusammenfassungIn dieser Arbeit wird eine Methode vorgestellt, die eine Ermittlung der mechanischen Übertragungsfunktionen von Kräften auf den Statorzähnen einer elektrischen Maschine bis hin zu Oberflächenschnellen an relevant abstrahlenden Oberflächen erlaubt. Die vorgestellte Methode ermöglicht es, Antriebsstränge in ihrer Zielanwendung und der realen Einbausituation effizient zu analysieren. Die ermittelten Übertragungsfunktionen werden in ein transientes akustisches Modell für die Simulation allgemeiner elektrischer Antriebsstränge integriert. Das vorgestellte Modell berücksichtigt die Leistungselektronik und ihre maßgeblichen Nichtlinearitäten, die digitale Regelung, die Sensorik, aber auch toleranzbehaftete Geometrien elektrischer Maschinen sowie reale und in der Toleranz abweichende elektromagnetische Materialeigenschaften. Eine Validierung des Modells anhand von Körperschallmessungen wird vorgestellt und der Vorteil einer geschlossenen Zeitbereichssimulation erklärt. Beispielhafte Anwendungsmöglichkeiten des vorgeschlagenen Modells werden diskutiert und das Potential einer Bewertung des akustischen Verhaltens im Auslegungsprozess somit aufgezeigt.AbstractThis work presents a method to determine mechanical transfer functions from forces, acting on the stator teeth of an electrical machine, to surface velocities at sound radiating surfaces. The method allows an efficient analysis of drive trains in their target application and real environment. The determined transfer functions are used in a transient acoustic model for the simulation of electrical drive trains. The proposed model takes care of the nonlinear power electronics, the digital control and sensors, as well as of tolerance afflicted geometries of electrical machines and real and in tolerance deviating material properties. The model is validated by means of vibration measurements. The benefits of a closed simulation in time domain are declared. Exemplary applications of the proposed model are discussed and the potential of the acoustic evaluation during the design process of an electrical machine is illustrated.

Interactive visualization of transient 3D electromagnetic and n‐dimensional parameter spaces in virtual reality

Purpose – Nowadays many parameter studies for the design and optimization of electromagnetic devices are carried out by means of 2D and 3D nonlinear finite element (FE) models. Through optimization algorithms selecting one design as optimal with respect to the chosen cost function, the user does not gain any intuitive clue of the interrelations existing between design parameters, although numerous computations have been performed across the whole parameter space of the system. The purpose of this paper is to visualize a complex nonlinear FE solution system, which is parameterized through a number of control variables, in virtual reality (VR).Design/methodology/approach – This paper presents a visualization approach for n‐dimensional parameter spaces of FE solutions in VR and the corresponding interpolation methods for enabling navigation through it.Findings – The solution of an arbitrary electromagnetic FE problem is categorized with respect to possible changes, due to chosen design parameters, within the...