S. Russenschuck and E. Ch. Andresen
A six pole 3 kW synchronous motor with rare earth magnet excitation is used as an ex‐ample for mathematical design optimization on the basis of the FD field calculation method…
Abstract
A six pole 3 kW synchronous motor with rare earth magnet excitation is used as an ex‐ample for mathematical design optimization on the basis of the FD field calculation method. The nonlinear field of the machine at full load, excited by both the rotor magnets and the stator current, is determined. The resulting vector‐optimization problem is transformed into a scalar problem, i.e. only one objective is minimized, while the others are considered by nonlinear constraints. Either the magnet mass or the machine volume is minimized for a restricted power input. The results of the investigations are presented by the material contours, flux plots and by the electrical and mechanical data of the optimized machines.
C. Völlinger, M. Aleksa and S. Russenschuck
Field variations in the LHC superconducting magnets, e.g.during the ramping of the magnets, induce magnetization currents in the superconducting material, the so‐called persistent…
Abstract
Field variations in the LHC superconducting magnets, e.g.during the ramping of the magnets, induce magnetization currents in the superconducting material, the so‐called persistent currents that do not decay but persist due to the lack of resistivity. This paper describes a semi‐analytical hysteresis model for hard superconductors, which has been developed for the computation of the total field errors arising from persistent currents. Since the superconducting coil is surrounded by a ferromagnetic yoke structure, the persistent current model is combined with the finite element method (FEM), as the non‐linear yoke can only be calculated numerically. The used finite element method is based on a reduced vector potential formulation that avoids the meshing of the coil while calculating the part of the field arising from the source currents by means of the Biot‐Savart Law. The combination allows the determination of persistent current induced field errors as a function of the excitation and for arbitrarily shaped iron yokes. The model has been implemented into the ROXIE program and is tested using the LHC dipole magnet as an example.
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B. Auchmann, S. Kurz, O. Rain and S. Russenschuck
To introduce a Whitney‐element based coupling of the Finite Element Method (FEM) and the Boundary Element Method (BEM); to discuss the algebraic properties of the resulting system…
Abstract
Purpose
To introduce a Whitney‐element based coupling of the Finite Element Method (FEM) and the Boundary Element Method (BEM); to discuss the algebraic properties of the resulting system and propose solver strategies.
Design/methodology/approach
The FEM is interpreted in the framework of the theory of discrete electromagnetism (DEM). The BEM formulation is given in a DEM‐compatible notation. This allows for a physical interpretation of the algebraic properties of the resulting BEM‐FEM system matrix. To these ends we give a concise introduction to the mathematical concepts of DEM.
Findings
Although the BEM‐FEM system matrix is not symmetric, its kernel is equivalent to the kernel of its transpose. This surprising finding allows for the use of two solution techniques: regularization or an adapted GMRES solver.
Research limitations/implications
The programming of the proposed techniques is a work in progress. The numerical results to support the presented theory are limited to a small number of test cases.
Practical implications
The paper will help to improve the understanding of the topological and geometrical implications in the algebraic structure of the BEM‐FEM coupling.
Originality/value
Several original concepts are presented: a new interpretation of the FEM boundary term leads to an intuitive understanding of the coupling of BEM and FEM. The adapted GMRES solver allows for an accurate solution of a singular, unsymetric system with a right‐hand side that is not in the image of the matrix. The issue of a grid‐transfer matrix is briefly mentioned.
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J.A. Gallardo and D.A. Lowther
The use of niching genetic algorithms can provide a method of a more widespread search of the design space for a device than more conventional methods. It provides, in effect, a…
Abstract
The use of niching genetic algorithms can provide a method of a more widespread search of the design space for a device than more conventional methods. It provides, in effect, a breadth first rather than a depth first search. Thus several alternative designs may be evaluated in parallel.
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Ping Yang, Yawei Wang, T. Chang, H. Ma, Zhuyong Li, Zhijian Jin and Zhiyong Hong
The purpose of this paper is to propose a hybrid driving system that couples a motor and flywheel energy storage (FES) for a megawatt-scale superconducting direct current (DC…
Abstract
Purpose
The purpose of this paper is to propose a hybrid driving system that couples a motor and flywheel energy storage (FES) for a megawatt-scale superconducting direct current (DC) induction heater. Previous studies have proven that a superconducting DC induction heater has great advantages in relation to its energy efficiency and heating quality. In this heater, a motor rotates an aluminium billet in a DC magnetic field and the induced eddy current causes it to be heated. When the aluminium billet begins to rotate, a high peak load torque appears at a low rotation speed. Therefore, driving the billet economically has been a great challenge when designing the driving system, which is the focus of this paper.
Design/methodology/approach
A hybrid driving system based on FES is designed to provide extra torque when the peak load torque occurs at a low rotation speed, which allows the successful start-up of the aluminium billet and the operation of the motor at its rated capacity. The mechanical structure of this hybrid driving system is introduced. A simulation model was constructed using Matlab/Simulink and the dynamic start-up process is analysed. The influence of the flywheel’s inertia and required minimum engagement speed are investigated.
Findings
The results of this paper show that the hybrid driving system that couples FES and a motor can successfully be used to start the aluminium billet rotating. The flywheel’s inertia and engagement speed are the most important parameters. The inertia of the flywheel decreases with an increase in its engagement speed.
Practical implications
The cost of the driving system is significantly reduced, which is very important in relation to the commercial potential of this apparatus.
Originality/value
A novel start-up strategy for driving the aluminium billet of a superconducting DC induction heater at low speed is proposed based on FES.
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Thomas Preisner, Christian Bolzmacher, Andreas Gerber, Karin Bauer, Eckhard Quandt and Wolfgang Mathis
The purpose of this paper is to investigate the accuracy of different force calculation methods and their impact on mechanical deformations. For this purpose, a micrometer scaled…
Abstract
Purpose
The purpose of this paper is to investigate the accuracy of different force calculation methods and their impact on mechanical deformations. For this purpose, a micrometer scaled actuator is considered, which consists of a micro‐coil and of a permanent magnet (PM) embedded in a deformable elastomeric layer.
Design/methodology/approach
For the magnetic field evaluation a hybrid numerical approach (finite element method/boundary element method (FEM/BEM) coupling and a FEM/BEM/Biot‐Savart approach) is used, whereas FEM is implemented for the mechanical deformation analysis. Furthermore, for the magneto‐mechanical coupling several force calculation methods, namely the Maxwell stress tensor, the virtual work approach and the equivalent magnetic sources methods, are considered and compared to each other and to laboratory measurements.
Findings
The numerically evaluated magnetic forces and the measured ones are in good accordance with each other with respect to the normal force acting on the PM. Nevertheless, depending on the used method the tangential force components differ from each other, which leads to slightly different mechanical deformations.
Research limitations/implications
Since the force calculations are compared to measurement data, it is possible to give a suggestion about their applicability. The mechanical behavior of the actuator due to the acting forces is solely calculated and therefore only an assumption concerning the deformation can be given.
Originality/value
A new kind of micrometer scaled actuator is numerically investigated by using two different hybrid approaches for the magnetic field evaluation. Based on those, the results of several force calculation methods are compared to measurement data. Furthermore, a subsequent structural analysis is performed, which shows slightly different mechanical deformations depending on the used force calculation method.
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The purpose of this paper is to establish the mathematical foundations of magnetic measurement methods based on translating-coil and rotating-coil magnetometers for accelerator…
Abstract
Purpose
The purpose of this paper is to establish the mathematical foundations of magnetic measurement methods based on translating-coil and rotating-coil magnetometers for accelerator magnets and solenoids. These field transducers allow a longitudinal scanning of the field distribution, but require a sophisticated post-processing step to extract the coefficients of the Fourier–Bessel series (known as pseudo-multipoles or generalized gradients) as well as a novel design of the rotating coil magnetometers.
Design/methodology/approach
Calculating the transversal field harmonics as a function of the longitudinal position in the magnet, or measuring these harmonics with a very short, rotating induction-coil scanner, allows the extraction of the coefficients of a Fourier–Bessel series, which can then be used in the thin lens approximation of the end regions of accelerator magnets.
Findings
The extraction of the leading term in the Fourier–Bessel series requires the solution of a differential equation by means of a Fourier transform. This yields a natural way to de-convolute the measured distribution of the multipole content. The author has shown that the measurement technique requires iso-parametric coils to avoid interception of the longitudinal field component. The compensation of the main signal cannot be done with the classical arrangement of search coils at different radii, because no easy scaling law exists. A new design of an iso-perimetric induction coil has been found.
Research limitations/implications
In the literature, it is stated that the pseudo-multipoles can be extracted from field computations or measurements. While this is true for computations, the author shows that the measurement of the field harmonics must be done with iso-parametric coils because otherwise the leading term in the Fourier–Bessel series cannot be extracted.
Practical implications
The author has now established the theory behind a number of field transducers, such as the moving fluxmeter, the rotational coil scanner and the solenoidal field transducer.
Originality/value
This paper brought together the known theory of the orthogonal expansion method with the methods and tools for magnetic field measurements to establish a field description in accelerator magnets.
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Introduces papers from this area of expertise from the ISEF 1999 Proceedings. States the goal herein is one of identifying devices or systems able to provide prescribed…
Abstract
Introduces papers from this area of expertise from the ISEF 1999 Proceedings. States the goal herein is one of identifying devices or systems able to provide prescribed performance. Notes that 18 papers from the Symposium are grouped in the area of automated optimal design. Describes the main challenges that condition computational electromagnetism’s future development. Concludes by itemizing the range of applications from small activators to optimization of induction heating systems in this third chapter.
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Massimiliano de Magistris and Alessandro Formisano
The identification of magnetic field profiles is crucial in many applications where a direct measurement is difficult. We discuss here a technique, based on the injection of…
Abstract
The identification of magnetic field profiles is crucial in many applications where a direct measurement is difficult. We discuss here a technique, based on the injection of charged particles in the region under examination, which promises to be an innovative and effective tool in the analysis of 1‐D field profiles in high current plasma discharges. After the decription of the inverse problem related to the field construction, we consider a suitable discrete identification scheme, and analyze some properties of the latter. The field map in the interest region is reconstructed via a minimization procedure, which identifies the coefficient of a well‐suited expansion for the field. In particular, we discuss the precision and robustness of the identification procedure, with respect to the chosen optimization scheme, the amount of data, the order in the field expansion, and the influence of noise on the data.
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Herbert De Gersem, Vaishnavi Srinivasan and Carsten Muehle
The purpose of this paper is to show that constructing magnetic equivalent circuits (MECs) for simulating accelerator magnets is possible by defining a three-port magnetic element…
Abstract
Purpose
The purpose of this paper is to show that constructing magnetic equivalent circuits (MECs) for simulating accelerator magnets is possible by defining a three-port magnetic element for modelling the T-shape field distribution, where the flux leaves the yoke and enters the aperture.
Design/methodology/approach
A linear three-port magnetic element is extracted from an analytical field solution and can be represented by a number of two-port elements. Its nonlinear counterpart is obtained as a combination of the corresponding nonlinear two-port elements. An improved nonlinear three-port element is developed on the basis of an embedded nonlinear one-dimensional finite element model.
Findings
The T-shaped field distribution comes together with a complicated interplay between the saturation of the ferromagnetic yoke parts and flux leaking to the aperture. This is more accurately modelled by the improved nonlinear three-port magnetic element.
Research limitations/implications
MECs have a limited validity range, especially for configurations where a high saturation level and fringing flux effects coexist.
Practical implications
The results of the paper appeal to be careful with applying nonlinear MECs for simulating bending magnets.
Originality/value
A new nonlinear three-port magnetic element for ferromagnetic yoke parts with T-shaped flux distribution has been developed.