1,720,984 research outputs found
Comparison of conditions v=0 and a-n=0 on conductor boundaries in ajv-a-h' formulations
No full textIn a previous paper the authors proposed a Coulomb gauge A,V-A-psi formulation for quasi-static transient eddy current problems using V=0, instead of A . n=0, as guage condition on the conductor boundary. Further numerical experimentation using either V=0 or A . n=0 on different parts of the conductor boundary, however, has shown that, rather unexpectedly, J . n=0 is numerically more weakly enforced where V=0 is used. Hence, in spite of some advantages of V=0, A . n=0 still seems to be a better choice, after all. A theoretical explanation for this unexpected drawback of V=0 has been found and is presented here in detail
A 2D finite element procedure for magnetic analysis involving non-linear and hysteretic materials
No full textIn this paper a 2D Finite Element procedure devised to handle both soft magnetic materials and hysteretic ones, on basis of Preisach's classical approach for scalar and vector hysteresis, is presented. In the scalar case, a model identified by a reduced set of experimental data is proposed, whereas for the vector case a more demanding identification procedure is required. The resulting modular “Preisach engines” are used to solve some problems of practical engineering typ
Optimisation of electromagnetic problems with uncertain parameters and tolerances in the design variables
No full textThe common approach to continuous and discrete optimisation problems in electromagnetics does not take into account uncertainties and variations of the design variables. Local sensitivity analysis is usually performed only after the optimisation run to study the behaviour of the objective function in the neighbourhood of the optimum. However, this procedure may prove inefficient if the optimum has to be rejected due to sensitivity considerations and a new run has then to be performed. In this paper an alternative approach, which takes into account uncertainties in the design variables and physical data, is presented, and an analytical function is used to highlight the features of the proposed method. The essence of the technique is to couple the optimisation with a series of worst case analyses which are embedded in the optimisation loop. The method is fully general and can be applied to any optimisation method. The additional computational costs associated with the procedure maybe relatively high, but in the authors’ opinion the obtained gains in user confidence in the solution and the computational savings in some cases far offset the possible drawbacks of the method
A combined advancing-front/Delaunay technique for the meshing of curved surfaces in 3D
No full textA combined advancing-front/Delaunay technique for the generation of triangular meshes on curved surfaces in 3D is presented. It is shown that geometrical considerations, which would be extremely beneficial from a theoretical point of view, cannot be applied in general in the case of the objects which have to be meshed in computational electromagnetics. The method presented in this paper is based on a combination of advancing-front and Delaunay techniques applied to local parametrizations of the surfaces to be meshed, and is able to treat surfaces with holes and thus with non-connected boundaries. The implemented techniques are described in detail and an analysis of the computational complexity of the algorithms and a description of the supporting data structures are presented
A WWW-based tool for the remote optimization of electromagnetic devices
No full textIn this paper, a World Wide Web-based tool for the remote definition and analysis of optimization problems in electromagnetic design is described. The tool can find effective applications both in advanced teaching and in industrial design activities, thanks to its user-friendliness. The architecture of the system and its current implementation, based on commonly available tools, are presented and discussed in detail. Examples of the use of the tool for the design of a magnet to be used in high energy physics experiments and a simple electromagnetic actuator are give
Comparison of conditions V=0 and A center dot n=0 on conductor boundaries in A,V-A-Psi formulations
No full textDrago et al. (1994) proposed a Coulomb gauge A,V-A-Ψ formulation for quasi-static transient eddy current problems using V=0, instead of A·n=0, as gauge condition on the conductor boundary. Further numerical experimentation using either V=0 or A·n=0 on different parts of the conductor boundary, however, has shown that, rather unexpectedly, J·n=0 is numerically more weakly enforced where V=0 is used. Hence, in spite of some advantages of V=0, A·n=0 still seems to be a better choice, after all. A theoretical explanation for this unexpected drawback of V=0 has been found and is presented in detai
Time-harmonic mesh adaption with error estimate based on the ''local field error'' approach
No full textAn implementation of a mesh adaption procedure for 2D “time-harmonic” solution, based on “h-refinement” criteria, using as error estimate the “local field error” approach, is presented. The error estimate is based on the solution, on an “element-by-element” basis, of an adjoint error problem cast in terms of magnetic induction. The “self-adapting” meshing procedure is iterative and is composed of a series of modules for the various functions. The electromagnetic problem is solved using the Esprit project MIDAS-2D “frequency domain” FEM solver. Some test cases at various frequencies are presented and results are discusse
An Overview on Reversible Sea Return Electrodes for HVDC Links
No full textHVDC electrodes are usually implemented in HVDC links to avoid the installation of a metallic return. Submarine cables, especially those dealing with lengths of thousands of kilometers, are expensive, and high costs of laying are normally expected. Due to the high number of reversible HVDC links, the marine electrodes must be able to withstand both anodic and cathodic operations, which leads to careful considerations in terms of the material to be used. This paper shows the state of the art of the currently installed reversible sea return electrodes, focusing on the type of installation (sea, shore or pond electrodes) and on the material used, from the first plant installed in 1954 up to the more recent ones established during the XXI century. All reported data derive from publicly available sources. Moreover, since nowadays environmental issues are among the most important topics, for each material and for each type of installation, a guideline on the possible interferences caused by marine electrodes with the surrounding environment is proposed
Mesh adaption and optimization techniques in magnet design
No full textIn this paper the results obtained in the realization of an automatic procedure for magnet design in 2D, plane and axisymmetric, will be presented. The proposed procedure combines mesh adaption, based on an “a-posteriori” error estimate, and deterministic optimization techniques. The use of an analysis module with mesh adaption capabilities gives the automatic design procedure a more stable behaviour in the evaluation of objective function. In particular, one of important features of this strategy is to allow wide variations in dimensional parameters, with high accuracy. The procedure has been realized with a modified version of the VF/OPERA 2d code, realized by the authors, and an optimization technique, based either on the “Response Surface” or on the “Pattern Search” algorithm, interacting with the analysis code using parametric command
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