Rafal M. Wojciechowski, Andrzej Demenko and Jan K. Sykulski
The purpose of this paper is to develop a reluctance‐resistance network (RRN) formulation for determining the induced current distributions in a 3D space of multiply connected…
Abstract
Purpose
The purpose of this paper is to develop a reluctance‐resistance network (RRN) formulation for determining the induced current distributions in a 3D space of multiply connected conducting systems.
Design/methodology/approach
The proposed RRN method has been applied to solve Problem No. 7 of the International TEAM Workshops. The induced currents in the conductive plate with an asymmetrically situated “hole” have been analysed. The RRN equations have been formed by means of the finite element method using the magnetic vector potential A and the electric vector potentials T and T0. The block relaxation method combined with the Cholesky decomposition procedure has been applied to solve the resultant RRN equations.
Findings
Comparison with results published in literature has demonstrated high accuracy of the proposed RRN computational scheme while offering significant savings in computing times.
Originality/value
A novel formulation of the RRN approach has been proposed and demonstrated to be computationally efficient.
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Song Xiao, Mihai Rotaru and Jan K. Sykulski
Design optimisation of electromagnetic devices is computationally expensive as use of finite element or similar codes is normally required. Thus, one of the objectives is to have…
Abstract
Purpose
Design optimisation of electromagnetic devices is computationally expensive as use of finite element or similar codes is normally required. Thus, one of the objectives is to have efficient algorithms minimising the number of necessary function calls. In such algorithms a balance between exploration and exploitation needs to be found not to miss the global optimum but at the same time to make efficient use of information already found. The purpose of this paper is a contribute to the search of such efficient algorithms.
Design/methodology/approach
This paper discusses the use of kriging surrogate modelling in multiobjective design optimisation in electromagnetics. The investigation relies on the use of special test functions.
Findings
The importance of achieving appropriate balance between exploration and exploitation is emphasised when searching for the global optimum. New strategies are proposed using kriging.
Originality/value
It is argued that the proposed approach will yield a procedure to solve time consuming electromagnetic design problems efficiently and will also assist the decision making process to achieve a robust design of practical devices considering tolerances and uncertainties.
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Andrzej Demenko and Jan. K. Sykulski
The purpose of this paper is to emphasise the analogies between variational and network formulations using geometrical forms, with the purpose of developing alternative but…
Abstract
Purpose
The purpose of this paper is to emphasise the analogies between variational and network formulations using geometrical forms, with the purpose of developing alternative but otherwise equivalent derivations of the finite element (FE) method.
Design/methodology/approach
FE equations for electromagnetic fields are examined, in particular nodal elements using scalar potential formulation and edge elements for vector potential formulation.
Findings
It is shown how the equations usually obtained via variational approach may be more conveniently derived using integral methods, employing a geometrical description of the interpolating functions of edge and facet elements. Moreover, the resultant equations describe the equivalent multi‐branch circuit models.
Originality/value
The approach proposed in the paper explores the analogy of the FE formulation to loop or nodal magnetic or electric networks and has been shown to be very beneficial in teaching, especially to students well familiar with circuit methods. The presented methods are also helpful when formulating classical network models. Finally, for the first time, the geometrical forms of edge and facet element functions have been demonstrated.
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Igor O. Golosnoy and Jan K. Sykulski
The purpose of this paper is to access performance of existing computational techniques to model strongly non‐linear coupled thermo‐electric problems.
Abstract
Purpose
The purpose of this paper is to access performance of existing computational techniques to model strongly non‐linear coupled thermo‐electric problems.
Design/methodology/approach
A thermistor is studied as an example of a strongly non‐linear diffusion problem. The temperature field and the current flow in the device are mutually coupled via ohmic heating and very rapid variations of electric conductivity with temperature and applied electric field, which makes the problem an ideal test case for the computational techniques. The finite volume fully coupled and fractional steps (splitting) approaches on a fixed computational grid are compared with a fully coupled front‐fixing method. The algorithms' input parameters are verified by comparison with published experiments.
Findings
It was found that fully coupled methods are more effective for non‐linear diffusion problems. The front fixing provides additional improvements in terms of accuracy and computational cost.
Originality/value
This paper for the first time compares in detail advantages and implementation complications of each method being applied to the coupled thermo‐electric problems. Particular attention is paid to conservation properties of the algorithms and accurate solutions in the transition region with rapid changes in material properties.
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Song Xiao, Mihai Rotaru and Jan K. Sykulski
Electromagnetic design utilising finite element or similar numerical methods is computationally expensive, thus efficient algorithms reducing the number of objective function…
Abstract
Purpose
Electromagnetic design utilising finite element or similar numerical methods is computationally expensive, thus efficient algorithms reducing the number of objective function calls to locate the optimum are sought. The balance between exploration and exploitation may be achieved using a reinforcement learning approach, as demonstrated previously. However, in practical design problems, in addition to finding the global optimum efficiently, information about the robustness of the solution may also be important. In this paper, the aim is to discuss the suitability of different search algorithms and to present their fitness to solve the optimization problem in conjunction with providing enough information on the robustness of the solution.
Design/methodology/approach
Two novel strategies enhanced by the surrogate model based weighted expected improvement approach are discussed. The algorithms are tested using a two‐variable test function. The emphasis of these strategies is on accurate approximation of the shape of the objective function to accomplish a robust design.
Findings
The two novel strategies aim to pursue the optimal value of weights for exploration and exploitation throughout the iterative process for better prediction of the shape of the objective function.
Originality/value
It is argued that the proposed strategies based on adaptively tuning weights perform better in predicting the shape of the objective function. Good accuracy of predicting the shape of the objective function is crucial for achieving a robust design.
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Thomas S. Parel, Mihai D. Rotaru, Jan K. Sykulski and Grant E. Hearn
The purpose of this paper is to optimise the cost‐based performance of a tubular linear generator and to minimise cogging forces.
Abstract
Purpose
The purpose of this paper is to optimise the cost‐based performance of a tubular linear generator and to minimise cogging forces.
Design/methodology/approach
Optimisation of a tubular linear generator with longitudinal flux topology has been undertaken using a finite element method. The computational models used have been verified experimentally.
Findings
The use of an oversized stator linear generator design as opposed to an oversized translator design has the potential to increase the output electromotive force per unit material cost by 25 per cent for slotless iron core topologies and approximately 14 per cent for air core topologies. For cogging force minimisation, optimisation of the length of the stator core is an effective technique for both oversized stator and oversized translator constructions. Comparisons of magnet materials also indicate that the higher cost of rare earth magnets to ferrites is compensated by their superior specific performances.
Originality/value
In this paper, a broader range of design parameters than in previous investigations has been optimised for the slotless iron core and air core topologies. The result relating to cogging force reduction and cost savings (in particular) has the potential to make direct drive wave energy extraction a more competitive technology in terms of reliability and cost.
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Richard D. Chippendale, Igor O. Golosnoy, Paul L. Lewin and Jan K. Sykulski
The purpose of this paper is to investigate and explain the unexpected current flow patterns and twisting equipotential surfaces observed in strongly anisotropic materials.
Abstract
Purpose
The purpose of this paper is to investigate and explain the unexpected current flow patterns and twisting equipotential surfaces observed in strongly anisotropic materials.
Design/methodology/approach
Potential distributions and current flow paths in highly anisotropic composite materials were studied via numerical simulation and experimentally. Simplified composite panels with two plyes were analysed using a finite‐element model; the predictions were then confirmed experimentally.
Findings
The unexpected twisting equipotential surfaces and current flow patterns were found to be consistent with minimising of Joule heat release in the material. Numerical modelling suggests that the twisted profiles of the potential are highly sensitive to the anisotropic electrical conductivity.
Originality/value
This paper discusses the reverse current flows witnessed in a two‐layer anisotropic system. Such behaviour has never been predicted or observed experimentally before. The reported results will be of interest to anyone who is considering using anisotropic materials such as carbon fibre composites which might experience applied potential difference, such as lightning strikes.