P. Alotto, P. Molfino and G. Molinari
The common approach to continuous and discrete optimisation problems in electromagnetics does not take into account uncertainties and variations of the design variables. Local…
Abstract
The 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.
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Th. Ebner, Ch. Magele, B.R. Brandstätter, M. Luschin and P.G. Alotto
Global optimization in electrical engineering using stochastic methods requires usually a large amount of CPU time to locate the optimum, if the objective function is calculated…
Abstract
Global optimization in electrical engineering using stochastic methods requires usually a large amount of CPU time to locate the optimum, if the objective function is calculated either with the finite element method (FEM) or the boundary element method (BEM). One approach to reduce the number of FEM or BEM calls using neural networks and another one using multiquadric functions have been introduced recently. This paper compares the efficiency of both methods, which are applied to a couple of test problems and the results are discussed.
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Gives introductory remarks about chapter 1 of this group of 31 papers, from ISEF 1999 Proceedings, in the methodologies for field analysis, in the electromagnetic community…
Abstract
Gives introductory remarks about chapter 1 of this group of 31 papers, from ISEF 1999 Proceedings, in the methodologies for field analysis, in the electromagnetic community. Observes that computer package implementation theory contributes to clarification. Discusses the areas covered by some of the papers ‐ such as artificial intelligence using fuzzy logic. Includes applications such as permanent magnets and looks at eddy current problems. States the finite element method is currently the most popular method used for field computation. Closes by pointing out the amalgam of topics.
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Jani Paavilainen, Jukka Tuhkuri and Arttu Polojärvi
The purpose of this paper is to present a 2D combined finite‐discrete element method (FEM‐DEM) to model the multi‐fracture of beam structures and an application of the method to…
Abstract
Purpose
The purpose of this paper is to present a 2D combined finite‐discrete element method (FEM‐DEM) to model the multi‐fracture of beam structures and an application of the method to an ice‐structure interaction problem.
Design/methodology/approach
In the method, elastic beams and their fracture are modelled according to FEM by using nonlinear Timoshenko beam elements and cohesive crack model. Additionally, the beam elements are used to tie the discrete elements together. The contact forces between the colliding beams are calculated by using the DEM.
Findings
Three numerical examples are given to verify the method. Further, the method is applied to model the failure process of a floating ice beam against an inclined structure. Based on the comparison of the experiments and the simulation, a good agreement between the results is observed.
Originality/value
In the context of combined FEM‐DEM, the two novel features presented in this paper are: the use of Timoshenko finite element beams with damping to calculate internal forces and to combine the discrete elements; and the bending failure by the cohesive crack approach while simultaneously keeping track of the position of the neutral axis of the beam.
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P. Alotto, A. De Cian, G. Molinari and M. Rossi
To show a possible implementation of surface impedance boundary conditions (SIBCs) in a time domain formulation based on the cell method (CM).
Abstract
Purpose
To show a possible implementation of surface impedance boundary conditions (SIBCs) in a time domain formulation based on the cell method (CM).
Design/methodology/approach
The implementation is based on vector fitting (VF), a technique which allows a time domain representation of a rational approximation of the surface impedance to be found.
Findings
It is shown that very little computational effort is needed to find a very good VF approximation of simple SIBCs and that such approximation is easily fitted into existing CM codes.
Research limitations/implications
The extension to higher order SIBCs has not been taken into account.
Practical implications
The proposed approach avoids the use of convolution integrals, is accurate and easy to implement.
Originality/value
This paper introduces the use of VF for the approximate time domain representation of SIBCs.
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P. Alotto, P. Molfino, G. Molinari, M. Nervi and R. Orlando
In this paper a code for the solution of nonlinear thermo‐magnetic problems, arising in the transient analysis of thermal and electromagnetic fields in resistive toroidal field…
Abstract
In this paper a code for the solution of nonlinear thermo‐magnetic problems, arising in the transient analysis of thermal and electromagnetic fields in resistive toroidal field coils of tokamak devices, is presented. A formulation based on the electric vector potential T and the magnetic total scalar potential Ψ for the analysis of the thermo‐magnetic skin effect phenomenon in the toroidal field coils of proposed tokamaks has been used, and the results obtained are reported, reviewed and discussed.
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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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Mohammad Alta’any, Venancio Tauringana and Laura Obwona Achiro
This paper aims to examine the impact of a board-level governance bundle (i.e. size, independence, expertise, meetings, gender diversity and multiple directorships) on the…
Abstract
Purpose
This paper aims to examine the impact of a board-level governance bundle (i.e. size, independence, expertise, meetings, gender diversity and multiple directorships) on the non-financial performance of National Health Service (NHS) hospitals – and, separately, by hospital type (i.e. trusts hospitals and foundation trusts hospitals).
Design/methodology/approach
A logit regression for panel data is used for a sample of 128 NHS trusts and foundation trusts across England from 2014 to 2018. The data was hand-collected from NHS hospitals’ annual reports and Care Quality Commission reports. The cancer waiting time target (i.e. 62-day cancer referral and treatment target) is used to measure non-financial performance.
Findings
The main findings for NHS hospitals indicate that multiple directorships positively and significantly affect non-financial performance. However, board expertise and gender diversity have a negative and significant influence. When the sample is partitioned, the results remain the same for the NHS foundation trusts hospitals. For NHS trust hospitals, except for multiple directorships having a positive and significant effect, all remaining governance attributes have an insignificant impact.
Practical implications
The findings have implications for policymakers and practitioners as they move to implement measures to improve hospital performance against the cancer waiting time targets in the English NHS.
Originality/value
To the best of the authors’ knowledge, this is the first study to examine the impact of corporate governance on cancer waiting time targets in public hospitals. Overall, this paper contributes to the corporate governance literature, especially in the context of public hospitals, and has significant practical and theoretical implications.
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Obaid Ur Rehman, Shiyou Yang and Shafi Ullah Khan
The purpose of this paper is to explore the potential of standard quantum-based particle swarm optimization (QPSO) methods for solving electromagnetic inverse problems.
Abstract
Purpose
The purpose of this paper is to explore the potential of standard quantum-based particle swarm optimization (QPSO) methods for solving electromagnetic inverse problems.
Design/methodology/approach
A modified QPSO algorithm is designed.
Findings
The modified QPSO algorithm is an efficient and robust global optimizer for optimizing electromagnetic inverse problems. More specially, the experimental results as reported on different case studies demonstrate that the proposed method can find better final optimal solution at an early stage of the iterating process (uses less iterations) as compared to other tested optimal algorithms.
Originality/value
The modifications include the design of a new position updating formula, the introduction of a new mutation strategy and a dynamic control parameter to intensify the convergence speed of the algorithm.