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Article
Publication date: 18 November 2013

Y.Z. Chen

This paper is devoted to the evaluation of the T-stress for a hypocycloid hole in an infinite plate. The remote tractions are applied for the infinite plate containing the…

Abstract

Purpose

This paper is devoted to the evaluation of the T-stress for a hypocycloid hole in an infinite plate. The remote tractions are applied for the infinite plate containing the hypocycloid hole. After using the conformal mapping, an elasticity solution is obtained, and the T-stress at the cusp tip can be abstracted from this solution. The paper aims to discuss these issues.

Design/methodology/approach

Conformal mapping technique is used for solving the T-stress problem for a hypocycloid cusp hole problem.

Findings

The present study proves that the cusp configuration has a significant influence to the value of T-stress at cusp crack tip.

Originality/value

A closed form solution for the T-stress in cusp crack is first obtained in the submission.

Details

Multidiscipline Modeling in Materials and Structures, vol. 9 no. 4
Type: Research Article
ISSN: 1573-6105

Keywords

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Article
Publication date: 3 July 2017

Jaime Renedo Anglada, Suleiman Sharkh and Arfakhshand Qazalbash

The purpose of this paper is to study the effect of curvature on the magnetic field distribution and no-load rotor eddy current losses in electric machines, particularly…

Abstract

Purpose

The purpose of this paper is to study the effect of curvature on the magnetic field distribution and no-load rotor eddy current losses in electric machines, particularly in high-speed permanent magnet (PM) machines.

Design/methodology/approach

The magnetic field distribution is obtained using conformal mapping, and the eddy current losses are obtained using a cylindrical multilayer model. The analytical results are validated using a two-dimensional finite element analysis. The analytical method is based on a proportional-logarithmic conformal transformation that maps the cylindrical geometry of a rotating electric machine into a rectangular configuration without modifying the length scale. In addition, the appropriate transformation of PM cylindrical domains into the rectangular domain is deduced. Based on this conformal transformation, a coefficient to quantify the effect of curvature is proposed.

Findings

Neglecting the effect of curvature can produce significant errors in the calculation of no-load rotor losses when the ratio between the air-gap length and the rotor diameter is large.

Originality/value

The appropriate transformation of PM cylindrical domains into the rectangular domain is deduced. The proportional-logarithmic transformation proposed provides an insight into the effect of curvature on the magnetic field distribution in the air-gap and no-load rotor losses. Furthermore, the proposed curvature coefficient gives a notion of the effect of curvature for any particular geometry without the necessity of any complicated calculation. The case study shows that neglecting the effect of curvature underestimates the rotor eddy-current losses significantly in machines with large gap-to-rotor diameter ratios.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 36 no. 4
Type: Research Article
ISSN: 0332-1649

Keywords

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Article
Publication date: 11 November 2013

Mirko Barbuto, Andrea Alù, Filiberto Bilotti, Alessandro Toscano and Lucio Vegni

– The purpose of this paper is to present an analytical expression for the characteristic impedance of a microstrip line in presence of a dielectric cover.

Abstract

Purpose

The purpose of this paper is to present an analytical expression for the characteristic impedance of a microstrip line in presence of a dielectric cover.

Design/methodology/approach

Assuming a quasi-TEM propagation mode, a rigorous conformal mapping based on the Schwarz-Christoffel transformation is employed to derive the equivalent capacitance model, which can then be applied to derive a closed analytical expression for the effective permittivity and the characteristic impedance of the line.

Findings

Such a formulation is not limited to the case of a single cover layer, but an arbitrary number of electric overlays can be considered as well. Comparisons with published numerical results and full-wave simulations in the case of a single cover layer have been also performed to test the validity of the proposed approach.

Originality/value

The new analytical formula for the characteristic impedance of a microstrip line with a single dielectric cover shows better performances compared to the one of closed formulas already presented in the literature.

Details

COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, vol. 32 no. 6
Type: Research Article
ISSN: 0332-1649

Keywords

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Article
Publication date: 16 November 2010

Christopher R. Lines, Willem A. Cronjé and Brian Wigdorowitz

The purpose of this paper is to devise a magnetic field modelling approach suitable for simulating the transient behaviour of a class of electromagnetic systems…

Abstract

Purpose

The purpose of this paper is to devise a magnetic field modelling approach suitable for simulating the transient behaviour of a class of electromagnetic systems (particularly linear synchronous motors).

Design/methodology/approach

The classical 2D magnetic equivalent circuit (MEC) approach is extended by separately accounting for leakage flux from highly permeable polygonal regions (where the MEC approach is most applicable). It capitalises on the computational efficiency of an MEC approach for regions where the flux can be assumed to be uniformly channelled through a coarse network of “flux tubes” and accounts for leakage flux from these regions by introducing mutual permeances. These mutual permeances are geometry dependent and can be calculated upfront using a surface‐current representation of the magnetomotive force attributed to each flux tube.

Findings

As demonstrated with a simple example, the magnetic field solution converges with an increasing subdivision of flux tubes, yielding a transparent trade‐off between simulation time and accuracy.

Research limitations/implications

Using Schwarz‐Christoffel mapping to approximate the mutual permeances is restrictive and introduces unnecessary error. Hence, the use of finite element or boundary element methods to obtain these permeances is under investigation. Furthermore, it is expected that introducing 2D flux tube elements for junction regions would be beneficial.

Originality/value

A novel approach is presented that aims to improve the accuracy of a traditional MEC solution, whilst retaining its computational advantage for the flux that is well channelled. The method has particular merit for the dynamic modelling of linear motors, where the machine's behaviour is dominated by the flux bridging the air gap.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 29 no. 6
Type: Research Article
ISSN: 0332-1649

Keywords

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Article
Publication date: 1 July 2006

E. Costamagna, P. Di Barba and A. Savini

The paper seeks to present a methodology using the numerical Schwarz‐Christoffel (SC) transformation in order to extract a subdomain from a simply‐connected source‐free…

Abstract

Purpose

The paper seeks to present a methodology using the numerical Schwarz‐Christoffel (SC) transformation in order to extract a subdomain from a simply‐connected source‐free two‐dimensional field domain. The aims to present an application to the design of an electrostatic micromotor.

Design/methodology/approach

The methodology can be usefully applied to reduce the size of complicated field regions with irregularly shaped boundaries. In the subdomain, finite‐element (FEM) analyses can then be performed with limited computational effort.

Findings

The synthesis of the conditions along the sub‐domain boundary, which is piecewise approximated by potential and flux lines, is carried out by performing repeated field analyses. Several comparisons among FEM and SC results are presented, to validate the proposed approach.

Originality/value

Refined techniques of conformal mapping are used in order to extract a suitable subdomain from a large field domain of an electrostatic micromotor. This allows one to focus the analysis directly on the region where the field distribution is to be investigated.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 25 no. 3
Type: Research Article
ISSN: 0332-1649

Keywords

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Article
Publication date: 1 March 1997

N. Nigro, M. Storti and S. Idelsohn

Addresses two difficulties which arise when using a compressible code with equal order interpolation (non‐staggered grids in the finite‐difference nomenclature) to capture…

Abstract

Addresses two difficulties which arise when using a compressible code with equal order interpolation (non‐staggered grids in the finite‐difference nomenclature) to capture a steady‐state solution in the incompressible limit, i.e. at low Mach numbers. Explains that, first, numerical instabilities in the form of spurious oscillations in pressure pollute the solution and, second, the convergence to the steady state becomes extremely slow owing to bad conditioning of the different speeds of propagation. By using a stabilized method, allows the use of equal‐order interpolations in a consistent (weighted‐residual) formulation which stabilizes both the convection and the continuity terms at the same time. On the other hand, by using specially devised preconditioning, assures a rate of convergence independent of Mach number.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 7 no. 2/3
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 1 November 1971

M.A. El‐Kadeem, Essam Salem and Hassan Ragab El‐Sayed

THIS PAPER presents a study of the performance characteristics of finite width stationary externally pressurized rectangular bearings. Two types of bearings are…

Abstract

THIS PAPER presents a study of the performance characteristics of finite width stationary externally pressurized rectangular bearings. Two types of bearings are considered, namely, the plain and initially tilted pad bearings. The bearings were lubricated by using incompressible fluid. The study includes:

Details

Industrial Lubrication and Tribology, vol. 23 no. 11
Type: Research Article
ISSN: 0036-8792

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Article
Publication date: 22 August 2008

I. Gavrilyuk, M. Hermann, I. Lukovsky, O. Solodun and A. Timokha

The main purpose of this paper is to develop two efficient and accurate numerical analytical methods for engineering computation of natural sloshing frequencies and modes…

Abstract

Purpose

The main purpose of this paper is to develop two efficient and accurate numerical analytical methods for engineering computation of natural sloshing frequencies and modes i the case of truncated circular conical tanks.

Design/methodology/approach

The numerical‐analytical methods are based on a Ritz Treftz variational scheme with two distinct analytical harmonic functional bases.

Findings

Comparative numerical analysis detects the limit of applicability of variational methods in terms of the semi‐apex angle and the ratio between radii of the mean free surface and the circular bottom. The limits are caused by different analytical properties of the employed functional bases. However, parallel use of two or more bases makes it possible to give an accurate approximation of the lower natural frequencies for relevant tanks. For V‐shaped tanks, dependencies of the lowest natural frequency versus the semi‐apex angle and the liquid depth are described.

Practical implications

The methods provide the natural sloshing frequencies for V‐shaped tanks that are valuable for designing elevated containers in seismic areas. Approximate natural modes can be used in derivations of nonlinear modal systems, which describe a resonant coupling with structural vibrations.

Originality/value

Although variational methods have been widely used for computing the natural sloshing frequencies, this paper presents their application for truncated conical tanks for the first time. An original point is the use of two distinct functional bases.

Details

Engineering Computations, vol. 25 no. 6
Type: Research Article
ISSN: 0264-4401

Keywords

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Article
Publication date: 1 July 1971

M.A. El Kadeem, Essam Salem and Hassan Ragab El‐Sayed

In this study, a rectangular, externally pressurized bearing, lubricated by incompressible fluid, and compensated by a capillary restrictor, is analysed. The analysis…

Abstract

In this study, a rectangular, externally pressurized bearing, lubricated by incompressible fluid, and compensated by a capillary restrictor, is analysed. The analysis includes an investigation into the effect of initial tilting of the pad, and the introduction of a step in the pad surface.

Details

Industrial Lubrication and Tribology, vol. 23 no. 7
Type: Research Article
ISSN: 0036-8792

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Article
Publication date: 3 October 2016

Linas Ardaravičius, Skirmantas Keršulis, Oleg Kiprijanovič, Česlovas Šimkevicius and Bonifacas Vengalis

The purpose of this paper is to investigate damaging processes in TaN thin film absorbers under action of high-voltage electrical pulse of nanosecond duration. Despite…

Abstract

Purpose

The purpose of this paper is to investigate damaging processes in TaN thin film absorbers under action of high-voltage electrical pulse of nanosecond duration. Despite having mechanical origin of crack opening, estimation based on the readings from oscillograms shows uncharacteristically high velocities of the crack propagation.

Design/methodology/approach

Microscopic images of damaged absorbers showing the final result of the damaging process provided initial information about its geometrical peculiarities. Then, to clarify the dynamics of the process, the authors create the model of the crack, having elements of self-similarities and multiple stage opening. The influence of heating induced by current concentration at crack tip and of magnetic stress of this concentrated current are both included in the model.

Findings

Using physical parameters of TaN layers with flowing current and performing calculations the authors define the conditions required to initiate the damaging process and to sustain it. Danger of such damage is relevant for high-Tc superconducting thin films after their switching to normal state which is induced by the high-voltage pulse.

Practical implications

There were made recommendations to manufactures aiming to improve electrical durability of the absorbers in an effort to prevent the damaging influence of power nanosecond electrical pulses.

Originality/value

Three stage opening model implies the appearance of zone of high-energy dissipation that can lead to detonation-like destruction of the film and, therefore, explain the high velocities of crack propagation.

Details

International Journal of Structural Integrity, vol. 7 no. 5
Type: Research Article
ISSN: 1757-9864

Keywords

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