Search results

1 – 10 of over 3000
Article
Publication date: 1 May 1998

Norbert Gebbeken

As far as steel‐rod structures are concerned the yield‐hinge theory is a very efficient approach of the ultimate‐load theory. Unfortunately, most of the published strategies…

Abstract

As far as steel‐rod structures are concerned the yield‐hinge theory is a very efficient approach of the ultimate‐load theory. Unfortunately, most of the published strategies suffer from considerable deficiencies which depend on two main reasons: first, the yield condition is not approximated very well, and, second, a flow rule is not incorporated at all. This may significantly affect the calculated load‐carrying behaviour and as a consequence the elasto‐plastic failure prediction. In the present paper a consistent formulation of a refined numerical method based on the yield‐hinge theory is consistently developed from the theory of plasticity. The derivation is carried out in the framework of a geometrically nonlinear Timoshenko beam theory discretized for the displacement based finite element method. The plastic deformations can be interpreted as three‐dimensional eccentric yield‐hinges (generalized yield‐hinges). The presented numerical xamples show the efficiency of the proposed method.

Details

Engineering Computations, vol. 15 no. 3
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 1 February 1987

M.S. Shephard, P.L. Baehmann and K.R. Grice

The general structure of geometrically‐based automatic finite element modelling systems is discussed. The development of a specific system employing the modified‐quadtree and…

Abstract

The general structure of geometrically‐based automatic finite element modelling systems is discussed. The development of a specific system employing the modified‐quadtree and modified‐octree mesh generators is presented. The application of this approach to metal forming analysis is then given.

Details

Engineering Computations, vol. 4 no. 2
Type: Research Article
ISSN: 0264-4401

Article
Publication date: 5 September 2023

Lucas Silva and Alfredo Gay Neto

When establishing a mathematical model to simulate solid mechanics, considering realistic geometries, special tools are needed to translate measured data, possibly with noise…

Abstract

Purpose

When establishing a mathematical model to simulate solid mechanics, considering realistic geometries, special tools are needed to translate measured data, possibly with noise, into idealized geometrical entities. As an engineering application, wheel-rail contact interactions are fundamental in the dynamic modeling of railway vehicles. Many approaches used to solve the contact problem require a continuous parametric description of the geometries involved. However, measured wheel and rail profiles are often available as sets of discrete points. A reconstruction method is needed to transform discrete data into a continuous geometry.

Design/methodology/approach

The authors present an approximation method based on optimization to solve the problem of fitting a set of points with an arc spline. It consists of an initial guess based on a curvature function estimated from the data, followed by a least-squares optimization to improve the approximation. The authors also present a segmentation scheme that allows the method to increment the number of segments of the spline, trying to keep it at a minimal value, to satisfy a given error tolerance.

Findings

The paper provides a better understanding of arc splines and how they can be deformed. Examples with parametric curves and slightly noisy data from realistic wheel and rail profiles show that the approach is successful.

Originality/value

The developed methods have theoretical value. Furthermore, they have practical value since the approximation approach is better suited to deal with the reconstruction of wheel/rail profiles than interpolation, which most methods use to some degree.

Details

Engineering Computations, vol. 40 no. 7/8
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 25 September 2009

Zhenghao Yeh and Behrokh Khoshnevis

The purpose of this paper is to present an introduction to geometric conformity principles for examining the geometric deviation between the desired (designed) and the fabricated…

1186

Abstract

Purpose

The purpose of this paper is to present an introduction to geometric conformity principles for examining the geometric deviation between the desired (designed) and the fabricated surfaces which may be generated by a class of surface ruling fabrication processes such as flank milling, wire electrical discharge machining (WEDM), and contour crafting (CC).

Design/methodology/approach

In general, it is computationally challenging to calculate error approximation based on points. This paper proposes methods that efficiently calculate error approximation based on curve, surface area, and volume.

Findings

This paper derives the equations for calculating the ruled surface areas and the volume of 3D slices in 3D object models. One may use the difference of surface areas or volumes to determine the extent of the global conformity of the ruled surfaces. Additionally, local conformity analysis through calculating curve deviation has been introduced to improve the reliability of the global conformity analysis.

Research limitations/implications

The research results apply only to fabrication processes that generate ruled surfaces. There are, however, numerous applications in which ruled surfaces are generated, such as WEDM, any numerical control machining which uses cylindrical or conical cutting bits, and CC.

Practical implications

The research results presented will be applicable to fabrication processes such as flank milling, WEDM, and CC.

Originality/value

All developments presented are original. Also, CC, which is a candidate process for the developments presented in the paper, has been invented and developed by the authors.

Details

Rapid Prototyping Journal, vol. 15 no. 5
Type: Research Article
ISSN: 1355-2546

Keywords

Article
Publication date: 5 September 2018

Markus Wick, Sebastian Grabmaier, Matthias Juettner and Wolfgang Rucker

The high computational effort of steady-state simulations limits the optimization of electrical machines. Stationary solvers calculate a fast but less accurate approximation

Abstract

Purpose

The high computational effort of steady-state simulations limits the optimization of electrical machines. Stationary solvers calculate a fast but less accurate approximation without eddy-currents and hysteresis losses. The harmonic balance approach is known for efficient and accurate simulations of magnetic devices in the frequency domain. But it lacks an efficient method for the motion of the geometry.

Design/methodology/approach

The high computational effort of steady-state simulations limits the optimization of electrical machines. Stationary solvers calculate a fast but less accurate approximation without eddy-currents and hysteresis losses. The harmonic balance approach is known for efficient and accurate simulations of magnetic devices in the frequency domain. But it lacks an efficient method for the motion of the geometry.

Findings

The three-phase symmetry reduces the simulated geometry to the sixth part of one pole. The motion transforms to a frequency offset in the angular Fourier series decomposition. The calculation overhead of the Fourier integrals is negligible. The air impedance approximation increases the accuracy and yields a convergence speed of three iterations per decade.

Research limitations/implications

Only linear materials and two-dimensional geometries are shown for clearness. Researchers are encouraged to adopt recent harmonic balance findings and to evaluate the performance and accuracy of both formulations for larger applications.

Practical implications

This method offers fast-frequency domain simulations in the optimization process of rotating machines and so an efficient way to treat time-dependent effects such as eddy-currents or voltage-driven coils.

Originality/value

This paper proposes a new, efficient and accurate method to simulate a rotating machine in the frequency domain.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 37 no. 4
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 1 April 1984

Lothar Haefner and Kaspar J. Willam

A simple beam element is developed for the solution of large deflection problems. The total Lagrangian formulation is based on the kinematic relations proposed by Reissner for…

Abstract

A simple beam element is developed for the solution of large deflection problems. The total Lagrangian formulation is based on the kinematic relations proposed by Reissner for finite rotations and stretching as well as shearing of plane beams. The motion is discretized by linear expansions of the global displacement components and the cross‐sectional rotation in two‐dimensional Euclidean space yielding a simple beam element with three degrees of freedom at the two nodes. The shear locking is reduced by selective integration in order to eliminate the spurious shear constraint similar to interdependent variable interpolation. The large rotation formulation is compared with two forms of moderate rotation theories which have been used in the past to develop the geometric stiffness properties for linear stability analysis of the so‐called Mindlin plate elements. The predictive value of different geometric stiffness approximations is assessed with several examples which range from the static and kinetic stability analysis of the classical Euler‐column to the large deflection problem of a clamped beam.

Details

Engineering Computations, vol. 1 no. 4
Type: Research Article
ISSN: 0264-4401

Article
Publication date: 1 February 2001

Yves Chiricota, Olivier Cochaux and André Provost

This paper describes a method for fast three‐dimensional approximation of clothing from flat patterns. The pictures obtained are closely related to technical sketches used in the…

1313

Abstract

This paper describes a method for fast three‐dimensional approximation of clothing from flat patterns. The pictures obtained are closely related to technical sketches used in the apparel industry. Our approach was implemented in a CAD program as currently used in the industry. Based on the parameterisation of flat polygonal curves and measurements, a geometrical approximation of the garment is achieved by reshaping the surfaces, using some curves as stating points. The methods herein described were applied to model certain elements inherent to the field of clothing design, such as collars, lapels and waistbands.

Details

International Journal of Clothing Science and Technology, vol. 13 no. 1
Type: Research Article
ISSN: 0955-6222

Keywords

Article
Publication date: 1 September 1999

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.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 18 no. 3
Type: Research Article
ISSN: 0332-1649

Keywords

Book part
Publication date: 27 February 2009

Chueh-Yung Tsao and Chao-Ching Liu

Owing to the fact that the over-the-counter (OTC) market has no organized exchange, the options traded in the OTC market are more likely to be exposed to credit risk, Asian…

Abstract

Owing to the fact that the over-the-counter (OTC) market has no organized exchange, the options traded in the OTC market are more likely to be exposed to credit risk, Asian options being one of them. In this chapter we first discuss the pricing of geometric Asian options and the Black–Scholes options model subject to credit risk. We then combine the two models to derive a closed-form formula for pricing a geometric Asian option subject to the credit risk. The numerical analysis reveals that other pricing formulae existing in the literature can cause serious pricing errors when there is a possibility of default in reality.

Details

Research in Finance
Type: Book
ISBN: 978-1-84855-447-4

Article
Publication date: 2 March 2010

Elena Chepelyuk, Valeriy Choogin, Jenny Cousens and Michael Hann

The purpose of this paper is to analyse the advantages of a new interpretation of the geometric disposition of threads within woven fabric structures, and to develop a method of…

Abstract

Purpose

The purpose of this paper is to analyse the advantages of a new interpretation of the geometric disposition of threads within woven fabric structures, and to develop a method of determining the parameters of threads, with reference to each order of their disposition.

Design/methodology/approach

Based on the analysis of the geometrical models proposed by Barker and Midgely, by Pierce and by Novikov, the substantiation of the advantages of a stricter model, offered by the authors, for determining the geometric disposition of threads within single layer woven fabric structures with the help of the tangent function is given. This model allows the substantial expansion of the actual bounds of the interval of the order of the geometric disposition of threads in woven fabric structures to 0.2‐9.8.

Findings

The tangent function can approximate the crimp height ratio of the warp threads within the woven fabric structure with accuracy within the limits of geometric disposition angle change from 1° to 89°.

Research limitations/implications

The work has applications in the industrial production of woven fabrics.

Practical implications

This research will allow the design of a woven fabric with practically any ratio of crimp height for the warp and weft threads to effectively achieve the required performance characteristics of the cloth.

Originality/value

This paper extends the knowledge of the geometrical characteristics of woven fabric structure, and proposes intelligent methods of determining the parameters of thread cross‐sections in accordance with the orders of the geometric disposition of threads in woven fabric structure.

Details

International Journal of Clothing Science and Technology, vol. 22 no. 1
Type: Research Article
ISSN: 0955-6222

Keywords

1 – 10 of over 3000