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1 – 10 of over 1000
Article
Publication date: 1 December 2003

J.I. Ramos

Non‐linear reaction‐diffusion processes with cross‐diffusion in two‐dimensional, anisotropic media are analyzed by means of an implicit, iterative, time‐linearized approximate…

Abstract

Non‐linear reaction‐diffusion processes with cross‐diffusion in two‐dimensional, anisotropic media are analyzed by means of an implicit, iterative, time‐linearized approximate factorization technique as functions of the anisotropy of the heat and species diffusivity tensors, the Soret and Dufour cross‐diffusion effects, and five types of boundary conditions. It is shown that anisotropy and cross‐diffusion deform the reaction front and affect the front velocity, and the magnitude of these effects increases as the magnitude of the off‐diagonal components of the heat and species diffusivity tensors is increased. It is also shown that the five types of boundary conditions employed in this study produce similar results except when there is either strong anisotropy in the species or heat diffusivity tensors and there are no Soret and Dufour effects, or the species and heat diffusivity tensors are isotropic, but the anisotropy of the Soret and Dufour effects is important. If the species and heat diffusivity tensors are isotropic, the effects of either the Soret or the Dufour cross‐diffusion effects are small for the cases considered in this study. The time required to achieve steady state depends on the anisotropy of the heat and diffusivity tensors, the cross‐diffusion effects, and the boundary conditions.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 13 no. 8
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 18 March 2020

Shruthy Myson and Smita Saklesh Nagouda

The effects of anisotropy and radiation cannot be considered negligible while investigating the stability of the fluid in convection. Hence, the purpose of this paper is to…

Abstract

Purpose

The effects of anisotropy and radiation cannot be considered negligible while investigating the stability of the fluid in convection. Hence, the purpose of this paper is to analyze how these effects could affect the system while considering a couple-stress dielectric fluid. Therefore, the study establishes the effect of thermal radiation in a couple-stress dielectric fluid with an anisotropic porous medium using Goody's approach (Goody, 1956).

Design/methodology/approach

To analyze the effect of radiation on the onset of convection, the Milne–Eddington approximation is employed to convert radiative heat flux to thermal heat flux. The equations are further developed to approximate for transparent and opaque medium. Stability of the quiescent state within the framework of linear theory is performed. The principle of exchange of stabilities is shown to be valid by means of single-term Galerkin method. Large values of conduction–radiation and absorptivity parameters are avoided as fluid is considered as liquid rather than gas.

Findings

The radiative heat transfer effect on a couple-stress dielectric fluid saturated anisotropic porous medium is examined in terms of Milne–Eddington approximation. The effect of couple-stress, dielectric, anisotropy and radiation parameters are analyzed graphically for both transparent and opaque medium. It is observed that the conduction–radiation parameter stabilizes the system; in addition, the critical Darcy–Rayleigh number also shows a stabilizing effect in the absence of couple-stress, dielectric and anisotropy parameters, for both transparent and opaque medium. Furthermore, the absorptivity parameter stabilizes the system in the transparent medium, whereas it exhibits a dual effect in the case of an opaque medium. It was also found that an increase in thermal and mechanical anisotropy parameters shows an increase in the cell size, whereas the increase in Darcy–Roberts number and conduction–radiation parameter decreases the cell size. The validity of principle of exchange of stability is performed and concluded that marginal stability is the preferred mode than oscillatory.

Originality/value

The effects of anisotropy and radiation on Rayleigh–Bénard convection by considering a couple-stress dielectric fluid has been analyzed for the first time.

Details

Multidiscipline Modeling in Materials and Structures, vol. 16 no. 5
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 30 September 2013

Vandana Gupta and S.B. Singh

The purpose of this paper is to investigate the effect of anisotropy in terms of a single parameter indicating strengthening or weakening in the tangential direction in composite…

Abstract

Purpose

The purpose of this paper is to investigate the effect of anisotropy in terms of a single parameter indicating strengthening or weakening in the tangential direction in composite disc with hyperbolically varying thickness introduced presumably by processing or due to alignment of dispersed reinforcements during flow of the matrix.

Design/methodology/approach

Mathematical model to describe steady-state creep behavior in an anisotropic rotating disc made of Al-SiCp composite containing 30 vol% of SiC particles. The creep behavior of the composite has been described by Sherby's law. The creep parameters in the law have been determined using the regression equations developed on the basis of available experimental results in the literature. Stress and strain rate distributions for isotropic disc (a=1) have been compared with those obtained for anisotropic composites with characteristic parameters a=0.7 and 1.3.

Findings

The study revealed that the change in the stresses by anisotropy in composite disc is relatively small while anisotropy introduces significant change in the strain rates. It is concluded that the radial strain rate always remained compressive for the isotropic composite as well as the anisotropic disc with a greater than unity (a=1.3). However, it becomes tensile in the middle region of the disc when it is less than unity (a=0.7). If a is reduced from 1.3 to 0.7, the variation of tensile strain rate in the tangential direction remains similar, but the magnitude reduces, i.e. the strength in tangential direction is enhanced.

Originality/value

This study puts forward an analytical framework for the analysis of creep stresses and creep rates in an anisotropic rotating disc with hyperbolically varying thickness.

Details

Multidiscipline Modeling in Materials and Structures, vol. 9 no. 3
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 1 January 2014

Sami Bedra, Siham Benkouda and Tarek Fortaki

The paper aims to propose an artificial neural network (ANN) in conjunction with spectral domain formulation for fast and accurate determination of the resonant frequency and…

Abstract

Purpose

The paper aims to propose an artificial neural network (ANN) in conjunction with spectral domain formulation for fast and accurate determination of the resonant frequency and quality factor of circular microstrip antenna printed on isotropic or anisotropic substrate. This neurospectral approach reduces the problem complexity.

Design/methodology/approach

The moment method implemented in the spectral domain provides good accuracy but its computational cost is high due to the evaluation of the slowly decaying integrals and the iterative nature of the solution process. The paper introduces the electromagnetic knowledge combined with ANN in the analysis of circular microstrip antenna on isotropic or uniaxially anisotropic substrate to reduce the complexity of the spectral approach and to minimize the CPU time necessary to obtain the numerical results.

Findings

The resonant frequency results obtained from the neural model are in very good agreement with the experimental and theoretical results available in the literature. Finally, numerical results for the substrate anisotropy effect on the resonant frequency, quality factor and radiation pattern are also presented.

Originality/value

The paper develops fast and accurate model based on ANN technique to calculate the resonant frequencies and quality factors of circular microstrip antennas. ANN is used to model the relationship between the parameters of the microstrip antenna and the resonant frequencies and quality factors obtained from the spectral domain approach. This relatively simple model allows designers to predict accurately the resonant frequencies and quality factors for a given design without having to develop or run the spectral method codes themselves. The main advantages of the method are: less computing time than the spectral model, results with accuracy equivalent to that of full-wave models and cost effectiveness, since the client can use a simple PC for implementation. Another advantage of the proposed ANN model is that it takes into account the uniaxial anisotropy in the substrate without increasing the network size. This is done by combining ANN with electromagnetic knowledge.

Details

COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, vol. 33 no. 1/2
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 1 September 1998

K. Aboubi, L. Robillard and P. Vasseur

The natural two‐dimensional convection taking place between horizontal concentric cylinders filled with a satured anisotropic porous medium is studied numerically. The anisotropy

Abstract

The natural two‐dimensional convection taking place between horizontal concentric cylinders filled with a satured anisotropic porous medium is studied numerically. The anisotropy concerns exclusively the permeability. Isothermal boundary conditions are applied on both inner and outer boundaries, with the outer boundary being warmer. The effects of the anisotropic permeability ratio K*, of the orientation angle of the principal axes defined by γ, and of the Rayleigh number Ra* on the flow and heat transfer are investigated. Results indicate that a net circulating flow around the annulus is generated, except for values of γ that preserve the symmetry of flow conditions with respect to the vertical diameter. It is also shown that the anisotropic part of the resistivity tensor is equivalent to a magnetic resistivity tensor.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 8 no. 6
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 6 September 2019

Mostafa Yakout, M.A. Elbestawi, S.C. Veldhuis and S. Nangle-Smith

Residual stresses are induced during selective laser melting (SLM) because of rapid melting, solidification and build plate removal. This paper aims to examine the thermal cycle…

1099

Abstract

Purpose

Residual stresses are induced during selective laser melting (SLM) because of rapid melting, solidification and build plate removal. This paper aims to examine the thermal cycle, residual stresses and part distortions for selected aerospace materials (i.e. Ti-6Al-4V, stainless steel 316L and Invar 36) using a thermo-mechanical finite element model. The numerical results are validated and compared to experimental data.

Design/methodology/approach

The model predicts the residual stress and part distortion after build plate removal. The residual stress field is validated using X-ray diffraction method and the part distortion is validated using dimensional measurements.

Findings

The trends found in the numerical results agree with those found experimentally. Invar 36 had the lowest tensile residual stresses because of its lowest coefficient of thermal expansion. The residual stresses of stainless steel 316L were lower than those of Ti-6Al-4V because of its high thermal diffusivity.

Research limitations/implications

The model predicts residual stresses at the optimal SLM process parameters. However, using any other process conditions could cause void formation and/or alloying element vaporization, which would require the inclusion of melt pool physics in the model.

Originality/value

The paper explains the influence of the coefficient of thermal expansion and thermal diffusivity on the induced thermal stresses using experimental and numerical results. The methodology can be used to predict the part distortions and residual stresses in complex designs of any of the three materials under optimal SLM process parameters.

Details

Rapid Prototyping Journal, vol. 26 no. 1
Type: Research Article
ISSN: 1355-2546

Keywords

Article
Publication date: 4 July 2016

Erfan Asaadi and P. Stephan Heyns

The purpose of this paper is to propose a progressive inverse identification algorithm to characterize flow stress of tubular materials from the material response, independent of…

Abstract

Purpose

The purpose of this paper is to propose a progressive inverse identification algorithm to characterize flow stress of tubular materials from the material response, independent of choosing an a priori hardening constitutive model.

Design/methodology/approach

In contrast to the conventional forward flow stress identification methods, the flow stress is characterized by a multi-linear curve rather than a limited number of hardening model parameters. The proposed algorithm optimizes the slopes and lengths of the curve increments simultaneously. The objective of the optimization is that the finite element (FE) simulation response of the test estimates the material response within a predefined accuracy.

Findings

The authors employ the algorithm to identify flow stress of a 304 stainless steel tube in a tube bulge test as an example to illustrate application of the algorithm. Comparing response of the FE simulation using the obtained flow stress with the material response shows that the method can accurately determine the flow stress of the tube.

Practical implications

The obtained flow stress can be employed for more accurate FE simulation of the metal forming processes as the material behaviour can be characterized in a similar state of stress as the target metal forming process. Moreover, since there is no need for a priori choosing the hardening model, there is no risk for choosing an improper hardening model, which in turn facilitates solving the inverse problem.

Originality/value

The proposed algorithm is more efficient than the conventional inverse flow stress identification methods. In the latter, each attempt to select a more accurate hardening model, if it is available, result in constructing an entirely new inverse problem. However, this problem is avoided in the proposed algorithm.

Details

Engineering Computations, vol. 33 no. 5
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 27 September 2023

Jiongyi Yan, Emrah Demirci and Andrew Gleadall

Extrusion width, the width of printed filaments, affects multiple critical aspects in mechanical properties in material extrusion additive manufacturing: filament geometry…

Abstract

Purpose

Extrusion width, the width of printed filaments, affects multiple critical aspects in mechanical properties in material extrusion additive manufacturing: filament geometry, interlayer load-bearing bonded area and fibre orientation for fibre-reinforced composites. However, this study aims to understand the effects of extrusion width on 3D printed composites, which has never been studied systematically.

Design/methodology/approach

Four polymers with and without short-fibre reinforcement were 3D printed into single-filament-wide specimens. Tensile properties, mechanical anisotropy and fracture mechanisms were evaluated along the direction of extruded filaments (F) and normal to the interlayer bond (Z). Extrusion width, nozzle temperature and layer height were studied separately via single-variable control. The extrusion width was controlled by adjusting polymer flow in the manufacturing procedure (gcode), where optimisation can be achieved with software/structure design as opposed to hardware.

Findings

Increasing extrusion width caused a transition from brittle to ductile fracture, and greatly reduced directional anisotropy for strength and ductility. For all short fibre composites, increasing width led to an increase in strain-at-break and decreased strength and stiffness in the F direction. In the Z direction, increasing width led to increased strength and strain-at-break, and stiffness decreased for less ductile materials but increased for more ductile materials.

Originality/value

The transformable fracture reveals the important role of extrusion width in processing-structure-property correlation. This study reveals a new direction for future research and industrial practice in controlling anisotropy in additive manufacturing. Increasing extrusion width may be the simplest way to reduce anisotropy while improving printing time and quality in additive manufacturing.

Details

Rapid Prototyping Journal, vol. 30 no. 1
Type: Research Article
ISSN: 1355-2546

Keywords

Article
Publication date: 7 August 2019

Ryoko Minehisa, Yasuhito Takahashi, Koji Fujiwara, Norio Takahashi, Masafumi Fujita, Kazuma Tsujikawa and Ken Nagakura

This paper aims to propose a homogenization method considering magnetic anisotropy for a magnetic field analysis of a turbine generator. To verify the validity of the proposed…

Abstract

Purpose

This paper aims to propose a homogenization method considering magnetic anisotropy for a magnetic field analysis of a turbine generator. To verify the validity of the proposed method, the effects of magnetic anisotropy and a space factor on a no-load saturation curve and no-load iron loss of the turbine generator are discussed.

Design/methodology/approach

The proposed method was derived from the combination of the homogenization of microscopic fields in a laminated iron core with the modelling of two-dimensional magnetic properties based on free energy. To verify the validity, the proposed method was applied to a finite-element analysis of a simple ring core model. Finally, a no-load saturation curve and iron loss of the turbine generator was investigated by using the proposed method.

Findings

The computational accuracy of the homogenization method considering magnetic anisotropy is almost the same as that of the detailed modelling of the laminated structure in the magnetic field analysis of the laminated iron core. Furthermore, it is clarified that magnetic anisotropy does not have a large influence on the no-load saturation curve of the turbine generator because of the large air gap. On the other hand, the space factor affects the shape of the no-load saturation curve.

Originality/value

This paper verifies the validity of the homogenization method considering magnetic anisotropy method and elucidates the effects of magnetic anisotropy and a space factor on no-load characteristics of the turbine generator.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering , vol. 38 no. 5
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 28 October 2014

Amgad Salama, Mohamed El Amin and Shuyu Sun

The problem of natural convection in two cavities separated by an anisotropic central solid wall is considered numerically. When the thermal conductivity of the central wall is…

Abstract

Purpose

The problem of natural convection in two cavities separated by an anisotropic central solid wall is considered numerically. When the thermal conductivity of the central wall is anisotropic, heat flux and temperature gradient vectors are no longer coincidence. This apparently has interesting influences on the heat and fluid flow patterns in this system. The paper aims to discuss these issues.

Design/methodology/approach

In this work, several flow patterns have been investigated covering a wide range of Rayleigh number up to 108. Several thermal conductivity anisotropy scenarios of the central wall have been investigated including 0, 30, 60, 120 and 150° principal anisotropy directions. The governing equations have been solved using control volume approach.

Findings

Probably the most intriguing is that, for some anisotropy scenarios it is found that the temperature at the same elevation at the side of the central wall which is closer to the colder wall is higher than that at the side closer to the hot wall. Apparently this defies intuition which suggests the reverse to have happened. However, this behavior may be explained in light of the effect of anisotropy. Furthermore, the patterns of streamlines and temperature fields in the two enclosures also changes as a consequence of the change of the central wall temperatures for the different anisotropy scenarios.

Originality/value

This work discusses a very interesting topic related to heat energy exchange among two compartments when the separating wall is anisotropic. In some anisotropy scenarios, this leads to more uniform distribution of Nusselt number than the case when the wall is isotropic. Interesting patterns of natural convection is investigated.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 24 no. 8
Type: Research Article
ISSN: 0961-5539

Keywords

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