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Article
Publication date: 1 March 2005

Marcin Kaminski and Marcin Pawlik

Effectiveness of the homogenization method for various heat transfer problems of engineering composites is the main aim of the paper. This comparative study is done for layered…

152

Abstract

Effectiveness of the homogenization method for various heat transfer problems of engineering composites is the main aim of the paper. This comparative study is done for layered, fiber and particle reinforced Representative Volume Elements (RVE) for composites made of widely used components. Mathematical model is based on the effective modules method introduced for periodic composites ‐ effective heat conductivity is calculated in the closed form for specific spatial distribution of the components, while effective volumetric heat capacity is obtained from a simple spatial averaging. Such a homogenization scheme makes possible to significantly simplify the numerical analysis of transient heat transfer phenomena in various types of composites. The comparison of temperature histories obtained for the real and homogenized composite models is carried out using the Finite Element Method system ANSYS. As is demonstrated for various boundary problems, a homogenization technique in terms of composites types collected in the paper give satisfactory agreement with the real structure modeling; further numerical studies on composite cells discretization should increase modeling efficiency and diminish the numerical errors.

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Multidiscipline Modeling in Materials and Structures, vol. 1 no. 3
Type: Research Article
ISSN: 1573-6105

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Article
Publication date: 1 October 2005

Marcin Kamiński and Graham F. Carey

To generalize the traditional 2nd order stochastic perturbation technique for input random variables and fields and to demonstrate for flow problems.

511

Abstract

Purpose

To generalize the traditional 2nd order stochastic perturbation technique for input random variables and fields and to demonstrate for flow problems.

Design/methodology/approach

The methodology is based on an n‐th order expansion (perturbation) for input random parameters and state functions around their expected value to recover probabilistic moments of the response. A finite element formulation permits stochastic simulations on irregular meshes for practical applications.

Findings

The methodology permits approximation of expected values and covariances of quantities such as the fluid pressure and flow velocity using both symbolic and discrete FEM computations. It is applied to inviscid irrotational flow, Poiseulle flow and viscous Couette flow with randomly perturbed boundary conditions, channel height and fluid viscosity to illustrate the scheme.

Research limitations/implications

The focus of the present work is on the basic concepts as a foundation for extension to engineering applications. The formulation for the viscous incompressible problem can be implemented by extending a 3D viscous primitive variable finite element code as outlined in the paper. For the case where the physical parameters are temperature dependent this will necessitate solution of highly non‐linear stochastic differential equations.

Practical implications

Techniques presented here provide an efficient approach for numerical analyses of heat transfer and fluid flow problems, where input design parameters and/or physical quantities may have small random fluctuations. Such an analysis provides a basis for stochastic computational reliability analysis.

Originality/value

The mathematical formulation and computational implementation of the generalized perturbation‐based stochastic finite element method (SFEM) is the main contribution of the paper.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 15 no. 7
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 8 May 2009

Teresa Orlowska‐Kowalska and Marcin Kaminski

The purpose of this paper is to obtain an estimation of not measured mechanical state variables of the drive system with elastic coupling between the driven motor and a load…

465

Abstract

Purpose

The purpose of this paper is to obtain an estimation of not measured mechanical state variables of the drive system with elastic coupling between the driven motor and a load machine, using neural networks (NN) of different type for the sensorless drive system.

Design/methodology/approach

The load‐side speed and the torsional torque are estimated using multi‐layer perceptron (MLP) and radial basis function (RBF) networks. The special forms of input vectors for neural state estimators were proposed and tested in open‐ and closed‐loop control structure. The estimation quality as well as sensitivity of neural estimators to the changes of the inertia moment of the load machine were evaluated and compared.

Findings

It is shown that an application of RBF‐based neural estimators can give better accuracy of the load speed and torsional torque estimation, especially for the proper choice of the input vector of NN, also in the case of a big change of the load machine time constant.

Research limitations/implications

The investigation and comparison is based on simulation tests and looked mainly at the quality of state variable estimation while the realisation cost in parallel processing devices (FPGA) still need to be addressed.

Practical implications

The proposed neural state variable estimators of two‐mass system can be practically implemented in the control structure of two‐mass drive with additional feedbacks from load machine speed and torsional torque, which results in the successive vibration damping.

Originality/value

The application of RBF neural state estimators for two‐mass drive and their comparison with commonly used MLP‐based estimators, as well as testing of both type of NN in the closed‐loop control structure with additional feedbacks based on state variables estimated by neural estimators.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 28 no. 3
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 12 October 2012

Stefan Larsson, Måns Svensson, Marcin de Kaminski, Kari Rönkkö and Johanna Alkan Olsson

The purpose of this study is to understand more of online anonymity in the global file sharing community in the context of social norms and copyright law. The study describes the…

2176

Abstract

Purpose

The purpose of this study is to understand more of online anonymity in the global file sharing community in the context of social norms and copyright law. The study describes the respondents in terms of use of VPN or similar service related to age, gender, geographical location, as well as analysing the correlation with file sharing frequencies.

Design/methodology/approach

This study is to a large extent descriptively collecting data through a web‐based survey. This was carried out in collaboration with the BitTorrent tracker The Pirate Bay (TPB), allowing the authors to link the survey from the main logo of their site. In 72 hours the authors received over 75,000 responses, which gives the opportunity to compare use of anonymity services with factors of age, geographical region, file sharing frequency, etc.

Findings

Overall, 17.8 per cent of the respondents use a VPN or similar service (free or paid). A core of high frequency uploaders is more inclined to use VPN or similar services than the average file sharer. Online anonymity practices in the file sharing community are depending on how legal and social norms correlate (more enforcement means more anonymity).

Research limitations/implications

The web‐based survey was in English and mainly attracted visitors on The Pirate Bays' web page. This means that it is likely that those who do not have the language skills necessary were excluded from the survey.

Practical implications

This study adds to the knowledge of anonymity practices online in terms of traceability and identification. This means that it shows some of the conditions for legal enforcement in a digital environment.

Social implications

This study adds to the knowledge of how the Internet is changing in terms of a polarization between stronger means of legally enforced identification and a growing awareness of how to be more untraceable.

Originality/value

The scale of the survey, with over 75,000 respondents from most parts of the world, has likely not been seen before on this topic. The descriptive study of anonymity practices in the global file sharing community is therefore likely unique.

Details

Journal of Research in Interactive Marketing, vol. 6 no. 4
Type: Research Article
ISSN: 2040-7122

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Article
Publication date: 16 April 2018

Jacek Ptaszny and Marcin Hatłas

The purpose of this paper is to evaluate the efficiency of the fast multipole boundary element method (FMBEM) in the analysis of stress and effective properties of 3D linear…

142

Abstract

Purpose

The purpose of this paper is to evaluate the efficiency of the fast multipole boundary element method (FMBEM) in the analysis of stress and effective properties of 3D linear elastic structures with cavities. In particular, a comparison between the FMBEM and the finite element method (FEM) is performed in terms of accuracy, model size and computation time.

Design/methodology/approach

The developed FMBEM uses eight-node Serendipity boundary elements with numerical integration based on the adaptive subdivision of elements. Multipole and local expansions and translations involve solid harmonics. The proposed model is used to analyse a solid body with two interacting spherical cavities, and to predict the homogenized response of a porous material under linear displacement boundary condition. The FEM results are generated in commercial codes Ansys and MSC Patran/Nastran, and the results are compared in terms of accuracy, model size and execution time. Analytical solutions available in the literature are also considered.

Findings

FMBEM and FEM approximate the geometry with similar accuracy and provide similar results. However, FMBEM requires a model size that is smaller by an order of magnitude in terms of the number of degrees of freedom. The problems under consideration can be solved by using FMBEM within the time comparable to the FEM with an iterative solver.

Research limitations/implications

The present results are limited to linear elasticity.

Originality/value

This work is a step towards a comprehensive efficiency evaluation of the FMBEM applied to selected problems of micromechanics, by comparison with the commercial FEM codes.

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Expert briefing
Publication date: 8 July 2024

Wos can now be prosecuted for his alleged role in mishandling a justice ministry fund when he was a member of previous governments led by the right-wing Law and Justice (PiS…

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DOI: 10.1108/OXAN-DB288148

ISSN: 2633-304X

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Expert briefing
Publication date: 16 September 2015

Right-wing Law and Justice (PiS), the main opposition party, may emerge from the elections as the largest parliamentary group. However, it could find itself in opposition for…

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