CMES-Vol. 31, No. 2, 2008

Open Access

ARTICLE

Numerical Simulation and Ventilation Efficiency of Bicycle Helmets
T.Z. Desta¹, G. De Bruyne¹, J.-M. Aerts¹, M. Baelmans², D. Berckmans¹
CMES-Computer Modeling in Engineering & Sciences, Vol.31, No.2, pp. 61-70, 2008, DOI:10.3970/cmes.2008.031.061
Abstract This paper demonstrates the use of the concept of the local mean age of air (LMAA) to quantify ventilation effectiveness under bicycle rider's safety helmets. The specific objective is to study the effect of helmet openings on the resulting ventilation effectiveness. To quantify ventilation effectiveness using the concept of LMAA, dynamic tracer gas data are necessary. The data were generated using a Computational Fluid Dynamics (CFD) model. Two bicycle helmet designs were used and compared with respect to ventilation performance. The result showed that the helmet with more openings had better performance especially at the More >

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ARTICLE

A Novel Time Integration Method for Solving A Large System of Non-Linear Algebraic Equations
Chein-Shan Liu¹, Satya N. Atluri²
CMES-Computer Modeling in Engineering & Sciences, Vol.31, No.2, pp. 71-84, 2008, DOI:10.3970/cmes.2008.031.071
Abstract Iterative algorithms for solving a nonlinear system of algebraic equations of the type: F_i(x_j) = 0, i,j = 1,…,n date back to the seminal work of Issac Newton. Nowadays a Newton-like algorithm is still the most popular one due to its easy numerical implementation. However, this type of algorithm is sensitive to the initial guess of the solution and is expensive in the computations of the Jacobian matrix ∂ F_i/ ∂ x_j and its inverse at each iterative step. In a time-integration of a system of nonlinear Ordinary Differential Equations (ODEs) of the type B_ijx_j + F_i = 0… More >

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Caveats on the Implementation of the Generalized Material Point Method
O. Buzzi¹, D. M. Pedroso², A. Giacomini¹
CMES-Computer Modeling in Engineering & Sciences, Vol.31, No.2, pp. 85-106, 2008, DOI:10.3970/cmes.2008.031.085
Abstract The material point method (MPM) is a numerical method for the solution of problems in continuum mechanics, including situations of large deformations. A generalization (GMPM) of this method was introduced by Bardenhagen and Kober (2004) in order to avoid some computational instabilities inherent to the original method (MPM). This generalization leads to a method more akin of the Petrov-Galerkin procedure. Although it is possible to find in the literature examples of the deduction and applications of the MPM/GMPM to specific problems, its detailed implementation is yet to be presented. Therefore, this paper attempts to describe… More >

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Examination and Analysis of Implementation Choices within the Material Point Method (MPM)
M. Steffen¹, P.C. Wallstedt², J.E. Guilkey^2,3, R.M. Kirby¹, M. Berzins¹
CMES-Computer Modeling in Engineering & Sciences, Vol.31, No.2, pp. 107-128, 2008, DOI:10.3970/cmes.2008.031.107
Abstract The Material Point Method (MPM) has shown itself to be a powerful tool in the simulation of large deformation problems, especially those involving complex geometries and contact where typical finite element type methods frequently fail. While these large complex problems lead to some impressive simulations and solutions, there has been a lack of basic analysis characterizing the errors present in the method, even on the simplest of problems. The large number of choices one has when implementing the method, such as the choice of basis functions and boundary treatments, further complicates this error analysis.\newline In More >

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