G. Suguinoshita¹, C. H. Silva¹, M. A. Luersen^{1, *}

CMES-Computer Modeling in Engineering & Sciences, Vol.117, No.1, pp. 59-71, 2018, DOI:10.31614/cmes.2018.01777

Abstract This paper describes a study of the effects of graphite nodule characteristics on a subsurface crack in austempered ductile iron (ADI). A representative specimen of ADI, subjected to sliding contact load, is modeled using finite elements aiming to obtain the shear stress intensity factor (K_II). The parameters varied were (i) the nodule diameter (two different values were considered), (ii) the distance between the nodule and the tip of the crack and (iii) the position of the load relative to the tip of the crack. The results of the numerical simulations show that the smaller diameter nodule has a larger influence… More >

Xia Li^1,2, Peifeng Niu^1,*, Jianping Liu², Qing Liu²

CMES-Computer Modeling in Engineering & Sciences, Vol.117, No.1, pp. 29-57, 2018, DOI:10.31614/cmes.2018.04020

Abstract An improved teaching-learning-based optimization (I-TLBO) algorithm is proposed to adjust the parameters of extreme learning machine with parallel layer perception (PELM), and a well-generalized I-TLBO-PELM model is obtained to build the model of NO_X emissions of a boiler. In the I-TLBO algorithm, there are four major highlights. Firstly, a quantum initialized population by using the qubits on Bloch sphere replaces a randomly initialized population. Secondly, two kinds of angles in Bloch sphere are generated by using cube chaos mapping. Thirdly, an adaptive control parameter is added into the teacher phase to speed up the convergent speed. And then, according to… More >

A. Aimi¹, M. Diligenti¹, S. Panizzi¹

CMES-Computer Modeling in Engineering & Sciences, Vol.58, No.2, pp. 185-220, 2010, DOI:10.3970/cmes.2010.058.185

Abstract In this paper we consider 2D wave propagation Neumann exterior problems reformulated in terms of a hypersingular boundary integral equation with retarded potential. Starting from a natural energy identity satisfied by the solution of the differential problem, the related integral equation is set in a suitable space-time weak form. Then, a theoretical analysis of the introduced formulation is proposed, pointing out the novelties with respect to existing literature results. At last, various numerical simulations will be presented and discussed, showing accuracy and stability of the space-time Galerkin boundary element method applied to the energetic weak problem. More >

S. Torii¹

CMES-Computer Modeling in Engineering & Sciences, Vol.5, No.3, pp. 257-268, 2004, DOI:10.3970/cmes.2004.005.257

Abstract A numerical study is performed to investigate the thermal fluid-flow transport phenomena in the concentric annulus with a slightly heated rotating inner core moving in the flow direction and a stationary insulated outer cylinder. Emphasis is placed on the effects of the axial rotation and streamwise movement of inner core on the flow structure and heat transfer performance. A k-ε turbulence model is employed to determine the turbulent viscosity and the turbulent kinetic energy. The turbulent heat flux is expressed by Boussinesq approximation in which the eddy diffusivity for heat is determined using two-equation heat transfer model. The governing equations… More >

Soon Wan Chung¹, Yoo Jin Choi¹, Seung Jo Kim¹

CMES-Computer Modeling in Engineering & Sciences, Vol.4, No.6, pp. 707-718, 2003, DOI:10.3970/cmes.2003.004.707

Abstract In this paper, an automatic finite element remeshing algorithm based on the bubble packing method is utilized for the purpose of numerical simulations of localized damage, because fine meshes are needed to represent the gradually concentrated damage. The bubble packing method introduces two parameters that easily control the remeshing criterion and the new mesh size. The refined area is determined by \textit {a posteriori} error estimation utilizing the value obtained from Superconvergent Patch Recovery. The isotropic ductile damage theory, founded on continuum damage mechanics, is used for this damage analysis. It was successfully shown in the numerical examples (upsetting and… More >

N. Sukumar¹, J. E. Bolander¹

CMES-Computer Modeling in Engineering & Sciences, Vol.4, No.6, pp. 691-706, 2003, DOI:10.3970/cmes.2003.004.691

Abstract In this paper, we explore the numerical approximation of discrete differential operators on non-uniform grids. The Voronoi cell and the notion of natural neighbors are used to approximate the Laplacian and the gradient operator on irregular grids. The underlying weight measure used in the numerical computations is the {\em Laplace weight function}, which has been previously adopted in meshless Galerkin methods. We develop a difference approximation for the diffusion operator on irregular grids, and present numerical solutions for the Poisson equation. On regular grids, the discrete Laplacian is shown to reduce to the classical finite difference scheme. Two techniques to… More >

Jiongyang Wu¹, Inanc Senocak¹, Guoyu Wang², Yulin Wu³, Wei Shyy¹

CMES-Computer Modeling in Engineering & Sciences, Vol.4, No.6, pp. 679-690, 2003, DOI:10.3970/cmes.2003.004.679

Abstract Cavitation appears in a wide variety of fluid machinery, and can often cause negative impacts on performance and structural integrity. A main computational difficulty for cavitation is the large density ratio between liquid and vapor phases, around 1000 for water under normal temperature and pressure conditions. Moreover, cavitating flows are usually turbulent and the interfacial dynamics is complex. The fast time scales associated with turbulent cavitation also poses substantial challenges computationally and experimentally. In the present study, pressure-based algorithms are adopted to simulate three-dimensional turbulent cavitating flows in a hollow-jet valve. The Favre-averaged Navier-Stokes equations are employed along with a… More >

Z. D. Han¹, S. N. Atluri¹

CMES-Computer Modeling in Engineering & Sciences, Vol.4, No.6, pp. 665-678, 2003, DOI:10.3970/cmes.2003.004.665

Abstract The numerical implementation of the truly Meshless Local Petrov-Galerkin (MLPG) type weak-forms of the displacement and traction boundary integral equations is presented, for solids undergoing small deformations. In the accompanying part I of this paper, the general MLPG/BIE weak-forms were presented [Atluri, Han and Shen (2003)]. The MLPG weak forms provide the most general basis for the numerical solution of the non-hyper-singular displacement and traction BIEs [given in Han, and Atluri (2003)], which are simply derived by using the gradients of the displacements of the fundamental solutions [Okada, Rajiyah, and Atluri (1989a,b)]. By employing the various types of test functions,… More >

J. A. Nairn¹

CMES-Computer Modeling in Engineering & Sciences, Vol.4, No.6, pp. 649-664, 2003, DOI:10.3970/cmes.2003.004.649

Abstract A new algorithm is described which extends the material point method (MPM) to allow explicit cracks within the model material. Conventional MPM enforces velocity and displacement continuity through its background grid. This approach is incompatible with cracks which are displacement and velocity discontinuities. By allowing multiple velocity fields at special nodes near cracks, the new method (called CRAMP) can model cracks. The results provide an ``exact'' MPM analysis for cracks. Comparison to finite element analysis and to experiments show it gets good results for crack problems. The intersection of crack surfaces is prevented by implementing a crack contact scheme. Crack… More >

Jan Sladek¹, Vladimir Sladek¹, Chuanzeng Zhang²

CMES-Computer Modeling in Engineering & Sciences, Vol.4, No.6, pp. 637-648, 2003, DOI:10.3970/cmes.2003.004.637

Abstract A new computational method for solving transient elastodynamic initial-boundary value problems in continuously non-homogeneous solids, based on the meshless local Petrov-Galerkin (MLPG) method, is proposed in the present paper. The moving least squares (MLS) is used for interpolation and the modified fundamental solution as the test function. The local Petrov-Galerkin method for unsymmetric weak form in such a way is transformed to the local boundary integral equations (LBIE). The analyzed domain is divided into small subdomains, in which a weak solution is assumed to exist. Nodal points are randomly spread in the analyzed domain and each one is surrounded by… More >