S.Y. Wang^1,2, K.M. Lim^2,3, B.C. Khoo^2,3, M.Y. Wang⁴

CMES-Computer Modeling in Engineering & Sciences, Vol.21, No.3, pp. 219-238, 2007, DOI:10.3970/cmes.2007.021.219

Abstract Hole nucleation is an important issue not yet fully addressed in structural topology optimization using the level set methods. In this paper, a consistent and robust nucleation method is proposed to overcome the inconsistencies in the existing implementations and to allow for smooth hole nucleation in the conventional shape derivatives-based level set methods to avoid getting stuck at a premature local optimum. The extension velocity field is constructed to be consistent with the mutual energy density and favorable for hole nucleation. A negative extension velocity driven nucleation mechanism is established due to the physically meaningful driving force. An extension velocity… More >

S.Y. Wang^1,2, K.M. Lim^2,3, B.C. Khoo^2,3, M.Y. Wang⁴

CMES-Computer Modeling in Engineering & Sciences, Vol.21, No.1, pp. 1-40, 2007, DOI:10.3970/cmes.2007.021.001

Abstract The level set method is a numerical technique for simulating moving interfaces. In this paper, an unconditionally BIBO (Bounded-Input-Bounded-Output) time-stable consistent meshfree level set method is proposed and applied as a more effective approach to simultaneous shape and topology optimization. In the present level set method, the meshfree infinitely smooth inverse multiquadric Radial Basis Functions (RBFs) are employed to discretize the implicit level set function. A high level of smoothness of the level set function and accuracy of the solution to the Hamilton-Jacobi partial differential equation (PDE) can be achieved. The resulting dynamic system of coupled Ordinary Differential Equations (ODEs)… More >

E. Ferretti¹

CMES-Computer Modeling in Engineering & Sciences, Vol.6, No.3, pp. 227-244, 2004, DOI:10.3970/cmes.2004.006.227

Abstract Defining the crack path in brittle and non-brittle crack is not easy, due to several unknowns. If the direction of crack propagation can be computed by means of one of the existing criteria, it is not known whether this direction will remain constant during crack propagation. A crack initiation leads to an enhanced stress field at crack tip. During propagation, the enhanced tip stress field propagates into the solid, locally interacting with the pre-existing stress field. This interaction can lead to modifications of the propagation direction, depending on the domain and crack geometry. Moreover, trajectory deviation affects the length of… More >

Chyou-Chi Chien, Tong-Yue Wu¹

CMES-Computer Modeling in Engineering & Sciences, Vol.2, No.2, pp. 213-226, 2001, DOI:10.3970/cmes.2001.002.213

Abstract This study presents a novel computational method for implementing the time finite element formulation for the equations of linear structural dynamics. The proposed method adopts the time-discontinuous Galerkin method, in which both the displacement and velocity variables are represented independently by second-order interpolation functions in the time domain. The solution algorithm derived utilizes a predictor/multi-corrector technique that can effectively obtain the solutions for the resulting system of coupled equations. The numerical implementation of the time-discontinuous Galerkin finite element method is verified through several benchmark problems. Numerical results are compared with exact and accepted solutions from previous literature. Since a fifth-order… More >

S. Rugonyi, K. J. Bathe¹

CMES-Computer Modeling in Engineering & Sciences, Vol.2, No.2, pp. 195-212, 2001, DOI:10.3970/cmes.2001.002.195

Abstract The solution of fluid flows, modeled using the Navier-Stokes or Euler equations, fully coupled with structures/solids is considered. Simultaneous and partitioned solution procedures, used in the solution of the coupled equations, are briefly discussed, and advantages and disadvantages of their use are mentioned. In addition, a simplified stability analysis of the interface equations is presented, and unconditional stability for certain choices of time integration schemes is shown. Furthermore, the long-term dynamic stability of fluid-structure interaction systems is assessed by the use of Lyapunov characteristic exponents, which allow differentiating between a chaotic and a regular system behavior. Some state-of-the-art numerical solutions… More >

S.T. Lie¹, Guoyou Yu, Z. Zhao²

CMES-Computer Modeling in Engineering & Sciences, Vol.2, No.2, pp. 171-182, 2001, DOI:10.3970/cmes.2001.002.171

Abstract The BEM/FEM coupling procedure is applied to 2-D time domain structural-acoustic interaction problems. The acoustic domain for fluid or air is modeled by BEM scheme that is suitable for both finite and infinite domains, while the structure is modeled by FEM scheme. The input impact, which can be either plane waves or non-plane waves, can either be forces acting directly on the structural-acoustic system or be explosion sources. The far field or near field explosion sources which are difficult to be simulated by finite element modeling, can be simulated exactly by boundary element modeling as internal sources. In order to… More >

D. S. Sophianopoulos¹, G. T. Michaltsos²

CMES-Computer Modeling in Engineering & Sciences, Vol.2, No.1, pp. 15-26, 2001, DOI:10.3970/cmes.2001.002.015

Abstract The present work deals with the global stability aspects of a simple two-degrees-of-freedom autonomous initially imperfect damped model, under step (conservative) loading. The proposed system is an extension of the classical limit point one firstly introduced by von Mises, with the addition of a linear rotational spring. The effect of its properties (stiffness and damping) are fully assessed and under certain combinations of the parameters involved a third possibility of postbuckling dynamic response is revealed. This is associated with a point attractor response on a stable prebuckling fixed point, although dynamic buckling has already occurred, a finding validating new relevant… More >

B. Pichler¹, H.A. Mang¹

CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.3, pp. 43-55, 2000, DOI:10.3970/cmes.2000.001.345

Abstract In order to avoid a fully nonlinear analysis to obtain stability limits on nonlinear load-displacement paths, linear eigenvalue problems may be used to compute estimates of such limits. In this paper an asymptotic approach for assessment of the errors resulting from such estimates is presented. Based on the consistent linearization of the geometrically nonlinear static stability criterion – the so-called consistently linearized eigenvalue problem – higher-order estimation functions can be calculated. They are obtained from a scalar post-calculation performed after the solution of the eigenproblem. Different extensions of these higher-order estimation functions are presented. An ab initio criterion for the… More >

V. N. Lad¹, Z. V. P. Murthy^1,2

FDMP-Fluid Dynamics & Materials Processing, Vol.11, No.3, pp. 241-255, 2015, DOI:10.3970/fdmp.2015.011.241

Abstract Free liquid jets are of great technical importance in a variety of applications like ink-jet printing, glass painting, spray coating and metal cutting. Here we consider the changes induced in the dynamics of such jets by the presence of obstructions at the tube exit. Using stainless steel bars of 1.5 mm diameter as obstruction objects and aqueous solutions of glycerol of varying concentrations as working fluids, we performed experiments for different configurations, including a single rod at the centre of the tube exit, two parallel rods equidistant from the centre of the tube, and a 10 mesh screen. Images of… More >

P. T. Hemamalini¹, S. P. Anjali Devi²

FDMP-Fluid Dynamics & Materials Processing, Vol.10, No.4, pp. 491-501, 2014, DOI:10.3970/fdmp.2014.010.491

Abstract The Rayleigh-Taylor instability (RTI) of two superposed ferrofluids subjected to rotation and a periodic tangential magnetic field is considered. Relevant solutions and related dispersion relations are obtained by using the method of multiple scales. More >