R. Amirante¹, L.A. Catalano², A. Dadone¹, V.S.E. Daloiso¹

CMES-Computer Modeling in Engineering & Sciences, Vol.18, No.1, pp. 17-30, 2007, DOI:10.3970/cmes.2007.018.017

Abstract This paper proposes a gradient-based progressive optimization technique, which can be efficiently combined with black-box simulation codes. Its efficiency relies on the simultaneous convergence of the flow solution, of the gradient evaluation, and of the design update, as well as on the use of progressively finer grids. The developed numerical technique has general validity and is here applied to the fluid-dynamic design optimization of the intake of a small-size turbojet engine, at high load and zero flight speed. Two simplified design criteria are proposed, which avoid simulating the flow in any turbojet components other than the intake itself. Using a… More >

Jae Bong Lee¹, Jai Hak Park¹, Sung Ho Lee², Hong-Deok Kim², Han-Sub Chung²

CMES-Computer Modeling in Engineering & Sciences, Vol.11, No.1, pp. 9-16, 2006, DOI:10.3970/cmes.2006.011.009

Abstract The growth of stress corrosion cracks in steam generator tubes is predicted using the Monte Carlo simulation and statistical approaches. The statistical parameters that represent the characteristics of crack growth and crack initiation are derived from in-service inspection (ISI) non-destructive evaluation (NDE) data. Based on the statistical approaches, crack growth models are proposed and applied to predict crack distribution at the end of cycle (EOC). Because in-service inspection (ISI) crack data is different from physical crack data, a simple method for predicting the physical number of cracks from periodic in-service inspection data is proposed in this study. Actual number of… More >

T. Yoda¹, N. Kodama²

CMES-Computer Modeling in Engineering & Sciences, Vol.11, No.1, pp. 1-8, 2006, DOI:10.3970/cmes.2006.011.001

Abstract A nonlinear dynamic response analysis of a box section steel rigid frame under seismic action is proposed on the basis of a beam model. The average stress-strain relation of the beam model can be formulated for transverse stiffener spacing, in which stress-strain relation after local buckling is assumed. As a result of the present study, the maximum lateral displacements and the residual displacements of a box section steel rigid frame were well estimated by the proposed beam element model that considers the deterioration effect due to local buckling. More >

R. Matsumoto, M. Nakagaki

CMES-Computer Modeling in Engineering & Sciences, Vol.10, No.3, pp. 187-198, 2005, DOI:10.3970/cmes.2005.010.187

Abstract Large-scale molecular dynamics simulations of tensile deformation of amorphous metals containing a nano-crystalline particle were performed in order to clarify the effects of particle size and crystal volume fraction on the deformation mechanism and strength. It became clear that particle size has very little effect, while crystal volume fraction has a substantial influence. Elastic modulus and flow stress intensify as crystal volume fraction increases. Furthermore, the stress in the crystal phase continues to increase, even after yielding in the amorphous phase. Consequently, work-hardening effects appear, preventing localization of plastic deformation. Thus, the dispersed nano-crystalline particles improve the amount of tensile… 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 >

T. Nishioka¹, F. Stan¹

CMES-Computer Modeling in Engineering & Sciences, Vol.4, No.1, pp. 119-140, 2003, DOI:10.3970/cmes.2003.004.119

Abstract In this paper we investigate the essentially unexplored area of three-dimensional dynamic fracture mechanics. The general objective sought by this investigation is the understanding of three-dimensional dynamic crack propagation and arrest, and, specifically, the effect that the specimen thickness has on the dynamic fracture mechanism. In particular, in the context of the present paper, it is intended to provide a summary of the achievements on the issue of three-dimensional dynamic fracture parameters. Furthermore, the behavior of the three-dimensional field near the crack front is investigated. The issue that will be addressed is the extent of regions over which plane stress… More >

Haruhiko Kohno, Takahiko Tanahashi¹

CMES-Computer Modeling in Engineering & Sciences, Vol.2, No.2, pp. 155-170, 2001, DOI:10.3970/cmes.2001.002.155

Abstract Three-dimensional (3D) unsteady numerical simulations are carried out by means of the finite element method (FEM) with the generalized simplified marker and cell (GSMAC) method in silicon melt with a non-deformable free surface with Prandtl number Pr = 1.8534 × 10^-2, Marangoni number Ma = 0.0 - 6.2067 × 10², Grashof number Gr = 7.1104 × 10⁶, and the aspect ratio As = 1.0 in the Czochralski (CZ) method. The flow state becomes unstable earlier by increasing the absolute value of the thermal coefficient of surface tension in the range of σ_T =0.0 - 1.5 × 10^-5N/mK. Although the velocity… More >

António Tadeu, Andreia Pereira, Luís Godinho¹

CMES-Computer Modeling in Engineering & Sciences, Vol.2, No.1, pp. 49-62, 2001, DOI:10.3970/cmes.2001.002.049

Abstract The Boundary Element Method (BEM) is used to compute the three-dimensional variation pressure field generated by a point pressure source inside a flat waveguide channel filled with a homogeneous fluid, in the presence of infinite rigid circular pipelines. The problem is solved in the frequency domain, using boundary elements to model the pipeline and an appropriate Green's function to simulate the free surface and the rigid floor of the channel. Because of the 2 ---1/2 ---D geometry of the problem, the separation of variables has been used, and the solution at each frequency is expressed in terms of waves with… More >

W.W. Liou¹, Y.C. Fang¹

CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.4, pp. 119-128, 2000, DOI:10.3970/cmes.2000.001.571

Abstract A simple implicit treatment for the low speed inflow and outflow boundary conditions for the direct simulation Monte Carlo (DSMC) of the flows in microelectromechanical systems (MEMS) is proposed. The local mean flow velocity, temperature, and number density near the subsonic boundaries were used to determine the number of molecules entering the computational domain and their corresponding velocities at every sample average step. The proposed boundary conditions were validated against micro-Poiseuille flows and micro-Couette flows. The results were compared with analytical solutions derived from the Navier-Stokes equations using first-order and second order slip-boundary conditions. The results show that the implicit… More >

Paulo Santos, Julieta António, António Tadeu¹

CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.4, pp. 79-98, 2000, DOI:10.3970/cmes.2000.001.531

Abstract This paper presents the three-dimensional scattering field obtained when 2D smooth topographical deformations are subjected to a dilatational point load placed at some point in the medium. The solution is formulated using boundary elements for a wide range of frequencies and spatially harmonic line loads, which are then used to obtain time series by means of (fast) inverse Fourier transforms into space-time. The topographical surface is modeled with a number of boundary elements, defined according to the excitation frequency of the harmonic source, and in such a way that the free surface can be discretized along a sufficient distance to… More >