• Structural Engineering and Mechanics
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• v.48 no.5
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• pp.711-736
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• 2013

In this paper new implicit time integration called N-IHOA is presented for dynamic analysis of high damping systems. Here, current displacement and velocity are assumed to be functions of the velocities and accelerations of several previous time steps, respectively. This definition causes that only one set of weighted factors is calculated from the Taylor series expansion which leads to a simple approach and reduce the computational efforts. Moreover a comprehensive study on stability of the proposed method i.e., N-IHOA compared with IHOA integration which is performed based on amplification matrices proves the ability of the N-IHOA in high damping vibrations such as control systems. Also, wide range of numerical examples which contains single/multi degrees of freedom, damped/un-damped, free/forced vibrations from finite element/finite difference demonstrate that the accuracy and efficiency of the proposed time integration is more than the common approaches such as the IHOA, the Wilson-${\theta}$ and the Newmark-${\beta}$.

• 한국전산유체공학회:학술대회논문집
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• 1995.10a
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• pp.113-117
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• 1995

Viscous analysis on incompressible flows is performed using unstructured triangular meshes. A two-dimensional and axisymmetric incompressible Navier-Stokes equations are solved in time-marching form by artificial compressibility method. The governing equations are discretized by a cell-centered based finite-volume method. and a centered scheme is used for inviscid and viscous fluxes with fourth order artificial dissipation. An explicit multi-stage Runge-Kutta method is used for the time integration with local time stepping and implicit residual smoothing. Convergence properties are examined and solution accuracies are also validated with benchmark solution and experiment.

• Geotechnical Engineering
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• v.12 no.6
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• pp.87-100
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• 1996

This paper verifies the accuracy and efficiency of the implicit stress integration algorithm for an anisotropic hardening constitutive model developed in a companion paper[Oh & Lee (1996)3. Simulation of undrained triaxial test results shows the accuracy of the method through an error estimation, and analyses of accuracy and convergence were performed for a numerical excavation problem. As a result, the stress was accurately integrated by the algorithm and the nonlinear solution was converged to be asymptotically quadratic. Furthermore nonlinear FE analysis of a real excavation problem was by performed considering the initial soil conditions and the in-situ construction sequences. The displacements of wall induced by excavation were more accurately estimated by the anisotropic hardening model than by the Cam-clay model.

• 한국전산유체공학회:학술대회논문집
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• 1996.05a
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• pp.131-136
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• 1996

The numerical method for the flow field of a gas atomization process is presented. For the analysis of the compressible supersonic jet flow of a gas. an axisymmetric Navier-Stokes equations are solved using a LU-factored upwind method. The MUSCL type TVD scheme is used for the discretization of inviscid flux, whereas Steger-Warming splitting and LU factorization is applied to the implicit operator. For the validation of the present method, we computed the flow field around the simple gas atomizer proposed by Issac. The numerical results has shown excellent agreement with the experimental data.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.8
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• pp.987-996
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• 1999

An algorithm for modeling the filling of metal into a mold and solidification has been developed. This algorithm uses the implicit VOF method for a filling and a general implicit source-based method for solidification. The model for simultaneous filling and solidification is applied to the two-dimensional filling and solidification of a square cavity. The effects of the wall temperature and gate position on the solidification are examined. The mixed natural convection flow and residual flow resulting from the completion of a filling are included in this study to investigate the coupled effects of the filling and natural convection on solidification. Two different filling configurations (assisting flow and opposite flow due to the gate position) are analysed to study the effects of residual flow on solidification. The results clearly show the necessity to carry out a coupled filling and solidification analysis including the effect of natural convection.

• Journal of the Korean Society of Combustion
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• v.1 no.1
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• pp.83-91
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• 1996

A numerical study is carried out to examine the ignition and propagation process of detonation wave in SCRam-accelerator operating in superdetonative mode. The time accurate solution of Reynolds averaged Navier-Stokes equations for chemically reacting flow is obtained by using the fully implicit numerical method and the higher order upwind scheme. As a result, it is clarified that the ignition process has its origin to the hot temperature region caused by shock-boundary layer interaction at the shoulder of projectile. After the ignition, the oblique detonation wave is generated and propagates toward the inlet while constructing complex shock-shock interaction and shock-boundary layer interaction. Finally, a standing oblique detonation wave is formed at the conical ramp.

• Proceedings of the Korea Water Resources Association Conference
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• 1982.07a
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• pp.91-98
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• 1982

The formulation of depth-averaged two-dimensional mathematical model for the analysis of tide induced circulation in a harbor by the Galerkin finite element techique is presented. In integration of the Galerkin approach in time both explicit and implicit method have been tested for one and two dimentional water bodies, and the two step Lax-Wendroff explicit method is found to be effective than the implicit in reducing computing time. The essential characteristics of the tide induced flow in Busan Harbor with two open boundaries has been foccud to be reproduceable in the numerical model and the simulated results encourage that the model can be used as a predictive tool.

• Structural Engineering and Mechanics
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• v.38 no.5
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• pp.651-674
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• 2011

This paper presents a novel method for predicting the failure probability of structural or mechanical systems subjected to random loads and material properties involving multiple design points. The method involves Multicut High Dimensional Model Representation (Multicut-HDMR) technique in conjunction with moving least squares to approximate the original implicit limit state/performance function with an explicit function. Depending on the order chosen sometimes truncated Cut-HDMR expansion is unable to approximate the original implicit limit state/performance function when multiple design points exist on the limit state/performance function or when the problem domain is large. Multicut-HDMR addresses this problem by using multiple reference points to improve accuracy of the approximate limit state/performance function. Numerical examples show the accuracy and efficiency of the proposed approach in estimating the failure probability.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.1000-1002
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• 2017

Here, the unsteady Navier-Stokes solver has been developed using implicit dual time stepping method. The implicit dual time stepping method introduced the pseudo time step for solving the new residual including the steady state residual and real time derivative. For the validation of code, Stokes 2nd problem, the laminar flow on the oscillating flat plate was selected and compare the calculating results with analytic solutions. The calculating velocity profile and skin friction has a good agreement with analytic solutions.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.1
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• pp.39-48
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• 2013

This paper develops a 2-D moving least squares(MLS) difference method for Stefan problem by extending the 1-D version of the conventional method. Unlike to 1-D interfacial modeling, the complex topology change in 2-D domain due to arbitrarily moving boundary is successfully modelled. The MLS derivative approximation that drives the kinetics of moving boundary is derived while the strong merit of MLS Difference Method that utilizes only nodal computation is effectively conserved. The governing equations are differentiated by an implicit scheme for achieving numerical stability and the moving boundary is updated by an explicit scheme for maximizing numerical efficiency. Numerical experiments prove that the MLS Difference Method shows very good accuracy and efficiency in solving complex 2-D Stefan problems.