• 한국해양공학회지
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• 제31권1호
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• pp.1-7
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• 2017

There are two wave modes induced by an oscillating body on the free surface of a two-layer fluid: the barotropic and baroclinic modes. To investigate the generated waves composed of two modes, a radiation problem involving a heaving rectangular body was solved in a numerical wave tank. A new artificial damping zone scheme was developed and applied in the frequency-domain analysis. The performance of this damping scheme was compared with given radiation boundary conditions for various conditions. The added mass and radiation damping coefficients for the heaving rectangular body were also calculated for various fluid-density ratios.

• 오토저널
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• 제11권3호
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• pp.29-36
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• 1989

A multidimensional numerical simulation for flows in an engine with axisymmetric geometry was performed. Three kinds of differencing schemes, namely, skew upwind differencing scheme (SUDS), interpolated upwind differencing scheme (IUDS), upwind differencing scheme (UDS), are used in a comparative study. Simultaneously, the effects of the artificial dampings and the grids on numerical results are estimated. Compared with the measurements, the calculations with SUDS and proper artificial damping show very similar qualitative tendency with observed results. But there are some discrepancies due to numerical errors and unclear boundary conditions.

• 대한전기학회논문지:전력기술부문A
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• 제48권7호
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• pp.815-823
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• 1999

This study considers an implementation of artificial neural networks to the receding horizon optimal control and is applications to power systems. The Generalized Backpropagation-Through-Time (GBTT) algorithm is presented to deal with a quadratic cost function defined in a finite-time horizon. A decentralized approach is used to control the complex global system with simpler local controllers that need only local information. A Neural network based Receding horizon Optimal Control (NROC) 1aw is derived for the local nonlinear systems. The proposed NROC scheme is implemented with two artificial neural networks, Identification Neural Network (IDNN) and Optimal Control Neural Network (OCNN). The proposed NROC is applied to a power system to improve the damping of the low-frequency oscillation. The simulation results show that the NROC based power system stabilizer performs well with good damping for different loading conditions and fault types.

• Structural Engineering and Mechanics
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• 제47권5호
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• pp.599-622
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• 2013

Seismic response of two dimensional liquid tanks is numerically simulated using fully nonlinear velocity potential theory. Galerkin-weighted-residual based finite element method is used for solving the governing Laplace equation with fully nonlinear free surface boundary conditions and also for velocity recovery. Based on mixed Eulerian-Lagrangian (MEL) method, fourth order explicit Runge-Kutta scheme is used for time integration of free surface boundary conditions. A cubic-spline fitted regridding technique is used at every time step to eliminate possible numerical instabilities on account of Lagrangian node induced mesh distortion. An artificial surface damping term is used which mimics the viscosity induced damping and brings in numerical stability. Four earthquake motions have been suitably selected to study the effect of frequency content on the dynamic response of tank-liquid system. The nonlinear seismic response vis-a-vis linear response of rectangular liquid tank has been studied. The impulsive and convective components of hydrodynamic forces, e.g., base shear, overturning base moment and pressure distribution on tank-wall are quantified. It is observed that the convective response of tank-liquid system is very much sensitive to the frequency content of the ground motion. Such sensitivity is more pronounced in shallow tanks.

• 대한조선학회논문집
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• 제29권3호
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• pp.80-89
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• 1992

자유표면파 문제에서의 방사조건을 위해 두가지 기법을 적용하여 보았다. 우선, 가상감쇠의 개념을 적용하여 일정한 구간에서 파를 감쇠시킴으로써 열린경계면(open boundary)에서 반사파를 제거하는 방법을 적용하여 보았다. 또 다른 방법으로서는 Orlanski의 방법을 변형하여 적용함으로써 단방향 파동에 대한 방사조건 처리기법을 다루었다. 몇가지의 전형적인 자유표면파문제에 대해 이들 기법을 적용하여 그 유용성을 고찰하였는데, 이들 기법은 그 적용방법이 간단하고 비선형문제에서도 사용될 수 있을 것으로 사료된다. 문제의 해법으로 기본 쏘오스 분포법이 사용되었고 비선형의 자유표면 경계조건이 적용되었다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1995년도 추계 학술대회논문집
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• pp.55-63
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• 1995

The flow field around a high-speed train including cross-wind effects has been simulated. This study solves 3-D unsteady incompressible Navier-Stokes equations in the inertial frame using the iterative time marching scheme. The governing equations are differenced with 1st-order accurate backward difference scheme for the time derivatives, 3th-order accurate QUICK scheme for the convective terms and 2nd-order accurate central difference scheme for the viscous terms. The Marker-and-Cell concept was applied to efficiently solve continuity equation, which is differenced with 2nd-order accurate central difference scheme. The 4th-order artificial damping is added to the continuity equation for numerical stability. A C-H type of elliptic grid system is generated around a high-speed train including ground. The Baldwin-Lomax turbulent model was implemented to simulate the turbulent flows. To validate the present procedure, the flow around a high speed train at constant yaw angle of $45^{\circ}\;and\;90^{\circ}$ has been simulated. The simulation shows 3-D vortex generation in the lee corner. The flow separation is also observed around the rear of the train. It has concluded that the results of present study properly agree with physical flow phenomena.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1996년도 춘계 학술대회논문집
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• pp.99-104
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• 1996

The jet pump is being used in many fields for several purposes because of its simple construction and easy operation. The characteristics of the geometrical variables, pressure gradient and velocity distribution of the jet pump are studied using the CFD technique. The flow calculations through a bended nozzle. a mixing chamber and a venturi are presented and phenomenological aspects are discussed. This study solve 3-D steady incompressible Navier-Stokes equations using the Iterative time marching scheme. The governing equations are differenced with 1st-order accurate backward difference scheme for the time derivatives and 3rd-order accurate QUICK scheme for the convective terms. The Mark-and-cell concept was applied efficiently to solve continuity equation, which is differenced 2nd-order accurate central differenced scheme. The 4th-order artificial damping is added to the continuity equation for numerical stability. A O-type of grid system is generated inside a nozzle and venturi of the jet pump. It has concluded that the results of present study properly agree with physical flow phenomena.

• Ocean Systems Engineering
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• 제4권2호
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• pp.83-97
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• 2014

Wave propagation in a three-dimensional (3D) fully nonlinear numerical wave tank (NWT) is studied based on velocity potential theory. The governing Laplace equation with fully nonlinear boundary conditions on the moving free surface is solved using the indirect desingularized boundary integral equation method (DBIEM). The fourth-order predictor-corrector Adams-Bashforth-Moulton scheme (ABM4) and mixed Eulerian-Lagrangian (MEL) method are used for the time-stepping integration of the free surface boundary conditions. A smoothing algorithm, B-spline, is applied to eliminate the possible saw-tooth instabilities. The artificial wave speed employed in MTF (multi-transmitting formula) approach is investigated for fully nonlinear wave problem. The numerical results from incorporating the damping zone (DZ), MTF and MTF coupled DZ (MTF+DZ) methods as radiation condition are compared with analytical solution. An effective MTF+DZ method is finally adopted to simulate the 3D linear wave, second-order wave and irregular wave propagation. It is shown that the MTF+DZ method can be used for simulating fully nonlinear wave propagation very efficiently.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 춘계 학술대회논문집
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• pp.153-158
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• 2000

For the analysis of compressible flow with real gas effect, characteristic form of Roe's Riemann solver was derived again using real gas equation of state and variable specific heal and it was extended to multi component reactive system. From this study, it is known that some correction should be made for the use of existing numerical algorithm. 1) Sonic speed and characteristic variable should be corrected with real gas effect. 2) Roe's average was applicable only with the assumption of constant properties. 3) Artificial damping term and characteristic variables should be corrected but their influence may not be significant.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 추계 학술대회논문집
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• pp.187-194
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• 2005

For the analysis of compressible multi-phase and real gas flows, characteristic form of Roe's Riemann solver was derived using real gas equation of state. It was extended to multi component reactive system considering variable specific heat. From this study, it is known that some correction should be made for the use of existing numerical algorithm. 1) Sonic speed and characteristic variable should be corrected with real gas effect. 2) Roe's average was applicable only with the assumption of constant properties. 3) Artificial damping term and characteristic variables should be corrected but their influences may not be significant.