• 한국수자원학회논문집
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• 제34권2호
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• pp.177-186
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• 2001

2차 이상의 정확도를 가지며 불연속면에서 수치진동이 발생하지 않는 수치모형의 개발을 위해 풍상차분기법에 기초한 TVD기법이 소개되었다. 이 수치모형을 불연속면 이 존재하는 경우와 존재하지 않는 경우에 대해 적용하였으며, 이 결과 1차 정확도의 풍상차분기법은 시간이 지나면서 수치점성의 영향이 커졌으며 2차 정확도의 Lax-Wendroff기법의 경우에는 불연속면에서 진동이 발생하였다. 그러나 TVD기법은 모든 경우에서 만족스러운 결과를 예측하였다.

• Journal of Mechanical Science and Technology
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• 제15권6호
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• pp.764-775
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• 2001

Oscillartory thermocapillary flow of high Prandtl number fluids in the half-zone configuration is investigated. Based on experimental observations, one oscillation cycle consists of an active period where the surface flow is strong and the hot corner region is extended and a slow period where the opposite occurs. It is found that during oscillations the deformation of free surface plays an important role and a surface deformation parameter S correlates the experimental data well on the onset of oscillations. A scaling analysis is performed to analyze the basic steady flow in the parametric ranges of previous ground-based experiments and shows that the flow is viscous dominant and is mainly driven in the hot corner. The predicted scaling laws agree well with the numerical results. It is postulated that the oscillations are caused by a time lag between the surface and return flows. A deformation parameter S represents the response time of the return flow to the surface flow.

• 한국컴퓨터산업학회논문지
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• 제5권3호
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• pp.355-362
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• 2004

이 연구는 갤럽핑 케이블과 현수교의 뒤틀린 진동에 관한 공통된 결과와 다른 결과를 제시하고 있다. 갤럽핑 케이블과 현수교의 뒤틀린 진동에 관한 수치적인 결과는 2차의 Runge Kutta 방법에 의한 것이다. 진동의 주파수와 진폭이 변함에 따라 다중근의 존재를 확인할 수 있으며, 대칭성이 벗어나고 일시적인 현상에서의 차이를 볼 수 있다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 1996년도 제7회 학술강연회논문집
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• pp.107-116
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• 1996

Numerical simulations have been conducted to characterize unsteady flow structures in an axisymmetric supersonic inlet diffuser with sinusoidal pressure oscillations at the diffuser exit. The formulation is based on the unsteady Navier-Stokes equations and turbulence closure is achieved using a two-layer model with a too-Reynolds-number scheme for the near-wall treatment. The governing equations are formulated in an integral form, and are discretized by the four-stage Runge-Kutta scheme for temporal terms and the Harten-Yee upwind TVD scheme for convective terms. Results indicated that the inlet shock characteristics are significantly modified by acoustic oscillations originating from the combustor. The characteristics of shock/boundarv-layer interactions (such as the size of separation bubble, terminal shock shape, and vorticity intensity) are also greatly iufluenced by the shock oscillation due to acoustic waves.

• 한국연소학회지
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• 제16권1호
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• pp.30-35
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• 2011

This study has been mainly motivated to numerically investigate the transient flame response to pressure oscillations in the gaseous hydrogen - liquid oxygen flames at supercritical pressures. The present analysis is based on the real-fluid transient flamlet model and the flame field is acoustically perturbed only by the sinewave oscillations in the frequency range from 1,000 Hz to 5,000 Hz. Based on numerical results, the detailed discussions are made for the flame response characteristics and the transient flamelet response associated with the high-frequency combustion instability in the liquid propellant rocket engines.

• 설비공학논문집
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• 제7권1호
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• pp.132-141
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• 1995

Characteristics of pressure-drop oscillations(PDO) in a boiling channel were studied numerically and compared with experimental data. Effects of initial and boundary conditions on PDO were investigated in terms of oscillation period and amplitude. The period and amplitude of PDO increased with increasing of the compressible volume in the surge tank and the heat input. PDO occurred within the specific range of the fluid temperature, at which oscillation period and amplitude diminished rapidly with the increase of the fluid temperature. The increase of the loss coefficient in fluid supply line resulted in slightly longer oscillation period and larger amplitude. Numerical results showed good agreement with the experimental data.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.404-411
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• 2010

The present paper deals with the continuous work of extending multi-dimensional limiting process (MLP), which has been quite successfully proposed on two- and three-dimensional structured grids, onto the unstructured grids. The basic idea of the present limiting strategy is to control the distribution of both cell-centered and cell-vertex physical properties to mimic a multi-dimensional nature of flow physics, which can be formulated as so called the MLP condition. The MLP condition can guarantee a high-order spatial accuracy without yielding spurious oscillations. Recently, MLP slope limiter was proposed based on the MUSCL-type reconstruction in two-dimensional case and it can be readily extended to three-dimensional case. Through various numerical analyses and extensive computations, it is observed that the proposed limiters are quite effective in controlling numerical oscillations and very accurate in capturing both discontinuous and continuous multi-dimensional flow features on 3-D tetrahedral grids.

• 대한조선학회지
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• 제25권3호
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• pp.3-12
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• 1988

A natural or an artificial harbor can exhibit frequency(or period) dependent water surface oscillations when excited by incident waves. Such oscillations in harbors can cause significant damage to moored ships and adjacent structures. This can also induce undesirable current in harbors. Many previous investigators have studied various aspects of harbor resonance problem. In the percent paper, both a localizes finite element method(LFEM) which is based on the functional constructed by Chen & Mei(1974) and Bai & Yeung(1974) and an integral equation method which was used by Lee(1969) are applied to harbor resonance problem. The present method(LFEM) shows computationally more efficient than the integral equation method. Our test results shows good agreement compared with other results. This enhanced computational efficiency is due to the fact that the present method gives a banded symmetric coefficients matrix and requires much less computational time in the calculation of the influence coefficients matrix than the integral equation method involved with Green's function. To test the present numerical scheme, two models are treated here. The present method(LFEM) can be extended to a fully three dimensional harbor problem with the similar computational advantage.

• 한국해안해양공학회지
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• 제8권1호
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• pp.72-80
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• 1996

직사각형 항만의 항내응답에 대한 두 가지 해석해를 제시하였다. 본 논문에서 올바른 정합점근 근사법의 해가 제시되었고 이 해는 Mei (1989)에 의해 처음 유도되었다. 다른 해석해는 특성함수 전개법을 이용하여 유도되었으며 보다 정밀한 수치적분 방법이 사용되었다. 해의 검증을 위해 해석적인 방법 및 수치방법인 경계적분요소법으로 내만에서의 파고증폭비를 계산하여 도시하였다.

• 한국추진공학회지
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• 제13권5호
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• pp.41-47
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• 2009

2차원 초음속 공동유동에서 발생하는 압력진동을 제어하기 위한 목적으로, 본 연구에서는 수치해석적 연구를 수행하였다. 본 계산에서는 압력진동을 제어하기 위하여 보조공동의 형상을 변화시켰으며, 유동의 마하수를 1.50, 1.83 그리고 2.50로 변화시켰다. 그 결과, 보조공동은 압력진동을 상당히 감소시켰으며, 압력진동의 제어효과는 유동의 마하수와 보조공동의 상세형상에 크게 의존함을 알았다.