• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.666-671
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• 2006

This paper proposes a method to calculate the stiffness and the damping coefficients of the coupled journal and thrust bearings. The Reynolds equations and their perturbation equations are transformed to the finite element equations by considering the continuity of pressure and flow at the interface between bearings. The Reynolds boundary condition is used in the numerical analysis to simulate the cavitation phenomena. The dynamic coefficients of the proposed method are compared with those of the numerical differentiation of the loads with respect to finite displacements and velocities of bearing center. It shows that the proposed method is more accurate and efficient than the differentiation method.

• 물과 미래
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• 제29권1호
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• pp.141-150
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• 1996

상수관망에서의 압력과 유량의 정상상태 해석은 수공학에 있어서 매우 중요한 문제이다. 이 경우의 기본방정식은 유량을 미지값으로 하는 연속 방정식과 에너지 방정식으로 구성되는 비선형 연립방정식이다. 이 연립방정식을 풀기 위하여 선형화 기법을 도입하여 반복적으로 해석하였고 그 결과로 나타나는 선형 연립방정식의 효율적인 해석을 위해서 frontal기법을 사용하여 계산하였다. 이 기법은 계수 메트릭스의 '0'이 아닌 요소만을 모아 계산하므로 효과적으로 분산 메트릭스를 해석할 수 있었고, 기존의 band 해석기법보다 적은 앙의 계산 기억용량으로 계산시간을 크게 단축시켜 해석할 수 있었다. 본 연구에서 제시한 상수관망의 해석모형은 기존의 해석방법보다 정확하고 효율적인 계산기법으로서 제시하였다.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제7권2호
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• pp.95-111
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• 2003

BDM mixed methods are obtained for a good approximation of velocity for flow equations. In this paper, we study an implementation issue of solving the algebraic system arising from the BDM mixed finite elements. First we discuss post-processing based on the use of Lagrange multipliers to enforce interelement continuity. Furthermore, we establish an equivalence between given mixed methods and projection finite element methods developed by Chen. Finally, we present the implementation of the first order BDM on rectangular grids and show it is as simple as solving the pressure equation.

• Wind and Structures
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• 제1권4호
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• pp.337-349
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• 1998

A numerical and experimental study was performed for the wind flow field in one area, comprising a group of several pavilions separated by passageways, of the EXPO '98 - a World Exposition (Lisbon, Portugal). The focus of this study is the characterization of the flow field to assess pedestrian comfort. The predictions were obtained employing the Reynolds averaged Navier-Stokes equations with the turbulence effects dealt with the ${\kappa}-{\varepsilon}$ RNG model. The discretization of the differential equations was accomplished with the control volume formulation in a Cartesian coordinate system, and an advanced segregated procedure was used to achieve the link between continuity and momentum equations. The evaluation of the overall numerical model was performed by comparing its predictions against experimental data for a square cylinder placed in a channel. The predicted values, for the practical geometry studied, are in a good agreement with the experimental data, showing the performance and the reliability of the ${\kappa}-{\varepsilon}$ RNG model and suggesting that the numerical simulation is a reliable methodology to provide the required information.

• 동력기계공학회지
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• 제5권1호
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• pp.50-56
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• 2001

Jet pumps are used in a great number of engineering applications. In the present study, jet shapes, mixing chamber shapes, and numerical methods for predicting the performance of an annular-type jet pump are investigated to determine the optimal turbulence model. The flow fields are simulated by solving the momentum and the continuity equations with the standard ${\kappa}-{\epsilon}$ and the RNG ${\kappa}-{\epsilon}$ turbulence models at different Reynolds numbers. After that, they are compared with the corresponding experimental data to determine the optimal model. Next, various calculations are conducted to find an optimal shape using the selected turbulence model. The study shows us that the RNG ${\kappa}-{\epsilon}$ model predicts the performance more exactly, and also shows that the most effective performance can be achieved with $12^{\circ}$ reducing angle and 130mm throat length.

• 한국지반환경공학회 논문집
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• 제15권3호
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• pp.41-48
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• 2014

준설토에 대한 연구는 주로 준설토의 1차원 침강 및 자중압밀 특성을 파악하는 실험적 연구가 진행되었다. 하지만 양질의 준설지반 확보를 위한 효과적인 투기장의 설계와 배출수에 의한 환경오염을 최소화하기 위해서는 준설토의 투기에 의한 유동특성의 체계적인 연구가 필요하다. 본 연구에서는 준설토 투기장의 펌핑에 의한 토사의 유동 형상을 모사하기 위하여 준설토사를 단일상으로 가정하고 연속 방정식을 유도하여 좌표축에 따른 힘 평형 방정식을 유도하였다. 준설토장의 3차원 거동 해석을 위한 컴퓨터 연산 부하와 모델링 소요시간을 최적화하기 위하여, 토체의 깊이 방향으로 적분을 수행하는 깊이 적분 방법을 지배 방정식에 적용하여, 3차원적 지형조건을 고려할 수 있도록 하였다. 지배 방정식의 보간함수를 이용한 공간분할에서 Petrov-Galerkin 수식화 기법을 적용하였다. 일반화된 사다리꼴 법칙으로 시간적분을 수행하고 Newton의 반복과정을 이용할 수 있도록 근사화시켰다. 가중행렬은 DG과 CDG 기법을 적용하였으며, 준설토 유동해석에서 가중행렬에 따른 수치적인 안정성을 평가하기 위하여 사각형 기둥 슬럼프 시뮬레이션을 수행하였다. 수치기법에 대한 비교 분석 결과는 DG 기법을 적용한 SU/PG 수식화가 유사진동을 최소화시키는 가장 안정적인 수치해석결과를 보여주는 것으로 나타났다.

• 한국항공우주학회지
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• 제49권6호
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• pp.449-456
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• 2021

본 연구에서는 저마하수 예조건화 기법이 적용된 기존 압축성 해석자의 해석 범위를 최소한의 수정으로 비압축성 유동해석이 가능하도록 확장하는 전략을 제시하였다. 이를 위해 압축성 총 에너지 방정식과 동일한 형태의 에너지 방정식을 사용하였다. 이러한 에너지 방정식은 비압축성 지배방정식인 연속방정식, 열에너지 방정식과 역학적 에너지방정식의 선형 조합을 통해 얻어진다. 이렇듯 압축성 방정식과 동일한 형태를 갖는 비압축성 지배방정식에 시간 전진 기법을 적용하기 위해 Turkel의 가상 압축성 기법을 적용하였다. 또한 Roe 평균이 공통의 압축성/비압축성 지배방정식에서 모두 유효함을 보였다. 압축성 해석자에 위 내용을 적용하여 비압축성 해석이 가능하도록 확장하는 과정은 본래의 압축성 해석자를 이용한 압축성 해석에 아무런 영향이 없다. 확장된 해석자를 통한 비압축성 해석 검증을 위해 비점성, 층류 그리고 난류 유동에 대한 순차적 해석을 수행하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 학술대회
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• pp.327-333
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• 2008

The cavitating flow simulation is of practical importance for many engineering systems, such as marine propellers, pump impellers, nozzles, injectors, torpedoes, etc. The present work has developed a base code for simulating cavitating flows past cylinders and hydrofoils. The governing equation is the Navier-Stokes equation based on homogeneous mixture model. The momentum and energy equation is in the mixture phase while the continuity equation is solved in liquid and vapor phase, separately. The solver employs an implicit preconditioning algorithm in curvilinear coordinates. The computations have been carried out for the cylinders with spherical, 1- and 0-caliber forebody and hydrofoil of ALE and NACA cross-section and, then, compared with experiments and other numerical results. Fairly good agreements with experiments and numerical results have been achieved. The present base code has shown the feasibility to solve the cavitating flow past supercavitating torpedo after the improvement for compressibility effects and interactions with hot exhaust gas of propulsive rocket.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년 추계학술대회논문집
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• pp.327-333
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• 2008

The cavitating flow simulation is of practical importance for many engineering systems, such as marine propellers, pump impellers, nozzles, injectors, torpedoes, etc. The present work has developed a base code for simulating cavitating flows past cylinders and hydrofoils. The governing equation is the Navier-Stokes equation based on homogeneous mixture model. The momentum and energy equation is in the mixture phase while the continuity equation is solved in liquid and vapor phase, separately. The solver employs an implicit preconditioning algorithm in curvilinear coordinates. The computations have been carried out for the cylinders with spherical, 1- and 0-caliber forebody and hydrofoil of ALE and NACA cross-section and, then, compared with experiments and other numerical results. Fairly good agreements with experiments and numerical results have been achieved. The present base code has shown the feasibility to solve the cavitating flow past supercavitating torpedo after the improvement for compressibility effects and interactions with hot exhaust gas of propulsive rocket.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 춘계 학술대회논문집
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• pp.95-98
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• 2007

A general purpose program NUFLEX has been extended for two-phase flows with topologically complex interface and cavitation flows with liquid-vapor phase change caused by large pressure drop. In analysis of two-phase flow, the phase interfaces are tracked by employing a LS(Level Set) method. Compared with the VOF(Volume-of-Fluid} method based on a non-smooth volume-fraction function, the LS method can calculate an interfacial curvature more accurately by using a smooth distance function. Also, it is quite straightforward to implement for 3-D irregular meshes compared with the VOF method requiring much more complicated geometric calculations. Also, the cavitation process is computed by including the effects of evaporation and condensation for bubble formation and collapse as well as turbulence in flows. The volume-faction and continuity equations are adapted for cavitation models with phase change. The LS and cavitation formulation are implemented into a general purpose program for 3-D flows and verified through several test problems.