• Journal of the KSME
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• v.23 no.3
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• pp.200-206
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• 1983

FAM의 기본적인 구상은 해석 하고자하는 선형 또는 비선형 편미분 방정식을 국부적으로 해석 적인 해를 구하여 이용하자는 것이다. 그러기 위하여 유한차분법(FDM)과 유한변분법(FEM)에 서와 같이 전체유동장을 작은 요소로 나누고 그 요소 내에서 국부해를 구한 다음 이들 요소를 중첩시킴으로써 각 요소의 미지수에 대한 대수식을 얻어서 수치해를 구하자는 것이다. 그러나 FDM에서와 같이 국부요소에서 미분항을 구하지 않고, FEM 에서와 같이 요소에서 형상함수를 도입하지 않는 상태에서 해석적인 해를 구하고 있기 때문에 수치해석에서 얻어지는 미분양들은 비교적 정확하게 구해진다. 따라서 Navier-Stokes 방정식이나 에너지 방정식에서 최고차항이 작은 파라메타, 즉 레이놀즈수나 피크리수의 역수로 곱하여서 있는 경우에도 안정된 해를 구할 수 있다고 알려져 있다. 요소자체의 계수를 구하는 데는 계산시간이 많이 소요되지만 수치해석 상의 안정성이나 수렴성이 좋기 때문에 전체계산시간은 오히려 적게 걸리는 경우도 있다고 한다.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.980-985
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• 2004

This paper shows a performance analysis for conical type sealless cylinders and rod bearings. The pistons without seal have partly cylindrical and conical shapes. 2 dimensional Reynolds equation and FD(finite differential) numerical techniques are utilized for the performance analysis. The relationship among self-centering forces and leakage flows are investigated. Also, optimal design values for a sealless cylinder are presented. A prototype of sealless cylinder which had rod bearing with four pockets, five pockets, and six pockets was manufactured respectively. Leakage flow test is conducted to evaluate performance of piston and rod bearing in sealless cylinder.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.11
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• pp.1399-1409
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• 1999

It is known that previous models are unsatisfactory in predicting adverse pressure gradient turbulent flows. In the present paper, a revised low Reynolds number $k-{\varepsilon}$ model is proposed. In this model, a newly developed term is added lo the dissipation rate equation. In order to reflect appropriate effects for an adverse pressure gradient. The added tenn is derived by considering the distribution of mean velocity and turbulent properties in the turbulent flow with, adverse pressure gradient. The new $k-{\varepsilon}$ model was applied to calculations of flat plate flow with adverse pressure gradient, conical diffuser flow and backward facing step flow. It was found that the three numerical results showed better agreement than other models compared with DNS results and experimental ones.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.241-241
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• 2011

일반적으로 식생흐름의 층 적분 모형은 층의 수에 따라 2층 및 3층 모형으로 구분한다. 즉, 전체 수심을 식생영역과 상부영역으로 구분하는 2층 모형과 식생영역을 바닥 조도의 영향 유무에 따라 내부 및 외부 식생영역으로 구분하는 3층 모형으로 나뉜다. 본 연구에 사용된 수리실험 자료는 기존의 연세대학교에서 수행한 실험결과를 이용하여 각 모형의 정확성을 예측해 보았다. 다양한 실험조건에 적용한 결과, 3층 모형이 식생영역에서 유속의 변화를 고려할 수 있지만 레이놀즈응력의 영향에 민감하고, 적분된 유속은 2층 모형에 의한 예측 결과가 더욱 정확하였다. 3층 모형에서는 내부 식생영역의 결과는 전체흐름구조에 미미한 영향을 미치므로 무시할 수 있으며, 이를 바탕으로 식생영역에서 유속 변화가 고려되는 수정 2층 모형을 제시하였다. 본 연구를 통하여 기존의 2층 모형과 3층 모형의 장점을 취합하여 수정된 2층 모형의 방정식을 바탕으로 모형의 정확성을 평가하기 위하여 2층 모형, 3층 모형, 수정 2층 모형의 유속 분포를 비교 분석하여 모형을 검증하였다.

• Proceeding of EDISON Challenge
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• 2012.04a
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• pp.73-76
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• 2012

변장비의 변화에 따른 타원형 실린더 주위의 유동장을 해석하기 위하여 Navier-Stokes 방정식을 사용한 EDISON 열유체 툴로 분석하였다. 본 논문은 기존의 연구와 비교 분석하는데 목적을 두었으며, 기존의 연구결과와 비교 분석하기 위하여 계산 영역을 동일하게 설정하였다. 타원형 실린더의 변장비를 0.5, 1, 2, 4로 변화시키고 레이놀즈수 200, 400, 1000인 조건하에 유동장을 해석하였다. 본 연구의 해석 결과를 통해 선행연구와 전체적인 경향이 같다는 것을 알 수 있었고, 또한 변장비와 레이놀즈수는 항력진폭과 양력진폭, 스트로할 수에 영향을 미침을 알 수 있었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.8
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• pp.1-11
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• 2004

A comprehensive study has been made for the investigation of the convergence and stability characteristics of the LU scheme for solving the Navier-Stokes equations on unstructured meshes. For this purpose the characteristics of the LU scheme was initially studied for a scalar model equation. Then the analysis was extended to the Navier-Stokes equations. It was shown that the LU scheme has an inherent stiffness in the streamwise direction. This stiffness increases when the grid aspect ratio becomes high and the cell Reynolds number becomes small. It was also shown that the stiffness related to the grid aspect ratio can be effectively eliminated by performing proper subiteration. The results were validated for a flat-plate turbulent flow.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1487-1494
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• 1990

In this paper the dynamic characteristics of self acting air lubricated slider bearing of hard disk/head system are investigated. The dynamic equations of magnetic head mechanism considering both parallel and pitch motion and the time dependent modified Reynolds equation are analyzed and the dynamic pressure distribution of air film is numerically calculated in frequency domain by small perturbation method and finite difference scheme with variable grid. The dynamic response of the slider spacing is obtained accordingly as the moving recording surface vibrates in parallel mode.

• Tribology and Lubricants
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• v.29 no.5
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• pp.275-285
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• 2013

The Reynolds equation is commonly used to investigate the lubrication characteristics of a spool valve. However, the applicability of the Reynolds equation is questionable for analyzing a spool valve because cavitation often occurs in the grooves of the valve and the depth of a groove is much higher than the clearance in most cases. In this study, the validity of the Reynolds equation in the spool valve analysis is investigated by comparing the results obtained from the Reynolds equation and those obtained from the Navier-Stokes equation. The results are compared in terms of the lateral forces, friction forces, and volume flow rates (leakages). A significant difference of more than 20% is found in the lateral forces in cases where cavitation occurs and there are many grooves. Therefore, the Navier-Stokes equation should be used to investigate the lubrication characteristics of a spool valve when cavitation occurs and when the spool valve contains many grooves.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.760-767
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• 2014

This paper proposes a method to calculate pressure and flow of the fluid dynamic bearings (FDBs) with a recirculation channel (RC) by solving the Reynolds and the Hagen-Poiseuille equations at the same time. The Hagen-Poiseuille equation is one-dimensional equation which describes the flow in a circular pipe such as the RC. This research developed a finite element program to solve the Reynolds and the Hagen-Poiseuille equation together. The proposed method was applied to calculate the pressure and flow of the FDBs which are composed of grooved or plain journal and thrust bearings, and RC. To verify the proposed method, it also developed a finite volume model of the FDBs, and pressure and flow were calculated by the commercial CFD solver. They agree well with the pressure and flow calculated by the proposed method. Finally, this research investigated the characteristics of the FDBs due to the radius change of the RC.

• Tribology and Lubricants
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• v.28 no.5
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• pp.218-232
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• 2012

In a spool valve analysis, the Reynolds equation is commonly used to investigate the lubrication characteristics. However, the validity of the Reynolds equation is questionable in a spool valve analysis because cavitation often occurs in the groove and the depth of the groove is much higher than the clearance in most cases. Therefore, the validity of the Reynolds equation in a spool valve analysis is investigated by comparing the results obtained from the Reynolds equation and the Navier-Stokes equation. Dimensionless parameters are determined from a nondimensional form of the governing equations. The differences between the lateral force, friction force, and volume flow rate (leakage) obtained by the Reynolds equation and those obtained by the Navier-Stokes equation are discussed. It is shown that there is little difference (less than 10%), except in the case of a spool valve with many grooves where no cavitation occurs in the grooves. In most cases, the Reynolds equation is effective for a spool valve analysis under a no cavitation condition.