• 설비공학논문집
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• 제30권4호
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• pp.195-203
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• 2018

Mohair is widely used as an airtight material for filling the gap between a window frame and sash. The purpose of this study is to investigate infiltration rate and opening force of sliding windows according to the mohair installation conditions. Infiltration experimental apparatus was set up, and the experimental results were applied to windows to find a correlation between infiltration rates and opening forces. When 4 rows of mohair were installed, the infiltration rate increase became 27.1% per clearance length increase of 1 mm, and the infiltration rate decrease became 5.7% per shortened length increase of 0.1 mm. For 4 rows of mohair, the opening force decreased by 28.2% as the clearance increased by 1 mm, and it increased by 9.3% as the shortened length increased by 0.1 mm.

• 한국유체기계학회 논문집
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• 제12권6호
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• pp.33-40
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• 2009

The temperature of vertical pump bearing metal in the pumped storage power plant has been high enough to shutdown the unit. Attempts such as decreasing the oil supply temperature, increasing the bearing oil gap etc. were performed to resolve the problem, but the issue was not resolved. Finally, the high bearing metal temperature was corrected by adjusting the bearing preload. The preload is formed by the oil wedge between the journal surface and bearing pad surface and the degree of preload is determined by the machined radial clearance, assembled radial clearance, rotor journal diameter etc. This paper focuses on the analysis of the preload depending on the bearing parameters and the result of the modification of the bearing following the analysis. The bearing metal temperature dropped as much as $20^{\circ}C$ which was similar as expected by software calculation. But the shaft vibration could increase when the assembled radial clearance is excessive. So, the adjustment of the bearing preload for the tilting pad type journal bearing should be carefully performed.

• 한국유체기계학회 논문집
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• 제7권5호
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• pp.36-42
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• 2004

The effect of tip clearance height on the three-dimensional flow and aerodynamic loss in the wake region of a high-turning turbine rotor cascade has been investigated with a miniature cone-type five-hole probe. Distributions of velocity magnitude, secondary velocity vectors, and total-pressure loss coefficient are presented for three tip gap-to-span ratios of h/s = 0.0, 0.5 and 1.0 percent. The result shows that with the increment of h/s, tip leakage vortex tends to be intensified and aerodynamic loss due to the leakage vortex is increased as well. In the case of h/s = 1.0 percent, aerodynamic loss in the tip-leakage flow region is found dominant in comparison with that in the passage vortex region. With increasing h/s, mass-averaged secondary loss coefficient has a greater portion in the mass-averaged total-pressure loss coefficient.

• 대한기계학회논문집B
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• 제25권3호
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• pp.414-421
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• 2001

The present study is conducted to investigate the local heat/mass transfer characteristics on the shroud with blade tip clearances. The relative motion between blade and shroud has little influence on the overall heat transfer characteristics, except some local effects. Therefore, the relative motion between the blade and shroud is neglected in this study. A naphthalene sublimation method is employed to determine the detailed local heat/mass transfer coefficients on the surface of the shroud. The tip clearance is changed from 0.66% to 2.85% of the blade chord length. The flow enters the gap between the blade tip and shroud at the pressure side due to the pressure difference. Therefore, the heat/mass transfer characteristics on the shroud are changed significantly from those with endwall. At first, high heat/mass transfer occurs along the profile of blade at the pressure side due to the entrance effect and acceleration of the gap flow. Then, the heat/mass transfer coefficients on the shroud increase along the suction side of the blade because tip leakage vortices are generated and interact with the main flow. The results show that the heat/mass transfer characteristics are changed largely with the gap distance between the tip of turbine blade and the shroud.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제29회 춘계학술대회
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• pp.197-202
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• 1999

A mechanical face seal is a tribe-element intended to control the leakage of working fluid at the interface of a rotating shaft and its housing. The leakage of working fluid decreases as the seal surfaces get closer each other. But a very small seal clearance results in a drastic reduction of seal life because of high wear and heat generation. Therefore, in the design of mechanical face seals the compromise between low leakage and acceptable life is important and presents a difficult design problem. And the gap geometry of seal clearance affects seal performance very much and becomes an important design variable. In this study the Reynolds equation for the sealing dam of mechanical face seals is numerically analyzed using the Galerkin Finite Element Method, which can be readily applied to various seal geometries. The film pressures of the sealing dam are analyzed, including the effects of the seal face coning and tilt. Then, opening forces, restoring moments, leakages, and dynamic coefficients are calculated.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.419-420
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• 2002

The piston-cylinder mechanism is widely adopted in the hydraulic machine components. In these cases, the hydrodynamic pressures are generated in the clearance gap between the piston and cylinder under lubrication action of the oils. Under the eccentric condition of the piston in the cylinder bore, the asymmetric pressure distributions in the circumferential direction result in lateral forces on the piston. When the lateral forces act as increasing the piston eccentricity, excessive wear can be occurs in the cylinder bore and piston. In this paper, the hydrodynamic pressures generated in the clearance are measured using a stationary piston and moving cylinder apparatus. The experimental results showed that the hydrodynamic pressure distributions are highly affected by the eccentricity of the piston.

• 한국기계가공학회지
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• 제10권6호
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• pp.77-82
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• 2011

The piston-cylinder mechanism is widely adopted in the hydraulic machine components. In these cases, the hydrodynamic pressures are generated in the clearance gap between the piston and cylinder under lubrication action of the piston. Under the eccentric and tilted condition of the piston in the cylinder bore, the non-symmetric pressure distributions in the circumferential direction result in lateral forces. When the lateral forces act as increasing the eccentricity and tilting ratios, excessive wear can be result in cylinder and piston which are well known 'hydraulic locking' phenomena. In this paper, the hydrodynamic pressures generated in the clearance are measured using a stationary piston and moving cylinder apparatus. The experimental results showed that the hydrodynamic pressure distributions are highly affected by the speed and eccentricity of the cylinder and the oil viscosity.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.517-520
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• 2017

본 논문은 추진기관 기밀체결부의 설계변수가 기밀조립부의 갭 거동과 오링의 기밀성능에 미치는 영향을 분석하고 효과적인 설계변수 설정 방안을 도출하였다. 체결부의 설계변수를 구성하는 요소로서 노즐 플랜지 두께, 체결볼트에 가하는 예비하중을 단계별로 변화하여 연소관 내압거동에 따른 기밀조립부 갭 벌어짐을 최소화하고 나아가서 기밀용 오링의 기밀성능을 효과적으로 유지할 수 있는 설계변수 조건을 평가함으로써 추진기관 연소관 노즐 기밀체결부의 효율적인 설계 방법론을 제시하였다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제31회 춘계학술대회
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• pp.237-242
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• 2000

In this paper, an experiment was carried out to measure the hydrodynamic oil pressure distribution in the clearance gap between a piston and cylinder. The results showed that the pressure distributions are highly affected by the eccentricity of the piston. Therefore present experimental method can be used to enhance the performance of hydraulic piston pumps. Further experimental studies for various operating conditions and improvement in data acquisition methods are required to obtain more accurate results.

• Structural Engineering and Mechanics
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• 제5권3호
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• pp.297-306
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• 1997

The bouncing of a cantilever with the free end pressed against a stop can create high-frequency vibration that the Bernoulli-Euler beam theory is inadequate to solve. An analytic procedure is presented using Timoshenko beam theory to obtain the non-linear response of a cantilever supported by an elastic stop with clearance at the free end. Through a numerical example, the bouncing behavior of the Timoshenko and Bernoulli-Euler beam models are compared and discussed.