• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2004년도 학술대회지
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• pp.269-274
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• 2004

It is important to decide the minimum film thickness and viscosity variations of a multigrade lubricant in the contact surface under the high pressure conditions. By carrying out acceleration, deceleration, and various sliding-rolling ratio movement between two contact bodies, it is experimented that film formation variations in the contact surface are captured with multigrade lubricants in order to exactly investigate the variations of film formations. Optical interference images are continuously captured with high resolution CCD camera during the captured period of acceleration, deceleration. The friction forces between the contacting bodies are also measured simultaneously with the film formation.

• 대한기계학회논문집A
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• 제36권11호
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• pp.1441-1446
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• 2012

유압피스톤모터는 정압베어링부분의 마찰손실과 용적손실, 기구적 운동부분의 마찰손실, 오일의 관로저항에 의한 압력저하, 압축성에 의한 체적손실 그리고 하우징 오일 처닝(churning) 손실 등이 있다. 이러한 손실 중에서 일정한 틈새의 유막(oil film, $8{\sim}15{\mu}m$)으로 고속 회전하는 피스톤 슈(piston shoe)와 슈 플레이트(shoe plate) 사이 정압베어링 부분의 마찰 및 용적손실이 유압모터의 전체효율을 좌우 한다. 본 연구에서는 최고압력 35MPa, 최고회전수 2500rpm, 배재용적 320cc/rev급 2속(2-speed) 초대형 굴삭기의 주행모터용 유압피스톤모터를 대상으로 정압베어링비가 유압모터의 전 효율에 미치는 영향을 실험적으로 분석하였다.

• 청정기술
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• 제5권2호
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• pp.69-78
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• 1999

수용성 에멀젼형 절삭유의 한외여과 및 정밀여과 특성을 실험적으로 연구하였다. 한외여과막의 경우 오일/물 에멀젼의 투과 거동은 film model을 잘 따랐으나 정밀여과막인 ASYPOR막의 경우에는 이러한 거동을 벗어났다. 본 연구에서 사용된 모든 분리막의 경우 운전압력이 투과유속에는 큰 효과를 나타내지 않았다. 저압에서는 투과 초기 및 후기에서의 투과유속 감소율이 적은 반면 고압에서는 초기 투과유속은 매우 컸으나 투과유속의 감소율이 커서 후기에는 모두 비슷한 투과유속을 보여 주었다. 소수성이 큰 polycarbonate 정밀여과막의 경우 일반적인 경우와는 달리 운전시간이 증가함에 따라 투과유속이 증가하는 경향을 나타내었다. 교반하지 않은 cell에서의 임계투과압력은 150 ppm의 에멀젼 농도에서 약 $2.2kg_f/cm^2$이었으나 500 ppm의 농도에서는 $3.8kg_f/cm^2$ 압력에서 나타났다.

• 한국압력기기공학회 논문집
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• 제7권2호
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• pp.7-13
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• 2011

Turbine journal bearings are designed to support the weight of the rotors on a hydrodynamic oil film and to provide dynamic stability to the rotor system. The life time of journal bearings is infinite theoretically because the journal bearings are separated from the shaft journal by oil film. But poor design, assembly, operation and maintenance can cause problems to the journal bearings. The FMEA(Failure Mode and Effects Analysis) results of the journal bearings show that frequent maintenance of the journal bearings can cause failures and reduction of the bearing life. Therefore, the maintenance periods and history of the journal bearings with the bearing FMEA results are reviewed in order to establish the optimized maintenance period of the journal bearing for the nuclear power plants. Consequently it is necessary to maintain a best condition of lubrication system, reject time-based maintenance and perform the condition-based maintenance of journal bearings in order to maintain optimum condition of the journal bearing.

• Tribology and Lubricants
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• 제33권3호
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• pp.112-118
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• 2017

Tilting pad journal bearings(TPJBs) are widely used for high speed rotating machinery owing to their rotordynamic stability and thermal management feature. With increase in the rotating speed of such machinery, an increasingly important aspect of TPJB design is the prediction of their thermal behaviors. Researchers have conducted detailed investigations in the last two decades, which provided design tools for the TPJBs. Based on these previous studies, this paper presents a thermohydrodynamic(THD) analysis model for TPJBs. To calculate pressure distribution, we solve the generalized Reynolds equation and to predict the lubricant temperature, we solve the 3D energy equation. We employ the oil mixing theory to calculate pad inlet temperature; further, to consider heat conduction via the pad, we solve the heat conduction equation for the pads. We assume the shaft temperature as the averaged oil film temperature and apply natural convection boundary conditions to the pad side and back surfaces. To validate the analysis model, we compare the predicted pad temperatures with those from previous research. The results show good agreement with previous research. In addition, we conduct parametric studies on a TPJB which was used in a gas turbine simulator system. The predicted results show that film temperature largely depends on the rotating speed and oil supply condition.

• Tribology and Lubricants
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• 제25권1호
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• pp.56-60
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• 2009

A journal bearing is used in a hydrodynamic lubrication state, but it becomes a boundary lubrication state that asperity of a contact part touch each other when pressure is too high and an enough oil film is not formed by viscosity change due to lubricating oil temperature. At this time, abrasion due to contact between a journal and a bearing is unavoidable, and scuffing damage that the journal adheres to the bearing occurs if the process is repeated. Damage of the journal bearing is an important problem because it gives huge damage to a machine and can generate large accidents such as economic loss and human life damage. In this study, method for using the pull-up resistor concept was introduced as the monitoring technology. This monitoring system is important to enhance reliability of the engine.

• Tribology and Lubricants
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• 제40권1호
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• pp.28-37
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• 2024

This paper presents the development of a squeeze film damper (SFD) test rig and experimental identification of the effects of clearance, damper length, journal eccentricity ratio, excitation amplitude, oil supply pressure, and oil flow rate on the damping coefficients of a test SFD with open ends and a central groove. Test data are compared with predictions from a simple model developed for short SFDs with open ends and a central groove. The test results show a significant decrease in the damping coefficient with increasing clearance and a dramatic increase with damper length, which are in good agreement with the simple model predictions. According to the simple model, the damping coefficient is inversely proportional to the cube of the clearance and directly proportional to the cube of the length. An increase in the journal eccentricity ratio results in a dramatic increase in the damping coefficient by as much as 15 times that of the concentric case, particularly at low excitation frequencies. By contrast, the measured damping coefficient remains almost constant with changes in the excitation amplitude and supply pressure, which are not major factors in the damper design. In general, the test data agree well with the simple model predictions, excluding cases that show increases in the SFD length and journal eccentricity, which indicate significant dependency on the excitation frequency.

• Tribology and Lubricants
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• 제33권5호
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• pp.207-213
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• 2017

In sliding bearings, viscous friction due to high shear acting on the bearing surface raises the oil temperature. One of the mechanisms responsible for generating the load-carrying capacity in parallel surfaces is known as the viscosity wedge effect. In this paper, we investigate the effect of film-temperature boundary conditions on the thermohydrodynamic (THD) lubrication of parallel slider bearings. For this purpose, the continuity equation, Navier-Stokes equation, and the energy equation with temperature-viscosity-density relations are numerically analyzed using the commercial computational fluid dynamics (CFD) code FLUENT. Two different film-temperature boundary conditions are adopted to investigate the pressure generation mechanism. The temperature and viscosity distributions in the film thickness and flow directions were obtained, and the factors related to the pressure generation in the equation of motion were examined in detail. It was confirmed that the temperature gradients in the film and flow directions contribute heavily to the thermal wedge effect, due to which parallel slider bearing can not only support a considerable load but also reduce the frictional force, and its effect is significantly changed with the film-temperature boundary conditions. The present results can be used as basic data for THD analysis of surface-textured sliding bearings; however, further studies on various film-temperature boundary conditions are required.

• 대한조선학회논문집
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• 제42권3호
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• pp.259-267
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• 2005

The effects of hull flexibility on shaft alignment are growing as ship sizes are increased mainly for container carrier and LNG carrier. In order to consider hull flexibility on a propulsion shafting system, standardization of ship service conditions is necessary because hull deformation is continuously variable according to ship service conditions. How to summarize ship service conditions is suggested based on practically applicable four viewpoints : hull, engine, loading and sea status. Effects of the external forces acting on a ship propulsion shafting system are generally commented. Several design criteria regulated by classification societies are pointed at issue which seems to have Insufficient technical background. A qualitative verification is carried out to point out the invalidity of the assumption of effective supporting position. In this work, an elastic nonlinear multi-supporting bearing system is introduced as a key concept of the elastic shaft alignment. Hertz contact theory is proved to be more proper one than projected area method in calculation of the nonlinear elastic stiffness of the bearing, The squeezing and oil film pressure calculations in the long journal bearing like an after stern tube bearing are recognized as a necessary process for elastic shaft alignment design.

• Tribology and Lubricants
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• 제21권4호
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• pp.159-164
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• 2005

An experimental study was conducted to evaluate characteristic variation of diluted engine oils in which contains diesel fuels and its tribological effects on engine components. In this study, diluted engine oils with $10\%,\;15\%,\;and\;20\%$ of initial fuel content rate have been used for measuring the viscosity reduction rate, blow-by gas increment rate, main gallery pressure reduction rate, and fuel content rate in engine oils. These parameters are strongly related to the tribological characteristics of key engine components. The kinematic viscosity of engine oils in which is contained by diesel fuels from $10\%\;to\;20\%$ in oils is decreasing to approximately $54\%$ of initial diluted fuel-oil volume ratios. The experimental results show that the distillated engine oil decrease the viscosity of engine oil and its oil film stiffness, and increase the wear rate of rubbing parts of engine components. Thus we recommend that the containing volume rate of fuels in engine oils should be restricted to $3\~4\%$ for a sophisticated Diesel engine and $5\~7\%$ for a standard one.