• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제29회 춘계학술대회
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• pp.175-181
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• 1999

The present work is an attempt to calculate the steady state pressure and perturbed pressure of journal bearings that has a helical groove. A coordinate is fitted to the helical groove and governing equation is derived by applying generalized coodinate system to the divergence formulation method. This method makes it possible to deal with an arbitrary configuration of a lubricated surface. The dynamical response of shaft-bearing system is calculated using the bearing reaction force and external force.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2003년도 학술대회지
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• pp.281-288
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• 2003

In this paper, seismic responses of large tilting pad journal bearings which have $3\~5$ tilting pads were numerically analyzed. The turbulent lubrication equation, the energy equation and motion equation were solved at each time step. The regime of operation of this bearing is laminar, turbulent and transitional. Also viscosity of working fluid was considered as function of only temperature and inlet pressure build-up was considered. Numerical results for a large tilting pad journal bearing showed journal center, maximum temperature, maximum pressure, friction torque. The relationship of bearing response and seismic intensity are discussed.

• Tribology and Lubricants
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• 제10권1호
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• pp.69-77
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• 1994

Oil flow pass of hermetic scroll compressor with back pressure chamber was described. Dynamic analysis was preceded in order to obtain the loads on the lubricating contacts. The mobility method of dynamically loaded journal bearings was applied to the crank jornal bearing and lower main bearing, and they could be designed to operate under fluid film lubrication. From the consideration of their film thicknesses and oil flow rates, optimal bearing clearances or other bearing dimensions could be assessed. The major friction loss was calculated to be from the axial force between the two scrolls. Therefore, it was suggested that the designers should be careful to reduce the over-turning moment on the orbiting scroll.

• Tribology and Lubricants
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• 제2권2호
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• pp.44-51
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• 1986

An experimental investigation is carried out to Study the cavitation in a journal bearing with pressurized lubricant supply. Visual observations are performed at various shaft speeds and supply pressure levels. Oil film pressure is measured at various shaft speeds under the submerged condition. Results from visual observations show that the extent of cavitation is reduced as supply pressure increases. The film pressure measurements indicate the occurrence of a negative pressure loop upstream of the cavitation region and a constant cavitation Pressure through the cavitation region.

• 대한기계학회논문집
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• 제17권8호
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• pp.1921-1930
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• 1993

In order to evaluate the inlet pressure correctly, the full Navier-Stokes equations are solved numerically for the computational domain which covers the cavity region between pads as well as the bearing film. A nonuiform grid system is adopted to reduce the number of grid points, and the numerical solutions are obtained for a wide range of Reynolds number in laminar regime with various values of the distance between pads. The numerical results show that the inlet pressure is significantly affected by Reynolds number and the distance between pads. An expression for the loss coefficient in terms of Reynolds number and non-dimensional distance between pads is obtained on the basis of the numerical results. It is found that the inlet pressure over the whole range of numerical solutions can be fairly accurately estimated by applying the formula for the loss coefficient to the extended Bernoulli equation.

• Tribology and Lubricants
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• 제5권2호
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• pp.68-76
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• 1989

In this paper, the influence of ram-pressure on the static and dynamic characteristics of infinite width tilting-pad journal bearing is investigated theoretically. The ram-pressure is obtained by assumption of conservation of mechanical energy of the lubricant flow through the leading edge of the pad. The pressure in the lubricating film is numerically calculated using the ram-pressure obtained as the inlet pressure boundary condition of the pad. The static equilibrium state of tilting-pad journal bearing is determined by Newton-Raphson iteration method. A numerical results are presented in graphic form and relationships between the ram-pressure and the static and dynamic characteristics are discussed.

• 한국지반공학회지:지반
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• 제12권4호
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• pp.33-46
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• 1996

지지력이 부족한 지반에 구조물을 축조할 경우 기초지반의 변형으로 인하여 구조물에 침하나 균열이 발생하게 된다. 이러한 기초지반을 보강하기 위하여 최근에는 고압분사주입공법으로 지중에 지반개량체를 조성하여 기초보강말뚝으로 사용하고 있다. 본 논문은 2중관 고압분사주입공법에 의해 기초지반에 시공된 지반개량체에 대하여 실내시험 및 현장말뚝재하시험을 실시하여 지반보강효과 및 지지력을 검토하였다. 시험결과 지반개량체는 원지반의 특성에 따라 약간의 차이는 있으나 충분한 지반보강효과를 얻을 수 있는 것으로 나타났으며 현장타설말뚝으로서 충분한 지지력을 유지하고 있어 구조물의 침하를 억제하는데 효과가 있는 것으로 나타났다.

• Tribology and Lubricants
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• 제34권3호
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• pp.107-114
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• 2018

This paper presents a computational model of a gas foil journal bearing with shim foils between the top foil and bumps, and predicts its static and dynamic performance. The analysis takes the previously developed simple elastic foundation model for the top foil-bump structure and advances it by adding foil models for the "shim foil" and "outer top foil." The outer top foil is installed between the (inner) top foil and bumps, and the shim foil is installed between the inner top foil and outer top foil. Both the inner and outer top foils have an arc length of $360^{\circ}$, but the arc length of the shim foil is shorter, which causes a ramp near its leading edge in the bearing clearance profile. The Reynolds equation for isothermal and isoviscous ideal gas solves the hydrodynamic pressure that develops within the bearing clearance with preloads due to the ramp. The centerline pressure and film thickness predictions show that the shim foil mitigates the peak pressure occurring at the loading direction, and broadens the positive pressure as well as minimum film thickness zones except for the shortest shim foil arc length of $180^{\circ}$. In general, the shim foil decreases the journal eccentricity, and increases the power loss, direct stiffness, and damping coefficients. As the shim foil arc length increases, the journal eccentricity decreases while the attitude angle, minimum film thickness, and direct stiffness/damping coefficients in the horizontal direction increase.

• 한국정밀공학회지
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• 제23권10호
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• pp.103-112
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• 2006

This paper describes a theoretical analysis and experimental verification on the performances of a vacuum-compatible air bearing, which is designed with a cascaded exhaust scheme to minimize the air leakage in a vacuum environment. The design of the vacuum-compatible air bearing equipped with the differential exhaust system requires great care because several design parameters, such as the number of exhaust stages, diameter of exhaust tube, pumping speed of a vacuum pump, and bearing clearance greatly influence the air leakage and thus degree of vacuum. In this study, a performance analysis method was proposed to estimate the performances of the air bearing, such as load capacity, stiffness, and air leakage. Results indicate that the load capacity and stiffness of the air bearing was improved as its boundary pressure, which was determined by the $1^{st}$ exhaust method, was lowered, and the dominant factors on the chamber's degree of vacuum were the number of exhaust stages, exhaust tube diameter and bearing clearance. A vacuum chamber and air bearing stage using porous pad were fabricated to verify the theoretical analysis. The results demonstrate that chamber pressure up to an order of $10^{-3}$ Pa was achieved with the air bearing stage operating inside the chamber, and this analysis method was valid by comparing predicted values with experimental data, for the mass flow rates from the porous pad, and pressures at each exhaust port and chamber, respectively.

• Geomechanics and Engineering
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• 제19권1호
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• pp.21-28
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• 2019

Use of cement in stabilizing the sulfate-bearing clay soils forms ettringite/ thaumasite in the presence of moisture leads to excessive swelling and causes damages to structures built on them. The development and use of non-traditional stabilisers such as alkali activated ground granulated blast-furnace slag (AGGBS) and enzyme for soil stabilisation is recommended because of its lower cost and the non detrimental effects on the environment. The objective of the study is to investigate the effectiveness of AGGBS and enzyme on improving the volume change properties of sulfate bearing soil as compared to ordinary Portland cement (OPC). The soil for present study has been collected from Tilda, Chhattisgarh, India and 5000 ppm of sodium sulfate has been added. Various dosages of the selected stabilizers have been used and the effect on plasticity index, differential swell index and swelling pressure has been evaluated. XRD, SEM and EDX were also done on the untreated and treated soil for identifying the mineralogical and microstructural changes. The tests results show that the AGGBS and enzyme treated soil reduces swelling and plasticity characteristics whereas OPC treated soil shows an increase in swelling behaviour. It is observed that the swell pressure of the OPC-treated sulfate bearing soil became 1.5 times higher than that of the OPC treated non-sulfate soil.