• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.345-348
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• 2006

In sheet metal forming process using press and draw die some defect can be made because of the high pressure of air pocket between draw die and the product. The purpose of this study is to develop a program to decide an optimal combination of air vent hole size and number to prevent those defect on product. The air inside air pocket is considered as ideal gas and the compression and expansion is assumed as isentropic process. The mass flow is computed in two flow condition: unchocked and chocked condition. The present computation obtains required cross-sectional area of air vent hole for not exceeding the user specified pressure such as the pressure for yielding strength of the product or the pressure for unchocked flow. To validate the program the present results are compared with the results of other researchers and commercial CFD code.

• Journal of the Society of Naval Architects of Korea
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• v.58 no.5
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• pp.271-280
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• 2021

The code developed using a pressure-based method for unified conservation laws of incompressible/compressible fluids is expanded to handle moving or deforming body boundaries using the hybrid Cartesian/immersed boundary method. An instantaneous pressure field is calculated from a pressure Poisson equation for the whole fluid domain, including the compressible gas region. The polytropic gas is assumed for the compressible fluid so that the energy equation is decoupled. Immersed boundary nodes are identified based on edges crossing body boundaries. The velocity vector is reconstructed at the immersed boundary node using an interpolation along the assigned local normal line. The developed code is validated by comparing the time histories of pressure and wave elevation for sloshing in a rectangular and a membrane-type tank. The validated code is applied to simulate air cushion effects in a rectangular tank under sway motion. Time variations of pressure fields are analyzed in detail as the air pocket pulsates. It is shown that the contraction and expansion of the air pocket dominate the pressure loads on the wall of the tank. The present results are in good agreement with other experimental and computational results for the amplitude and the decay of the pressure oscillations measured at the pressure gauges.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.6
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• pp.10-18
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• 2008

Metal stamping is widely used in the mass-production process of the automobile industry. During the stamping process, air may be trapped between the draw die and the panel. The high pressure of trapped air induces imperfections on the panel surface and creates a situation where an extremely high tonnage of punch is required. To prevent these problems, many air ventilation holes are drilled through the draw die and the punch. The present work has developed a simplified mathematical formulation for computing the pressure of the air pocket based on the ideal gas law and isentropic relation. The pressure of the air pocket was compared to the results by the commercial CFD code, Fluent, and experiments. The present work also used the Bisection method to calculate the optimum cross-sectional area of the air ventilation holes, which did not make the pressure of the air pocket exceed the prescribed maximum value.

• Journal of the Society of Naval Architects of Korea
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• v.60 no.3
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• pp.193-201
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• 2023

A developed code based on the unified conservation laws of incompressible/compressible fluids is applied to analyze similarity in pressure oscillations caused by pulsating air pockets in sloshing tanks. It is shown that the nondimensional time histories of pressure show good agreements under Froude and geometric similarities, provided that there are no pulsating entrapped air pockets. However, the nondimesional period of pressure oscillation due to the pulsating air pocket becomes longer as the size of the sloshing tank increases. The discrepancy in the nondimensional period is attributed to the compressibility bias of the entrapped air. To get rid of the compressibility bias, the ullage pressure in a sloshing tank is adjusted based on the Bagnold's impact number. The variation in the period of pressure oscillation according to the ullage pressure is explained based on the spring-mass system. It is shown that the nondimensional period of pressure oscillation is virtually constant when the ullage pressure is adjusted based on the Bagnold's impact number, regardless of tank size. It is found that the Bagold's impact number should be the same, if the time history of pressure is important while an entrapped air pocket pulsates.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.5
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• pp.119-125
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• 2017

In this paper, the characteristics and load carrying capacity of square pocket surfaces on a slider bearing are discussed for the thin film effect by the square pocket slider bearing. To study the lubrication, a Reynolds equation is used in this paper for the analysis of the slider bearing characteristics with square pocket surfaces. For numerical analysis, the central differencing scheme finite difference method is used. In a slider bearing with square pocket surfaces, the simulation dependent parameters such as pressure and load carrying capacity of the bearing can be acquired from the independent parameters, the slope of the slider bearing and number of pockets on the upper slider. These results can be acquired by the programmed softwar,e and they can be analyzed and stored in a sequential data file for later analysis. Furthermore, their pressure and load capacity distribution can be displayed easily by using the developed program with the Matlab GUI.

• Tribology and Lubricants
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• v.22 no.2
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• pp.93-98
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• 2006

The numerical analysis of the negative pressure porous gas bearings is presented. The pressure distribution is calculated using the finite difference method. The Reynolds equation and Darcy's equation are solved simultaneously. The air bearing stiffness and damping are evaluated using the perturbation method. Rectangular uniform grid is employed to model the bearing. The vacuum preloading is considered. The pressure in the vacuum pocket is assumed to be a constant negative pressure. The total load, stiffness, damping and flow rate are calculated fur several geometrical configurations and several values of negative pressure. It is found that too large vacuum pocket can result in negative total force.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1989.11a
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• pp.94-99
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• 1989

This paper analyzes file stiffness, damping coefficient, friction force and flow coefficient of externally pressurized oil journal beating, including the effect of journal rotation according to the Sommerfeld number. This paper assumed that the oil in the whole pocket has constant pressure, and that the oil in the whole bearing region has constant viscosity, temperature and density. Reynolds equation is derived from Nuvier - Stokes equation and continuity equation. And solved bearing pressure by ADI method for whole bearing region and fitted with out flow rate of pocket region. The model for numerical simulation is hydro - static oil journal bearing for high-speed, high-accuracy lathe spindle.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.186-193
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• 2001

In the high pressure state, the leakage flow rate of hydraulics is one of serious problems and the great reason to decrease the volume efficiency. In this paper, I tried to clarify tribology characteristics for the slipper hydrostatic bearing in swash plate type axial piston pumps and motors by means of experiment . I measured the leakage flow rate between swash plate and piston shoe with change the supply pressure and oil temperature at a swash plate angle of 0。 . And I also investigated the slipper pocket pressure and calculated oil film thickness for theoretical method. So. 1 have analyzed the tribology characteristics of hydrostatic bearing for leakage flow rate and oil film thickness with oil temperature and supply pressure.

• Journal of Power System Engineering
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• v.20 no.6
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• pp.34-39
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• 2016

This paper is the numerical study on the correlation of leakage by the variation of inlet pressure and clearance in hydrostatic bearing. The main goal of this study is to apply to the design of hydro system the results that the pocket pressure and the leakage rate according to the inlet pressure and the clearance between piston and cylinder tube. Because the hydrostatic bearing in hydraulic cylinder has the narrow rectangular channel between piston and cylinder tube, so to verify the numerical scheme, it has been compared with the experimental results of Brackbill and Kandlikar. The pressure data of numerical results inside narrow rectangular channel correlate was showed a good agreement with experimental results, thereby the numerical scheme was applied to the real model that is a hydraulic cylinder with the hydrostatic bearing. In conclusion, the pressure differences between inlet and pocket were shown within 3%. Leakage rates were showed rapidly increased pattern between about 4.5 and 6.7 times because the section area to calculate the leakage rates were proportioned to a square of diameter. The correlation equation was calculated among the inlet pressure, the clearance and the leakage rate by using the linear regression.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.181-186
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• 2002

Lately, as going on increasing in the demand of high power density(power/weight), it is necessary for hydraulic axial piston pump/motor to operate more high pressure and speed. But in these condition, there are some trouble like as friction loss. To reduce this friction loss, hydrostatic bearing is used far axial piston pump/motor frequently. In general, it is difficult to measure accurate friction torque of spherical hydrostatic bearing in the use of the existing devices. So, we have developed the measurement device using the reaction torque sensor to obtain the pure friction torque, fitted in the casing. In this report, we intend to make an introduction about this measurement device for friction torque of the spherical wear part and clarify the effect of friction characteristics on supply pressure and rotational speed with three types of pocket size by using this measurement device.