• Journal of computational fluids engineering
• /
• v.19 no.4
• /
• pp.20-28
• /
• 2014

An efficient solution algorithm for simulating free surface problem is presented. Navier-Stokes equations for variable density incompressible flow are employed as the governing equation on Cartesian meshes. In order to describe the free surface motion efficiently, VOF(Volume Of Fluid) method utilizing THINC(Tangent of Hyperbola for Interface Capturing) scheme is employed. The most time-consuming part of the current free surface flow simulations is the solution step of the linear system, derived by the pressure Poisson equation. To solve a pressure Poisson equation efficiently, the PCG(Preconditioned Conjugate Gradient) method is utilized. This study showed that the proper application of the preconditioner is the key for the efficient solution of the free surface flow when its pressure Poisson equation is solved by the CG method. To demonstrate the efficiency of the current approach, we compared the convergence histories of different algorithms for solving the pressure Poisson equation.

• Tribology and Lubricants
• /
• v.30 no.5
• /
• pp.284-290
• /
• 2014

The influence of round embossed surface on slider bearing characteristics and its load carrying capacity is discussed for thin film effect of embossed slider bearing. For the numerical computation of lubrication parameters such as pressure, load capacity and shear stress that are normalized and a Reynolds equation is used for the analysis of embossed slider bearing characteristics. For this purpose, the finite difference method of central difference scheme is used in this study. In a slider bearing with embossed form, several simulation parameters such as pressure, load capacity and shear stress of the bearing can be obtained according to independent parameters such as the slope of the slider bearing and number of embossing in the upper slider. Also this results can be summarized and be stored in sequential data file for latter analysis. After all, their distribution of the pressure and shear stress parameters can be displayed and be analyzed easily by using the developed program with matlab GUI technique. The independent parameters such as a number of embossing and a slope of the embossed surface slider are used for discussing simulation parameters of pressure distribution, shear stress and load carrying capacity of the round embossing. These study results reported in this paper should be applied to the other shaped slider bearing with a rectangular embossed surface or rectangular waved surface.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2004.03a
• /
• pp.774-778
• /
• 2004

The atomization process of a circular $SF_{6}$ liquid jet issued into an otherwise quiescent, high-pressure $N_2$ gas was observed to explore the breakup mechanism of liquid ligaments involved in turbulent atomization. Both liquid and gas temperatures were fixed at a room temperature but the gas pressure was elevated to more than twice the critical pressure of $SF_{6}$. Therefore, the liquid surface was in a thermodynamic state close to a critical mixing condition with suppressed vaporization. Since the surface tension and the surface gas density approach zero and the surface liquid density, respectively, phenomena equivalent to those which would appear when a very high speed laminar flow of water were injected into the atmospheric-pressure air can be observed by issuing $SF_{6}$ liquid at low speeds in micro-gravity environment which avoid disturbances due to gravity forces. The instability ob near-critical mixing surface jet was quantitatively characterized using a newly developed device, which could issue a very small amount of $SF_{6}$ liquid at small constant velocity into a very high-pressure $N_2$ gas.

• Nuclear Engineering and Technology
• /
• v.52 no.10
• /
• pp.2183-2195
• /
• 2020

A mathematical model for the flowrate and rotation speed of RCP during idling was established. The numerical calculation method and dimensionless method were used to analyze the flow, head, torque and pressure and speed changes under idle conditions. Regularity, using the Q criterion vortex identification judgment method combined with surface flow spectrum morphology analysis to diagnose the vortex dynamic characteristics on RCP blade. On impeller blade, there is two oscillations in the pressure ratio on pressure surface in blade outlet region. The velocity on the suction surface is two times more oscillating than the inlet of blade, and there is an intersection with the velocity ratio curve on pressure surface. On blade of guide vane, the pressure ratio increases along the inlet to outlet direction, and the speed ratio decreases with the increase of idle time. There is a vortex that rotates counterclockwise on the suction surface, and the streamline on the suction surface of blade is subjected to the entrainment and blocking action of the vortex creates a large reverse flow in the main flow region. There are two vortices at the outlet of guide vane suction side and the vortices are in opposite directions.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
• /
• 2002.02a
• /
• pp.253-255
• /
• 2002

Since a butt Joint is smaller than a lap type joint, it is expected to have smaller AC losses. The butt joint is produced by the diffusion bonding of the contacting surface under pressured and heated condition. It is important to find robust joining conditions, because butt joint has small contact area and has the shape by which the quality of bonding is hard to be checked. In this research, the loading pressure is considered as the joining parameter to find optimum joining condition. The DC resistance of the joint may be changed by the surface pressure during joining process, because the superconducting strands near the contact surface are failed by large plastic deformation. The range from 10 MPa to 18 MPa is expected optimum surface pressure in the conditions of 1 hour heating time and $750^{\circ}C$ temperature in the vacuum furnace.

• Journal of the Korean Society for Precision Engineering
• /
• v.25 no.7
• /
• pp.124-130
• /
• 2008

The effect of nitrogen gas pressure in arc ion plating on surface properties of the TiN-coated high speed steel(SKH51) is presented in this paper. The surface roughness, micro-particle, micro-hardness, coated thickness, atomic distribution of TiN, and adhesion strength are measured fur various nitrogen gas pressures. It has been shown that the nitrogen gas pressure has a considerable effect on the surface roughness, adhesion strength, atomic distribution of TiN, and surface deposition of TiN of the high speed steels but that it has little influence on the micro-hardness and coated thickness.

• Journal of Mechanical Science and Technology
• /
• v.15 no.3
• /
• pp.384-391
• /
• 2001

The aerodynamic effects of a 3-dimensional Wing in Ground Effect (WIG) which moves above the free surface has been numerically investigated via finite difference techniques. The air flow field around a WIG is analyzed by a Marker & Cell (MAC) based method, and the interactions between WIG and the free surface are studied by the pressure distributions on the free surface. Waves are generated by the surface pressure distribution, and a Navier-Stokes solver has been employed, to include the nonlinearities in the free surface conditions. The pressure values Cp and lift/drag ratio are reviewed by changing the height/chord ratio. In the present computations a NACA0012 airfoil with a span/chord ratio of 3.0 are treated. Through computational results, it is confirmed that the free surface can be treated as a rigid wavy wall.

• Proceedings of the KSR Conference
• /
• 2011.05a
• /
• pp.70-77
• /
• 2011

When a train passes a conventional tunnel at high speed, an environmental noise issue arises by pressure variation and micro-pressure waves at the exit of the tunnel. It is known that this issue can be reduced by using dummy tunnel duct on the tunnel entrance. We studied the variances of micro-pressure waves at the exit of tunnel and pressure variation within the tunnel, by altering surface area and length of the dummy tunnel duct. For analyze this train-tunnel relation problem, axi-simmetric steady compressible flow solver was used. Changing the length of the dummy tunnel duct can adjust pressure variation, changing the surface area of the dummy tunnel duct can adjust volume and pressure variation of the micro-pressure wave. Thus, optimized surface area and length of the dummy tunnel duct can simultaneously reduce environmental noise pollution by micro-pressure wave and issues by the pressure variation.

• Journal of Biosystems Engineering
• /
• v.42 no.3
• /
• pp.136-146
• /
• 2017

Purpose: This paper presents an appropriate wrapping method by analyzing the pressure distribution applied to a bale surface, along with the change in pressure according to an increase in the number of film layers in rice straw bales, which account for 74% of the total bulky feed supply in Korea. Methods: A model with the shape of an actual bale was fabricated to analyze the distribution of surface pressure in bale wrapping, and the pressure was measured. Experiments were conducted to analyze the pressure using eight different layer numbers (2, 4, 6, 8 10, 12, 14, and 16 layers) at five wrapping speeds (27, 29, 31, 33, and 35 rpm). Results: The maximum pressure applied to a circular bale by the film occurred at the center of the end of the bale, whereas the minimum pressure occurred at the center of the bale side. An extreme value ratio between the minimum and maximum pressures was distributed as 8.5-56.6%, which was improved with an increase in rotation speed. The an uneven pressure distribution occurred because the number of film overlaps was 8.24-times greater at the center of the bale's end than at the center of the ba le side. At a level 5 rotation speed, the minimum pressure was $P_{LV5-M1}=0.0625{\sigma}^2+36.173{\sigma}-36.753$ ($R^2=0.9845$) at $M_1$, and the maximum pressure was $P_{LV5-M6}=5.5552{\sigma}^2+41.05{\sigma}-39.071$ at $M_2$, revealing a correlation of $R^2=0.9983$. Conclusions: To replace four layers with six layers, 2-4 layers were added only to the side of the bale, and the minimum pressure at $M_1$ was then improved from that at four layers to that at six layers, and the amount of film consumed for 4-6 layers was reduced by 84.6%.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.21 no.2
• /
• pp.9-16
• /
• 2013

The comparisons of performance characteristics between the super-mirror face grinding machine using variable air pressure developed in this laboratory to grind precisely the sliding face of a surface hardened workpiece with thermal spray and the conventional one are investigated by measuring the surface roughness and hardness for a SCM440. To process variously workpiece according to shape, size and materials, the rotating and contacting forces of the developed grinding machine can be changed by air pressure. The surface roughness of processed workpiece can be also attained to state of mirror face by grinding precisely the sliding face with changing the rotating speed of diamond wheel. It is possible to be attached to the various machine tools because the super-mirror face grinding machine using variable air pressure is a small size. The grinding efficiency is elevated because it can be worked by two or more grinding machines attached to concurrently a machine tool for the large workpiece. In this study, results show that the cusp height of the super-mirror face grinding machine for the particle size of 100 and $1500No./mm^2$ is lower than that of the conventional one because the vibration is reduced by rotating very fast the diamond wheel with a pressed air and it can be processed by rotating the diamond wheel with a constantly varied air pressure perpendicular to workpiece surface, and that the workpiece in the super-mirror face grinding machine for the particle size of $3000No./mm^2$ can be processed to state of mirror face that is rarely seen by the cusp height. It is also found that the surface hardness of both the conventional and the super-mirror face grinding machines are increased as the particle size of diamond wheel is reduced, and the surface hardness of the super-mirror face grinding machine is HRC 1.1 ~ 1.8 higher than that of the conventional one.