• Journal of the Society of Naval Architects of Korea
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• v.51 no.4
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• pp.328-333
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• 2014

A hybrid particle-mesh method based on the vorticity-velocity formulation for solving the incompressible Navier-Stokes equations is a combination of the Vortex-In-Cell(VIC) method for convection and the penalization method for diffusion. The key feature of the numerical methods is to determine velocity and vorticity fields around a solid body on a temporary grid, and then the time evolution of the flow is computed by tracing the convection of each vortex element using the Lagrangian approach. Assuming that the vorticity and velocity fields are to be computed in time domain analysis, pressure fields are estimated through a complete set of solutions at present time step. It is possible to obtain vorticity and velocity fields prior to any pressure calculation since the pressure term is eliminated in the vorticity-velocity formulation. Therefore, pressure field is explicitly treated by solving a suitable Poisson equation. In this paper, we propose a simple way to numerically implement the vorticity-velocity-pressure formulation including a penalty term. For validation of the proposed numerical scheme, we illustrate the early development of viscous flows around an impulsive started circular cylinder for Reynolds number of 9500.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.3
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• pp.357-366
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• 2003

An experimental study is performed to investigate characteristics of near of wakes of circular cylinders with serrated fins using a hot-wire anemometer for various freestream velocities. The main focus of this paper is to investigate a reason why a vortex formation length is increased suddenly. Velocity of the fluid which flow through fins decreases as fin's height and freestream velocity increases and fin pitch decreases, and a thickness of boundary layer increases. The finned tube has a lower velocity gradient when the higher boundary layer grows. This velocity gradient on finned tube makes a weak shear force in the wake and moves to downstream in a state of lower momentum transfer between the freestream and the wake. The phenomenon makes a vortex formation length increased suddenly. The fluctuations of the velocity distributions on the finned tube and (equation omitted) = 1.0 contour line in the vortex formation region decreases when the fin height increases and the pitch decreases.

• The KSFM Journal of Fluid Machinery
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• v.11 no.2
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• pp.29-37
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• 2008

Air supply is required to the cathode of fuel cells for the provision of oxygen to produce electricity through chemical reaction with hydrogen in the cell, and supplied air should be free of impurities such as oil mist and tiny particles separated from sliding surfaces. Hence, air compressor for fuel cell air supply must be oil-less type and have no severe sliding surfaces inside. This paper introduces the concept of single-vane type rotary air compressor whose structure is particularly suitable for the fuel cell application: sliding action of the vane against the cylinder wall, which causes severe friction in the conventional vane rotary compressors, is made to be prevented by attaching the vane to the driving shaft with the compliant device between the vane and the rotor in this new design. For 2 kW fuel cell application, preliminary design has been carried out, and its performance has been estimated by using computer simulation program: for discharge pressure of 2 bar, the volumetric, adiabatic, and mechanical efficiencies are calculated to be 82.5%, 92.5%, and 96.3%, respectively.

• Transactions of Materials Processing
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• v.13 no.7
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• pp.635-641
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• 2004

Today the specific outputs of modern supercharger DI diesel engine for passenger cars reach values exceeding 50kw/1. By development of the articulated piston, specific output of up to 70kw/1 are sought. In doing so, peak cylinder pressure increases from the current 14-16MPa to 18-20MPa. The Articulated piston was composed Al cast skirt part and steel forged crown part. We have the target fer the design of forging process and die of the steel forged crown part. The design parameters of the forging process of the piston were obtained by the forging industry experiences and our experimental data and analysis result of finite element simulation. Especially, the design parameter of preform in blocker die was decided by finite element simulation using numerical package DEFROM3D. And also we can verify the design parameter by conducting visio-plasticity test using plasticine material. When we compared the results of analysis and experiment, a metal flow and load curve showed good agreement. Through this research, we could design optimal preform shape of articulated piston for this supercharged DI diesel engine.

• Journal of Hydrogen and New Energy
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• v.8 no.2
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• pp.91-97
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• 1997

The goals of this research are to understand the $NO_x$ emission in direct injected diesel engine with premixed hydrogen fuel. Hydrogen fuel was supplied into the test engine through the intake pipe. Amount of hydrogen-supplemented fuel was 70 percent basis heating value of the total fuel. The effects of intake air temperature on $NO_x$ emission were studied. The intake air temperature was controlled by flow rate of liquid nitrogen. The major conclusions of this work include : (i) the tested engine was run without backfire under 70 percent hydrogen fuel supplemented. (ii) radicals of nitrogen gas in the intake pipe were increased by 30 percent and cylinder gas temperature was decreased by 24 percent as the intake air temperature were changed from $23^{\circ}C$ to $0^{\circ}C$ ; and (iii) $NO_x$ emission per unit heating value of supplied fuel was decreased by 45 percent with same decrease of intake air temperature.

• Journal of Mechanical Science and Technology
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• v.18 no.7
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• pp.1169-1176
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• 2004

Soot has a great effect on the formation of PM (Particulate Matter) in D.I. (Direct Injection) Diesel engines. Soot in diesel flame is formed by incomplete combustion when the fuel atomization and mixture formation were poor. Therefore, the understanding of soot formation in a D.I. diesel engine is mandatory to reduce PM in exhaust gas. To investigate soot formation in diesel combustion, various measurements have been performed with laser diagnostics. In this study, the relative soot diameter and the relative number density in a DJ. engine was measured by using LIS (Laser Induced Scattering) and LII (Laser Induced Incandescence) methods simultaneously which are planar imaging techniques. And a visualization D.I. diesel engine was used to introduce a laser beam into the combustion chamber and investigate the diffusion flame characteristics. To find the optimal condition that reduces soot formation in diesel combustion, various injection timing and the swirl flow in the cylinder using the SCV (Swirl Control Valve) were applied. From this experiment, the effects of injection timing and swirl on soot formation were established. Effective reduction of soot formation is possible through the control of these two factors.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.5
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• pp.549-555
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• 2016

This research was performed to determine the oil separation characteristics of the specially designed oil filter installed in a PCV cylinder head passage. The oil filter was specially designed with fleece for separating oil mist from blow-by gas. The fleece, made of fiber fabric material, is placed in the oil filter case to absorb oil mist with a small pressure drop during blow-by gas through the filter. To do this, 3-D CFD analysis was simulated for the simplified PCV system with the oil filter using the commercial code, Ansys CFX. Results showed that the oil filter's efficiency with fleece sharply increased as oil droplet size increased.

• 한국해양학회지
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• v.29 no.3
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• pp.296-303
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• 1994

Rotating right cylinder of rigid sloping boundaries(top-bottom) is filled with two-layered fluid. External fluid which has the same density as the lower-layer is pumped through the rim boundary at the bottom, and this induces uniform vertical velocity in the interior that produces the Sverdrup type motion such as southward flowing western boundary current with northward interior horizontal motion. The rigid sloping upper boundary meets with lower layer to simulate so called "polar front", and the upper-layer motion influenced by the lower-layer flow has been observed. Barotropic motion in the western part of the basin while baroclinic motion in the eastern half is always present. In particular, both southward flowing eastern boundary flow and western boundary flow meets near the western wall and it induces northward western boundary flow to separate from the boundary With increased ${\beta}$-effect on the upper0layer the width of western boundary decreases and the separated western boundary flow moves into the interior to form an eddy-like motion. Baroclinic Rosebay wave clearly observed in the easter boundary slowly propagates to the west but it seems to be decayed before travelling to the western boundary. A local topograpic effect imposed on the lower-layer causes very sensitive response of upper layer boundary flows. In the east standing0wave0like features are observed in the west whereas the width of the boundary increases without any evidence of the separation of the western boundary flow.This may be due to the gact that even the lower-lauer barotropic motion feels the topography its influence does not propagate into the upper-layer. With large ${\beta}$-effect on the upper-layer,relatively large scale waves whose wavelengths are greater than the internal radius deformation exist in the interior.

• Journal of Ocean Engineering and Technology
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• v.27 no.3
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• pp.43-52
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• 2013

In the present study, a flow analysis for estimating the wave loads acting on a stationary floating body inside a viscous numerical wave tank was performed using the commercial software FLUENT. The governing equations for the viscous and incompressible fluid motion were the continuity and Navier-Stokes equations, and a piston-type wavemaker was employed to reproduce wave environments. First, the optimal simulation conditions were derived through numerical tests for the wavemaker and wave absorber, and then the wave loads and wave run-up on a vertical truncated cylinder were estimated and compared with the experimental and other numerical results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1575-1582
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• 1992

This study describes the response performances of actual engine speed, turbocharger speed, air mass flow rate through engine, boost pressure ratio, exhaust temperature and combustion efficiency for a six-cylinder four-stroke turbocharged diesel engine during the change in operating conditions by using the computer simulation with test bed. In order to obtain the transient conditions, a suddenly large load was applied to the simulation engine with the several kinds of inertia moment in turbocharger and engine, and engine set speed. From the results of this study, the following conclusions were summarized The inferior response performances was mainly caused by turbocharger lag, and air mass flow rate and boost pressure ratio were closely related to the turbocharger speed. A reduced moment of turbocharger inertia resulted in less transient speed drop and much faster recovery to the steady state of the engine. The increase of moment of engine inertia reduced cyclic variation of engine speed. When a large load was applied to the engine at high speed, the engine could be fastly recovered. However, when the same load was applied to the engine at low speed, the engine was stalled.