• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.531-535
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• 2008

Present study examines the detonation wave propagation characteristics in annular channel. A normalized value of channel width to the annular radius was considered as a geometric parameter. Numerical approaches used in the previous studies of detonation wave propagation were extended to the present study with OpenMP parallelization for multicore SMP machines. The major effect of the curved geometry on the detonation wave propagation seems to be a flow compression effect, regardless of the detonation regimes. The flow compression behind the detonation wave by the curved geometry of the circular channel pushes the detonation wave front and results in the overdriven detonation waves with increased detonation speed beyond the Chapmann-Jouguet speed. This effect gets stronger as the normalized radius smaller, as expected. The effect seems to be negligible beyond the normalized radius of 10.

• Steel and Composite Structures
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• v.18 no.4
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• pp.1023-1044
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• 2015

Concrete-filled tubes (CFT), formed by an outer steel tube filled with plain or reinforced concrete inside, have been increasingly used these recent decades as columns or beam-columns, especially for tall buildings in seismic areas due to their excellent structural response. This improved behavior is derived from the effect of confinement provided by the tube, since the compressive strength of concrete increases when being subjected to hydrostatic pressure. In circular CFTs under compression, the whole tube is uniformly tensioned due to the radial expansion of concrete. Contrarily, in rectangular and square-shaped CFTs, the lateral flanges become subjected to in-plane bending derived from this volumetric expansion, and this fact implies a reduction of the confinement effect of the core. This study presents a numerical analysis of different configurations of CFT stub columns with inner stiffening plates, limited to the study of the influence of these plates on the compressive behavior without eccentricity. The final purpose is to evaluate the efficiency in terms of strength and ductility of introducing stiffeners into circular and square CFT sections under large deformation axial loading.

• Journal of Energy Engineering
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• v.11 no.1
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• pp.74-80
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• 2002

In this study, a numerical method for fuel droplet evaporation in cylinder of S.I. engine is presented. This study was newly defined non-dimensional critical droplet lifetime and modeled heating and evaporation processes of fuel droplet during intake and compression stroke of gasoline engine. The simulation results show that simultaneous increase of gas temperature and pressure in compression stroke seems to have compensative effect on droplet gasification rate. The environment variations in cylinder have little effect on the fuel droplet gasification process. The droplet size for full evaporation at the end of compression stroke can be estimated using this program.

• Journal of the Korean Society of Combustion
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• v.15 no.4
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• pp.53-57
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• 2010

The purpose of the present work is to investigate the effect of gasoline-premixing on a combustion and emissions characteristics in a compression ignition engine. For studying combustion characteristics, a combustion pressure and rate of heat release (ROHR) were measured using a single-cylinder DI compression ignition engine with a common-rail injection system and premixed fuel injection system. In addition, exhaust emissions characteristics were studied using emission analyzers and smoke meter. The experimental results showed that the case of gasoline-premixing had longer ignition delay and lower combustion pressure compared to the cases of diesel direct injection. Furthermore, premixed gasoline-air mixture reduced NOx emissions due to low peak of ROHR.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.311-318
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• 2000

In constructions of dams and ports structure, gravels are used as principle structural materials. Gravels have different material property compared with other materials like soil and concretes, etc. For example, material properties of gravels obtained from normal triaxial compression test are usually overestimated due to scale and penetration effects. Also, material properties of gravels under dynamic loads are the main interest when structural behavior of rockfill dam under earthquake loads is analyzed. The development of large triaxial compression apparatus is needed for the better estimation of material property of gravel. This paper reports work in progress to development of large triaxial compression apparatus.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.863-864
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• 2005

In recent years, we use overdriving scheme to improve the response time of the liquid crystal. Since conventional overdriving scheme uses memory to perform ideal processing, it is desired to reduce system cost by decreasing the data stored in these SDRAMs. As a general compression method, quantization, sub-sampling and Block Truncation Coding ( BTC ) are used, which process data in block base and cause block effect. So we proposed new data compression method by color space conversion. Because this method compresses luminance and chrominance signal by different ratio, it can efficiently reduce error of block effect in decompression image.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.777-781
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• 1997

In this study, the effect of strain-rate and inital solid fraction on the deformation behaviour of semi-solid material is investigated, when semi-solid forging is performed by the process of closed-die compression using A356 alloy of which the above results can be practically applied for industrical purpose. In order to simulate densification in the deformation of semi-solid material, the semi-solid material is assumed to be composed of solid region following rigid visco-plastic material, the liquid region following Darcy's law for the liquid flow saturated in the interstitial space. Simulation results of closed-die compression and simple upsetting under different strain-rate and initial solid fraction are compared.

• Transactions of Materials Processing
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• v.6 no.4
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• pp.338-345
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• 1997

The behaviour of alloys in the semi-solid state strongly depends on the imposed stress stage and on the morphology of the phase which can vary from dendritic to globular. To optimal net shape forging of semi-solid materials, it is important to investigate for material behaviour for variation of strain rate. Therefore, to investigate the effect of compression speed on deformation of aluminum alloy with globular microstructure, the compression test for semi-solid aluminum alloy with controlled solid fraction is perform by material test system which is attracted with furance. The behavior of semi-solid aluminum alloy were discussed for the various solid fraction and die speed. The material constants in stress-strain were are also proposed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.737-740
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• 2002

Pressure fluctuation in the cylinder is one of the major sources on noise emission in oil hydraulic piston pumps. This paper reports an experimental study of pressure fluctuation characteristics in the cylinder of oil hydraulic piston pumps. We measured pressure fluctuation at BDC with delivery pressure, rotational speed. Because the pre-compression and the V-grooves in the valve plate is known of noise reduction, we investigated also the effect of pre-compression and V-grooves at the ends of the kidney ports with four types valve plates. We found that the pre-compression and the V-grooves in valve plate could reduce the noise of oil hydraulic piston pumps.

• Proceedings of the KSR Conference
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• 1999.05a
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• pp.406-413
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• 1999

A compression wave is generated by the high speed train which enters a tunnel, and it propagates along the tunnel. When the compression wave emerges from the exit of the tunnel, it causes an impulsive noise, and the strength of the impulsive noise depends on the pressure gradient of the first compression wave. So it needs to reduce the pressure gradient for the minimization of impulsive noise. The entrance hood is used for the reduction of the pressure gradient. In the present study, the pressure transients were numerically calculated for three shapes of hood, In order to validate the numerical simulation, the pressure and pressure gradient were compared with the experimental data of moving model rig. The calculation results won well agreed with the experimental data, and also showed that the hood had an effect on the pressure gradient of the tunnel inside.