• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1384-1388
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• 2003

In structural fires, flashover is characterized by the rapid transition in fire behavior from localized burning of fuel to the involvement of all combustibles in the enclosure. An investigation of parameter effects on the time to reach flashover conditions in a typical single room fire is undertaken using a zone method (FAST) and Thomas method. Major parameters affecting the time to reach flashover are found to be fire growth rate, ventilation opening area and internal room surface. The results of the FAST and the Thomas Method give very similar results of the time to reach flashover..

• 설비공학논문집
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• 제25권11호
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• pp.612-616
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• 2013

A circular CAV damper has been developed, based on the investigation of the pressure loss, and the flow-resisting moment by the damper blade. When a torsional spring is attached to the damper axle, and the setting angle is adjusted to around $82^{\circ}$, the volume rate across the damper is almost independent of the static pressure. Such a CAV characteristic appears at an opening angle between $40^{\circ}$ and $60^{\circ}$, where the normalized moment decreases linearly with the angle. In addition, by adjusting the setting angle, the volume rate can be controlled to within 10% error, regardless of the pressure loss.

• 동력기계공학회지
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• 제13권1호
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• pp.13-18
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• 2009

In this study, flow characteristics at the regulators, which is very important for clean gas supply systems for semiconductors and LCD industries, are investigated. Numerical simulations are carried out to visualize flows at regulators for several flow rates and to investigate pressure losses at some parts in the regulator. Velocity field at the regulator along with the detailed velocity field near the spring and near the valve is shown. New regulator models are proposed in this paper, and numerical simulations are also carried out to visualize flows at regulator for several flow rates, and to investigate pressure losses at the parts in new models. Pressure drops a lot across the valve seat. Pressure drop increases as mass flow rate increases. Especially for small opening, pressure drop increases rapidly as mass flow rate becomes large.

• 한국자동차공학회논문집
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• 제12권4호
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• pp.58-64
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• 2004

The purpose of this study is to predict the behavior of fatigue crack propagation as one of fracture mechanics on the compressive residual stress. We got the following characteristics from fatigue crack growth test carried out in the environment of room temperature and low temperature at $25^{\circ}C$, -6$0^{\circ}C$, -8$0^{\circ}C$, and -10$0^{\circ}C$ in the range of stress ratio of 0.3 by means of opening mode displacement. There is a difference between shot peened specimen and unpeened specimen. Fatigue crack growth rate of shot peened specimen was lower than that of unpeened specimen. Shot peening is improve the resistance of crack growth by fatigue that make a compressive residual stress on surface. That is the constrained force about plasticity deformation was strengthened by resultant stress, which resulted from plasticity deformation and compressive residual stress in the process of fatigue crack propagation. Temperature goes down, fatigue crack growth rate decreased.

• International Journal of Korean Welding Society
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• 제3권2호
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• pp.15-23
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• 2003

A genetic algorithm was applied to an arc welding process to determine near optimal settings of welding process parameters which produce good weld quality. This method searches for optimal settings of welding parameters through systematic experiments without a model between input and output variables. It has an advantage of being able to find optimal conditions with a fewer number of experiments than conventional full factorial design. A genetic algorithm was applied to optimization of weld bead geometry. In the optimization problem, the input variables were wire feed rate, welding voltage, and welding speed, root opening and the output variables were bead height, bead width, penetration and back bead width. The number of level for each input variable is 8, 16, 8 and 3, respectively. Therefore, according to the conventional full factorial design, in order to find the optimal welding conditions, 3,072 experiments must be performed. The genetic algorithm, however, found the near optimal welding conditions from less than 48 experiments.

• 한국의류학회지
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• 제21권8호
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• pp.1387-1395
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• 1997

Effects of the ambient air temperature and the opening position on the pattern of the clothing ventilation of a thermal manikin wearing an impermeable blouse were investigated by the trace gas method. Under an isothermal condition, the ventilation was governed by diffusion, and the ventilation rate through the wrist-openings was greatly affected by the distance from the openings. Under non-isothermal conditions, however, the ventilation was accelerated by the convection driven by the temperature gradient between the clothing microclimate and the surrounding air; the greater the temperature gradient, the greater the ventilation. Even though it was certainly affected by the ambient air temperature, the ventilation rate was more significantly influenced by the position of openings. The ventilation patterns at the arm and the body were distinctive.

• 대한의용생체공학회:의공학회지
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• 제10권2호
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• pp.91-93
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• 1989

We have developed a monoleaflet polymer valve as an inexpensive and viable alternative, especially for short-term use in the ventricular assist device or total artificial heart. The frame and leaflet of the polymer valve were made from polyurethane, To evaluate the hemodynamic performance of the polymer valve a comparative study of flow dynamics past a polymer valve and a St. Jude Medical prosthetic valve under physiological pulsatile flow conditions in vitro was made. Comparisons between the valves were made on the transvalvular pressure drop, regurgitation volume and maximum valve opening area. The polymer valve showed smaller regurgitation volume and transvalvular pressure drop compared to the mechanical valve at higher heart rate. The results showed that the functional characteristics of the polymer valve compared favorably with those of the mechanical valve at higher heart rate.

• 한국농공학회지
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• 제38권3호
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• pp.41-49
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• 1996

One of the typically simple structures in protected horticulture is the rain shelter, which is widely applied in summer regardless of its poor ventilation. To evaluate ventilation performance of rain shelters, the ventilation rate as well as inside temperature of one conventional and two improved rain shelters were predicted and compared under various wind speeds and irradiations. More accurate model in which the inside space of rain shelter was subdivided into three parts considering the crops grown, was developed. The ventilation rate of each opening and the general direction of air flow in the rain shelter can be predicted by the model. The ventilation rates as well as inside temperatures of each rain shelter obtained by the model and the actual measurement, proved that the ventilation performance of improved rain shelters were superior to that of conventional one.

• 대한의용생체공학회:의공학회지
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• 제16권1호
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• pp.61-66
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• 1995

We have developed a monoleaflet polymer valve as an inexpensive and viable alternative, especially for short-term use in the ventricular assist device or total artificial heart. The frame and leaflet of the polymer valve were made from polyurethane. To evaluate the hemodynamic performance of the polymer valve a comparative study of flow dynamics past a polymer valve and a St. Jude Medicals prosthetic valve under physiological pulsatile flow conditions in vitro was made. Comparisons between the valves were made on the transvalvular pressure drop, regurgitation volume and maximum valve opening area. The polymer valve showed smaller regurgitation volllme and transvalvular pressure drop compared to the mechanical valve at higher heart rate. The results showed that the functional characteristics of the polymer valve compared favorably with those of the mechanical valve at higher heart rate.

• Bulletin of the Korean Chemical Society
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• 제19권6호
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• pp.680-685
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• 1998

Two kinds of new aliphatic diols were synthesized by the ring-opening reaction of lactide and glycolide with 1,4-butanediol, a difunctional initiator, in the presence of stannous octoate. The resulting aliphatic diols were melt-polymerized with D-tartaric acid at 150 ℃ to produce new crosslinkable polyesters. They were reacted with hexamethylene diisocyanate in THF at 65 ℃ in a teflon mold for 24 h to prepare sequentially ordered crosslinked polyesters (BD/LT/GL/D-tartarate). Degradation of the prepared yellow crosslinked films was carried out in a buffer solution in order to examine the effect of time, pH, temperature and crosslinking degree on their degradation rate and mechanism. The rate of degradation increased with an increase in pH and temperature, but it decreased with increasing degree of crosslinkage incorporated into the crosslinked polyesters. We also found that the crosslinked polymers were converted into the acidic compounds such as lactic, glycolic, and D-tartaric acids during the degradation.