• Journal of Biosystems Engineering
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• 제20권4호
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• pp.351-359
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• 1995

In pressure cooling system, produce were packed in vented box and cooled rapidly by producing a difference in air pressure on opposite faces of stacks of vented box. So, energy requirements and performance of pressure cooling system depended upon the air flow rate and the static pressure drop through packed produce in vented box. The static pressure drop across packed produce in vented box normally depended upon air flow rate, vent area of box and conditions of produce bed (depth, porosity, stacking patterns, size and shape of products) in box. The objectives of this study were to investigate the effect of vent area and air flow rate on airflow resistance of empty box and packed produce in vented box, and to investigate the relationship between the air flow resistance of packed products in vented box and sum of air flow resistance of empty box only and products in bulk only. Mandarins and tomatoes were used in the experiment. The airflow rate were in the range of 0.02~1.0$m^3$/s.$m^2$, the opening ratio of vent hole were in the range of 2.5~20% of the side area. The results were summerized as follows. 1. The pressure drops across vented box increased in proportion to superficial air velocity and decreased in proportion to opening ratio of vent hole. A regression equation to calculate airflow resistance of vented box was derived as a function of superficial air velocity and opening ratio of vent hole. 2. The pressure drops across packed produce in vented box increased in proportion to superficial air velocity and decreased in proportion to opening ratio of vent hole. 3. Because of the air velocity increase in the vicinity of vent hole in box, the airflow resistances of packed products in vented box were always higher than sum of air flow resistance of empty box only and products in bulk only. 4. Based on the airflow resistance of empty box and products in bulk, a regression equation to calculate airflow resistance of packed products in vented box was derived.

• 한국지반신소재학회논문집
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• 제22권4호
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• pp.27-34
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• 2023

본 연구에서는 말뚝에 작용하는 구속압과 지반의 세립분 함유율을 고려한 말뚝 인발실험을 실시하였다. 그리고 실험 결과를 이용하여 말뚝의 인발저항에 미치는 지중 구속압의 영향을 분석하여 인발저항정수를 고찰하였다. 인발실험 결과, 모형지반의 세립분 함유율과 구속압의 크기에 관계없이 약 7mm~9mm의 인발변위에서 최대인발저항력이 발생되었다. 말뚝의 최대인발저항력은 모형지반의 세립분 함유율이 증가할수록 감소하였고, 이러한 경향은 구속압이 클수록 현격하게 나타났다. 말뚝인발실험 결과의 신뢰성을 검토하기 위해 인발저항력을 이론식으로 산정해 실험결과와 비교한 결과, 모든 구속압 조건에서 세립분 함유율 증가에 따라 실험값과 이론값 모두 동일하게 인발저항력이 감소하는 경향을 보였다. 인발저항정수에 대한 분석 결과, 말뚝과 지반의 경계에서 발생하는 인발저항력에 있어서 주변 지반의 세립분 함유율이 증가할수록 경계면 마찰각보다 부착력의 영향이 커지는 것을 확인하였다.

• 한국분말재료학회지
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• 제22권3호
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• pp.203-207
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• 2015

This study investigated the microstructure and wear resistance property of HPHT(high pressure high temperature) sintered PDC(polycrystalline diamond compact) in accordance with initial molding pressure. After quantifying an identical amount of diamond powder, the powder was inserted in top of WC-Co sintered material, and molded under four different pressure conditions (50, 100, 150, $200kgf/cm^2$). The obtained diamond compact underwent sintering in high pressure, high temperature conditions. In the case of the $50kgf/cm^2$ initial molding pressure condition, cracks were formed on the surface of PDC. On the other hand, PDCs obtained from $100{\sim}200kgf/cm^2$ initial molding pressure conditions showed a meticulous structure. As molding pressure increased, low Co composition within PDC was detected. A wear resistance test was performed on the PDC, and the $200kgf/cm^2$ condition PDC showed the highest wear resistance property.

• 한국환경보건학회지
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• 제21권2호
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• pp.7-11
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• 1995

This study was carried out to investigate the change of average specific resistance according to filtration pressure, suspension concentration and filters for study phenomena occurring in cake filtration. As the results of this study, the following conclusions were obtained. It was estimated that the average specific resistance of filtration Was decreased in proportion to decreased of filtration pressure. But in very pressure, average specific resistance was increased. The average specific resistance value on filter medium by various pressure was showed as same trends under constant suspension concentration. This phenomenon was though that a carrain amount of fine particles in the cake was found to migrate throught the cake in the case of very thin at very low pressure. In relation to the change of suspension concentration, average specific resistance value become low according to decreased in supension concentration.

• International Journal of Safety
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• 제4권2호
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• pp.6-11
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• 2005

The goals of the paper are to understand the impact damage behavior and identify the effect of surface protective materials on impact resistance in filament wound composite pressure vessels. For these, a series of low velocity impact tests was performed on specimens cutting from the full scale pressure vessel by the instrumented impact testing machine. The specimens are classified into two types, which are with and without surface protective material. The visualization for impact damage by two different impactors is made by metallurgical microscope. Based on the impact force history and damage, the impact resistance parameters were employed,rod its validity in identifying the damage resistance of filament wound composite pressure vessel was reviewed. As the results, the impact resistance of the filament wound composites and its dependency on the surface protective material were evaluated quantitatively

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.679-682
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• 2002

Resistance spot welding using air gun has been used for joining the sheet metal in automotive manufacturing process. Although air gun has many advantages, it also has the limitation to control the pressure as a factor to improve weld quality. In this study, we apply servo gun using servo motor to resistance spot welding and find the relationship between welding pressure and welding quality. Trough the experiment to change welding pressure during the welding cycle, we can make it clear that the change of welding pressure is greatly influence on the welding quality. To get in a. using response surface methodology, drew out the optimal welding pressure profile for welding quality progresses. We made an optimal profile of welding pressure which improves welding quality using response surface methodology.

• Journal of Biosystems Engineering
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• 제30권2호
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• pp.69-74
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• 2005

This study was carried out to investigate experimentally the effect of the ground condition and tire inflation pressure on rolling characteristics of towed wheel, including the deformation, sinkage, effective rolling radius and motion resistance of tire. The experiment was performed at soil bin for the three levels of off-road conditions(ground-I, ground-II and ground-III) and a on-road condition(ground-IV), and for the four levels of tire inflation pressure which were 80 kPa, 160 kPa, 240 kPa and 320 kPa. The results of this study are summarized as follows: 1. As the tire inflation pressure of towed wheel increased, the tire deformation decreased exponentially, but the tire sinkage increased exponentially. This trend was getting bigger as ground condition was getting softer. 2. The increase of tire inflation pressure increased the effective rolling radius of towed wheel, and this kind of trend occurred greatly as ground condition was soft. As a result, the effective rolling radius for the off-road condition was always larger than that for on-road condition. 3. For the on-road condition, as the tire inflation pressure of towed wheel increased, the motion resistance decreased, but for the off-road condition, augmentation of tire inflation pressure increased the motion resistance. Also, the effect of inflation pressure on motion resistance appeared great as ground condition was soft. Therefore, in order to improve the tire performance by the control of inflation pressure, it is desirable to reduce the tire inflation pressure for off-road condition and to increase the tire inflation pressure for on-road condition.

• Journal of Advanced Marine Engineering and Technology
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• 제38권9호
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• pp.1106-1111
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• 2014

본 연구는 Hydrofoil 선박용 POD의 형상변화에 따른 압력분포 특성을 파악하기 위하여 CFD기법을 적용하여 수행하였다. POD 단면의 기본형상을 원점(상단)으로 하여 x축 방향으로 0cm(원본형상)에서 8cm까지 절단했을 때, 점성저항은 조금씩 감소하였으나, 압력저항은 조금씩 증가하는 결과를 얻었다. 하지만 동일한 조건하에서 9cm를 절단했을 경우에는 점성저항은 증가하고, 압력저항은 감소하는 경향을 보였다. 결론적으로, 압력저항이 점성저항에 비해 POD형상의 압력분포 특성에 많은 영향을 미친다는 것과 9cm를 절단한 근처에서 전체저항이 감소한다는 결론을 얻었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.72-77
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• 2007

A pressure sensor is a sensing device to perceive inputing pressure and convert pressure with an electric signal. Currently, a domestic pressure sensor mostly uses mechanical methods. So, it uses many parts and its cost is high. Therefore, It is necessary to improve the weak points of an existing pressure sensor and develop the accurate and reliable pressure sensor using piezo resistance strain gages.

• 대한기계학회논문집A
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• 제29권8호
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• pp.1109-1117
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• 2005

To identify damage that develops in filament wound composite pressure vessels subjected to low velocity impact, a series of impact tests was performed on specimens cutting from the full scale pressure vessel. The resulting damages by the three different impactors were assessed by the scanning acoustic and metallurgical microscope. Based on the impact force history and damage, the resistance parameters were proposed and its validity in identifying the damage resistance of CFRP pressure vessel was reviewed. As the results, the impact resistance of the filament wound composites and its dependency on the impactor shape were estimated quantitatively.