• 한국표면공학회지
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• 제34권5호
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• pp.367-377
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• 2001

Plasma is generated by electrical discharge. Most plasma generation has been carried out at low-pressure gas typically less than one millionth of atmospheric pressure. Plasmas are in general generated from impact ionization of neutral gas molecules by accelerated electrons. The energy gain of electrons accelerated in an electrical field is proportional to the mean free path. Electrons gain more energy at low-pressure gas and generate plasma easily by ionization of neutrals, because the mean free path is longer. For this reason conventional plasma generation is carried out at low pressures. However, many practical applications require plasmas at high-pressure. In order to avoid the requirement for vacuum pumps, researchers in Korea start to develop plasmas in high-pressure chambers where the pressure is 1 atmosphere or greater. Material processing, environmental protection/restoration and improved energy production efficiency using plasmas are only possible for inexpensive bulk plasmas. We thus generate plasmas by new methods and plan to set foundations for new plasma technologies for $21^{st}$ / century industries. This technological research will play a central role in material processing, environmental and energy production industries.

• Tribology and Lubricants
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• 제10권2호
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• pp.30-38
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• 1994

The thermohydrodynamic(THD) performance of a large tilting pad journal bearing is investigated both theoretically and experimentally. The theory takes into account the three dimensional variation of lubricant viscosity and eddy viscosity, and the inlet pressure. Owing to the inlet pressure effect, the film pressure and load capacity are increased but the mixing temperature and bearing surface temperature are decreased. The continuous distribution of the film pressure and film thickness and the bearing surface temperature are measured along with the shaft speed and the bearing load, and they are compared with the theoretical results. The results obtained by the experiment are in good agreement with those by the theory including the inlet pressure effect. It is suggested that the three dimensional turbulent THD analysis including the inlet pressure effect is very useful to predict the performance of the large tilting pad journal bearing more accurately.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2004년도 추계학술대회 논문집
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• pp.10-13
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• 2004

The PSP(pressure sensitive paint) technique has recently received a large attention as a new revolutionary optical method to measure absolute pressure distribution on a model surface. The PSP technique can be applied to quantitatively investigate flow structure using a CCD camera and image processing technique. In the static calibration, the luminescent intensity of PSP coatings was measured from 0kPa to 11kPa with 0.5, 1, 2kPa increments. In this study, the low-pressure PSP technique was applied to an oblique impinging jet to measure pressure field variations on the impingement plate with varying angle of an oblique jet. The flow structure over the impingement plate was visualized using a surface tracing method. As a result, the detail pressure field distributions of the oblique low-speed impinging jet were visualized effectively using the PSP technique.

• Tribology and Lubricants
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• 제4권1호
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• pp.69-73
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• 1988

The effects of journal speed and bearing load on pressure distribution and the temperature distribution of bearing surface are investigated experimentally. The journal bearing which has 219.94mm diameter, length-to-diameter ratio of L/D=0.8 and clearance ratio of 0.004 is used. Journal has a built-in pressure transducer for the measurement of pressure distribution in the mid plane of bearing. Bearing surface temperatures are measured at 60 points. The bearing load is varied from 300 N to 5900 N and journal speed from 300 rpm to 2500 rpm. As the load is increased under constant speed, the location of maximum pressure moves to the site of minimum film thickness, and maximum pressure and absolute value of minimum pressure are increased. The temperature distribution in vicinity of oil inlet shows that heated lubricant's carry-over exists around the oil inlet.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2000년도 춘계학술발표회 초록집
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• pp.5-5
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• 2000

In the severe accident case like LOCA, Zircaloy(Zry) claddings are oxidized not only in high temperature but also in high pressures. It is a concem whether the safety of high bum up fuels can be maintained during severe accident. The effects of steam pressure on Zry-4 oxidation, and the effect of prc-existing oxide layer on the cladding in the high temperature-high pressure oxidation of Ziy-4 were investigated. The experimental temperature range was $700-900^{\circ}C$, and the pressures were between 0.1 and l5.0MPa. Partial pressure of steam tumed out to be the important one rather than total gas pressure. The higher the steam pressure was applied, the thicker the oxide became. nle effect of st,earn pressure on the oxidation of claddings with preexisting oxide was about 40-60% less effective than that of pickled cladding. Aocelerated oxidation in highpressure slean1 seems to be originated from the formation of microcracks produced during the transformation of tetragonal zirconia to monoclinic phase. Steam pressure seems to affect the stability of tetragonal phase.

• Wind and Structures
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• 제16권6호
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• pp.617-627
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• 2013

In wind load calculations based on pressure measurements, the concept of 'tributary area' is usually used. The literature has less guidance for a systematic computational methodology for calculating tributary areas, in general, and for scattered pressure taps, in particular. To the best of the author's knowledge, there is no generic mathematical equation that helps calculate the tributary areas for irregular pressure taps. Traditionally, the drawing of tributary boundaries for scattered and intensively distributed taps may not be feasible (a time and resource consuming task). To alleviate this problem, this paper presents a proposed numerical approach for tributary area calculations on rectangular surfaces. The approach makes use of the available coordinates of the pressure taps and the dimensions of the surface. The proposed technique is illustrated by two application examples: first, quasi-regularly distributed pressure taps, and second, taps that have scattered distribution on a rectangular surface. The accuracy and the efficacy of the approach are assessed, and a comparison with a traditional method is presented.

• 한국기계가공학회지
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• 제3권3호
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• pp.64-70
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• 2004

The sub-surface stress field beneath the spur gear's contact surface in lubricated condition has been analysed. The surface pressure was obtained by the elasto-hydrodynamic lubrication analysis using the accurate geometric clearances around the contact region of the teeth. The sub-surface stress field was calculated by using the Love's rectangular patch solution. The analysis results show that the sub-surface stress distribution is quite dependent on the surface pressure distribution. The pattern of sub-surface stress field is similar to that of the external load. The depth where the maximum effective stress occurs is not proportional to the intensity of the external load.

• Tribology and Lubricants
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• 제32권2호
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• pp.67-71
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• 2016

This study investigates the characteristics of the sapphire wafer chemical mechanical polishing (CMP) process. The material removal rate is one of the most important factors since it has a significant impact on the production efficiency of a sapphire wafer. Some of the factors affecting the material removal rate include the pressure, platen speed and slurry. Among the factors affecting the CMP process, we analyzed the trends in the material removal rate and surface roughness, which are mechanical factors corresponding to both the pressure and platen speed, were analyzed. We also analyzed the increase in the material removal rate, which is proportional to the pressure and platen speed, using the Preston equation. In the experiment, after polishing a 4-inch sapphire wafer with increasing pressure and platen speed, we confirmed the material removal rate via thickness measurements. Further, surface roughness measurements of the sapphire wafer were performed using atomic force microscopy (AFM) equipment. Using the measurement results, we analyzed the trends in the surface roughness with the increase in material removal rate. In addition, the experimental results, confirmed that the material removal rate increases in proportion to the pressure and platen speed. However, the results showed no association between the material removal rate and surface roughness. The surface roughness after the CMP process showed a largely consistent trend. This study demonstrates the possibility to improve the production efficiency of sapphire wafer while maintaining stable quality via mechanical factors associated with the CMP process.

• Smart Structures and Systems
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• 제25권4호
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• pp.433-446
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• 2020

In this paper the effect of confining pressure and tunnel depth on the ground vertical settlement has been investigated using particle flow code (PFC2D). For this perpuse firstly calibration of PFC2D was performed using both of tensile test and triaxial test. Then a model with dimention of 100 m × 100 m was built. A circular tunnel with diameter of 20 m was drillled in the middle of the model. Also, a rectangular tunnel with wide of 10 m and length of 20 m was drilled in the model. The center of tunnel was situated 15 m, 20 m, 25 m, 30 m, 35 m, 40 m, 45 m, 50 m, 55 m and 60 m below the ground surface. these models are under confining pressure of 0.001 GPa, 0.005 GPa, 0.01 GPa, 0.03 GPa, 0.05 GPa and 0.07 GPa. The results show that the volume of colapce zone is constant by increasing the distance between ground surface and tunnel position. Also, the volume of colapce zone was increased by decreasing of confining pressure. The maximum of settlement occurs at the top of the tunnel roof. The maximum of settlement occurs when center of tunnel was situated 15 m below the ground surface. The settlement decreases by increasing the distance between tunnel center line and measuring circles in the ground surface. The minimum of settlement occurs when center of circular tunnel was situated 60 m below the surface ground. Its to be note that the settlement increase by decreasing the confining pressure.

• Spatial Information Research
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• 제19권1호
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• pp.13-19
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• 2011

도시화가 진행됨에 띠라 고층아파트와 고층빌딩 등 지형지물의 변화가 많이 일어나고 있다. 지형지물의 변화는 강풍 발생의 원인으로 작용하며, 풍속은 풍상측 지형지물의 영향으로 같은 속도의 바람이 붙어올지라도 그 값이 증가 또는 감소한다. 설계기준에서는 이러한 변화를 풍속고도분포계수로 정의하고, 지표면조도에 따라 그 값을 산정하여 반영하도록 하고 있지만 현실에서는 설계자의 주관적 판단에 따라 지표면조도를 결정하야 풍속고도분포계수를 산정하고 있으며, 건설지점의 지표면조도를 구분하기 위한 연구와 자료 또한 부족한 실정이다. 본 논문에서든 최근 고층주거건물이 많이 건설된 지역을 대상으로 건축물의 수직높이에 따분 지표면조도를 GIS프로그램을 이용하여 정량적으로 구분함으로써 풍속 고도분포계수를 보다 합리적으로 산정하고자 한다. 풍하중을 고려한 구조물 설계 시 본 연구에서 제안한 풍속고도분포계수 산정방법을 이용함으로써 설계의 합리성과 구조물의 안전성을 더 높일 수 있을 것이다.