• Journal of the Korean GEO-environmental Society
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• v.13 no.11
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• pp.51-60
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• 2012

In order to characterize the shear strength of the frozen sand for foundation design in cold region and prediction of adfreeze bond strength, many researchers developed test techniques and carried out many tests to analyze shear strength properties of the frozen sand for half a century. However, many studies for shear strength properties of the frozen sand have been carried out with limited circumstances, even though shear strength of the froze sand can be affected by various influence factors such as soil type, temperature conditions, and magnitude of normal stress. In this study, direct shear test equipment was used to analyze the shear strength characteristics of the frozen sand. Direct shear test equipment was designed for cold weather, and the direct shear tests were carried out inside of large-scaled low temperature chamber. Three soil types-two uniform sands and one well graded soil were used to analyze the shear strength of the frozen sand with three different temperature conditions and three different vertical confining pressures. In this research, a series of direct shear tests for shear strength of the frozen sand have been conducted to demonstrate the efficiency of effectiveness of the test equipment and low temperature chamber. This research also showed that shear strength of the froze sand increased with decreasing temperature condition, but the influence of vertical confining pressure was insignificant to the shear strength of the frozen sand.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2013.04a
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• pp.77-77
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• 2013

최근의 산업활동에서는 신규 원료 개발과 생산 효율성을 높이기 위하여 분체 공정이 증가하고 있는데, 미세 분진의 취급으로 분진운의 형성과 착화가 용이해지므로 분진폭발이나 화재 위험성이 증가하고 있다. 분진을 안전하게 사용하고 저장, 취급하기 위해서는 착화 전의 위험성 지표로서 최저발화온도(MIT ; Minimum Ignition Temperature)를 사전에 파악해 두는 것이 중요하다. 분진농도의 발화온도는 장치 내의 발화위험성이나 분진 취급 공정의 사고예방대책 관리를 위한 실용적 관점에서 중요하게 활용되는 폭발특성값이다. 또한 분진의 발화온도는 분진농도에 의존하며 농도변화에 따른 가장 낮은 온도를 MIT라고 한다. 본 연구에서는 화재폭발사고 빈도가 줄지 않고 있는 Mg 및 Mg-Al합금(60:40 wt%, 50:50 wt%, 40:60 wt%)을 대상으로 조성비율에 따른 최저발화온도를 실험적으로 조사하였다. Mg 및 Mg-Al(60:40 wt%), Mg-Al(50:50 wt%), Mg-Al(40:60 wt%) 시료의 평균입경은 142, 160, 151, $152{\mu}m$이다. MIT실험장치는 IEC 61241-2-1(Methods for Determining the Minimum Ignition Temperatures of Dust, 1994)에 준거하여 제작하여 사용하였다. 실험장치는 가열로, 분진운 시료홀더, 온도조절장치, 압축공기 제어장치 등으로 구성되어 있다. 구체적인 실험방법은 시험분진를 분진홀더에 장착하고 0.5 bar의 압축공기를 0.3 sec 동안 사용하여 일정 온도로 가열된 로의 내부로 분진운을 부유시킬 때에 분진운이 발화하여 가열로 하단부의 개방구에까지 화염이 전파하는지를 디지털비데오카메라로 기록, 평가하여 발화 유무를 판정하였다. Mg합금에 대한 MIT를 측정한 결과 $740^{\circ}C$가 얻어졌으며, Mg-Al(60:40 wt%)의 MIT는 $820^{\circ}C$로 조사되었다. 그러나 Mg-Al(50:50 wt%) 및 Mg-Al(40:60 wt%)에 대해서는 최대 가열로의 설정온도를 $890^{\circ}C$까지로 하여 농도를 변화시키면서 조사하였으나 발화가 일어나지 않았다. 문헌에 따르면 Mg입자 표면의 산화피막은 다공성으로 일정 온도에서 산화반응이 시간에 따라 직선적으로 증가하는데 반하여, Al의 산화피막은 보호 작용을 하여 일정 온도에서 산화반응속도가 표면과 내부의 농도 기울기에 의한 확산속도에 의존한다고 보고하고 있다. 본 연구결과를 토대로 Mg-Al합금의 발화특성을 고찰해 보면, Mg-Al합금에서 자기 전파성이 작은 Al성분의 증가는 착화지연이 증가하여 연소성이 감소하여 최저발화온도의 증가로 이어지는 것으로 추정되었다. 또한 발화온도는 주어진 조건의 온도장에서 분진이 존재하는 시간 길이에 따라 변화하므로, 발화온도를 실험적으로 측정하는 경우에는 측정장치나 방법에 따라 달라지므로 사업장의 현장에 발화온도를 적용하는 경우에는 장치 내의 분진의 존재시간을 고려할 필요가 있다.

• Journal of Digital Convergence
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• v.14 no.3
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• pp.279-285
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• 2016

With the development of nanotechnology, the amount of nanomaterials increases and the problems of environment and the toxic property associated with it have become a social problem. But regulations and laws of nanomaterials have not yet been established. The purpose of this study is to utilize as the database of safety guidelines for research activities' workers associated with nanomaterials to conduct a behavior evaluation of aluminium oxide, which is most widely used in thirteen kinds of WPMN manufactured nanomaterials in the country. The experiment proceeds in the chamber reduced to 1/6 size of the actual laboratory, the test method was performed in NIOSH 0500. As the results of the study, the mass concentration was in inverse proportion to the particle size of the nanomaterials. And the mass concentration during the operation of ventilation equipment was reduced to about 1/8 times. In the future, it can be utilized as the database of safety guidelines for research activities' workers associated with nanomaterials. However, in order to increase the reliability of the study, the experiment of the mass concentration by particle size and Condensation Particle Counters will be needed additionally.

• Korean Journal of Agricultural Science
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• v.7 no.2
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• pp.109-118
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• 1980

This test was carried out to present criterion to measure the liquid limit of weathered granite soil by using the flow-table method whose operation is easier and more convenient than slump test. The results are as follows. 1. Since liquid limit of weathered granite soil depends upon the particle size distribution, weatheredness and content of colored minerals, maximum particle size should be prescribed when the testing rule of liquid limit by flow-table method is enacted. 2. If take the averaged water content as liquid limit where the height and width of flow are 1 cm respectively by 10 times dropping, this liquid limit is slightly less than the one by slump test. The differance of liquid limit between flow table method and slump test is about 10%. 3. Correlation curves of flow width-water content and flow hight-water content show similar shapes. Those are straight lines in semi-logarithm paper just as liquid limit test. 4. This flow-table method is more convenient and has less personal error of measurement than slump test does. So flow-table method would be favourably utilized for judging the engineering properties of soil.

• Journal of Korea Water Resources Association
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• v.52 no.7
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• pp.493-503
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• 2019

This study presents a new method of estimating the size distribution of river bed gravel through image processing. The analysis was done in two steps; first the individual grain images were analyzed and then the grain particle segmentation of river-bed images were processed. In the first part of the analysis, the relationships (long axes, intermediate axes and projective areas) between grain features from images and those measured were compared. For this analysis, 240 gravel particles were collected at three river stations. All particles were measured with vernier calipers and weighed with scales. The measured data showed that river gravel had shape factors of 0.514~0.585. It was found that the weight of gravel had a stronger correlation with the projective areas than the long or intermediate axes. Using these results, we were able to establish an area-weight formula. In the second step, we calculated the projective areas of the river-bed gravels by detecting their edge lines using the ImageJ program. The projective areas of the gravels were converted to the grain-size distribution using the formula previously established. The proposed method was applied to 3 small- and medium- sized rivers in Korea. Comparisons of the analyzed size distributions with those measured showed that the proposed method could estimate the median diameter within a fair error range. However, the estimated distributions showed a slight deviation from the observed value, which is something that needs improvement in the future.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.2
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• pp.367-378
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• 1994

The wastewater treatment characteristics of the fluidized bed filled with sand media and intermediately aerated were studied experimentally, and the obtained results were as follows; 1. The formations of biofilm on the media were greatly affected by the recirculation velocities. 2. Under the experimental condition that BOD loading rate was $4.2kg-BOD_5/m^3{\cdot}d$, the optimum media concentration was $261kg/m^3$ and the optimum recirculation velocity 1.35 cm/sec. 3. For the effluent quality of 20 mg-BOD/l and 20 mg-SS/l, the maximum allowable loading rate was about $8kg-BOD_5/m^3{\cdot}d$. 4. The dry density of biofilm was about 5.6% regardless of the filled media quantities and recirculation velocities. 5. Under the experimental conditions, the effluent solids concentration was below 20 mg/l, and the elimination of final clarifier can be expected.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.10
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• pp.1498-1507
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• 2003

A SMPS(scanning mobility particle sizer) system measures the number size distribution of particles using electrical mobility detection technique. An aerosol charge neutralizer, which is a component of the SMPS, is a bipolar charger using a radioactive source to apply an equilibrium charge distribution to aerosols of unknown charge distribution. However, the performance of aerosol charge neutralizers is not well known, especially for highly charged particles. In this study, the effect of the particle charging characteristics of two aerosol charge neutralizers on the measurement using a SMPS system was experimentally investigated for highly charged polydisperse particles. One has radioactive source of $^{85}$ Kr (beta source, 2 mCi) and the other has $^{210}$ Po (alpha source, 0.5 mCi). The air flow rate passing through each aerosol charge neutralizer was changed from 0.3 to 3.0 L/min. The results show that the non-equilibrium character in particle charge distribution appears as the air flow rate increases although the particle number concentration is relatively low in the range of 1.5∼2x10$^{6}$ particles/㎤. The low neutralizing efficiency of the $^{85}$ Kr aerosol charge neutralizer for highly charged particles can cause to bring an artifact in the measurement using a SMPS system. However, the performance of the $^{210}$ Po aerosol charge neutralizer is insensitive to the air flow rate.

• Journal of Korean Society for Atmospheric Environment
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• v.20 no.5
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• pp.685-695
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• 2004

Size-segregated measurements of aerosol composition are used to estimate the transport of natural and anthropogenic aerosols at Gosan site during May 2002. The results of measurement show that not only soil dust but also anthropogenic aerosols, including sulfur and enriched trace metals such as Pb, Zn, Cu, are transported to Gosan. This study combines the size- and time-resolved aerosol composition measurements with factor analysis in order to identify some source materials. As a result, coarse particles (2.5${\mu}m$~12${\mu}m$) are influenced by soil, sea-salt, coal, coal combustion, and nonferrous sources. But fine particles have different sources. The fine particles, which the diameter is from 0.56${\mu}m$ to 2.5${\mu}m$, are more affected by road dust, oil combustion, industry. municipal incineration, and ferrous metal sources. The very fine particles, from 0.09${\mu}m$ to 0.56${\mu}m$, mainly supplied by biomass burning, oil combustion, nonferrous and ferrous metal sources.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.583-587
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• 2006

국부세굴의 발생은 일반적으로 흐름조건, 구조물 조건과 하상재료 세 가지의 주 원인으로 구분할 수 있다. 흐름조건의 경우 구조물 영향으로 발생되는 3차원적인 와류가 주요원인이며 하상재료의 경우 여러 요인이 있겠지만 비중이 같은 입자라 가정할 경우 입자의 크기를 주요 변수로 정할 수 있다. 교각 국부세굴에 관한 연구는 1960년대 이후 연구자들에 의해 매우 다양하게 수행되어 졌으며 많은 산정공식도 제시되었다. 하지만 기존 연구는 최대세굴심 조건으로 다양한 하상재료와 시간에 대한 세굴변동(홍수사상 등)에 대한 영향을 고려하는데 어려움이 있다. 특히 국내의 경우 다양한 하상재료와 홍수빈도를 고려할 때 이에 대한 세굴적용은 매우 중요한 인자라 할 수 있다. 따라서 교각세굴에 대한 궁극적인 목적은 다양한 하상재료와 홍수빈도를 고려할 수 있는 세굴평가를 제안하는데 있다. 이를 위해 본 연구에서는 우선적인 연구로 입자의 다양성과 이미지 기법을 이용한 실시간 측정을 통해 보완하여 입자에 따른 시간적 변화를 분석하였다. 현재 4가지의 하상재료의 입경차이에 따른 국부세굴의 시간적 변화와 초기세굴 발생의 수리적 조건을 파악하고 기존연구와 비교분석하였으며, 이를 기초자료로 세굴심$(S,\;S_{max})$, 교량주변 전단력$({\tau}_p,\;{\tau}_{pc})$, 접근수로부 전단력$({\tau}_a)$와 입자한계전단력$({\tau}_c)$에 대한 시간분석 (time effect)을 통해 다양한 하상재료와 홍수빈도를 해석을 위한 초기분석을 수행하는데 목적이 있다. 수리모형실험에 사용된 가변경사수로의 제원은 $0.6m(W){\times}20m(L){\times}2m(H)$이며 모형구조물은 투명한 아크릴로 제작하였다. 실험방법은 교각 내부에 CC카메라를 전 후면 및 상측면에 설치하여 세굴 발생을 실시간으로 촬영한 후 이미지 분석을 통해 분석하였다.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.7
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• pp.834-843
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• 2014

A two-stage electrostatic precipitator (ESP) using a carbon brush charger and a plate-plate parallel aluminum collector was developed and its application for removal of oil mist aerosols was investigated. Charge number per particle and particle collection efficiency at different applied voltage to the carbon brush charger were measured and compared to those obtained by theoretical calculations. A long-term operation of the ESP during 9 weeks was also performed to evaluate its performance durability for oil mists. Average charge number per mist particle increased with the applied voltage to the charger, and thus the collection efficiency of the mist particles also increased overall at the particle size range of 0.26 - 3 mm. The tendencies of the average charge number per particle and particle collection efficiency obtained from theoretical calculations were considerably consistent with those of the experimental results. Particle collection efficiency of ~99 % at 0.3 mm could be achieved by power consumption of only 0.0033 W/($m^3/h$) at the face velocity of 1 m/s and its collection performance maintained stably during every 8 hr operation per day for 9 weeks with little increase of pressure drop.