• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.149-149
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• 2011

청정 에너지원으로 높은 잠재력을 가지고 있는 가스하이드레이트는 상업적 기술개발이 미확보된 상태임에도, 우리나라에서 부존이 직접적으로 확인되었기 때문에 에너지원으로서 그 중요성이 부각되고 있다. 현재 전세계적으로 가스하이드레이트 개발 및 생산에 관한 연구가 활발히 진행되고 있으며 이에 대한 기초자료로서 가스하이드레이트가 함유된 퇴적층의 물성자료가 필요하다. 이에 따라 본 연구에서는 입도 분포별 총 5가지의 미고결 시료를 대상으로 투과도, p파속도, 전기비저항 측정을 수행하였다. 연구에 사용된 미고결 시료는 Hama#5($774{\mu}m$), #6($485{\mu}m$), #7($258{\mu}m$), #8($106{\mu}m$) 4가지와 Hama#6과 Hama#7을 1:1($371{\mu}m$)로 혼합하여 사용하였다. 실험에 사용된 장비는 가스하이드레이트를 인공적으로 생성시키기 위해 퇴적층을 모사할 수 있는 고압셀과 자료획득장비, 유체 주입장비, 온도 유지장비이다. 또한 투과도 측정에는 차압계, 전기비저항 측정에 RLC meter, p파속도 측정에 음파 송수신장비를 사용하여 각각의 물성을 측정하였다. 실험과정을 단계별로 요약하면 먼저 시료를 고압셀에 충진한 뒤 주입된 물의 양으로부터 공극률을 측정하고, 절대 투수계수를 측정하였다. 그 후, 메탄가스를 주입하여 퇴적층 내 수포화도(water saturation)를 잔류상태(irreducible saturation)로 유지시키고 메탄가스를 추가적으로 주입하여 원하는 압력까지 가압한 뒤 온도를 $1^{\circ}C$로 낮추었다. 가스하이드레이트의 생성은 급격한 압력강하로부터 알 수 있다. 최종적으로 가스하이트레이트가 함유된 퇴적층의 상대 투수계수를 측정하기 위해 메탄가스를 주입하였고 각각의 측정장비를 통해 전기비저항 및 p파 속도를 측정하였다.$V_g$, $V_h$, $V_w$, $V_ss$는 각각 가스의 부피, 하이드레이트의 부피, 물의 부피, 모래의 부피이다. 또한 수포화도, $S_w=\frac{V_w}{V_v}$이며 하이드레이트 포화도, $S_h=\frac{V_w}{V_v}$, 가스 포화도, $S_g=\frac{V_g}{V_v}$로 정의된다. 본 실험의 결과 투과도는 가스의 부피비, $\frac{V_g}{V}=nS_g$에 민감한 반응을 보였으며, 비저항은 공극수의 부피비, $\frac{V_w}{V}=nS_w$에 민감한 반응을 보였다. 또한 p파 속도는 고체의 부피비, $\frac{V_s+V_h}{V}=n(1-S_h)$에 민감한 반응을 보였다. 이러한 실험의 결과는 가스하이드레이트 개발, 생산 연구에 있어 기초 물성자료로 활용되는데 도움을 줄 것이다.

• Journal of the Korean Society for Nondestructive Testing
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• v.14 no.2
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• pp.122-131
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• 1994

Journal bearings in the rotating machineries are vulnerable to the contamination or the insufficient supply of lubricating oil, which is likely to be the cause of unexpected shutdown or malfunction of these systems. Various destructive and nondestructive testing methods had been used for the reduction of maintenance cost and the operational safety problems due to the accidents related to bearing damages. In this experimental approach, acoustic emission monitoring is employed to the detection of incipient failure caused by intervention of foreign particles most probable in the journal bearing systems. Experimental schedules for the intervention of foreign particles was composed to be more quantitative and systematic than last study in consideration of minimum oil film thickness and particle size. The experiment was conducted under such designed conditions as inserting alumina particles to the lubrication layer in the simulated journal bearing system. Several parameters such as AE rms level, waveform, AE energy distribution and other AE event parameters are used for analysis and characterization of damage source. The results showed that the history of damage was well correlated with the changes of AE rms level and the type of damage source signal can be verified using other informations such as waveform, distributions of AE parameters etc.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.3
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• pp.575-583
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• 2017

Various types of flow patterns around the stepped weir and spillway, such as the skimming flow over such structures and the wave-type flow with a standing undular hydraulic jump and roller downstream of the structures, are developed in open channels. Unsteady three-dimensional numerical simulations are carried out using a hybrid RANS-LES turbulence modeling approach and the volume of fluid method for resolving free surface fluctuations to represent the turbulent flow including the skimming flow and wave-type flow over a stepped weir installed in a rectangular channel. The comparison of numerical results with an existing experimental measurement reveals that the present numerical simulations reasonably well reproduce the turbulent flow passing the stepped weir, in terms of time-averaged velocity profiles at selected locations downstream of the weir, flow topology characterized by the wave-type and skimming flows, the maximum height and length of the standing wave and the length of reattachment of recirculating zone. The numerical result further elucidates the distinct flow behaviors of the wave-type and skimming flow by presenting instantaneous intense variations of free surface and velocity vectors, the distributions of Reynolds shear stress and turbulent kinetic energy and three-dimensional complex features of coherent structures and total pressure distribution.

• Economic and Environmental Geology
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• v.50 no.2
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• pp.159-170
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• 2017

The temporal and spatial temperature distribution of the heat storage mortar made of porous feldspar was measured and the thermal properties and electricity consumption were analyzed. For the experiment, two real size chambers (control model and test model) with hot water pipes were constructed. Two large scale models with hot water pipes were constructed. The surface temperature change of the heat storage layer was remotely monitored during the heating and cooling process using infrared thermal imaging camera and temperature sensor. The temperature increased from $20^{\circ}C$ to $30^{\circ}C$ under the heating condition. The temperature of the heat storage layer of the test model was $2.0-3.5^{\circ}C$ higher than the control model and the time to reach the target temperature was shortened. As the distance from the hot water pipe increased, the temperature gap increased from $4.0^{\circ}C$ to $4.8^{\circ}C$. The power consumed until the surface temperature of the heat storage layer reached $30^{\circ}C$ was 2.2 times that of the control model. From the heating experiment, the stepwise temperature and electricity consumption were calculated, and the electricity consumption of the heat storage layer of the test model was reduced by 66%. In the cooling experiment, the surface temperature of the heat storage layer of the test model was maintained $2^{\circ}C$ higher than that of the control model. The heat storage effect of the porous feldspar mortar was confirmed by the temperature experiment. With considering that the time to reheat the heat storage layer is extended, the energy efficiency will be increased.

• The Journal of Engineering Geology
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• v.15 no.2 s.42
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• pp.185-199
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• 2005

Properties of sliding materials are dependent on the lithology because debris is the product of rock weathering processes. In order to characterize transportation behavior of debris dependent of debris types, this study selected 26 debris flows over three areas composed with different rock weathering types and topographic conditions. Analyses of lithology, weathering, and topographic characteristics were performed by detailed field survey. Based on the field survey data, transportation behavior of debris was studied at the aspect of the relationship of grain size and volume of debris as well as topographic conditions. According to the study results, change of slope angle is very influential factor on runout distance of debris among the topographic factors. Because the sliding velocity and the energy of debris are frequently changed and more irregular on an undulating slope, the unout distance of debris is larger than that of an uniformly dipping slope. Runout distance of debris is also influenced by volume and grain size of debris. Volume of debris in the gabbro is four or five times larger than that of the granite area because it is controlled by the lithology. Considered with grain size distribution, runout distance of debris is longer in the gabbro area which is composed with irregular grain size bearing large corestones than that in the medium grained granite area.

• The Journal of Engineering Geology
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• v.20 no.4
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• pp.425-436
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• 2010

We established a stochastic 3-D fracture network system for fractured rock masses located in Il-Gwang Mine, Busan, to explore the relationship between the acidity of mine drainage and fracture geometry. A field scanline survey and borehole image processing were performed to estimate the best probability distributions of fracture geometry parameters. The stochastic 3-D fracture network system constructed for the rock masses was validated and deemed to be successful. The 3-D fracture network model was suitable for developing conceptual ideas on fluid flow in fractures at a field experimental site. An injection well and three observation wells were drilled at the field experimental site to monitor the acidity of mine drainage induced by the injection of fresh water. The field experiment, which was run for 29 days, yielded a significant relationship (with a high coefficient of determination) between the fracture geometry parameters and the acidity of mine drainage. The results show that pH increased with increasing relative frequency of fracture strike, and decreased with increasing fracture density. The concentration of $SO^{2-}_4$ decreased with increasing relative frequency of fracture strike, and increased with increasing fracture density.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.4
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• pp.300-307
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• 2009

The transport of landfill leachate in the subsurface formations of unlined landfill sites is considered. The impacts of hydrogeological and chemical heterogeneities on the leachate transport are assessed by examining the results from a series of Monte-Carlo simulations. The landfill system simulated in this study is hypothetically represented with three levels of spatial variability for the hydrogeological and chemical parameter; (1) homogeneous hydraulic conductivity (K) and distribution coefficient ($K_d$), (2) K heterogeneity only, and (3) combined heterogeneities of K and $K_d$. To calculate the transport of leachate through negatively-correlated random hypothetical K-$K_d$ fields generated using geostatistical input parameters, a saturated flow model is linked with a contaminant transport model. Point statistic values such as mean, standard deviation, and coefficient of variation of the concentration were obtained from 100 Monte-Carlo trials. Results of point statistics show that the heterogeneities of K and $K_d$ in the landfill site prove to be an important parameter in controlling leachate concentrations. Consideration of combined K and $K_d$ heterogeneities results in enhancing the variability of contaminant transport. The variability in the leachate concentration for different realizations also increases as the distance between source and monitoring well increase.

• Korean Journal of Agricultural and Forest Meteorology
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• v.13 no.2
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• pp.48-55
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• 2011

Solar radiation components reflected by the sea surface ($R_{ss}\uparrow$) are additional energy sources comprising the solar radiation regime. Previous studies, based on observational approaches, indicated that $R_{ss}\uparrow$ is an available climatological resource. However, an estimation process for $R_{ss}\uparrow$ has not been established. In this case study over Jeju Island in South Korea, we applied a new estimation process to solar radiation modeling and discussed the spatial distribution of $R_{ss}\uparrow$ and its seasonal variation. Our results showed that the illuminated area and the intensity of $R_{ss}\uparrow$ became greatest at the winter solstice and least at the summer solstice. We estimated the illuminated area of $R_{ss}\uparrow$ as it expanded over the southern slope of Jeju Island. At the winter solstice, on a daily basis, the area and intensity of illumination by $R_{ss}\uparrow$ were $182.3km^2$ and $0.41\;MJ\;m^{-2}\;day\;{-1}$, respectively. Comparing the daily accumulative and instantaneous values of $R_{ss}\uparrow$ intensity, the difference was about 20 times greater in daily cases than in instantaneous cases. On the other hand, for instantaneous values, the $R_{ss}\uparrow$ intensity accounted for up to 33% of the three components, i.e., direct, diffuse and reflected radiation in winter solstice. In addition, it was estimated that the sea surface reflectance depended on the wind speed. Therefore, in a practical use of this revised model, wind conditions should be considered as a critical factor in estimating $R_{ss}\uparrow$.

• Journal of Biosystems Engineering
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• v.9 no.1
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• pp.22-33
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• 1984

Husk separator is an indispensable equipment in rice milling plants. However, any basic research on the designing and operating criteria of the husk separator have rarely been conducted in Korea. According to the survey results reported recently, grain loss occurs in the process of rice husk separation at custom rice milling plants in Korea and the performance of husk separator has also not been identified. With this regard this study was conducted with a typical commercial husk separator to investigate the effect of the operational factors such as feed rate, blower speed and opening ratio on the velocity distribution in the air duct and the performance of the separator. The results are summerized as follows: 1. The average wind velocity in the primary air duct increased linearly with the blower rpm and the size of air inlet port in both cases of double type and single type operations. 2. The coefficient of variation in the horizontal wind velocities in the primary air duct was the minimum when the opening ratio was 0.22 ($0.052m^2$ of air inlet port) in both cases of single type and double type operations regardless of the blower speeds used in this test. The average wind velocity at the upper part of air duct was greater by 2-5 m/s than the velocity at the bottom part in double type operation. In case of single type operation, however, the average velocity in the middle part was greater than the upper or bottom part when the opening ratio was greater than 0.74. 3. The relationship between the overall effectiveness of separation(Ed for double type and Es for single type) and the average wind velocity (Va) in the primary air duct was expressed in the following quadratic functions. $$Ed=-190.84+106.18Va-10.052Va^2$$ ($r^2$ = 0.97782) $$Es=-223.76+106.23Va-9.1935Va^2$$ ($r^2$ = 0.97029) The average wind velocity required to obtain the overall effectiveness of separation more than 80% ranged from 4.04 m/sec to 5.84 m/sec in case of double type operation, and from 4.70 m/sec to 6.20 m/sec in case of single type. 4. An optimum wind velocity can be obtained with an increase in the blower speed or the size of air inlet port as presented in Figure 8. There was a tendency that the faster the blower speed, the narrower the control range of the air inlet port. 5. The feed rates (1850kg/hr and 2100kg/hr) adopted in this experiment did not bring about a significant difference in both the overall effectiveness of separation and the power consumption. 6. The energy consumption increased cubically with the blower speed but linearly with the size of the air inlet port. On the basis of the results described in items 1, 3, and 6, it would be more economic to adjust the size of the air inlet port larger with a relatively low blower speed than to adjust the size smaller with a relatively high speed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.2
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• pp.597-603
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• 2010

The amount of pollutants from stationary sources of businesses classified into 1-3 type in Gyeongju was found to be 0.70 ton/yr for PM-10, 13.95 ton/yr for $SO_2$, and 37.12 ton/yr for NOx ; with respect to area sources, 1.02 ton/yr for PM-10, 13.44 ton/yr for $SO_2$, and 21.10 ton/yr for NOx ; and with respect to mobile sources 963.91 ton/yr for PM-10, 1415.02 ton/yr for $SO_2$, and 5612.70 ton/yr for NOx. This study surveyed the concentration distribution of PM-10, $SO_2$, and NO2 in the air in around Gyeongju and Pohang, and found that high concentration was mainly distributed around Pohang Steel Industrial Complex and the around of mobile sources. In Gyeongju area, $SO_2$ was predicted to increase from 0.002 ppm in 2006 to 0.005 ppm in 2015, and that of $NO_2$ was predicted to increase from 0.004 ppm to 0.010 ppm during the same period. At this point, practicing guidelines to reduce air pollutants and management plan for environmental pollutants should be devised, and also practicing and management programs to protect the stone cultural properties from environmental pollutants and other chemical, physical, and biological factors should be actively introduced.