• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.7
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• pp.477-483
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• 2018

A transparent antenna designed on the front glass of an automobile operating in the FM broadcast band(88~108 MHz) is proposed. A transparent antenna designed on the front glass of the automobile to avoid space limitation is typically positioned as a roof-mounted shark-fin antenna. An antenna designed on the front glass can reasonably solve the problems of low reception sensitivity and radiated interference from antennas for other service bands. The front glass has a unique closed-line structure, and this structure causes the surface current to flow to the front glass's surroundings; thus, the first resonance is caused before the broadcast band. Through the use of this closed-line structure, the surface current distribution is controlled, and an antenna for which the first resonance is operating in the frequency-modulated(FM) band can be designed. Moreover, the use of a micro-metal-mesh film that is a transparent electrode, suitable for designing a radio frequency device, enables the antenna to minimize visual perception through its transparency. The measured reflection coefficient($S_{11}$) of the antenna is less than -6 dB, and the average peak gain is -0.9 dB in the FM band. Experiments show that the transparent antenna on the front glass offers both the space and design freedom required to develop future automotive antennas.

• Journal of Environmental Science International
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• v.23 no.5
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• pp.839-852
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• 2014

The Ministry of Environment (MOE) has made more effort in managing point source pollution rather than in nonpoint source pollution in order to improve water quality of the four major rivers. However, it would be difficult to meet water quality targets solely by managing the point source pollution. As a result of the comprehensive measures established in 2004 under the leadership of the Prime Minister's Office, a variety of policies such as the designation of control areas to manage nonpoint source pollution are now in place. Various action plans to manage nonpoint source pollution have been implemented in the Soyang-dam watershed as one of the control areas designed in 2007. However, there are no tools to comprehensively assess the effectiveness of the action plans. Therefore, this study would assess the action plans (especially, BMPs) designed to manage Soyang-dam watershed with the WinHSPF and the CE-QUAL-W2. To this end, we simulated the rainfall-runoff and the water quality (SS) of the watershed and the reservoir after conducting model calibration and the model validation. As the results of the calibration for the WinHSPF, the determination coefficient ($R^2$) for the flow (Q, $m^3/s$) was 0.87 and the $R^2$ for the SS was 0.78. As the results of the validation, the former was 0.78 and the latter was 0.67. The results seem to be acceptable. Similarly, the calibration results of the CE-QUAL-W2 showed that the RMSE for the water level was 1.08 and the RMSE for the SS was 1.11. The validation results(RMSE) of the water level was 1.86 and the SS was 1.86. Based on the daily simulation results, the water quality target (turbidity 50 NTU) was not exceeded for 2009~2011, as results of maximum turbidity in '09, '10, and '11 were 3.1, 2.5, 5.6 NTU, respectively. The maximum turbidity in the years with the maximum, the minimum, and the average of yearly precipitation (1982~2011) were 15.5, 7.8, and 9.0, respectively, and therefore the water quality target was satisfied. It was discharged high turbidity at Inbuk, Gaa, Naerin, Gwidun, Woogak, Jeongja watershed resulting of the maximum turbidity by sub-basins in 3years(2009~2011). The results indicated that the water quality target for the nonpoint source pollution management should be changed and management area should be adjusted and reduced.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.10
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• pp.881-887
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• 2014

Micro-sized Peltier coolers are generally employed for uniformly distributing heat generated in the multi-chip packages. These coolers are commonly classified into vertical and planar devices, depending on the heat flow direction and the arrangement of thermoelectric materials on the used substrate. Owing to the strong need for evaluation of performance of thermoelectric modules, at present an establishment of proper theoretical model has been highly required. The design theory for micro-sized thermoelectric cooler should be considered with contact resistance. Cooling performance of these modules was significantly affected by their contact resistance such as electrical and thermal junction. In this paper, we introduce the useful and optimal design model of small dimension thermoelectric module.

• Journal of Bio-Environment Control
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• v.22 no.3
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• pp.270-278
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• 2013

The objective of the present study is to provide data needed to decide covering method to be able to increase the thermal insulation and light transmittance efficiency of commercial greenhouse. The thermal insulation effect, PPF transmittance and quantity of condensation water were estimated in experimental tomato greenhouses covered with three types of coverings of single layer, air inflated and conventional double layers covering. The overall heat flow of air inflated double layers greenhouse was similar to that of conventional double layers greenhouse, but the temperature between covering material and thermal screen in air inflated double layers greenhouse was lower than that in conventional double layers greenhouse at the same outside temperature condition due to air leakage through the gap of roof vent. The overall heat transfer coefficients acquired by experiment that was performed in single layer and conventional double layers greenhouses were close to those obtained from model experiment. Even though the PPF transmittance of air inflated double layers greenhouse was lower than that of single layer greenhouse, which was greater than that of conventional double layers greenhouse. The quantity of condensation water on covering surface of single layer greenhouse was greater than that of air inflated double layers greenhouse due to lower covering surface temperature.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.3
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• pp.275-282
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• 2014

Particle-reinforced metal matrix composites exhibit a strengthening effect due to the particle size-dependent length scale that arises from the strain gradient, and thus from the geometrically necessary dislocations between the particles and matrix that result from their CTE(Coefficient of Thermal Expansion) and elastic-plastic mismatches. In this study, the influence of the size-dependent length scale on the particle-matrix interface failure and ductile failure in the matrix was examined using finite-element punch zone modeling whereby an augmented strength was assigned around the particle. The failure behavior was observed by a parametric study, while varying the interface failure properties such as the interface strength and debonding energy with different particle sizes and volume fractions. It is shown that the two failure modes (interface failure and ductile failure in the matrix) interact with each other and are closely related to the particle size-dependent length scale; in other words, the composite with the smaller particles, which is surrounded by a denser dislocation than that with the larger particles, retards the initiation and growth of the interface and matrix failures, and also leads to a smaller amount of decrease in the flow stress during failure.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.10
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• pp.558-565
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• 2016

Water quality data including flow rates and BOD/COD/T-N/T-P/SS/TOC concentrations in Nakdong river tributaries were analyzed to determine priority management areas using 699 data sets from 195 locations in 2015. It was pointed out that the coefficients of variation, the ratio of the standard deviation to the mean, for the concentrations and loading rates of BOD, T-P, and TOC in each monitoring location were so large that average values of water quality monitoring data might be not appropriate to determine the priority management areas among all 195 monitoring stations in Nakdoing river. Therefore we suggested two evaluation methods using each water quality data independently. In the first method the excess numbers of the BOD, T-P, and TOC concentrations comparing to the water quality standards in the medium-sized management areas in Nakdong river was evaluated for each monitoring station. In the second method the percentile ranks of the loading rates of the BOD, T-P, and TOC were obtained for each monitoring data. The two groups of the priority management areas determined by each method were compared and the water quality characteristics in Nakdoing river were investigated.

• 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.

• The Journal of Engineering Geology
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• v.20 no.3
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• pp.281-295
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• 2010

A new, automated apparatus is proposed for calculating the Soil-Water Characteristic Curve (SWCC), representing a simple and easily applied testing device for continuous measurements of the volumetric water content and suction of unsaturated soils. The use of this apparatus helps to avoid the errors that arise when performing experiments. Consequently, the apparatus provides greater accuracy in calculating the SWCC of unsaturated soils. The apparatus is composed of a pressure panel, flow cell, water reservoir, air bubble trap, balance, sample-preparation accessories, and measurement system, among other components. The air pressure can attain 300 kPa, and a general test can be completed in a short time. The apparatus can simply control the drying process and wetting process. The changes in volumetric water content that occur during the drying and wetting processes are shown directly in the SWRC program, in real time. As a case study, we performed an SWCC test of Joomunjin sand (75% relative density) to measure matric suction and volumetric water content during both the drying and wetting processes. The test revealed hysteresis behavior, whereby the water content on the wetting curve is always lower than that on the drying curve for a specific matric suction, during the wetting and drying processes. Based on the test results, SWCCs were estimated using the Brooks and Corey, van Genuchten, and Fredlund and Xing models. The van Genuchten model performed best for the given soil conditions, as it yielded the highest coefficient of determination.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.2
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• pp.528-534
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• 2020

The early development and use of plate heat exchangers (PHE) were in response to stringent statutory requirements from dairy products in the late 19th century, but PHEs were not exploited commercially until the 1920s. Since then, although the basic concept of PHEs has changed little, its design and construction have progressed significantly to accommodate higher temperatures and pressures, as well as large heat exchanging capacities. The development of current chevron-type corrugated heat plates has been ongoing since the oil shock in the 1970s to improve energy efficiency. The development trend of PHEs is consistent with the development of larger heat plates with better thermal efficiency, lower pressure drop, and good flow distribution. In this study, the thermal performance of small heat plates (PHE-S) and large heat plates (PHE-L) with the same plate depth and corrugation pitch were analyzed experimentally for each channel (H, M, and L type) to suggest development directions of heat plates. The test results showed that for the convectional heat transfer coefficient, the PHE-S was on average, 16.5% higher in the H type, 25% higher in the M type, and 40% higher in the L type than PHE-L. In the case of the pressure drop, the PHE-S was 19% higher in the H type, 46% higher in the M type, and 61% higher in the L type than PHE-L. These results were attributed to the differences in fluid distribution areas between the PHE-S and PHE-L, among other potential causes.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.7
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• pp.536-543
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• 2011

In order to find the best design of artificial stream for the riverbed filtration in multi-purpose filtration pond, a mathematical model was developed employing the energy line and the Manning's formula and was analyzed by the Euler's technique. Various design factors were investigated through scenario analyses of the artificial stream using the model. Results showed that the appropriate slope of the stream bottom was 2/10,000 and the appropriate infiltration rate at the streambed was $2.5m^3/m^2-day$ for the pond with the area of 100 ha, and that the Manning's roughness coefficient in this case was expected to be about 0.026 and the maximum water-depth was less than 1m. It was also shown that the longer the artificial stream the more advantageous it became for the riverbed filtration. Furthermore, results showed that it was not an efficient way to prevent clogging of the streambed by increasing the flow velocity of the stream and that the performance was higher near a weir with a large head drop.