• Journal of the Korean Solar Energy Society
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• v.32 no.spc3
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• pp.255-261
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• 2012

Since PV PCS uses output current sensor for ac output current control, the sensor's sensing value includes unnecessary offset inevitably. If PV inverter is controlled by the included offset value, it's output current will generate DC offset. The DC offset of output current for trans-less PV inverter is fatal to grid, which results in saturating grid side transformer. Usually DSP controller of PV inverter reads several times sensing value during initial operation and, finally, it's average value is used for offset calibration. However, if temperature changes, the offset changes, too. And also, the switch device is not ideal, both each switching element of the voltage drop difference and on & off time delay difference generate DC offset. Thus, to compensate for deadtime and the switch voltage drop, feedback control by output current DC offset should be provided to compensate additional distortion of the output current. The validity of the proposed method is confirmed through PSIM simulation.

• Journal of Power System Engineering
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• v.20 no.1
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• pp.5-10
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• 2016

Swing check valve is opened when the flow direction is forward, when the flow is reversed, the valve is automatically closed by back pressure. In this study, the internal flow field analysis of the valve was conducted by Fluent. The working fluid used in the study, using liquefied methane $-165^{\circ}C$ (CH4) and velocity field, pressure field, pressure drop coefficient were simulated by varying separately the opening divergence into four intervals from 0 to 100%. The approximate research result are as follow : When the opening divergence is smaller, it appears high pressure on the upstream side, this value is relaxed when the opening divergence is large. Flow rate coefficient of the valve shows a larger value as the degree of opening becomes larger, confirming that the check valve used in the study is in the effective flow rate counting range.

• Journal of environmental and Sanitary engineering
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• v.15 no.3
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• pp.94-100
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• 2000

This study was carried out to interpret hydraulic behavior and CO2 gas desorption in counter-current packing tower which packed 50mm plastic Hiflow-ring. The results are as follow : To compare with conventional packing, 50mm Hiflow-ring could save energy because of low pressure drop under high load. As relative error between calculated value and investigated value was less than 6% in the loading point and flooding point we found that we are predict results mathematically which occur in packing tower. The unique magnitude of packing which was used are as follows. $C_L=2.1{\times}10^{-4}$, n=0.787 so we can predict efficiency which occur

• Journal of the Korean Society for Precision Engineering
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• v.24 no.11
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• pp.101-107
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• 2007

Jettability analysis using one-dimensional(1D) lumped parameter model has been investigated to design the industrial inkjet head with proper drop velocity and drop volume. By simplifying the inkjet head system into an equivalent electrical circuit, lumped model has been developed. Performance of the lumped model is verified by the comparison between measured results of droplet velocity and ejection volume and predicted value. Also, the jetting performance of an inkjet head is characterized by varying the design parameter and driving condition. As a result, simulation results shows good agreement with the experimentally measured value. The developed lumped model enables to easily understand the effect of dimension change and predict the jetting performance.

• Proceedings of the Safety Management and Science Conference
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• 2007.04a
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• pp.347-351
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• 2007

The main objective of this paper is to provide analysis of obesity index of residents in six metropolitan cities. According to analysis of $R{\ddot{o}}hrer$ Index, there was significant difference regionally between men and women in metropolitan cities. Through analysis of Drop Value, it was found that there were significant differences regionally between men and women in metropolitan cities on circumferences of chest, waist and buttocks. The result of this research can be utilized in manufacturing and design of uniforms and equipments for safety.

• Journal of the Korea Safety Management & Science
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• v.9 no.5
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• pp.37-41
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• 2007

There are two parts(middle and southern) according to dividing line of district in Korea. Middle part contains Kang Won, Chung Chung, Gyeong Gi, Seoul, In Cheon and Dae Jeon. Southern part contains Gyeong Sang, Jeol La, Je Ju, Bu San, Dae Gu, Ul San, and Gwang Ju. It is known that there are some differences between middle and southern part on weather. The climatic differences might affect human body. Thus, the mall objective of this study is to analyze effects of climatic differences which influence somatotype characteristics on residents in two regions. In order to compare and analyze data, $R\ddot{o}hrer$ index and drop-value were used. Also, this paper provides typical ratios according to dividing line of district.

• Journal of the Korea Safety Management & Science
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• v.9 no.4
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• pp.113-119
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• 2007

Recently, due to economic growth, living environment has been convenient and comfortable and so human activities were decreased. Consequently energy consumption was also decreased. Also the habit of food intake has been changed and the tendency of obesity has been increased. The main objective of this paper is to provide analysis of obesity index of residents in six metropolitan cities. According to analysis of $R\"{o}hrer$ Index, there were significant differences regionally between men and women in metropolitan cities. Through analysis of Drop Value, it was found that there were significant differences regionally between men and women in metropolitan cities on circumferences of chest, waist and buttocks. The result of this research can be utilized in manufacturing and design of uniforms and equipments for safety.

• Proceedings of the Safety Management and Science Conference
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• 2008.11a
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• pp.353-359
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• 2008

Somatotype is a very important factor for the comfortable and safe work environments. Many researches are trying to find the characteristics of somatotype according to age. Thus, the main objective of this study is to analyze somatotype of male residents in Seoul. The data used in this study included 267 men subjects who are living in Seoul. In order to analyze a detailed somatotype of citizens, age groups are divided into six groups. In order to compare and analyze data, Coefficient of Variance, Cronbach's Alpha, $R\ddot{o}hrer$ Index and Drop Value were used in this study. The results of this study can be applied to the comfortable and safe work environments for workers.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.4
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• pp.78-87
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• 2021

Understanding the liquid propellant transport phenomena in low gravity is essential for developing Korea Space Launch Vehicle (KSLV) upper-stage for the diversity of space missions. A low-gravity environment can be simulated via the free-fall method on the ground; however, the air drag is inevitable. To reduce air resistance during free fall, air-drag shield is usually adopted. In this study, the free-fall method was performed with an air-drag shield from a 7-m height tower. The acceleration of a falling object was measured and analyzed. Low gravity below 0.01 g was achieved during 1.2-s free fall with the air-drag shield. The minimum gravitational acceleration value at 1.2-s after free fall was ±0.005 g, which is comparable to the value obtained from Bremen drop tower experiments, ±0.002 g. A prolonged free-fall duration may enhance the low-gravity quality during the drop tower experiments.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.5
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• pp.77-82
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• 2003

A parametric study was conducted on pressure drop in a catalytic converter for automobile. In this work, we proposed a new pressure drop relation which contains the various parameters needed to calculate and got a few results. In a monolith of catalyst, the flow originally turbulent flow changes to laminar flow and thus the pressure drop through the monolith is linearly proportional to the velocity. The exhaust pressure is doubly affected by the increase of mean velocity and length when we decrease the diameter of monolith while the volume keeps constant. Theoretical parameters such as $\alpha$ and $\beta$ are suggested to use as a reference value when there is no a experimental data. Especially in the part load test, these values should be modified to consider the property change of exhaust gas.