• Transactions of the KSME C: Technology and Education
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• v.1 no.2
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• pp.153-165
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• 2013

The established gait analysis studies have regarded leg as one single spring. If we can design a knee-ankle actuating mechanism as a primary actuator for supporting knee extension, it might be possible to revolutionary store or release elastic strain energy, which is consumed during the gait cycle, and as a result leg stiffness is expected to increase. An ankle joint actuating mechanism that stores and releases the energy in ankle joint is expected to support and solve excessive artificial leg stiffness caused by the knee actuator (primary actuator) to a reasonable extent. If unnecessary kinematic energy is released with the artificial speed reduction control designed to prevent increase in gait speed caused by increase in time passed, it naturally brings question to the effectiveness of the actuator. As opposed to the already established studies, the authors are currently developing knee-ankle two actuator system under the concept of increasing lower limb stiffness by controlling the speed of gait in relative angular velocity of the two segments. Therefore, the author is convinced that compensatory mechanism caused by knee actuating must exist only in ankle joint. Ankle joint compensatory mechanism can be solved by reverse-examining the change in metatarso-phalangeal joint (MTPJ) tilt angle (${\theta}_1=0^{\circ}$, ${\theta}_2=17^{\circ}$, ${\theta}_3=30^{\circ}$) and the effect of change in gait speed on knee activity.

• Journal of Korea Water Resources Association
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• v.53 no.10
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• pp.871-876
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• 2020

Understanding the wave characteristics near the outlet of coastal power plants for cooling water in the vicinity of the dredged areas is critically important for the construction and operation of the plants. By Employing the eigenfunction expansion method, in this study, we analyzed the reflection of monochromatic water waves over (1) shear currents near the outlet and (2) multi-arrayed trenches representing dredged areas. We firstly optimized the number of grids expressing shear currents and the number of evanescent modes based on a convergence test. We then analyzed the sensitivity of the reflection coefficients depending on (1) magnitude of shear currents, (2) width of shear currents, (3) a distance between adjacent trenches, and (4) a number of trenches. The results showed that the reflection coefficient was more sensitive to the number of trenches and the distance between trenches than the velocity of shear currents and the width of shear currents. We also found that even the effect of shear currents is relatively small, the effect is not negligible in a relative water depth from shallow to near shallow water waves (0.01 < kh ≦ 0.70).

• Journal of Korean Society of Environmental Engineers
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• v.30 no.3
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• pp.293-301
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• 2008

A study on the operational variables of the UV-TiO$_2$ based photocatalytic air cleaning system was tried. In this study, to examine effects as various air cleaning system conditions, a duct-type reactor was made, and TiO$_2$ was immobilized on a stainless mesh. Benzene was chosen as a target compound. Removal experiments for benzene were done under different initial benzene concentration, air velocity, TiO$_2$ loading, area coated TiO$_2$ as the same TiO$_2$ loading, and UV light intensity conditions. During the experiments, relative humidity was 55%, and reactor temperature was 45$^{\circ}C$. As a result, the photocatalytic degradation of benzene decreased as the inlet concentration increased. But the photocatalytic degradation increased as the concentration boundary layer thickness, amount of TiO$_2$, area coated TiO$_2$ as the same amount of TiO$_2$, and UV light intensity increased. Based on results of current study, they can be applied to the design of air cleaning system over low level VOCs in the indoor air.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.200-214
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• 1993

This paper presents the results of fluidelastic instability analysis performed for the U-tube bundle of a Westinghouse model 51 steam generator, one of the recirculating types designed at an early stage, in which the principal region of external cross-flow is associated with the U-bend portion of tube. The prerequisites for this analysis are detailed informations of the secondary side flow conditions in the steam generator and the free vibration behaviours of the U-tubes. In this study, the three-dimensional two-phase flow field in the steam generator has been calculated employing the ATHOS3 steam generator two-phase flow code and the ANSYS engineering analysis code has been used to calculate the free vibration responses of specific U tubes under consideration. The assessment of the potential instability for the suspect U-tubes, which is the final analysis process of the present work, has been accomplished by combining the secondary side velocity and density distributions obtained from the ATHOS3 prediction with the relative modal displacement and natural frequency data calculated using the ANSYS code. The damping of tubes in two-phase flow has been deduced from the existing experimental data by taking into account the secondary side void fraction effect. In operation of the steam generator, the tube support conditions at the tube-to-tube support plate intersections due to either tube denting degradation or deposition of tube support plate corrosion products or ingression of dregs. Thus, various hypothetical cases regarding the tube support conditions at the tube-to-tube support plate intersections have been considered to investigate the clamped support effects on the forced vibration response of the tube. Also, the effect of anti-vibration bars support in the curved portion of tube has been examined.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.4
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• pp.1576-1581
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• 2013

In the present study, the performance of a PF heat exchanger for heat pump dryer was investigated. Capacity and dehumidification amount of the PF heat exchangers(PF1, PF2, PF3) by different inclination angles($0^{\circ}$, $30^{\circ}$, $60^{\circ}$) were studied. Experimental conditions were an air velocity crossing to the heat exchanger(0.5m/s), an air dry-bulb temperature($60^{\circ}C$) and relative humidity(70%). The experimental results have shown that the performance of the inclined PF heat exchangers was better than that of the vertically installed one. PF3 showed better performance compared to PF1 and PF2 due to the large pin pitch which are leading to more draining for dehumidified water. But, capacity and dehumidification amount of the PF heat exchanger at the inclination angles of $60^{\circ}$ was decreased due to pressure drop. Also, to predict the experimental data of the PF heat exchanger, the performance program was developed for the inclination angles of $0^{\circ}$. PF heat exchanger performance between experiment data and calculation data was satisfied within the maximum 2% for capacity and 3% for dehumidification amount.

• Journal of Korean Society for Atmospheric Environment
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• v.22 no.5
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• pp.642-652
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• 2006

In order to understand the characteristics of surface ozone concentration and high $O_3$ concentration days, regional data from seven air quality monitoring stations which were operated by local governments were analyzed Regional characteristics of $O_3$ concentration were analyzed with the data of $O_3$ concentration and the characteristics of $O_3$ generation and weather conditions by the selection of the days in which the concentration was higher than 80 ppb. In the case of daily variation, the lowest $O_3$ concentration was shown in all regions from 7am to 8am and the highest around at 4 pm. The monthly variation of mean $O_3$ concentration and ${\Delta}O_3$ values revealed a reducing pattern in July and August following the peak in June, and again a gradual increasing trend in September and October. The result shows that the amount of ozone is dependent on photochemical reaction. The days of $O_3$ generated more than 80 ppb in the region of Gwangyang-bay were 544 days(1,760 hrs). The frequency of occurrence in the region revealed a strong pattern with the order of Samil-dong, Jinsang, and Gwangmu-dong stations in the Gwangyang region. However, Tein-dong, which is the nearest station to air pollution material generation source, showed the lowest frequency in the study area. Consequently, the meteorological parameters which can easily generate the high concentration of $O_3$ in the region of Gwangyang-bay are characterized as follows; atmospheric temperature which is higher than $19^{\circ}C$, relative humidity with the range of $60{\sim}85%$, the less average wind velocity than 5 m/s, cloud cover which is less than 5/10, and the more duration of sunshine than 8 hours.

• Korean Journal of Ecology and Environment
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• v.37 no.2 s.107
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• pp.227-235
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• 2004

Fish fauna and community structure were surveyed in the Nakdong River, Gumi City, Kyeongpook province from April 2001 to July 2002. During the surveyed Period, 39 species, 32 genera belonging to 10 families were collected. Cyprinid fish occupied 64.1% (25 species) and cobitid fish had 7.7% (3 species). Fourteen species(35.9%) of observed species were known as endemic species. The exotic fish was Micropterus salmoides (2.5%) . The dominant species were Zacco platypus (relative abundance: 36.7%) and Opsariichthys uncirorstris amurensis (22.7%). Carassius aurafus and Microphysogobio rapidus were numerous (4.0${\sim}$4.3%). The rare species comprising less than 0.15% were Acheilognathus koreensis, Aphyocypris chinensis, Iksookimia longicorpus, Coreoleuciscus splendidus, Rhinogobius giurinus, Sarcocheilichthys variagatus wakiyae, Silurus asotus astus, and Channa argus. It was found that the population density of carnivorous Opsariichthys uncirostris amurensis increased drastically in the mid-reach of the Nakdong river since it had been introduced from the other native rivers in the middle 1990s. Gobiobotia nakdongensis inhabit riffle (water velocity : 0.43${\sim}$0.67 m $s^{-1}$) of which the river bed is mainly sand. This species is considered to be in need of conservation. As the result of analyzing fish community in the surveyed area, the species diversity, evenness and dominant indices were 1.008, 0.663 and 0.196 respectively. The findings showed that the tributary, which the waterside plants were abundant and had various habitats, had a higher species diversity (1.112) than the main river (0.787). Sand mining had been disturbing the river ecosystem of the study stations 3, 11, 13 & 14, and these stations showed a quite low species diversity (0.421 ${\sim}$0.574).

• Journal of The Korean Astronomical Society
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• v.36 no.4
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• pp.271-282
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• 2003

We present results of a $H^{13}CN$ J=1-0 mapping survey of molecular clouds toward the Galactic Center (GC) region of $-1.6^{\circ}{\le}{\iota}{\le}2^{\circ}$ and $-0.23^{\circ}{\le}b{\le}0.30^{\circ}$ with 2' grid resolution. The $H^{13}CN$ emissions show similar distribution and velocity structures to those of the $H^{12}CN$ emissions, but are found to better trace the feature saturated with $H^{12}CN$ (1-0). The bright components among multi-components of $H^{12}CN$ line profiles usually appear in the $H^{13}CN$ line while most of the dynamically forbidden, weak $H^{12}CN$ components are seldom detected in the $H^{13}CN$ line. We also present results of other complementary observations in $^{12}CO$ (J=1-0) and $^{13}CO$ (J=1-0) lines to estimate physical quantities of the GC clouds, such as fractional abundance of HCN isotopes and mass of the GC cloud complexes. We confirm that the GC has very rich chemistry. The overall fractional abundance of $H^{12}CN$ and $H^{13}CN$ relative to $H_2$ in the GC region is found to be significantly higher than those of any other regions, such as star forming region and dark cloud. Especially cloud complexes nearer to the GC tend to have various higher abundance of HCN. Total mass of the HCN molecular clouds within $[{\iota}]{\le}6^{\circ}$ is estimated to be ${\~}2 {\times}10^7\;M_{\bigodot}$ using the abundances of HCN isotopes, which is fairly consistent with previous other estimates. Masses of four main complexes in the GC range from a few $10^5$ to ${\~}10^7\;M_{\bigodot}$ All the HCN spectra with multi-components for the four main cloud complexes were investigated to compare the line widths of the complexes. The largest mode (45 km $s^{-1}$) of the FWHM distributions among the complexes is in the Clump 2. The value of the mode tends to be smaller at the farther complexes from the GC.

• Informatization Policy
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• v.19 no.4
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• pp.63-82
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• 2012

The world's best level of ICT(Information, Communication and Technology) infrastructure has experienced the world's worst level of ICT accident in Korea. The number of major accidents of privacy invasion has been three times larger than the total number of Internet user of Korea. The cause of the severe accident was due to big data environment. As a result, big data environment has become an important policy agenda. This paper has conducted analyzing the accident case of data spill to study policy issues for ICT security from a social science perspective focusing on risk. The results from case analysis are as follows. First, ICT risk can be categorized 'severe, strong, intensive and individual'from the level of both probability and impact. Second, strategy of risk management can be designated 'avoid, transfer, mitigate, accept' by understanding their own culture type of relative group such as 'hierarchy, egalitarianism, fatalism and individualism'. Third, personal data has contained characteristics of big data such like 'volume, velocity, variety' for each risk situation. Therefore, government needs to establish a standing organization responsible for ICT risk policy and management in a new big data era. And the policy for ICT risk management needs to balance in considering 'technology, norms, laws, and market'in big data era.

• Journal of Digital Convergence
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• v.14 no.8
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• pp.245-252
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• 2016

The purpose of this study is to make up for missing of weather informations from ASOS and AWS using artificial neural networks. We collected temperature, relative humidity and wind velocity for August during 5-yr (2011-2015) and sample designed artificial neural networks, assuming the Seoul weather station was missing. The result of sensitivity study on number of epoch shows that early stopping appeared at 2,000 epochs. Correlation between observation and prediction was higher than 0.6, especially temperature and humidity was higher than 0.9, 0.8 respectively. RMSE decreased gradually and training time increased exponentially with respect to increase of number of epochs. The predictability at 40 epoch was more than 80% effect on of improved results by the time the early stopping. It is expected to make it possible to use more detailed weather information via the rapid missing complemented by quick learning time within 2 seconds.