• Journal of Korea Water Resources Association
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• v.45 no.12
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• pp.1275-1292
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• 2012

This study investigates the characteristics of stem waves along a vertical structure under overtopping conditions through laboratory experiments in a wave basin. The uni-directional random waves with Bretschneider-Mitsuyasu frequency spectrum as incident waves were used. This study is focused on the reduction of wave height due to the variation of relative freeboard height (R) and the results for wave overtopping conditions are compared with those for non-overtopping conditions. Though the relative wave height along a vertical structure decreases with the decrease of relative freeboard, the variation of stem width is not significant. For the relative freeboard is greater than 1, the reduction effect of stem wave height by overtopping can be ignored in this experiments. The reduction effect of wave height along the structure for R =0.5 is about 10% comparing with R =1.5.

• Korean Journal of Agricultural Science
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• v.51 no.1
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• pp.25-39
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• 2024

This study aimed to determine a method for restoring grasslands to forests in mountainous areas. The study was conducted in an area damaged by trampling due to construction activity and herding. Additionally, there were concerns of hindered tree growth due to the alpine region climate, characterized by the low temperatures, drying, and strong winds. Therefore, forest restoration treatments such as tillage, furrow, and shading were performed to improve growth conditions. From July 2021 to April 2023, soil temperature and moisture were monitored for each treatment plot, and changes in the initial growth and survival rate of Abies holophylla were investigated. Both soil temperature and soil moisture showed significantly higher values during the four seasons in the grassland-furrow treatment plot (p < 0.05). Compared to the grassland-control plot, the average soil temperature in winter was as high as 1.1℃, and the soil moisture in summer was as high as 20.3%. Additionally, the survival rate and relative growth rate were the largest in the grassland-furrow treatment plot. The survival rate was 87.5%, the relative growth rate in terms of height was 0.013, and the relative growth rate in terms of diameter at root collar was 0.023, indicating that furrow treatment had a positive effect on the initial survival and growth of seedlings. These results suggest that furrow treatment may be an appropriate restoration method when implementing forest restoration projects in areas where tree growth is challenged.

• Journal of the Korean Applied Science and Technology
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• v.40 no.6
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• pp.1249-1258
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• 2023

The purpose of this study was to reveal the effect of COP variable of support feet on relative reach distance and composite score of active feet during YBT. 29 adults in their 20s(age: 24.4±3.0 yrs, height: 171.0±10.5 cm, weight: 72.1±12.1 kg, leg length: 88.2±5.8 cm) participated in the study. Using YBT, relative reach distance and composite score of active feet were calculated, and COP variables of support feet were measured on left and right support feet. Multiple regression analysis was used to determine the effect of COP variables of support feet during YBT on relative reach distance and composite score. As a result of the study, during YBT, when supporting right feet, the influence of AP COP velocity, ML COP velocity and COP velocity in posterolateral direction was significant, and when supporting left feet, the influence of AP COP velocity, ML COP velocity in posteromedial direction improved relative reach distance and composite score.

• Proceedings of the KSMRM Conference
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• 2004.09a
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• pp.16-16
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• 2004

• Proceedings of the Korean Magnestics Society Conference
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• 2017.05a
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• pp.181-181
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• 2017

• Journal of the Korean Geotechnical Society
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• v.28 no.8
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• pp.21-29
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• 2012

At-rest lateral stress coefficient that is used for the evaluation of geotechnical structures such as foundations and retaining walls plays a significant role in the analysis and design, as a state variable of in-situ stress condition. In the widely applied Jaky's Ko equation stress condition can be inferred from the internal friction angle obtainable from the laboratory experimentation whereas the eguation mares it challenging to evaluate the influences and criteria of particle characteristics which is essential for the application of friction angles in practices. Thus, this study experimentally explored the behaviors of Ko depending on the relative density, particle shape, and surface roughness effect during a range of loading stages. The Ko values of Jumumjin sand, glass beads, and etched glass beads were measured using a customized Ko device housing strain gauges during loading-unloading-reloading steps, and the effect of dominant factors on Ko is analyzed. Results show that the high Ko prevails for both round and angular specimens with low relative density and the surface roughness has a nominal effect. The angular particles exhibit low Ko for specimens with similar relative density. The characteristics of relevance between Ko and friction angles with varying relative density are also investigated based on the experimental results using empirical correlations and previously reported values.

• Journal of Powder Materials
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• v.15 no.5
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• pp.365-370
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• 2008

In this study, bottom-up powder processing and top-down severe plastic deformation processing approaches were combined in order to achieve both full density and grain refinement with least grain growth. The numerical modeling of the powder process requires the appropriate constitutive model for densification of the powder materials. The present research investigates the effect of representative powder yield function of the Shima-Oyane model and the critical relative density model. It was found that the critical relative density model is better than the Shima-Oyane model for powder densification behavior, especially for initial stage.

• Journal of the Korean Ceramic Society
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• v.53 no.1
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• pp.99-104
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• 2016

High purity Si-C (99.999%) powder prepared by mechanical alloying was added to a commercial SiC powder as a sintering additive. Reaction bonded silicon carbide balls and jars with high purity (99.98%) were used for the mechanical alloying. As a result, the purity of the sintered Si-C was higher than 99.99%. When sintered at $2200^{\circ}C$ under 50 MPa pressure for 1 h, SiC containing 10 wt% of high purity Si-C showed a relative density of 95.3%, similar to the relative density of commercial SiC (95%). However, the relative density of SiC decreased to 90.6% without the additive when the applied pressure decreased to 40 MPa. In contrast, the relative density was nearly unaffected by the decrease of the pressure when using the Si-C additive. Therefore, the addition of Si-C powder promoted the densification of SiC above $2000^{\circ}C$ under 40 MPa pressure.

• Journal of Power Electronics
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• v.15 no.3
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• pp.841-848
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• 2015

As a vital part of renewable energy and electrical traction, power converters are supposed to have high reliability and good performance. However, power semiconductors produce considerable heat when the power converter works, which results in high junction temperatures that lower the reliability and performance of the power semiconductors. Many studies show that ambient humidity has a significant effect on power devices, but the influence of high humidity on junction temperatures has yet to be studied. Therefore, this paper presents a thermal model for power converters in moist air to obtain the junction temperature increase, which is utilized for the power converter used in a Switched Reluctance Motor System. Simulation results show that the law of converter temperature distribution is independent of the relative humidity in the case of fixed ambient temperature, whereas the temperature in the power converter decreases as the ambient relative humidity increases. These simulation results are validated with the experimental results.

• Advances in Energy Research
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• v.5 no.1
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• pp.65-77
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• 2017

The latest UK Climate Projections (UKCP09) show that mean daily temperatures will increase everywhere in the United Kingdom. This will significantly affect the thermal and energy performance of the current building stock. This study examines an institutional fully glazed building and looks into the changes in the cooling loads and thermal comfort of the occupants during the occupied hours of the non-heating period. Furthermore, it investigates the effect of relative humidity (RH) on thermal comfort. The Design Summer Year (DSY) 2003 for London Heathrow has been used as a baseline for this study and the DSY 2050s High Emissions scenario was used to examine the performance of the building under future weather conditions. Results show a 21% increase of the cooling loads between the two examined scenarios. Thermal comfort appears to be slightly improved during the months of May and September and marginally worsen during the summer months. Results of the simulation show that a relative humidity control at 40% can improve the thermal comfort for 53% of the occupied hours. A comparison of the thermal comfort performance during the hottest week of the year, shows that when the relative humidity control is applied thermal comfort performance of the 2050s is similar or better compared to the thermal comfort performance under the baseline.