• Journal of the Korean Geotechnical Society
• /
• v.33 no.11
• /
• pp.73-82
• /
• 2017

Recently, offshore bucket cut-off walls were developed to solve several problems in conventional offshore cut-off walls. In this study, a numerical analysis was carried out to investigate the seepage stability of offshore bucket cut-off walls. The ground was assumed as uniform homogeneous sand and steady state flow conditions were applied. The flow condition was compared among 2-dimensional flow (2-D), 2-dimensional concentrated flow (2-DC), and axisymmetric flow. The analysis results showed that the seepage velocities in axisymmetric flow were about 1.5 and 2 times larger than those of 2-DC and 2-D flow conditions, respectively. Thereafter, the axisymmetric flow condition was applied because the seepage flow was concentrated toward the center of the circular-shaped wall. A parametric study was performed varying bucket radius, penetration depth, total head difference between in and outside of the wall. The exit gradient, which used for the calculation of piping stability, decreased with increase of the penetration depth and bucket radius. Design charts were proposed to estimate the factor of safety and the exit gradient at various analysis conditions. Finally, the design equation was proposed to calculate the exit gradient for the preliminary design of the bucket cut-off wall.

• Journal of Korean Society of Forest Science
• /
• v.90 no.6
• /
• pp.692-698
• /
• 2001

This study has been carried out to estimate aboveground biomass and net primary production(NPP) in an average 41-years-old Quercus variabilis stand of Gongju area, 45-years-old Quercus variabilis stand of Pohang area, and 54-years-old Quercus variabilis stand of Yangyang area. Ten sample trees were cut in each forest and soil samples were collected in July to August, 2000. Estimation for aboveground biomass and net primary production were made by the equation model $Wt=aD^b$ where Wt is oven dry weight in kg and D is DBH in cm. Total aboveground biomass was 91.31ton/ha in Gongju area, 207.6ton/ha in Pohang area, and 71.39ton/ha in Yangyang area. The aboveground biomass 207.6ton/ha in Pohang area is the highest biomass production among the amount of biomass in Quercus variabils stands reported in Korea. The proportion of each tree component to total aboveground biomass was high in order of bolewood, bolebark, branches and leaves in the three forests. Aboveground total net primary production was estimated at 7.8ton/ha in Gongju area, 11.5ton/ha in Pohang area, and 6.40ton/ha in Yangyang area. There were at least 2 times higher total aboveground biomass in Pohang area than in the Gongju and Yangyang areas because of climate difference among the study areas.

• Korean Journal of Social Welfare Studies
• /
• v.45 no.3
• /
• pp.237-262
• /
• 2014

Little is known about the relationships among adolescents'academic stress, self-efficacy, and internalization externalization. Much less is known about whether there is gender differences in the relationships. This study aims to examine (1) the effects of academic stress on internalization externalization, (2) whether self-efficacy mediates the relationships between academic stress and internalization externalization, and (3) whether there is gender difference in the relationships. For these purposes, we used Structural Equation Modeling and multi group analysis involving 2,844 middle school students participated in the Korean Youth Panel Survey. The results are as follows. First, adolescent's academic stress affected internalization externalization. Second, self-efficacy mediated the relationship between academic stress and internalization externalization. Finally, the multiple group analysis results indicated that the path coefficient between academic stress and internalization of girls was significantly greater than that of boys. Based on these results, we discussed theoretical and practical implications and suggested directions for future research on academic stress coping processes among adolescents.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
• /
• v.14 no.5
• /
• pp.115-125
• /
• 2019

This study examined the effects of entrepreneurship and perception of entrepreneurial environment on business performance. In particular, this study analyzed the difference in the effect of each independent variable on the dependent variable by using the government's participation in the start-up support project as a moderate variable. In order to achieve the purpose of this study, the researcher drew the variables corresponding to entrepreneurship and the variables related to entrepreneurship awareness. Innovativeness and risk sensitivity were selected as variables for entrepreneurship, and market environment and product environment were selected as variables for perception of entrepreneurial environment. Based on the above variables the research model was completed including the degree of participation in the government's start-up support project as a moderating variable. The data for the empirical analysis were collected from start-up companies in Daegu in 2018. A total of 601 questionnaires were collected and 399 copies of the data were used in this study after removing the unfaithful answers. The results of the analysis showed that innovation had a negative effect on management performance, and risk sensitivity, market environment, and product environment had a positive effect on management performance. In terms of the moderating effect, in the case of innovation, the higher the participation in government support projects, the lesser the negative effect. Risk sensitivity and product environment showed a strong impact on companies with a lot of government support projects, and the market environment had a strong impact on those who participated less. This study confirmed the importance and necessity of entrepreneurship and perception of entrepreneurial environment that influence the management performance of entrepreneurs. It is also meaningful in that it deals with the practical effects of the government's start-up support project on the start-up performance.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
• /
• v.17 no.4
• /
• pp.418-425
• /
• 1988

Since conventional computer program is workable only with velocity boundary condition, in practical fluid passage such as clean room which usually have wide inlets and outlets, it is not easy to measure velocity itself because of its vector property. Furthermore a certain assumption of velocity at boundaries may lead to physically unreasonable results. From this motivation, we have developed a computer program to predict whole flow field imposed on pressure-based boundary condition which can be measured by relatively simple method. The only additional velocity boundary condition that should be imposed on to make the problem unique, are no slip condition at all walls and zero cross stream velocity at inlet. The result of present study was compared with that by Bernoulli equation being used practically. They were coincident well each other within 5%, therefore the validity of the present method is proved. In the present work, the flow field in a clean room subject to pressure-based boundary conditions at an inlet and two exits was predicted numerically. The pressure difference between the inlet and the left exit which keeps relatively low pressure among two exits is fixed as 150[Pa] and the pressure at the right exit is varied from zero to 150[Pa] by the increment of 25[Pa]. For each cases the flow characteristics in the clean room, the velocity profile at the inlet, and the flow rate through the two exits was predicted. The flow rate through the right exit imposed on relatively higher pressure than the left exit decreased linearly according to the increase of pressure of the right exit. When the pressure of the right exit is increased enough to cause back flow at the exit, the flow rate is rapidly decreased.

• Korean Journal of Soil Science and Fertilizer
• /
• v.40 no.5
• /
• pp.364-368
• /
• 2007

The objective of this study was to characterize organic mater decomposition with application of livestock manure compost in upland soil. Six different composts, which were chicken (CHM), pig (PIM), and cow (COM) manure compost added and chicken (CHMS), pig (PIMS), cow (COMS) manure compost with sawdust added, were prepared for this study. These composts have different composition of crude carbohydrate (hemicellulose, cellulose, and lignin). The buried-bag method was used to determine the rate of organic mater decomposition and the changes of crude carbohydrate content during 36 months in the field. In all treatment, hemicellulose content was sharply decreased within 8 months, but considerable amount of lignin was remained after 36 months. After 40 months, the rates of carbon decreasing were 81, 80, 72, 69, 67, and 64 % for CHM, PIM, COM, CHMS, PIMS, and COMS, respectively. The estimated equation of carbon decreasing rate (D), $D=aT^b$, was fit to the carbon decreasing rate vs. elapsed time (T) using a non-linear regression procedure. After 40 months, significant difference of carbon decreasing rate between observed and estimated was not found. The relationship between constant a, b and hemicellulose content in the compost was not observed in this experiment. The cellulose and lignin content in the compost were positively correlated to the constant b and negatively correlated to the constant a.

• 한국노년학
• /
• v.38 no.1
• /
• pp.125-142
• /
• 2018

This study aims to investigate the relationship between filial piety, family exchange, and social exchange and perception of intergenerational solidarity and to find the differences of those relationships among different age groups. '2017 Age Integration Survey' data, which were collected under the support of Social Science Korea (SSK) project of National Research Foundation of Korea. 300 participants for each three age group such as the young, middle-aged and older adult were randomly selected among 1,017 and data were analyzed by structural equation modeling method. Findings were as follows. Firstly, filial piety, family exchange, social exchange affected the perception of intergenerational solidarity. Secondly, there is a significant difference in those relationships among different age groups. Family exchange and social exchange were statistically significant variables to explain the perception of intergenerational solidarity in the young age group; filial piety, family exchange, and social exchange, all three variables were related statistically significantly to the perception of intergenerational solidarity in the middle-aged group. For older adult group, filial piety and social exchange appeared as the significant variables. Based on these findings, several suggestions in policies and practices were made to increase the perception of intergenerational solidarity by reflecting the characteristics of each age groups.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.8
• /
• pp.8-14
• /
• 2019

Bird-strike is one of the most important design factors for safety in the aviation industry. Bird-strikes have been the cause of significant damage to aircraft and rotorcraft structures and the loss of life. This study used DYTRAN software to simulate the transient response of an Euler-Lagrangian composite helicopter blade that has been impacted by a bird. The Arbitrary Lagrangian Eulerian (ALE) method and a suitable equation of state were applied to model the bird. ALE was applied to the bird-strike analysis due to the large difference between the properties of the blade and bird. The debris of the bird was assumed to be a fluid and applied as Euler elements after the collision. Through the analysis of bird impacts, the leading-edge of the rotor blade (50.8 mm) was used to identify a positive margin of 1.18 based on the TSAI-FILL criteria. The results are assessed to be sufficiently reliable and may be evaluated to replace tests with various analysis conditions. The structural stability of the rotor blade could be assessed by applying various load conditions and different modeling methods in the future.

• Journal of the Korean Institute of Gas
• /
• v.23 no.3
• /
• pp.7-19
• /
• 2019

In this study, a model was developed for estimating deliverability considering the pressure dependent permeability and predicting production profile with Material Balance Equation(MBE) for Coalbed Methane(CBM) fields. The estimated deliverability was compared with the conventional deliverability based on CBM well testing data with coefficient of determination($R^2$). As a result, the former was 0.76 and the latter was 0.69. It was confirmed that the deliverability which consider the pressure dependent permeability is more adoptable when representing the productivity of CBM fields. Through this process, in order to calculate pressure dependent permeability when well testing data exist, a method to infer reservoir pressure within the radius of investigation was proposed. The production profile of 31 gas wells was predicted for 15 years, using the estimated deliverability and the MBE. After that, the results was compared with simulation results of the literature. The simulation results did not account the pressure dependent permeability and the developed model results considered that. As the applied field permeability rised 1.17 times, field production rate was increased approximately 15% than the literature results. According to other researches, the permeability of CBM fields can be rise 6 ~ 25 times. For these cases, the production profiles may have significant difference with conventional gas fields.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.1
• /
• pp.409-418
• /
• 2019

Debris flows occur in mountainous areas due to heavy rains resulting from climate change and result in disasters in the downstream area. The purpose of this study is to estimate the impact force of a debris flow when a check dam according is installed in various locations in the channel of a highly mountainous area. A Finite Differential Element Method (FDM) model was used to simulate the erosion and deposition based on the equation for the mass conservation and momentum conservation while considering the continuity of the fluid. The peak impact force from the debris flow occurred at 0 to 5 sec and 15 to 20 sec. When the supplied water discharge was increased, greater peak impact force was generated at 16 to 19 sec. This means that when increasing the water supply, the velocity of the debris flow became faster, which results in increased energy of the consolidation between the particles of the water and the sediment made. If a number of check dams were to be set up, it would be necessary to investigate the impact force at each location of the check dam. The results of this study could provide useful information in predicting the impact force of the debris flow and in installing the check dams in appropriate locations.