• Journal of the Korean Society of Marine Environment & Safety
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• 제24권7호
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• pp.930-938
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• 2018

Underwater noise radiated from submarines is directly related to the probability of being detected by the sonar of an enemy vessel. Therefore, minimizing the noise of a submarine is essential for improving survival outcomes. For modern submarines, as the speed and size of a submarine increase and noise reduction technology is developed, interest in flow noise around the hull has been increasing. In this study, a noise analysis technique was developed to predict flow noise generated around a submarine shape considering the free surface effect. When a submarine is operated near a free surface, turbulence-induced noise due to the turbulence of the flow and bubble noise from breaking waves arise. First, to analyze the flow around a submarine, VOF-based incompressible two-phase flow analysis was performed to derive flow field data and the shape of the free surface around the submarine. Turbulence-induced noise was analyzed by applying permeable FW-H, which is an acoustic analogy technique. Bubble noise was derived through a noise model for breaking waves based on the turbulent kinetic energy distribution results obtained from the CFD results. The analysis method developed was verified by comparison with experimental results for a submarine model measured in a Large Cavitation Tunnel (LCT).

• Journal of the Korean Society of Food Science and Nutrition
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• 제44권12호
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• pp.1881-1894
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• 2015

The objective of this study was to provide information on difficulty of performing tasks, degree of task satisfaction, job satisfaction, organizational commitment, and turnover intention as well as investigate correlations among these factors. Data were collected on employees working at Centers for Children's Foodservice Management, which had been operating for over 6 months until December 2013. The recruitment period was from December 16, 2013 to January 30, 2014. A total of 228 employees (79.7%) participated in the study, and 227 completed questionnaires were analyzed. Statistical analyses were performed on the data utilizing the SPSS V20.0 and AMOS V21.0 programs. The main results of this study were as follows: task satisfaction of employees in charge of 'visiting-teaching' for children was highest (4.24 points), whereas that of employees in charge of financial management was lowest (2.92 points). In terms of evaluation of job satisfaction factors, the score of 'co-worker' was highest (3.99 points) while that of 'payment' was lowest (2.45 points). Average scores of general job satisfaction, organizational commitment, and turnover intention were 3.56 points, 3.54 points, and 3.07 points, respectively. Job achievement was the most significant influencing factor on general job satisfaction, organizational commitment, and turnover intention. According to the path analysis results, the degree of task satisfaction affected job satisfaction. Organizational commitment had a more significant effect on turnover intention than job satisfaction and mediate both job satisfaction and turnover intention. Although employees of CCFSMs endeavor to improve the quality of child-care facility foodservice, some facilities do not. Controlling turnover intention of employees is especially critical for CCFSMs since it is important for each employees to form strong bonds with child-care facilities as well as to shorten the time required to train new employees. Thus, job satisfaction, which is related to organizational commitment and turnover intention, can be improved by considering poorly scored job satisfaction factors such as wage or workload.

• Management & Information Systems Review
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• 제37권3호
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• pp.1-25
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• 2018

This research performed the empirical test for the effects of learning transfer on perceived usefulness, perceived ease of use, self-efficacy and work environment using 390 employees who have experienced e-learning in domestic and foreign companies. Analyzed the mediating effects of self-efficacy and work environment in addition to direct effect of each factor on learning transfer. The results showed that perceived usefulness and perceived ease-of-use of e-learning learner had a positive(＋) effect on self-efficacy and a positive influence on supervisor and peer support and organizational climate. Self-efficacy showed a positive effect on learning transfer, and supervisor support, peer support and organizational climate had a positive influence on learning transfer as well. Perceived usefulness also had a positive effect on learning transfer. However, perceived ease-of-use had no significant effect on learning transfer. As a result of the mediating effect analysis, self-efficacy and work environment were analyzed to have mediating effects between perceived usefulness, perceived ease of use, and learning transfer. The implications of this study are as follows. First, this study designed a new research model that reflects factors influencing the effect of learning transfer on acceptance of e-learning that is common in corporate education. It has derived a research model of perceived usefulness and perceived ease-of-use, which were used as mediating variables for external characteristics factors, as independent variables, using self-efficacy and work environment as mediating variables, which were studied as external factors. Second, most of the studies on technology acceptance model and learning transfer are conducted in a single country. The reliability was enhanced by testing the study models using different samples from 26 countries. Third, perceived usefulness and ease-of-use in existing studies have been considered as key determinants of acceptance intention and learning transfer. This study explored the mediating effects of learner and environmental factors on the accepted information technology and strengthened and supplemented the path of learning transfer of perceived usefulness and ease-of-use. In addition, based on the sample analysis of various countries used in this study, it is expected that future international comparative studies will be possible.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2011년도 정기 학술발표대회
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• pp.101-101
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• 2011

현재 국내에서 시행되고 있는 '4대강 살리기 사업'은 하천에서 발생하는 홍수 및 가뭄재해방지를 위한 다양한 공학적 노력을 시도하고 있다. 특히 안정적인 수위 및 유량확보와 홍수방지를 위한 보(weir)가 4대강 유역에 16개 설치되고 있다. 이러한 보 구간에는 고정보와 가동보가 복합적으로 설치되고 있으며 가동보는 그 형상과 운영방식에 따라 다양한 설계방안이 적용되었다. '4대강 살리기 사업' 중 낙동강 23공구의 강정보 공사 구간에는 원호형태의 측면 형상을 갖는 라이징 섹터게이트(Rising sector gate)가 적용되었다. 라이징 섹터게이트는 구조물의 높이가 낮고 수문의 개폐장치가 수문피어 구조물 내에 설치되어 경관이 우수하며, 구조가 간단하여 비체와 수류의 안정성이 뛰어나기 때문에 4개의 공사구간에 적용되었다. 따라서 본 연구에서는 강정보의 가동보 구간 2문 중 1문을 1/100 축척으로 제작하여 가변경사 개수로에 설치하고, 홍수 빈도별 상류 유량 조건과 하류단 수위조건으로 케이스를 정하여 실험을 수행하였다. 본 실험에서 사용한 개수로 장치는 너비 0.6 m, 높이 0.8 m, 그리고 길이 15.0 m(측정가능 구간, 헤드탱크와 테일게이트 부제외)의 개수로 실험장치이다. 측부는 모두 강화유리로 되어 육안관찰 및 계측 시 용이하게 제작되었으며, 순환식 유량 공급장치를 구축하여 수로의 하부에 설치된 유량탱크로부터 계속적으로 순환하도록 설계되었다. 또한 수로 하단으로부터 상단방향으로 약 33 m 지점에 전동 유압식 Jack screw 2기가 설치되어 경사도를 조절할 수 있도록 제작되었다. 유량조절용 판넬의 제어기판에는 디지털 경사계가 설치되어 있기 때문에 보다 정확한 경사도의 조절이 가능하다. 보 모형의 총연장은 53 cm이며 폭은 45 cm이다. 섹터게이트의 게이트부분은 직경 15 cm로 설계하였다. 문주부분을 포함한 모든 모형은 아크릴로 제작하며 레이저의 주사를 방해하지 않으며 투과율을 최대로 할 수 있도록 고강도의 아크릴을 가장 얇게 하여 중공형태를 채택하였다. 실험조건은 우선 보의 운영방안에 따라 게이트의 4가지 개방도를 설정하였고, 특히 평수위조건에서는 보의 상류부에 퇴적된 퇴적물의 세척을 위한 flushing 운영개방도 포함되어 있다. 홍수시에 대한 유량조건은 2년 빈도에 해당하는 유량을 수문의 비율과 상사법칙에 따라 설정하였으며 하류단 수위조건도 동일한 조건에 대한 값을 채택하여 적용하였다. 유동장의 해석을 위해서는 비접촉식 계측방법인 PIV(Particle Image Velocimetry) 시스템을 채택하여 2차원(x-z 방향) laser sheet를 생성하고 주입된 particle에서 반사된 변위(displacement) 정보를 상호상관(cross-correlation)기법으로 유동장을 계산하였다. 또한 수리모형과 동일한 지형격자를 구축하여 3차원 CFD 프로그램인 FLOW-3D로 계산하여 결과를 비교하였다. 특히 flushing 운영방안에 대한 게이트부의 개방도를 세가지(30, 45, $60^{\circ}$)로 구분하여 모의하였고, 적절한 개방도를 제안하고자 하였다. 실험결과는 우선 4가지 운영방안에 대한 가동보 주변에서의 유속장을 파악하였고, 최대유속의 발생위치의 변화를 확인할 수 있었다. 그리고 이에 따른 보의 바닥에서 최대유속이 발생할 경우, 하상보호공 위치와 거리 등에 대해서 분석하였다. 이를 통해 가동보 운영에 따른 다양한 유속구조를 파악할 수 있게 되며 구조적 안정성 확보를 위한 검증자료로 활용될 수 있을 것으로 예상된다. 향후, 가동보 운영방안 중 수세효과(flushing effect)에 대한 효과분석을 위해 게이트부 상류구간에 적절한 입경과 비중의 퇴적물질을 설치하는 연구와 상류부에서의 유입유사농도 및 시간변화에 따른 퇴적에 관한 연구를 수행할 계획이다.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제11권6호
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• pp.2169-2177
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• 2010

The effects of job related factors on psychosocial health status were examined by taking job stress into account. The self-administered questionnaires were performed, during the period between Oct. 1st, 2009 and Nov. 30th, 2009, to 805 individuals in the service of general administration located in Daejeon City. Causal relationships between job related factors, job stress, and, psychosocial health status were examined by structural equation model. The main finding as follows: For correlations of such indices of psychosocial health status as PWI and MFS with various studied items, all of these two indices were found to be in a negative correlation with the job position, job career, satisfaction in job life, autonomy of job, supervisors support and coworkers support, whereas in positive correlation with the experience of sick absence per year and job demand. With the analysis of structural equation model, the degree of job stress factors was more influential on the level of psychosocial health status than job related factors in such a manner as that the greater the job stress, while the lower the job related factors, the higher the psychosocial health status(PWI and MFS). Moreover, it was found to have the inter-relational effects that the greater the job related factors, the lower the job stress factors. Thus the effective strategy for stress and fatigue symptoms reduction among governmental employees requires additional programs focusing on innovated job specifications.

• Tunnel and Underground Space
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• 제16권6호
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• pp.526-535
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• 2006

An experimental study was carried out on a reduced scale tunnel model to grasp the behavioral feature of fire-induced smoke in the long tunnels. Based on Froude modeling, the 1/50 scaled tunnel model (20 m long) was constructed by acrylic tubes and paraffin gas was released inside the tunnel to simulate the 20 MW fire-induced smoke. me test results show, that after approximately 2 minutes of fire generation, was descended from the tunnel ceiling through the decrease of buoyancy, then it was symmetrically propagated about 90 meters for 4 minutes before jet fans were operated. The smoke was effectively controlled when the jet fans were operated and an air stream velocity was getting closed to reach a critical velocity (the minimum air velocity that requires to suppress the smoke spreading against the longitudinal ventilation flow during the tunnel fire situations). It was also found out that a range of smoke was spreaded about 3 meters from the origin of fire but the range was not propagated to the escape direction anymore. The early stage of the In operation, however, showed that the smoke was hardly controlled. It means that the operation of emergency ventilation system has many dangerous factors such as an intercepting breathing zone.

• Korean Journal of Construction Engineering and Management
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• 제14권1호
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• pp.101-114
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• 2013

This paper presents the findings relative to the influence factors on the safety of construction worker's actions. It identifies the factors which are involved in the safety behavior exercised by construction worker. They are compiled from existing studies that investigates the factors relative to the safety behavior. This study finds some factors which have powerful direct effects on safety behavior of construction workers. In addition, a model which defines the relationship between the factors and the behaviors of workers is established to analyze the effects. This study contributes to designe a theoretical model that shows workers' behaviors and analyzes the effects attributed to these factors: i.e., organizational commitment, stress reaction, safety motivation, safety knowledge, and safety climate. Survey questionaries are administered to the workers on the construction job sites located in Daegu metropolitan city. using SPSS18.0 and AMOS18.0, Exploratory Factor Analysis, Cronbach's alpha, Confirmatory Factor Analysis, Structural Equations Model analysis were performed. The research findings are as follows; The communication and educational training have the direct effect on the safety behavior. The factors of the safety climate constraints and/or contributes to the safety motivation, safety knowledge, and organizational commitment.

• Journal of Korean Society of Steel Construction
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• 제15권3호
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• pp.321-329
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• 2003

To effectively use the cross section of concrete decks, analytical and experimental studies on prestressed steel-box-girder bridges were performed in this study. The method of applying prestress was determined in the analytical study and the longitudinal behavior of the prestressed steel-box-girder bridge was considered in the experimental study. The object model for these studies was a two-span continuous bridge. The method of applying prestress determined herein was divided into two parts: one is that apply prestress to the concrete deck at its intermediate support, and the other is that apply prestress to the lower flange of the steel-box-girder bridge at its end support. The prototype bridge for the experiment was simulated based on the rule of similitude and was fabricated according to construction steps to apply prestress effectively. From the results of the experimental study, it has demonstrated that the prestressed steel-box-girder bridge provides better performance than the general steel-box-girder bridge in view of the increase of the design live load, the reduction of the tensile stress of the concrete deck at intermediate support, and the reduction of the displacement.

• The Journal of the Korea Contents Association
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• 제11권5호
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• pp.369-383
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• 2011

The purpose of this study was to investigate the determinants of intent to leave among IT industry employees, based on the Price's structural model of employee turnover. The sample used in this study were composed of 370 employees from 10 IT firms located in Seoul and Gyeonggi-Do. Data were collected with self-administered questionnaires and analyzed using structural equation modelling technique. This study found that four task reward variables(job variety, job autonomy, job challenge, and role ambiguity), two social reward variables (supervisory support and coworker support), three organizational reward variables(promotional chances, job security, and distributive justice) and one environmental variable(job opportunity), had significant effects on IT industry employees' intent to leave in terms of total effects and his directions of those significant effects were consistent with theoretical predictions; and that two mediating variables, job satisfaction and organizational commitment had the most important effects on IT industry employees' intent to leave in terms of total effects. The theoretical and practical implications of the research findings were discussed and the directions for future research were suggested.

• Fire Science and Engineering
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• 제32권3호
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• pp.51-59
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• 2018

Although a fire curtain plays an important role in preventing smoke from spreading to the auditorium in a theater fire, there has been insufficient research on fire curtains. In this study, to check the accuracy of numerical simulation, for previous experiments using a reduced scale model, a numerical simulation was carried out, and the results were compared with previous experimental data. The fire curtain effect was then predicted numerically. A Fire Dynamics Simulator (FDS) was used, and the natural exhaust vent sizes were set to ~10%, ~5%, and ~1% of the stage floor area. The smoke movement was visualized, and the mass flow rates and temperatures were measured and analyzed. In addition, the law of similarity was used to examine the influence of a fire curtain in a real scale theater fire. Without the fire curtain, the present numerical simulation results were in agreement with the previous experimental data within reasonable accuracy. Meanwhile, the fire curtain affects the mass flow rates through the natural exhaust vent and proscenium opening, as well as the start time of soot outflow to the auditorium. Overall, the present results can be used to develop a fire curtain system.