• Wind and Structures
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• 제36권3호
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• pp.175-200
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• 2023

The large eddy simulation (LES) of the flow around a circular cylinder is not only affected by the sub-grid scale (SGS) model but also by the grid resolution of the computational domain. To study the influence of different grids on the LES results, the LES simulations of the flow around a circular cylinder with different grids at Reynolds number (Re) = 3900 was performed. A circular computational domain with different radial growth rates and circumferential and spanwise grid numbers was adopted for the simulations. Meanwhile, the aerodynamic forces, wind pressure coefficients, mean and instantaneous flow fields, and the effect of grid resolution on them were comprehensively analyzed. The results indicate that the lift coefficient, wind pressure coefficient, and recirculation length are significantly affected by the radial growth rate of the grid and the circumferential grid number. The spanwise grid number has a significant influence on the three-dimensionality of the flow and plays an important role in velocity fluctuations in the wake region. Nevertheless, the aerodynamic coefficients and recirculation length are not sufficiently sensitive to the grid number in the spanwise direction. By comparing the results, it can be concluded that suitable and reliable LES results can be obtained when the radial growth rate is 1.03 or 1.05, the circumferential grid number is 160, 200, or 240, and the spanwise grid number is 64. A radial growth rate 1.05, circumferential grid number 160, and spanwise grid number 64 are recommended to reduce the grid amount and further improve the efficiency.

• 한국병원경영학회지
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• 제7권1호
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• pp.41-63
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• 2002

The purpose of this study is to analyze the interrelation of influential factors in organizational conflict and organizational commitment. The data for this study were collected through a self-administered survey with a structured Questionnaire to 1,167 subjects from several nursing staff members, administration staff members and medical technicians of six hospitals. In this analysis frequency test, t-test, ANOVA, hierarchical multiple regression and structural equation model were used. The main findings of this study are as follows. 1. Factors which influence organizational conflict were analyzed. The type of occupation and the year of service were socio-demographic variables which influenced organizational conflict positively. Adjusted R square was 0.03. Perceptions on organizational structure and organizational culture were analyzed with two- level variables that were added. The findings were as follows. Adjusted R square increased to 0.25. The year of service, internal process culture and rational goal culture were positive variables. The design of organizational structure, human relations culture and open system culture were negative variables. 2. Variables which influence organizational commitment were analyzed. Age and the year of service were positive variables, while academic background based on high school education was a negative variable. Adjusted R square was 0.16. Perceptions on organizational structure and organizational culture were analyzed with two-level variables that were added. The findings were as follows. The characteristics of organizational structure, human relations culture and organizational culture were positive variables. Adjusted R square increased to 0.55. The variables of organizational conflict were added in 3 steps. Findings were as follows. The variables of hierarchical conflict showed negative influence and were included in two-level influential variables. Adjusted R square increased to 0.56. 3. Structural equation model was analyzed in order to examine the relation between organizational structure and the variables of organizational culture, organizational conflict and organizational commitment. Thirteen path coefficients out of seventeen path coefficients were significant. Age had negative influence on organizational conflict and positive influence on organizational commitment. The year of service had positive influence on organizational conflict and organizational commitment. The design of organizational structure, human relations culture and open system culture had negative influence on organizational. conflict. They had positive influence on organizational commitment. Internal process culture and rational goal culture had positive influence on organizational conflict. Organizational conflict had negative influence on organizational commitment. The squared multiple correlation of this model was 25.1% in organizational conflict and 52.7% in organizational commitment. The conclusion of this study is as follows. Factors in organizational structure and organizational culture, rather than socio-demographic factors, had a stronger influence on the organizational conflict and organizational commitment of hospitals. In order to decrease organizational conflict, to increase organizational commitment and to maximize the effectiveness of hospital management, it is necessary to understand the overall relation between organizational structure, organizational culture, organizational conflict and organizational commitment, with the effort of improving personalized factors and individual factors of organization management.

• 대한기계학회논문집
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• 제12권3호
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• pp.409-418
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• 1988

본 연구에서는 상반상반정리가 성립되는 선형계의 경우에 있어서 회전체를 회 전시키지 않고 시험추도 사용하지 않으며 베어링부를 가진하는 것에 의한 영향계수 측 정법을 제안한다. 대상으로 하는 영향계수는 베어링부와 각 수정점 사이의 영향계수 로서 비회전가진실험에 의해 베어링부에 힘을 가한 경우의 각 수정점에서의 비회전 영 향계수를 측정한다. 회전시험에서는 베어링부에 시험추를 부가하는 것이 구조상 곤 란하므로 각 수정점에 시험추를 부착하여 각 수정점에 힘을 가한 경우에 대한 베어링 부에서의 영향계수를 측정한다.그리고 수치계산으로 전달매트릭스법에 의해 베어링 부에 시험추를 부착하고 회전체를 회전시켜 각 수정점에서의 회전영향계수를 계산하고 실험결과와 비교한다. 상에서 구하여진 비회전과 회전영향계수의 실험결과를 비교하 므로서 비회전 영향계수의 특성을 파악하고, 이를 이용하여 탄성회전체의 평형잡이를 하는 새로운 방법을 제안한다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 연약지반처리위원회 학술세미나
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• pp.93-112
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• 2000

The permeability of converter slag, replacing material of sand mat on improving soft clay foundation, was evaluated in the laboratory. The effects of grain size, flow water time and aging were investigated using sea and fresh water. Converter slag being submerged with fresh water, the coefficients of permeability in A and B samples less than 10mm grain sizes were measured as 6.52${\times}$10$\^$-2/cm/sec and 5.99${\times}$10$\^$-1/cm/sec, while changed as 1.88${\times}$10$\^$-2/cm/sec, 3.86${\times}$10$\^$-1/cm/sec under sea water condition. Also, the condition of turbulent flow may exit and was experimentally identified from the relationship between hydraulic gradient and seepage velocity. After 180 days on using sea water, the coefficients of permeability of sample A and B samples decreased ten times smaller than those initial values. And after that time continually decreased as for till 360 days. The reduction of permeability coefficient was considered to influence filled with voids in high-calcium quicklime(CaO). However, in-situ coefficient of permeability was practically satisfactory.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 연약지반처리위원회 학술세미나
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• pp.12-31
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• 2000

The permeability of converter slag, replacing material of sand mat on improving soft clay foundation, was evaluated in the laboratory. The effects of grain size, flow water time and aging were investigated using sea and fresh water. Converter slag being submerged with fresh water, the coefficients of permeability in A and B samples less than 10mm grain sizes were measured as 6.52${\times}$10$\^$-2/cm/sec and 5,99${\times}$10$\^$-1/cm/sec, while changed as 1,88${\times}$10$\^$-2/cm/sec, 3.86${\times}$10$\^$-1/cm/sec under sea water condition. Also, the condition of turbulent flow may exit and was experimentally identified from the relationship between hydraulic gradient and seepage velocity. After 180 days on using sea water, the coefficients of permeability of sample A and B samples decreased ten times smaller than those initial values. And after that time continually decreased as for till 360 days. The reduction of permeability coefficient was considered to influence filled with voids in high-calcium quicklime(CaO). However, in-situ coefficient of permeability was practically satisfactory.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.765-770
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• 2001

The objective of the present study is to investigate the effects of the various inlet boundary layer thickness on convective heat transfer distribution in a turbine cascade endwall and blade suction surface. In addition, the proper height of the boundary layer fences for various inlet boundary layer thickness were applied to turbine cascade endwall in order to reduce the secondary flow, and to verify its influence on the heat transfer process within the turbine cascade. Convective heat transfer distributions on the experimental regions were measured by the image processing system. The results show that heat transfer coefficients on the blade suction surface were increased with an augmentation of inlet boundary layer thickness. However, in a turbine cascade endwall, magnitude of heat transfer coefficients did not change with variation of inlet boundary layer thickness. The results also present that the boundary layer fence is effective in reducing heat transfer on the suction surface. On the other hand, in the endwall region, boundary layer fence brought about the subsidiary heat transfer increment.

• Journal of Mechanical Science and Technology
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• 제18권9호
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• pp.1668-1679
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• 2004

The design of an axial piston pump for electro-hydrostatic transmission systems requires accurate information where and how much the internal friction and flow losses are produced. This study is particularly focused on the friction losses of a bent-axis type hydraulic piston pump, aiming at finding out which design factors influence its torque efficiency most significantly. To this end, the friction coefficients of the pump parts such as piston heads, spherical joints, shaft bearings, and valve plate were experimentally identified by a specially constructed tribometer. Applying the experimental data to the equations of motion for pistons as well as to the theoretical friction models for the pump parts, the friction torques produced by them were computed. The accuracy of the computed results was confirmed by the comparison with the practical input torque of the pump. In this paper, it is shown that the viscous friction forces on the valve plate and input shaft bearing are the primary source of the friction losses of the bent-axis type pump, while the friction forces and moments on the piston are of little significance.

• 수산해양기술연구
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• 제40권2호
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• pp.149-154
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• 2004

본 논문에서는 펌프 노즐이 부착된 잠수 선형의 유동에 관해 수치해석 결과를 보여준다. 이는 속도분포, 양력계수, 영각의 값을 갖는 펌프젯 노즐이 선체와 부착되었을 때와 부착되지 않았을 때의 종강도 모멘트 등의 값들을 계산한다. 선형의 속도 분포에 따른 노즐의 영향면적과 양력계수(변호의 특성요인) 종강도 모멘트, 영각에 따른 도함수 등을 보여준다.

• 한국컴퓨터산업학회논문지
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• 제3권9호
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• pp.1287-1294
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• 2002

본 논문에서는 DWT기반의 점진적 영상부호화를 위한 알고리즘 기법을 제안해보고자 한다. DWT와 에지부분을 추출하고 확장된 EZW 알고리즘을 이용하여 기존의 Embedded Coding 보다 효과적인 부호화 방법을 설계해 보았다. 일반적으로 에지 부분은 원 영상을 복원하는데 있어 매우 중요한 역할을 하게 된다. 영상에 대해 DWT를 거치게 되면 계수들은 중요계수와 비중요계수 두가지의 그룹으로 분류할 수 있다. 본 논문에서는 에지부분이 영상에서는 중요계수처럼 나타난다는 것을 이용하였다. 특히 DWT 영상에서는 방향성에 의해서 고주파 부대역에서 이러한 특성이 그대로 나타난다는 것을 확인할 수 있다. 또한 Embedded Coding에서 중요계수처럼 영상을 복원하는데 중요한 정보들은 전송순서에서 보다 우선순위를 가지게 된다. 따라서 본 논문에서 제안하려는 시스템은 영상의 점진적 전송이 요구되는 응용분야에 효과적으로 이용될 수 있을것으로 기대할 수 있을 것이다.

• 한국방재학회 논문집
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• 제8권3호
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• pp.137-147
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• 2008

본 연구는 운동량방정식을 이루는 각 항의 상대적 크기를 해석적 방법으로 비교분석하였다. 운동량방정식의 매개변수인 하상 경사와 조도계수를 유출영향인자로 하여 각항의 시간적 변화를 분석하였다. 국지가속도와 대류가속도항의 크기는 서로 상쇄되는 경향을 보이며, 중력항을 제외한 나머지항들의 첨두치 발생시각은 수문곡선 상승부의 변곡점 발생시각과 일치함을 알 수 있다. 각 항의 상대적 크기는 하도특성에 따라 변하며, 특히 완경사 하천과 조도계수가 큰 경우는 압력항을 무시할 수 없음을 알 수 있다.