• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.586-591
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• 2009

권 등(2008)은 수면보다 높은 정방형 다열기둥의 수리실험을 수행하여 바닥마찰과 구조물에 의한 흐름저항을 포함하고 항력상호작용계수가 적용된 Manning계수 형태의 상당저항계수 이론식을 제안하였으나 저항체의 횡방향 간격에 대해서는 충분한 연구가 수행되지 못하였다. 따라서 본 연구에서는 오리피스의 에너지 손실계수를 적용하여 횡방향 간격에 따른 항력상호작용계수식을 제안하였다. 또한 정방형 다열기둥의 다양한 횡방향 간격에 따른 흐름양상을 FLOW-3D를 이용한 수치실험을 수행하여 상당저항계수 n을 측정하였으며 수치실험 결과를 본 연구에서 제안한 횡방향 항력상호작용계수식이 적용된 이론식과 비교하였다. 이론식과 수치실험 결과는 잘 일치하였으며 이 결과로부터 본 논문에서 제안한 횡방향 항력상호작용계수식이 유효함을 확인하였다.

• Journal of the Korean Geotechnical Society
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• v.16 no.3
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• pp.157-162
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• 2000

측발유동을 받는 일렬 군말뚝의 그룹효과를 파악하이 위해 3차원 유한요소해석을 수행하였다. 국내의 대표적인 화강풍화토 지반에 선단지지된 말뚝을 대상으로 측방으로 지반변위 발생시 말뚝 두부조건과 중심간격(2.5D, 5.0D, 7.0D, 단독말뚝) 및 말뚝주면의 접촉효과를 고려한 군말뚝의 상호작용계수를 산정하였다. 본 연구 결과, 단독말뚝과 비교하여 군말뚝의 간격이 좁아짐에 따라 상호작용계수는 현저하게 감소하였으며 말뚝 두부조건이 회전구속, 힌지,자유단의 순으로 감소정도가 크게 나타났다. 이는 실내모형실험을 통해 산정된 상호작용계수와도 비교적 잘 일치함을 보였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.2
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• pp.343-354
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• 1994

The group effect which causes different downdrag distribution in individual piles within the group was investigated by using a numerical analysis and an analytical study. The interaction factors due to group spacing and total number of piles in a group were estimated by using a three dimensional non-linear finite element approach. Based on the results obtained, it is shown that the interaction factors of pile groups varies remarkably according to the group spacing, a major influencing parameter for the group effect. Also the downdrag prediction by the proposed method was compared with the other analytical methods through an example of calculations.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.3
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• pp.216-223
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• 2009

A transverse drag interaction coefficient of the equivalent resistance coefficient formula for square multi-piers higher than water depth and arranged with equal intervals was studied. From the assumption that the energy loss due to drag interaction according to transverse intervals of resistance bodies is essentially identical to the energy loss due to thick orifice according to porosities, the transverse drag interaction coefficient was derived by employing the orifice's energy loss coefficient. The equivalent resistance coefficient formula including the drag interaction coefficient was compared with the numerical experiments using FLOW-3D, the performance of which was verified by Kim et al.(2008) in the experimental condition with the multi-piers. The comparisons showed good agreement and thus, the equivalent resistance coefficient formula, which does not only consider frictional resistance but also consider the multi-piers' drag resistance varied according to the intervals in longitudinal or transverse direction, was verified.

• Journal of the Korean GEO-environmental Society
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• v.10 no.5
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• pp.69-73
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• 2009

In this study, three dimensional numerical analyses were performed with variation of pile spacing (S=3D, 4D, 5D) to compare the behaviour of single pile and pile group with cap in granite soil. In order to compare and analyze the lateral resistance of single pile and pile group by changing pile spacing, the pile group with array of $1{\times}3$ was employed. To reduce the computation time the symmetric boundary condition was used. And Druker-Prager model and elasticity model were used for granite soil and for concrete pile and cap, respectively. Using the analyses results of pile group in granite soil under lateral loading, p-y curve for pile group and single pile with changing pile spacing was drawn. With p-y curve p-multiplier was evaluated. As a result of analysis, the value of p-multiplier was increased with increasing pile spacing under 1.0 due to pile shadow effects.

• Tribology and Lubricants
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• v.12 no.3
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• pp.26-32
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• 1996

오랜 역사에 걸쳐 연구자들은, 마찰력은 주로 접착에 의한 것으로 믿어 왔으며, 이러한 주장은 실험적으로 증명되지 못했다. 한편, 미끄럼 두 표면 사이의 건식 마찰력은 두 표면 사이의 기계적인 상호작용에 의한 것으로 알려져 있다. 이 연구에서는 두 표면 사이의 기계적 상호작용을 제거함으로써 마찰계수를 감소시키는 방법을 제시하였다. 매끄러운 경한 표면에 얇은 elastomer층을 입힌 비윤활 최소 마찰계수에 대한 본 실험결과는 앞으로 정밀기계부품의 충격을 받는 부위에 응용할 수 있을 것으로 기대된다.

• The Journal of Korean Association of Computer Education
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• v.7 no.1
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• pp.79-88
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• 2004

Since computer integrated technology was introduced to the field of education, it has offered an expanding range of interactive possibilities which are remarkably powerful and helpful for the learners, especially constructing the cyber learning environments. Interactivity, the critical element in cyber learning, is categorized into three dimensions: student-to-contents, student-to-student and student-to-instructors. Six surrogate variables are introduced, and two quantitative model are developed for evaluating the degree of interactivity. The first model, which is called Data Envelopment Analysis model, is a linear programming based technique for measuring the relative performance of organizational units where the presence of multiple inputs and outputs makes comparison difficult. DEA model allows each unit to adopt a set of weight that shows it in the most favorable light in comparison to the other unit. The Second model employes the weighted average of standardized input variables for evaluation. Actual data have been collected from the Cyber IT university and these two models are applied for comparison. The analysis shows that the results from these two models are very much similar to each other, and are highly correlated to the level of class satisfaction.

• Journal of the Earthquake Engineering Society of Korea
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• v.4 no.3
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• pp.107-115
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• 2000

충적지반에 건설된 원형 단면을 갖는 터널은 지진시에 지반의 전단 변형의 영향을 받아 좌우교차로 경사진 타원형상의 변형을 반복한다. 본 논문에서는 이 특별한 진동모드를 이용하여 지반-터널계의 상호작용 및 면진 효과가 검토되었다. 지반과 터널의 경계가 완전히 결합되어 있는 경우에 대한 지반 -터널계의 상호작용 효과 및 지하 구조물의 지진피해를 줄이는 한가지 방법으로써 터널 주위를 면진재로 피복하는 방법에 대한 면진효과가 토론되었다. 그 결과 면진재의 포아송비를 작게 하거나 지반과 면진재의 전단탄성계수의 비를 증가시킴으로서 면진 효가가 증가함을 알 수 있었다.

• Journal of the Korean GEO-environmental Society
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• v.11 no.3
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• pp.17-22
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• 2010

This paper analyzed the characteristics of p-multiplier and the load distribution of H-pile group installed in weathered soil under horizontal loading. The results of this study conducted in pile arrangement ($2{\times}3$, $3{\times}3$), the pile center to center spacing (2D, 4D, 6D), and soil density (relative density: 40%, 80%) were drawn as follows. As to the average horizontal loading applied to each pile in pile groups, the fewer number of piles was, the larger average horizontal resistance became. As the result of analysis on p-y curves of single piles and pile groups according to the pile distance and the soil density, as the pile spacing was increased from 2D to 6D, the interaction coefficients of pile group showed 0.85~0.94 (piles in the front row), 0.57~0.79 (piles in the middle row), and 0.60~0.71 (piles in the rear row) in the loose ground and showed 0.76~0.82 (piles in the front row), 0.58~0.73 (piles in the middle row), and 0.53~0.70 (piles in the rear row) in the dense ground. As above, the wider pile distance was, the larger interaction coefficient value was shown among piles. In addition, piles in the front row showed bigger interaction coefficients than that of piles in the middle and back row.

• The Journal of Korean Association of Computer Education
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• v.14 no.3
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• pp.63-72
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• 2011

Satisfactory e-learning experience of working part-time adult students is a truly dynamic and multidimensional process that reflects learning needs and abilities. Special attention is given to understanding the role of student-to-faculty interaction, student-to-student interaction, e-learning content and course structure, flow, periodic off-line class meetings and synchronous Q&A sessions. Survey questions were developed and distributed to adult graduate students. Some of them were asked to complete the questions with the most interesting subjects or classes in their mind, and others with the most difficult subjects in their mind. The structural model for each group was tested. The values of path coefficients corresponding to the group with the difficult subjects turn out to be higher for the following paths; a) interaction among professors and students and satisfaction, b) contents quality and flow, c) Q&A and interaction among professors and students, d) Q&A and interaction among students. For the other paths such as interaction among students and satisfaction, contents structure and flow, the coefficient values corresponding to the group with the interesting subjects are higher. Some implications for e-learning design were provided as well.