• 대한토목학회논문집
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• 제30권2B호
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• pp.149-157
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• 2010

본 연구는 국내 9개 하천에서 실측한 자료를 사용하여 하상재료의 입경에 기초한 자갈하천의 조도계수 특성을 분석하는데 그 목적이 있다. 조도계수는 Manning 식을 역산하여 산정하였다. 산정된 조도계수는 유량에 따라 대체로 감소하였으며, 일정한 유량 이상에서는 수렴하는 특성을 나타냈다. 마찬가지로, 상대수심(R/D)이 증가함에 따라 조도계수는 감소하는 경향을 보여주었으며, 실측 자료를 이용하여 적합식을 구한 결과 Limerinos(1970) 식과 매우 유사한 결과를 보여주었다. 일정한 유량 이상에서 수렴된 조도계수값은 0.024~0.045의 범위에 있었으며, 이를 기초로 하상재료만을 고려한 조도계수 산정식을 도출하고 기존의 식과 비교하였다.

• Wind and Structures
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• 제37권6호
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• pp.425-444
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• 2023

This study is to investigate the effect of interference between two C-shaped high-rise buildings by computational fluid dynamics (CFD), focusing on the variation of the local pressure coefficient (C_P) and the mean pressure coefficient (C_PMEAN). Sixteen building position cases are considered for the present study. These cases were based on the position and height of the interference building (IB). The pressure coefficient (C_P) is calculated on the principal building (PB) and is compared with an isolated building identical in shape and size. The interference effect on PB has also been presented in reference for the interference factor (IF). According to the findings, the maximum force coefficient on the PB is 0.971 and it is 10.97% more than the isolated PB when IB is located at position 2b (two times the width of the building), and the interfering height of 13H/15 mm. The moment coefficient on PB is 1.27, which is 27.36% less than the isolated case in which IB pushed 2b to 3b in the y direction with 750 mm height. In most of the cases, because of the shielding effect of the IB, the value of force coefficient (C_F) on PB has been reduced. On the face of the PB, there are also considerable differences in the mean pressure coefficient C_PMEAN. When IB was positioned at a location of 2b in Y direction and an interfering height of 13H/15 mm, the maximum C_PMEAN (1.58) was observed on the leeward face of PB.

• 한국구조물진단유지관리공학회 논문집
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• 제27권5호
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• pp.75-83
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• 2023

프리스트레스트 콘크리트 철도 교량에서 발생하는 과다한 솟음 문제를 분석하는 연구의 일환으로, 이 논문에서는 콘크리트 구조물의 시간에 따른 솟음 증가량을 나타내는 크리프 계수에 대하여 산정 방법과 분석 결과를 제시한다. 설계기준의 크리프 계수 산정식을 사용하여 국내 12개 지역의 기후 조건(상대습도와 온도)을 적용한 크리프 계수를 구하고, 기후 조건에 대한 지역별 및 재하 시기별 차이가 크리프 계수에 미치는 영향을 분석한다. 재하 초기에 많이 발생하는 크리프를 적절하게 산정하기 위하여 시기별 기후조건을 구분하여 고려하도록 시간 단계해석 방법을 적용하여 상세 분석한다. 지역의 평균 기후조건을 적용하여 구한 크리프 계수는 시간 단계 해석으로 구한 크리프 계수의 평균과 비슷하며, 시간 단계 해석을 통하여 크리프 계수에 미치는 상대습도와 온도의 상쇄, 중첩 효과 및 재하 초기 기후 효과를 적절하게 나타낼 수 있음을 보인다.

• 대한수학회논문집
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• 제12권2호
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• pp.419-425
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• 1997

Consider a d-dimensional domain D that has finite Lebesque measure and a Dirichlet form which has discontinuous coefficient. Then the stationary Markov process corresponding to the given Dirichlet form is a semimartingale under suitable condition for D and the coefficient.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1989년도 한국자동제어학술회의논문집; Seoul, Korea; 27-28 Oct. 1989
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• pp.477-482
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• 1989

In this paper, the effect of coefficient quantization error is analyzed for digital PID controllers. Stability margins are used as peformance criteria, and the statistical wordlength concept is adopted for coefficient wordlength selection. Finally, an illustrative example is given.

• Kyungpook Mathematical Journal
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• 제46권4호
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• pp.509-525
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• 2006

We give formulas for the first four coefficient polynomials of the Kauffman's link polynomial involving linking numbers and the coefficient polynomials of the Kauffman polynomials of the one- and two-component sublinks. We use mainly the Dubrovnik polynomial, a version of the Kauffman polynomial.

• Journal of Mechanical Science and Technology
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• 제17권6호
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• pp.805-815
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• 2003

In order to execute efficiently the free vibration analysis of 2-dimensional structures like plate structures, the author developed the finite element-transfer stiffness coefficient method. This method is based on the combination of the modeling techniques in the FEM and the transfer technique of the stiffness coefficient in the transfer stiffness coefficient method. Numerical results of the simply supported and the elastic supported rectangular plates showed that the present method can be successfully applied to the free vibration analysis of plate structures on a personal computer. We confirmed that, in the case of analyzing the free vibration of rectangular plate structures, the present method is superior to the FEM from the viewpoint of computation time and storage.

• KIEE International Transactions on Electrophysics and Applications
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• 제4C권4호
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• pp.185-189
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• 2004

The temporal variation of a secondary electron emission coefficient (${\gamma}$ coefficient) of hydrogenated amorphous silicon (a-Si:H) was investigated in a dc silane plasma. Estimated ${\gamma}$ coefficients have a value of 2.73 ${\times}$ 10$^{-2}$ on the pure aluminum electrode and 1.5 ${\times}$ 10$^{-3}$ after 2 hours deposition of -Si:H thin films on a cathode. It showed an abrupt decrease for about 30 minutes before saturation. The variation of the ${\gamma}$ coefficient was estimated as a function of the thin film thickness, and the film thickness was about 80 nm after 30 minutes deposition time. These results are compared with the results of a computer simulation for ion penetration into a cathode.

• Tribology and Lubricants
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• 제27권5호
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• pp.264-268
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• 2011

In this study, we examined the friction characteristics of a dimple pattern on a carbon nitride coating. The study was conducted with a hexagonal array 40 ${\mu}m$ dimple pattern on a steel bearing containing a CNx coating. The area density of the dimple patterns were varied between 5% and 25%, the speed was varied from 0.06-0.26 m/s, and the load was varied between 20-100N. In general, we found that as the velocity increased, the friction coefficient increased. Furthermore, the friction coefficient was lowest at a load of 40N. The friction coefficient of the non-coated specimen was 0.025-0.15; on the other hand, the friction coefficient of the coated specimen was 0.002-0.02. Thus, we determined that the coated materials could reduce the friction coefficient by a factor of 7.5.

• 상하수도학회지
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• 제18권4호
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• pp.493-499
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• 2004

Rejection characteristics of heavy metals by nanofiltration membranes were investigated. Nanofiltration membranes rejected heavy metals much better than chloride, sulfate and TOC, of which concentration in synthetic wastewater was higher than that of heavy metals. To consider rejection characteristics of various metals by nanofiltration membranes, separation coefficient, which is the ratio of the metal permeation rate to the chloride ion or TOC permeation rate, was introduced. In spite of different materials and different nominal salt rejection of nanofiltration membrane used, the separation coefficients of metals were nearly the same. In particular, the separation coefficient of arsenic against chloride ion and TOC was larger than any other separation coefficient of heavy metals. These phenomena were observed in the relationship between the molar conductivity and the separation coefficient for heavy metals.