• Journal of Korea Water Resources Association
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• v.51 no.7
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• pp.543-554
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• 2018

A methodology has been presented for evaluating the partial safety factors on the sliding failure mode of vertical caissons of composite breakwaters and for determining the cross sections of those by Level I reliability-based design method. Especially, a mathematical model has been suggested for the sake of a consistency of code format as well as convenience of application in practical design, for which the uncertainties associated with buoyancy and its own weight can be taken into account straightforwardly. Furthermore, design criteria equation has been derived by considering accurately the effect of uplift pressure, so that the cross sections of caissons can be assessed which must be safe against the sliding failure. It has been found that cross sections estimated from partial safety factors proposed in this paper are in very good agreement with the results of Level II AFDA and Level III MCS under the same target probability of failure. However, partial safety factors of the Technical Standards and Commentaries for Port and Harbour Facilities in Japan and Coastal Engineering Manual in USA tend to estimate much bigger or smaller cross sections in comparison to the present results. Finally, many reliability re-analyses have been performed in order to conform whether the stability level of cross section estimated by Level I reliability-based design method is satisfied with the target probability of failure of partial safety factors or not.

• Journal of the Korea Concrete Institute
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• v.25 no.4
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• pp.429-438
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• 2013

An object oriented numerical analysis program of axial-flexural elements and the step-by-step method (SSM) has been developed to analyze concrete long-term behaviors of structures constrained internally and externally. The results of the numerical analysis for simple and continuous prestressed (PS) concrete box and composite girders, pre-cast slab of continuous steel composite girder, and simple preflex composite girder show that the adjusting coefficient decreases by increasing constraint. The loss rates of pre-tension force were not sensitive but those of pre-compression force were increased rapidly by decreasing adjusting coefficient. This indicates that the design based on the loss rate of pre-tension can over-estimate the pre-compression force in a concrete section constrained internally and externally. The adjusting coefficients which satisfy results of the numerical analysis are 0.35~0.95, and it can be used as an index of constraint of concrete long-term deformation. The adjusting coefficient 0.5 of Bridge Design Specifications can under-estimate residual stress of PS concrete slab, and the coefficient 0.7 or 0.8 of LRFD Bridge Designing Specifications can under-estimate the loss rates of continuous PS concrete girders. The adjusting coefficient of hybrid structures should be less then 0.4.

• Journal of Korea Water Resources Association
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• v.48 no.4
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• pp.291-298
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• 2015

The aim of this study is that a theoretical formula for estimating the one-dimensional longitudinal dispersion coefficient is derived based on a transverse distribution equation for the depth averaged stream-wise velocity in open channel. In "Part I. Theoretical equation for stream-wise velocity" which is the former volume of this article, the velocity distribution equation is derived analytically based on the Shiono-Knight Model (SKM). And then incorporating the velocity distribution equation into a triple integral formula which was proposed by Fischer (1968), the one-dimensional longitudinal dispersion coefficient can be derived theoretically in "Part II. Longitudinal dispersion coefficient" which is the latter volume of this article. SKM has presented an analytical solution to the Navier-Stokes equation to describe the transverse variations, and originally been applied to straight and nearly straight compound channel. In order to use SKM in modeling non-prismatic and meandering channels, the shape of cross-section is regarded as a triangle in this study. The analytical solution for the velocity distribution is verified using Manning's equation and applied to velocity data measured at natural streams. Although the velocity equation developed in this study do not agree well with measured data case by case, the equation has a merit that the velocity distribution can be calculated only using geometric data including Manning's roughness coefficient without any measured velocity data.

• Journal of Ocean Engineering and Technology
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• v.11 no.4
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• pp.130-140
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• 1997

원형주상체 주위의 유동을 규명하기 위해 회류수조에서 원주방향으로 24개의 위치에 대하여 압력을 계측하였으며, laser sheet을 이용하여 유동을 가시화 하였다. Reynolds수가 4800에서 40000인 범위에 대하여 실험을 수행하였다. 또한, 원형단면체 주위의 비정상 층류유동에 대한 Navier-Stokes방정식의 해를 구하는 수치해석기법을 개발하였다. 효과적인 격자배치를 위하여 H와 O-type의 중첩격자를 사용하였고, 이산화 방법으로는 정규격자시스템에서 유한차분법을 적용하였다. 실험과 수치해석결과에서 뚜렷한 와류박리현상을 볼 수 있었으며, 압력계수 (C$_{p}$ ), 항력계수(C$_{D}$), 스트로얼수(St)를 정량적으로 비교하였을 때, 비교적 잘 일치하는 것을 확인하였다.다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.2
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• pp.71-76
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• 2018

Recently, various technologies have been developed for road facilities to reduce the load, some of which use technologies employing perforated plates for wind load reduction. Currently, there are no regulations concerning the drag coefficient of perforated plates for domestic road facilities. In the United States, the regulations regarding the drag coefficient of perforated plates in the 'Minimum design loads for buildings and other structures' were revised based on the studies of Letchford (2001) and Giannoulis (2012). In this study, a wind tunnel test was carried out to analyze the feasibility of applying regulations involving the perforated plates' drag coefficient. The results of the wind tunnel test and the drag coefficient used in the regulation were compared and analyzed. In addition, the reduction effect of the cross area of road signs calculated by applying the drag coefficient was analyzed. The results of the wind tunnel test and the value of the drag coefficient used in the regulation in the US were found to be very similar. Therefore, it was found that it is possible to apply the formula involving the drag coefficient of the perforated plate to the regulation and that the cross area of the perforated plate used for the post of the road sign is reduced by about 9.45% and that of the horizontal post by about 6.45%.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.7
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• pp.722-729
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• 2013

This paper presents the influence on the transmission characteristics of dimensional tolerances of rectangular waveguides usually used as a low-loss transmission line in the millimeter-wave band. We derived the Green's functions of the waveguide with eigenfunction expansion method. The reflection coefficient of the waveguide with a post is calculated by using internal impedance in order to investigate the influence of dimensional tolerances of the waveguide. In order to check the validity of the theoretical analysis, the calculated reflection coefficients are compared with the measured results.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.235-235
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• 2018

홍수 시의 산지하천 만곡부는 2차류 발생과 편수위 상승에 따른 하상세굴 및 홍수범람 위험이 크다. 만곡부 외측에 주로 설치되어 있는 콘크리트 옹벽호안은 표면이 매끄러워 홍수피해를 가중 시킨다. 이러한 피해를 저감시키기 위해 콘크리트 옹벽에 돌출줄눈을 설치하여 유속조감 및 설치효과를 분석한 바 있다. 본 연구에서는 기존에 제안된 직사각형 단면의 돌출줄눈보다 내구성을 추구한 사다리꼴 단면의 돌출줄눈을 제시하여 수리모형 실험을 수행하였다. 수리모형 실험은 개수로 직선수로에서 수로경사 0.0035 조건에서 수로 출구 게이트를 조절하면서 이루어졌다. 모형 돌출줄눈의 조도높이는 3cm로 하였으며, 사다리꼴 밑각은 $45^{\circ}$로 완만한 경우이다. 설치간격은 무차원 돌출줄눈 간격을 기준으로 ?형 조도인 6으로 하였다. 돌출줄눈의 설치 유무에 따라 유량에 따른 수위를 측정하고 유속을 산정하여, 마찰저항의 변화를 파악하였다. 공급유량에 따른 Froude 수는 0.168~0.359 범위였으며, 유량이 증가에 따라 Manning의 조도계수는 감소하였다. Froude 수가 0.25보다 큰 경우 돌출줄눈설치의 조도계수가 미설치보다 큰 것으로 파악되었다. 그러나 사다리꼴 돌출줄눈의 흐름저항효과는 직사각형 돌출줄눈에 비해 상대적으로 작았다. 수로 횡단면의 수위분포에 따르면, 돌출줄눈 설치 측벽 주변에서 흐름저항에 따른 유속감소와 수위상승 효과가 나타나는 것으로 파악되었다. 이번 사다리꼴 돌출줄눈은 흐름저항 효과가 크지 않았기 때문에 사다리꼴 밑각을 조정하여 새로운 단면에 대한 추가적인 실험이 필요할 것으로 보인다.

• The Journal of Engineering Geology
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• v.15 no.3
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• pp.269-280
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• 2005

We assigned points on surface of standard roughness profile by 0.1mm along the length and measured coordinates of points. Then, the lengths of profile were measured with different scales using modified divider method. The fractal dimensions and intercepts of slopes were determined by plotting the length vs scale in log-log scale. The fractal dimensions as well as intercepts of slopes show well correlation with joint roughness coefficients(JRC). However, multiplication of the kactal dimension by intercept show better correlation with IRC and we derived a new equation to estimate JRC from fractal dimension and intercept. The crossover length in which we can determine the correct fractal dimension was between 0.3-3.2mm. We measured joint roughness of 26 natural joints and calculated JRC using the equation suggested by Tse and Cruden(1979) and new equation derived by us. IRC values calculated by both equations are almost the same, indicating new equation is effective in measuring IRC.

• Electrical & Electronic Materials
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• v.4 no.2
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• pp.143-149
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• 1991

전계가 인가된 H$_{2}$와 CO기체중을 통과하는 전자의 탄성과 비탄성 충돌 단면적을 볼츠만방정식을 이용하여 추정하였는데 충돌 단면적은 운동량변환, 진동여기, 해리, 전자 여기 및 전리 충돌 단면적을 이동속도의 측정값 및 계산값을 비교하므로써 결정하였다. Gibson과 Phelps가 각각 계산한 H$_{2}$ 및 CO의 운동량변환 충돌단면적을 본 연구의 결과와 비교하였으며 이를 기초로하여 온도는 293.deg.K, 상대전계의 세기 E/N은 1*$10^{-17}$ [V$cm^{2}$].leq.E/N.leq.200*10 $^{17}$ [V$cm^{2}$]의 범위에서 전자에너지 분포함수를 산출하였으며 이렇게 산출된 에너지 분포함수 및 충돌단면적은 실험적으로 측정한 모든 수송계수의 값들을 만족하였다.

• Proceeding of EDISON Challenge
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• 2017.03a
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• pp.346-350
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• 2017

고속도로에서 자주 사용되고 있는 2way 가드레일 형상의 효율성을 탐구해보기 위하여 가드레일 형상과 이와 단면적이 같은 여러 종류의 단면을 가진 보들과 응력 값을 비교하였다. vonMises stress값의 비교를 통해 기존 가드레일의 W모양 단면과 경제적으로는 동일하고 형태는 상이하며 구조적으로 더 안정적인 단면 형상을 찾아보고자 한다. 그 결과 2way 단면의 가드레일 보다는 반원 단면의 가드레일이, 두께가 4T인 2way 모델 보다는 3T인 모델의 안전계수가 더 높음을 확인하였다. 이를 통해 향후 가정이 없는 실제 상황에서는 어떠한 이유 때문에 2way 가드레일 형상을 사용하고 3T보단 4T, 5T를 보편적으로 사용하는지 연구해보면 좋을 듯 하다.