• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.3
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• pp.409-418
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• 1988

Steam turbines, gas turbines, multistage centrifugal compressors are operated over the range of the first critical speed. In these rotors flexible rotor balancing technique is necessary. In such balancing, influence coefficients are measured by rotating a rotor with trial weight. But for the large rotor, the measurement of influence coefficient takes much time and it reduces the cost efficiency. In this paper the new influence coefficient with rotation of rotor is proposed. First the theoretical background of the method is presented and it is applied to the simple flexible rotor model. Then the experiments are performed and the results of presented method are compared with those of analytical method. By using the obtained influence coefficient, balancing of the flexible rotor is performed.

• Proceedings of the Korea Water Resources Association Conference
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• 2004.05b
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• pp.409-413
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• 2004

자연하천에서의 횡혼합 특성을 분석하고 횡분산계수를 산정하기 위해서 추적자 실험을 실시하였다. 추적자 실험은 섬강에서 세번, 홍천강에서 두번, 청미천에서 한번, 총 여섯 군데에서 실행되었다. 각각의 실험에서 속도, 수심, 유속과 같은 수리량이 측정되었다. 추적자로서는 미량으로도 관측이 용이하며 병원에서 진찰용으로 사용할 만큼 인체에 해롭지 않은 방사성 동위원소 (I-131)를 사용하였다. 추적자 실험을 통해 얻어진 농도데이터와 수리량 데이터를 이용하여 횡분산계수를 산정하였으며 이때 모멘트 방법과 수정모멘트 방법 그리고 유관모형 추적법이 사용되었다. 세가지 방법을 이용하여 산정된 횡분산계수를 토대로 각각의 방법이 자연하천에서의 횡분산계수를 산정하는데 합당할지를 비교 분석하였다. 또한 여섯 경우의 지형이 다른 자연하천에서 구한 횡분산계수를 토대로 하천의 형상에 의해 하천에서의 횡분산 거동이 어떻게 달라지는가를 분석하였다.

• Journal of the Korean Geotechnical Society
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• v.25 no.12
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• pp.47-55
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• 2009

As a conventional line-fitting method, the Bouwer and Rice method has been popularly adopted to estimate the hydraulic conductivity of an aquifer through a slug test. Because a vertical cutoff wall is usually very compressible and features a small wall thickness, the Bouwer and Rice method should be carefully applied to analyzing slug test results to estimate the hydraulic conductivity of vertical cutoff walls. In addition, a relatively impermeable layer, called a filter cake, formed at the interface between the cutoff wall and the natural soil formation makes it difficult to use the Bouwer and Rice method directly. In order to overcome such limitations, the original Bouwer and Rice method has been modified by incorporating the concept of the flow net method. In this modification, the geometry condition of cutoff walls including the filter cake is effectively considered in evaluating the hydraulic conductivity of a vertical cutoff wall.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.2 s.54
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• pp.11-17
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• 2007

In current seismic design practice, the response modification factor (R-factor) is used as a factor to reduce the elastic base shear demand to the design force level. As is well-known, the R-factor is a committee-consensus factor and, as such, highly qualitative and empirical. The relationship between the R-factor and the connection rotation capacity available in a particular structural system has remained a missing link. In this paper, a rational procedure to evaluate the R-factor is proposed. To this end, the relationship between the available connection rotation capacity and the R-factor is defined and quantified using nonlinear pushover analysis. An RRS steel frame designed according to IBC 2000 was used to illustrate and verify the proposed procedure. Nonlinear time history analysis results indicated that the R-factor definition proposed in this study is generally conservative from design perspective.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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• pp.463-474
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• 1995

Modified Vainshtok weight function method is developed. The thermal shock stress intensity factors for elliptical surface cracks existed in the thin and thick walled cylinders are determined. The present results are compared with previous solutions and shown to be good agreement with them.

• 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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2A
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• pp.179-186
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• 2008

To analyzing the validity for using the stiffness ratio in evaluating edge stiffness effect of the composite girder bridges, modification factors are analyzed with changing girder spacing. The relation between stiffness ratio, loading type, girder spacing and modification factors is analyzed. From the results of comparing modification factors analyzed from the field loading test and the established design method with the modification factor analyzed from this study, it was concluded that evaluating the edge stiffness effect using stiffness ratio is possible.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.1
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• pp.65-72
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• 2009

‘Korean Highway Bridge Design Code’ provides the spectrum analysis method with response modification factors for the seismic design of typical bridges. However, considering that korean peninsula is classified as moderate seismic regions and domestic circumstances for bridge design and construction are different from other countries, the applicability of this code is not yet proved. Therefore it is required to verify that applying the spectrum analysis method fulfills the no collapse requirement which is set forth as the basic seismic design concept. In this study two typical bridges with T and ${\prod}$ type piers are selected as analysis bridges and seismic designs are carried out by applying the spectrum analysis method with design conditions given for moderate seismic regions. Based on the results obtained through deign procedures, the role of the response modification factors and fulfillment of the no collapse requirement are discussed, from which supplementary provisions for the design code are identified.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.45-50
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• 2006

본 연구는 Manta형 무인잠수정(Manta-type Unmanned Undersea Vehicle)의 동안정성을 검토한 후에 이 데이터를 기초로 하여 6자유도 수치 시뮬레이션을 실시하였다. 또한, 수치 시뮬레이션을 통하여 각각의 유체력미계수가 UUV의 6자유도 운동에서 미치는 영향에 대하여 검토하였다. 민감도 해석(Sensitivity Analysis)을 위한 방법은 간접법(Indirect Method)을 사용하였다. 수학모델 및 유체력미계수의 추정은 손경호 등(2006)의 결과를 이용하여 수행하였다. 연구를 통하여 UUV의 조종운동 모델에서 각각의 유체력미계수가 가지는 상대적 중요도를 알 수 있었다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.2
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• pp.149-154
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• 2012

While the Earthquake Resistant Design Part of Korean Roadway Bridge Design Code provides design procedures for the No Collapse Requirement, requirements for the Serviceability Limit State are not clearly provided. The basic design method to meet the No Collapse Requirement is the spectrum analysis method using response modification factors and the Serviceability Limit State is determined by both the importance factor and the response modification factor applied in the design procedure. The importance factor can be simply applied according to the bridge importance category, however, in moderate/low seismic regions the application of the response modification factor may bring different result according to design conditions. In this study, for a typical bridge in the moderate/low seismic regions, determination procedures for the Serviceability Limit State are reviewed by carrying out earthquake resistant design and supplementary provisions for the Earthquake Resistant Design Part are identified based on the study results.