• Journal of the Korean Geotechnical Society
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• v.28 no.2
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• pp.23-31
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• 2012

The purpose of this study is to analyze earth pressure acting on a circular shaft-tunnel considering arching effect by centrifuge modeling test on sands. The centrifuge testing method provides a way to model an in-situ stress state condition with a stress gradient within a laboratory specimen. A small-scale model of circular shaft-tunnel, which has a real diameter of 6.0 m and height of 15.0 m, was designed and tested twice under 75g-level. Additionally, an effect of excavation was presented by separating two segments of circular shaft wall to find behavioral properties and strength of earth pressure along with excavating ground. The test results were compared with those of the proposed earth pressure equation. The test results showed that earth pressure decreased by about 70% in comparison with existing two-dimensional earth pressure. This fact might be attributed to three-dimensional arching effects.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.2C
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• pp.49-60
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• 2012

In this study, the behaviors of friction pile groups are investigated using 3D finite element (FE) analysis. The emphasis was quantifying on the shear load transfer (f-w) characteristics of pile groups and the shaft group effects. A framework for determining the f-w curve is proposed based on both theoretical analysis and field load test database. Through comparisons with case histories and FE results, it is shown that the proposed f-w curve is capable of predicting the behavior of a friction pile in deep soft clay. Additionally, a numerical analysis that takes into account the group efficiency factors were performed for major parameter on group pile-soil interaction, such as the pile spacing, pile arrangement, soil condition, and location of pile cap. Based on these results, the shaft group efficiency factors were also proposed.

• Korean Chemical Engineering Research
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• v.58 no.2
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• pp.319-324
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• 2020

Electroconvective instability is a non-linear transport phenomenon which can be found in ion-selective transport system such as electrodialysis, Galvanic cell and electrolytic cell. The instability is triggered by the fluctuation of space charge layer in adjacent of ion-selective surface, leading to increase of mass transport rate. Thus, in the aspect of mass transport, the instability has an important meaning. Although recent experimental techniques have opened up an avenue to direct visualize the instability, fundamental investigations have been conducted in limited area due to several experimental limitations. In this work, the electroconvective instability under potentiostatic mode was solved by numerical method in order to demonstrate correlation between current-time curve and the instability behavior. By rigorous time-resolved analysis, the transition behaviors can be divided into three stages; formation of space charge layer - growth of electroconvective instability - steady state. Furthermore, scaling laws of transition time were numerically obtained according to applied voltage as well.

• Journal of the Korean Geotechnical Society
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• v.29 no.11
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• pp.5-15
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• 2013

The end bearing capacity of rock-socketed drilled shafts under axial loading is investigated by Hoek-cell tests and a numerical analysis. From the test results, it was found that the ultimate end bearing capacity ($q_{max}$) was influenced by pile diameter, rock mass modulus and the spacing of discontinuity. A new ultimate end bearing capacity method is proposed by taking end bearing capacity influence factors, including rock mass discontinuity, based on field data. Through comparisons with other field data, the proposed $q_{max}$ method represents a definite improvement in the prediction of ultimate end bearing capacity of rock-socketed drilled shafts.

• Journal of the Korean Geotechnical Society
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• v.38 no.1
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• pp.17-33
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• 2022

This study describes the effect of ground water table on the dynamic analysis of single piles subjected to earthquake loading. The dynamic numerical analysis was performed for different dry and saturated soils with varying the relative densities of surrounding weathered soils (SM). The test soil was a weathered soil encountered in the engineering field and bender element tests were conducted to estimate the dynamic properties of test soil. The Mohr-Coulomb model and Finn model were used for soil, dry and saturated conditions, respectively. These models validated with results of centrifuge tests. When compared with the results from the soil conditions, saturated cases showed more lateral displacement and bending moment of piles than dry cases, and this difference caused from the generation of excess porewater pressure. It means that the kinematic effect of the soil decreased as the excess pore water pressure was generated, and it was changed to the inertial behavior of the pile.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.88-88
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• 2020

수심평균 2차원 혼합모형은 하천환경에서 다양한 용존성 오염물질의 혼합현상을 모의하기 위해 널리 활용되어왔다. 2차원 혼합모형에서 분산계수는 하천의 전단 흐름에 의해 야기되는 오염물질의 퍼짐 현상을 표현하는 중요한 인자로서 작용하기 때문에 정교한 오염물질 혼합거동을 모의하기 위해서는 적합한 분산계수를 산정하는 것이 필수적이다. 분산계수를 실험적으로 산정하는 방법으로는 크게 모멘트법과 추적법으로 나뉘며, 비정상상태의 혼합거동에 대해 종방향 및 횡방향 분산계수를 동시에 산정할 수 있는 방법은 추적법 계열의 2차원 유관추적법(2D STRP)이 유일하다. 본 연구에서는 하천에 유입된 오염물질의 2차원 혼합해석을 위한 수치모형을 개발하였으며, 개발된 모형의 수치해를 바탕으로 다양한 Peclet 수의 범위에 대해 기존연구에서 제시된 2D STRP의 적용범위 및 성능을 정량적으로 분석하였다. 분석된 정보를 바탕으로 기존 2D STRP의 한계를 극복하기 위한 개선된 2차원 유관추적법(2D STRP-i)을 개발하고, 사행하천을 모형화한 실규모 하천실험시설에서 검증하였다. 기존 2D STRP의 성능평가 결과, Peclet 수가 낮은 조건일수록 농도분포의 예측 정확도가 감소하는 경향을 보였으며, 하안 경계에 도달하는 농도가 증가할수록 부정확한 결과를 초래하는 것으로 나타났다. 본 연구에서는 기존 2D STRP의 한계를 보완하여 더욱 정확한 분산계수를 산정하고자 하안 경계면 조건을 고려한 2차원 유관추적법(2D STRP-i)을 개발하였다. 2D STRP-i는 직교-곡선좌표계 기반의 2차원 이송-분산 방정식을 바탕으로 횡방향 유속분포 및 하안 경계조건을 고려할 수 있도록 개선되었다. 2D STRP-i는 공간적으로 상이한 이송효과 및 하안경계 조건을 적절히 반영함으로써 농도분포의 예측 정확도를 개선 시키는 것으로 평가되었으며, 하안경계면에서 농도가 증가하는 구간에서 기존 2D STRP의 결과와 비교하여 더욱 정확한 농도분포 및 분산계수를 제공하는 것으로 밝혀졌다.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.173-173
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• 2021

현재까지 상수도관망 내 수질적 거동에 대한 분석은 (1) 네트워크 수질 모델(EPANET 수질모의 등)에 기반한 방법과 (2) 시공간적 저해상도 데이터에 기반한 데이터 분석법이 주를 이루었다. 그러나 현존 네트워크 수질 모델은 수질 사고의 복잡한 물리·화학적 거동을 상세히 모의하기 어렵다. 반면 계측 및 통신기술의 발달로 고해상도 수질 데이터의 실시간 수집이 가능해지면서 사고의 사전감지, 발생시 즉각적 탐지 및 대응을 위한 데이터 분석법에 관심이 증가하고 있다. 서울 문래동, 인천, 포항의 경우에서도 알 수 있듯이, 수질사고 발생 시 원인물질의 시공간적 이송 또는 전파에 대한 정보는 사고대응에 유용하게 활용된다. 본 연구는, 비정상적인 수질변화의 계통 내 전달 시간을 계산하기 위해 고해상도 수질 스마트 미터 데이터에 기반한 데이터 분석법을 개발하였다. 물공급 하류방향의 수질변화 전달 시간 정량화를 위해 화음탐색법 기반 동적시간워핑(Dynamic time warping; DTW) 기술을 이용하였고, 원데이터의 전처리를 위해 이동평균필터링을 수행하였다. 개발된 분석법은 A시 생산 및 배·급수과정의 감시지점에서 10초 단위로 계측된 다양한 수질변수(pH, 탁도, 잔류염소, 전기전도도, 수온 등)의 공간적 변이 전파시간을 결정하기 위해 적용되었다. 분석에 활용한 데이터는 데이터 통신 및 측정 기기에 의한 이상값과 운영상황의 변화에 따라 변동한 값을 처리하기 이전의 데이터이다. 데이터 품질에 의한 영향을 배제하기 위해 이상값이 발생하지 않은 기간을 파악한 후, 그 기간에 대하여 분석하였다. 계통 내 위계에 따라 두 지점의 측정값의 전파시간을 정량화한 결과, 지점에 따라 전파시간이 다르게 나타났다. 또한, 같은 두 지점에 적용한 결과라도 DTW를 적용하는 기간과 이동평균필터링의 크기에 따라 수질변화 전달 시간이 다르게 나타나는 것을 확인할 수 있었다. 본 연구에서 개발된 분석법은 다변량 수질변수 간의 영향관계를 파악하는데 확장 적용이 가능하다. 또한, 이 방법의 실시간 적용을 통해 동적으로 변화하는 전달시간을 주기적, 공간적으로 갱신하여 관망 수질 변화 모니터링이 가능하다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.4C
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• pp.175-183
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• 2010

The load distribution and deflection of large diameter piles are investigated by lateral load transfer method (p-y curve). The emphasis is on the effect of the soil continuity in a laterally loaded pile using 3D finite element analysis. A framework for determining a p-y curve is calculated based on the surrounding soil stress. The parametric studies that take into account the soil continuity are also presented in this paper. Through comparisons with results of field load tests, it is found that the prediction by the present approach is in good agreement with the general trend observed by in situ measurements and thus, represents a significant improvement in the prediction of a laterally loaded pile behavior. Therefore, a present study considering the soil continuity would be more economical pile design.

• Journal of Navigation and Port Research
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• v.31 no.3 s.119
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• pp.223-228
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• 2007

In recent trends of the enlargement and specialization, container ship, LNCG, PCC and passenger ship which have relatively large hull and superstructure above the water line, are already being operated in the world It is very important information for the safety operation of these vessels to estimate the ship's performance under the specific wind condition while berthing, unberthing or low-speed sailing. In this paper, the effect of wind force and moment acting on the training ship HANNARA is investigated by using the numerical calculations. The results of drift angle and counter rudder angle with the relative wind direction and force, the critical wind velocity with the ratio of wind velocity and ship's speed and maximum heeling angle with the wind velocity are shown The presented results can be applied directly to T/S HANNARA in berthing maneuver and avoiding typhoons, and utilized as an educational materials.

• The Korean Journal of Rheology
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• v.11 no.1
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• pp.1-8
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• 1999

This paper experimentally investigates the steady shear behaviors of electro-rheological(ER) fluids under flow mode at high pressure level. As for the ER fluid to be tested, two types of ER fluids are employed; water-based ER fluids (ERF 1, ERF 2) and water-free ER fluid(ERF 3). The water-based ER fluids are composed inhousingly, and the concentrations of dispersed particles are 20 wt% and 30 wt% for ERF 1 and ERF 2, respectively. To generate the flow mode at high pressure, an experimental apparatus operated by two-way hydraulic cylinder is constructed and utilized. The pressure difference is measured by the pressure sensor, while the flow rate is calculated using the measured data of the displacement sensor(LVDT). Consequently, the shear stress and shear rate are distilled by incorporating the measured data; the pressure difference and the flow rate.