• 한국지하수토양환경학회지:지하수토양환경
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• 제19권3호
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• pp.39-46
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• 2014

Hydraulic conductivity is an important parameter, representing permeable property of the groundwater in aquifers, in the issues of groundwater development, groundwater contamination, and groundwater flow, etc. We estimated a relationship between hydraulic conductivity and electrical properties (formation factor, chargeability, and time constant) of silty sand in the laboratory. For this study, we conducted grain size analysis, constant head permeameter test, and measured electrical resistivity and spectral induced polarization of silty sand samples collected from the riverside alluvium of the Nakdong River in Nogok-ri area, Dasan-myeon, Goryeong-gun in Gyeongbook Province, Korea. In the laboratory test, we used soil samples of approximately uniform porosity with 0.5% error range, and kept the electrical resistivity of pore water with 100 ohm-m. As a result, the relationship between effective particle size and hydraulic conductivity agrees fairly well with the existing empirical formulas. Hydraulic conductivity was correlated with formation factor, chargeability, and time constant: hydraulic conductivity increased with increasing formation factor and time constant as well as with decreasing chargeability.

• International Journal of Fluid Machinery and Systems
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• 제3권4호
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• pp.369-378
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• 2010

The creation of the hydraulic turbine flow factor map will undoubtedly benefit its design by decreasing both the design cycle time and product cost. In this paper, the geometry and flow variables, which effectively affect the flow factor, are proposed, analyzed and determined. These flow variables are further used to create the operating condition maps by using different model approaches categorized into Response Surface Method (RSM) and Artificial Neural Network (ANN). The accuracies of models created by different approaches are compared and the performances of model approaches are analyzed. The influences of chosen variables and the combination of Principle Component Analysis (PCA) and model approaches are also studied. The comparison results between predicted and actual flow factors suggest that two-hidden-layer Feed-forward Neural Network (FFNN), and one.hidden-layer FFNN with PCA has the best performance on forming this mapping, and are accurate sufficiently for hydraulic turbine design.

• 한국기계기술학회지
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• 제20권6호
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• pp.929-935
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• 2018

This paper develops a flow control block for a hydraulic system of a tunnel boring machine. The flow control block is a necessary component to ensure stability in the operation of the hydraulic system. In order to know the pressure distribution of the flow control block, the flow analysis was performed using the ANSYS-CFX. It was confirmed that the pressure and flow rate were normally supplied to the hydraulic system even if one of the four ports of the flow control block was not operated. In order to evaluate the structural stability of the flow control block, structural analysis was performed using the ANSYS WORKBENCH. As a result, the safety factor of the flow control block is 1.54 and the structural stability is secured.

• 한국지반공학회논문집
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• 제31권6호
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• pp.45-58
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• 2015

본 연구에서는 이론적 고찰을 통해 Kozeny-Carman식을 변형하여 전기전도도 측정을 통한 사질토의 투수계수 추정식을 제안하였다. 제안된 예측식에 대한 실험적 검증을 위해 6종류의 사질토에 대하여 4개의 전극을 설치한 정수위 투수시험을 실시하였으며, 다양한 변수들 하에 시험을 진행하였다. 시험 결과, 사질토에서 흙 입자 표면을 통한 전기전도는 미미하였으며, 간극수의 전기전도도가 투수계수와 formation facotor에 미치는 영향은 제한적이었다. 흙 입자의 유효입경이 formation factor에 미치는 영향은 미미하였으나 투수계수에는 큰 영향을 주었다. 제안된 식을 활용하여 투수계수를 예측하기 위해서는 형상계수와 Archie's m에 대한 정보가 필요하여 error norm방법을 사용해 형상계수를 구하였다. 또한, 간극률을 변화시키며 측정된 formation factor를 사용하여 Archie's m을 구하였다. formation factor를 사용하여 계산한 투수계수를 측정값과 같이 도시한 결과, 계산된 투수계수는 측정된 투수계수와 유사한 값을 보여주었다. 기존 Kozeny-Carman식과 본 연구에서 제안하는 전기전도도를 이용한 투수식 간의 정량적인 비교를 위해, 정규화된 투수계수를 사용하여 형상계수, Archie's m, 간극률에 따른 정규화된 투수계수의 변화를 비교한 결과, 형상계수와 Archie's m의 변화에 따른 정규화된 투수계수의 변화 폭에 비해, 간극률의 변화에 따른 정규화된 투수계수는 매우 큰 폭으로 변하였다. 따라서 본 연구에서 제안하는 전기전도도를 이용한 투수계수 예측식이 기존 Kozeny-Carman식보다 더 높은 신뢰도를 보일 것으로 판단된다.

• 터널과지하공간
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• 제20권3호
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• pp.225-232
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• 2010

본 연구에서는 절리에 작용하는 수직변형과 전단 팽창을 고려할 수 있는 수정된 3차원 변형률 의존성 수리전도도 변화 방정식을 제안하였다. 현지 암반을 직교절리가 발달한 매질로 가정하기 때문에 제시된 방정식을 사용하여 수리전도도의 이방성을 평가할 수 있다. 현지암반의 변형계수를 필요로 하는 탄성계수감소비를 손쉽게 결정하기 위하여 GSI와 교란계수를 기초로 하는 경험식을 사용하였다. 현지 암반 내에 존재하는 절리는 일반적으로 전체좌표계와 평행하지 않고 기울어져 있는 경우가 많기 때문에 기울어진 방향에서의 수리전도도를 구하기 위하여 변형률 회전식을 사용하였다. 해석 결과 GSI가 증가함에 따라 수리전도도는 감소하는 것으로 나타났다. 교란계수는 수리전도도의 변화 거동에 영향을 미치는 것으로 나타났는데 특히 GSI가 50 이상인 암반의 수리전도도 변화에 큰 영향을 미치는 것으로 해석되었다. 절리의 경사도 수리전도도 변화에 영향을 미치는 것으로 나타났다.

• Geomechanics and Engineering
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• 제33권2호
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• pp.141-154
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• 2023

This study investigated the effect of water retention characteristics between aged and fresh Municipal Solid Waste (MSW) on the stability of the landfill. A series of transient numerical modeling for the slope of an MSW landfill was performed considering the variation of water retention characteristics due to leachate circulation. Four different scenarios were considered in this analysis depending on how to obtain hydraulic conductivity and the aging degree of materials. Unsaturated hydraulic properties of the MSW used for the modeling were evaluated through modified hanging column tests. Different water retention properties and various landfill conditions, such as subgrade stiffness, leachate injection frequency, and gas and leachate collection system, were considered to investigate the pore water distribution and slope stability. The stability analyses related to the factor of safety showed that unsaturated properties under those varied conditions significantly impacted the slope stability, where the factor of safety decreased, ranging between 9.4 and 22%. The aged materials resulted in a higher factor of safety than fresh materials; however, after 1000 days, the factor of safety decreased by around 10.6% due to pore pressure buildup. The analysis results indicated that using fresh materials yielded higher factor of safety values. The landfill subgrade was found to have a significant impact on the factor of safety, which resulted in an average of 34% lower factor of safety in soft subgrades. The results also revealed that a failed leachate collection system (e.g., clogging) could result in landfill failure (factor of safety < 1) after around 298 days, while the leachate recirculation frequency has no critical impact on stability. In addition, the accumulation of gas pressure within the waste body resulted in factor of safety reductions as high as 24%. It is essential to consider factors related to the unsaturated hydraulic properties in designing a landfill to prevent landfill instability.

• Design & Manufacturing
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• 제12권1호
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• pp.41-46
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• 2018

This study proves the causes of cylinder and piston jam by scratches which is the fatal problem of hydraulic breaker through the thermal analysis and thermal-structural coupled field analysis. The trouble from the scratch is a complex problem which can be caused by manufacturing process (this is an internal factor) and the users mistake or contamination in the hydraulic circuit (these are an external factor). Hence, it's not easy to investigate the causes, also hard to prevent the recurrence. In this reason, hydraulic breaker manufacturers are trying to improve the manufacturing process such as machining, heat treatment, grinding, cleaning, also to prevent the contamination in hydraulic circuit and to remove the remains. It's being managed thoroughly by manufacturers. This study shows the effect of the temperature rise by the frictional heat generated when the piston hits the tool on the hydraulic oil while the hydraulic breaker is operating, also the temperature distribution when it starts to affect main components of hydraulic breaker. The stress and the amount of deformation also could be found through thermal-structural coupled field analysis. It proved that the stress and deformation are proportionally increased according to the temperature rise in hit area, and it affects the cylinder and the viscosity of hydraulic oil inside the cylinder when it heats up beyond the certain temperature.

• 한국구조물진단유지관리공학회 논문집
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• 제2권4호
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• pp.194-200
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• 1998

Risk, probability of failure, which includes various uncertainties and influential factors of performance should be accounted for in engineering system. Recently, several different methods to analysis risk evaluation evolved and one of the practical method is FOSM (First Order Second Moment Method ). FOSM method is derived in terms of terms coefficient of variance to uncertainties which influence various factor. For risk evaluation and uncertainty analysis in hydraulic design system, load-capacity relationship is adopted in this paper. Sample catchment with design of sewer system is applied, which plots safety factor vs. risk. Risk evaluation and uncertainty analysis are very to important develop optimal design model in hydraulic system

• 상하수도학회지
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• 제21권2호
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• pp.177-185
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• 2007

Hydraulic efficiency($T_{10}/T$) in clearwell is often estimated by L/W ratio. However, this estimation is not accurate because other factors which give an effect on hydraulic efficiency such as shape of basin, diffuser wall and intra-basin is ignored. Therefore, in this research, hydraulic efficiency is predicted by the quantitative analysis of dead zone using CFD simulation in a pilot scale clearwell. The results show that the reason why higher L/W ratio increase the hydraulic efficiency is to decrease the dead zone of linear region which is located between baffles. Diffuser wall or intra-basin also affects on hydraulic efficiency with this process. Also, we conclude that hydraulic efficiency can not be reached to 0.8 or higher.

• 한국지반공학회논문집
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• 제37권4호
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• pp.5-17
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• 2021

본 논문은 만곡부 제방에 대해 곡률각도, 곡률반경에 따라 3차원 해석을 실시하여 침투특성을 규명하였다. 제방만곡부에서 동수경사는 2차원 해석 결과에 비해 외측제방에서는 감소하였고, 내측제방에서는 증가하였다. 곡률각도와 곡률반경이 작을수록 2차원 해석 대비 동수경사의 변화가 큰 경향을 나타내었으며, 곡률각도보다는 곡률반경이 동수경사에 미치는 영향이 큰 것으로 나타났다. 한계동수경사에 의한 파이핑 안전율 산정결과, 2차원 해석에 대비하여 안전율은 외측제방에서는 2~5%가 증가되었고, 내측제방에서는 4~12%가 감소되었다. 이 감소폭을 고려해 볼 때 제방만곡부에 대해 2차원 해석을 실시하고 파이핑에 대한 허용안전율 Fs=2.0보다 0.1~0.3정도 더 크게 설계하면 만곡부의 안전율은 약간 감소되지만 안정성 확보에는 무리가 없는 것으로 판단되었다.