• Journal of Korea Water Resources Association
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• v.51 no.2
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• pp.109-120
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• 2018

In this study, we conducted flume experiments to investigate the three-dimensional flow structures around a half-submerged spur dike in a straight open channel flume. The experiments were carried out under the two different Froude numbers, 0.10 and 0.18. The results were compared with the previous experimental result conducted for non-submerged spur dike. Three-dimensional instantaneous velocities were measured using Acoustic Doppler Velocimetry (ADV) and water elevation data were collected using ultra sonic distance sensor. The results show that submergence conditions of the spur dike largely influence the three-dimensional flow structures around a spur dike.

• The Journal of Engineering Geology
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• v.16 no.3 s.49
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• pp.245-254
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• 2006

Using a natural gradient tracer test, the characteristics of hydrodynamic dispersion according to each depth of a fractured rock were studied, and the effective porosity and longitudinal dispersivity of the fractured rock were estimated. The difference of vertical hydrodynamic dispersion was identified by concentration breakthrough curves linear regression analyses of bromide concentrations according to depths versus time, and hydraulic fracture characteristics at two intervals of the monitoring well. Higher concentration and faster arrival time at GL- 18 m depth (RQD 13%, average joint spacing 2 cm, TCR 100%) than at GL- 25 m depth (RQD 41%, average joint spacing 7 cm, TCR 100%) resulted from shorter distance and more fractures. Tracer was transported through the 1 st fractures until the arrival of its peak concentration and through the 2nd fractures or matrix diffusion after the arrival of its peak concentration. The increase/decrease slopes of bromide concentration versus time were 3.46/-1.57 at GL-18 m depth and 3.l9/-0.47 at GL- 25 m depth of the monitoring well. So the faster bromide transport was confirmed at GL- 18 m depth with more fractures. The concentration increment of bromide was fitted by a Gaussian function and the concentration decrement of bromide was fitted by an exponential function. Effective porosity and longitudinal dispersivity estimated by CATTI code were 10.50% and 0.85 m, respectively.

• Journal of the Korea Society of Computer and Information
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• v.26 no.9
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• pp.1-12
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• 2021

In this paper, we propose a tool called ARCAV (Atomatic Recovery of CUDA Atomicity violation) to automatically repair atomicity violations in GPU (Graphics Processing Unit) program. ARCAV monitors information of every barrier and memory to make actual memory writes occur at the end of the barrier region or to make the program execute barrier region again. Existing methods do not repair atomicity violations but only detect the atomicity violations in GPU programs because GPU programs generally do not support lock and sleep instructions which are necessary for repairing the atomicity violations. Proposed ARCAV is designed for GPU execution model. ARCAV detects and repairs four patterns of atomicity violations which represent real-world cases. Moreover, ARCAV is independent of memory hierarchy and thread configuration. Our experiments show that the performance of ARCAV is stable regardless of the number of threads or blocks. The overhead of ARCAV is evaluated using four real-world kernels, and its slowdown is 2.1x, in average, of native execution time.

• Journal of Korean Society on Water Environment
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• v.33 no.6
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• pp.715-721
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• 2017

Tree box filters, an example of bioretention systems, were compacted and versatile urban stormwater low impact development technique which allowed volume and water quality treatment performance to be adjusted based on the hydrologic, runoff quality and catchment characteristics. In this study, the overall performance of a 6 year-old tree box filter receiving parking lot stormwater runoff was evaluated. Hydrologic and hydraulic factors affecting the treatment performance of the tree box filter were also identified and investigated. Based on the results, the increase in rainfall depth caused a decrease in hydrologic and hydraulic performance of the tree box filter including volume, average flow, and peak flow reduction (r = -0.53 to -0.59; p<0.01). TSS, organics, nutrients, and total and soluble heavy metals constituents were significantly reduced by the system through media filtration, adsorption, infiltration, and evapotranspiration mechanisms employed in the tree box filter (p<0.001). This significant pollutant reduction by the tree box filter was also found to have been caused by hydrologic and hydraulic factors including volume, average flow, peak flow, hydraulic retention time (HRT) and runoff duration. These findings were especially useful in applying similarly designed tree box filter by considering tree box filter surface area to catchment area of less than 1 %.

• Journal of Biosystems Engineering
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• v.6 no.2
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• pp.65-76
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• 1982

This survey was conducted to investigate the status of repair and maintenance of 4 wheel tractor for a basic reference to the improvement of quality and proper utilization of tractors. Thirty two counties from eight provinces, except Jeju, were covered in this study in order to investigate annual break-down and repair of tractor in 1980. The analyzed results are summarized as follows; 1. The average number of break-down of large size tractors(47ps) was 5.0 times in a year and it was about twice of that of small size tractors(19-23ps). The break-down frequency per 100 hours of use was 1.11 times in the large size and 0.65 times in the small size tractors. 2. 75.6 percent of total break-down was occured in main body of tractor and 24.4 percent in attachments. In particular, the break-down of plow and rotavator was more than 80 percent of total break-down of the small size tractor attachments. 3. The large size tractors which were occured more than one times of break-down a year was 75 percent and its rate of the small size tractor was 62 percent. But 9 percent of tractor surveyed had more than ten times of break-down in a year 4. The frequency of break-down had a peak in May, and it was directly proportional to the hours of use. 5. The causes of break-down were poor maintenance and operation by 29.8 precent, old parts by 30.2 percent, poor quality of parts by 20.6 percent, poor field condition by 16.3 percent and others by 3.1 percent. 6. Annual number of repair was 5.5 times and among them 55.6 percent was done by shop and 44.4 percent by operator. 7. Total required repair time was 30.6 hours a year in the large size tractor and 19.9 hours in the small size tractor. Average repair time was 3.62 hours a time. 8. Annual repair cost was 278 thousand won in the large size tractor and 70 thousand won in the small size tractor. The repair cost per hour of use was 621 won in the large size and 198 won in the small size tractor. 9. The repair cost rate of tractor(Y) was regulated with tractor age (X) as follow; Y=0.752X In case of the service life of tractor was 10 years, the total repair cost rate was 64 percent.

• Journal of Korea Water Resources Association
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• v.48 no.8
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• pp.635-645
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• 2015

The objective of this study is to examine the three-dimensional turbulent flows occurring in the meandering channel with presence of a groyne. A series of laboratory experiments are carried out in a meandering channel with trapezoidal cross sections. The channel is a 24.4 m long, 1.5 m wide, and the bottom slope in the longitudinal direction is 0.02. Two cases with and without the groyne are considered in the experiment. Three-dimensional velocity fields are measured using an acoustic Doppler velocimetry (ADV) at approximately sixty locations in each cross section. The measured velocity fields are averaged in time, and the time-averaged flow revealed that the mean velocity magnitude along the outer bank of the channel was reduced significantly and the direction of the primary flow was directed toward the center of the channel due to the presence of the groyne.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.493-493
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• 2017

부유사 수리실험에서 부유사의 농도를 측정하는 것은 불확실성이 매우 크다. Einstein(1950)은 유사의 pickup function 결정에서 이러한 불확실성 때문에 유사입자의 거동을 발생시키는 양력의 확률을 적용하기도 하였다. 일반적으로 부유사의 측정은 부유사 채집기를 통해 수행하지만, 시간적으로 비효율 적이며, 채집 시 채집기의 부피로 인한 난류 발생으로 채집 후 흐름 변화가 발생할 수 있다. 수리실험의 규모라면 이 문제는 더욱 부각될 수 있다. 연속적인 부유사의 농도 측정을 위해 이러한 점은 개선되어야 하는 문제이다. 본 연구에서는 유사 실험의 이러한 단점을 극복하고자 image processing 기법을 적용하였다. Image processing은 부유사의 농도가 증가할수록 탁도가 증가하는 특성을 이용하여, 부유사 농도를 추정하는 방법이다. 이 과정에서 RGB(Red-Green-Blue)로 색을 표시하는 방식에서 image를 변환하여 gray scale로 전환해야 하며, 파(wave)의 전파에 의한 image 결과의 변형은 없다고 가정하였다. Gray scale과 탁도와의 관계를 도출하기 위해 하상에 유사를 포설하고, 단파(surge)를 발생 시켰다. 실험은 길이 12.0m, 폭 0.8m, 높이 0.75m의 개수로에서 수행하였으며, 수로 상류에 sluice형 gate를 급격하게 개방하는 것으로 단파를 재현하였다. 탁도 측정을 위해 유사 채집기를 이용하였으며, 상기에서 제시한 흐름 교란문제로, 1지점에서 1개의 시간동안만 채집을 수행하였으며, image의 촬영을 병행하였다. 또한 data의 정확도를 높이기 위해 3번의 반복실험을 수행하였다. 실험결과 gray scale과 탁도와는 일정한 관계가 나타났으며, 이를 토대로 gray scale-SSC(suspended sediment concentration)와의 관계를 도출하였다. Bayesian 분석을 이용하여 image processing의 보정(확률적 보정)을 추가적으로 수행하였다. 최종적으로 실측한 값과 image processing을 통한 값을 1:1 curve를 통해 비교하였으며, 약 9%의 평균 오차가 발생하여, image processing과 bayesian 적용을 통한 부유사 농도 측정은 신뢰할 만한 결과를 도출하는 것으로 판단된다.

• Journal of Ocean Engineering and Technology
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• v.11 no.3
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• pp.153-162
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• 1997

시간평균된 해안의 지하수위는 내륙쪽에 강우가 없는 경우에도 평균해수면 (Mean Sea Level)보다 1내지 2미터 정도 높은 것으로 관측되었다. 이러한 해안의 지하수위상승현상은 주로 파랑과 조석의 작용에 의해 나타난다. 본 연구에서는 지하수위상승에 미치는 조석 및 파랑의 효과를 현장관측결과를 통해 정량적으로 보여주었으며, 또한 이들 각각의 작용에 기인한 지하수위상승에 대한 해석해 및 최근 이론들을 제시하였다. 특히, 최근 지하수의 수리학적 모델링에 관한 연구에서 파랑의 침투 (wave runup infiltration)효과의 중요성이 강조되었는 바, 본 연구를 통해 종래에 보고된 바 없는 swash zone (shoreline과 runup limit사이)에서의 파랑의 침투속도(분포)를 지하수위관측자료를 이용해 간접적으로 산정함으로써 해안의 지하수위예측모델링을 보다 정확히 수행할 수 있으리라 사료된다.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.04a
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• pp.92-96
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• 2004

본 연구에서는 지하수위 변동 분석을 위한 프로그램을 개발하고, 건설교통부에서 설치, 운영하고 있는 169개 국가 지하수 관측소의 264개 지하수관측정에서 측정된 지하수위자료에 적용하였다. 분석결과 암반대수층과 충적층대수층의 평균수위 및 변동양상이 대체적으로 비슷하게 나타났으며, 이는 관측소 설치 지역의 대부분에서 충적층(10m 내외)과 암반층(70m 내외)이 수리적으로 연결되어 있다는 것을 시사한다. 6시간 간격의 지하수위 관측 자료를 이용하여 지하수위가 상승하는 횟수, 상승량의 합계 산정 등 변동양상을 분석하였다. 분석 결과 해양 및 지구 조석의 영향을 받는 관측정의 경우 지하수위 상승 개수가 450개/yr 이상이 대부분이며, 수위 변동량은 0.1 ～ 1m 정도이고, 수위변동 자료를 시계열로 나타내 보면 하루에 약 2번의 상승과 하강을 반복하는 수위변동 형태를 볼 수 있었다. 양수의 영향이 우세한 관측정에서는 수위 상승 개수가 약 360개/yr, 수위 변동량은 1m 이상의 값이 우세하게 나타났다. 지하수위 상승량은 암반/충적 관측정 모든 관측정에서 전반적으로 강수량과의 상관계수가 높았으며, 같은 관측정의 .자료라도 6시간 간격의 관측 자료보다, 12시간 및 24시간 관측 간격으로 분석한 결과에서 상관관계가 더 높게 나타났다. 12시간 및 24시간 관측 간격으로 분석할 경우 조석 및 양수에 의해 발생된 주기적인 지하수위 변동 성분이 제거되면서 강수에 대한 지하수위 반응의 상관도가 높아진 것으로 해석된다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.2
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• pp.157-164
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• 2012

When designing a multifunctional system consisting of many components performing many functions or missions, it is important to determine the reliability, availability, and maintainability (RAM) of the system and components, and we consider system availability to be the optimization criterion. For given intervals of mean time between failure (MTBF) and mean time to repair (MTTR) of the components, we want to determine the values of MTBF and MTTR for all components that satisfy the target availability. A heuristic method is proposed for finding near-optimal solutions through simulation. We also study numerical examples to check effects of model parameters on the optimal solutions.