• Journal of Korea Water Resources Association
• /
• v.38 no.12 s.161
• /
• pp.1061-1072
• /
• 2005

A hydrological grey model is developed to forecast short-term river runoff from the Naju watershed located at upstream of the Youngsan estuary dam in Korea. The runoff of the Naju watershed is measured in real time at the Naju streamflow gauge station, which is a key station for forecasting the upstream inflow and operating the gates of the estuary dam in flood period. The model's governing equation is formulated on the basis of the grey system theory. The model parameters are reparameterized in combination with the grey system parameters and estimated with the annealing-simplex method In conjunction with an objective function, HMLE. To forecast accurately runoff, the fifth order differential equation was adopted as the governing equation of the model in consideration of the statistic values between the observed and forecast runoff. In calibration, RMSE values between the observed and simulated runoff of two and six Hours ahead using the model range from 3.1 to 290.5 $m^{3}/s,\;R^2$ values range from 0.909 to 0.999. In verification, RMSE values range from 26.4 to 147.4 $m^{3}/s,\;R^2$ values range from 0.940 to 0.998, compared to the observed data. In forecasting runoff in real time, the relative error values with lead-time and river stage range from -23.4 to $14.3\%$ and increase as the lead time increases. The results in this study demonstrate that the proposed model can reasonably and efficiently forecast runoff for one to six Hours ahead.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1996.05b
• /
• pp.473-480
• /
• 1996

영광 3/4호기 mid-loop 운전중 잔열제거(RHR) 기능 상실사고시 열수력적 현상을 최적 전산코드인 CATHARE2를 이용하여 해석하였다. 이러한 사고시 열수력적 현상은 일,이차측 냉각재 방출유로와 계통내 비응축성 가스의 거동에 의해 크게 영향을 받는다. 본 연구에서는 2개의 경우를 모의하였는데, 하나는 계통내 방출유로가 있는 경우이며 다른 하나는 방출유로가 없는 경우를 계산하였다. 이 때 사용된 가정은 다음과 같다. (가) 계통은 부분충수 운전 상태로 상부에 비응축성 가스나 증기로 가득 차 있다. (나) 증기발생기는 1대만이 이용 가능하고 이차측은 습식보관 상태이며, 보조급수는 공급되지 않고 이차측 압력은 대기압 상태이다 (다) 사고는 원자로 정지후 2일후 발생한다. 이와같은 조건하에서 사고시 계통 최대압력은 방출유로가 있는 경우 사고후 6,000 초에 0.27 MPa이며, 방출유로를 통한 유량은 총 2.4 kg/s이다. 이 방출유량을 외삽하여 계통수위가 고온관 바닦까지 도달하는데 걸린 시간은 사고후 약 5.67시간이다. 증기발생기 U-튜브를 통한 열전달에 의해 이차측 증기 발생으로 이차측 수위가 하락하면 증기발생기 reflux cooling은 제한을 받을 수 있다. 이 경우 이차측 수위가 U-튜브의 active 영역 상부까지 도달하는데 걸리는 시간은 사고후 약 10시간으로 계산되었다. 그러므로 이 경우 보조급수 공급 여유시간보다 노심 노출시간이 더 빨리 도달하여 노심을 손상시킨다. 사고시 수위지시계는 계통감압에 큰 영향을 주지 못하기 때문에 가능한 빨리 닫아 계통 inventory를 유지하는 것이 이차측 보조급수공급보다 우선한다.합한 설계방안으로 분석되었다.크다는 단점이 있다.TEX>$_2$O$_3$ 흡착제 제조시 TiO$_2$ 함량에 따른 Co$^{2＋}$ 흡착량과 25$0^{\circ}C$의 고온에서 ZrO$_2$와 $Al_2$O$_3$의 표면에 생성된 코발트 화합물을 XPS와 EPMA로 부터 확인하였다.인을 명시적으로 설명할 수 있다. 둘째, 오류의 시발점을 정확히 포착하여 동기가 분명한 수정대책을 강구할 수 있다. 셋째, 음운 과 정의 분석 모델은 새로운 언어 학습시에 관련된 언어 상호간의 구조적 마찰을 설명해 줄 수 있다. 넷째, 불규칙적이며 종잡기 힘들고 단편적인 것으로만 보이던 중간언어도 일정한 체계 속에서 변화한다는 사실을 알 수 있다. 다섯째, 종전의 오류 분석에서는 지나치게 모국어의 영향만 강조하고 다른 요인들에 대해서는 다분히 추상적인 언급으로 끝났지만 이 분석을 통 해서 배경어, 목표어, 특히 중간규칙의 역할이 괄목할 만한 것임을 가시적으로 관찰할 수 있 다. 이와 같은 오류분석 방법은 학습자의 모국어 및 관련 외국어의 음운규칙만 알면 어느 학습대상 외국어에라도 적용할 수 있는 보편성을 지니는 것으로 사료된다.없다. 그렇다면 겹의문사를 [-wh]의리를 지 닌 의문사의 병렬로 분석할 수 없다. 예를 들어 누구누구를 [주구-이-ν가] [누구누구-이- ν가]로부터 생성되었다고 볼 수 없다. 그러므로 [-wh] 겹의문사는 복수 의미를 지닐 수 없 다. 그러면 단수 의미는 어떻게 생성되는가\

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.6
• /
• pp.614-627
• /
• 2018

Urban railway lines have been constructed adjacent to residential buildings and urban areas. The expansion of transportation networks and reconstruction of residential buildings in highly populated urban areas require deep excavations in areas adjacent to urban railways. Mobilized soil stresses and changes in the groundwater level induced by deep excavations results in track irregularities in urban railways. In this study, a three-dimensional finite difference model using the commercial program FLAC3D was adopted to estimate the horizontal displacements of earth retaining structures, settlements of backfill, the stability of track irregularity and underground box structure based on the criteria of each railway organization and its relationships. In deep excavations, a change in groundwater level induces relatively very small differences for track gauge irregularities, whereas relatively large differences for longitudinal irregularities of 72.5%, twist irregularities of 83.3%, cross level irregularities of 61.9%, and alignments of 43.3% were found to be the maximum differences when the horizontal displacement of earth retaining wall and settlement of backfill were 65.1% and 21.4%, respectively, because the groundwater level (GWL) on the ground surface-mobilized tensile strength of the underground box structure exceeds the allowable value. Therefore, three-dimensional numerical analysis was performed in this study. Overall, real-time monitoring should be carried out to prevent railway accidents in advance when a deep excavation adjacent to urban railway structures is constructed.

• Journal of Korea Water Resources Association
• /
• v.41 no.9
• /
• pp.943-958
• /
• 2008

This study employs Bayesian regression analysis for fitting discharge rating curves. The parameter estimates using the Bayesian regression analysis were compared to ordinary least square method using the t-distribution. In these comparisons, the mean values from the t-distribution and the Bayesian regression are not significantly different. However, the difference between upper and lower limits are remarkably reduced with the Bayesian regression. Therefore, from the point of view of uncertainty analysis, the Bayesian regression is more attractive than the conventional method based on a t-distribution because the data size at the site of interest is typically insufficient to estimate the parameters in rating curve. The merits and demerits of the two types of estimation methods are analyzed through the statistical simulation considering heteroscedasticity. The validation of the Bayesian regression is also performed using real stage-discharge data which were observed at 5 gauges on the Anyangcheon basin. Because the true parameters at 5 gauges are unknown, the quantitative accuracy of the Bayesian regression can not be assessed. However, it can be suggested that the uncertainty in rating curves at 5 gauges be reduced by Bayesian regression.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.24 no.3
• /
• pp.189-202
• /
• 2012

An Oscillating Water Column (OWC) wave generation system uses the air flow induced by the vertical motion of water column in the air chamber as a driving force of turbine. It is well known that OWC is one of the most efficient devices to harness wave power. This study estimated the air flow velocity from the time variation of the water level fluctuation in the air chamber under regular wave conditions using 3-dimensional numerical irregular wave tank (3D-NIT) model that can simulate the 3-dimensional irregular wave field. The applicability of the 3D-NIT model was validated by comparing numerically predicted air flow velocities with hydraulic experimental results. In addition, the characteristics of air flow frequency spectrum variation due to the incident frequency spectrum change, and the variations of frequency spectrum and wave reflection due to the existence of converter inside the air chamber were discussed. It is found that the phase difference exists in between the air flow velocity and the water level fluctuation inside the air chamber, and the peak frequency of the spectrum in water level fluctuation is amplified by the resonance in the air chamber.

• Nuclear Engineering and Technology
• /
• v.25 no.1
• /
• pp.125-135
• /
• 1993

The safe and efficient operation of nuclear plants is recognized to be accomplished through the application of plant automation using digital technology, which is one of main targets of the next generation nuclear plants. For plant level automation, it is first required that each major subsystem be digitalized, and the steam generator water level control system is discussed in this study. The transfer functions between inputs and the level are derived by employing the thermal hydraulic model of the steam generator and are applied to the analysis of the current three-element control system. Since the control scheme in this study includes the steam generator itself as a process plant, the system order is high and the numerical instability arises in digitalizing. Together with this, the unreliability of the feedwater feedback signal at low power level leads to the proposal of a two-element control system with a proper digital controller. The digital PI controller developed for this system has the initial power adaptive gain and integration time constant. And it makes the overall system response satisfy the stability and other necessary control specifications simultaneously. Since the two-element control system using this controller depends on the initial power only, it is simple to define and it shows a similar level response behavior to that of its corresponding analog system.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.39 no.2
• /
• pp.307-316
• /
• 2019

Development of vegetation in stream channel increases resistance to flow, resulting in increase in river stage upon flood and affecting change in stage-discharge relationship. Vegetation revealed in stream by water level reaching a peak and then declined upon flood is mostly found as prone. Taking an account of flow distribution with the number of vegetation, prone vegetation layer might be at height where discharge rate is zero (0) (Stephan and Guthnecht, 2002). However, there is a tendency that flow rate is overestimated when applying the height of river bed to flow area with no consideration of the height of vegetation layer in flow rate by float measurement. In this study, reliable flow measurement in stream with vegetation was calculated by measuring the height of vegetation layer after flood and excluding the vegetation layer-projected area from the flow area. The result showed the minimum 4.34 % to maximum 10.82 % of flow deviation depending on the scale of discharge. Accordingly, reliable velocity-area methods would be determined if vegetation layer-projected area in stream is considered in flow rate estimation using the flow area during the flood.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2020.06a
• /
• pp.150-150
• /
• 2020

본 연구에서는 수리모형실험을 통하여 원형 다단 실린더 게이트 형식의 취수시설에서 발생하는 공기연행을 분석하였다. 수리모형실험의 원형은 경상북도 청도군에 위치한 운문댐의 "운문댐 안전성 강화사업"에서 계획되고 있는 신설취수탑을 기준으로 상사법칙은 Froude상사법칙을 적용하고 1/20의 모형 축척을 가지는 취수탑의 국부모형에 하류단 수위를 고려하기 위해 유량조절시설을 설치하여 실험을 실시하였다. 실험조건은 크게 두 가지로 구분하였으며, 수면으로부터 유입구 상단부까지의 거리 ∆h1(m)과 유입부 저수지 저류 수위와 하류단 유량조절시설간의 수위차인 ∆h2(m)이며, ∆h1에 대한 조건은 0.01m~0.06m로 0.01m 간격으로 6가지, ∆h2에 대한 조건은 0.10m~1.70m로 0.20m간격으로 9가지로 이를 조합하여 총 54개 CASE에 대해 진행하였다. 실험결과 공기연행 발생 시 그에 따른 영향을 평가하기 위해 발생 정도에 따라 미발생(Not Occur), 간헐적(Intermittent), 빈번한(Frequent), 지속적(Continuation), 공기 폭발(Air Explosion)로 분류하였으며, 각 공기연행 발생 시 취수유량의 감소율 및 영향을 분석한 결과 간헐적 공기연행 발생 시 최대 약 3.75%의 취수유량 감소, 빈번한 공기연행 발생 시 취수유량은 전체적으로 10%, 최대 약 13.19% 감소하였으며, 지속적 공기연행 발생 시 발생 이후 ∆h2증가에 의한 취수유량의 증가가 거의 이루어지지 않으며, 최대 56.25%의 취수유량이 감소, 공기 폭발 발생 시 취수유량의 영향은 지속적 발생과 비슷하나 관내 공기 포집 후 유입구로 방출 시 관에 강한 충격을 주어 안정성에도 큰 영향을 미칠 것으로 판단되어, 이에 안정성 및 취수유량 감소율을 고려하여 빈번, 지속, 공기 폭발 발생 영역에서의 취수는 적합하지 않으며, 공기연행 미발생 및 간헐적 발생 영역에서의 취수 시 목표 취수유량이 1.00~4.00(㎥/s)일 때 ∆h1= 0.40m 이상, 4.00~9.30(㎥/s) 일 때 ∆h1= 0.60m 이상, 9.30~9.53(㎥/s) 일 때 ∆h1=0.80m 이상, 9.53~9.65(㎥/s) 일 때 ∆h1= 1.00m 이상에서 취수유량 감소율 3.75% 이내로 취수유량의 확보가 가능하다. 이러한 결과는 원형 다단 실린더 게이트 형식의 취수시설에 대해 취수 시 수면와류에 의한 Air Core와 그에 따른 공기연행의 발생 조건과 영향을 수리모형실험을 통해 확인함으로써 실제 운용 시 보다 안정적이고 효율적인 운용에 대한 자료로 활용될 수 있을 것으로 판단되며, 추가로 수치해석을 통한 비교 및 공기연행과 관내 공기포집 정도에 대한 연구를 통해 보다 정확한 자료제시가 가능할 것으로 판단된다.

• Journal of Korea Water Resources Association
• /
• v.57 no.3
• /
• pp.209-223
• /
• 2024

In the context of the fourth industrial revolution, data-driven decision-making has increasingly become pivotal. However, the integrity of data analysis is compromised if data quality is not adequately ensured, potentially leading to biased interpretations. This is particularly critical for water level data, essential for water resource management, which often encounters quality issues such as missing values, spikes, and noise. This study addresses the challenge of noise-induced data quality deterioration, which complicates trend analysis and may produce anomalous outliers. To mitigate this issue, we propose a noise removal strategy employing Wavelet Transform, a technique renowned for its efficacy in signal processing and noise elimination. The advantage of Wavelet Transform lies in its operational efficiency - it reduces both time and costs as it obviates the need for acquiring the true values of collected data. This study conducted a comparative performance evaluation between our Wavelet Transform-based approach and the Denoising Autoencoder, a prominent machine learning method for noise reduction.. The findings demonstrate that the Coiflets wavelet function outperforms the Denoising Autoencoder across various metrics, including Mean Absolute Error (MAE), Mean Absolute Percentage Error (MAPE), and Mean Squared Error (MSE). The superiority of the Coiflets function suggests that selecting an appropriate wavelet function tailored to the specific application environment can effectively address data quality issues caused by noise. This study underscores the potential of Wavelet Transform as a robust tool for enhancing the quality of water level data, thereby contributing to the reliability of water resource management decisions.

• Journal of Korea Water Resources Association
• /
• v.48 no.12
• /
• pp.1065-1075
• /
• 2015

In the estuary where the structure such as river-mouth weir has been installed, the flow is developed very complicatedly due to river water from upstream, tide of the sea and floodgate operation. Especially, if basin outlets more than one exists in one estuary, the boundary conditions will be significantly more complex form. Saemangeum(SMG) project area in Korea is the most typical example. There are Mankyung river and Dongjin river in upstream. The water of them inflows into SMG project area. In the downstream, river flow was drained from inland to sea over the SMG sea dike through the sluice. The connecting channel was located between Mankyung and Dongjin basins. It functions not only as transportation by ship in ordinary period but also as flood sharing by sending flood flow to each other in flood period. Therefore, in order to secure the safety against flood, it is very important to understand the flood sharing capacity for connecting channel. In this study, the flood control effect was analyzed using numerical simulation. Delft3D was used to numerical simulation and simulated period was set up with neap tide, in which the maximum flood stage occurred due to poor drainage. Actually, three connecting channels were designed in land use plan of the SMG Master Plan, but they were simplified to a single channel for conciseness of analysis in this study. According to the results of numerical analysis, the water level difference between two basins was increased and the maximum flood stage at dike sluice was also upraised depending on decrease of conveyance. And the velocity induced by same water level difference was decreased when the conveyance became smaller. In certain conveyance above, there was almost no flood control effect. Therefore, if the results of this study are considered for design of connecting channel, it will be expected to draw the optimal conveyance for minimizing dredging construction cost while maximizing the flood control effect.