• Proceedings of the Korea Water Resources Association Conference
• /
• 2018.05a
• /
• pp.132-132
• /
• 2018

홍수피해 발생 시 각 지역의 특성에 따라 피해의 정도가 다르게 나타나고 있다. 도시지역의 경우 포장도로로 인하여 불투수 면적이 넓어 배제 시설의 허용 용량을 초과하는 강우 발생 시 지표면 위로 유량이 누적된다. 특히 농촌지역에 비해 도시지역에서 국지적으로 기습적인 강우에 빈번히 침수피해가 발생한다. 우리나라 도시지역은 인구와 건물이 밀집되어 재산과 인명피해 및 교통체증 등으로 인한 간접피해 등 농촌지역에 비해 더 큰 피해가 발생할 수 있다. 도시 지역의 침수 피해 저감을 위해 우수 유출 저감시설과 내수배제 시설을 설치하여 우수의 유출을 지연시키거나 인위적으로 방류부 하천으로 방류시키는 방법이 있지만 이러한 시설의 설치에는 막대한 비용이 필요하며, 내수배제시설이 설치된 장소에 따라 침수현상이 다르게 나타나 저감시설 설치 전 공간적, 효율적으로 설치 가능한 장소와 침수 저감 효율에 대한 분석이 필요하다. 본 연구는 도림1 배수분구를 대상으로 XP-SWMM모델을 이용하였으며, 2010년 09월 21일 침수 발생 당시의 강우를 적용하여, 연구대상지역의 도시유출해석을 진행하였다. 또한, 어린이 공원과 학교운동장에 가상지하저류조를 설치하였을 시 침수저감 효과에 대하여 연구를 진행하였으며, 다양한 지하저류조 설치 시나리오에 따른 침수저감효과를 수심별 침수면적으로 나타내어 분석을 실시하였다. 본 연구를 통해, 도심지 지하 저류시설 도입의 기초자료로 활용될 수 있을 것으로 판단된다.

• Nuclear Engineering and Technology
• /
• v.52 no.5
• /
• pp.878-888
• /
• 2020

This paper presents the validation of UNIST in-house Monte Carlo code MCS used for the high-fidelity simulation of commercial pressurized water reactors (PWRs). Its focus is on the accurate, spatially detailed neutronic analyses of startup physics tests for the initial core of the Watts Bar Nuclear 1 reactor, which is a vital step in evaluating core phenomena in an operating nuclear power reactor. The MCS solutions for the Consortium for Advanced Simulation of Light Water Reactors (CASL) Virtual Environment for Reactor Applications (VERA) core physics benchmark progression problems 1 to 5 were verified with KENO-VI and Serpent 2 solutions for geometries ranging from a single-pin cell to a full core. MCS was also validated by comparing with results of reactor zero-power physics tests in a full-core simulation. MCS exhibits an excellent consistency against the measured data with a bias of ±3 pcm at the initial criticality whole-core problem. Furthermore, MCS solutions for rod worth are consistent with measured data, and reasonable agreement is obtained for the isothermal temperature coefficient and soluble boron worth. This favorable comparison with measured parameters exhibited by MCS continues to broaden its validation basis. These results provide confidence in MCS's capability in high-fidelity calculations for practical PWR cores.

• Nuclear Engineering and Technology
• /
• v.51 no.4
• /
• pp.1008-1016
• /
• 2019

In the SG (steam generator) of PWR (pressurized water reactor) for a nuclear plant, hundreds of U-shaped tubes are used for the heat exchanger system. They interact with primary pressurized cooling water flow, generating flow-induced vibration in the secondary flow region. A simplified U-tube model is proposed in this study to apply for experiment and its counterpart computation. Using the commercial code, ANSYS-CFX, we first verified the Moody chart, comparing the straight pipe theory with the results derived from CFD (computational fluid dynamics) analysis. Considering the virtual mass of fluid, we computed the major modes with the low natural frequencies through the comparison with impact hammer test, and then investigated the effect of pump flow in the frequency domain using FFT (fast Fourier transform) analysis of the experimental data. Using two-way fluid-structure interaction module in the CFD code, we studied the influence on mean flow rate to generate the displacement data. A feasible CFD method has been setup in this research that could be applied potentially in the field of nuclear thermal-hydraulics.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.13 no.1
• /
• pp.466-477
• /
• 2021

There are three different well-known methods for predicting the manoeuvrability of ships: (1) free running model test, (2) direct manoeuvring simulation using CFD and (3) system-based manoeuvring simulation. In this paper, the manoeuvrability of the KVLCC2 was estimated using CFD with rigid body motion and body force propeller method. The free running manoeuvre at the different time steps were also simulated. The yaw checking ability and the turning ability of KVLCC2 were predicted using CFD and could have been confirmed that the IMO criteria was satisfied. When the results were compared with the model test and system-based method, the free running simulation showed better agreement to that of the model test. It could also be confirmed that the results vary depending on the time step. Overall, the CFD results using the body force propeller method estimated most accurately the test results.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2022.05a
• /
• pp.275-275
• /
• 2022

Tsunamis triggered by undersea earthquakes have the characteristic of longer wavelengths and can propagate a very long distance. Although the occurrence frequency of tsunami is low, it can cause casualties and properties. Historically, tsunamis that occurred on the western coast of Japan attacked the eastern coast of the Korean Peninsula and damaged the property and the loss of human life in 1983 and 1993. By tsunami in 1983 especially, 2 people were killed, and more than 200 casualties occurred. In addition, it caused 2 million dollars in property damage at Imwon Port. In 2011, The eastern cities of Japan: Iwate, Miyagi, Ibaraki, and Fukushima were damaged by a tsunami that occurred near onshore along the Pacific ocean and caused more than 300 billion dollars in property damage, and 20,000 casualties occurred. Moreover, those provoked nuclear power plant meltdown at Fukushima. In this study, it was carried out a relationship between maximum tsunami heights and fault parameters of earthquake: strike angle, dip angle, and slip angle at Imwon port. Those fault parameters are known that it does not relate to the magnitude of earthquake directly. Virtual tsunamis, which could be triggered by probable undersea earthquakes in the future, were investigated and mutual information based on probability and information theory was introduced to figure out the relationship between maximum tsunami height and fault parameters. Fault parameters were evaluated according to the strong relationship with maximum tsunami heights finally.

• Journal of the Korean Chemical Society
• /
• v.44 no.4
• /
• pp.337-342
• /
• 2000

Many kinds of experiments were performed for the quality control of antifoaming agents used in thermal power pIants of KEPCO. We tried to establish more convenient ans more accurate quantitative analytical method to determine the amount of silicone oil in silicone oil type antifoaming agent regardless of the amount and/or the type of involved surface active agents. First, the amount of silicone oil was measured by gravimetric method or centrifugal method using very simple apparatus, and then was compared to the results of FT-lR spectroscopy. The centrifugal method was turned out a poor method depending upon the recovery test and virtual experiments. Some antifoaming agents showed very similar results between gravimetric method and spectroscopic methods, and the others gave very different results. We concluded that FT-lR spectroscopy is the most convenient and reliable methodto determine the amounts of silicone oil in the antifoaming agents.

• The Journal of Korean Society for Radiation Therapy
• /
• v.29 no.1
• /
• pp.77-84
• /
• 2017

Purpose: To evaluate the image quality improvement and dosimetric effects on virtual monochromatic images of a Dual Source-Dual Energy CT(DS-DECT) for radiotherapy planning. Materials and Methods: Dual energy(80/Sn 140 kVp) and single energy(120 kVp) scans were obtained with dual source CT scanner. Virtual monochromatic images were reconstructed at 40-140 keV for the catphan phantom study. The solid water-equivalent phantom for dosimetry performs an analytical calculation, which is implemented in TPS, of a 10 MV, $10{\times}10cm^2$ photon beam incident into the solid phantom with the existence of stainless steel. The dose profiles along the central axis at depths were discussed. The dosimetric consequences in computed treatment plans were evaluated based on polychromatic images at 120 kVp. Results: The magnitude of differences was large at lower monochromatic energy levels. The measurements at over 70 keV shows stable HU for polystyrene, acrylic. For CT to ED conversion curve, the shape of the curve at 120 kVp was close to that at 80 keV. 105 keV virtual monochromatic images were more successful than other energies at reducing streak artifacts, which some residual artifacts remained in the corrected image. The dose-calculation variations in radiotherapy treatment planning do not exceed ${\pm}0.7%$. Conclusion: Radiation doses with dual energy CT imaging can be lower than those with single energy CT imaging. The virtual monochromatic images were useful for the revision of CT number, which can be improved for target coverage and electron densities distribution.

• Korean Journal of Computational Design and Engineering
• /
• v.20 no.3
• /
• pp.230-237
• /
• 2015

Soil deformation on the off-load ground is significantly affected by soil conditions, such as soil type, water content, and etc. Thus, the soil characteristics should be estimated for predicting vehicle movements on the off-load conditions. The plate-sinkage test, a widely-used experimental test for predicting the wheel-soil interaction, provides the soil characteristic parameters from the relationship between soil stress and plate sinkage. In this study, soil stress under the plate-sinkage situation is calculated by the DEM (Discrete Element Method) model. We developed a virtual soil bin with DEM to obtain the vertical reaction forces under the plate pressing the soil surface. Also parametric studies to investigate effects of DEM model parameters, such as, particle density, Young's modulus, dynamic friction, rolling friction, and adhesion, on the characteristic soil parameters were performed.

• Proceedings of the Korea Contents Association Conference
• /
• 2003.11a
• /
• pp.395-401
• /
• 2003

다목적 대형 댐의 건설로 수몰된 과거의 삶의 공간을 20년이 지나서 다시 복원한다는 것은 그곳에 살던 실향민 등에게는 참으로 반가운 소식이다. 본 연구에서는 1980년대 초에 완공된 충주댐으로 인하여 물 속에 잠긴 청풍지구를 수몰이전의 입체 지형 공간적으로 원형복원하기 위한 원격탐사 기법을 적용한 것이다. 비교적 해상도가 좋은 인공위성 사진자료와 댐 수몰이전의 디지털 위성영상 데이터를 수집하고, 수몰직전에 제작된 지형도를 이용하여 위성영상자료의 통합 적용하여 수몰직전의 지형공간정보를 현재시간으로 영상 복원하기 위하여 원격탐사 기법을 적용한 것이다 이를 위하여 지형도에서 추출한 등고선과 현재의 등고선과의 접목을 통하여 청풍 주변지역을 중심으로 당시의 수치표고모형을 생성하였다. 또한 이를 입체적으로 보여주기 위한 투시조감도를 각 방향에서 생성함으로서 수몰이전의 아름다운 모습을 3차원적으로 영상복원 하였다. 또한 좀더 가까이서 수몰마을을 보기 위한 근접비행시뮬레이션 동영상을 제작하여 과거 기억 속의 고향을 영상에서 찾아볼 수 있도록 한 것이다.

• Geomechanics and Engineering
• /
• v.13 no.2
• /
• pp.217-235
• /
• 2017

The stability prediction of shallow buried tunnels is one of the most difficult tasks in civil engineering. The aim of this work is to predict the state of collapse in shallow tunnel in layered soils by employing non-associated flow rule and nonlinear failure criterion within the framework of upper bound theorem. Particular emphasis is first given to consider the effects of dilation on the collapse mechanism of shallow tunnel. Furthermore, the seepage forces and surface settlement are considered to analyze the influence of different dilation coefficients on the collapse shape. Two different curve functions which describe two different soil layers are obtained by virtual work equations under the variational principle. The distinct characteristics of falling blocks up and down the water level are discussed in the present work. According to the numerical results, the potential collapse range decreases with the increase of the dilation coefficient. In layered soils, both of the single layer's dilation coefficient and two layers' dilation coefficients increase, the range of the potential collapse block reduces.