• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.593-596
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• 2008

The scour phenomenon involves the erosive potential of flowing water and the relative ability of the soil to resist erosion. The scour phenomenon in cohesive soils is much different from that in non-cohesive soils. Granular soils resist erosion by their buoyant weight and the friction between the particles. The soil particles are dislodged individually from the bed under the action of the eroding fluid. Scour in cohesive soils is much slower and more dependent on soil properties than that in non-cohesive soils. Therefore the analysis models for estimating erosion characteristics of cohesive soils should consider not only flowing water but also the relative ability of the soil to resist erosion. In this study, erosion characteristics for the clay-silt mixed soil will be analyzed as a fundamental study for development of bridge scour analysis and design system considering scour resistance capacity of a soil. For this analysis, the relationship between scour characteristics and soil properties was evaluated through scour rate test with Kaolinite samples remolded using various loading and contents of silt.

• 연구논문집
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• 통권24호
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• pp.41-48
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• 1994

This experimental study deals with the extinguishiment characteristics of an oil pool flame using the water spray. The water through the six different atomizers is ejected over the freely burning pool flame in the quiescent surrounding air. Injection direction is vertical to the surface of oil in a small tank with a diameter of 100mm and a height of 10mm. In order to estimate quantitatively the extinction, the burning rate as well as the effective water flux are measured. The effective water flux is the amount of the water which reach the pool from the nozzle. The burning rate with the water spray increases until the injection pressure increases to reach some value, which gives the maximum burning rate, while the effective water flux without the flame decreases or does not change according to increasing of the injection pressure. This maximum burning rate is greater than 2.5 times of burning rate of the fire without the water spray. As a matter of the extinguishiment, it is found that the water drops of which size is too small can not extinguish the fire because too small drops does not reach the fuel surface.

• ALGAE
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• 제34권2호
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• pp.91-97
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• 2019

Chilean species of marine macroalgae with amphitropical distributions oftentimes result from introductions out of the Northern Hemisphere. This possibility was investigated using haplotype data in an amphitropical red macroalgae present in Chile, Callophyllis variegata. Published sequence records from Canada and the United States were supplemented with new collections from Chile (April 2014-November 2015). Specimens of C. variegata were amplified for the 5′ end of the cytochrome c oxidase subunit I gene (COI-5P) and the full length nuclear internal transcribed spacer region. Haplotype networks and biogeographic distributions were used to infer whether C. variegata was introduced between hemispheres, and several population parameters were estimated using IMa2 analyses. C. variegata displayed a natural amphitropical distribution, with an isolation time of approximately 938 ka between hemispheres. It is hypothesized that contemporary populations of C. variegata were established from a refugial population during the late Pleistocene, and may have crossed the tropics via rafting on buoyant species of kelp or along deep-water refugia coincident with global cooling, representing a rare case of a non-human mediated amphitropical distribution.

• 한국해양생명과학회지
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• 제7권2호
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• pp.139-144
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• 2022

본 연구는 붉바리 어미의 사육환경에 따른 난질의 변화를 난의 생화학적 분석을 통하여 난질에 영향을 미칠 수 있는 요소를 구명하기 위하여 수행하였다. 그 결과 육상수조에서 사육하는 것보다 해상가두리에서 사육할 때 부상률, 수정률, 난 발생 생존율 및 부화율이 우수하였다. 그리고 해상가두리에서 생산한 수정란의 유리아미노산의 함량이 높았다. 즉, 해상가두리에서 사육관리할 때 난질이 우수한 수정란을 생산할 수 있고, 난질이 우수할수록 유리아미노산의 함량이 높았다.

• Nuclear Engineering and Technology
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• 제55권5호
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• pp.1742-1756
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• 2023

The hydrogen behavior in a nuclear containment vessel is a significant issue when discussing the potential of hydrogen combustion during a severe accident. After the Fukushima-Daiichi accident in Japan, we have investigated in-depth the hydrogen transport mechanisms by utilizing experimental and numerical approaches. Computational fluid dynamics is a powerful tool for better understanding the transport behavior of gas mixtures, including hydrogen. This paper describes a Large-eddy simulation of gas mixing driven by a high-buoyancy flow. We focused on the interaction behavior of heat and mass transfers driven by the horizontal high-buoyant flow during density stratification. For validation, the experimental data of the Containment InteGral effects Measurement Apparatus (CIGMA) facility were used. With a high-power heater for the gas-injection line in the CIGMA facility, a high-temperature flow of approximately 390 ℃ was injected into the test vessel. By using the CIGMA facility, we can extend the experimental data to the high-temperature region. The phenomenological discussion in this paper helps understand the heat and mass transfer induced by the high-buoyancy flow in the containment vessel during a severe accident.

• Nuclear Engineering and Technology
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• 제55권10호
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• pp.3754-3767
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• 2023

Turbulent jet discharges in subcooled water pools are essential for safety systems in nuclear power plants, specifically in the pressure suppression pool of boiling water reactors and In-containment Refueling Water Storage Tank of advanced pressurized water reactors. The gas and liquid flow in these systems is investigated using multiphase flow analysis. This field has been extensively examined using a combination of experiments, theoretical models, and Computational Fluid Dynamics (CFD) simulations. ANSYS CFX offers two approaches to model multiphase flow behavior. The non-homogeneous Eulerian-Eulerian Model has been used in this work; it computes global information and is more convenient to study interpenetrated fluids. This study utilized the Large Eddy Simulation Model as the turbulence model, as it is better suited for non-stationary and buoyant flows. The CFD results of this study were validated with experimental data and theoretical results previously obtained. The figures of merit dimensionless penetration length and the dimensionless buoyancy length show good agreement with the experimental measurements. Correlations for these variables were obtained as a function of dimensionless numbers to give generality using only initial boundary conditions. CFD numerical model developed in this research has the capability to simulate the behavior of non-condensable gases discharged in water.

• Ocean Systems Engineering
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• 제14권1호
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• pp.17-52
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• 2024

In this paper, the authors explore the modeling and control of a point absorber wave energy converter, which is connected to the electric grid via a power converter that is based on a linear permanent magnet synchronous generator (LPMSG). The device utilizes a buoyant mechanism to convert the energy of ocean waves into electrical power, and the LPMSG-based power converter is utilized to change the variable frequency and voltage output from the wave energy converter to a fixed frequency and voltage suitable for the electric grid. The article concentrates on the creation of a predictive control system that regulates the speed, voltage, and current of the LPMSG, and the modeling of the system to simulate its behavior and optimize its design. The predictive model control is created to guarantee maximum energy output and stable grid connection, using Matlab Simulink to validate the proposed strategy, including control side generator and predictive current grid-side converter loops.

• 대한기계학회논문집B
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• 제36권3호
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• pp.309-314
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• 2012

풀화재에서 화염진동은 주위공기와의 밀도차에 의한 부력효과에 기인하여 주로 발생한다. 본 연구에서는 부력이 지배적인 풀화재의 불안전성에 대하여 산화제유속의 효과를 검토하기 위해 컵버너 실험을 수행하였다. 실험결과는 진동주파수가 산화제의 유속이 증가함에 따라 감소함을 보인다. 무차원 변수로 표현되는 주파수와 부력의 관계로 도시하였을 때 다양한 속도스케일을 사용할 수 있었지만, 연료와 산화제의 유속차로 정의되는 특성속도인 경우에 정지되어 있는 공기중에서의 풀화재 진동과 일치하는 관계식을 얻을 수 있었다. 이러한 사실은 부력이 지배적인 화염에서 불안전성의 원인은 전단면에서의 Kelvin-Helmholtz 불안전성이 주된 기구라는 것을 증명해준다. 산화제의 농도를 변화시켰을 경우에는 산화제의 불활성기체의 농도가 증가할수록 청염의 길이가 길어지고 컵버너 끝단으로부터 부상되는 것이 관찰된다. 또한 진동주파수는 희석율과는 특정한 관계를 보이지 않는데 이는 국부적 화염구조와 연관성을 가지기 때문으로 판단된다.

• 대기
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• 제26권4호
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• pp.495-508
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• 2016

In order to determine the prediction possibility of heavy rainfall, a variety of analyses was conducted by using three-dimensional data obtained from Korea Local Analysis and Prediction System (KLAPS) re-analysis data. Strong moisture convergence occurring around the time of the heavy rainfall is consistent with the results of previous studies on such continuous production. Heavy rainfall occurred in the cloud system with a thick convective clouds. The moisture convergence, temperature and potential temperature advection showed increase into the heavy rainfall occurrence area. The distribution of integrated liquid water content tended to decrease as rainfall increased and was characterized by accelerated convective instability along with increased buoyant energy. In addition, changes were noted in the various characteristics of instability indices such as K-index (KI), Showalter Stability Index (SSI), and lifted index (LI). The meteorological variables used in the analysis showed clear increases or decreases according to the changes in rainfall amount. These rapid changes as well as the meteorological variables changes are attributed to the surrounding and meteorological conditions. Thus, we verified that heavy rainfall can be predicted according to such increase, decrease, or changes. This study focused on quantitative values and change characteristics of diagnostic variables calculated by using numerical models rather than by focusing on synoptic analysis at the time of the heavy rainfall occurrence, thereby utilizing them as prognostic variables in the study of the predictability of heavy rainfall. These results can contribute to the identification of production and development mechanisms of heavy rainfall and can be used in applied research for prediction of such precipitation. In the analysis of various case studies of heavy rainfall in the future, our study result can be utilized to show the development of the prediction of severe weather.

• 터널과지하공간
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• 제12권1호
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• pp.31-36
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• 2002

터널화재시 화원의 크기에 따른 연기기동을 파악하기 위하여 모현실험 및 수치해석이 수행되었다. 모형실험의 결과를 실제 터널에 대해 적용하기 위하여 Frode상사법을 이용하였다. 터널공간내의 화재 해석에 대한 수치해석의 타간성을 입증하기 위하여 모형실험과 수치해석에서 얻어진 연층의 온도분포를 비교하였다. 터널내 온도분포를 해석함으로써 배기장치가 없는 짧은 터널에 대하여 연층은 전체 터널 높이의 절반 이하로 하강하지 않는다는 사실을 파악하였다. 또한 실험에서 얻어진 연층선단의 전파속도는 화재 발생부의 1/3 풍에 비례한다는 사실을 파악하였으며 이는 기존의 경험식 및 수치해석결과와도 잘 일치하였다. 따라서 짧은 터널에서 화재시 피난대책을 수립하는데 있어서 연층의 수평전파가 수직전파에 비해 중요한 설계변수임을 본 연구를 통하여 제시하였다.