• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.405-405
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• 2017

기후변화로 인해 수자원에 발생할 수 있는 가장 큰 영향은 유역에서의 유출량의 변화이다. 유출량의 변화는 가용한 수자원양의 변화를 의미하므로 미래 가뭄 등에 대한 대책 마련 등을 위해 합리적인 추정과 분석이 필요하다. 본 연구에서는 기후변화로 인한 유역 유출량의 변화를 추정하기 위해 기상청의 과거 기상관측자료와 RCP 시나리오 자료를 기반으로 SWAT-K와 Tank 모형을 이용해 팔당댐 상류지역에서의 유역 유출량을 모의하였다. 특히 팔당댐 상류는 수도권의 2천만명에 가까운 인구에 대한 수자원의 공급을 담당하는 유역으로서 이 지역의 가뭄은 국가적인 재난을 일으킬 수 있어 매우 중요할 것이므로 기후변화에 의한 가용 수자원의 변화를 미리 예측해 볼 필요가 있을 것으로 판단되었다. 모의 시 모의 대상 지역에 대한 지형학적 인자와 인문학적 인자 등은 변화가 없는 것으로 가정하고 단순하게 기후변화에 의한 강수량과 증발산량 등의 증감만 있는 것으로 가정하였으며, 모의한 결과를 바탕으로 갈수량과 홍수량 등에 대한 빈도를 분석하여 유출의 변화를 살펴보았다. 분석 결과를 통해 팔당댐 상류의 유역 유출량 변화를 통계적으로 예측해 볼 수 있으며, 해당 자료는 지자체의 수자원계획 수립 등에 유용하게 활용 될 수 있을 것으로 판단된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.153-153
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• 2020

우리나라에선 크고 작은 가뭄 피해가 자주 일어나고 있으며 최근엔 유래 없는 다년가뭄이 발생하면서 가뭄에 대한 경각심이 커지고 있다. 가뭄에 적절하게 대응하여 피해를 경감시키기 위해서는 신뢰도 높은 가뭄 예측이 선행되어야 한다. 이에 본 연구는 앙상블 예측과 베이즈이론(Bayes' theorem)을 수문학적 가뭄지수 중 하나인 SRI(Standardized Runoff Index)에 적용해 가뭄 확률 전망을 실시했으며 이를 EDP(Ensemble Drought Prediction)라고 칭하였다. 국내 8개 댐유역에서 EDP를 생성하고 개선하는 과정은 다음과 같이 진행된다. 우선 TANK모형을 활용한 1개월 선행 유량 예측(Ensemble Streamflow Prediction, ESP)의 결과를 SRI로 변환하여 EDP 확률분포를 생성한다. 그런 다음, EDP를 개선하기 위해 그 기초인 ESP에서 미흡한 토양수분 초기조건을 보완하고자 베이즈이론을 활용했다. APCC(APEC Climate Center)의 위성 관측 SMI(Soil Moisture Index) 자료로 SRI와의 회귀식을 구축, 이를 우도함수로 정의해 사전 EDP 분포를 업데이트한 EDP+ 확률분포를 생성했다. 그 결과, EDP와 EDP+ 모두 심도가 깊은 가뭄을 전망할수록 예측력이 기후학적 예측보다 좋지 않았다. 그럼에도 우도함수로 사용한 회귀식의 정확도가 높을수록 EDP+의 정확도도 향상되는 경향이 나타났으며, 이는 베이즈이론을 사용한다면 가뭄 확률 전망을 개선할 수 있다는 것을 의미하고 있다. 하지만, 확정 전망 정확도는 확률 전망 정확도와는 관계가 없었는데 이는 확정 전망과 확률 전망이 본질적으로 다르기 때문인 것으로 사료된다.

• Fire Science and Engineering
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• v.33 no.6
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• pp.173-180
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• 2019

Oil tank fires need to be suppressed differently from other oil-related fires, due to the high-temperature flames and hot updraft above the tank, in the former case, that cause the destruction of large amounts of foam. We studied high-capacity foam discharge systems based on the standards of the American Petroleum Institute (API), National Fire Protection Association (NFPA), British Standard European Norm (BS EN), and the laws of Japan. The performance of a high-capacity foam discharge system was measured by conducting real fire experiments with model oil tanks. We concluded that lightweight and easily movable high-capacity foam discharge systems should be urgently introduced in domestic operations. Additionally, the obstacles faced by major tanks, such as long-distance installation of large-diameter fire hoses and narrowing of firefighting spaces, should be resolved depending on the conditions of the site.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.5
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• pp.488-497
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• 2009

The freak wave, also known as New-Year-Wave in the north Atlantic, is relatively large and spontaneous ocean surface wave that can sink even large ships and destroy maritime structures. To understand oceanic conditions that develop freak waves, we simulated and generated two versions of scale-downed waves (1:64 and 1:42) in a numerical wave tank and compared the results with the experiment in wave flume. Both of the breaking and non-breaking waves were generated in the simulation. The numerical simulation was implemented based on the finite volume method and a genetic optimization algorithm. Random values were assigned as the initial values for the parameter in the control function, which produced signals representing the motion of wave-maker. The same signal obtained from the optimization process was used for both of the simulation and the experiment. By varying the object function and restrictions of the simulation, a best profile of design wave was selected based on the characteristics, height and period of simulated waves. Results showed that the simulation and experiment with the scale of 1:42 agreed better with freak waves in the natural condition. The presented simulation method will contribute to saving the time and cost for conducting subsequent response analyses of motion under freak waves in the course of the model test for ship and maritime structure.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.1
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• pp.26-39
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• 2000

This paper presents the influence of Reynolds number on propeller open-water performance at the towing tank and the cavitation tunnel for series propellers(No. of blade=4, $0.3{\leq}A_E/A_O{\leq}0.75,\;0.5{\leq}P/D{\leq}1.1$). It is shown that the Reynolds number recommanded by 15th and 17th ITTC is not large enough to obtain reliable P.O.W. test results and then the suitable test conditions for the both facilities is suggested. The correlation of the propeller open-water characteristics at the cavitation tunnel and the towing tank is described and a correlation factor $\kappa$ is deduced from those test results. The viscous effect of the flow around the propeller shaft on the propeller characteristics is investigated from the velocity measurement by Laser Doppler Velocitimetry(L.D.V.). The measured velocity distribution shows that viscous flow effect is not negligible.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.5
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• pp.390-395
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• 2011

The main purpose of ice model basin is to assess and evaluate the performance of the Arctic ships and offshore structures because the full-scale tests in ice covered sea are usually very expensive and difficult. There are various ice conditions, such as level ice, brash ice, pack ice and ice ridge, in the real sea. To estimate their capacities in ice tank accurately, an appropriate model ice sheet and prepared ice conditions copied from actual sea ice conditions are needed. Pack ice is a floating ice that has been driven together into a single mass and a mixture of ice fragments of varying size and age that are squeezed together and cover the sea surface with little or no open water. So Ice-class vessels and Icebreaker are usually operated in pack ice conditions for the long time of her voyage. The most ice model tests include the pack ice test with the change of pack ice concentration. In this paper, the effect of pack ice size and channel breadth in pack ice model test is conducted and analyzed. Also we presented some techniques for the calculation of pack ice concentration in the model test. Finally, we developed a new model test methodology of pack ice condition in square type ice tank.

• Journal of Ocean Engineering and Technology
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• v.32 no.3
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• pp.202-207
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• 2018

This paper presents the efficiency of a floating vertical axis wind turbine with variable-pitch. A model was designed to use the lift force and drag force for blades with various pitch angles. The blade's pitch angle is controlled by the stopper. To validate the efficiency of the wind turbine discussed in this paper, a model test was carried out through a single model efficiency experiment and wave tank experiment. The parameters of the single model efficiency experiment were the wind speed, electronic load, and pitch angle. The wave tank experiment was performed using the most efficient pitch angle from the results of the single model efficiency experiment. According to the results of the wave tank experiment, the surge and pitch motion of a structure slightly affect the efficiency of a wind turbine, but the heave motion has a large effect because the heights of the wind turbine and wind generator are almost the same.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.5
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• pp.484-491
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• 2007

Numerical experiments using a numerical wave tank have been performed to verier the nonlinear interaction between monochromatic waves and a submerged horizontal plate. As a model for numerical wave tank, we used a higher-order Boundary Element Method(BEM) based on fully nonlinear potential flow theory and CADMAS-SURF for solving Navier Stokes equations and exact free surface conditions. Both nonlinear models are able to predict the higher harmonic generation in the shallow water region over a submerged horizontal plate. CADMAS-SURF, which involves the viscous effect, can evaluate the higher harmonic generation by flow separation and vortices at the each ends of plate. The comparison of reflection and transmission coefficients with experimental results(Patarapanich and Cheong, 1989) at different lengths and submergence depths of a horizontal plate are presented with a good agreement. It is found that the transfer of energy from the incident fundamental waves to higher harmonics becomes larger as the submergence depth ratio decreases and the length ratio increases.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.531-538
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• 2011

To ensure the structural integrity of membrane type LNG tank, the rational assessment of impact pressure and structural responses due to sloshing should be preceded. The sloshing impact pressures acting on the insulation system of LNG tank are typical irregular loads and the structural responses caused by them also very complex behaviors including fluid structure interaction. So it is not easy to estimate them accurately and huge time consuming process would be necessary. In this research, a simplified method to analyze the dynamic structural responses of LNG tank insulation system under pressure time histories obtained by sloshing model test or numerical analysis was proposed. This technique basically based on the concept of linear combination of the triangular response functions which are obtained by the transient response analysis under the unit triangular impact pressure acting on structures in time domain. The validity of suggested method was verified through the example calculations and applied to the structural analysis of real Mark III type insulation system using the sloshing impact pressure time histories obtained by model test.

• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.5
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• pp.67-75
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• 2014

In this study, the large-scale hydraulic model test was performed to investigate the hydraulic characteristics for development of the non-power soil cleaning and keeping system at the dike gate. The outlet height, outflow number, outflow discharge, and outflow cycle were compared and analyzed. The non-power soil cleaning and keeping system was most effective at 11.2 mm in the outlet height. And then the mean outflow cycle was 1.09 sec, and the mean outflow discharge was $0.00164m^3/s$. The total outflow number increased gradually as the water level of a water tank increased, and the outlet height decreased. As a level of water tank decreased, the mean outflow cycle was lengthened, and the unit outflow discharge increased. This result showed this system was most effective. To remove the silty clay deposited in facilities, the methods of excavation, dredging, high pressure washing, etc have been applied to the tidal facilities such as land reclamation, a small size fishing port, and a harbor for maintenance. However, this is extremely cost-ineffective, whereas the non-power soil cleaning and keeping system will bring about an enormously positive economic effect. In addition, when the non-power soil cleaning and keeping system is applied to the dike gate of land reclamation, a thorough examination of the local tidal data and the careful system planning are required to prevent the disaster damage caused by flooding.