• Special Issue of the Society of Naval Architects of Korea
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• 2011.09a
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• pp.12-16
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• 2011

During the shipbuilding construction, the repair works will be occurred by various reasons such as the natural disaster, mistakes of engineers or workers, defect of material, and so on. The one of the engineer's responsibilities is to design considering every possibility and to prevent the repair works due to the mistakes during construction stages, but actually it is very difficult and impossible to avoid every mistake. However, it is also the responsibility of engineers to find the best solution for the unavoidable mistakes which is to maintain the capacity of vessel and guarantee the safety for the repair works considering the construction schedules and economic cost. In this paper, it will be introduced the brief of repair works to the structural damage of the moon-pool structure in drillship which is built in our shipyard. For the verification of the structural strength, the fatigue analysis has been carried out based on the guide of Classification society. Furthermore, the modifications of structure design and welding procedure have been applied to avoid the stress concentration in the moon-pool structure.

• Journal of Ocean Engineering and Technology
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• v.22 no.2
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• pp.20-27
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• 2008

A moon-pool is a vertical well in a floating barge, drilling ship, or offshore support vessel. In this study, numerical simulation of two-dimensional moon-pool flaw coupled with a ship's motion in waves is carried out using a particle method, the so-called MPS method. The particle method, which is recognized as one of the gridless methods, was developed to investigate nonlinear free-surface motions interacting with structures. The method is more feasible and effective than convectional grid methods in order to solve a flaw field with complicated boundary shapes.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.262-262
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• 2015

풍수해보험은 국민안전처가 관장하고 민영보험사가 운영하는 정책보험으로 국민이 예기치 못한 풍수해 피해에 대처할 수 있도록 보험료의 일부를 국가 및 지방자치단체에서 보조해 주는 제도이다. 그러나 풍수해보험은 불합리한 보험요율체계 등의 문제점으로 인해 저조한 가입률을 보이고 있다. 현재 풍수해보험요율 산정시 과거의 피해이력만을 근거로 보험요율을 산정하고 있다. 또한 풍수해 보험은 태풍, 홍수, 호우, 강풍, 풍랑, 해일, 대설, 지진을 대상재해로 분류하고 있으나 동일 시군구 내에서는 재해요인별 원인별 가중치가 동일하게 적용되어 단일 보험요율을 적용하고 있다. 현재의 불합리한 보험요율체계의 문제점을 보완하고 향후 피해발생 위험을 고려하여 피해 특성에 따라 지역적으로 차등화된 보험요율을 적용하는 방안이 필요하다. 이에 따라 본 연구에서는 풍수해보험요율 산정을 위해 풍수해보험 대상재해 중 내수침수에 대한 분석 방안을 제시하고 적용성을 검토하고자 하였다. 우선 다양한 내수침수분석방법 중 전국단위의 내수침수분석을 위해 경제성, 간편성, 정확성을 고려하여 Level-Pool 방법을 선정하였다. 그리고 기존 Level-Pool 방법의 문제점을 보완하기 위해 내수침수분석 결과의 정확성을 향상시킬 수 있도록 도시계획 용도지역을 고려한 수정 Level-Pool 방법을 제시하고, 풍수해저감종합계획과 비교 검토를 실시하여 적용성을 검토하였다. 또한, 제시한 수정 Level-Pool 방법을 울산, 대구, 경북, 강원지역에 적용하여 내수침수위험지역을 도출하였다. 본 연구에서 제시한 수정 Level-Pool 방법을 통해 전국단위 내수침수 해석시 지역별로 차등화되고, 정확도가 높은 내수침수지역을 도출하여 풍수해보험요율 산정을 위한 기초자료로 활용할 수 있을 것으로 판단된다.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.1332-1337
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• 2008

Fire model shall be verified and validated to reliably predict the consequences of fires within its limitations. This study aims to predict pool fire with two rooms using FDS and to coompare FDS simulation results with PRISME experimental data which can be applicable to the fire of nuclear power plant facility. Four different sizes of grid (0.08m, 0.1m, 0.125m, 0.2m) are used in the simulation and the simulated results of specific quantities such as temperature, chemical composition, heat flux and heat release rate are compared to the experimental data. From this study, the FDS simulation results with the finer grid resolution show better similarity and trend with pool fire experimental data. The sensitivity analysis and the selection of the proper size grid are essential to predict the consequences of pool fire with two rooms reliably.

• Journal of Ocean Engineering and Technology
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• v.17 no.3 s.52
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• pp.27-32
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• 2003

The welding distortion of a hull structure in the shipbuilding industry is inevitable at each assembly stage. The geometric inaccuracy caused by the distortion tends to preclude the introduction of automation and mechanization. Thus, additional man-hours are needed for the adjusting work in the assembly stage. To overcome this problem, a distortion control method should be applied. For this purpose, it is necessary to develop an accurate prediction method that can explicitly account for the influence of various factors on the welding distortion. In order to minimize the weld-induced residual deformation, this paper proposes the optimum welding sequence as a method for distortion control. The validity of this method has been substantiated by a number of numerical simulations and experiments.

• Journal of Mechanical Science and Technology
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• v.15 no.4
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• pp.482-491
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• 2001

An experimental study has been carried out to investigate an I-type sparger-performance in view of pressure oscillation and thermal mixing in a pool. Its pitch-to-hole diameter, P/D, varies from 2 to 5. The test conditions are restricted to the condensation oscillation regime. In the present study, two different hole patterns, staggered and parallel types, are employed under various test conditions. The amplitude of the pressure pulse shows a peak for pool temperatures of 45∼85$\^{C}$, which depends on P/D and the steam mass flux. The effect of hole pattern on the pressure load is smaller than that of P/D. The dominant frequency increases with the subcooling temperature of pool water and P/D. A correlation for the dominant frequency is proposed in terms of the pitch-to-hole diameter ratio and other dimensionless thermal hydraulic parameters.

• Proceedings of the KIEE Conference
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• 2001.11b
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• pp.167-169
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• 2001

This paper introduces the principal pool rules of the wholesale power market scheduled to be commissioned in January 2003 in Korea. The pool rules includes electricity trading procedures such as bidding, determining and publishing of forecasted market price, and 5 minute unconstrained dispatch scheduling for generation/market price, which are required for settlement after dispatching and should be conformed by KPX and participants in the market. Detailed procedures of the rules are under development and additional provisions for stable market operation are under discussion.

• Journal of Ocean Engineering and Technology
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• v.19 no.5 s.66
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• pp.16-25
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• 2005

The effect of vertical riser support system on the dynamic behaviour of a classical spar platform is investigated. Spar platform generally uses buoyancy-can riser support system, but as water depth gets deeper the alternative riser support system is required due to safety and cost issues. The alternative riser support system is to hang risers off the spar platform using pneumatic cylinders rather than the buoyancy-can. The existing numerical model for hull/mooring/riser coupled dynamics analysis treats riser as an elastic rod truncated at the keel (truncated riser model), thus, in this model, the effect of riser support system can not be modeled correctly. Due to this reason, the truncated riser model tends to overestimate the spar pitch and heave motion. To evaluate more realistic global spar motion, mechanical coupling among risers, guide frames and support cylinders inside of spar moon-pool should be modeled. In the newly developed model, the risers are extended through the moon-pool by using nonlinear finite element methods with realistic boundary condition at multiple guide frames. In the simulation, the vertical tension from pneumatic cylinders is modeled by using ideal-gas equation and the vertical tension from buoyancy-cans is modeled as constant top tension. The different dynamic characteristics between buoyancy-can riser support system and pneumatic riser support system are extensively studied. The alternative riser support system tends to increase spar heave motion and needs damper system to reduce the spar heave motion.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.51 no.12
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• pp.597-602
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• 2002

The restructuring of power industry is still going on all over the world for last several decades. Many kinds of restructuring model have been studied, proposed, and applied. Among those models, power pool is more popular than other. This paper assumes the power pool market structure having competitive generation sector, and a new method is presented to build a bidding strategy in that market. The utilities participating in the market have the perfect information of their cost and price functions, but they don't know which strategy to be chosen by others. To define one's strategy as a vector, we make utility's cost/price functions into discrete step functions. An utility knows only his own strategy, so he estimates the other's cost/price functions into discrete step functions. An utility knows only his own strategy, so he estimates the other's strategy using Nash equilibrium or stochastic methods. And he also has to forecast the system demand. According to this forecasting result, his payoffs can be changed. Considering these all conditions, we formulate a bidding game problem and apply noncooperative game theory to that problem for the optimal strategy or solution. Some restrictive assumption are added for simplification of solving process. A numerical example is given in Case Study to show essential features and concrete results of this approach.

• Journal of the Korean Solar Energy Society
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• v.30 no.5
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• pp.93-99
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• 2010

Nucleate pool boiling experiments with constant heat flux condition were performed using pure R113 for various channel heights under saturated pool condition. A circular heater of 1mm diameter, with artificial cavity in the center, fabricated using MEMS technique and the high-speed controller were used to maintain the constant heat flux. Images of bubble growth were taken at 5,000 frames per second using a high-speed CCD camera. The bubble geometry was obtained from the captured bubble images. The effects of channel height on the bubble growth behaviors were analyzed as dimensional scales for the initial and thermal growth regions. The parameters for the bubble growth behaviors were bubble radius, bubble growth rate, and bubble shapes. These phenomena require further analysis for various surface angles, but this study will provide good experimental data with constant heat flux boundary condition for such works.