Jae-Moon Lew

Note on the Development of Ballast Water Shifting System for Solar Tracking of the Floating Photovoltaic Plant

지구온난화로 인하여 탄소배출을 줄이는 문제가 세계적 관심의 대상이 되면서 강력한 불변의 자원인 태양광을 이용하는 문제가 주요한 과제로 대두되고 있다. 태양광 발전시스템은 일조량 확보 가 일차적 조건이므로 사막이나 초지와 같은 지리적 조건을 활용 하는 것이 유리하다. 이에 대하여 호수나 하천과 같은 수면 상에 설치하는 경우에는 육상에 설치할 때 반드시 필요한 부지 조성과 기초공사 등과 같은 부대 공사가 줄어들며 임목벌채와 같은 환경 을 저해하는 공사가 불필요하게 된다. 또한, 태양광 발전 시스템을 수면 상에 설치하면 태양 전지판이 수면에서 일어나는 자연대류현 상으로 인한 냉각효과가 있어서 발전효율이 높아지는 이점이 있다. (Choi, et al., 2013; 2014; Trapani, 2013) 부유식 발전시스템 (Kim, 2011; Lee, 2011)의 규모는 시스템 생산과 설치수역으로의 운송 및 설치, 유지 보수를 운용상의 편 익을 고려하여 설계하여야 한다. 또한 수역의 수심변화나 흐름의 유무 등을 고려하여야 하며 태풍 등의 바람 영향을 함께 고려하 여 설계하여야 한다. 그리고 설계된 단위 시스템들은 집단화하여 경제성을 갖춘 대단위발전시스템으로 구축할 수 있어야 한다. 태 양광 발전 시스템은 효과적으로 계류 고정하는 기술이 필요하게 된다. 태양광 발전시스템은 고정위치에 계류된 상태에서 밸러스트 수의 적재만으로 태양 전지판이 항상 태양을 향하도록 제어하는 것이 가능하다. 이때 부유체는 강한 바람을 받더라도 충분한 복원 안정성을 가져야 하는 동시에 최소한의 밸러스트 수를 사용하여 밸러스트 수 이동으로 태양을 추적하는 부유식

Development of Bench Tester for Designing the Passive Anti-Rolling Tanks

It is important to use bench test results in the design process of anti-rolling tanks. Traditional bench tester is usually designed to perform only roll motions about a fixed axis and relatively small so that the viscous effects may not be neglected. Novel bench tester which could adjust the motion center to realize the coupled motion of sway and roll has been devised and manufactured therefore, large scaled bench tester could be utilized for designing the passive anti-rolling tanks. The time history of the reference signal from the rotation sensor of the bench tester have been recorded and processed to determine the phase angle to derive the Response Amplitude Operator(RAO) of the stabilized ship. The breadth of ART tank model should be large up to 2 m to diminish viscous scale effect and the vertical position of the tank can be varied with the ships center of motion. The periods and the amplitude of roll motion can be varied from 1.5 sec to 5 sec and up to ±20°, respectively. The components of the tester was expressed in three dimensional digital mockup (DMU) and assembled together in the CAD space. The final configuration of the bench tester has been determined by confirming the smooth operation of the moving parts without interference through the animation in CAD space. New analytic logic are introduced for the determination of hydrodynamic moment and phase difference due to fluid motion in ART and verified through the test. The developed bench tester is believed to be effective and accurate for the verification of stabilization effect of ART taking into the consideration of the sway effect in the design stage.

Numerical Computations of Impact Forces Acting on Breakwater Plate of Bow Deck of Container Carrier

In this study, numerical studies using a Computational Fluid Dynamics(CFD) method were carried out to estimate the green water load acting on the breakwater plate of bow deck of container carrier, KCS. For the green load water load analysis, a full load condition was considered. The relative motions at bow deck were calculated from the seakeepig analysis. Statistical analysis were carried out to estimate the long term response of the relative motions with the North Atlantic wave scatter diagram. The equivalent design wave was determined from the RAO of the relative motions at bow and the long term responses. CFD geometry modeling with three different locations and simulations for the green water loads were carried out in the equivalent design waves. A commercial CFD program, STAR-CCM+ Ver. 8.04, was used and the green water pressures on the breakwater plate were calculated successfully. The CFD analysis for green water loads can be used as a useful design tool for the evaluation of the breakwater plate of the container vessel. Ke ywords : Green water(그린 워터), Bow deck(선수 갑판), Breakwater plate(쇄파판)

Development of New Experimental Devices and Methods to Measure Shaft Forces of Ships

New experimental devices and methods to measure shaft forces of ships are proposed in this paper. The strain gauge type six-component load cell was newly designed and installed to the end of the propeller shaft. The signals generated from the sensor in the propeller rotating are transferred to the new data amplifying and processing board on the shaft and the data is transmitted to the self-made wireless receiver. To find out the characteristics of shaft forces during port and starboard turning motions in sea trial, oblique and combined yaw maneuvering tests at straight, transient, maximum yaw rate, steady conditions were performed with the model ship installed the shaft forces measuring device using circular motion tester of Samsung Ship Model Basin. Characteristics of the measured shaft forces in model tests show quantitatively good agreement with the computed values obtained by the CFD programs using the measured wake data in oblique towing conditions. In the near future, It is hoped that the estimated shaft forces for a ship from this experimental method could be validated through comparison with directly measured values of a ship.

Experimental Study on Lift Characteristics Considering Moving Ground Effects of Low Aspect Ratio Wings for Wing-In Ground Effect Crafts

In this study, we are focusing our attention on lift characteristics of the low aspect wings for Wing-In Ground effect crafts (WIG). Experimental measurements at an open-type wind tunnel are carried out and results are comparatively presented. In order to simulate the realistic ground condition in where the WIG craft is flying, moving ground is implemented by a conveyor belt rotating with the same velocity of the inflow. We consider two different wings (NACA0012 and DHMTU section) which have four different aspect ratios (0.5, 1.0, 1.5 and 2.0). Forces acting on the wings are measured and lift characteristics are elaborately investigated for various different conditions. In addition, end-plate effects are estimated. Results are validated by comparing with theoretic solutions of the symmetric airfoil. Present results show that ground effects are differently generated in moving or fixed ground conditions, and hence left characteristics are affected by the ground condition. Consequen tly, accurate aerodynamic forces acting on the WIG craft are guaranteed in a realistic moving ground condition.