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홍기용(KEYYONG HONG),양찬규(CHAN-KYU YANG),최학선(HARK SUN CHOI) 한국해양공학회 2001 韓國海洋工學會誌 Vol.15 No.3
An experimental method to investigate the dynamic characteristics of buoys in extreme environmental condition is established. Because the buoy model requires a resonable size for accurate experiment, the test condition in model basin that satisfies the similarity law is hardly compatible with capability of test facilities. It is suggested that the linear wave component that is unable to satisfy similarity is separated with others. The model experiment is carried out with mitigated condition for the linear wave components while others including wave drift, current and wind are keeping the similarities. Then, the result can be extrapolated to give the dynamic behavior of buoys in extreme condition because linear wave component is solely responsible to oscillatory buoy motion and other environmental components are applied as a initial tension. The similarity for current and wind conditions is viewed as equivalence of restoring forces. The validity of proposed method is examined with different types of standard ocean buoys and it indicates that the linearity of measured characteristics is assured with a limitation of resonable distance between test and estimated wave conditions.
경사진 실린더에 작용하는 플런징 쇄파 충격력의 불안정성 고찰
홍기용(Keyyong Hong),신승호(Seung-Ho Shin) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
Impact on cylindrical surface caused by plunging breaking waves is investigated experimentally. The breaking waves are generated in a wave fume by decreasing the wavemaker frequencies linearly and focusing the generated wave components at one specific location. The breaking wave packets are based on Pierson-Moskowitz spectrum. Three forward and one backward inclination angles of cylinder are applied to examine the effect of contact angle between cylinder and front surface of breaking waves. Also, the effect of cylinder diameter on pressure distribution and its peak value is investigated by adopting four cylinders with different diameters. The longitudinal location of cylinder is slightly moved in five different points to find out a probable maximum value of impact pressure. The pressures and total force on cylinder surface are measured by piezo-electric pressure sensors and 3-compoinents load cell with 30kHz sampling rate. The variation of peak impact pressures and force is analyzed in terms of cylinder diameter, inclination angle and location. Also, the pressure distribution on cylindrical surface is examined. The cylinder location and surface position are more important parameters that govern the magnitude and shape of peak pressures, while the cylinder diameter and inclined angle are relatively insignificant. In a certain conditions, the impact phenomenon becomes very unstable which results in a large variation of measured values in repeated runs.