심해수조 피트(pit)를 이용한 라이저 강제가진 실험

Abstract

Ocean thermal energy conversion(OTEC) system produces electricity by changing thermal energy from deep ocean water and surface ocean water to mechanical energy. The intake riser made of a FRP has 4m of inner diameter. The OTEC riser has a small slenderness ratio of 250 comparing that of a general riser. In this study, an experimental study was performed to analyze the behavior characteristics of the designed OTEC riser. The geometric and Froudes similarities were applied to approximate the dynamic characteristics of the designed riser. The top of the riser is excited with amplitudes and periods depending on the current. The strains along the riser length were measured with 24 strain gauges respectively in the direction of inline and cross-flow in order to analyze the global response characteristics of a free hanging riser. The response with the excited period was shown to be dominant at the low K.C. number. Whereas, the peaks with multi-frequencies including the excitation component were shown due to VIV at the high K.C. number. On the condition of forced oscillation with the current, the strains in the direction of inline and cross-flow were respectively diminished and increased. It was found that the high relative velocity by the current induced VIV, resulting in the large strains in the cross-flow direction.mall slenderness ratio of 250 comparing that of a general riser. In this study, an experimental study was performed to analyze the behavior characteristics of the designed OTEC riser. The geometric and Froudes similarities were applied to approximate the dynamic characteristics of the designed riser. The top of the riser is excited with amplitudes and periods depending on the current. The strains along the riser length were measured with 24 strain gauges respectively in the direction of inline and cross-flow in order to analyze the global response characteristics of a free hanging riser. The response with the excited period was shown to be dominant at the low K.C. number. Whereas, the peaks with multi-frequencies including the excitation component were shown due to VIV at the high K.C. number. On the condition of forced oscillation with the current, the strains in the direction of inline and cross-flow were respectively diminished and increased. It was found that the high relative velocity by the current induced VIV, resulting in the large strains in the cross-flow direction.