A Study for forced oscillation experiment for OTEC riser under current

Abstract

The present study investigates the dynamic behavioral characteristics of a free hanging riser under forced oscillation in current. The geometric and Froudes similarities are 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 are 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 is shown to be dominant at the low K.C. number. Whereas, the peaks with multi-frequencies including the excitation component are 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 are respectively diminished and increased. It is found that the high relative velocity by the current induced VIV, resulting in the large strains in the cross-flow directioned riser. The top of the riser is excited with amplitudes and periods depending on the current. The strains along the riser length are 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 is shown to be dominant at the low K.C. number. Whereas, the peaks with multi-frequencies including the excitation component are 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 are respectively diminished and increased. It is found that the high relative velocity by the current induced VIV, resulting in the large strains in the cross-flow direction