Vibration of highly flexible free hanging pipe in calm water

The measured results are analyzed for the first vibration mode and found that the maximum response amplitude occurs at much smaller frequency than its natural frequency and the deviation is much larger than a usual damped vibration system. The large deviation is presumably due to high flexibility of the model where a structural wave speed is rather slow. The comparison between numerical and experimental results shows a good agreement for the upper mid part of the model but with some differences for the bottom part. The difference is due to the large interaction between in-line motion and vortex-induced transverse motion that is largest at the bottom part. In the case of slender marine structures with free end at bottom, the dynamic behavior of the bottom part is very important to safely operate the system but is difficult to analyze exactly in a numerical method due to large vortex shedding.