EXPERIMENT ON BEHAVIOURS OF LONG AND FLEXIBLE PIPE IN WATER.

Forced motion tests of pipe models were done in a model basin. Fluid dynamic forces on the pipe models hanging and oscillating in water were estimated with measured forces required to give that oscillation to the models. The magnitude of the fluid dynamic forces thus measured was near that expected on a cylinder oscillating in a rigid body mode. However an unexpected behavior, lateral vibration induced by heaving motion, was observed at some special frequencies of the oscillation. A mathematical model used for lateral vibration of elastic pipe in water was found to be capable of describing this behaviour as a parametric excitation of Mathieu type and a theoretical method was proposed to predict the magnitude of this excitation. A mathematical model was proposed to improve the quantitative accuracy of prediction.