A study on dynamic Behavior of a light and flexible riser for upwelling deep ocean water

A numerical study on the dynamic behavior of a flexible riser for upwelling deep ocean water is presented. In the numerical study, an implicit finite difference algorithm is employed for three-dimensional riser equations. Fluid and geometric non-linearities and bending stiffness are considered and solved by Newton-Raphson iteration technique. In order to keep the riser intake depth under a strong surface current, a weight is attached at the end point of the riser. In-line displacements of the riser under current loads and top end oscillations are calculated. The top end oscillations are consisted of surge, heave and two combined excitations. It is found that high tension is occurred in the excitation periods for 5similar to10 seconds and the original design condition is greatly changed. The tension variation at the top point of the riser shows non-linearity and seems to be snap load under severe combined excitation. It is expected that result of this research can be utilized as a good tool for the detailed design of a riser.