The Significance of Low Velocity Near Bottom Currents on the In-Line Vortex-Induced Vibration Response of Rigid Subsea Jumpers

Event:
Subsea Houston
Date:
September 2004
Author:
M. Hariharan, M. Cerkovnik - 2H Offshore Inc. H. Thompson - ChevronTexaco

Subsea jumpers are susceptible to in-line and cross-flow vortex-induced vibration (VIV) fatigue damage due to bottom currents. From a design viewpoint, longer and less flexible jumpers are desirable in order to mitigate the effects of stresses due to high temperature and high pressure. The downside of this design is that these jumpers have low natural frequencies. A low velocity bottom current can, therefore, result in VIV excitation in the jumper. Cross-flow VIV amplitudes are typically much higher than in-line VIV amplitudes, but it is noted that the frequency of cross-flow VIV excitation is higher than the in-line VIV excitation frequency. In addition, the probability of occurrence of low velocity currents that result in low frequency vibration, is high. Therefore, the in-line VIV fatigue response of the jumper cannot be neglected, and may result in a requirement for vortex-suppression devices such as strakes.

The objective of this paper is to highlight the susceptibility of the subsea jumpers to inline VIV due to low velocity near bottom currents. An illustrative example of a rigid jumper located in 1,300ft water depth, West Africa is presented.

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