The evaluation of fatigue damage due to vortex induced vibrations is an important part of riser design. For asymmetric configurations like steel catenary riser, or export line, the modal basis is divided into in-plane and out-of-plane modes, corresponding respectively to an eigenshape in the plane or perpendicular to the plane of the structure. Most industrial codes computing VIV response are based on a frequency analysis to obtain the amplitude of vibrations perpendicular to the current direction. Therefore, for current which are not in-plane or out-of-plane, the mode selection is not possible. Either the current direction is modified or the current is projected into the main direction of the configuration. In the present article, we investigate the influence of current direction on SCR response. Calculations are performed with a coupled fluid structure solver based on strip theory. Navier-Stokes equations are solved in two dimensions in slices perpendicular to the riser axis, and provides the hydrodynamic loading to the structural code. The displacement of the riser is then computed and used as boundary conditions for the new fluid step. Three directions and two upper depth current profiles are investigated. The first profile excites the low modes of the riser and the response is direction dependant. For the second profile with higher velocity, the crossflow responses are similar for all three current directions while the in-line responses differ mainly due to a low frequency first mode motion. Comparisons with a modal approach are then discussed.
- Ocean, Offshore, and Arctic Engineering Division
Influence of Current Direction on VIV of a Steel Catenary Riser
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Le Cunff, C, Averbuch, D, & Biolley, F. "Influence of Current Direction on VIV of a Steel Catenary Riser." Proceedings of the ASME 2004 23rd International Conference on Offshore Mechanics and Arctic Engineering. 23rd International Conference on Offshore Mechanics and Arctic Engineering, Volume 1, Parts A and B. Vancouver, British Columbia, Canada. June 20–25, 2004. pp. 23-30. ASME. https://doi.org/10.1115/OMAE2004-51014
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