VIV Prediction of Steel Catenary Riser - A Reynolds number Sensitivity Study

Steel Catenary Riser (SCR) is a common structure which connects a subsea installation to a floating or fixed platform. SCRs are subjected to environmental loads from waves and currents. As water depth increases, the wave effects will decrease significantly, while the entire SCR length is subject to currents. Vortex Induced Vibrations (VIV) due to the currents can cause severe fatigue damage, especially at the touch down point. A sensitivity study on fatigue accumulation from VIV has been carried out by using a semi-empirical software. The motivation for this work has been to reduce the uncertainty of VIV predictions in practical design when the Reynolds number effects are considered. The sensitivity study deals with hydrodynamic coefficients for VIV prediction. Built-in hydrodynamic coefficients in the applied software are based on rigid cylinder experiments at subcritical flow (low Reynolds number) conditions, while full-scale SCRs will experience critical and even super-critical conditions. In addition, the riser surface roughness is found to be an important parameter for VIV, but has so far not been explicitly taken into account in engineering analyses. A large amount of experimental results have been reviewed, and a method has been suggested for how hydrodynamic coefficients in empirical programs can be modified to account for varying flow conditions and roughness. VIV analyses have been carried out for a typical SCR to illustrate the sensitivity of predicted fatigue damage from varying sets of coefficients. However, the study is not conclusive with respect to recommended sets of coefficients since experimental data is still limited.