INVESTIGATION ON VORTEX INDUCED OSCILLATIONS AND HELICAL STRAKES EFFECTIVENESS AT VERY HIGH INCIDENCE ANGLES

The demand to develop steel catenary riser (SCR) technology for floating production systems requires the capability to predict and eventually reduce the vortex induced vibrations (VIV) of slender tubular structures when subjected to steady flows at high angles of incidence. The SCR looks to be a prime candidate for future deepwater developments, but the means of VIV suppression of such a structure within its other stringent design requirements is only in its development phase, particularly for harsh environments such as the Atlantic margin and West Africa. An in-house helical strake design has been developed to satisfy potential response mitigation requirements. A reduced scale model experimental programme has been undertaken, to better address the full scale open water test campaign, aimed to determine both the VIV response and the helical strakes effectiveness at very high incidence angles. The reduced scale tests were carried out by towing in a tank a 6 m long, 0.152 m diameter pipe model at different velocities and inclination angles. The full scale tests were carried out by towing in open water a 200 m long, 0.274 m diameter pipe model at different velocities and inclination angles. A description of the towing arrangement and relevant instrumentation of both the test programmes is given.