VIV Response of a Long Flexible Cylinder in Uniform and Linearly Sheared Currents

摘要

In June 2003, ExxonMobil performed vortex-inducedrnvibration (VIV) testing on a long flexible cylinder to assessrnthe validity of key theoretical assumptions that underly VIVrnprediction methods presently used by industry for riser design.rnA rotating test rig was used to expose a 9.63-m long testrnpipe with 20-mm diameter to flow conditions simulatingrnuniform and linearly sheared current. The model was heavilyrninstrumented to acquire records of bending strain and lateralrnacceleration in both cross-flow and in-line directions at arnsufficient number of stations to allow accurate reconstructionrnof static and dynamic bending deflections along the riser as arnfunction of time. The dense array of sensors permits anrnunprecedented level of detail in visualizing and interpretingrnresponse data.rnThe data were analyzed to examine the amplitudes andrnfrequency content of the vibrations, extract the wavenumbersrnof bending variations along the riser, and compute fatiguerndamage rates due to combined cross-flow and in-line bendingrnat many positions along the riser. Results show that commonrnmodeling assumptions reproduce response trends for barernrisers with no VIV suppression devices and lead to arnreasonable qualitative description of the vibration character.rnThe data from these experiments provide a benchmark forrnboth qualitative and quantitative validation of present andrnfuture riser VIV prediction formulations and prediction codes.