Vortex shedding oscillations for submarine pipelines: comparison between full-scale experiments and analytical models

The results of two experimental investigations, which were carried out in order to obtain information on the amplitude of vortex-excited oscillations of submarine pipelines, are analyzed. The first research, performed in a wind tunnel, concerned the measurement of the lift and drag forces acting on a model cylinder, in the proximity of a plane simulating the sea bottom. In the second research, a full scale pipeline span was placed in a test field, where tidal currents were known to-closely reproduce the design conditions. The response of the pipeline was recorded for different types of surface roughness, and the effectiveness of some devices aimed at reducing the vortex excited response were also checked. The tests confirmed the importance of vortex shedding, which gives rise to significant oscillatory phenomena (max. amplitude as high as twice the O.D. were found for a simply supported 68 m span,:20" O.D. - 1" W.T.) The synchronization of vortex shedding on the natural frequencies of a pipeline free span must be adequately anticipated and analyzed, in order to control and reduce the dynamic overstressing by means of remedial work on the laid pipeline