Flexible pipe model tests in steady current, carried out as part of Submarine Vortex Shedding (S.V.S.) Project, are briefly outlined, as far as the effects on hydroelastic synchronization, induced by the pretensioning level in the models, the static sagged shape and the gap ratio are concerned. The results are presented and extensively discussed. The mathematical model set up to Interpret the above results is described and the theoretical findings are used to explain possible mechanisms of hydroelastic synchronization, coupled with the non-linear dynamic behaviour of the model.
S.V.S. research Project aimed at studying extensively the dynamic behaviour of the free spanning pipelines when exposed to hydroelastic phenomena in various flow conditions (see Refs. 11/, 12/). Extensive laboratory testing and full-scale in field data monitoring were carried out as part of the Project activities (see Refs. 13/, 14/), from 1985 to 1988. The tests herein described and used as basis for mathematical modelling were part of those performed in laboratory with three dimensional flexible models. The main objective was to measure the response of the pipeline model when exposed to a steady current flow of varying intensities, with different starting structural and geometrical parameters characterizing the pipe span.
The model consisted of a long flexible pipe suspended between two low friction hinges, which restrained it torsionally. The model pipe was built using an inner aluminium pipe giving stiffness and strength, and outer plastic shells providing the external (hydraulic) diameter and surface roughness. The pipe was suspended to a frame which offered the possibility of varying the static tension of the model and its vertical position with respect to the flat plate simulating the sea bed. Furthermore, the axial stiffness of restraints could be adjusted, to simulate different pipe-soil interactions at the free-span shoulders.
