NONLINEAR STATIC AND DYNAMIC ANALYSIS OF MARINE PIPELINES DURING LAYING

When installing an offshore pipeline, a long unsupported pipe span is lowered from the laying vessel to the seabed. Pipe bending stresses are reduced by pulling the pipeline with a tensioner on board of the moored laying vessel. In the seaway, the moving vessel causes pipe oscillations. Two tensioning methods are investigated: a blocked tensioner which avoids any relative motion between pipe and laying vessel, and a compensating tensioner ruling out dynamic pipe tension. Differential equations for pipe oscillations are deduced and solved, including, besides other nonlinear effects, the interaction between bending oscillations and dynamic tension. Linearised soil damping and elasticity at the lower end of the suspended span is taken into account. The computed results are validated by experiments based on a new model testing technique which assures similarity by considering all relevant non-dimensional parameters.