Numerical and experimental studies of submerged towing of a subsea template

During submerged towing of marine structural modules, the vessel motions will induce dynamic loads on the towing configuration. These dynamic loads are important when evaluating different submerged towing concepts and will have implications on structural design with respect to the relevant limit states. The focus of the present work is accordingly on the dynamic forces, which act in the main lifting wire that connects a subsea structure to the hang-off point above the moonpool of a vessel. Three alternative approaches for estimation of the tension are considered: A simple 1-degree-of-freedom system is integrated in the time domain by means of the Newmark-beta method and comparison is subsequently made with results obtained by application of detailed multibody time domain analysis by the Marintek software SIMO (Simulation Of Marine Operations). The results from the 1-degree-of-freedom system and the calculations by SIMO are also compared with measured response obtained from an experimental investigation. In general it is found that all the three methods show good agreement.