ALE-ANCF modeling of the lowering process of a J-lay pipeline coupled with dynamic positioning

A novel structural dynamics model for the lowering process of a J-lay pipeline is established by combining the absolute nodal coordinate formula with the arbitrary Lagrangian-Eulerian description. The constraint on the top of the pipeline is introduced into the dynamic equation in the form of generalized coordinates by using a material transport boundary to simulate the lowering process of the top end of the pipeline. A mesh scheme is adopted to control the element length and prevent numerical disturbances. The accuracy of the material transport boundary and mesh scheme is verified for the case of a pendulum with a time-varying length. Then, a coupled analysis program is developed to investigate J-lay deployment by a vessel using dynamic positioning. The tensioner is modeled as a damper to adjust the pay-out speed of the upper end of the pipeline. The numerical analysis is carried out on an explanatory example of a 16-inch pipeline being laid at a 1000-m water depth. The results show that the lowering process strongly affects the dynamic characteristics of the touch-down zone.

Automated summary

A novel structural dynamics model is proposed for the lowering process of a J-lay pipeline, which combines the absolute nodal coordinate formula with the arbitrary Lagrangian-Eulerian description. The material transport boundary and mesh scheme are validated through a pendulum example. A coupled analysis program is developed to study J-lay deployment by a vessel, considering the tensioner as a damper. The lowering process significantly impacts the dynamic characteristics of the touch-down zone.