NON-LINEAR ANALYSIS OF SOME SLENDER PIPELINES

We study some typical problems which arise during the installation of seabed pipelines which have already been laid down and must be moved into a correct position. These motions typically involve very large translations and rotations. The problems are highly nonlinear, involving both geometric nonlinearity (because of the large rotations) and frictional effects caused by the pipeline lying directly on the seabed and by the usual practice of attaching dragging chains at various points on the pipeline. The pipelines are very slender, so that the usual stiffness formulation is not practicable. Numerical models are developed for the components of the system (pipeline, friction, drag chains, towing cable) and are shown by example to lead to the efficient solution of typical problems. The implementation uses an incremental scheme (which is essential because of the strong path dependency of the systems being studied), and Newton's method is used to solve each nonlinear increment. It is pointed out that the problems addressed not only are of practical importance in themselves but also provide an excellent test for algorithms proposed for use in such highly nonlinear structural applications. © 1979.