Dynamics of Suspended Marine Pipelines

As the development of offshore oil and gas production proceeds, the dynamic stresses in pipelines induced by laying operations become more important. The contribution of this paper is to the finite-element modelling of the dynamics of a large pipeline where nonlinear bottom reactions and ocean fluid drag are included. A time domain simulation procedure is described for computing the dynamic motion and stress response for arbitrary time history inputs at the surface. Also, a method of linearizing the seaway fluid drag terms and of handling the nonlinear bottom reactions is shown for harmonic seaway inputs. The two methods are compared and illustrate the reasonable accuracy of the linearized method. It is shown that dynamic bending stressess can be significant in the sag bend regions indicating the need for evaluation for future deep water applications. Additionally, it was found that dynamic bending stress magnitudes increased with ocean bottom rigidity. The model concentrates on the pipeline analysis and assumes a ramp-style stinger, the dynamics of which has not been included.