Computation of Interaction Between Deepwater Risers: Collision Statistics and Stress Analysis

A methodology for computing the dynamics of interacting risers is presented. During the time simulations, riser impacts (if any) are recorded. The relative velocity and angle between the axes of the risers are recorded at each hit, so that the actual stress and accumulated fatigue damage may be computed in a post-processing operation. Detailed material properties, such as properties of coating, the actual composite material properties, etc. are used in that process. The methodology is based on a pre-established database of forces acting on the cylinders. At each time step, all riser elements are loaded with a combination of in-line and transverse forces, depending on local relative distance to the neighbouring riser. This imply that the methodology is based on quasi-static assumptions. The paper presents a validation of the computed force database by comparison with measured results. Examples of results from simulation with top tensioned risers on a TLP are given.