Deepwater Riser Interaction: Computational Method and Validation

A method for predicting interaction between risers is presented. The method is efficient and handles different riser systems exposed to complex environmental data. To achieve this, the method utilizes pre-established data for forces on risers in close proximity. Interaction effects concerning mean values as well as the dynamic forces at vortex shedding frequencies are stored. The interaction effects cause large wake induced oscillations (WIO), and the vortex induced vibrations (VIV) are influenced as well. The method uses the database of forces in a strip theory manner to obtain excitation forces on risers and other slender bodies exposed to current. The method is implemented in a non-linear dynamic finite element tool, HYBER. During the simulation, the clearance between the risers is followed up. If collisions occur, relevant data are recorded, and the simulation continues. Fatigue and possible single event damage are assessed. In the present paper, results from the method are compared with comprehensive measurements in model scale, and the computed results show good agreement with the measurements. Databases exist for bare cylinders with equal and unequal diameters as well as for two geometries of strakes.