Hydrodynamic Aspects of Flexible Risers

For the evaluation of extreme loads and the assessment of the fatigue life of flex risers, use is made of discrete element models. Most of the models describe the fluid forces by means of empirical formulations using coefficients from 2-D cylinder tests. Recent research has shown that the fluid force modelling should incorporate lift forces perpendicular to the incoming flow. Moreover, model tests on typical flex riser sections have proven that the 2-D cylinder formulations are not applicable and may lead to significant errors.In this paper a new fluid model formulation is presented. This formulation is derived from both model tests and theoretical vortex simulations. Results of systematic drag tests for riser sections are discussed. Capabilities of vortex simulations are evaluated.