VIV Assessment of Deepwater Lazy-Wave Risers

The steel lazy wave riser is an emerging solution for deepwater applications in harsh conditions. The addition of buoyancy to provide the unique “lazy wave” shape reduces the dynamic stresses at the touchdown zone resulting in improved performance due to vessel motions and waves. However as the buoyant region cannot be easily fitted with Vortex-Induced Vibration (VIV) suppression, VIV becomes a critical aspect of the design. The present study focuses on understanding the global response of a deepwater lazy wave riser with a combination of computational fluid dynamics (CFD) and semi-empirical software analysis. An industry first full scale CFD simulation with different buoyancy region geometries is presented and analyzed to understand the field response and provide guidance on important aspects of design. Results show a different response than what was expected based on previous testing of similar systems, introducing a new parameter related to the aspect ratio of the buoyancy modules.