Investigation of VIV Responses of Slender Structures Under Waves and Currents

Abstract The slender marine structures, such as marine risers and dynamic power cables, etc. are exposed to waves and currents. Vibrations due to periodic vortex shedding around the structure can lead to fast accumulation of fatigue damage and amplified drag loads. Vortex Induced Vibrations (VIV) often represent a safety risk and a major design consideration adding notable costs to all stages of the system development. It is known that the presence of waves may disrupt organized vortex shedding and affect structures’ dynamic responses and resulting drag loads. However, the present frequency domain VIV prediction tools can only consider constant current. The fatigue damages due to VIV and waves have to be calculated independently, and then combined afterwards. In addition, the influences on the drag loads are neglected. These have been some of the major uncertainties in the present design practice, which is more pronounced for shallow water applications, e.g., power cables to floating wind turbines. There are both lack of understanding of the wave-VIV interactions and reliable prediction tools. In present study, a model test of a steel catenary riser (SCR) subjected to wave and VIV loads carried out at SINTEF Ocean were studied. Relevant test cases were selected and analysed to understand the influences of wave loads on VIV responses. Nonlinear time domain VIV simulation using VIVANA-TD were also carried out, which showed good agreement between prediction and model test results. Other relevant studies were also examined and parameters that may affect structure responses under wave and VIV loads were discussed.