Experimental investigation on energy conversion and vortex-induced vibration suppression of marine risers with turbine-type external devices

A turbine-type external device dubbed TVSEHD is proposed to harvest ocean current energy and suppress VIV simultaneously, and the optimum design is carried out. In the optimization design, the number of blades was designed to be 3, 4, 5, and 6, while they were installed on the smooth riser for the outflow excitation experiment. The VIV response and energy harvesting parameters are investigated to reveal the mechanism of the two. The comprehensive evaluation method is presented to evaluate TVSEHDs. The results demonstrate that TVSEHD disrupts the vortex shedding and causes the vortex shedding separation point to shift from the riser surface to the blade end. Therefore, the riser vibration frequency is changed, suppressing the VIV. The maximum vibration amplitude suppression rate reaches 97.65 %, and the maximum riser vibration frequency suppression efficiency reaches 67.95 %. The rotation of TVSEHD can effectively cut the magnetic induction line to harvest electric energy, and the energy conversion efficiency under four blades is the largest. The number of blades is a crucial factor in the optimum design. A decrease in TVSEHD velocity and output power occurs as the number of blades increases, due to an increase in section moment of inertia and resistance to fluid motion.