Abstract: The utilization of vortex-induced vibration for harvesting oceanic kinetic energy with VIVACE device has emerged as a research hotspot in the field of renewable energy. Utilizing FLUENT software with k-ω SST turbulence model and Newmark-β method, the flow-induced vibration characteristics of a D-section prism were investigated at an incident flow angle of 90° with four different mass ratios (2, 5, 7, and 10). The study systematically analyzed the vibration amplitude, frequency, average displacement, shedding modes of wake vortices, and energy conversion efficiency of the D-section prism. Simulations were conducted over a Reynolds number range of 288 to 2880, corresponding to reduced velocities of 2 to 20. Results revealed that the mass ratio can significantly influence the flow-induced vibration response of the D-section prism. As the mass ratio increases, the cylinder is more prone to galloping. With increasing mass ratio, the cylinder exhibited phenomena such as vortex-induced vibration, vortex-induced vibration-gallop, and lock-in galloping. Moreover, it was observed that the device achieves higher energy conversion efficiency when the cylinder was in the vortex-induced vibration branch other than the galloping branch. The first-stage energy conversion efficiency reaches a maximum value of 44% at mass ratio of 10 and reduced velocity of 4.5. These findings provide insights into oscillator selection for VIVACE devices.