A circular cylinder with a pair of fin-shaped strips symmetrically mounted on its surface is proposed to harness the hydrokinetic energy of ocean currents. The flow induced vibration of a single converter is numerically investigated using a fluid-structure interaction (FSI) approach in Reynolds number range of 30480 <= Re <= 152400, falling in the TrSL3 flow regime (transition of shear layer 3). The numerical model is validated with the reported data for a cylinder with rectangular strips. By placing a pair of fin-shaped strips on the front surface of the cylinder, the VIV and galloping occur back-to-back. A recirculation region is generated behind the strips, resulting in a disturbance to the flow around the cylinder. The noncircular geometric shape contributes to the hydrodynamic instability, which is enhanced as the flow speed increases. The responses for the cylinder with fins at 20 degrees and 45 degrees fall in hard galloping zone 1, while the responses for fins placed at 0 degrees and 60 degrees belong to hard galloping zone 2. The maximum power of more than 60 W/m is harnessed at u(in) = 1.5 m/s (a typical ocean current speed). Nevertheless, the power efficiency decreases in galloping as the incoming fluid power increases with the response amplitude. Thus the maximum power efficiency occurs at the VIV upper branch or the onset of galloping. When the strips move to 90 degrees, galloping is disappeared and the vibration is suppressed as the strips further move to 120 degrees By arranging the converters in a staggered configuration, the maximum power density could reach 441.11 W/m(3). (C) 2018 Elsevier Ltd. All rights reserved.