Hydrokinetic energy conversion of Flow-induced motion for triangular prism by varying magnetic flux density of generator

Highlights: • The damping of FIMEC system is modeled as a quadratic function of excitation voltages V_B. • As the excitation voltages V_B increasing, the performance of the triangular prism transforms from SG to CG and finally to HG. • Galloping could be self-excited by adjusting the magnetic of generator. The advantageous performance on energy conversion of triangular prisms in Flow Induced Motion Energy Conversion (FIMEC) system has been verified by previous researches. In this paper, the magnetic flux density (B) was introduced into the mathematical model to analyze damping (c_total), active power (P_harn) and energy conversion efficiency (η_harn) in FIMEC system. A physical model was established to adjusted the magnetic flux density (B) by varying the excitation voltages (V_B) of Power Take-Off System (PTO). Free decay tests proved that physical model matched well with the mathematical model. Based on the physical model, the Flow Induced Motion (FIM) characteristic and energy conversion were analyzed and discussed, furthermore a control strategy to harness energy in galloping branch for Hard Galloping (HG) was proposed and verified. As B is high HG occurs, otherwise soft galloping (SG) occurs. By using the control strategy, the galloping can be self-excited by adjusting B, which is beneficial to the energy conversion of FIM. In the tests, the peaks of active power and efficiency are P_harn ≈ 2W and η_harn ≈ 3.1% in Vortex Induced Vibration (VIV) upper branch, P_harn ≈ 21.5 W and η_harn ≈ 3.5% in galloping branch.