Dynamic model of a vortex-induced energy converter

Vortex-induced energy converters (VIECs) are attracting the attention of researchers looking for energy-harvesting systems in the marine environment. These energy converters, while probably less efficient than many other specialized devices, have very few moving parts and are particularly suitable for operation in harsh environments, such as those encountered in the ocean and in offshore platforms. The principle of operation of VIECs is tapping the transverse vibration of a blunt slender body immersed in a stream, induced by unsteady flow separation (Von Karman vortex street). The simplest device is an array of cylinders: under specific conditions and with careful design, it is possible to work close to resonance and thereby to obtain large amplitudes of oscillation, which are converted into electricity by suitable devices (linear electrical generators or piezoelectric cells). The system was developed experimentally at University of Michigan, with several patents pending and scientific material published on preliminary tests. Numerical simulations of system dynamics allow to simulate more realistic operating conditions and to perform the mechanical optimization of the system in relation to a specific sea location. A model of the system was thus developed, resulting in a nonlinear dynamic mathematical formulation; this last is solved in the time domain using MATLAB/SIMULINK programming. The sensitivity of the efficiency to the main design variables is investigated. The results demonstrate that the efficiency and power density are not attractive for the typical Mediterranean Sea conditions; however, as energy can be harvested over large surfaces, the system appears to deserve attention.