Infrastructure / Energy futureEnergy from vortices

Whirlpools created by currents as they flow over obstacles are powerful enough to tear apart bridges and offshore rigs. Why not use them as a source of renewable power? Earlier attempts to harness energy from the flow of the world’s rivers and oceans have had limited success, at best. Tidal flow can only be tapped at certain times of day, while underwater turbines are only viable if they are mounted in rapid currents. Now researchers led by Michael Bernitsas at the University of Michigan are preparing for the first outdoor trials of a technology that makes use of the slow-moving currents down rivers and across the ocean. When water flows over an underwater obstacle, whirlpools or vortices form alternately above and below it. The vortices create a tugging effect, so the result is an alternating force that yanks the object up and down (since we are talking about vortex-induced vibrations: Back in October we reported on the interesting work of John Dabiri at the California Institute of Technology in Pasadena: He realized that it might be possible for a mechanical system to extract energy from vortex wakes and has developed a mathematical model, based on the way fish move, to help put this into practice).

Technical background
The university of Michigan Web site offers interesting technical details about VIVACE. Bernitsas invented, designed, and model-tested for the VIVACE (Vortex Induced Vibration Aquatic Clean Energy) energy converter (patent pending UofM#2973). VIVACE is an ocean/river current energy converter based on the idea of enhancing rather than spoiling vortex shedding, increasing rather than suppressing vortex-induced vibrations (VIV) under high damping, and harnessing rather than mitigating VIV energy. VIV was first observed by Leonardo daVinci in 1504 A.D. in the form of Aeolian Tones. Since then engineers have been trying to suppress VIV which damage aero, civil, mechanical, marine, offshore, and nuclear engineering structures. The VIVACE Converter takes this destructive force in nature and utilizes for the benefit of mankind. The VIVACE Converter is designed to be in high damping VIV — thus extracting energy at high efficiency — over the range of current velocity which is of practical interest: 0.25-2.5 m/sec (0.5-5.0 knots) [79-80]. Testing of the VIVACE Converter in the Low Turbulence Free Surface Water Channel of Ocean Renewable Energy Laboratory at the University of Michigan for high damping resulted in a power harnessing rate of P_VIVACE=0.22p_wDLU³ for