Pilot projects aimed at generating electrical energy from the motion of ocean waves have gotten a lot of press. The Scottish government, for example, has now approved the installation of a 40-MW wave energy generation facility in the Shetland Islands.
To these efforts you can now add those of a company called Vortex Hydro Energy in Michigan. Founded by two engineering professors from the University of Michigan (U of M), the firm takes a different approach to generating power than those of traditional wave generation schemes. Wave energy harvesters generally employ bobbing buoys or some similar means of extracting energy from the movement of passing waves. In contrast, the VHE device consists of cylinders that move up and down as vortexes in the current move past them, creating kinetic energy. Each bobbing cylinder moves a magnet up and down past a coil of wire, thus creating electrical current from water currents.
Unlike traditional wave generators, the VHE device needs no wave action to operate, only currents as might arise in lakes or streams. That makes it more versatile in the eyes of its creators, Michael Bernitsas of the U of M Naval Architecture and Marine Engineering department, and James MacBain, also formerly with U of M’s College of Engineering. The vortex induced vibration (VIV) that provides the kinetic energy is an extensively studied phenomenon where vortices are formed and shed on the downstream side of rounded objects in a fluid current. The vortex shedding alternates from one side of a body to the other, thus creating a pressure imbalance causing an oscillatory lift.
The cylinder oscillations happen at a relatively slow, one-cycle-per-second rate. This lets fish easily navigate around the cylinders, the creators said.
VIM is a nonlinear resonance, as opposed to linear resonance which happens only when the frequency of excitation from the flow, such as waves, equals the natural frequency of the oscillating body. In contrast, linear resonance is the principle used in energy devices with oscillating buoys, flaps, foils, or water columns. It has a limited range of large amplitude oscillations.
VHE has gotten to the prototype stage with its technology, which it calls VIVACE, or Vortex Induced Vibrations for Aquatic Clean Energy. It now has a pilot project in place in Michigan’s St. Clair River near Detroit. VHE hopes to commercialize the technology, which was invented and patented at U of M. Plans are to deploy another small prototype this summer and a bigger one next year. So far, the company has deployed cylinders about 12 ft long. Plans are to next build an installation with cylinders about 20 ft long in an apparatus that is about 27 ft high.
One irony of VHE’s technique is that the VIV effect it employs has, until now, been considered mainly a source of structural damage. The original Tacoma Narrows Bridge collapsed in 1940 when vortex shedding caused torsional vibrations that ripped the bridge apart.
Reference:
Vortex Hydro Energy
www.vortexhydroenergy.com
Filed Under: Power Electronic Tips