Renewable energy source inspired by fish

An engineer in the US has built a machine that can harness energy fromthe slow-moving currents found in oceans and rivers around the world.By exploiting the vortices that fish use to propel themselves forward,the device could, he says, provide a new kind of reliable, affordableand environmentally friendly energy source.

Turbines and water mills can generate electricity from flowingwater, but can only do so in currents with speeds of around 8-10 km/hif they are to operate efficiently. Unfortunately, most of the currentsfound in nature move at less than 3 km/h.

The new device is called VIVACE, which stands for vortex inducedvibrations for aquatic clean energy, and its inventor claims it canoperate in such slow-moving flows.

As such, it works like a moving fish. Fish cannot propel themselvesforward using muscle power alone; instead they curve their bodies sothat they form a vortex on one side of their body, straighten out, andthen curve the other way to form a vortex on their other side, in orderto glide between vortices. VIVACE remains in a fixed position in thewater but is pushed and pulled by the vortices on either side, andthese vibrations are then converted into electrical energy (the currentcylinder is smooth, but future versions will have scale-like structureson the surface to enhance vortices).

Bernitsas explains that engineers usually do all they can to suppresssuch vibrations, which can occur in either water or air, as they cancause enormous damage. They were, for example, responsible fordestroying the Tacoma Narrows bridge in the US in 1940. "But," he says, "it dawned on me four years ago that I can enhance these vibrations toharness energy. My colleagues and I searched the scientific literatureand patents and found out to our surprise that no one had done thisbefore."

The total amount of energy generated by the Earth's slow-movingcurrents is vast, but the density of this energy is low. This meansthat the VIVACE technology, like any other ocean-based device, willonly ever be part of the solution to the world's energy needs. However,Bernitsas believes it has a number of advantages over alternativeocean-based sources, pointing out that, unlike wave devices, forexample, it is unobtrusive, and should also pose no harm to marinelife.

Source: physicsworld.comAdded: 5 January 2009