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EnergySeabed carpet could harness wave energy

Published 18 June 2012

A synthetic “seabed carpet” that mimics the wave-damping effect of a muddy seafloor could be used to extract energy from waves passing over it. As well as offering a new way to produce clean and cheap electricity, the carpet — which has not yet been built — could be used to protect coastal areas against strong waves and provide areas of safe haven for boats in stormy seas

A synthetic “seabed carpet” that mimics the wave-damping effect of a muddy seafloor could be used to extract energy from waves passing over it. As well as offering a new way to produce clean and cheap electricity, the carpet — which has not yet been built — could be used to protect coastal areas against strong waves and provide areas of safe haven for boats in stormy seas.

An Institute of Physics release reports that the ability of muddy seafloors to dampen ocean waves is well documented at various locations around the world. In the Gulf of Mexico, fishermen have learned to steer their boats into a local muddy spot known as the “mud hole” when a storm is brewing. Here, the wave-mud interaction is so strong that the storm waves are damped within a distance of a couple of wavelengths (100-200 meters) and the boats there are completely safe.

Springs and generators
“If mud can seriously take so much energy out of ocean waves, then why don’t we use this idea to design a wave-energy convertor that’s very efficient?” asks the carpet’s inventor, Mohammad-Reza Alam of the University of California, Berkeley. He came up with the idea using a viscoelastic “carpet of wave-energy conversion” (CWEC) placed over a network of vertically oriented springs and generators on the coastal seafloor. The flexible carpet responds just like mud: as waves pass overhead, they induce dynamic ripples and undulations in its sprung surface, and these perturbations can be used to generate electricity.

Modeling the interaction of ocean waves with the proposed carpet, Alam was able to show that the system can easily absorb 50 percent of incident wave energy over short distances of about 10 meters. For typical North Sea waves, the simulation suggested energy absorption rates of up to 6.5 kW m-2, which is more than double the maximum possible with wind turbines and at least twenty times greater than currently achieved by solar-power convertors.

Short waves are better
All oceanic motion is a combination of long and short waves. It has long been known that the short waves associated with choppy seas are dampened faster than far-reaching long waves (swells) for various reasons, but it was only recently that surprising field observations revealed that short waves are actually much better than long waves at imparting their energy to a muddy seafloor in shallow waters.

Alam developed a computer simulation that took into account hundreds of different waves