Wave concentrator could help capture renewable energy from the sea

18 Sep 2018

Wave function: the new concentrator could be coming to a coastline near you. (Courtesy: C Li et al/Phys. Rev. Lett. (2018))

A new device that can triple the amplitude of a water wave by concentrating it into a small, shallow space has been unveiled by researchers in China and the US. As well as concentrating waves incident on the device, it does not reflect a significant amount of wave energy back into open water. As a result, the team believes that their prototype could soon be scaled-up to tap into the enormous potential for power generation provided by the oceans.

As waves crash into coastlines around the world, they dissipate a vast amount of kinetic energy. Over previous decades, there have been numerous attempts to collect this abundant source of renewable energy by concentrating waves into small areas, where their combined energy can be harvested more efficiently. However, the unwanted reflection of a sizable portion of wave energy from harvesting systems diminishes the actual amount of energy that is collected.

Now, an international team led by Huanyang Chen at Xiamen University and Zhenyu Wang at Zhejiang University have created a device that minimizes wave reflection. To do this, they built an annular structure consisting of a central open region surrounded by 50 thin, vertical metal sheets extending radially outwards from the centre (see figure). The top of the device stands above the incoming waves and the device has a solid floor that slopes up from the outer edges – gradually decreasing the water depth towards the centre.

Designer slope

The metal sheets create narrowing channels that that focus incoming waves towards the central region. The wavelength of a shallow-water wave is strongly dependent on water depth. This allows the upward slope of the floor to be designed so that incoming waves with certain wavelengths pass through the channels with a minimum of reflection.

The team tested their design calculations through both simulations and practical demonstrations, including a device with an outer radius of 43 cm. For incoming waves of two particular wavelengths, the measured amplitudes were tripled in the shallow central region of the concentrator. However, waves in the water surrounding the device were almost entirely undisturbed.

Chen, Wang and their colleagues now want to implement their device on the much larger scales required to make ocean energy harvesting a viable economic option. Already, they have planned to test a large-scale device in the city of Xiamen in the near future. In the longer term, the researchers expect their work will have a significant influence over coastline engineering – perhaps allowing wave power to join solar, wind and hydroelectric energy as a dominant force in the renewable energy industry.

The concentrator is described in Physical Review Letters.

19/9/2018 from PHYSICSWORLD.COM