A device made of cylinders tethered to the ocean floor could lessen the ferocity of waves, preventing them from eroding the shore

A system of upside-down pendulums tethered to the seafloor could significantly reduce the size of waves, helping limit beach erosion.

Waves that wear down beaches are often stopped with walls of rocks built parallel to the shore, but these large structures are intrusive and hard to adjust or move, and they can trap muddy water or disrupt marine habitats. Paolo Pezzutto at the Italian National Research Council, Institute of Marine Science and his colleagues built a prototype for a smaller device called MetaReef that calms the waves by absorbing their energy from beneath the water.

In the lab, Pezzutto and his colleagues used a narrow tank 50 metres long and filled with water to test the system. They tethered a line of 11 plastic cylinders, each about half a metre long, to the bottom of the box with steel cables. The cables were tightened enough to keep each cylinder submerged but still allow it to move back and forth, like an upside-down pendulum, when there was a wave on the water’s surface above.

The team then created waves of different frequencies with a piston-like device at one end of the box, and tested the ideal spacing for the cylinders as the waves rolled over them. At its most successful, MetaReef reduced the amplitude of the waves by about 80 per cent.

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Pezzutto says that the MetaReef idea seems simple, but he and his collaborators had to space the cylinders just right so that they wouldn’t interact with each other and produce new waves that could combine and become even stronger. By adjusting the spacing or size of the cylinders, the device could be tailored for individual beaches where waves have different amplitudes and frequencies, says Miguel Onorato at the University of Turin in Italy, who was part of the project.

The researchers say that this adaptability makes MetaReef more resilient to changes in the oceans, including sea level rise. But, it could still be torn apart by some giant storm, says Mike Meylan at the University of Newcastle in Australia. It may take more mathematical modelling of different wave scenarios, but it seems plausible that the device could eventually be successful outside of the lab, he says.

To that end, the team wants to run more tests on MetaReef, now creating waves that have multiple frequencies at once, as they do in nature.

Reference: arXivDOI: 10.48550/arXiv.2104.08243