Engineers Tim Finnigan and Andrew Caska harness the power of the sea

3 April 2006

With streamlined bodies and stiff, high fins, sharks are among the most efficient swimmers in the ocean: up to 90 per cent of the body energy used is converted directly into forward motion.

In an innovative engineering feat, two University researchers are developing devices that harness the waves and tides of the world's oceans for conversion into clean renewable energy - and one of their designs is directly modelled on a shark's caudal fin.

Their project was one of nine winners of the University's Innovation Challenge competition, which rewards exciting new research projects.

"We are applying the concept of biomimicry, which refers to the use of natural biological traits in engineered systems," said Tim Finnigan from Sydney's Schoolof Civil Engineering.

Using the hydrodynamics of the tails of sharks, mackerel and tuna, Dr Finnigan has designed a biomimetic tail - 15 metres long with a fin spanning 12 metres - that can produce 1 megawatt of power. "A fish uses muscle energy to drive the side-to-side motion of its tail which propels it forward. Instead, we will use ocean energy - from tidal streams - to drive the fin back and forth against an electrical generator," explained Dr Finnigan.

Tim Finnigan
Tim Finnigan

Marine fauna was not the only source of inspiration for the researchers. Sea plants have inspired a design modelled on the motion of large plants under wave action. "Kelp has adapted a mechanism to anchor itself to the ocean floor and to sway back and forth under constant waves. We have copied that anatomy - the capacity to capture a wide swath of incident wave energy - and applied hydrodynamic engineering to produce a wave energy conversion concept," said Dr Finnigan. Sydney doctoral student Andrew Caska is working alongside Dr Finnigan. He is currently conducting research on optimising the hydrodynamic interaction of the plant-like device with the wave forces so that maximum energy is absorbed.

The giant fin and wave-plant designs are fixed to the seabed by a small-base footprint which is modelled on the hold-fast anchor of sea plants. The footprint distributes the forces from a single stem into the seabed through multiple roots.

The beauty of the designs is their survivability. The researchers have diverged from traditional marine engineering structures which are built to stand firm and react against the forces of the ocean. Ocean energy devices are designed to convert energy in moderate day-to-day conditions, explained Dr Finnigan, but they must also be engineered to withstand the largest forces that occur during extreme weather events. This tends to drive up capital costs.

Andrew Caska
Andrew Caska

The University researchers are the first to apply biomimicry to ocean energy technology. "Our devices are lightweight, pliable, and move and respond with the forces of the ocean. They are naturally adapted for survival. For example, in stormy weather, the giant wave-plant device will lie flat on the ocean floor, much the way kelp does to avoid being thrashed around. And both devices can continually adjust to the changing orientation of the currents," he said.

Dr Finnigan and Mr Caska won the Spruson & Fergurson IP Prize of $20,000 worth of cash and services as part of the University's 2005 Innovation Challenge. Their modelling so far has focussed on computer simulation and they are now preparing to test the systems in the hydraulic laboratory.

This article first appeared in Uni News, 10 March 2006.
Photograph credit: Ted Sealey