A grey reef shark, Cairns Aquarium, Australia. (Photo by Unsplash)A shark of inspiration
Submarines and ships rely on towed sonar arrays (TSAs) for underwater exploration and security operations, but dragging these sensors through water, especially at high cruising speeds, creates excess noise that can mask target signals and compromise the sonar’s detection capabilities. Now, engineers are attempting to solve this problem with a little inspiration from Mother Nature.
Berkeley researchers, in a collaboration with MIT Lincoln Laboratory, demonstrated how a textured surface designed to mimic patterns on shark skin, known as riblets, can reduce drag and mitigate flow-based noise on TSAs. Grace Gu, assistant professor of mechanical engineering, said the idea of using riblets was inspired by serrations, which help owls achieve silent flight and are used on surfaces to mitigate noise in aeronautic systems.
To test their theory, the researchers — including Berkeley graduate students Zilan Zhang and Dahyun Daniel Lim, along with MIT Lincoln Laboratory’s Justin Rey and Matthew Jones — used computational modeling to simulate riblet surfaces with different shapes and patterns and then simulated the movement of water around them. Of the designs tested, the rectangular riblet design was most effective at both diminishing noise generated by water flow and decreasing hydrodynamic drag.
The magnitude of these improvements was most evident for turbulent flows. Under these conditions, rectangular riblets reduced noise by up to 14.3%, along with a 5.1% decrease in hydrodynamic drag, in comparison to a smooth array surface. In addition, riblets with finer, more closely spaced geometries further reduced drag by another 25.7%.
According to Gu, this research could lead to key advancements for underwater vehicles and instruments. And the quieter operation of these underwater devices also benefits the environment by reducing the impact on marine life.
Learn more: Bioinspired design reduces drag and noise production for towed sonar arrays; Influence of bioinspired riblet topographies on the mitigation of flow-induced noise in towed sonar arrays (Extreme Mechanics Letters)