How to get a robot out of the water

Two researchers from Cornell University – Sunghwan Jung and Brian Chang – wanted to know how a robot could do it.

"We collected data on aquatic animals of various sizes, ranging from about 1 mm to several tens of meters, jumping out of the water and were able to reveal how their maximum jump height is related to the size of their body, "said Jung. "Since the water is 1,000 times denser than the air, getting in or out of the water requires a lot of effort, so aquatic animals face mechanical challenges."

A boundary is known as a "mass of entrained water" – an object – a dolphin or a copepod – jumps into the water, the water is entrained in the animal's flow, which limits the height of the water. jump.

"We are trying to understand how biological systems are able to overcome challenges in order to optimize their performance, which could also illuminate engineering systems for entering or exiting air-water interfaces," said Jung. .

Most aquatic animals are contoured, limiting the mass that can be dragged when it slips out of shape.

However, how, they asked, un-simplified creatures like frogs and copepods (a small crustacean) do?

The team discovered and designed a small articulated mechanism that is closed by an elastic band.

Once printed in 3d, it worked – and there is a video to prove it.

"This robot shows the importance of entrained water when an object jumps out of the water," Jung said.

The work is being presented this week at the annual meeting of the Fluid Dynamics Division of the American Society of Physics, Georgia, in a paper titled "How Aquatic Animals Exit from Water" (Presentation M20. 2).

According to the abstract of the articles, far from the entrained water: "By balancing the power produced by the animal dissipated by the drag, we show that the normalized jump height, H / L, is proportional to the number of Froude, H / LFr .². Simplified experiments were conducted by drawing axisymmetric bodies across the surface of the water. Here we see a transition in which the partial outputs are scaled as H / L~Fr and the full outputs are scaled as H / LFr². "

The next item on the group's agenda is to reach heights similar to those of copepods and frogs.