Solving the Jellyfish Puzzle

May 1, 2012 - via Seapower


The Office of Naval Research in 2009 awarded a grant for a multiuniversity research initiative entitled “Jelly Fish Autonomous Node and Colonies: Modeling Biological Structure and Behavior, System Architecture Design and Implementation.” The goal is to design and build an unmanned underwater vehicle (UUV) that mimics the morphology and propulsion mechanism used by jellyfish to swim in complex ocean states.

Virginia Polytechnic Institute and State University (Virginia Tech) is designing the vehicle, while the University of Texas-Dallas is working on nano materials such as sensors and actuators. UCLA is designing control systems and electrostatic (distance) sensing. Experiments with jellyfish at Providence College provide schematic and biological data. Stanford University is providing chemical sensors that are used to guide the vehicle. Other universities, government laboratories, agencies and industry also are participating in the program.

The universities have a program review with Navy program managers every six months and will conclude their work next March.

Shashank Priya is associate professor in the Department of Materials Science and Engineering and Department of Mechanical Engineering at Virginia Tech, Blacksburg, Va.

The ultimate goal is to completely solve the physics involved in the propulsion of jellyfish, and then the industry people will be able to take our research and develop a vehicle which will be of use to the Navy.

The jellyfish is about 95 percent water. When we started designing, we looked at the form factor. The jellyfish contracts, relaxes, contracts, relaxes. So we thought that it was a very simple mechanism, where we can make a bell which is similar to the mechanical characteristics of the jellyfish bell and when we contract and relax it would start to move.

Actually, that was not the case. Making any gel material that has the mechanical properties like the jellyfish bell is very, very hard. Any solid object cannot hold 95 percent water, and if it holds it, it cannot have the mechanical rigidity to perform actuating cycles as desired.

Even if we make the material and just expand and contract, the velocity doesn’t even come close to that of a jellyfish. Its muscles, which are only a percent of the total volume fraction, are so powerful that they are able to contract the bell by almost 55 percent and then relax back, without consuming any energy, to its original state. So it was challenging — the design of the muscles … the design of the bell material and solving the problem of how to get the thrust production even if we can contract and expand.

It took time to solve these puzzles. We were able to make some hydro-gel materials by using nanotechnologies that can hold 70 to 83 percent water and still have decent mechanical rigidity. And then we were able to make actuators based on shape-memory alloy wires and use some strain amplification mechanisms, which can provide the 55 percent contraction.

[The UUV is] a very elegant object. It looks [and performs] very similar to a jellyfish. We feel that in addition to surveillance, you could also have applications for chemical pollution monitoring and environmental changes, studying the various kinds of organisms in the water, for oil-cleaning purposes. … We are working on a little bit larger-scale jellyfish, which could carry some payload. So it could do some serious work in the ocean.

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