We study two related cases of shape change in order to illicit fundamental vorticity creation and annihilation mechanisms that can add to our understanding of vortex creation and control for improved underwater vehicle maneuverability. Since vorticity creation and manipulation is the main control method exhibited by animals, especially in underwater creatures that must avoid costly drag penalties, we look to apply lessons from shrinking and retracting shapes to vorticity control methods.

Octopus, Squid, and Shrinking Cylinders

Octopus and squid are amazing animals that exhibit fast jetting responses when in need of escape from predators. These cephalopods intake a large amount of water into their mantle to prepare for the escape jetting maneuver. Interestingly, the initially bluff shape of the mantle does not prevent the animals from performing a fast escape. We are studying how the shape change of the mantle during the escape maneuver dictates and actually facilitates the fast escape maneuver, by modeling the shape change of the mantle as a shrinking cylinder.

 

Figure 1. Left: A squid drastically changes the shape of its mantle as it jet-propels through the water. Right: We model the mechanics of shape-change- enhanced propulsion with a shrinking cylinder. Contours of vorticity are plotted.

 

 

Figure 2. An octopus’ initially bluff mantle does not prevent it from an extraordinary escape.

 

References:

1. Cephalopods on the Move, Monterey Bay Aquarium, https://www.youtube.com/watch?v=PPYbjHwjNQc
2. Octopus vulgaris Camouflage Change, Roger Hanlon, https://www.youtube.com/watch?v=JSq8nghQZqA