Meeting Abstract

S5.5  Wednesday, Jan. 5  Razor Clam to RoboClam: Biologically Inspired Mechanisms for Subsea Burrowing WINTER, V, A.G.*; DEITS, R.L.H.; DORSCH, D.S.; HOSOI, A.E.; SLOCUM, A.H.; Massachusetts Institute of Technology; Massachusetts Institute of Technology; Massachusetts Institute of Technology; Massachusetts Institute of Technology; Massachusetts Institute of Technology awinter@mit.edu

Ensis directus, the Atlantic razor clam, should be too weak to dig. Estimates based on its strength, size, and shape indicate that its burrow depth should be limited to a few centimeters; yet it can dig as deep as 70cm. By visualizing soil deformations around burrowing Ensis using particle image velocimetry, we discovered that these animals reduce drag by using motions of their valves to locally fluidize the surrounding substrate. Moving through fluidized, rather than static, soil reduces drag forces on Ensis to a level within the animal’s strength capabilities and results in burrowing energy that scales linearly with depth, rather than depth squared. As Ensis contracts its valves, the resulting stress imbalance creates a failure surface around the clam, within which the soil can freely fluidize, and outside of which the soil remains static. Theoretical derivations and experimental results demonstrate that the location of the failure surface can be predicted using only two parameters commonly measured in geotechnical surveys: coefficient of lateral earth pressure and friction angle. For engineers, localized fluidization offers a method to dramatically reduce burrowing energy with a mechanically simple, self-contained digging device. With RoboClam, a robotic prototype of such a system, we have used a genetic algorithm to find optimal digging kinematics, achieving burrowing performance comparable to that of the live organism, in soil types ranging from ideally granular to Ensis’ cohesive mudflat habitat.