Biologically Inspired Mechanisms for Burrowing in Undersea Substrates

Abstract

The aim of the research presented in this thesis is to generate compact, lightweight, low-energy, reversible, and dynamic burrowing systems for use in subsea applications such as anchoring, oil recovery, underwater cable installation, mine detonation, and sensor placement. As many organisms have evolved to embed themselves within undersea substrates, unsurprisingly, nature has provided a viable basis for a novel, efficient burrowing technology. This work centers around understanding the burrowing mechanisms of Ensis directus, the Atlantic razor clam, which was discovered to burrow by using motions of its valves to locally fluidize the surrounding substrate. Moving through fluidized, rather than static, soil reduces drag forces 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 within the soil creates a failure surface around the clam, within which particles can freely move and 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. To explore the feasibility of transferring localized fluidization burrowing into engineering applications, RoboClam, a robot that burrows using the same mechanisms as Ensis, was designed, constructed, and tested. Experimental data show the machine is able to match the animal's linear burrowing energy versus depth relationship and achieve localized fluidization in both granular and cohesive substrates.