Design of a Biologically Inspired Underwater Burrowing Robot That Utilizes Localized Fluidization

The Atlantic razor clam (Ensis directus) digs by contracting its valves, fluidizing the surrounding soil and reducing burrowing drag. Moving through a fluidized, rather than static, soil requires energy that scales linearly with depth, rather than depth squared. In addition to providing an advantage for the animal, localized fluidization may provide significant value to engineering applications such as vehicle anchoring and underwater pipe installation. This paper presents the design of a self-actuated, radially expanding burrowing mechanism that utilizes E. directus burrowing methods. The device is sized to be a platform for an anchoring system for autonomous underwater vehicles. Scaling relationships presented allow for design of burrowing systems of different sizes for a variety of applications. The motion to sufficiently create soil fluidization is presented. Max force for the actuator to contract is based on force to pump fluid out of the device, and max expansion force is determined by the soil. Friction force in the device and potential considerations for increased force are presented. Data from laboratory tests are used to characterize how power is split between pumping water out of the device versus accelerating the mechanism itself. These relationships provide the optimal sizing and power needs for various size subsea burrowing systems.