Drag coefficients on razor clams in slightly fluidized granular media

Abstract

Razor clams are able to burrow deeply into granular media with only a small fraction of force required by traditional anchoring devices. It is hypothesized that the collapse of their shell and subsequent localized fluidization of the media is responsible for a large reduction in drag, thereby allowing the clam to burrow. A test setup comprised of a fluidized bed connected to a pump with an attached ball valve for flow regulation is constructed which allows testing of drag force in conditions similar to that the clam experiences, as well as in an environment void of wall effects. Testing is done using a dead clam attached to a stainless steel rod which is passed through the fluidized bed to obtain accurate data for the razor clam. The result is that a slight fluidization to a void fraction between 40-45% gives a drag reduction which is more than sufficient for a clam to burrow at velocities seen in nature.