Engineering Nature: Razor Clams
This week’s continuation of the biomimicry in engineering series will examine the unique properties that allow a razor clam, Ensis directus, to burrow in everything from hard-packed sand to thick sediment at relatively fast rates. If you simply looked at a razor clam, it would not appear to be an impressive specimen. It looks like a fat straw or a sawed off walrus tusk, but once it springs into action the awkwardly shaped clam can burrow almost 3 feet in just a couple of minutes. Engineers are currently examining what gives these incredible clams their ability to travel almost effortlessly into the earth and what applications it could unleash in the modern world.
When examining the muscle structure of a razor clam, many scientists came to the same conclusion: “In lab tests, the MIT researchers were puzzled to find that real-life clams were burrowing at velocities that seemed physiologically impossible, seemingly requiring far more force to push through the sand than the animals could exert.”i This is because it is not through strength that the clams are able to burrow into the ground, but through suction. First the clam sticks a small fleshy foot into the sand below while two small valves help push its body upwards. This then creates a tiny pocket of space under the shell which sucks in both sand and water; simultaneously it clamps its shell tightly shut with a twitch to disturb the sand even more. Creating an effect similar to quicksand, the clam is able to easily dig into and slide beneath the earth. Perhaps the most impressive fact about the razor clam is its efficiency while burrowing. The bivalves in the razor clam, next to the foot, have an elastic ligament that acts as a torsional spring that stores energy when the valves contract. This energy can later be reused for expansion. It is estimated that the razor clam only expends 0.21 J/cm, which may not sound like much, but to add some perspective: the razor clam could travel over half of a kilometer through sand on the energy in a standard AA battery.ii This amazing ability coupled with the incredible efficiency demonstrated by the razor clam have many mechanical engineers excited about the possible advances in many underwater fields.
Real World Applications
One of the most widely used and scarcely updated technologies on a boat is the anchor. The design of an anchor has remained basically unchanged in form for centuries, and it was not until a group of researchers from MIT set out to create the first “smart” anchor did it have any hope of modernization. The goal was to make an anchor that “can dig itself down to the right position to hold the vessel securely – and then, just as critically, easily reposition or free itself.”iii The anchor force of a razor clam blew every other tested anchoring method out of the water, including the most advanced anchors by a factor of at least 10.iv Another prospective innovation for the smart anchor is the ability to respond to real world conditions in conjunction with small robotic surveillance vehicles so that they can anchor whenever necessary and for whatever reason. However, many computational fluid dynamic simulations are unhelpful in exhibiting the true effects of the ocean floor so it is difficult to know how the smart anchors will hold up. The military has also looked heavily into creating an extremely inexpensive version that would be able to burrow into the ocean floor and detonate buried mines. With the many complex scientific advancements, the smart anchor offers a simple and efficient way to ensure that something stays where it is supposed to.
The extremely simple, yet efficient process of the Razor Clam is another example of taking nature and applying it to the many disciplines of science and engineering. By mimicking nature and its advances scientists can create products that are not only environmentally friendly and economical, but continue to push the boundaries of technological advances into an ever expanding array of disciplines.