Bio-Inspired Dual-Anchor Burrowing: Effect of Vertical Curvature of the Shell

Many organisms rely on dual-anchor strategy to burrow. A prominent biological role model is the Atlantic razor clam. By concerting the shape changing of various body parts: opening/closing of a rigid shell, extension/contraction of the muscular foot, and inflation/relief of the distal pedal, razor clams can burrow very effectively and efficiently. Using 3D discrete element method modeling, the interactions between two clam inspired dual-anchor penetrators and the surrounding granular media were captured at multiscale. A penetrator includes two major parts: a slender "shell" with time-varying diameter, and a conical "foot". Two different penetrators were considered: one with a uniform cylindrical shell and the other with a fusiform shell. The granular material consists of spherical particles with an upscaled particle size distribution of Ottawa F65. Microscale parameters are calibrated and validated with experimental triaxial test data. The impact of shell morphology is studied. It is found that opening of the shells compresses the soil around the shell to form anchorage, and at the same time releases the stress around the foot. A fusiform shell morphology is found to have limited influence on the penetration resistance and the shell anchorage during the foot penetration process. A systematic parametric study is still needed to test the hypothesis that a streamlined shell improves the burrowing performance of razor clams.