Meeting Abstract

65.2  Thursday, Jan. 6  The effects of head shape on drag and lift during subsurface sand-swimming MALADEN, RD*; DING, Y; UMBANHOWAR, PB; MASSE, A; GOLDMAN, DI; Georgia Tech, Atlanta; Georgia Tech, Atlanta; Northwestern Univ., Illinois; Georgia Tech, Atlanta; Georgia Tech, Atlanta Dingyang@gatech.edu

Morphological adaptations such as a sharp wedge-shaped head are hypothesized to reduce sand-swimming drag in desert dwelling reptiles. To determine if and how head shape affects performance we systematically study resistive forces on granular intruders with different shapes, and the effect of those same forces on robot subsurface locomotion. Inspired by the head shape of the sandfish lizard Scincus scincus, we dragged triangular prisms (wedges) with the leading edge at different vertical positions within the projection of the wedge. The drag on any wedge was within 15% of a square block shape. Intruders also produced lift forces that were comparable in peak magnitude to the drag forces but varied continuously from positive to negative as the ratio of the projected area of the upper to lower surface increased. Forces qualitatively agreed with an empirical model of granular lift force. To test the effect of these forces on a sand-swimmer, we attached the wedges at the head-end of a sandfish inspired robot which uses an undulatory gait to swim in sand. Swimming speed for a streamlined wedge-shaped head that generated zero lift force was comparable to that of a square block head. Heads made from wedges that produced lift resulted in significant positive or negative vertical displacement during locomotion: as the robot moved forward it pitched about the tail due to the torque imbalance in the same direction as the lift force on an isolated wedge. Variation of wedge surface angles can also be achieved by adjusting the incline of wedge-shaped heads which suggests a mechanism for sand-swimmers to control their vertical trajectory by head tilting.