Meeting Abstract
The effectiveness of animal locomotion on natural substrates like sand, soil, and snow depends on foot morphology, kinematics of foot motion, and substrate properties. The behavior of flowable ground is often complex, and the medium can both solidify and flow in a single step. We used the discrete element method to model the impact of the foot on dry granular substrate. The simulation was calibrated and the results were validated using intrusion experiments performed with a linear actuator (ETT model, Parker Hannifin Corp.) impacting a 28x28x7.5 cm container of poppy seeds at intrusion speeds up to 2 m/s. A circular disk, and a disk with three toes attached were used as intruder shapes, and the total force generated on the foot over the depth of intrusion was calculated. The presence of toes generated a larger amount of force on the foot and a larger volume of fluidized medium. Intrusion at greater speeds produced a larger peak force on impact and a greater rise in force subsequently with depth. Simulations were also performed at various angles of attack of the intruder where the foot was oriented at an angle to the substrate surface during intrusion. The greatest amount of impact force was observed when the surface of the foot made an angle less than 10 degrees with the free surface of the granular medium, beyond which the impact force rapidly decreased to less than 65 percent of the maximum value. These results demonstrate that the foot geometry and kinematics can significantly affect the force response experienced by the animal, and consequently determine locomotor performance.
