Locomotion within granular media: sand swimming skinks

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In this proposal the PI will study how a desert dwelling lizard, the Sandfish, swims beneath the surface of a granular material. Imaging methods will be developed to surmount the difficulties of visualizing biological systems in opaque terrestrial media and computational modeling tools will be created to study the interaction of the organism with materials whose equations of motion are unknown. These efforts will occur in three interacting thrust areas: (1) Measurements of organism motion and dynamics: A multiplane, high speed and resolution x-ray imaging system will be built to obtain the first three dimensional kinematics of an organism moving within a complex medium. Both the kinematics and forces will be characterized as the substrate properties are systematically varied by use of an air fluidized bed. (2) Physics experiment to characterize response of granular media to swimming motions: Developing models of the locomotion will require understanding the physics of the material response in this regime in which the bulk of the material behaves like a solid except for a small region surrounding the organism which behaves like a fluid. The forces associated with maneuvering objects through the granular medium will be measured and the results use to produce an empirical model of force production. (3) Computer models of organism and granular media: As granular media are amenable to direct numerical simulation, development of a 3D Molecular Dynamics simulation interacting with the actuated objects (lizard models) used in experiment will result in numerical environment interaction models that can be used to interrogate the motion at the grain level as well as to create the first models of biological organisms moving within this material. The experimental data obtained from studying the organism will suggest actuation strategies that will be played through the physics experiments and validated models. This study will initiate the beginnings of a deeper understanding of movement within non-Newtonian media and thus will result in a new model system for locomotion biology, as well as models for locomotion. This work will create rapid modeling tools to aid design of robotic exploration and search & rescue devices that must burrow through challenging terrain. It will also gather students from a diverse range of backgrounds: physics students will interact with biology students to make progress on experiments and models. This program will serve as a springboard to develop a course examining control of locomotion, mechanical properties of biological actuators (muscle), skin friction, rheology of complex matter, etc. Outside the university, the program will provide outreach by engaging the public in visible and graspable science.