Intruder dynamics in fluid saturated granular medium

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Media composed of solid grains and fluids occur in geology, oil recovery, and chemical and food processing industries. The motion of an intruder in these situations, for example, the burrowing or locomotion of an octopus through the sea bed, is currently difficult to predict. This is true whether the intruder is a large, rigid object that is denser than the solid grains or an active object such as a robot or worm. This research will develop a set of models that predict the detailed motion of intruders as a function of their physical properties and those of the medium. In addition, experiments will be performed with three-dimensional imaging techniques that allow simultaneous measurement of the intruder motion and the motion of the surrounding grains and fluid. The experiments and models will focus first on spherical intruders, and then extend to rods and multi-link robot intruders. Design rules for these robots, which might be used to probe marine sediments, will be developed by studying the motion of freshwater worms. Ultimately, the results will be applied to efficient processing of wet granular materials in industry and the development of robots that can move through complex environments. The project will provide research experience for students at various stages of their educational careers in a collaborative environment focused on STEM.Intruder motion in dry granular materials has been studied to understand non-ergodic behavior in dynamical systems and segregation mechanisms. However, an understanding of intruder dynamics in fluid saturated granular medium, important to an even wider range of natural and industrial systems, is largely underdeveloped. Rheological descriptions of the medium developed recently as a function of dimensionless inertial and viscous numbers from granular and suspensions research will be combined with low-Reynolds number hydrodynamic resistive force theory to describe the motion of the intruder in multi-phase particulate systems. Closely coupled fluorescence-tagged internal imaging techniques will be further developed and used to measure the rearrangements of the granular and fluid phase at the single-grain level. Detailed measurement of the shape and orientation dependent drag of the intruder combined with the connection of the observed drag to the micromechanics of the medium will enable the development of a fundamental rheology model of active and passive intruder dynamics through wet granular medium. The project activities will also support a range of educational activities including enabling undergraduate and graduate laboratory research experience, and outreach activities targeting school students and members of the public.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.