Description:

Granular and particulate flows are ubiquitous in our world, from river sediment transport to the formation of planetesimals in a solar system. However, a predictive granular theory and associated model are still out of reach. Because collisions between solid particles are inelastic, a granular system is essentially dissipative and far-from equilibrium, which results in the clustering of particles. There is no consensus about the decay rate of particle kinetic energy in a free cooling state after the occurrence of clustering. In this research, predictions by existing theories will be examined experimentally. The results will validate and improve the theories. 

Problem Statement 
The proposed research will use a novel experimental technology known as magnetic particle tracking (MPT). Since a dense granular flow is usually opaque, advanced optical diagnostic techniques are useless. The magnetic tracking method, in contrast, relies on the magnetic field of a few labeled tracers, which can penetrate commonly used non-ferromagnetic materials. The magnetic tracking method is able to provide the Lagrangian trajectory and orientation of a magnetic particle. Hence, its velocity and kinetic energy can be calculated. The research constructs a payload with automated MPT measurements of a large ensemble of particles distributed in 3D suitable for flight on a reduced gravity aircraft. This aircraft will expose the payload to short periods of microgravity (~20 s) by flying a parabolic path. 

Technology Maturation
The flight tests will collec at least 100 such observations, between which the experiment is reset. The MPT technique will allow for 10 trajectories of particles in each experiment to be reconstructed, allowing computation of the free cooling rate for comparison to theory. Observation and measurement of such a visually obscured particle distribution in microgravity has never been done before.

Benefits: The long-term goal is to improve understanding of complex granular motion. This project is focused on the study of dissipation and related phenomena such as clustering and velocity distributions, in pursuit of a theoretical model capable of predicting these behaviors.