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theses

Granular materials are quite common in our everyday lives in both nature and industry. Yet much of the phenomena that they exhibit is not well understood and in fact quite complex and non-linear. For example, it has been known since Faraday‘s time that swirling sandstorms are able to generate electric charge that manifest as multi-million volt lightning discharges. Poured glass beads have been demonstrated to also charge electrically, causing random ejections of grains and creating interesting raised clump structures known as razorbacks. Lastly, granular materials are known to exhibit self- segregation based on size. An example of this phenomenon is the landscape observed on the asteroid 25143/Itokawa, which has spatially separated boulder fields and sand seas. In this work, we discuss three projects that examine non-linear behavior in granu- lar materials. In our first chapter, we discuss a computational electrostatic model of vibrated identical granular particles. We show in our model that granular materials are able to exponentially generate charge and polarization through 1/r2 electric field interactions. By adding neutralization between neighboring particles, we find complex phenomena such as charge and polarization waves that propagate through the particles. In closing, we reproduce a polarized state experimentally using vibrated glass beads which represents one of the phenomena that we observe in our model phase diagram; we also discuss our experimental efforts to image charge and polarization waves. In the second chapter, we examine the dynamical behavior of charged granular par- ticles. We find that by experimentally exposing grains to simple electric fields, a number of novel behaviors appear including dust clouds, dust columns and tendrils. In addi- tion, in our experiments and simulations we find evidence for non-linear electrostatic interactions between particles including asymmetries and particle trajectories that do not adhere to naive electric field lines. In our final chapter, we deal with granular segregation found on the asteroid known as 25143/Itokawa. On the asteroid there exists segregation between smaller sized dust and rocks on the centimeter size, from large boulders with diameters on the order of meters. While current explanations attribute the segregation to the phenomenon known as the Brazil Nut Effect, we show that "ballistic segregation" or a difference of collision types on the asteroid surface can be responsible for the separation between different sized particles. We show that the surface area growth of particles can be modeled using the non-linear Hill Equation, which shows that increasing amounts of dust accumulation promotes further dust accumulation.

ETD_7469

Ph.D.

Includes bibliographical references

by Theodore Lordin Siu

doi:10.7282/T3JQ13CV

ETD doctoral

The author owns the copyright to this work.