Date of Award
Doctor of Philosophy (PhD)
Physical Sciences and Mathematics | Physics
This thesis presents a study of random self-organized systems using computer-simulated models inspired by cyclically-sheared non-Brownian suspensions of monodisperse spherical particles in a density-matched fluid. When driven at low Reynolds number, such systems have vanishing thermal fluctuations and only short-range interactions between individual particles. Nevertheless, they show intriguing collective behaviors at large length scales, such as a strong suppression of fluctuations in the number density. Such self-organized "hyperuniform" states can useful in industrial applications where well-controlled states can ease the processing of such materials.In Chapter 2, we propose a new way of generating hyperuniform suspensions, by incorporating slow gravity-driven sedimentation into a cyclically-sheared suspension. The effect of self-compaction drives the particle system towards its critical state automatically. We thus achieve quality hyperuniform distribution without fine-tuning of the system parameters. Computer simulations were conducted that mimic an experimental setup, and we successfully demonstrated a process leading to hyperuniformity in the steady state in the simulations. To this end, we characterize the spatial structure in both real space and reciprocal space to bolster our findings. In Chapter 3, we were inspired by dynamical jamming fronts , which prompted us to conduct a detailed study of our sheared suspension system with sedimentation that shows a qualitatively similar propagating front. We conducted extensive measurements to better describe the compaction front in this dilute system that is far from jamming. We found that the density profile of the front is solely dependent on geometric parameters of the system; its surprisingly does not vary with the effective diffusion rate. To further investigate the formation of the compaction front, we conducted point perturbation simulations to extract a correlation length in homogeneous systems as the critical packing fraction is approached from below. We show that the scaling exponent of the compaction front width compares favorably with the correlation length from our point perturbation measurements, and could be consistent with either the directed percolation universality class or conserved directed percolation. In Chapter 4, we summarize this body of work and present an outlook for future directions.
Wang, Jikai, "Self-organization in Models of Cyclically Sheared Suspensions" (2021). Dissertations - ALL. 1356.