题 目：Self-assembly of granular particles at low-thermal states
报告人：Dr. Kejun Dong
Dr. Kejun Dongis a Senior Lecturer in Infrastructure Computations at Western Sydney University. He earned both his bachelor and master degrees from Department of Applied Physics, Hunan University (China) in 1996 and 1999 respectively, and received his PhD from School of Materials Science and Engineering, University of New South Wales (UNSW) in 2007. He then worked as a research fellow and Lecturer in the world-renowned Laboratory for Simulation and Modelling for Particulate Systems (SIMPAS) at UNSW prior to joining WSU. He has attracted a number of research and industrial projects and been awarded Australian Discovery Early Career Researcher Award (DECRA) (2012).
His research focuses on simulation and modelling of granular materials and amorphous systems, with interdisciplinary applications in environmental, civil, material and chemical engineering. He has authored/co-authored over 100 scholarly publications (including over 70 journal publications), two of them published on a very prestigious journal, Physical Review Letters. He has received about total 2000 citations and scored H-index 26.
Granular materials are ubiquitous in nature and industry, but their fundamentals are poorly understood. A statistical description of this kind of materials remains a physics challenge. Granular packings, as the basic state of granular materials, have been severed as a structural model for glass, colloids, and jamming systems for a long history. Normally they present disordered structures which are jammed under gravity, as the granular particles are athermal. However, under certain vibrational conditions equivalent to low-thermal states, a disordered granular packing can transform to ordered or partially ordered structures, which will critically affect the related transportation properties. So far it has not been clearly understood under what kind of vibrational conditions, such changes will happen.
Here we present our recent investigation in the transition of disordered structure to ordered structure in a vibrating bed composed of uniform spherical particles by discrete element method (DEM). The simulated bed is analyzed by the so-called adaptive-Common Neighbor Analysis (a-CNA), which is able to identify the local ordered structures with slight distortion, which is commonly seen in a granular packing. The effects of the vibrational condition, boundary shape and particle properties on the structure change are studied by a series of controlled numerical experiments. A phase diagram of the system’s order as a function of the vibrational amplitude and frequency was established.
It is found that the vibrational velocity amplitude can more effectively characterize the structure of a vibrating bed than the commonly used vibration intensity. In particular, particles can easily form the ordered and dense structures locally when the dimensional vibrational velocity amplitude is about 2. And the local ordered structures can be initiated from the wall and gradually propagate to the center of the bed. In addition, different movements of the wall can have different effects on the formation of the ordered structures, which is also dependent on the vibrational condition. Moreover, the closed-packed plane of an ordered cluster is generally parallel to the wall that initiates its formation. These findings can not only improve the understanding on granular materials, but also be inspiring to the order transition in other amorphous systems.