Mechanical and Civil Engineering Seminar

Mechanical and Civil Engineering Seminar Series

Granular and particle-laden flow: Novel approaches to characterize avalanches and dunes across scales

Abstract: Flowing granular materials arise everywhere around us, in industry from pharmaceutical processes to bulk good transport lines, and in nature from snow avalanches to captivating dune fields. An interesting length-scale separation exists between the particle and system-scale. At the micro-scale, collisions between individual particles are directly influenced by the particle size. In contrast, large desert dunes are composed of the same particles, but the effect of particle size may disappear entirely when analyzing entire dunes. In this talk, we will illustrate this length-scale separation with two examples of our experimental work on granular flows. At the macro-scale, we present a unique, recirculating, laboratory experiment in which we create and trace aqueous dunes over long times. We examine the interaction between two dunes of different sizes, and present a phase-space diagram with interaction outcomes. Furthermore, we explore the feedback mechanism between a bedform and the flow providing the forcing, and identify a repulsion mechanism that ensures that bedforms do not coarsen without limit. At the micro-scale, we discover stress distributions in 2D granular avalanches, visualized with bespoke, superior-quality birefringent photoelastic particles. This technique gives us for the first time access to the full velocity, density and stress fields inside of a dynamic avalanche, and allows us to experimentally validate granular rheological models.

Bio: Nathalie Vriend obtained her ingenieurs (B.Sc. and M.Sc.) degree in Mechanical Engineering (2004) from the University of Twente, The Netherlands and her M.Sc. (2005, in Aeronautics) and Ph.D. degree (2010, in Mechanical Engineering and Geophysics) from the California Institute of Technology, USA. After a short postdoctoral position (2010 – 2011) and obtaining a competitive personal postdoctoral fellowship (2011 – 2013), she started her own research group in 2014 at the University of Cambridge. Since January 2014, Nathalie has been group leader and Royal Society Research Fellow, first as a Dorothy Hodgkin Research Fellow in DAMTP (Department of Applied Mathematics and Theoretical Physics) and now as a University Research Fellow at the BP Institute, both at the University of Cambridge. Her research program on granular materials involves detailed laboratory experiments and targeted field work, but she also employs numerical simulations and theoretical modelling to complement observations, often in collaboration with scientists from multidisciplinary fields. She has active projects in granular rheology and avalanching, dune structure and migration, and sound propagation. In the past she worked on the dynamics of real snow avalanches, singing sand dunes and seismic wave propagation.

NOTE: At this time, in-person Mechanical and Civil Engineering Lectures are open to all Caltech students/staff/faculty/visitors with a valid Caltech ID. Outside community members are welcome to join our online webinar.

Zoom link: https://caltech.zoom.us/j/84507084178?pwd=VUpmRW9OM0NvcG92MU1ySGZUcWg4UT09
Passcode: 626249