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The particulars of particulates
Nathalie M. Vriend, DAMTP, April 20th, 2016PhD-students: Josh Caplan, Matthew Arran, Jonny Tsang, Amalia Thomas,
PDRA: Andrew Edwards, MSc-student: Elze Porte
Collaborators: Michel Louge (Cornell), Karen Daniels (NCSU)
Granular Research
Phase?
Scale?
Solid particles of different shape, density and/or size
Separate, collide & interact due to a variety of physical processes
Constitutive relations for all scales and phases do not exist
Applications of granular materials
Industrial processes:
Fabrication: pharmaceutics
Transport & storage: oil/gas, bulk goods
capacity loss, quality assurance
Nature’s geophysical processes
Geophysical mass flows (snow avalanches,
rock slides, debris flows, landslides, …)
mobility and run-out
Dune formation & migration (Earth, Mars)
desertification, sand transport
Credit: Petter E. Bjørstad
M.L. Hunt & N.M. Vriend, Annual Review
of Earth and Planetary Sciences, 2010
My granular interest…
My first (scientific) love: desert dunes
Mechanical engineering background
Booming sand dunes: “desert ghosts”
Wave propagation in sand
Coarse-grained structure: rain-events
Popular & scientific media attention
Cambridge work:
What happens at the grain-scale?
Fine-grained structure: avalanches
How does this connect back to large-scale?
Micro-macro scaling? Laboratory experiments & repeatability
Outline: our particulate work
Pattern formation across scales:
Granular segregation
Dune migration processes
Wave propagation through grains
Nonlinear and linear interactions
Photoelasticity in granular avalanches
Failure & avalanching:
Avalanching sequence on an erodible bed
Theme 1: Pattern formation
Size, density & shape segregation:
Cause: various physical processes
Gravity, rotation, shear, shaking
Effect: separation of particles
Large to the top, small to the bottom
Kinetic sieving & squeeze expulsion
Consequence: major effects in flow
Non-uniformities
Change of the overall behavior
Altered run-out of avalanches
Segregation (1)
Parameters:
= 25º
Compartment:
4x10x15cm
Monodisperse:
1kg released
White ballotini
Sieved:
0.425 – 0.600 mm
Work with Elze Porte (MSc-student)
Segregation (2)
Parameters:
= 25º
Compartment:
4x10x15cm
Monodisperse:
1kg released
Red ballotini
Sieved:
1.00 – 1.30 mm
Segregation (3)
Parameters:
= 25º
Compartment:
4x10x15cm
Bidisperse:
1kg released
50% red - 50%
white ballotini
Sieved:
1.00 – 1.30 mm &
0.425 – 0.600 mm
Segregation in avalanches (rigid bed)
Segregation in a closed-end 2D channel (†)
Bidisperse mixture segregates
Granular bore, frozen deposit
Concentration & velocity profiles
† Work with Andrew Edwards (PDRA), submitted to Physical Review Fluids
Segregation in avalanches (erodible)
Segregation in depth: alternating pattern
Goal: understand effect particle size in meso-structure
Continuous avalanching, layer formation, self-organization
Pattern formation in a dune corridor: lab set-up
† Work with Prof. Michel Louge (Cornell)
Theme 2: wave propagation
Connection between nonlinear small-scale …
Hertzian deformation
Force chains
… and linear large-scale:
Industrial seismic surveys (CASE): effect of sand dunes Dunes create noise in surveys for oil & gas (Schlumberger, †)
Computer simulations with SpecFEM3D on wave propagation
Reverberations within the dunes are significant
† Work with Matthew Arran (PhD-student)
and Everhard Muyzert (Schlumberger)
Forces in small-scale
Photoelasticity in granular systems (†):
Particle shows change of refractive index when stressed
Stress-Optic law:
† Work with Amalia Thomas (PhD-student)
“Force chains”“Calibration”
Segregation in avalanches
Avalanches of photoelastic particles:
Resolve fringes: high spatial resolution
Collisions: short-lived interactions
What goes on in the larger system?
Anticipated future work:
Large-scale force localizations
Tracking grain- and bulk-interactions concurrently?
photoelastic particle with piezoelectric wire in centre
† Work with Amalia Thomas (PhD-student) & Professor Karen Daniels (NCSU)
Theme 3: Rheology and failure
Avalanche statistics on erodible beds
Goal: discrete avalanches on an erodible bed
Slow sand inflow: 4mm or 6mm nozzle
Inclined (32º) channel: 2m long, 5cm wide
† Work with M. Arran (PhD-student)
Dynamic intermittency: two regimes
First-time observation!
Quasi-periodic, no stopping:
Avalanches at constant intervals
Run-out beyond end of chute
1st order phase transition
Irregular, stacking on slope:
Avalanches at variable intervals
Most stop part-way down chute
Sometimes clearing of deposit
2nd order phase transition
Delving deeper: frequency, length
Modelling avalanches on erodible beds
Dynamic intermittency, effect of erosion & deposition
Rheology modelling, including instabilities
“long-term profile variation in time”
Conclusion: our granular research
Pattern formation:
Granular segregation under gravity
Bridge physics of dune-building across scales
Wave propagation:
Custom-made photoelastic particles
Granular processes micro/macro-scale
Rheology and failure:
Erosion and deposition processes
Instabilities in granular flows
