Mechanics of granular column collapse in fluid


Krishna Kumar, kks32@cam.ac.uk
University of Cambridge

Jean-Yves Delenne, INRA, University of Montpellier 2, France.

Kenichi Soga, University of California, Berkeley.



Reggio Calabria, Italy
30th May 2018

Mechanism of submarine landslides

Modelling Test at 1g Condition

  • Material type influences the mode of the flow.
  • Target: Clay‐rich flow (Less diffusive, Hydroplaning).

LBM - DEM simulation of granular collapse in a fluid




aspect ratio 'a' of 6

Lattice Boltzmann - MRT

Real Fluid vs LBM Idealisation
LBM D2Q9 Model

\[f_{i}(x + dx, t +\Delta t) - f_{i}(x, t) = -S_{\alpha i}( f_{i}(x, t) - f_{i} ^ {eq}(x, t))\]
  • $S_{\alpha i}$ is the collisional matrix.
  • Probability density of finding a particle : $f(x,\varepsilon, t) $, where, x is position, $\varepsilon$ is velocity, and t is time.
Streaming
Collision

Granular collapse in a fluid: Effect of aspect ratio



aspect ratio 'a' of 0.4

aspect ratio 'a' of 4

Collapse in a fluid: Runout evolution

a = 0.4
a = 4

Critical time $\tau_c=\sqrt{H/g}$ (Staron and Hinch, 2005)
where, H = Height of the granular pile.

Runout: dry vs fluid

Dry collapse flowed further than the underwater collapse

Collapse on an inclined plane




aspect ratio 'a' of 6 on a slope of 5*

Collapse of a dense column on an inclined plane

aspect ratio 'a' of 0.8 on a slope of 5* (dense)

Collapse of a dense column on an inclined plane

aspect ratio 'a' of 0.8 on a slope of 5* (dense)

Collapse of a dense column on slopes: runout

aspect ratio 'a' of 0.8 (dense)

Collapse of a loose column on slopes: runout

aspect ratio 'a' of 0.8 (loose)

Loose v dense: Initiation phase

initial runout evolution ('a' of 0.8)

Loose v dense: Initiation phase

Loose
Dense

Pore-pressure distribution along the failure plane during initiation.

Loose v dense: Runout phase

Attack angle ('a' of 0.8) $t = 3 \tau_c $

Loose v dense: Runout phase

Loose
Dense
Water entrainment front (~15d length) at a slope of 5*

Loose v dense: Runout phase

Froude's number - hydroplaning ('a' of 0.8)

Loose v dense: Effective stresses

Effective stresses at the bottom ~15d at the flow front at a slope of 5*

Loose v dense: Settlement phase

volume evolution ('a' of 0.8)

Collapse on slopes: loose v dense

runout evolution ('a' of 0.8)

LBM - DEM a = 0.8 & 10,000 particles



  • LBM Nodes = 50 Million : DEM grains = 10000 discs
  • Run-time = 4 hours
  • Speedup = 125x on a Pascal P100

Thank you!



Krishna Kumar, Kenichi Soga, and Jean-Yves Delenne

kks32@cam.ac.uk