Monday, 10/7: Friction and fingering.

B. Sandnes, E.G. Flekkøy, H.A. Knudsen, K.J. Måløy, K. J. and H. See, Patterns and flow in frictional fluid dynamics, Nature Comm. 2, 288, 2011.

Basic premise of paper: authors use a granular material that settles in a Newtonian fluid to explore displacement dynamics in frictional and viscous regimes.

Group Comments:

• Several people found the 3D plot confusing and would like to have seen two planes of data presented. The general consensus is that it would be easier to interpret.

• Discussed the Hele-Shaw cell, which is an excellent tool for visualizing 2D flows. It provides a good analog for poreous medium, and the mathmatics / theory is easier to develop in two dimensions.
  

• Group noted that the influence of vertical stratification on the grains could add a 3D effect to the experiments.

• Many of the references in the paper are fairly recent.

• The ordering of the paper was unique, the experiment was not strictly motivated by problems in the geosciences. Physicics often choose problems that are interesting or innovative.

• To continue this work, the group would vary the grain size and particle geometry.

• Noticed that bubbles occured near the front more often than the rear. Dicussed possibilities for why this may be happening and the physics involved.
  

• Discussed stick-slips, and if they play a role in different fluids / elastic materials.

• Mentioned frictional healing, Hertzian contact theory. Older bubbles may be surrounded by strongly bonded material.

• Discussed what the group thought about the figures, and what the best way was to convey the information in the paper. Figures 3 and 4 were chosen as the most effictive. The group felt the text was consise and well written.
  

• How were these experiments different from real-world geological mechanics? No gravity, homogenous material.