1141 Catalina Drive, PMB #270

Livermore, CA 94550

[This site is still (occasionally) under construction 19 Nov 2015]

Click Here to go to Branden's Page

Selected Papers/Presentations & Simulation videos:

Poster Presentation from 2013 Lunar Science Forum (virtual workshop) describing the simulations in the following videos (pdf) "Micro Gravity Screw Conveying: Robust and Efficient. Is This Possible?"

Vertical Screw Conveyor
"Simulation of vertical 0.75in dia screw conveyor, "

"Sliced image of vertical 0.75in dia screw conveyor, "

"Review of Adhesion Fundamentals for Micron-Scale Particles (pdf)" OR Walton, KONA Powder and Particle Journal No.26, 129-141(2008)

"Effects of Interparticle Friction and Particle Shape on Dynamic Angles of Repose via Particle-Dynamics Simulation, (pdf)" OR Walton, Workshop on Mechanics & Stat. Phys. of Particulate Mat'l, (1994) La Jolla, CA

Grainflow Dynamics
"Simulation of cohesive powder flow in a rotating drum, "
200 micron particles each particle represented as a small clusters of 8 smaller (100-micron) spheres
in a cubical geometry. Cohesive pull-off force set to ~1% of theoretical
van der Waals force for 200mJ/m^2 surface energy. Periodic boundaries along axis.
Colors are for visualization convenience only. (July 2008).
[click on title or figure above to download Quick-Time mov (~14Mb)]

Grainflow Dynamics
"Simulation of cohesive powder flow in a rotating drum under Lunar gravity conditions, "
(July 2008).
[click on title or figure above to download Quick-Time mov (~14Mb)]

Grainflow Dynamics
"Simulation of weak powder flow in a rotating drum, "
200 micron particles each particle represented as a small clusters of 8 smaller (100-micron) spheres
in a cubical geometry.

Grainflow Dynamics
"Simulation of weakly-cohesive powder flow in a rotating drum under Lunar gravity conditions, "
(July 2008).
[click on title or figure above to download Quick-Time mov (~14Mb)]

Grainflow Dynamics
"Simulation of very cohesive powder flow in co-axial rotating drums, "
600 micron particles each particle represented as a small clusters of 8 smaller (300-micron) spheres
in a cubical geometry. Cohesive pull-off force set to 25e-6N, approximately equal to theoretical
van der Waals force for 18mJ/m^2 surface energy. Periodic boundaries along axis.
Colors are for visualization convenience only. (April 2009).
[click on title or figure above to download Quick-Time mov (~20Mb)]

Selected Publications:

Walton, O.R.
"Dust-Off 2005 a.k.a. 'Dunes Bury' USA,"
Grainflow Dynamics informal report, NASA contract NNM05AA88C, Oct 2005.
[click on title or figure above to download pdf (~650Kb)]

Walton, O.R., C.P. De Moor, and K.S. Gill
"Effects of gravity on cohesive behavior of fine powders:
implications for processing Lunar regolith,"
Preprint: *Granular Matter* (to appear 2007)
[click on title or any figure above to download pdf (~930Kb)]

Walton, Otis R., "Potential discrete element
simulation applications ranging from airborne fines to pellet beds,"
*SAE 2004 Transactions J. Aerospace* paper 2004-01-2329
[click on title or any figure above to download pdf (~413Kb)]

Walton, O.R., and R.L. Braun,
"Simulation of Rotary-Drum and Repose Tests for Frictional Spheres and Rigid Sphere Clusters,"
*Joint DOE/NSF Workshop on Flow of Particulates and Fluids* Sept. 29 - Oct. 1, 1993,
Ithaca, NY [click on title or figure above to download pdf (~4Mb)]

Walton, O.R.,
"Numerical simulation of inclined chute flows of monodisperse, inelastic, frictional spheres,"
* Mechanics of Materials * **16 ** (1993) 239-247. [click on title or figure above for pdf
(~600Kb)]

Walton, O.R.
"Chapter 25: Numerical Simulation of Inelastic Frictional Particle-Particle-Interactions,"
*Particulate Two-Phase Flow* M.C. Roco, ed., Butterworth-Heinemann, 1993,
Stoneham, MA [click on title or figure above to download pdf (~5.4Mb)]

[click on figure above for large mpg file (~90MB) of simulation from NEPTIS-1 of small spheres flowing through an fcc array of large spheres] or on .avi or .mov symbol below for other formats of same video.

Walton, O.R.,
"Simulation of Gravity Flow and Packing of Spheres,"
* Nisshin Eng. Powder Tech. Int'l Seminar (NEPTIS-1)* Osaka, Japan (1993). [click on title or figure above for pdf
(~7.4Mb)]

Walton, O.R., D.M. Maddix, T.R. Butkovich, and F.E. Heuze
"Redirection of Dynamic Compressive Waves in Materials with Nearly Orthogonal and Random Joint Sets,"
AMD Vol. **117** p65-73, *Recent Advances in Mechanics of Structured Continua * M. Massoudi and K.R. Rajagopal, ed., ASME, 1991
[click on title or figure above to download pdf (~660Kb)]