Mark Stock

DLA-ND

dla-nd is an open-source, ANSI C, arbitrary-dimensional, stand-alone, off-lattice diffusion-limited aggregation simulator. It uses a 2^D-tree system for hierarchical space subdivision and can take into account a number of extra model parameters including stickiness and bulk motion. It correctly recreates the theoretical mass dimensions of DLA clusters in 2 and 3 dimensions (1.715 and 2.5, respectively). It is a rewrite of dla3d, a code which was spontaneusly written in December of 2003.

Files

Head to dla-nd on github.

Features

dla-nd supports the following features

Automatic, persistent, adaptive 2^D-tree space subdivision
Statistically-correct particle motion bias (bulk motion) numerically solves quartic equation each step
Stubbornness (Nittman and Stanley's artificial surface tension model)
Tunable stickiness and grippiness
2-d or 3-d density field construction
Raw, Radiance, and generic OBJ output for particle positions and connectivities
PNG and ASCII PGM output for particle locations and density field
Restart from an old simulation, or merge multiple simulations using raw .part files

Images

101k particles aggregating in 2D, all other options are off; 80 minutes on P4-1.6 run09.dnd run09.mpg (5.8 MB)

102k particles aggregating in 3D, all other options are off; 8 hours on P4-1.6 run10.dnd run10.mpg (3.7 MB)

101k particles aggregating in 4D, all other options are off; 21 hours on Athlon 2500+ run12.dnd run12.mpg (1.4 MB)

107k particles aggregating in 2D, stickiness changed from default of 1.0 to 0.1; 6 hours on P4-1.6 run11.dnd run11.mpg (5.6 MB)

100k particles aggregating in 2D, stickiness changed from default of 1.0 to 0.01; 11 hours on P4-1.6 run13.dnd run13.mpg (7.5 MB)

100k particles aggregating in 2D, with deprecated "rotex" growth corresponding to source and vortex influences located at the origin; 11 hours on P4-1.6 run14.dnd run14.mpg (11 MB)

100k particles aggregating in 2D, with bulk motion; 10.5 hours on P4-1.6 run15.dnd run15.mpg (6.7 MB)

102k particles aggregating in 2D, with 0.9 grip---effectively behaves as if the particles were 10 times as small, but with the same contact radius; 12 hours on P4-1.6 run16.dnd run16.mpg (3.4 MB)

100k particles aggregating in 2D, with new "chiral" growth, radius = 500, exponent = 2; 21 minutes on P4-1.6 run24_01.dnd run24_01.mpg (3.5 MB)

100k particles aggregating in 2D, with new "chiral" growth, radius = 500, exponent = 0.04; 21 minutes on P4-1.6 run24_02.dnd run24_02.mpg (3.1 MB)

For more simulations possible with dla-nd, see the dla3d page.

Future plans

Future versions of dla-nd may address the following needs:

Impart preferential circumferential motion on the incoming particles, such to create branching structures with directionality---chirality or rotex growth.
Use existing infrastructure from part-nd to compute a gradient field, and thus additionally bias the incoming particles' motion.
Use pthreads to allow multithreading, thus using all available cores or processors on an SMP machine.
Create symmetry in the resulting structures by multiply adding each new particle.
Set the resulting segment radii such that the bending strain at each segment is equivalent---resulting in thicker segments at the core, and thinner ones at the tips.

Please e-mail me if you'd like to see some particular feature in dla-nd, or if you use it to make something creative.

References

P. Meakin and T. Vicsek, Diffusion-limited aggregation with radial bias, Journal of Physics A 20 L171-L175 (1987)

J. Nittman and H.E. Stanley, Tip splitting without interfacial tension and dendritic growth patterns arising from molecular anisotropy, Nature 321, 663 (1986)

T. Witten and L. Sander, Diffusion-limited aggregation, Physical Review B 27, 5686-5697 (1983)