This project, originally part of my honor's thesis at Bucknell University entitled "The effects of convective flows on dendritic crystal growth," simulates the dynamics of ballistic aggregation in a macroscopic scale. This work was completed in 1996. The results are published in the Phys. Rev. E article, Solomon, et. al 60, p 3063-71 (1999).
Under the proper conditions, a saturated solution of NH4Cl will begin to solidify spontaneously. These small seed crystals will fall out of solution and migrate towards the bottom of the apparatus, their path influenced by the convective flows present in the system.
This is a Diffusion Limited Aggregation-based (DLA) model where the particle (a seed crystal) follows a (nearly) random walk towards the bottom of the screen weighted towards a particular angle. When it hits anything , it sticks irreversibly. The interesting phenomenon to observe are the voids or "gaps" that form in the evolving structure.
Originally, these programs were written in (Ugh!) GW-Basic for my Dad's 386. Since this time, I have compiled the programs in C++ for a Matrox Image Series video display, decreased the generation time from ~8 hours to 1 minute 30 seconds, and increased the resolution by an order of magnitude from ~10,000 particles to ~130,000 particles.
The hopes of this project are to show that the microscopic world of thin-film deposition has a macroscopic counterpart, namely the solidification of NH4Cl.
Simple sample source for QuickBasic (4.0) can be viewed here.
A standard 2-D model of variably-sized particles falling vertically downward.
In solution, very rarely do we find uniform downward flows. Thus, this represents a model where the particles stream in from an angle.
Large-scale (> 130,000 particles) simulation after image-processing to fill in holes and generally make it look more "real". Directly below, an actual image of the aggregate structure can be found. The scale is approximately 4 cm.
