Barchan Swarm Simulations Using the Two-Flank Agent-Based Model

This archive contains several animations of barchan swarms simulated using the Two-Flank Agent-Based model introduced in following article:  

Robson, Dominic T., and Andreas CW Baas. "A Simple Agent‐Based Model That Reproduces All Types of Barchan Interactions." Geophysical Research Letters 50.19 (2023): e2023GL105182.  

which is Open Access and available at  https://doi.org/10.1029/2023GL105182

The Two-Flank Agent-Based Model has been developed openly on GitHub by Dominic T Robson and Andreas CW Baas.  All the necessary source files together with an example run file can be found at:

https://github.com/DTRobson/TwoFlankABModel/releases/tag/ABM

The following model parameters and initial conditions were used for all these simulations:

   simwidth = 15000 #(m)

   simlength = 8000 #(m)

   fieldwidth = 5000 #(m)

   qsatinit = 79 #(m^2 year^{-1})

   q0 = 0.25 #(q_sat)

   dt = 1/12 #(years)          

   collson = True

   inject = True

   injectdist = Uniform                

   periodic = False

   lambda1 = 1.

   lambda2 = 1.8

   lambda3 = 1/3

   alpha = 0.05

   delta = 4.6 #(m)

   eqw = 2.3/(q0 - 0.05)

   injectparams = [2*eqw, 2*eqw]

   lws = [eqw]

   rws = [eqw]

   xs = [fieldwidth*1.5]  

   ys = [simlength - 1]

   c = 45.  

   w0 = 16.6 #(m)

   outfluxmode = 'Hersen'

   plottinghornflux = False

   keep_coll_rec = True

   helpplotting = True

The remaining model parameters varied across the different runs and took the values shown in the filenames.  Where the filename does not list the angular separation of the secondary wind mode (thetab) simulations were unidirectional.  The primary mode was normally distributed with mean 270degrees and standard deviation theta_sd. The list of all values used are shown here:

   initdensity = 12 or 24 or 37 or 61 #(km^{-2}) this sets the rate at which dunes are injected into the model

   qshift = 0. or 0.1 or 0.2 or 0.3 or 0.4 #(q_sat)

   thetab = 36 or 72 or 108 or 120 #(degrees)

   theta_sd = 3 #(degrees)  

In bimodal simulations the secondary mode angle was normally distributed with mean 270+thetab and standard deviation theta_sd.  Each year (12 iterations) the first 9 iterations had wind direction taken from the primary mode and the final 3 iterations were from the secondary mode i.e. the 3:1 seasons of primary:secondary wind direction.  Note that, in the simulations the primary mode 270deg means that dunes migrate in the negative y-direction, to produce the plots and revert to the convention of the primary wind being in the x-direction, the dunes were then rotated.

The archive contains two folders, the first shows animations of the swarms only with each frame taken as the final state of each year of the simulation.  The second folder shows the same simulations but alongside several properties of the swarms:

   The mean dune width and population size

   Normalised histograms of the dune width

   Normalised histograms of the ratio of port and starboard widths of the dunes.

The simulations were performed by Dominic T Robson using a 12th Gen Intel(R) Core(TM) i7-1255U   1.70 GHz processor and 16.0GB of RAM.