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TurbSim CPU Times

Posted: Thu Dec 23, 2010 1:24 pm
by Bonnie.Jonkman
I occasionally get questions regarding the approximate time that it takes to create large grids in TurbSim, so I thought I would post some plots to illustrate the relationship between the number of grid points (on an n by n grid) and computation time. The computation time is dominated by the Cholesky decomposition of an n^2 by n^2 matrix at each time step.

These plots were created using the IECKAI model with TurbSim v1.50 (non-IEC models can take at least 2 times longer because they compute a Cholesky decomposition on the v- and w- wind components as well). I used AnalysisTime = 600 seconds and TimeStep = 0.05 seconds, and I ran this on a 32-bit WinXP Duo Core CPU (2.83 GHz) with 4 GB RAM. For each simulation, I used the same input file, changing only NumGrid_z and NumGrid_y (which are equal in each case), and plotted the CPU time listed at the end of the simulation.

Here are the results, plotted in two different ways:
TurbSim_Timing_1.PNG
TurbSim_Timing_1.PNG (12.77 KiB) Viewed 18327 times

TurbSim_Timing_2.PNG
TurbSim_Timing_2.PNG (16.34 KiB) Viewed 18327 times


The 41 x 41 grid required a little less than 0.5 GB RAM, so all of these cases ran well within memory.

NOTE: I used a 10 m/s mean hub-height wind speed and 140 m x 140 m grids for these simulations. Interestingly, when I ran the 17 x 17 case using 12.368 m/s and a 50 m x 50 m grid instead (everything else was the same), the CPU time increased from approximately 39 s to 94 s. This is due to the fact that the coherence matrix is more difficult to factor. Keep this in mind when comparing specific CPU times with these plots.