[MITgcm-support] The way to accelerate the calculation speed or to expand deltaT of MITgcm

[Jason Goodman]

On Oct 28, 2010, at 5:27 AM, 姊佹湅 wrote:
> 
> > Dear Sir:
> >         I'm trying to use the MITgcm to run an experiment.To
> > simulate this experiment 
> > successfully it is necessary to set the grid interval to be very
> > small.Now the number of the horizontal grids is 114*104,and the
> > number of the vertical grids is 139.The minimum interval of the
> > horizontal grids is 5 km ,and the minimum interval of the vertical
> > grids is 10m.And now I find that the maximum deltaT in the data file
> > to keep the model steady is 60s. The minimum time that is needed is
> > 30 years,so the minimum number of timesteps (nTimeSteps in the data
> > file)is 16000000.Now I have used 48 cpu to run the model,and it
> > needs 210 days to finish the calculation.The time is too long!! So
> > can you tell me how to  set the model parameters or modify the model
> > code to  accelerate the calculation speed or to expand deltaT.

If your fluid is strongly stratified, the deltaT is probably limited by
the frequency of oscillation of internal gravity waves.  If you're not
interested in gravity wave dynamics or strong vertical motion, you can
experiment with setting

nonHydrostatic=.FALSE.,
implicitIntGravWave=.TRUE.,

I have not used the implicit gravity wave solver: it may have risks I
don't understand.  But if it works it may allow you to increase the
timestep toward the Courant limit for horizontal motions -- dt < dx/U =
2000 seconds or so.  (Viscosity may need to be adjusted to allow this.)

BUT, if you really do need to look at flow with strong vertical motions
where gravity waves or non-hydrostatic effects are important, I don't
think you can do much better than what you have now.  You will have to
either decrease the vertical resolution or be satisfied with a much
shorter simulation than 30 years.