GfsTime

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Revision as of 15:21, 24 July 2012
GeordieMcBain (Talk | contribs)
(general tidy and rewrite, proceeding mention of suppression of initial projection when i>0)
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GeordieMcBain (Talk | contribs)
(noted that i>0 suppresses the divergence-free projection of initial velocity)
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GfsTime { t = 1.4 i = 32 end = 0 } GfsTime { t = 1.4 i = 32 end = 0 }
-and it will be found that this is done in the files produced by [[GfsOutputSimulation]] so that these can be used to restart runs. +and it will be found that this is done in the files produced by [[GfsOutputSimulation]] so that these can be used to restart runs. (''Technical note:'' if ''i'' is zero, as it is by default but not in a restart, the initial velocity field is projected onto the divergence-free subspace before the simulation begins.)
The ''end'' and ''iend'' identifiers specify that the simulation should stop when the floating-point model time reaches the given value or the prescribed number of steps have been taken, whichever comes first; either stopping criterion is ignored if its keyword is omitted. The ''end'' and ''iend'' identifiers specify that the simulation should stop when the floating-point model time reaches the given value or the prescribed number of steps have been taken, whichever comes first; either stopping criterion is ignored if its keyword is omitted.

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GfsTime defines the starting and finishing time for the run, either in terms of the floating-point model time or the integer time-step number, or a combination. By default both floating-point t and time-step number i are zero when the program starts, but it is possible to set different values using for example

 GfsTime { t = 1.4 i = 32 end = 0 }

and it will be found that this is done in the files produced by GfsOutputSimulation so that these can be used to restart runs. (Technical note: if i is zero, as it is by default but not in a restart, the initial velocity field is projected onto the divergence-free subspace before the simulation begins.)

The end and iend identifiers specify that the simulation should stop when the floating-point model time reaches the given value or the prescribed number of steps have been taken, whichever comes first; either stopping criterion is ignored if its keyword is omitted.

Another parameter, dtmax, can be used to cap the time-step, as in the Rayleigh–Taylor example

 Time { end = 1 dtmax = 5e-3 }
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