[CIG-SHORT] pylith error in model with big time step and low viscosity

[Brad Aagaard]

David,

I am not sure what you mean by adding a second viscous layer with a high 
viscosity. The rate of the viscoelastic deformation is controlled by the 
material with the smallest viscosity, so as long as a low viscosity 
material is present, the appropriate time step to resolve the 
deformation will be small.

Regards,
Brad


On 06/10/2016 02:18 PM, David Rodrigo Mora Cofré wrote:
> Mr.Brad Aagaard:
>
> Thank you very much. I will check the manual. I think that adding a
> second viscous layer (with high viscosity) will fix the problem.
>
> best regards,
> David.
>
> 2016-06-10 12:28 GMT-03:00 Brad Aagaard <baagaard at usgs.gov
> <mailto:baagaard at usgs.gov>>:
>
>     David,
>
>     The error message you are getting is associated with a built-in
>     check that compares the Maxwell relaxation time with the time step.
>     PyLith generates an error if the time step is greater than 1/5 of
>     the Maxwell time. This insures that the simulation will be able to
>     resolve the viscoelastic deformation with a reasonable accuracy.
>
>     It is possible to circumvent this by using the TimeStepAdapt time
>     stepper with a stability factor much less than 1.0, but you should
>     be aware that your simulations will have significant errors in
>     resolving the viscoelastic relaxation.
>
>     Regards,
>     Brad
>
>
>     On 06/10/2016 08:07 AM, David Rodrigo Mora Cofré wrote:
>
>         Mr.Brad Aagaard:
>
>         I'm testing a surface load model with 2 elastic layers + 1
>         viscoelastic
>         layer  for study a postglacial rebound. When i use a viscosity
>         1.0e21
>         Pas (dt=100*year), pylith computing my model very well. But,
>         when a use
>         a viscosity =<1.0e20 Pas (dt=100*year , total_time=10000*year),
>         pylith
>         not computing my model because my dt > stable time step.  The stable
>         time step suggested by pylith is < 10*year. As this dt (<
>         10*year) is
>         very small, pylith will take long time to computing the model.
>         How i can
>         force to pylith to computing the model with dt>=100*year and a low
>         viscosity?
>
>         The following is the error message:
>         -------------------------------------------------------------------------------------------------
>
>         File
>         "/Users/rodrigo/fem/pylith-2.1.1-darwin-10.6.8/lib/python2.7/site-packages/pylith/problems/TimeStepUniform.py",
>         line 87, in timeStep
>
>               "step of %12.4e." % (self.dtN, dtStable))
>
>         RuntimeError: Current nondimensionalized time step of 1.0000e+02
>         exceeds
>         the nondimensionalized stable time step of   9.2050e+00.
>
>         application called MPI_Abort(MPI_COMM_WORLD, -1) - process 0
>
>         /Users/rodrigo/fem/pylith-2.1.1-darwin-10.6.8/bin/nemesis:
>         mpirun: exit 255
>         ---------------------------------------------------------------------------------------------------
>
>         best regards,
>
>         PhD(c) David Mora
>         Doctorado en Ciencias De La Tierra
>         Universidad de Concepción
>         Chile
>
>
>