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

[Brad Aagaard]

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