[CIG-SHORT] pylith time stepping

[Brad Aagaard]

Chris-

As Charles noted, the time step for the Maxwell model is independent of 
the deformation rate, so the adaptive time step is uniform. It does 
depend on the Maxwell time. The time step for an elastic material is 
infinite (actually 1.0e+30); any time step gives a numerically stable 
solution. If you use an elastic material with adaptive time stepping, 
the time step is 1.0e+30, so the number of time steps is being rounded 
off to 0. The output manager currently uses the number of time steps as 
a flag to decide whether it is writing "info" or "data". If the number 
of time steps is 0, it thinks it is writing "info".

The adaptive time stepping correctly writes "data" files when using a 
Maxwell model. See examples/3d/hex8/savageprescott.cfg.

Brad


Charles Williams wrote:
> At present, the automatic time stepping is controlled purely by the 
> Maxwell time (for viscoelastic materials).  Since the current 
> viscoelastic materials are all linear, the time step size is independent 
> of the deformation rate.  Once we include nonlinear materials (e.g, 
> power-law rheology), this will no longer be true.
> 
> We will have to look at the second thing you mention.  I don't think we 
> had noticed that before.
> 
> Thanks,
> Charles
> 
> 
> On 12/05/2009, at 3:55 PM, Christopher DiCaprio wrote:
> 
>> Hi,
>>
>> It's not clear to me what is supported for the nonuniform, automatic  
>> time stepping. The release notes for 1.3.0 say "For the current bulk  
>> constitutive models, the automatically determined time step is  
>> independent of the deformation rate, so it is uniform."
>>
>> The release notes for 1.3.1 don't mention time stepping, but the  
>> manual implies that there is support for non-uniform time steps.
>>
>> One other thing: when using nonuniform, automatic time stepping, the  
>> *_info.vtk files are overwritten with what should go in the  
>> *_t0000.vtk files. This doesn't happen when using user-specified time  
>> stepping.
>>
>> Thanks,
>> Chris
>>
>>
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> 
> Charles A. Williams
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