[CIG-SHORT] Time step

[Christian Baillard]

Brad,

I better understand why it didn't work then. The values that I took for viscosity are related to oceanic asthenospheres, I'll test it using 1e20 Pa.s.

Regards,

Christian

Le 11 nov. 2013 à 18:09, Brad Aagaard a écrit :

> Christian,
> 
> For linear viscoelastic models in quasi-static simulations, we define the stable time step to be 0.2 times the Maxwell time (viscosity / mu). This should result in sufficient resolution of the relaxation process. For your relatively low viscosity and larger shear modulus, the relaxation time is very short (less than 0.3 years).
> 
> We seem to be missing a discussion of the stable time step for quasi-static simulations in the PyLith manual. We will add in this section for the next release.
> 
> Regards,
> Brad
> 
> 
> On 11/11/13 8:47 AM, Christian Baillard wrote:
>> Hi Brad,
>> 
>> Here are my .spatialdb for the lithosphere and the asthenopshere. I use a viscosity of 5.0e+17 for the visco-elastic asthenosphere. For the elastic part I use a density of about 3300 kg/m3  and Vp / Vs are taken from the IASP model.
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 'E' stands for East, The two lithospheres(/astheno) on both side of the trench have the same parameters.
>> I run a quasi static simulation, convergence rate is 3.5 cm/yr
>> Here is the parameter file for simulation
>> 
>> 
>> 
>> 
>> 
>> And my mesh looks like that:
>> 
>> 
>> 
>> 
>> 
>> 
>> Regards,
>> 
>> Christian
>> 
>> Le 11 nov. 2013 à 17:34, Brad Aagaard a écrit :
>> 
>>> On 11/11/13 4:23 AM, Christian Baillard wrote:
>>>> Hi developers,
>>>> 
>>>> I do not want to stuff up the mailing list with all of my problems so that's why I'm sending this message to you personally.
>>>> When running pylith I have a problem with the time step:
>>> 
>>> Please keep sending to cig-short at geodynamics.org. As Matt said, all users benefit from hearing the questions and responses.
>>> 
>>>> File "/Users/baillard/pylith/pylith-1.9.0-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   5.0000e+00 exceeds the nondimensionalized stable time step of   4.6202e-02
>>>> 
>>>> I use the same dt (5 yr)  and total_time (100 yr) as in the example given in the 2d/subduction problem.
>>>> I really appreciate the support you are giving, it helps me a lot.
>>> 
>>> We need more info to understand what is causing PyLith to calculate a stable time step much smaller than your time step. Are you running a quasi-static or dynamic simulation? What bulk rheology and corresponding parameters are you using?
>>> 
>>> Regards,
>>> Brad
>>> 
>> 
> 
>