[aspect-devel] Question on Thermal Viscosity thresholds

[FELIPE ORELLANA ROVIROSA]

 Hi Lev,

      Thanks a lot for replying.

       I am referring to section A.77 Parameters in section Material model

             then subsection model 'simple'

Temperature prefactor for viscosity:

      there is a definition tau(T) = H(exp...), H(x) = { .. 3 cases..}

     I have inspected the formula several times and it seems to me that it
would create a discontinuity if the values {tau min, tau max} are not {0.01
and 100}.

     I plotted the formula on matlab using values different than those, and
indeed created a discontinuity. ALternatively, depending on how you program
the formula, it will leave an unspecified interval.

     It's nothing grave I think, but if one is not wary when using the
model parameters tau max-min, the issue could get under the hood.

cheers,
thank you.

Felipe


On Wed, Apr 25, 2018 at 10:44 PM, Lev Karatun <lev.karatun at gmail.com> wrote:

> Hi Felippe,
>
> I didn't write the plugin, but I'll try to give you an answer based on
> looking at the code and the manual.
> As long as temperature range is continuous, I don't think there will be
> any discontinuities in the viscosity. Thermal prefactors (which are set
> using the "Maximum thermal prefactor" and "Minimum thermal prefactor"
> parameters) are just limiters, they don't add any non-linearity into the
> calculations. If you make the range too wide, the solver might have
> problems converging, but other than that it should be fine. Is this what
> you were asking?
>
> As a side note, a new version of the manual is generated every day, so
> page numbers aren't too helpful to locate the part you're referring to.
> Maybe you could quote it instead or specify a section title?
>
> Best regards,
> Lev Karatun.
>
> 2018-04-25 16:50 GMT-04:00 FELIPE ORELLANA ROVIROSA <
> f_orellana at berkeley.edu>:
>
>>
>>  Hi,
>>
>>       Hope you guys are having a nice day.
>>
>>        I am crafting and trying different models on a 3D convecting
>> system, and considering Temperature-dependent viscosity among other things.
>>
>>        For the material model 'simple', the viscosity depends on
>> temperature as a negative exponential (a classic), but some
>> thresholds/bounds are imposed on it.
>>
>>        According to Aspect manual 1.5.0, page 289; if the exponential is
>> out of the bounds [ 0.01 , 100 ], that part of the viscosity will assume
>> the user-defined threshold values given by (Tau min, Tau max). Later the
>> amplitude will be given by the scaling constant eta0.
>>
>>        But, if a user chooses values for {Tau min, Tau max} different
>> than {0.01 , 100}, then discontinuities in viscosity will be produced over
>> the temperature range.
>>
>>        The question is the following: are those limits 10^-2 < x < 10^2
>> only a handbook example?, or will those limits assume the user-specified
>> values of Taumin, Taumax?
>>
>> warm regards,
>> Felipe
>>
>>
>>
>>
>>
>>
>> _______________________________________________
>> Aspect-devel mailing list
>> Aspect-devel at geodynamics.org
>> http://lists.geodynamics.org/cgi-bin/mailman/listinfo/aspect-devel
>>
>
>
> _______________________________________________
> Aspect-devel mailing list
> Aspect-devel at geodynamics.org
> http://lists.geodynamics.org/cgi-bin/mailman/listinfo/aspect-devel
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.geodynamics.org/pipermail/aspect-devel/attachments/20180425/b77a61de/attachment.html>