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Hi Klaus,</div>
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Thanks so much for clarifying things.</div>
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Nitish</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> flash-users-bounces@flash.uchicago.edu <flash-users-bounces@flash.uchicago.edu> on behalf of Klaus Weide <klaus@flash.uchicago.edu><br>
<b>Sent:</b> Friday, June 19, 2020 4:42 PM<br>
<b>To:</b> flash-users@flash.uchicago.edu <flash-users@flash.uchicago.edu><br>
<b>Subject:</b> [EXTERNAL] Re: [FLASH-USERS] Adding viscous term in the momentum equation</font>
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<div class="PlainText">On Fri, 19 Jun 2020, Acharya, Nitish wrote:<br>
<br>
> In addition to last question, when I went through the manual it seems <br>
> DiffuseFluxBased implementation only works with PPM implementation of <br>
> the Hydro unit. How is this done for unsplit hydro solver?<br>
<br>
In a flux-based implementation of a diffusive term, the Hydro <br>
implementation does something to modify fluxes in flux arrays.<br>
(Paraphrased from the User's Guide.)<br>
<br>
When using split PPM Hydro: In the flux-based implementation of viscosity,<br>
the Hydro implementation calls Diffuse_visc to modify fluxes.<br>
Diffuse_visc is implemented in the DiffuseFluxBased subunit of the<br>
Diffuse unit.<br>
<br>
When using unsplit Hydro: In the flux-based implementation of <br>
viscosity, the Hydro implementation calls[*] hy_uhd_addViscousFluxes<br>
to modify fluxes. The subroutine hy_uhd_addViscousFluxes exists<br>
as part of the unsplit Hydro implementation; so strictly speaking,<br>
it may not be necessary to include the DiffuseFluxBased subunit<br>
since the corresponding functionality is already taken care of<br>
by the Hydro implementation.<br>
<br>
That is basically what the User's Guide is trying to say with the <br>
following sentence:<br>
<br>
| Other Hydro implementations, in particular the MHD implementations, <br>
| currently implement some diffusive effects in their own flux-based way <br>
| that does not use the DiffuseFluxBased unit.<br>
<br>
(The Hydro implementations mentioned here include Hydro_Unsplit.)<br>
<br>
[*] The calls are in hy_uhd_getFaceFlux.F90.<br>
Look at your favorite implementation thereof, <br>
find where hy_uhd_addViscousFluxes is called,<br>
and make sure that the relevant logical flags that enable<br>
the calls are all true. (Find corresponding runtime parameters.)<br>
That and including an implementation of Viscosity (the material <br>
property) in the configuration may be all that's needed.<br>
<br>
Klaus<br>
<br>
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