[FLASH-USERS] Resistive MHD

[ERNESTO ZURBRIGGEN]

Hi Matthew!
The answer to your questions is: it depends.
In order to include "standard" magnetic resistivity in your simulation (see
the section 15.3.5.3, user guide release 4.8),
you need to set up the runtime parameters:


*useDiffuse            =.true.useMagneticResistivity=.true.resistivity
      =some_value *

And to choose among the available implementations, e.g.: the ”Constant”
version, ”SpitzerHighZ”, as well as the ”DaviesWen”.
For which you need to add the right path in the Config file, e.g.:


*# For Constant resistivityREQUIRES
physics/materialProperties/MagneticResistivity/MagneticResistivityMain/Constant*




*# For SpitzerHighZ resistivityREQUIRES
physics/materialProperties/MagneticResistivity/MagneticResistivityMain/SpitzerHighZ*
*# For DaviesWen resistivity*
*REQUIRES
physics/materialProperties/MagneticResistivity/MagneticResistivityMain/DaviesWen*

But, you may also want to consider *"extended MHD" *(see section 15.3.5).
With this you can consider more MHD effects:
Hall, Biermann battery, anisotropic magnetic resistivity, Seebeck,
Nernst, and cross-field terms.
The runtime parameter useCrossMagRes enable/disable the anisotropic
magnetic resistivity.

So, if you want to include anisotropic magnetic resistivity in your
simulation, you need to enable useCrossMagRes,
otherwise you don't.

Best.
Ernesto.







On Fri, 30 Jan 2026 at 10:33, Matthew Trantham <mtrantha at umich.edu> wrote:

> Dear Users and Developers,
>
> I am confused regarding the implementation of resistive MHD. In the
> manual, it implies that you need to use the term useCrossMagRes = .true.,
> but without the Hall, this is turned off by the code.  I also noticed that
> example problems like ZPinch don't use this term (useCrossMagRes). Is it
> needed?
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