[FLASH-USERS] hydrostatic models in flash

[dongwook at flash.uchicago.edu]

Hi Phil,

> Hi everyone,
>
> I'm working with the new flash 4 in 2.5 d simulating a white dwarf at
> sits in hydrostatic balance; the white dwarf has significant rotation
> and hence the 2.5 d.  However, I am finding that when I put in a
> hydrostatic white dwarf, the white dwarf initially oscillates a little,
> but soon these oscillations grow to be very violent over a few hundred
> seconds.  Obviously there is a source of energy that is being tapped.
>
> Looking at Zingale et al (2002, ApJ 143, 539), it seems that one thing
> might be that these oscillations arise from the imperfect cancellation
> between pressure and gravity.  What he did was to subtract out \rho g
> from pressure gradient before calculating the state.  This was
> implemented in the PPM code and can be turned on with the
> ppm_modifystates = .true. flag.
>
> As I am using 2.5 d (and hence, the unsplit solvers), I don't have this
> same luxury.

You can still check your simulations runs as you expected by using the
split PPM solver for the testing purpose if needed. But in order to
understand your concern correctly, I would like to understand more on your
statement "2.5d (and hence, the unsplit solvers)". Can you explain this to
me more?

> However, as I am reading FLASH, it seems that this
> cancellation may be built in.  In particular, for the unsplit solvers,

Just to understand correctly: You say "unsplit solvers". And I am guessing
you are using the unsplit "hydro" solver, rather than the MHD one,
correct?

> it seem that gravity is used to calculate the various fluxes.  But I am
> not sure.  Is there some combination of use_gravHalfUpdate,
> use_gravConsv, or use_GravPotUpdate in the unsplit solver that would
> have the same effect as ppm_modifystates = .true. in the split PPM solver?

Such implementation of ppm_modifistates=.true. in the split PPM solver has
not been implemented in the unsplit (hydro & MHD) solvers, but it can
certainly be done easily.

As for those gravity switches, the choices you want to use are the
following (although they are not giving you the same effect as
ppm_modifystates=.true.):

use_gravHalfUpdate = .true.
use_gravConsv = .false.
use_gravPotUpdate = .false.

If you wish you can send me your log file and flash.par, I will have a
look at them.

Thanks,
Dongwook

> Cheers,
> Phil
>
>

=========================================
Dongwook Lee, Ph.D., Research Scientist
The Flash Center for Computational Science
The University of Chicago
5747 S. Ellis Ave., Room 319
Chicago, IL 60637
(773) 834-6830