[FLASH-USERS] Sedov explosion in 3D reaches max simTime very fast without actually simulating the explosion

Ryan Farber rjfarber at umich.edu
Fri Jul 11 14:11:07 EDT 2025


Hi Sumit,

I'd say the best way to learn what parameters mean for your simulation is
to look at how they get used. For the Sedov problem, take a look in
/PATH_TO_FLASH/source/Simulation/SimulationMain/Sedov

More specifically, you can do "grep -rin sim_rInit *.F90" to see which
subroutines that parameter shows up in. Simulation_initBlock.F90 would be
the most important one to take a look at :)

Or, you can ask your favorite AI large language model. They were terrible
1-1.5 years ago, but they're good enough now perhaps. Asking Gemini this
prompt "what does sim_rInit do for the Sedov problem in the FLASH mhd
code?" resulted in the following.

In the FLASH MHD code, sim_rInit is a runtime parameter that plays a
crucial role in initializing the Sedov problem (also known as the
Sedov-Taylor blast wave problem).

Here's a breakdown of what it does:

   -

   *Defines the initial energy deposition region:* The Sedov problem models
   the self-similar evolution of a blast wave from a point-like energy
   release. In practice, since a true "point" is impossible to simulate
   numerically, the energy is deposited within a small, spherical (or
   cylindrical/1D) region at the center of the grid. sim_rInit specifies
   the *radius* of this initial energy deposition region.
   -

   *Calculates initial pressure:* The energy sim_expEnergy is deposited
   into this volume defined by sim_rInit. The initial pressure within this
   region (p'0) is then calculated based on the total energy, the adiabatic
   index (γ), and the volume of this initial region. The specific formula
   depends on the geometry (1D, 2D cylindrical, or 3D spherical).

   For example, for spherical geometry, the pressure p0′ inside the initial
   volume is given by:

   p0′=(n+1)Vinit3(γ−1)E

   where E is sim_expEnergy, n is the dimension (3 for spherical), and Vinit
   is the initial volume defined by sim_rInit.
   -

   *Impact on discretization and accuracy:* As noted in the FLASH
   documentation, while the theoretical Sedov solution assumes a point-like
   energy source, numerical simulations use a finite volume. The choice of
   sim_rInit affects the accuracy of the initial energy deposition and how
   well it approximates a point source. Increasing sim_rInit (or increasing
   the effective resolution) can help minimize discretization effects and
   achieve a closer approximation to the input total energy.

In essence, sim_rInit allows you to control the size of the initial
"explosion" region, which is critical for setting up the Sedov problem
correctly and influencing the numerical accuracy of the simulation's early
stages.

Best wishes,
--------
Ryan


On Fri, Jul 11, 2025 at 9:26 AM Sumit Banerjee <sumitb at g.clemson.edu> wrote:

> Ryan,
>
> Thank you very much. I think your solution worked. I will let you know
> what I find.
>
> Would you mind explaining what these parameters mean and how they impact
> the simulation? If there is a section in the user guide that explains this,
> let me know and I shall refer to it.
>
> *Clear Skies,*
> *Sumit (Sam)*
>
>
> On Thu, Jul 10, 2025 at 10:55 AM Ryan Farber <rjfarber at umich.edu> wrote:
>
>> Hi Sumit,
>>
>> Thank you for attaching your log file. You set sim_rInit to ~ 0.01 but
>> your linear box dimensions are 1. That means the initial linear resolution
>> is 0.125 > sim_rInit and no refinement occurs.
>>
>> Increase lrefine_min (or the similar parameter for the initial
>> refinement) or increase sim_rInit.
>>
>> Best wishes,
>> Ryan
>>
>> Sent from my iPhone
>>
>> On 10. Jul 2025, at 07:13, Sumit Banerjee <sumitb at g.clemson.edu> wrote:
>>
>> 
>> Ryan,
>>
>> My bad. That was a type indeed. I meant the parameters zmin and zmax. I
>> cross checked them in the par file and they appear fine. I have attached
>> the parameter file here for your reference. Also attached is the log file
>> generated by the run.
>>
>> Let me know if you find something.
>>
>> *Clear Skies,*
>> *Sumit (Sam)*
>>
>>
>> On Wed, Jul 9, 2025 at 6:57 PM Ryan Farber <rjfarber at umich.edu> wrote:
>>
>>> Hi Sumit,
>>>
>>> The parameter names are zmin and zmax, not z_min and z_max. Maybe that’s
>>> one issue.
>>>
>>> Anyway, from what you shared there’s just a single block (no refinement
>>> occurred). The question is why. It’d be helpful if you shared your.log file.
>>>
>>> If you’re just trying to run the default Sedov problem in 3D with only
>>> changes in flash.par I’m a bit surprised you have this issue. Though as you
>>> wrote, setting lrefine_min can be helpful if you aren’t initially resolving
>>> the features you’re trying to refine on.
>>>
>>> Best wishes,
>>> Ryan
>>>
>>> Sent from my iPhone
>>>
>>> On 9. Jul 2025, at 15:43, Sumit Banerjee <sumitb at g.clemson.edu> wrote:
>>>
>>> 
>>> Flash users,
>>>
>>> I hope everything is fine.
>>>
>>> I am trying to run the Sedov explosion in 3D and I changed the flash.par
>>> by adding the parameters, z_min, z_max, zl_boundary_type and
>>> zr_boundary_type. However, when I run the simulation, it reaches the max
>>> simTime real quick and the output files do not show any explosion. Below is
>>> the output of the run..
>>>
>>>  Grid_init: resolution based on runtime params:
>>>>   lrefine          dx              dy              dz
>>>>       1             0.125           0.125           0.125
>>>>       2             0.062           0.062           0.062
>>>>       3             0.031           0.031           0.031
>>>>       4             0.016           0.016           0.016
>>>>       5             0.008           0.008           0.008
>>>>       6             0.004           0.004           0.004
>>>>  MaterialProperties initialized
>>>>  Cosmology initialized
>>>>  Source terms initialized
>>>>  sim_rhoAmbient is   1.0000000000000000
>>>>   iteration, no. not moved =            0           0
>>>>  refined: total leaf blocks =            1
>>>>  refined: total blocks =            1
>>>>  [amr_morton_process]: Initializing surr_blks using standard orrery
>>>> implementation
>>>>   Finished with Grid_initDomain, no restart
>>>>  Ready to call Hydro_init
>>>>  Hydro initialized
>>>>  Gravity initialized
>>>>  Initial dt verified
>>>>  *** Wrote checkpoint file to sedov_hdf5_chk_0000 ****
>>>>  *** Wrote plotfile to sedov_hdf5_plt_cnt_0000 ****
>>>>  Initial plotfile written
>>>>  Driver init all done
>>>>        n          t         dt  (         x,          y,          z) |
>>>>  dt_hydro  dt_Diff
>>>>        1 1.0000E-10 2.0000E-10  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>        2 3.0000E-10 4.0000E-10  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>        3 7.0000E-10 8.0000E-10  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>        4 1.5000E-09 1.6000E-09  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>        5 3.1000E-09 3.2000E-09  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>        6 6.3000E-09 6.4000E-09  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>        7 1.2700E-08 1.2800E-08  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>        8 2.5500E-08 2.5600E-08  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>        9 5.1100E-08 5.1200E-08  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       10 1.0230E-07 1.0240E-07  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       11 2.0470E-07 2.0480E-07  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       12 4.0950E-07 4.0960E-07  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       13 8.1910E-07 8.1920E-07  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       14 1.6383E-06 1.6384E-06  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       15 3.2767E-06 3.2768E-06  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       16 6.5535E-06 6.5536E-06  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       17 1.3107E-05 1.3107E-05  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       18 2.6214E-05 2.6214E-05  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       19 5.2429E-05 5.2429E-05  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       20 1.0486E-04 1.0486E-04  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       21 2.0972E-04 2.0972E-04  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       22 4.1943E-04 4.1943E-04  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       23 8.3886E-04 8.3886E-04  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       24 1.6777E-03 1.6777E-03  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       25 3.3554E-03 3.3554E-03  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       26 6.7109E-03 6.7109E-03  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       27 1.3422E-02 1.3422E-02  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       28 2.6844E-02 2.6844E-02  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       29 5.3687E-02 5.3687E-02  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>       30 1.0737E-01 1.0737E-01  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>  *** Wrote checkpoint file to sedov_hdf5_chk_0001 ****
>>>>       31 2.1475E-01 2.1475E-01  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>  *** Wrote checkpoint file to sedov_hdf5_chk_0002 ****
>>>>       32 4.2950E-01 4.2950E-01  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>  *** Wrote checkpoint file to sedov_hdf5_chk_0003 ****
>>>>       33 8.5899E-01 8.5899E-01  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>  *** Wrote checkpoint file to sedov_hdf5_chk_0004 ****
>>>>       34 1.7180E+00 1.7180E+00  ( 6.250E-02,  6.250E-02,  6.250E-02) |
>>>>  2.673E+01 6.250E+27
>>>>  *** Wrote checkpoint file to sedov_hdf5_chk_0005 ****
>>>>  exiting: reached max SimTime
>>>>  *** Wrote plotfile to sedov_forced_hdf5_plt_cnt_0000 ****
>>>
>>>
>>> I tried reading through the past issues and found out a suggestion to
>>> increase the parameters lrefine_min or lrefine_min_init but they aren't
>>> there in the flash.par file under the
>>> source/Simulation/SimulationMain/Sedov/flash.par file. I tried checking a
>>> few par files written for 3D runs but couldn't find anything useful yet.
>>>
>>> I tried running the Sod problem in 3D and it runs successfully with the
>>> similar adjustments to the par file as above so I have no idea what's going
>>> on here.
>>>
>>> Could somebody explain what is going on and how I can get over this
>>> problem?
>>>
>>> *Clear Skies,*
>>> *Sumit (Sam)*
>>> _______________________________________________
>>> flash-users mailing list
>>> flash-users at flash.rochester.edu
>>>
>>> For list info, including unsubscribe:
>>> https://flash.rochester.edu/mailman/listinfo/flash-users
>>>
>>>
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