[FLASH-USERS] The problem of Negative Internal Energy in 3T MHD simulation with laser generated plasmas

[Klaus Weide]

On Wed, 17 Apr 2019, Huo Wenyi wrote:

> Dear all:
> 
> I am using FLASH to simulate the magnetohydrodynamics in laser generated 
> plasmas. However, I always encounter a problem of negative internal 
> energy both in FLASH 4.5 and FLASH4.6. Does anyone encounter such a 
> similar problem?  The error information in the Log file is as follows:

Dear Huo Wenyi,

Welcome to the club. :)

You are definitely not the only one encountering these kinds of errors.
Unfortunately, there is a variety of causes for problems that ultimately 
show up as "negative [or zero] internal energy". The details will depend 
on your specific simulation, and what goes on in different locations of 
it.

One thing to try early on when you encounter this, as an attempt to work 
around it, is making the time step smaller - usually by lowering the CFL 
factor.

The message you quote shows the coordinate location where the problem 
occurs (or where the underlying problem first becomes so severe that the 
simulation cannot continue), see "CELL X" / "CELL Y". Is there anything 
unusual or unphysical going on at that location, BEFORE the time step that 
fails? You may want to drop a plot file (or checkpoint) right before the
error happens, to examine the state of the simulation more closely.

One thing I notice from your quoted message is that density seems rather
low (DENS_OLD, DENS_NEW) at the problem cell. Whether 1.E-09 is 
actually low, maybe unphysically low, depends on your simulation.
For your simulation it is most likely unphysical. Maybe changing your
initial condition can improve this. Maybe change the "smlrho" runtime 
parameter.

I have a suspicion that magnetic energy plays a large role in the
energy balance of the region where the error manifests. You could check 
that, for example by comparing the size of the variable MAGP (magnetic 
pressure or magnetic energy density) with that dens*ener, dens*eint, 
dens*eele.

More information would be needed to analyze this further. (setup command, 
log file, initial conditions and other code changes, ...)

Klaus

> [ 04-16-2019  14:34:35.488 ] [hy_uhd_ragelike] ERROR DETECTED
> [ 04-16-2019  14:34:35.488 ]   Zero or negative advected specific internal energy detected
> [ 04-16-2019  14:34:35.488 ]   DENS_OLD =  1.0000904290291E-09
> [ 04-16-2019  14:34:35.488 ]   DENS_NEW =  1.0000983091349E-09
> [ 04-16-2019  14:34:35.488 ]   UTOT_NEW = -3.7386802822434E-01
> [ 04-16-2019  14:34:35.488 ]   UEXTRA = -1.7491864582091E+01
> [ 04-16-2019  14:34:35.488 ]     UELE_NEW = -3.7135596091566E-01
> [ 04-16-2019  14:34:35.488 ]     UION_NEW = -2.5120492887951E-03
> [ 04-16-2019  14:34:35.488 ]     URAD_NEW = -1.8019885718467E-08
> [ 04-16-2019  14:34:35.488 ]     EELE_VAR =  1.7001438966846E+10
> [ 04-16-2019  14:34:35.488 ]     EION_VAR =  1.1498940630502E+08
> [ 04-16-2019  14:34:35.488 ]     ERAD_VAR =  8.2498749422145E+02
> [ 04-16-2019  14:34:35.488 ]     EELE     = -3.7131945682109E+08
> [ 04-16-2019  14:34:35.488 ]     EION     = -2.5118023556785E+06
> [ 04-16-2019  14:34:35.488 ]     ERAD     = -1.8018114373230E+01
> [ 04-16-2019  14:34:35.488 ]     uele_adv  =  1.7002978536045E+01
> [ 04-16-2019  14:34:35.488 ]     uion_adv  =  1.1501719275908E-01
> [ 04-16-2019  14:34:35.488 ]     urad_adv  =  8.2506210304961E-07
> [ 04-16-2019  14:34:35.488 ]   PELE_VAR =  1.2145270532940E+00
> [ 04-16-2019  14:34:35.488 ]   PION_VAR =  7.6660475248193E-02
> [ 04-16-2019  14:34:35.488 ]   PRAD_VAR =  2.7502069901319E-07
> [ 04-16-2019  14:34:35.488 ]   PELE_ADV =  1.2145343502140E+00
> [ 04-16-2019  14:34:35.488 ]   PION_ADV =  7.6672066071296E-02
> [ 04-16-2019  14:34:35.488 ]   PRAD_ADV =  2.7502070101654E-07
> [ 04-16-2019  14:34:35.488 ]   TELE_VAR =  6.0996867323016E+02
> [ 04-16-2019  14:34:35.488 ]   TION_VAR =  3.6907447766733E+00
> [ 04-16-2019  14:34:35.489 ]   TRAD_VAR =  1.0219015193890E+02
> [ 04-16-2019  14:34:35.489 ]   CELL X =  3.3222656250000E-01
> [ 04-16-2019  14:34:35.489 ]   CELL Y =  6.9890625000000E-01
> [ 04-16-2019  14:34:35.489 ]   CELL Z =  0.0000000000000E+00
> [ 04-16-2019  14:34:35.489 ]   You might be able to get things to keep running by trying
> [ 04-16-2019  14:34:35.489 ]   more diffusive hydro options (reduce CFL, order, etc...)
> [ 04-16-2019  22:00:17.496 ] [hy_uhd_ragelike] Negative internal energies in 3T update
> [ 04-16-2019  22:00:17.496 ]   Falling back to using internal energy ratios instead of pressure ratios

It also seems that you have combined log file output from at least two 
different runs here (note time stamps), which have failed (or not) in 
different ways. It would better not to do this.

Klaus