[FLASH-USERS] Changing the system of units

[Aaron Froese]

Hi Sean,

The two runtime parameters that determine what unit system the solver works in are

UnitSystem = "CGS" or "SI"
pc_unitsbase = "CGS" or "MKS"

In most of the initialization routines, these parameters are read and then used to calculate constant factors.  In Hydro_init.F90, for example:

call RuntimeParameters_get("UnitSystem",          hy_units)

if ( hy_units == "SI" .or. hy_units == "si" ) then
    hy_bref = hy_vref*sqrt(4.0*PI*hy_dref*1.e-7)
else if ( hy_units == "CGS" .or. hy_units == "cgs" ) then
    hy_bref = hy_vref*sqrt(4.0*PI*hy_dref)
else
    hy_bref = hy_vref*sqrt(hy_dref)
end if

As you can see, only CGS and SI are provided in the distribution copy, so changing the solver to use parsecs, solar masses, and mega years would require additional coding.  I think it would be simpler to convert the simulation results from CGS or SI in post-processing.

Cheers,
Aaron


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Today's Topics:

   1.  Changing the system of units (Sean Lynch)


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Message: 1
Date: Mon, 1 Aug 2011 12:53:34 -0400
From: Sean Lynch <sean.m.lynch at drexel.edu>
Subject: [FLASH-USERS] Changing the system of units
To: flash-users <flash-users at flash.uchicago.edu>
Message-ID: <11522DB1-D682-4A7C-A9D8-7AB6B7D92791 at drexel.edu>
Content-Type: text/plain; charset=us-ascii

Hello,

I'm trying to set up a simulation that uses parsec, solar mass, and mega year as the base units. I know that I can use PhysicalConstants_get to convert a constant to the correct units. But how would I go about getting the solvers to use the correct units. For instance, how would I make sure that the eos unit is using the correct value of the gas constant, or that the gravity solver is using the correct value of G.

Thanks for your help.

-Sean

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