[Users] HydroBase description

[Aaryn Tonita]

Actually, the units of "Whisky" is a myth I have been trying to dispel from
some of the people at the AEI for a while now. In the hydro equations, the
only place that a mass scale enters is through the equation of state. So
HydroBase will work with any choice of mass unit (defined through the
equation of state) so long as G=c=1 is used consistently. I have run quite
successfully using polytropic units and kilometres.

As for the ideal magnetohydrodynamic equations, Whisky_Exp chooses
div(Faraday) = 4-current without any constant of nature, so this is
equivalent to choosing the permeability of free space (\mu_0) to be unity.
However, this would not be defined by HydroBase unless HydroBase sets the
stress energy tensor.

Cheers,

Aaryn

-----Original Message-----
From: users-bounces at einsteintoolkit.org
[mailto:users-bounces at einsteintoolkit.org] On Behalf Of Roland Haas
Sent: Monday, April 26, 2010 10:04 PM
To: Einstein Toolkit Users
Subject: [Users] HydroBase description

Hello all,

I have put a short description of HydroBase, its grid-variables and the
units used into the wiki. It is really just what can be found in the
documentation (currently out of date) and interface.ccl.

Since I have never done MHD and don't know the conventions used in that
field would someone who is knowledgeable mind reading through it and
checking in particular the units I give for B and its definition in terms of
the (dual) Faraday tensor, please?

One could also add descriptions for the parameters, but these would really
be just copies of what is in param.ccl.

Also it would be nice to note if these choices for units of the various
quantities exhaust the freedom to choose units (I would think that with
temperature and specific entropy they should, even determine the mass of the
(ideal gas) particle that makes up the fluid).

Yours,
Roland

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