[Developers] Add magnetic fields to HydroBase

Bruno Giacomazzo bgiacoma at astro.umd.edu
Tue Nov 24 13:45:38 CST 2009


On Nov 24, 2009, at 1:36 PM, Erik Schnetter wrote:

> I suggest to add magnetic fields to HydroBase, using the same  
> conventions and units as in Whisky.
>
> Similar to the three-velocity, the magnetic field should be a  
> vector group.  A single-letter name such as "B" is a bad idea.  I  
> would suggest "Bmag[3]" as variable name; Frank Löffler prefers  
> "EM_B[3]".  Comments?
>

	For those who don't know, the field defined in HydroBase would be  
the magnetic field B^i as defined in Anton et al. 2006 ("Numerical 3 
+1 General Relativistic Magnetohydrodynamics: A Local Characteristic  
Approach"), i.e. the one measured by an Eulerian observer in analogy  
with the definition of the velocity (which is also measured by an  
Eulerian observer).

	I imagine Frank is thinking also of adding the electric field in the  
future and in that case one would have EM_B and EM_E. Another  
possibility could be Bvec and Evec. Also the electric field should be  
considered as the one measured by an Eulerian observer to keep  
everything consistent. In ideal MHD the electric field is not used  
since it is a simple function of the magnetic field and of the  
velocity, so when doing storage of these quantities you should keep  
them separate and have two different parameters to switch on the  
magnetic and the electric field components.

Cheers,
Bruno

Dr. Bruno Giacomazzo
Department of Astronomy
University of Maryland
College Park
MD 20742-2421
USA

Tel.  : +1 301 405 0676
Fax  : +1 301 314 9067
Cell. : +1 443 535 5846
email : bgiacoma at astro.umd.edu

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