[FLASH-USERS] Problem of having B=0 in MHD simulation

[pchang]

Hi all,

I am trying to simulate magnetic field compression in an imploding 
cylindrical Liner with an initial imploding speed. I set up an aluminum 
liner. I have Helium gas as the filled gas within the liner and as the 
background gas outside the liner. I started with simulating pure 
hydrodynamics, i.e., no magnetic field. Then, I put a uniform Bz in the 
filled gas region and no magnetic field in the liner region nor 
background gas region. Just to test if the magnetic field in the filled 
gas is compressed. I found that right after one time step, the magnetic 
field became 0. Therefore, I changed the Bz to Bphi as the example in 
magnetoHD/NohCylindrical. Similar to the NohCylindrical example, the 
Bphi was set as a function of r. Then, I found the magnetic field was 
compressed as the liner was imploded. So, I did a further test. I 
changed the Bphi in the example magnetoHD/NohCylindrical to a constant 
Bz. I found that the magnetic field also became 0. In all tests, I tried 
using +usm, +usm3T, and 8wave as default. They all gave similar results.

So, my question is,

(1) what should be the proper way to set up an MHD simulation?
(2) what should be the proper way to provide the initial condition of an 
MHD simulation?

Thank you.

Best,

Po-Yu

-- 
Po-Yu Chang
Assistant Professor
Institute of Space and Plasma Sciences (ISAPS)
National Cheng Kung University (NCKU)
No.1, University Road,
Tainan City 70101, Taiwan
(TEL) +886-6-2757575 ext. 65916
pchang at mail.ncku.edu.tw
http://capst.ncku.edu.tw/PGS/