[Nek5000-users] Dynamo set up with weird results

[nek5000-users at lists.mcs.anl.gov]

Hello everyone,
I am currently looking into using Nek5000 for a (kinematic) dynamo 
problem in a spheroid. I started by combining the mhd example from the 
examples with a working case which only solved for the velocity the 
following way:
- lbelv=lelv, lbx1=lx1 etc. in SIZE
- adding (dummy) bc's for Temperature to the rea file and setting 
ifheat=.false. in usrchk
- adding bc's for the magnetic field to the rea file as Passive Scalar 
1, after the temperature. The string is 'E  ' inside the Volume and 'v  
' at the boundary
- ux,uy,uz=0.0 in userbc for both (ifield .eq. 1) and (ifield .eq. ifldmhd)
- ux,uy,uz=0.0 in useric for both (ifield .eq. 1) and (ifield .eq. ifldmhd)
- param(29) is set to the magn. viscosity
My actual problem is of course more complicated in regards to init. and 
boundary conditions, but this simple example produces weird output. The 
magnetic field should stay zero, but grows with the same rate as the 
velocityfield (computed via 
glsc3(bm1,bx,bx,n)+glsc3(bm1,by,by,n)+glsc3(bm1,bz,bz,n) and 
(glsc3(bm1,vx,vx,n)+glsc3(bm1,vy,vy,n)+glsc3(bm1,vz,vz,n))).
  I then removed the custom forcing to the velocity in userf, which 
caused the simulation to produce NaNs after 4 timesteps (everything is 
zero before, as expected).
Without the additions for the magnetic field, the case runs fine with 
the same resolution and timestep length (but has a slightly lower 
growthrate for the velocity).

Has anyone seen similar behaviour? I think that I am missing something 
obvious in the the mhd setup.

Cheers,
Jan