Download CO5BOLD User Manual

5.3
Parameter File: rhd.par
77
• character bottom_bound:
The boundary condition at the bottom of the model is given for instance by
character bottom_bound f=A80 b=80 n=’bottom boundary conditions’ &
c0=closedbottom
transmitting
Possible values are:
◦ reflective: closed wall, no gravity, no radiation. Like the velocity field, the magnetic
field is mirrored at the boundary. This boundary condition is unphysical, because
the magnetic field is an axial vector and it violates the divergence free property of
the magnetic field. Therefore, this boundary condition should not be used in MHD
simulations. Use closed boundary conditions instead.
◦ constant: open boundary with constant extrapolation of all values, no gravity, no
radiation
◦ closed, closedtop: closed wall, can handle gravity, open for outward radiation. Magnetic field lines are orthogonal to the boundary, i.e. the tangential component of the
magnetic field vanishes at the boundary.
◦ closedbottom: closed wall, handles gravity, radiation in diffusion approximation.
Magnetic field lines are orthogonal to the boundary, i.e. the tangential component
of the magnetic field vanishes at the boundary.
◦ periodic: periodic boundaries for hydrodynamics, radiation, and magnetic fields
◦ transmitting: transmitting boundary for hydro and outward radiation. The parameters real c_tchange, real c_tsurf, and real c_hptopfactor have to be specified.
Magnetic field lines are orthogonal to the boundary, i.e. the tangential component of
the magnetic field vanishes at the boundary.
◦ inoutflow: ”classical” open lower boundary for deep convection, gravity and radiation
possible. The parameters real s_inflow, real c_schange, and real c_pchange
have to be specified. Magnetic field lines are orthogonal to the boundary, i.e. the
tangential component of the magnetic field vanishes at the boundary.
◦ inoutflow2: variant of the open lower boundary condition. The parameters
real s_inflow, real c_schange, real c_pchange, and real B1_inflow have to be
specified.
In simulations of a solar-like star with the MSrad radiation transport module the bottom boundary is typically of type “inoutflow”. A supergiant simulation will have a
transmitting lower boundary.
• character heat_mode:
The mode in which energy is supplied can be adjusted with this parameter. The classical
choice is to leave it empty, in which case the mode is chosen from s_inflow (see Sect. 5.3.4)
and luminositypervolume (see Sect. 5.3.4). Example:
character heat_mode f=A80 b=80 n=’Heating mode’ &
c0=’-/bottom_entropy1/bottom_energy1’
bottom_entropy1
Possible values, so far:
◦
: (empty). The classical value. For local models the energy comes through the lower
boundary, either by radiation (for a closed bottom boundary closedbottom) or by
convection + radiation (for an open bottom boundary inoutflow).
◦ bottom_entropy1: The entropy in the bottom layers (defined as being less than
r0_grav above the bottom of the model) is adjusted towards s_inflow on a rate
given by c_schange.