- 7.1.5.1 character side_bound_mag_x1 and side_bound_mag_x2
- 7.1.5.2 character top_bound_mag
- 7.1.5.3 character bottom_bound_mag
- 7.1.5.4 real b1_inflow
- 7.1.5.5 real c_magthetab
- 7.1.5.6 real c_magphib

7.1.5 Boundary conditions (MHD only)

The following parameters are specific to MHD simulations. For MHD calculations they must be set additional to the hydrodynamic boundary parameters.

7.1.5.1 character side_bound_mag_x1 and side_bound_mag_x2

fixed

character side_bound_mag_x2 f=A80 b=80 n='side boundary conditions magnetic x2'

periodic

`constant`

: constant extrapolation of all magnetic field components into the ghost cells.`periodic`

: periodic continuation of all magnetic field components into the ghost cells.`fixed`

: the component normal to the boundary is kept fixed at its inital value. Constant extrapolation applies for the transversal components.`vertical`

: constant extrapolation for the vertical component. The transversal cell-centered field is mirrored, with the opposite sign. That should result in transversal components of the boundary-centered field being zero at the boundary.`vertical2`

: constant extrapolation for the vertical component. The transversal cell-centered field is set to zero.`reflective`

: The magnetic field is mirrored at the boundary. This boundary condition is unphysical, because the magnetic field is an axial vector and because it violates the divergence free property of the magnetic field. Therefore, this boundary condition should be used with caution.

`fixed`

conditions are realized by setting the electric field at those cell edges that
coincide with the physical boundary zero. This is done in the constrained transport module.

vertical

`constant`

: constant extrapolation of all magnetic field components into the ghost cells.`periodic`

: periodic continuation of all magnetic field components into the ghost cells.`fixed`

: the component normal to the boundary is kept fixed at its inital value. Constant extrapolation applies for the transversal components.`vertical`

: constant extrapolation for the vertical component. The transversal cell-centered field is mirrored, with the opposite sign. That should result in transversal components of the boundary-centered field being zero at the boundary.`vertical2`

: constant extrapolation for the vertical component. The transversal cell-centered field is set to zero.`oblique`

: magnetic fields with a given inclination at the boundary. The inclination is specified through parameters`C_magthetaB`

and`C_magphiB`

.

inoutflow

`constant`

: constant extrapolation of all magnetic field components into the ghost cells.`periodic`

: periodic continuation of all magnetic field components into the ghost cells.`fixed`

: the component normal to the boundary is kept fixed at its inital value. Constant extrapolation applies for the transversal components.`vertical`

: constant extrapolation for the vertical component. The transversal cell-centered field is mirrored, with the opposite sign. That should result in transversal components of the boundary-centered field being zero at the boundary.`vertical2`

: constant extrapolation for the vertical component. The transversal cell-centered field is set to zero.`oblique`

: magnetic fields with a given inclination at the boundary. The inclination is specified through parameters`C_magthetaB`

and`C_magphiB`

.`inoutflow`

: magnetic field can be advected into the computational domain by ascending material flow. Its strength can be specified with the parameter`b1_inflow`

. The boundary condition for the hydrodynamic variables must be set to`inoutflow`

too, otherwise this boundary condition is the same like constant.

`inoutflow`

the magnetic field, which is advected into the computational domain
has a unique component which is in the x1 direction and it is only present where a velocity in
the positive x3 direction exists. In all other places, the magnetic field components are constantly
extrapolated into the ghost cells.

`bottom_bound_mag=inoutflow`

.
The default value is `0.0`

.
Example:
n='Strength of inflowing horizontal magnetic field' u=G

10.0

`oblique`

boundary conditions.
The default value is `0.0`

.
Example:
n='angle magnetic field w.r. to the vertical direction' &

u=rad c0='used in combination with oblique conditions'

0.523598775598299

`oblique`

boundary conditions. The default value is `0.0`

.
Example:
u=rad c0='used in combination with oblique conditions'

0.0