In this part of the parameter file the radiation transport module has to be selected. Depending on this selection a couple of additional parameters have to be specified.
character radscheme f=A80 b=80 n='Radiation transport scheme' & c0='LHDrad/MSrad/SHORTrad' & c1='None (skip radiation transport step entirely)' SHORTradPossible values are
None: Skip radiation transport entirely.
LHDrad: (old ``supergiant module'') It uses long characteristics and is restricted to an equidistant grid and open boundaries at all surfaces. Note that the switch
-Drhd_r01=1has to be set during compilation (see Sect. 3.4).
MSrad: (``solar module'') It uses long characteristics. The lateral boundaries have to be periodic. Top and bottom can be closed or open. Note that the switch
-Drhd_r02=1has to be set during compilation (see Sect. 3.4).
SHORTrad: (new ``supergiant module'') It uses short characteristics and is restricted to an equidistant grid and open boundaries at all surfaces. Note that the switch
-Drhd_r03=1has to be set during compilation (see Sect. 3.4).
integer n_radminiter f=I4 b=4 & n='Minimum number of radiation transport iterations' c0=8 1If less iterations are needed the time step limit for the next step is increased. This value will in almost any case (for explicit radiation transport) be set to
1. In the implicit case it is set to a higher value (typically
n_raditeriterations will (probably) needed. The parameter can be set e.g. with
integer n_raditer f=I4 b=4 & n='Number of radiation transport iterations' c0=10 8For a simulation of a solar-type star (with comparatively long radiative time scales) it will typically be set to
1. For starts with shorter radiative time scales values around
10may be considered. All three radiation transport modules understand this parameter.
integer n_radmaxiter f=I4 b=4 & n='Maximum number of rad. transport iterations' c0=30 0If more iterations are needed the computation for the current time step is stopped and resumed with a smaller one (which means that the hydrodynamics and the tensor viscosity step have to be done again). Usually,
n_radmaxiterwill either be set to a values somewhat larger than the recommended number of iterations (
n_raditer) or to
0which disable the check for too many iterations completely. This can be safely allowed in many cases and has the advantage that there is no need to save the initial model before calling the radiation transport module, which saves some memory. To disable the iteration of the radiation transport sub-step set
1. All three radiation transport modules understand this parameter.
SHORTradthe orientation of the base axis system can be selected e.g. with
character radraybase f=A80 b=80 n='Base axis system' & c0='unity/random/randomgroup' randomAllowed values are
unity: (default) During all time steps and radiative sub-steps the direction of the rays stays the same.
random: At each time step (and radiative sub-step) a new base axis system is chosen at random
randomgroup: At each new time step a new base axis system is chosen at random. It is kept for all radiative sub-steps.
radraystar) it is advisable to vary the directions of the rays (by choosing
randomgroup) to cover the entire sphere at least over a longer time.
SHORTradthe list of ray directions (i.e. the number of rays and their coordinates) relative to the base axis system can be specified with e.g.
character radraystar f=A80 b=80 n='List of relative ray directions' & c0='x1(1)/x2(1)/x3(1)/oktaeder(3)/tetraeder(4)/cube(4)' & c1='ikosaeder(6)/dodekaeder(10)' oktaederExamples for allowed values are
x1: (N=1) one single ray along x1 axis (not enough to specify fluxes in all directions)
x2: (N=1) one single ray along x2 axis (not enough to specify fluxes in all directions)
x3: (N=1) one single ray along x3 axis (not enough to specify fluxes in all directions)
oktaeder: (N=3, default) octahedron
tetraeder: (N=4) tetrahedron
ikosaeder: (N=6) icosahedron
dodekaeder: (N=10) dodecahedron
MSradmodule the ray directions have to specified in a different way: The number of ray sets in theta direction can be chosen with e.g.
integer n_radtheta f=I4 b=4 & n='NTHETA: Number of ray sets in theta direction' c0=2 2
MSradmodule the number of ray sets in phi direction can be set e.g. with
integer n_radphi f=I4 b=4 & n='NPHI: Number of ray sets in phi direction' c0=2 2
MSradmodule the number of rays per cell (with the same direction) can be specified e.g. with
integer n_radsubray f=I4 b=4 n='KPHI: Number of rays per cell' c0=2 2
integer n_radband f=I4 b=4 n='Number of frequency bins' & c0='1: grey opacities' & c1='2: non-grey opacities (if available from table)' 1Allowed values are
1: Use the grey part of the table
2: Use the other (possibly non-grey, frequency-dependent) part of the table
MSradmodule so far can handle non-grey tables.
LHDradmodule (tentatively) supports implicit radiation transport. It can be activated with the parameter
real c_radimplicitmu f=E15.8 b=4 & n='Implicitness parameter for radiation transport' u=1 & c0='0.0: explicit / 0.5: time centered / 1.0: fully implicit' 0.0Allowed values are
0.0: Fully explicit radiation transport (possible with all modules)
1.0: Partly implicit radiation transport
0.5: Radiation transport time-centered
1.0: Fully implicit radiation transport
LHDradmodule only) the requested convergence accuracy of the iteration can be set e.g. with
real c_raditereps f=E15.8 b=4 & n='Relative accuracy for radiation iteration' u=1 & c0='Typical value: 1.0E-03' 2.0E-03
LHDradmodule only) the step size of the iteration can be restricted with e.g.
real c_raditerstep f=E15.8 b=4 & n='Step size of radiation iteration' u=1 & c0='Typical values: 0.7,0.81' 1.0Allowed values are
1.0: Restricted step size
1.0: No restriction, standard step size
1.0: Extra large steps
LHDradmodule the limit in delta optical depth (rho*kappa*dx) below which the ``radiative temperature viscosity'' (=temperature smoothing) is to be applied can be set with e.g.
real c_radtvisdtau f=E15.8 b=4 & n='Optical depth limit for temperature viscosity' u=1 0.1The introduction of this ``temperature diffusion'' is a somewhat desperate and inelegant attempt to improve the behavior of the Greens function (hot cells should be cooled, cool cells should be heated). This diffusion is necessary for not well resolved models. It is switched off with
LHDradmodule the amount of the ``radiative temperature viscosity'' (=temperature smoothing) can be specified e.g. with
real c_radtvis f=E15.8 b=4 n='Temperature viscosity' u=1 1.6For well resolved models it should be switched off (with
0.0). But often its use is necessary.