Card 2b - Analyzer Control (steady state)

This optional card executes Analyzer to calculate temperatures for a steady state solution.

Parameters: GRADNT, TABS, DTP, DT, TST, TF, TRDMP

GRADNT

GRADNT is the convergence criterion and must be > 0. Convergence is achieved when GRADNT > TDMAX, where TDMAX is the maximum temperature difference between two iterations.

  • GRADNT = 0 defaults to 0.001.
  • GRADNT = -9 specifies that the Analyzer is not run.

An additional energy balance convergence criterion may be specified on a Card 9 PARAM ENGBAL.

TABS

TABS is the temperature of absolute zero. It is used to evaluate radiative conductances and air densities for hydraulic elements. It can be greater than 0 or less than 0, e.g., ±273 or ±460.

DTP

DTP is the number of iterations between printouts.

  • DTP = 0 defaults to a single printout at the end of the run.

DT

DT is the iteration damping parameter and must be between 0 and 1.

  • DT = 0 defaults to 1.0.

At each iteration, for each element, the thermal solver computes an equilibrium temperature Teq at which the element is in thermal equilibrium with its neighbors. Tnew is then the mixture of Teq and the temperature Told of the previous iteration:

Larger DT values speed up convergence for well-behaved models. Smaller DT values increase stability.

If hydraulic elements are used in the model, smaller DT values, such as DT = 0.3, are recommended.

TST

TST is the time value at which the time-dependent heat load and sink temperature boundary conditions are evaluated for the run.

  • TST = 0 may be used if all boundary conditions are specified as CONSTANT, there are no time-dependent boundary conditions specified.
  • TST must not exceed the largest time value of the table, if time-dependent parameters are defined in tables on TABDATA Cards.
  • TST = -89990 uses an integrated average of the time-dependent heat loads with TIME values > 0 for boundary conditions.

TF

TF is the maximum number of iterations.

TRDMP

TRDMP is ignored for steady-state runs.

Code example


 0 -273 0 0 0 100  $ STEADY STATE, 100 ITERATIONS, DEFAULT DAMPING
 $ PARAMETER IS USED

Notes

For more information, see Analyzer module. For more information on table interpolation and other analyzer options, see Card 9.

  • Temperatures are written on TEMPF file at each DTP printout interval.

    Initial temperatures default to zero, unless specified by Card 9 TINIT cards or if a file TEMPF is present at the start of a run, in which case the set of temperatures whose time value is closest to the TST parameter are used as the starting temperatures. This is useful for restarting steady–state runs that have not completely converged. TINIT Cards override temperatures specified in a TEMPF file.

  • Temperature printouts are specified with Card 9 PRINT cards.
  • Temperature boundary conditions are specified with Card 9 SINK cards. Heat load boundary conditions may be calculated from geometry (orbital heat loads), or specified with Card 9 QNODE cards. Both temperature and heat load boundary conditions may be specified to be table-dependent with Card 9 INTERP cards or varied in a user-written subroutine.