VUFAC module information

The VUFAC module calculates view factors, orbital view factors (solar view factors, albedo view factors, Earth view factors), heat flux view factors, view factor for axisymmetric modeling with plane stress, and thermal couplings.

View factor requests

The ray-tracing process starts with a Card 6 view factor calculation request. The view factor request for which ray-tracing is done may be a:

  • Card 6b Solar View Factor Request - ray-tracing is always done for solar view factors.
  • Card 6n Heat Flux View Factor Request - ray-tracing is always done for heat flux view factors.
  • Card 6a VFSALL View Factor Request with the VFTRACE flag.
  • Card 6r Enclosure View Factor Request with the VFTRACE flag.
  • Card 6k, Card 6t, and Card 6u Orbit cards: ray-tracing is always done for solar view factors; but it is only done for albedo view factors and Earth view factors if the PARAM EXEARTH option is active.

Ray-Tracing with the PARAM EXEARTH option

If the PARAM EXEARTH option is present, ray-tracing is done for Earth view factors and albedo view factors for a:

  • Card 6k Orbit Definition
  • Card 6t ORBDEF Orbit and Attitude Modeling Request cards
  • Card 6d Earth view factor requests
  • With the PARAM EXEARTH flag the Earth is modeled explicitly as a separate set of shell elements for each orbital position in the appropriate location with respect to the model. For more information see Card 9 PARAM Parameter, the EXEARTH option.

Choosing the source elements in a view factor request

The elements i and j for which the calculations are performed are determined by the view factor requests. Element i is chosen from the specified set of source elements, and element j is chosen from the specified set of receiver elements.

  • If Card 6n heat flux view factors are requested, the set of source and receiver elements are specified on the heat flux view factor request card.
  • If solar view factors are requested through Card 6b, Card 6k, Card 6t, or Card 6u, the source element i is the sun, and the receiver elements are specified on the on the solar view factor request cards.
  • If Card 6r view factors are requested with ray-tracing in an enclosure, the source elements and the receiver elements are both specified to be all the elements in the enclosure.
  • If all the view factors in the model are requested with ray-tracing through Card 6a, then the source and receiver elements are both specified to be all the elements in the model.
  • If albedo and Earth view factors are requested with the PARAM EXEARTH option with Cards 6k, 6d, or 6t, the source elements are the explicitly modeled Earth elements, and the receiver elements are the ones appropriately specified on the card.

Outputting of results

The calculated view factors are written on file VUFF with the following convention:

  • Solar view factors are written in the solar spectrum only with the code MNM=SVF.
  • Ray-traced albedo view factors are written with the code MNM = ALR. Albedo view factors that have not been ray-traced are written with the code MNM = ALB.
  • Ray-traced Earth view factors are written with the code MNM = EVR. Earth view factors that have not been ray-traced are written with the code MNM = EVF.
  • Heat flux view factors are ray-traced in both the IR and solar spectra. Heat flux view factors in the solar spectrum are written with the code MNM = HVF, while heat flux view factors in the IR spectrum are written with the code MNM = HVI.

  • Both ray-traced and non-ray-traced view factors are written with MNM = BVF.

    View factors that have been ray-traced in the solar spectrum are written with the code TIME=-1.1E36.

    View factors that have been ray-traced in the IR spectrum are written with the code TIME=-1.2E36.

    View factors which have not been ray-traced (and hence apply to both spectra) are written with the code TIME = -1.0E36.

  • Ray-traced view factors for elements that have specular or transparent surface properties are written with their areas, emissivities, and absorptivities redefined to take into account the reduction area. The following relationships are used:

where

  • Ainewsol is the area written on file VUFF for solar spectrum view factors.
  • AinewIR is the are written on file VUFF for IR spectrum view factors.
  • εinew is the emissivity written on file VUFF for IR spectrum view factors.
  • αinew is the solar spectrum absorptivity written on file VUFF for solar spectrum view factors.

Thermal coupling calculations

Thermal couplings are calculated between elements N1 and N2 if requested by the Card 6e. The VUFAC module must recognize element N1. N2 may be specified directly, or if one if the NEARx options is used, it may be automatically chosen by TMG to be the closest element to N1 from a pre-selected group of elements.

Thermal couplings created by the Card 6e are written in MODLF.