POWER module information

The POWER module calculates IR and solar spectrum radiative heat loads from the orbital view factors, heat flux view factors, and view factors of the VUFF file.

The following steps outline the POWER module algorithm:

1. Reads in the view factor matrix from VUFF (MNM = BVF).
   • If TIME=-1.0E36 on the BVF card, then the view factor applies to both the IR and solar spectra.
   • If TIME=-1.1E36 on the BVF card, then the view factor was calculated by ray-tracing with the VFTRACE option and it applies to the solar spectrum only.
   • If TIME=-1.2E36 on the BVF card, then the view factor was calculated by ray-tracing with the VFTRACE option and it applies to the IR spectrum only.
2. Adjusts the view factors using the Card 2a KSP parameter. However, the method differs slightly from that employed in the GRAYB module: All view factors are adjusted, not only the view factors calculated without shadowing. The reciprocity relationship of the view factors is still maintained after this adjustment.
3. Scales the view factors to ensure their sum becomes 1. The reciprocity relationships between them is no longer maintained at this stage.
4. Computes for each element i, the effective properties such as the effective transmissivity τ_i,eff, the effective reflectivity ρ_i,eff, and the effective absorptivity E_i,eff from the surface properties and self-view factors. The effective properties are the surface properties of the element adjusted for self-reflection and self-transmission. For table-dependent emissivities, the first emissivity value of the table is used to calculate these parameters. Note that for temperature-dependent emissivity tables, this will in general be the emissivity value for the lowest temperature. For source elements, E_i,eff is set to zero, to ensure none of the emitted heat flux is reabsorbed by the source itself.
5. Creates the distribution matrix D. The terms D_ij consist of the sum of the reflectivity and transmissivity terms.

   where;

   • M_ii is a multiplier associated with element i.
   • M_irir is a multiplier associated with the reverse side of element i.
   • V_ij is the view factor from the front side of element i to element j.
   • V_irj is the view factor from the reverse side of element i to elementj.
6. Reads in the heat flux view factors from VUFF. Optionally, these may be put through an adjustment algorithm to ensure the total energy specified on the Card 6 SOURCE is maintained.
7. Calculates for each heat flux view factor the energy packets qq_i, qq_i,trace, qq_i,abs, qq_i,inc, qq_i,spec, and qq_i,trans.
8. Addresses a special case. If ray-tracing was not performed on heat flux view factors (this occurs if file VUFF MNM=EVF or MNM=ALB, i.e. albedo and Earth view factors calculated without the PARAM EXEARTH option), and element i is specular or transparent, then qq_i,trans is redistributed among the elements j the reverse side of i sees, and qq_i,spec is redistributed among the elements j element i sees. The redistribution weighting factor used is the view factor from the reverse sides of element i to j, and the view factor from i to j respectively. The redistributed heat flux is considered as incident on element j.
9. Calculates all the diffusely incident fluxes qq_i,inc. Next, the diffusely incident flux for each element i is redistributed to all the elements it sees through reflection or transmission.

   where:

   • qq_iabs is the new total absorbed energy calculated for i.
   • qq_iinc is the new diffusely incident energy calculated for i.
   • E_ieff is the effective absorptivity of element i.

For the first iteration, the transmissive portion of the D matrix is set to zero. The rationale for this is that all incident heat fluxes are considered to have been ray-traced, and thus transmission has already been taken into account. The above redistribution process continues iteratively until a maximum of 30 iterations, or until the absorbed energy is 99.99% of the total initial incident energy. If this convergence criterion is not reached, then the remaining unabsorbed energy is redistributed to all the element in proportion to their computed absorbed energies.

To output the calculated heat inputs in the MODLF file, the thermal solver writes the string:

'RDF COLLIMATED SOLAR LOADS' or
'RDF IR LOADS' or
'RDF DIFFUSE SOLAR LOADS'