Setting the View Factors Calculator Model Parameters

Patching Parameters

The Patching feature provides you with two control parameters: the number of patches and the angularity.

The control parameters (options and values) are defined by default on a regionwise basis in each region where the View Factors Calculator model is active under the Physics Conditions and Physics Values nodes.

Patch Specification Properties

Patch Specification

Sets the number of patches specification method.

Patch Specification	Corresponding Value Nodes
Proportion of Faces	Patch/Face Proportion Specifies the target for the fraction of patch allocated to each boundary face. The target number patches on a boundary = (Patch/Face Proportion /100 )* number of faces on boundary (or the portion of the boundary in the part subgroup, if Specify by Part Subgroup is on). A setting of 25 means that the target is to give each face 25% of a patch, so that 80 faces would be targeted to get 20 patches and each patch covers four faces. The default setting is 100, that is, each gets 100% of a patch—each boundary face has a patch. This setting is also the maximum. Specify by Part Subgroup When On, allows you to specify the target for the fraction of patches allocated by subgroups within the boundary or region. See Applying Quantities by Subgroup. When Off, allows specification by Patch/Face Proportion for the entire boundary or region. The default is Off.
Total	Number of Patches Specifies the target for total number of patches using Number Of Patches under Physics Values. If the value is entered at Region > Physics Values, the specification method then seeks to allocate patches from the total number in proportion to the number of discretized faces on each boundary (or, with Specify by Part Subgroup on, the portion of the boundary in the part subgroup) so that a boundary with twice as many faces gets twice as many patches. The total number of patches for a region cannot be less than the total number of boundaries or more than the total number of faces on all boundaries. The total number of patches for a boundary cannot be less than one and cannot be more than the total number of faces on that boundary. Specify by Part Subgroup When On, allows you to specify the target for the total number of patches allocated by subgroups within the boundary or region. See Applying Quantities by Subgroup. When Off, allows specification by Number of Patches for the entire boundary or region. The default is Off.

Custom Patch Specification

The number of patches and patch angularity can be further refined or customized at individual boundaries under the Physics Conditions node. Specifies whether the number of patches is set to Use Region Values or custom values. When you choose either Proportion of Faces or Total, the corresponding value node appears for the boundary, and you can then enable Specify by Part Subgroup.

Note	If a region-level patching specification has Specify by Part Subgroup on, the Use Region Values option cannot be used for interface boundaries corresponding to boundary-mode interfaces in that region. Boundaries for contact-mode interfaces do support this option. See Interface Options.

The patching parameters are handled automatically for non-emissive boundaries such as symmetry planes and periodic internal interfaces.

Angularity

This parameter defines the maximum allowed angle between the normals to contiguous boundary faces for these faces to belong to the same patch. It provides a control over the patch planarity and is used to detect sharp angles in the geometry, such as would happen at a corner, and to prevent patches from bridging such features. The angularity is set at 150 degrees by default and would require changing only in cases where specific geometric features must be captured.

Custom Patch Angularity Specification Properties

Custom Patch Angularity Specification

For patch angularity, specifies whether to Use Region Values or custom values on the boundary.

View Factors Parameters

The view factors are calculated by shooting beams from each patch and computing the amount of energy that is deposited at intercepting patches. This amount is a function of the optical properties of the surface.

For diffuse reflection, the view factors calculator only keep track of irradiated and transmitted energy and would formally only require specification of transmissivity at the boundary. However, for completeness, and because the individual spectrum models enforce Kirchhoff's law, for Thermal spectral bands, emissivity, reflectivity, and transmissivity are provided at boundaries.

For transparent or partially transparent external walls, a black body, whose temperature is characterized by an environmental temperature, can absorb the beams which are transmitted out of the enclosure.

These radiative properties of the boundary surfaces, Surface Emissivity, Surface Reflectivity and Surface Transmissivity, are defined in the same way as for thermal models (see Setting Thermal Radiation Model Parameters).