Card 6f - MESH Redefinition

L

L is the code MESH (or 14).

M = ERROR

M = ERROR (or -3) computes the MESH value for subsequent radiation calculations from the value of ERR, where ERR is the target residual view factor for each element.

where:

• VFij is the view factor from element i to element j

ERR should be between 0 and 1. Lower ERR values (e.g. .02) will result in higher MESH values, and vice versa.

This option is not valid for Card 6e thermal coupling calculation requests. If a thermal coupling request is encountered while this option is active, it will be performed with the Card 2a MESH value.

M = RESET

M = RESET (or -2) performs subsequent radiation requests with the Card 2a MESH value, until another MESH Card is encountered.

Subsequent Card 6e thermal coupling calculation requests are performed such that only a single conductance is calculated for each element in the primary N1 group, even when the element overlaps several other elements.

• ERR = OVERLAP performs subsequent Card 6e thermal coupling calculations with the provision that no thermal couplings are created for elements that do not overlap. The overlap test is done by projecting the primary element N1 onto the secondary element N2. gpname specifies the normal used for the projection of N1onto N2. If gpname is PRIMARY, the overlap test uses the primary element normal for the projection. If gpname is SECONDARY or blank, the overlap test uses the secondary element normal for the projection. The surface normal of a beam element is perpendicular to the beam axial direction, and lies on the surface formed by the beam axial direction, and the line joining the CG of the primary element and the CG of secondary element.

• ERR = OVERFLP performs subsequent Card 6e thermal coupling calculations with the proviso that no thermal couplings are created for elements that do not overlap. With this option, the overlap test uses the secondary element normal for the projection of the primary element onto the secondary element. In addition, the primary N1 and secondary N2 groups on Card 6e are interchanged if the average area of the primary group is greater than the average area of the secondary group, and the thermal coupling is of the NEAR type. This is done to minimize heat flow concentration effects. If the primary N1 and the secondary N2 groups are interchanged, the overlap test uses the original primary element normals for the projection of the primary elements onto the secondary elements. This option is not recommended.

M = SINGLEONLY

M = SINGLEONLY (or -4) is ignored for radiation requests and is used only for thermal coupling requests.

• ERR = ON: This addresses the case when common elements exist in both the primary N1 and secondary N2 groups in a subsequent request. If a coupling is created between two elements which occur in both the primary N1 and secondary N2 groups, then its value is multiplied by .5, in order to compensate for the possible creation of duplicate thermal couplings.
• ERR = OFF: This is the default option. For subsequent Card 6e thermal coupling requests, duplicate thermal couplings may be calculated for the same element if the primary and secondary groups N1 and N2 have common elements.
• gpname is ignored.

M = TOLERANCE

M = TOLERANCE (or -5) is used only for subsequent Card 6e proximity-dependent (NEARx option) thermal coupling requests.

• ERR is a tolerance value. A thermal coupling will be calculated only if:
• where:
• D is the distance between the primary N1 and secondary N2 elements
• A1, A2 are the areas of the primary N1 and secondary elements N2
• gpname is ignored.

M = integer value

This option defines the MESH value explicitly. M may be an integer from 0 to 20, and sets the value of the MESH parameter.

• ERR = SUNRAYS: This is a global parameter, all collimated solar spectrum calculations are performed with the specified MESH = M value.
• ERR = EARTH: This is a global parameter, all Earth view factor and albedo factor calculations are performed with the specified MESH = M value.
• ERR = GROUPNAME: This is a global parameter, all view factor and heat flux view factor calculations involving any element of the group gpname are performed with the specified M value. This option is not supported with the Hemicube method.
• ERR = SPACE: This is a global parameter, all view factors to the Card 5d SPACE elements are performed with the specified MESH = M value.
• ERR = OVERLAP: Subsequent Card 6e thermal coupling calculations are performed with the proviso that no thermal couplings are created for elements that do not overlap. The overlap test is done by projecting the primary element N1 onto the secondary element N2. gpname specifies the normal used for the projection of N1 onto N2. If gpname is PRIMARY, the overlap test uses the primary element normal for the projection. If gpname is SECONDARY or blank, the overlap test uses the secondary element normal for the projection. The surface normal of a beam element is perpendicular to the beam axial direction, and lies on the surface formed by the beam axial direction, and the line joining the CG of the primary element and the CG of secondary element.
• ERR = OVERFLP: As with the ERR = OVERLAP option, subsequent Card 6e thermal coupling calculations are performed with the proviso that no thermal couplings are created for elements that do not overlap. With this option, the overlap test uses the secondary element normal for the projection of the primary element onto the secondary element. In addition, the primary N1 and secondary N2 groups on Card 6e are interchanged if the average area of the primary group is greater than the average area of the secondary group, and the thermal coupling is of the NEAR type. This is done to minimize heat flow concentration effects. If the primary N1 and the secondary N2 groups are interchanged, the overlap test uses the original primary element normals for the projection of the primary elements onto the secondary elements. This option is not recommended.

Code example

In the following example, all radiation calculations are performed with MESH=2, with the following exceptions:

• For element 100 the targeted view factor sum error is .02.
• For the elements of the group CRITICAL, MESH=3 is used.
• All solar spectrum calculations are performed with MESH=4.
• Card 6e thermal couplings will be created with a single coupling only.

 MESH ERROR .02
 VFS1ALL 100
 MESH 3 GROUPNAME CRITICAL
 MESH 2
 VFSALL
 MESH RESET
 AREA N1 0 0 N2 0 1 NEARA
 MESH 4 SUNRAYS
 SOLSALL 0 0 0 0
 

Notes

In general, higher MESH values result in more accurate computations.

Unless otherwise specified, Card 6f overrides the default Card 2a MESH parameter.

For a discussion of how the MESH parameter subdivides an element, see Card 2a - Program Control.