Subdivision Tab

If a custom conic surface is being edited, the Subdivision tab (shown in Figure 4-7) will be present in the Thin Shell Data dialog box. The Subdivision tab will not be present if more than one surface or a converted mesh surface is being edited.

The user must first decide the location of the nodes on the surface. The Centered Nodes option places the nodes at the node center. The Edge Nodes option also places the nodes at the center of the nodal area, but will make the nodes span the entire surface by adding “half” nodes on the edges and “quarter” nodes at the corners. Figure 4-8 shows a graphical representation of the difference between centered nodes and edge nodes. Users should use the Edge Nodes option when connections between custom conic surfaces is desired. Please note that to use the Edge Nodes option, the user must input more than 1 node in that direction. Special logic is also in place to merge nodes that coincide for conics that wrap around 360 degrees (for example, a full cylinder).

When two surfaces that have edge nodes share a common edge and have the same nodal breakdown, the nodes that they share may be merged into a common set of nodes. The “half” nodes now become “whole” nodes again, and the connection is equivalent to folding a regular centered node surface along a nodal centerline. Edge nodes are usually preferred for edge contact calculations as well, since conductors will be computed all the way to the edge of the surface.

The Subdivision tab consists of two identical sections for specifying the nodal break- down in each of the two principle directions of the surface. The labels indicate the nodal breakdown directions according to the type of surface being edited. A uniform spacing of nodal boundaries can be obtained by selecting the Equal radio button and entering the number of nodes desired in the particular direction into the corresponding input field.

Nodal boundaries can be placed at arbitrary positions by selecting the List radio button, activating the List input field, and entering nodal boundary values. Nodal boundaries are entered as a distance from 0.0 to 1.0 and must be entered in ascending order. Since there is always a nodal boundary at 0.0 and 1.0, those nodal boundaries are not input and are implied in the list. The list is edited by placing the cursor in the List input field and clicking the mouse button. The cursor will change shape to that of the edit insertion cursor and changes

Figure 4-8 Centered Versus Edge Node Locations

may be made to the values. New values are input by pressing the <Enter> key; cut and paste operations are available using the <Ctrl><C> and <Ctrl><V> key commands (as are all input fields).

4.3.1.2 Numbering Tab

The Numbering tab of the Thin Shell Data dialog box, shown in Figure 4-9, specifies the submodels and node IDs for the Top/Out and the Bottom/In sides of a surface. The “top” side of a flat surface is in the +Z direction of the local coordinate system, determined by traversing the vertices in a counter-clockwise direction using the right-hand rule. The “out” side refers to the exterior side of curved Thermal Desktop custom surfaces. The “bottom” or “in” side is the opposing side.

Submodel names may be defined ahead of time using the Thermal > SINDA Submod- els menu choice so they can be available on the Thin Shell Data dialog box (Section 4.2). Only defined submodels will appear in the drop-down list. The SINDA/FLUINT submodel name “MAIN” is automatically defined. Submodel names entered as text that are not in the Submodel Manager will automatically be added to the Submodel Manager after the user confirms the operation by selecting OK on a pop-up message dialog box.

The submodel name and the ID may be edited on Numbering tab or on the Node dialog box (see "Nodes" on page 4-62). The nodes on a surface may all be in the same submodel or may be in different submodels. If they are all in the same submodel, but not sequential, then the submodel name will be in the Submodel field, and the node IDs will be in the list.

If nodes are in more than one submodel, than the submodel name of the first node will be in the Submodel field, only the IDs will be displayed for nodes in that submodel, and the entire submodel.id will be input for the nodes that are in different submodels.

If more than one surface is selected for the Edit operation, node ID input is restricted to the submodel and whether or not same side node numbering should be used. Node IDs for an arbitrary group of surfaces may be modified using the Resequence IDs menu choice (see “Resequence IDs” on page 7-2).

The Use same ID’s on both sides check box allows choosing between a true 2D thermal network for the surface (checked) or a 3D thermal network which includes two nodes through the thickness of the surface (unchecked). This second method, with the check box unchecked is used for simplified modeling of a sandwich or honeycomb panel. The materials and material thicknesses are specified on the Cond/Cap tab (Section 4.3.1.4). This option is only available for finite difference surfaces. Further description of the thermal network is provided in Section 9.1.1 and Section 9.2.1.

Note: Unchecking Use same ID’s on both sides is typically used when a low conductivity material separates two higher con- ductivity materials. This would be typical of a foam-core sand- wich or perhaps a honeycomb sandwich. If the gradient through the thickness is due to a low conductivity material on one or both sides of a high conductivity material, then the Insulation tab (Sec- tion 4.3.1.6) should be used instead. If the plate is sufficiently thick or the conductivity through the thickness sufficiently low to produce a significant gradient, a better option may be to use a finite difference solid (Section 4.4) or solid finite elements (Sec- tion 4.5).

Node IDs may be numbered sequentially on a surface by selecting Use Start ID and entering the desired initial ID number. Alternatively, a list of node IDs may be entered by selecting Use List and entering the IDs in the list field. The number of IDs entered must match the number of nodes on the surface given by the subdivision page. Node IDs are ordered by traversing the first direction listed on the subdivision page before incrementing along the second direction. For example, a disk has the angular direction as the first direction, and the radial direction as the second direction. Nodes are input starting with the smallest radius value and traversing along the angular direction. When the first radius “row” is complete, values are entered for the first to last angular locations for the second radius “row”. Node ID assignments may be verified using the Model Checking commands.

4.3.1.3 Radiation Tab

The Radiation tab of the Thin Shell Data dialog box, shown in Figure 4-10, allows the selected surface(s) to be assigned to one or more analysis groups (see “Radiation Analysis Groups” on page 4-1) and also allows the optical properties of the surface to be defined. A RadCAD analysis group is used to compute view factors, radks, or heating rates. Surfaces

may be placed in any number of RadCAD analysis groups, with different active sides. Analysis group names must be defined ahead of time with the Radiation Analysis Groups menu choice before they can be used in the Thin Shell Data dialog box.

The user may edit the active side of an analysis group by either double clicking on the name in the list or by selecting one or more names in the list and then selecting Edit. Upon editing, an Edit Active Side dialog box will appear and user can select the active side for the edited set (see "Analysis Group Active Sides" on page 4-5).

This page also assigns optical property references to each side of the surface. Names may be typed directly into the fields, or they may be set from the pulldown list of defined properties. The pulldown list contains the list of currently defined property aliases, followed by the list of properties defined in the current property database file (Section 3.1).

The property name “DEFAULT” is always defined, even if no property database file is associated with the current drawing. If only dialog box factors are being computed, the property “DEFAULT” may be used without having to perform the unnecessary step of creating a property database file. The property “DEFAULT” is defined internally to be opaque, diffuse, and black.

The property “NORMAL” is also always defined and will cause all rays that are shot from the surface to be emitted normal to the surface. This is useful for using the surface to simulate a heating source. The surface will emit with an emissivity of unity, but will also appear 100% specularly transparent to the rest of the model, so that the surface only behaves as a heat source.

The Top Side Overrides and Bottom Side Overrides buttons allow the user to input a different optical property for each node. In the Optics Override window, type the node number in smn.# format (e.g. MAIN.1) followed by a comma. On the right side of the window, select the desired optical property from the drop-down list and click on Insert. This capability is similar to the TRASYS MODPR capability.

4.3.1.4 Conductance/Capacitance Tab

Output of capacitance and conductance data to SINDA/FLUINT may be specified by the Thin Shell Data dialog box Cond/Cap tab as shown in Figure 4-11.

Generate Cond/Cap or Not Generated. The Generate Cond/Cap (or Not Generated)

button opens an expression editor to allow the user to define a symbolic expression to determine whether the nodes and conductors of the surface are included in the SINDA/ FLUINT solution. If the expression is left black or equals one, the surface will be part of the thermal solution. If expression is set to zero, then nodes and conductors, as well as any defined insulation data, will not be generated; the button reads Not Generated when the expression equals zero.

Cond Submodel. This field allows the user to specify which submodel the intra-surface

conductors are placed in. Note that the Model Browser uses this field in the List By Sur- faces/Solids and also Contact Conductance modes.

Gen Nodes. The user may specify to have the nodes generated based on the material prop-

erty or simply as arithmetic nodes. If based on material properties, the nodes will be diffusion nodes only if enough information is provided (density, specific heat, and thickness).

Material. The drop-down field allows selecting a material from the thermophysical prop-

erties database (Section 3.2) or from alias names (Section 3.2.4) created in the current DWG file. When Use same ID’s on both sides check box is unchecked on the Numbering tab (Section 4.3.1.2), the material must be specified for both sides (Top/Out and Bottom/In) and the user must also specify the material and distance between the nodes (Separation). See Section 9.2.1 "Double-Sided Surfaces" for information on the double-sided surface thermal network. The material use for the Separation can have an effective emissivity spec- ified (Section 3.2.3.1).

Surfaces that reference properties with anisotropic inputs will be modeled orthotropi- cally. That is, the principle directions of conduction will line up with the principle coordi- nates of the surface. The principle directions are provided in Table 3-1. Finite element surfaces that reference anisotropic materials must have the name of a material orienter specified in the field Material Orientation name. See Section 3.2.6for more information about material orienters.

Multipliers

The multiplier fields allow adjusting the thermophysical properties for the surface. The Density multiplier can be used to adjust the mass of a surface. The fields for U or X Cond, V or Y Cond, and W or Z Cond adjust the conductivity in the principle directions for primitives (Table 3-1) or the directions defined by the material orienter (Section 3.2.6).

4.3.1.5 Contact Conductance Tab

Note: When thermal connections must be modeled between sur- faces or solids, three choices are available: global contact (dis- cussed here), contactors (see “Contactors” on page 4-74), and merge nodes (see “Merge Coincident Nodes” on page 4-108). For finite conductances, global contact is generally outdated: please consider using contactors instead. For very large conductances or perfect contact (infinite conductance), use merge nodes, if pos- sible.

The Thin Shell Data dialog box Contact tab is shown in Figure 4-12. A surface may have contact associated with the top and bottom side and also along the edges. Simply check the box for the associated conductance and input the value in the associated field. Thermal Desktop will calculate which surface/edge is closest to the checked edge or face, and output the connection between the appropriate nodes. For a summary of how these calculations are made, please see “Area Contact Calculations” on page 9-3 and "Edge Contact Calculations" on page 9-6.

Each conductance can be input as either absolute or as a function of the area or length of the edge. For the area calculations, the user can select to have the test points generated at the exterior of the face (using the thickness of the surface) or at the mid plane of the

surface (where the thickness value is ignored). The user can check these calculations by using the Thermal > Model Checks > Show Contact Markers command. (See "Display Contact/Contactor Markers" on page 8-6).

Caution to users: Thermal Desktop does not calculate the conductance from the edge

of a surface to a center node. Therefore when adding contact, the value must include that conductance, or alternately the user should use edge nodes. Please see see “Circuit Board Conduction Example” on page 20-67 for guidance.

4.3.1.6 Insulation Tab

Insulation may be placed on the top/out side or bottom/in side of a surface with the Insulation tab shown in Figure 4-13. By checking the Put on top/out side and/or the Put on bottom/in side boxes, the user places insulation on that side of the surface. The P button allows the user to specify insulation or no insulation based on a symbolic expression (Section 2.10.9). Restrictions and assumptions of insulation applied through the Insulation tab are: • Insulation conductors are based on constant area. Area changes due to changing radius

are not accounted.

• The thickness of the insulation is not used in radiation calculations

• The optical properties of the insulation are applied on the Radiation tab as the optical properties of the surface. If insulation is turned off by programming or overrides (both described below), then the optical properties should be changed, as appropriate. • Insulation is assumed to be 1D with conductors only in the thickness direction. The

exception to this is the use of Material Stacks (Section 3.2.5).

• The insulation will generate linear and radiation conductors within the insulation based on the material properties:

• if the effective emissivity of the material is positive (non-zero), then a radiation conductor will be created with the value of _eff*Area

• if the conductivity of the material and the Thickness of the insulation are both positive, then a linear conductor will be created with a value of k*Area/Thickness • if both of the above conditions are met, then both a linear and radiation conduc- tor will be created.

A schematic of the SINDA model is shown in Figure 4-14. The actual insulation SINDA nodes are not represented graphically in Thermal Desktop. The optical properties used for radiation calculations of the insulating material must be set on the radiation page (See "Radiation Tab" on page 4-13). A special postprocessing check box has been added so that the user may select to display the calculated insulation node temperatures on the model (See "SINDA/FLUINT Dataset" on page 17-13).