Model Browser Usage for Large Models

Several options in the model browser can speed up its usage for large models. They are ‘Auto Update’, ‘Auto Select’, ‘Copy Selection Set to AutoCAD’, and ‘Do Not Expand Nodes’. For the speed up, turn off ‘Auto Update’, ‘Auto Select’, and ‘Copy Selection Set to AutoCAD’, and turn on ‘Do Not Expand Nodes’. ‘Auto Select’ is the algorithm that determines what is selected. When it is on, the program will determine the selection set every time the user makes a selection in the tree. When it is off, the program will only determine the selection set when a command is issued.

The ‘Do Not Expand Nodes’ options only affects the generation of the ‘Submodel.Id’ tree. Only the node names are in the tree, the objects are not, thus making the tree build significantly faster. The user can still edit objects in the model, but cannot specifically pick on them in the tree.

2.5

Domain Tag Sets

A Domain Tag Set is a set of nodes, edges, faces, solids, lumps or paths that define a region of the model that is distinctive in purpose. Domain tag sets can be used to specify regions for thermal entities such as conductors, contactors, heat loads, and ties. For example, instead of applying a heat load directly to a group of planar elements, it could be applied to a Domain Tag Set consisting of a collection of planar elements.

The term “domain tag set” is derived from the TD Direct feature called “domains” that are used to mark, or tag, regions of the geometry within SpaceClaim. Nodes and elements created by TD Direct are placed in domain tag sets representing the domain created in SpaceClaim.

Domain tag set names remain persistent in the thermal entities that use them, even if the domain tag set is empty or all entities are replaced. If the same heatload is desired to be applied to another set of elements, the domain tag set could be modified instead of the heat load.

Domain tag sets allow thermal entities to exist without an active connection to nodes, lumps, or analysis geometry. This permits thermal objects to use domain tag sets as place- holders, to be defined at a later stage in the analysis process. It also allows the objects to which a thermal entity connects to be deleted and replaced without affecting the lifetime of the thermal entity.

Without using domain tag sets, if the geometry to which a node-to-surface conductor is connected is deleted, the conductor itself would also be deleted. With domain tag sets, the geometry can be deleted without deleting the definition of the conductor (the conductor would not be included in the solution since it is not connected to any nodes).

Although domain tag sets are useful for a thermal model that exists in a single drawing (*.dwg) file, the real utility is when domain tag sets are used to connect models that exist in separate drawings. A domain tag set can be defined in one drawing, and referenced by

thermal entities in another drawing. When the first drawing is XREF’d into the second drawing, Domain tag sets defined in the first drawing are available for use by thermal entities in the second drawing. This allows a complicated system-level thermal model to exist in separate drawings, rather than requiring combination by cutting and pasting. Maintaining separate drawings allows different engineers in different locations to collaborate on a single model, and allows modular updates - simply provide an a update to the XREF’d drawings, and the master drawing is automatically updated.

Note: In order to use External References as part of a thermal model, the user must check the Load External References Into Radiation and Cond/Cap calculations checkbox on the User Pref- erences Advanced tab (see “Advanced Preferences” on page 2- 32). For more information about external references see “Work- ing with External References” on page 19-10 or AutoCAD help on External References or XREF’s.

Domain tag sets can also be defined externally in imported FE models and used to connect to other portions of the thermal model. If an update to the FE model is reimported, and the updated FE model retains the same domain tag set names, the model is automatically reconnected to the new elements defined in the domain tag sets. If the finite element format supports element groups, they will be placed into a domain tag set of type Face Set using the group defined in the FE import file with “_2D” appended for surface elements and “_3D” appended for solid elements. If the format supports node groups, they will be placed into a domain tag set of type Node Set with “_Nodes” appended to the FE defined group name.

To create a domain tag set directly in Thermal Desktop, choose Thermal > Tag Set Manager. The Tag Set Manager dialog appears (Figure 2-10). Selecting the Create button opens the Create New Tag Set dialog (also shown in Figure 2-10). This dialog allows the user to specify a name for the domain tag set and the domain tag set type. Domain tag set types are:

• Face set - set of specific object faces (top, bottom, etc) • Edge set - set of specific object edges (X at Y= 0, etc) • Node set - set of nodes

• Solid set - set of solid objects • Lump set - set of lumps • Path set - set of paths

If a domain tag set is renamed, all the references to it used by thermal entities are also renamed. If a domain tag set is deleted, it is also removed from any thermal entities that were referencing it. Domain tag sets are edited by selecting the domain tag set name in the upper list box, and then using the controls in the lower region to add and delete objects. The lower section works identically to the standard object selection editing control used in all of the Thermal Desktop entities.

Domain tag sets can be used in place of directly selected entities whenever the “Select entities...” prompt is displayed by a thermal entity. The domain tag set type, however, must match the type expected by the thermal entity. For example, a Node Set domain tag set cannot be used for the definition of Heat Load on Surface: a Face Set domain tag set must be used.

Domain tag sets are connected to a thermal entity when the keyword tag is entered at the Select entities prompt. A form will appear allowing the selection of a domain tag set. Only the domain tag sets valid for the type of selection are displayed. For example, if the object issuing the selection prompt requires nodes, only those domain tag sets of type Node Set are displayed.

Domain tag sets are similar to AutoCAD groups, and in fact are a special type of Auto- CAD group. Domain tag sets defined using the Tag Set Manager are also available as a generic AutoCAD group and can be used wherever AutoCAD groups are used. Domain tag sets differ from AutoCAD groups in that additional information is saved about the collection of entities, for example, the particular edges of a collection of surfaces.

The use of domain tag sets also differs from the use of AutoCAD groups in that groups are just a short hand way of selecting objects. When the group keyword is used at a Select entities prompt, then name of a group may be entered. The thermal entity will select all the objects that are in the group as if they were selected by picking on the screen. The objects that are in the group are expanded and placed in the selection set at that time.

Domain tag sets, on the other hand, delay the expansion until the thermal entity is used in an analysis. When the tag keyword is used, only the name of the domain tag set is saved with the thermal entity doing the selection and the set of objects in the domain tag set are not obtained until analysis time. The delayed expansion allows redefinition of a domain tag set without invalidating or causing thermal entities to be deleted.

For example, in a drawing of a spacecraft bus, one side of spacecraft panel can be connected to a contactor, with the “to” surfaces specified as the panel, and the “from” surfaces specified as a domain tag set named “BasePlate”. In this master drawing, an empty domain tag set named BasePlate is created as a placeholder so it is available at the Select entities prompt when the contactor prompts for the “from” surfaces.

In a second drawing, a thermal model of an antenna boom can be created that contains a domain tag set named BasePlate that includes the surfaces that make up the mounting plate of the boom. These are the surfaces that attach the boom to the side of the panel. When the boom drawing is externally referenced by the spacecraft drawing, the contactor will automatically be connected between the surfaces on the panel of the spacecraft, and the mounting plate surfaces in the boom drawing. The contents of the domain tag set named BasePlate in the XREF’d drawing is automatically included in the contents of the domain tag set named BasePlate in the master drawing. More specifically, when a thermal entity references the name of a domain tag set, all objects from all drawings that have the same domain tag set name are included in the master domain tag set.

Changes to the boom drawing can be made, including what surfaces are used for the mounting plate, and the model will remain valid as long as the desired surfaces are included in the domain tag set named BasePlate. Different drawings with different boom concepts can be XREF’d into the master drawing. As long as the XREF’d drawings define a domain tag set named BasePlate, the connection to the master thermal model will be automatic.

2.6

Defaults

The Thermal > Defaults > * commands are used to set the defaults for the creation of any Thermal Desktop entity. For example, the Thermal > Defaults > Conductor command will bring up the Conductor dialog box. When a new conductor is created, it will have the properties of the default. Defaults that are assigned within the template file will be available for all models created with that template.

2.7

Preferences

The Thermal > Preferences command brings up a tabbed User Preferences dialog box that allows the user to:

• select the units

• specify graphics visibility of objects • specify graphics size

• set SINDA preferences

• control the format of the global output of SINDA/FLUINT data

Want "Hands-On" Information? Most of the exercises in the tutorial

chapters give the user experience using and changing User Preferences. But to obtain a basic understanding of the preferences and how to work with them, see Section 20.5 "Circuit Board Conduction Example" on page 20-67 and Section 20.6 "Beer Can Example" on page 20-89.

2.7.1 Units

The Thermal > Preferences command will display the User Preferences dialog box. This dialog box consists of multiple tabbed sections. The Units tab is shown in Figure 2- 11. The Units tab in the dialog box allows the user to control which units they are working in. All data in other dialog boxes will be displayed in the units the user chooses in this dialog box and the units displayed under Derived Units. All calculated output will also be in the user units, except if a FloCAD® model is present (see Output Units for FLUINT Models, below). The SINDA/FLUINT input file that is created - specifically the *.cc file - will be in the user units also. This means that all logic and registers used in the solution must be consistent with the units selection in models without FloCAD objects.

Note: Power units are Energy/Time. To have Power in Watts and Time in Hours, select Hours for Time and WattHours for Energy.

When the model length units are changed, the geometry is automatically scaled to the new units. For example, if a 1 by 1 meter rectangle placed at the origin was previously input and the user changed the model length units from meters to centimeters, the model will be scaled by 100. The rectangle end point will now be point 100, 0. The command tests for locked layers and will temporarily unlock the layer to perform the scale operation.

To prevent the model from being scaled, check the Don’t scale model to new length units check box. For example, the model may have been input using values for inches, but the units were set to meters at the time. Changing the units to inches will apply a scale factor of 39.37 to convert the model lengths from meters to inches. Since the model was already input in inches, scaling is not required and this check box should be selected.

Important: Please note that this option only affects the graph- ical entities, and will not have any effect on the properties of those objects, such as thickness.

The model may be scaled at any time using the SCALE command. Type the command scale into the Command line, followed by the keyword all (with 0,0 as the base point) and the desired factor. Be sure that the layers that contain geometry that you want to scale are on and unlocked. Individual portions of the model may be scaled by selecting objects rather than entering the keyword all.