Shell Pair Definition
Creo Simulate allows you to define shell pairs for both part and assembly models. Creo Simulate uses the shell pairs that you define to form a network of compressed surfaces called the midsurface. Creo Simulate places elements only on the midsurface, using the thickness associated with each portion of the shell to determine the depth of the elements.
Click
Refine Model >
Shell Pair. The
Shell Pair Definition dialog box opens.
Use the items in this dialog box to define shell pairs and assign materials and material orientation to the shell pair. You can also use these items to edit shell pairs. The items on the Shell Pair Definition dialog box are as follows:
• Name—Type a name for a shell pair or use the default name.
• Type—Creo Simulate uses the thickness associated with each shell pair to calculate the thickness of the shell elements. If it encounters unopposed surfaces in your model, Creo Simulate uses the thickness of a neighboring or related pair to define the thickness for that portion of the model. Assign one of the following types to the shell pair based on the thickness of the shell pair:
◦ Constant—Select opposing paired surfaces that are parallel to each other and equidistant from the opposing surfaces. You can also select concentric surfaces for constant thickness shell pairs.
◦ Variable—Select opposing surfaces that are neither parallel nor concentric. You also can select multiple surfaces that are parallel to the opposing surfaces but not equidistant from the opposing surfaces. See the example on
variable thickness shell pairs.
A model must satisfy the following criteria to be appropriate for defining variable thickness shell pairs.
▪ Does not require high accuracy or solution quality near the variable thickness pairs.
▪ The behavior of shell pairs during meshing is not sensitive to minor shape changes.
|  Shell pairs that are defined as multiconstant thickness shell pairs in Pro/ENGINEER Wildfire 5.0 or earlier are converted to variable thickness shell pairs. |
• References—Select top and bottom surfaces on the same volume or part. The first surface you pick is the top surface. You can use:
◦ Auto Select Opposing Surfaces—This check box is selected by default to automatically select the opposing surface of a shell pair. This check box is active only for constant thickness type shell pairs.
• Pair Properties—Define various shell pair properties:
◦ Placement
▪ Midsurface—The shell is placed at the midsurface of the shell pair. This is the default for constant thickness type of shell pair.
▪ Top
—The shell is placed at the position of the top surface of the shell pair.
▪ Bottom—The shell is placed at the position of the bottom surface of the shell pair.
▪ Selected Surface—Specify the surface on which you want to place a compressed shell pair. A solid surface, a quilt surface, or a datum plane can be selected as a placement surface. The shell is placed at the specified position. The surface collector below the Placement list is activated when you select Selected Surface.
For a Midsurface placement type, you can define a variable thickness shell pair only for the following reference surface types:
any two planes
coaxial cylinders
coaxial cylinder and cone
coaxial cones
For all other reference surface types, the shell pair definition fails if you select the Midsurface placement type.
| If you place the surface pair at any location other than the midsurface, Creo Simulate calculates the distance between the selected location and the midsurface and writes the value to the MSC/NASTRAN output file. Creo Simulate does not write the offset value to the ANSYS output file. |
To review the shell pair placement using the
Simulation Geometry dialog box, click
Refine Model >
Review Geometry in native mode or click
Home >
Review Geometry in FEM mode, respectively. The
Simulation Geometry dialog box opens.
◦ Extend Adjacent Surfaces—This check box is cleared by default. For mixed models, that is
Solid / Midsurface compression
Creo Simulate inserts cleave surfaces at the boundaries of the top and bottom shell pair surfaces. The angle between the shell pair surfaces and the adjacent tangent solid surfaces must be less than the angle specified by the configuration option
sim_extend_surf_max_angle. If this check box is selected,
Creo Simulate extends the adjacent surfaces regardless of the value of
sim_extend_surf_max_angle. Solid Midsurface compression fails since extensions of the adjacent surfaces cannot intersect the shell placement surface. For shell pairs defined in Pro/ENGINEER Mechanica 4.0 and earlier versions, this check box is selected by default. See the example.
Example: Extend Adjacent Surfaces.
• Material Properties—Assign material properties to the shell pair.
◦ Material—Use the part material or click
More to open the
Materials dialog box and assign a material to the shell pair. By default the shell pair will have the same material as the part. If you select
Part Material for assembly level models, the shell pair inherits material properties assigned to the part that the shell pair surfaces belong to.
• Use these options to perform the following tasks:
◦ 
—Creates the current shell pair and begins the creation of another shell pair by erasing references but retaining all options of the previous pair. This is very useful when you want to quickly create several shell pairs with the same properties.
◦ 
—Accepts the selections and closes the dialog box.
◦ 
—Rejects the selections and closes the dialog box.