Creating user-defined midsurfaces

Use the User Defined Midsurface command to specify an existing sheet body as the midsurface of a selected solid body. With User Defined Midsurface, you can relate any sheet body to any solid body; the software does not perform any checks to ensure that the sheet body you specify as the midsurface is in proximity to the associated solid body. As a best practice, however, the sheet body you designate as the midsurface should lie within the confines of the associated solid body. User Defined Midsurface can be useful in situations where alternate methods of midsurface creation do not produce satisfactory results.

User-defined midsurfaces that extend beyond the solid body

A user- defined midsurface can contain surfaces that extend beyond the limits of the associated solid body.

• In some cases, only a very small portion of the midsurface protrudes outside the solid body. This can occur because of slight variations in trimming around the edges of the midsurface. When you mesh these types of midsurfaces, some elements may lie either partially or entirely outside the solid body.

• In other cases, the midsurface may extend grossly outside the solid body, as shown below. Here, both the yellow and green regions are considered to lie outside the solid body.

Computing the thickness of a user-defined midsurface

The software does not determine the thickness of a user-defined midsurface until you query the thickness of the mesh the midsurface. You can use either the Thickness Information or the Display 2D Element Thickness command to query the midsurface's thickness.

Note:

For the software to apply the thickness data from the midsurface to the mesh, you must set the Thickness Source option in the Mesh Associated Data dialog box to Midsurface.

To determine the thickness of a user defined midsurface the software casts a ray along the normal from each node in the mesh on the midsurface to the solid body. The software sums the calculated lengths of the rays to determine the appropriate thickness at that node.

For nodes that lie completely within the associated solid body, the software then compares the computed thickness to the specified Inside Minimum and Inside Maximum thickness values in the User Defined Midsurface dialog box:

• If the computed thickness value falls between the specified Inside Minimum and Inside Maximum, the software assigns the computed thickness value to the node.

• If the computed thickness value is greater than the specified range, the software assigns the specified Inside Maximum thickness value to the node.

• If the computed thickness value is less than the specified range, the software assigns the specified Inside Minimum thickness value to the node.

For nodes that lie completely outside solid body, the software uses the specified Outside setting as the thickness at that node.

Assigning appropriate thickness setting values

With a user-defined midsurface, you must define appropriate values for the Thickness Settings options in the User Defined Midsurface dialog box.

• The Inside Minimum thickness is the minimum thickness the software can assign to any node that lies inside the associated solid body.

• The Inside Maximum thickness is the maximum thickness the software can assign to any node that lies inside the associated solid body. If your model contains excessively thick regions that you do not want to be considered in the thickness calculation, you can use the Inside Maximum value to place an upper limit on the thickness. In many cases, you may want to set the Inside Maximum value to the average thickness of the body.For example, consider the following solid body in which the midsurface is shown in blue. The average thickness of the body is 4mm, though the thickness in the rib is 10mm. When the software casts rays from the point shown in red below, the calculated thickness will be 10mm. If you want the software to ignore the thickness through the rib at that point, you can use the Inside Maximum field to specify a maximum thickness of 4mm.

• The Outside thickness is the thickness that the software assigns to all nodes that lie outside the associated solid body. A model will not solve if it contains an element with a thickness value of 0. Therefore, in most cases, you should specify a value greater than 0 for this option. However, in some modeling situations, you may want to assign selected nodes a thickness of 0. For example, if you create a midsurface on an airfoil, you may want selected nodes on the trailing edge to have a thickness of 0. As long as other nodes in the associated element have an assigned thickness, the model will solve.

Tools for validating the assigned thickness values

After you create and mesh a midsurface, you should validate that the assigned thickness values are correct.

• You can use the Thickness Information command to create a hedgehog type display of the 2D element thickness values in your model.

• You can use the Display 2D Element Thickness option in the Mesh Display dialog box to have the software display the elements in the graphics window with their assigned thickness values.

If you find problems with the assigned thickness values, you can edit the midsurface and adjust the Thickness Settings.

For more information, see Creating displays to validate element thickness.

How do I

Create a midsurface by face pairs

Modify the face pairs in an existing midsurface

Define a midsurface with the Offset method

Define a midsurface with the User Defined method

Insert a replacement mid-sheet into a face pair

Learn more

Creating midsurfaces before meshing

Selecting appropriate parts for midsurfacing

Creating a midsurface by pairing faces

Understanding face pair creation

Working with the Face Pair list

Understanding midsurface creation and trimming methods

Controlling midsurface display

Creating a midsurface with the Offset method

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Creating user-defined midsurfaces, Simcenter 3D 2021.1 Series

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