Shell elements allow you to analyze face parts and thin-walled parts. You must define a shell element before you can properly analyze these types of parts.
If you define a shell thickness for a face part, you must specify the thickness either as thickness for symmetric shells or two values if you want to use asymmetric shells.
To define a shell element,
1. Click Modify and then, in the Mesh group, click the arrow next to Shell Thickness.
2. Click Create. The Shell Thickness dialog box opens.
3. Click Study and select an analysis study in the Structure Browser.
4. Type a Name for the shell element.
5. Now you must select the reference faces:
◦ Click Ref. Faces and select the face or faces you want to use as the reference.
◦ Click Ref. Parts and select a part in the viewport to select all the faces of a part.
◦ Click Start Face and select the first face on the surface you want to use as a reference. All faces tangentially connected to the first face will be automatically selected.
to complete the operation.