FEM ElementGeometry2D/ro

ElementGeometry2D is used to define the thickness of 2D (shell and introduced in 1.0: plane stress/strain) FEM elements, all or lying on the chosen surface. It has to be defined also for axisymmetric models, even though the thickness value is irrelevant in such a case.

2D mesh (on the left) and its expansion to solid elements done internally by CalculiX based on the specified thickness (on the right)

1. There are several ways to invoke the command:
   • Press the Shell Plate Thickness button.
   • Select the Model → Element Geometry → Shell Plate Thickness option from the menu.
2. Specify the shell thickness.
3. Optionally press the Add button in the task panel and then click on the face you want to have a prescribed thickness. If the face selection is empty, all the remaining faces (whose thickness is not defined by other FEM ElementGeometry2D objects) will be automatically assigned. introduced in 1.1: To remove faces from the selection, press the Remove button.

Limitations

• Currently, analyses combining shell elements with solid or edge (beam) elements are not supported.

Properties

• DateThickness: Specifies the thickness of the 2D elements.
• DateOffset - introduced in 1.1: Used only by CalculiX. Specifies offset of the shell mid-surface with respect to the meshed geometry. The unit is the shell thickness. Positive values indicate offset in the positive normal direction, negative values indicate offset in the opposite direction. Zero means no offset (mid-surface located on the meshed geometrical surface). For example, 0.5 means that the meshed geometrical surface will be the top surface of the expanded shell, while -0.5 means that it will be the bottom surface.

Offset examples on square plates (view from the side). Each blue line represents the actual geometry for which a 2D shell mesh is generated. The surface mesh is internally expanded to solid elements (green rectangles) by the solver. Offset direction depends on the sign of the specified offset value o and on the surface normal n. Normals in the bottom row were inverted. The offset is measured from the midsurface of the expanded mesh (red dashed line) to the surface of the geometry and 2D mesh (blue solid line) - in this direction indicated by the pink arrows. Thus, as explained above, it follows the normal direction when the offset value is positive and opposes it when the offset value is negative.

Notes

• For viewing results from CalculiX solver on the mesh expanded to the prescribed thickness, the property Beam Shell Result Output 3D in the FEM SolverCalculixCcxtools needs to be set to True. To just visualize the defined thicknesses before running actual calculations, one may run a check type analysis with this property set to True.
• This feature uses the *SHELL SECTION card in CalculiX for shell elements and *SOLID SECTION card for plane stress/strain and axisymmetric elements.