Translations:FEM ConstraintTie/11/en

From FreeCAD Documentation

introduced in version 1.0: Tie constraint can also be used to define cyclic symmetry. This allows the models exhibiting rotational periodic symmetry (repetitive circular patterns around a symmetry axis) to be analyzed using just a single representative sector. It can be particularly useful for rotors, shafts, turbines, fans, flywheels and similar parts, often in combination with centrifugal load (loading must also exhibit this form of symmetry). Cyclic symmetry can be defined by selecting the two faces of the cut for tie constraint and setting the following properties:

  • DataCyclic Symmetry: setting to true activates cyclic symmetry
  • DataSectors: total number of sectors, equal to 360° divided by the angle of the representative sector (e.g. 8 for 45° sector or 6 for 60° sector)
  • DataConnected Sectors: number of sectors displayed in results, set it to the same number as DataSectors if you want to visualize the whole 360° part
  • DataSymmetry Axis - axis of cyclic symmetry - global Z axis by default, can be moved by applying the Placement transformation to the Z versor (similar to what can be done with Part Lines - to understand how to move the symmetry axis, it might in fact be helpful to change the Placement of Part Line which is usually needed for centrifugal load anyway).

One important limitation of this feature in FEM is that boundary conditions can't be applied to the nodes of the slave surface of cyclic symmetry (slave surface in tie constraint definition) since that would cause an overconstraint. So in some cases, it might be necessary to remove the nodes lying on the edge between the face with the boundary condition and the slave surface of cyclic symmetry from the boundary condition definition. Unfortunately, FreeCAD doesn't operate on node sets and individual nodes can't be deselected so one would have to use workarounds like adding a narrow face partition as a transition between the slave surface and the surface with the boundary condition.