When running a CAE analysis, depending on the model size and the type of analysis, it can demand high computational power and take many hours to run. Taking the advantage of the structure symmetry conditions can lead to huge savings in modelling effort, computational time, and file storage. The reduction of the model could also allow the user to use a finer mesh, resulting in a more accurate analysis than a coarsely meshed full model. In this article, we will see how to use this technique correctly and the necessary constraints and updates in the boundary conditions.
Of course, the existence of a symmetric plane with respect to which geometry, constraints, and loads are symmetric is a prerequisite for using this boundary condition.
The general rule for a symmetry displacement condition is that the displacement vector component perpendicular to the plane is zero and the rotational vector components parallel to the plane are zero. In other words:
|
Symmetry Plan |
Constrained DOFs |
|
xy |
Tz, Rx e Ry (dofs 3,4,5) |
|
xz |
Ty, Rx e Rz (dofs 2,4,6) |
|
yz |
Tx, Ry e Rz (dofs 1,4,6) |
Where:
Ti: Translational DOF
Ri: Rotational DOF
The example below shows the contact between two cylinders. We can notice that it is possible to model only 1/8 of each cylinder:
For solid element nodes, since they support only translational DOFs, the rotational DOFs do not need to be constrained.
It is important to note that geometry AND loads should be symmetric. The load should also be divided based on applied symmetry:
- ½ MODEL → ½ LOAD
- ¼ MODEL → ¼ LOAD
- Etc.
NOTE: For PRESSURE loads, since pressure acts on an area, there is no need to change the value of the pressure at all.