Symmetry
The Symmetry node adds an edge (3D), boundary (2D), or point (2D and 3D) condition that defines asymmetry edge, boundary, or point.
Coordinate System Selection
Specify the coordinate system to use for specifying the orientation of the symmetry plane. See the section Coordinate System Selection for Edge Load.
Symmetry
Select an Axis to use as symmetry plane normal to specify the direction of the normal to the symmetry plane in the selected coordinate system.
•
For 2D models, select 1 or 2 for the first or second axis, respectively.
•
For 3D models, select 1, 2, or 3 for the first, second, or third axis, respectively.
Normal Direction Condition
You can allow a symmetry plane to move along its normal direction. This can be used to model some situations where you want a plane to remain strictly planar but still relax the property of it being fixed.
From the drop-down list, select No displacement, Free Displacement, Prescribed force, or Prescribed displacement.
The value No displacement gives a standard symmetry condition.
Select Free Displacement to allow the symmetry plane to translate in the normal direction. The displacement is determined by the criterion that there is no resulting reaction force in the normal direction.
Select Prescribed force to prescribe the total reaction force acting on the direction normal to the symmetry plane. Enter the Normal force Fn. The force is defined as positive when acting along the outward normal of the symmetry plane. Setting the prescribed force to zero gives the same effect as using Free Displacement.
Select Prescribed displacement to prescribe the displacement in the direction normal to the symmetry plane. Enter the Normal displacement un0. Setting the prescribed displacement to zero gives the same effect as using No displacement.
•
Using Free Displacement, Prescribed force, or Prescribed displacement is only meaningful if the geometry selection corresponds to a single symmetry plane.
•
When using Free Displacement or Prescribed force, an extra global degree of freedom is added for determining the displacement in the normal direction. This degree of freedom will have a name of the type <component>.<interface>.<symmetry_tag>.un, for example comp1.beam.sym1.un.
Constraint Settings
To display this section, click the Show button () and select Advanced Physics Options.
In the COMSOL Multiphysics Reference Manual:
•
Constraint Reaction Terms
•
Weak Constraints
•
Constraint Settings
Symmetry Constraints
You can activate and deactivate this boundary condition by assigning it to a constraint group. See Load Cases in the Structural Mechanics Modeling chapter.
Location in User Interface
Context Menus
 Beam>Line Constraints>Symmetry
 Beam>More Constraints>Symmetry (Point)
Ribbon
Physics tab with Beam selected:
Edges>Line Constraints>Symmetry
Points>More Constraints>Symmetry