Symmetry
The Symmetry node adds an edge or boundary condition that defines a symmetry edge or boundary.
Coordinate System Selection (Edges Only)
Specify the coordinate system to use for specifying a symmetry edge. From the Coordinate system list select from:
Local edge system (the default).
Global coordinate system (the standard global coordinate system).
Face Defining the Local Orientations
This setting is used in conjunction with a Local edge system. and Shell Local System. If symmetry is prescribed for an edge which is shared between boundaries, the edge system can be ambiguous. Select the boundary which should define the edge system. The default is Use face with lowest number.
Symmetry
If another coordinate system than the Local edge system is used, select an Axis to use as symmetry plane normal. 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.shell.sym1.un.
In the Plate interface, this section is only present when Use 3D formulation is selected in the interface settings.
Constraint Settings
To display this section, click the Show button () and select Advanced Physics Options.
In the COMSOL Multiphysics Reference Manual:
Location in User Interface
Context Menus
Shell>Face Constraints>Symmetry
Shell>More Constraints>Symmetry (Edge)
Plate>More Constraints>Symmetry (Boundary)
Ribbon
Physics tab with Shell selected:
Boundaries>Face Constraints>Symmetry
Edges>More Constraints>Symmetry
Physics tab with Plate selected:
Boundaries>More Constraints>Symmetry