Symmetry
The Symmetry node adds a boundary condition that represents symmetry in the geometry and in the loads. A symmetry condition is free in the plane and fixed in the out-of-plane direction. The symmetry plane is formed by the normal to the membrane surface and the edge tangent.
Coordinate System Selection
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 section is only shown if the Local Edge System is chosen in the Coordinate System Selection. 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.
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 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.mbrn.sym1.un.
Constraint Settings
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box.
In the COMSOL Multiphysics Reference Manual:
Location in User Interface
Context Menus
Ribbon
Physics tab with Membrane selected: