Symmetry

The 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.

When applied to an edge (in the Membrane interface) the symmetry plane is formed by the normal to the boundary and the edge tangent.

When the model is axisymmetric, use the Symmetry Plane node instead.

The node is only available with some COMSOL products (see https://www.comsol.com/products/specifications/). The constraint is not available in 1D and 1D axisymmetry; use a instead.

The symmetry constraint implies constraining the displacement in the normal direction, u·n = a. For a standard symmetry condition, a = 0, but this can be modified by settings in the section.

You can select boundaries that represent different symmetry planes in a single node. There are however some cases when such a selection should be avoided.

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If all selected boundaries, to within a small tolerance, are located in the same plane, then the normal vector, n, is computed using an averaging scheme. This remedies problems that can occur for example when not all nodes on a symmetry plane of an imported mesh lie exactly on the same plane. However, averaging is not possible if several symmetry planes are selected.

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In the section, you have the possibility to select as . The nodal method is more efficient than the default method. However, if two element faces that do not represent the same plane are part of the selection, the generated constraint will be incorrect at their intersection.

Shell Properties


	This section is only present in the Layered Shell interface, where it is described in the documentation for the Symmetry node.

Normal Direction Condition

You can allow a symmetry plane to move along its normal direction. This can be used to model situations where you want a plane to remain strictly planar but still relax the property of it being fixed.

From the list, select , , , or .

The value gives a standard symmetry condition.

Select 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 to prescribe the total reaction force acting on the direction normal to the symmetry plane. Enter the 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 .

Select to prescribe the displacement in the direction normal to the symmetry plane. Enter the un0. Setting the prescribed displacement to zero gives the same effect as using .

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Using , , or is only meaningful if the geometry selection corresponds to a single symmetry plane.

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When using or , 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.solid.sym1.un).

Constraint Settings

To display this section, click the button (

) and select in the dialog box.

In the COMSOL Multiphysics Reference Manual:

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Constraint Reaction Terms

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Weak Constraints

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Constraint Settings

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Excluded Surfaces, Excluded Edges, and Excluded Points


	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

Ribbon

Physics tab with selected:

Physics tab with or selected: