# How to apply symmetry

Symmetry conditions are important in FEA as they substantially reduce the computational burden and solve time. When applying symmetry it is crucial that you scale the component geometry accordingly, i.e. when applying symmetry in the width dimension ensure that the model you build is half the width of your final requirement.

There are several ways the can be applied in OnScale:

• Plane strain symmetry
• Half model: 2D and 3D - one axis only
• Quarter model: 2D and 3D two axes
• Eighth model: 3D only – all axes
• ‘Hall of mirrors’ effect: 2D and 3D – applied at minimum and maximum ranges of an axis causes an infinite number of copies in both directions.
`boun   side xmin symm /* Apply symmetry at minimum side of X   side xmax symm /* Apply symmetry at maximum side of X`
• Axisymmetric (2D only – takes a shape and revolves it around 360 degrees)
• Single axis only: axiy or axix
`grid \$indgrd \$jndgrd axix`

Also, when using symmetry ensure that you scale the electrode area accordingly if applying a piezoelectric load. Area scaling is used so that the solver knows the 'real' area of the electrodes on your device. For example, if half symmetry is used an area scaling factor of 2 is used when defining your electrode. The following are examples of typical cases:

• 3D full model => none required
• 3D Half symmetry => x 2
• 3D Quarter symmetry => x 4
• 2D model => x zlength
• 2D model half symmetry => x 2 x zlength
• 2D axisymmetric model => none required (radius allows area to be calculated)
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