## General Mechanical

#### Properly implementing symmetric boundary conditions

• enina1992
Subscriber

I am trying to emulate the picture below by imposing symmetric boundary conditions so that I can improve my mesh size by reducing the geometry.

• peteroznewman
Subscriber
nThank you for fully documenting your question, it makes it easy to give you guidance.nThe shaft is bending up, so you can only use two planes of symmetry, a vertical one through the center of the wheel, and a vertical one through the axle. Because the axle is bending up, you can't slice horizontally through the axle. You haven't shown a triad, so I don't know which direction is up, but I will assume it is the Y axis.nYou either use Symmetry Regions or you use Displacement supports, you don't do both because they each do the same thing, but if you did both correctly, it wouldn't hurt, it is just a waste of time setting it up.nBut you have a mistake in two of the symmetry regions. The Symmetry region Details window has a Symmetry Normal setting and its default value is X axis and that doesn't automatically change when you pick the faces, you have to manually match the Symmetry Normal and type in the correct normal, such as Y and Z. However, you only want two planes, X and Z and you don't want a Symmetry Region for Y, as that is the horizontal plane.nThere is a better constraint than Fixed Support for the end of the axle. Delete that. Delete the two Displacements and use the two corrected Symmetry Regions. Those take away 5 degrees of freedom of the wheel. The last constraint is in the Y direction. Put a Remote Displacement on the end face of the axle where you had the Fixed Support. Now you can leave everything Free except put a 0 for Y.nIf the total force on the full model was F, then you apply F/4 because you only have 1/4 of the model when you make two vertical cuts. n