General Mechanical

High and low boundary in Linear periodic symmetry

• Gijoys4v
Subscriber

Hello Ansys,

what is this High and low boundary options in the details window of the Symmetry region under the session 'scope' in Linear periodic symmetry? How to use periodic linear symmetry?

• SaiD
Ansys Employee

Hello,

The part under "Structural and Thermal Linear Periodic Symmetry" explains how to use periodic linear symmetry: https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v201/en/wb_sim/ds_Symmetry_Region.html

Periodic Linear symmetry is used when a given structure repeats itself infinitely in a particular direction. The low and the high boundaries are basically 2 boundaries of the object in the direction in which the repetition occurs (see the figure in the documentation above). You can define the DOFs of the two boundaries to be the same or you can define constraint equations relating the DOFs of the low and high boundary.

Hope this helps,

Sai

• Wenlong
Ansys Employee

Hi Gijoys4v,

As the name suggests, the low boundary is the periodic boundary at the "low position" and the high boundary is the boundary at the "high position", they should be paired (have the same area, same properties) to make the symmetric boundary condition.

For example, in the manual, there is an example in which the part is shifted in the Y direction for -8mm, thus the negative Y direction is the "high position". For more information, please refer to https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v201/en/wb_sim/ds_Symmetry_Simulation.html.

If you want more theoretical part of the linear periodic symmetry, please refer to :https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v201/en/wb_sim/ds_Symmetry_Region.html%23ds_linear_periodic

Regards,

Wenlong

• Wenlong
Ansys Employee

Hi Gijoys4v,

Let me rephrase it and use the same image in the previous post. You can imagine the distance in the shifting direction as height, thus the origin point in the above figure is like the horizon, and the further away you move towards the negative Y direction, the higher you stand (because in the image negative Y direction is the shifting direction). So as a result, the red face is "higher" than the blue face, and that's why the red face is the high boundary and the blue face is the low boundary.

Hopefully this makes sense

Regards,

Wenlong

• Gijoys4v
Subscriber

Thanks for the reply Mr. Wenlong and Mr. Sdeogeka

But if I am having a model (say a rectangular bar) which is given periodic symmetry (because say the model is cut out from a very long rectangular Bar).

If I give one end face 'low position' and the other end face 'high position', then how can I give a displacement boundary condition to one end face. (because I want to give an axial tensile load to a very long rectangular bar)

• Wenlong
Ansys Employee

Hi,

I don't think that can be simulated using linear periodic anymore if you need to apply load to the symmetric faces. Also, as Sdeogeka pointed out to me, even though your geometry is repeating, the stress and strain may not.

Alternatively, I would just take a representative segment of the bar, and directly apply axial tensile load to the ends.

Regards,

Wenlong

• Gijoys4v
Subscriber

Thank you very much Mr. Wenlong and thank you Mr. Sdeogeka for the suggestions