## General Mechanical

#### How to use Linear Periodic Symmetry

• AchilleasMil
Subscriber

Hello,

I am trying to set a symmetry on a model which has a repetitive structure so I am trying to use a symmetry region of a linear periodic type.

My model is a sandwich panel with a kagome lattice type core. The core consists of beam bodies and the facesheets of surface bodies:

The original sandwich is after hiding the top face can be seen here:

I want to cut the panel in half and model the 1/2 of it by applying a symmetry boundary condition, but since the core is not normal symmetrical but has a repetitive pattern I am trying to use linear periodeic symmetry region.

After cutting accordingly the repetitive half that remains is the following:

I set the low boundary in the following edges of the facesheets:

and the high boundary in the according opposite edges of the facesheets :

I set the coordinate system at the high boundary edges:

and set the linear shift value as the distance of these edges: 36,83mm in the Y periodicity direction.

The model gets meshed but it doesn't run, I get different pivot warnings each time and have to limit a node every time with a remote displacement bc.

After setting the grapcical extension in ΔY :

I hit show mesh and I get the following :

(again the upper facesheet is hided).

So the linear periodic symmetry is not applied, or at least is not shown to be applied. A normal symmetry is showed and the core is not as it should be.

The surface bodies of the facesheets and the beam bodies of the core share topology from spaceclaim. The setup is a three point bending test:

How can I correctly set the symmetry in this model? It is also of interest to model th 1/4th of the panel by applying another linear periodic symmetry bc along the X direction.

Also does this idea of linear periodic symmetry make sense for two repetitions, or is the linear periodic feature only for infinite repetitions?

I want to use the symmetry in order to get necessary constraints in the static structural analysis of the sandwich panel.

Can you help me?

With Gratitude,

Achilleas Milios

• peteroznewman
Subscriber

Hello Achilleas,

Periodic symmetry is for an infinite array of blocks.

If you want to do a 1/2 model, you want just Symmetry or for a 1/4 model, two planes of Symmetry.

Regards,

Peter

• AchilleasMil
Subscriber

Hi sir,

My core is not symmetrical as shown above, so as I understand, there isn't another way (as I thought the linear periodic symmetry could be applied) to denote symmetry there and cut the model.

So in correlation to your suggestions for my question last week, is there any way here to simulate similarly with the other models (1/4th of the whole panel - two planes of symmetry) without applying symmetry?

Gratefully,

Achilleas

• peteroznewman
Subscriber

Hello Achilleas,

Your core looks symmetric from the top view. Why do you say it is not symmetric?

Here is one quarter section:

Here is that section mirrored by a vertical symmetry plane.

Here are those two mirrored by a horizontal symmetry plane.

It looks to me like you can use symmetry.

Regards,

Peter

• AchilleasMil
Subscriber

I know it looks but it isn't. Kagome lattice is a complex geometry which has a repetition pattern but doesn't have symmetry, so it cannot be mirrored.

The line which you draw cuts down beam bodies which have a comlex 3d geometry:

• Ashish Khemka
Ansys Employee

If it is not completely symmetric, then do you have a portion which can be considered for overall symmetry? If no then I do not see a way.

Regards,

Ashish Khemka

• suprtramp
Subscriber

Hello,

i have a question reagarding the linear periodic symmetry. I want to model an infinite array of blocks like in the picture.

I am not sure about the right settings for the symmetry. As low and high boundary i choosed the three faces on each side (you can see the blue faces in the picture). The direction of periodicity is the x - axis, but what is meant with linear shift? No matter what i choose - i will get an error message with a failed meshing.

Beste regards,

Niels