Symmetry Expansion in CGX

Making use of problem symmetries can significantly reduce the model size and complexity. However, sometimes it is useful, to display the full model. This page explains how to do that.

To enable these procedures, some new functions in CGX were required. Their development was supported by Brandenburg University of Applied Sciences, Germany.

Expanding Axisymmetric Models

You can expand axisymmetric models with the swep command in CGX 2.10. You have to use 2D-output in CCX.

swep <2Dset> <3Dset> rot <angle> <div>

Set <2Dset> is swept together with the results and then deleted. The new elements are stored in <3Dset>. If you want to keep the 2D elements, then you have to create a copy first and make sure not to sweep the set all.

Command Template

To plot the full expansion:

swep all new rot y 360 40
trfm cyl y
plot fv all

To plot a partial expansion in grey and the colored base region:

seta base all
copy base 2D tra 0 0 0.001
swep base new rot y 270 30
trfm cyl y
plot f new n
plus ev 2D

Example 1

Circular plates with hole under axial load

Plotting the colored faces of the base region on top of the shaded expanded model fails due both having the same surface positions, which leads to a random mixture of grey and colored display.

In order to avoid that, create a copy of the base region with a slight offset in tangential (z) direction

seta base all
copy base 2D tra 0 0 0.001

Then sweep the base region (the non-translated version) to the desired angle

swep base new rot y 270 30

If you want to see the results in cylindrical co-ordinates, take care to transform the results first:

trfm cyl y

This created a full colored plot of the expanded region (right image above)

plot fv all

This creates a shaded plot of the expanded region with a superimposed color plot of the (shifted) base region. In the left image above, also the nodes in the base region are marked, in order to visualize the element type (with or without midside nodes)

plot f new n
plus ev 2D
plus n 2D

Expanding Mirror Symmetry

In CGX 2.10 the mirror copy function has been simplified. Now it is sufficient to just specify the normal axis to the mirror plane:

copy <set> <newset> mir x|y|z

This is sufficient for symmetry expansion of most models, as usually the symmetry boundary planes go through the origin.

Command Template

This template assumes that results have been read into CGX and a dataset has been selected for display. It expands a base model in all three directions and plots the expanded parts in grey and the base region in color (according to the dataset values)

seta base all
copy all new mir x
copy all new mir y
copy all new mir z
comp new do
plot f new n
plus fv base

Example 1

Inflation of a square pillow

Example 2

IShrinkage model for weld distortion

Example 3

4-point bending of a sandwich structure

Here, the colored plot in the base model has been limited to the sandwich core.

read core.nam inp
plot f new n
plus fv core