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symmetry and pressure loads...

PAULKORENKIEWIC
1-Newbie

symmetry and pressure loads...

Guru's,

I have been getting some odd results on an analysis that I've been
running with symmetry and a pressure load. As a check, I set up a
simple analysis of a cylinder with a hole drilled in it. The bottom of
the cylinder is fixed and the hole has an applied pressure load to it's
surfaces. I created measures in x,y and z on the constraint to measure
reaction loads. I anticipated seeing ZERO z and x reaction forces as
the internal pressure should be completely balanced. The model looks
like this:


I was shocked to see the following reaction load measures: x = 0,
y=189,673 and z= -15,896 ! Is this the way it's supposed to work? My
understanding was the creating a symmetry plane would essentially create
a mirror image of everything; part, loads, constraints.... As a check
to this, I ran without symmetry. The model looks like this:


Results for the reaction load measures were: x=0, y=379,347 and z=0
which is just what I expected from both analysis.

So is it correct that I am wrong, and that creating a symmetry plane
ONLY creates a mirror of the model and constraints but NOT the loads?

Also, if I was applying a force to the top surface of my example above
and no pressure load, if I was running symmetry, I would apply HALF the
force, is that correct?

thanks in advance...

Paul Korenkiewicz
FEV , Inc.
4554 Glenmeade
Auburn Hills, MI, 48326-1766

2 REPLIES 2

Paul,

My guess is that if you look at the reaction from your symmetry
constraint, you will see the opposing balance of the -15.896 (in the Z
direction) located there.

Regards,

Chris

A couple responses, and it seems the answer is that the symmetry
constraint does mirror everything; model, loads and constraints. THE
measures, however, only report on what is present in the model. I
confirmed this by comparing the results of the simple analyses done
below. You can see displacement is identical. IF there really was an
unbalanced force being applied the results would be drastically
different. Thanks...


Paul Korenkiewicz
FEV , Inc.
4554 Glenmeade
Auburn Hills, MI, 48326-1766

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