Software Use > Analyzing & Optimizing Composite Layups

Hard to understand HyperSizer calculation in sandwich optimization

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iankim:
Hi,

I've been working on sizing a structure with unstiffened panel/sandwich panel concept.
As I've been accumulating results after several iterations,
I found that HyperSizer seemed to distribute the load too unevenly,
and it led the panel with too much load to be too thick, which is unreasonable.
Attachments I put to this message shows that evenly distributed Nx originally
(1st run) gets to be changed such that bottom face carries too much compressive load
(3rd run).
This causes the total weight to increase considerably(top face has smallest thickness
and cannot become 0 in the real world) and hinder speedy convergence.

I'd like your any advice or comment on this topic, thanks.

Ian.

iankim:
If you check the trend of variables change as shown in the figures attached
(result of 1st run, 3rd run and 5th run respectively),
you'll find the thickness of bottom panel and honeycomb are going to extreme,
and it leads the weight to increase continuously.

The weight of 'Skin_Up_A' group changes from

40.3 -> 42.1 -> 47.4 -> 51.1 -> 54.2 kg

as iteration progresses, and it doesn't seem to me that it converges to any value.

What's the problem supposed to be???

Phil:
Hi,

What kind of loading do you have on this panel?  Are there pressure loads?  Are you superimposing pressure.  One thing I am thinking it could possibly be is that if you are superimposing pressure and also have moments from the FEM then you could be double-bookkeeping the moment load, which would cause one facesheet to see a higher load than the other.   If this is the case you might try "zeroing" the moments from the FEA using the checkbox on the FBD tab.  If you do not have the "Superimpose Pressure" button turned on, then do not zero out the FEA moments.

One thing you could try is to link the top and bottom facesheet material and thickness (these options are found on the Concept tab).    Doing this will cause the optimized result to have identical facesheets.

iankim:
Thanks, Phil.

As shown in the attachments of this post,
there is no superimposed pressure.
All load are nodal loads in FEM, so your first comment doesn't apply to this case.

Secondly, I tried to optimize the problem with top and bottom facesheets
linked together in the first place as found in the second attachment,
only to witness the weight becomes even greater.
That's because the thickness of top facesheet follows that of bottom facesheet,
while bottom sheet has to be thick but top sheet doesn't need to be so, though.
This means I think that load distribution to each part doesn't change
regardless of whether two sheets are linked or not.

What do you think of this...?

Phil:
It seems like you are getting a very large bending moment introduced into your panel in addition to an axial load.  This would cause the panel to load up heavily in one face and not the other.   For example, if you have pure moment, then you would get a tension in one face and compression in the other.  Then if you apply a membrane tension to the panel in addition to the moment, then it would make the tension face worse while relieving the force in the compression face.

On the Options tab of the sizing form, do you have sandwich midplane (the second option) chosen as the reference plane?  If not, then you might be loading your panel in the FEM in one of the facesheets which might cause this behavior.

Can you help me understand the loading that you are applying to your panel?  Do you have free rotation edges on your model or are they fixed edges?

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