Recent Posts

21

Analyzing & Optimizing Stiffened Panels / Re: Discrete modelled stiffener - Web Beam concept offsets

« Last post by Gawain on January 16, 2020, 12:56:54 PM »

Thanks Stephen

Post processing the updated FEM before the Nastran run seems a possible solution.  I'll try that.

Thanks

Gawain 

22

Analyzing & Optimizing Stiffened Panels / Re: CBAR pin flags removal

« Last post by Stephen on January 16, 2020, 12:50:06 PM »

Gawain,

Interesting, I'll have to look into that. Thanks for the update and I'm glad it seems to be working as expected now!

-Stephen

23

Analyzing & Optimizing Stiffened Panels / Re: CBAR pin flags removal

« Last post by Gawain on January 16, 2020, 12:49:08 PM »

Stephen

Yes it only worked once I reimport the FEM.  It didn't recognise the pin flags until I reimported the FEM.

Gawain 

24

Analyzing & Optimizing Stiffened Panels / Re: Discrete modelled stiffener - Web Beam concept offsets

« Last post by Stephen on January 16, 2020, 10:43:26 AM »

Gawain,

This issue was actually previously identified and fixed in a more recent version of HyperSizer. It was indeed a bug and not the intended functionality.

If updating to the latest version is going to be a challenge, I think the remaining options would be to use DSM from the beginning (which will have implications on the speed of sizing and analysis), or to have a script that post-processes the updated FEM and corrects the bar offsets. The latter is definitely possible but would be somewhat involved (as you would need to map between property IDs and CBAR elements to determine the appropriate element offset).

Apologies that I can't really think of a better solution right now..

-Stephen

25

Analyzing & Optimizing Stiffened Panels / Re: CBAR pin flags removal

« Last post by Stephen on January 16, 2020, 09:15:59 AM »

Gawain,

HyperSizer does store a simplified representation of the FEM in the software for visualization purposes, but when iterating with HyperFEA it goes back to the FEM file(s) indicated on the Setup form. So if you make a change to those FEM files after import and begin iterating with FEA, it should include your changes.

Were you able to confirm that it is working as expected if you reimport the FEM? I would not have expected this to be necessary either.

-Stephen

26

Analyzing & Optimizing Stiffened Panels / Discrete modelled stiffener - Web Beam concept offsets

« Last post by Gawain on January 16, 2020, 09:11:55 AM »

Hi

I’m currently trying to size a single sided Orthogrid panel which has been discretely modelled with BAR and QUADS.  I’m using a ‘One stack unstiffened’ concept for the plate and a ‘Web Beam’ concept for the stiffener.  At this moment in time I’m not using Stringer Segments, as I believe the preferred process is to size a panel using Plates and Bars first, and then use Stringer Segments as a final check as this is a quicker way of doing things.

The issues that I’m having relates to defining the BAR ‘reference plane’ and how this calculates the Offset within the BAR element when it updates the FEM.  At this moment I’m trying to size a single sided machined stiffened panel, hence as the elements are modelled on the plate centroid then I’m using either the ‘Top’ or ‘Bottom’ reference plane, depending on which side I’m offsetting the stiffeners.  The first issue is that the ‘Top’ reference plane does not seem to change the BAR offset during the HyperFEA loops, whereas the ‘Bottom’ reference plane does.  Is there a reason why I can only Offset the BAR in one direction? 

The next issue is regarding to the BAR Offsets during the HyperFEA process, as it looks like the full stiffener height is being used as the BAR offset instead of using ½ the stiffener height during the FEM update.  This would produce an incorrect panel stiffness/frequency and therefore an incorrect load redistribution.  Is there a reason why the BAR offsets are set to the full height of the stiffener and is there a setting to correct this?  This does not seem to happen when using stringer segment.

Regards
Gawain

27

Analyzing & Optimizing Stiffened Panels / Re: CBAR pin flags removal

« Last post by Gawain on January 16, 2020, 04:51:23 AM »

Hi Stephen

I think the issue was I didn't reimport the FEM after I changed the pin flags for a couple of the CBAR elements, as I didn't think I needed to this.  I was under the impression that Hypersizer would just take a copy of the original .bdf/.dat file and update that file, but I'm assuming on import something trigger that I have pin flags on those BAR elements.  Does Hypersizer store a copy of the FEM within the software? 

Thanks
Gawain

28

Analyzing & Optimizing Stiffened Panels / Re: CBAR pin flags removal

« Last post by Stephen on January 15, 2020, 03:38:59 PM »

Hi Gawain,

I did some testing with a simple test model myself running version 7.3.72, and I was not able to reproduce the behavior you're seeing. My test model does not modify the CBAR element entry in the input file.

Did you confirm this was happening by inspecting the _i iteration FEM?

Thanks,
Stephen

29

Analyzing & Optimizing Stiffened Panels / CBAR pin flags removal

« Last post by Gawain on January 15, 2020, 01:07:05 PM »

Hi

Is there anyway to stop the removal of pin flags within CBAR element during the FEA update within HyperFEA?

30

Analyzing & Optimizing Stiffened Panels / Re: MOI of Stiffener for simple supports

« Last post by Stephen on November 22, 2019, 09:26:01 AM »

Hi Ruben,

HyperSizer does not natively compute a required MOI for simple support of grid-stiffened structure, which is why that criterion is available in the grid-stiffened plugin package. In general, we would recommend enabling this method to prevent unconservatism if you are concerned that the stiffeners would not otherwise size up sufficiently due to other criteria.

Thanks,
Stephen