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Author Topic: Grid-stiffened panels angle web spacing  (Read 6662 times)

phoenixxp

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Grid-stiffened panels angle web spacing
« on: June 26, 2012, 05:28:34 AM »
Dear Lady/Sir,

I have one other thing that kept me wondering while working with Hypersizer. I am using the Angle-grid Concept of the Grid-Stiffened Panels family to optimize the structure for the loads I have derived. I am also using the analytic model developed by me for comparison. The approaches to most of the failure modes/stiffness calculations, etc. used in my software is to a large extent different from what is used in Hypersizer. One thing that I recently found not matching in the 2 approaches is actually related to geometry. I will try to explain it with the help of the two pictures attached below.

The first picture is a sketch made in CATIA to help me explain my point. The green lines indicate that the sketch is fully fully constrained and therefore it is the only geometrical solution available for the dimensions shown. I have drawn 2 cells of 3 different Angle grid panels with Angles of 60°, 45° and 30°. The Axial stiffened spacing used is 50mm. The way I understand "spacing" is as the distance between 2 adjacent parallel webs. And from my CATIA sketch one can recognize that the angle web spacing for the 3 cases is: 50, 70.711, 86.603 (all dimensions in mm). And the  length of the web segment in between two adjacent angle webs (crippling/Euler buckling length) is 57.735, 70.711 and 100 mm respectively. The dimensions in brackets are the so-called reference dimensions.

When I look at the way Hypersizer is visualizing the same values I can see that the abovementioned spacing is 57.74, 70.71 and 100 mm. This actually means that Hypersizer shows the value of the web segment length instead of taking the distance between two parallel webs as the web spacing.

I am trying to match the results from Hypersizer with my theoretical approach and, since my stiffness and local buckling formulation is spacing-based, I need to know if this is just a visualization mistake or if it runs deeper. I suppose it is just in the way it is visualized in the sizing form and it is not related to any computations.

Thanks a lot for your help and for letting me use your great software!

Kind regards,

Leonid

James

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Re: Grid-stiffened panels angle web spacing
« Reply #1 on: June 27, 2012, 08:44:29 AM »
You are correct, the Angle Web - Stiffener Spacing (Dependent Variable) is actually the "angle web object length". This is the 'a' length in the local buckling calculation for the angle web. You can see the details of the panel buckling and local buckling calculations in the buckling detail file.

Project Sizing Form > Options > Buckling Detail...

Also, if you are doing any verification with HyperSizer's local buckling for the grid stiffened panel family, I suggest you update to v6.2.45. In v6.2.45, there have been two changes made which will affect the local buckling results for the grid stiffened panel family. These are:

1. Isogrid/Anglegrid pocket buckling correlation on facesheet local buckling based on 84 FEA data points
2. Implemented Niu SSSF local buckling equation for web objects, with correlation to account for facesheet fixity for all orthogrid panels (except 0Grid and 90Grid concepts)

Please contact us for the download.

phoenixxp

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Re: Grid-stiffened panels angle web spacing
« Reply #2 on: June 27, 2012, 09:58:10 AM »
Thank you, James!

I actually thought so, but wanted to let you know just to make sure.