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Layer Generation Error - "Cannot calculate a positive vector !!"

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Old   March 15, 2017, 21:41
Default Layer Generation Error - "Cannot calculate a positive vector !!"
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Brett Johnson
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Hello everyone,
(picture included)

I'm trying to create prism layers on the target model of my research (which happens to be the JAXA JSM model for AIAA's high lift prediction workshop) but for certain parts I keep running into an error.

Basically I have found the source of the problem to be when I try creating the mesh on the wing, slat, and slat-tracks(?) simultaneously. If I try generating the layers on each part individually there is no problem. In addition, I can generate the layers on the rest of the parts (fuselage, flaps, flap-tracks, etc.) simultaneously without issue.

The error that I'm getting is: "Cannot calculate a positive vector !!"

I'm using ANSA 15.1.2 and I know this is vague, but pretty standard layer generation settings.

Thanks in advance for any help anyone can provide!
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Old   March 16, 2017, 03:30
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Brett Johnson
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**UPDATE**
(picture included)

I think I found the exact cause for the error. I made a simple model to mimic the interface between the wing and the slat, created the surface mesh, tried creating the layers, and then ANSA provided the same error message.

From this I can conclude that the error actually is not related to the slat-tracks as mentioned in my original post, but it is instead related to the interface between the wing and the slat.

The picture I've included shows what I believe to be the problem areas (circled in red), with the white arrows representing the normal vectors to each of the planes where the interface is. Because they are pointing to opposite directions, ANSA (understandably) has some trouble generating layers there.

If anyone has any input, or thoughts on how I can get around this without altering the geometry too much, I will be happy to read your response. Thanks in advance!
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Old   March 17, 2017, 11:40
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Vangelis Skaperdas
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Hi Brett,

These are indeed nasty areas for layers generation.

You can see how they were tackled in ANSA in this presentation.

You basically need to make some small local geometry modifications.

Usually we use the function Surfaces>Volume>Sphere to create small spheres and intesect them with the geometry. This makes layers generation possible

ftp://hiliftpw-ftp.larc.nasa.gov/out...LW3_JSM_v2.pdf

Hope this helps
Vangelis
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Old   March 17, 2017, 20:59
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Brett Johnson
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Hi Vangelis,

Thanks for the information! Actually I had been checking that repository site fairly often (as I had seen your PDF for the CRM), but I must have missed the JSM PDF.

The spheres seem like a good solution to the problem, so I will give that a try.

Thank you again for your help!

Best,
Brett
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