[giordy]

Dear All.

I'm using netgen for Meshing. I input a *stl file without any warning or error message. after some time during surface meshing i got many lines with the following message:

"SYSTEM ERROR: hash table si not fitting for segment"

Someone can tell me what does it mean this message?

Netgen went on for some minutes and it stopped and closed.
Someone can help me?
Thanks in advance.

Stefano

[philippose]

Hello Stefano,

A Good Evening to you!

Would it be possible for you to send me an STL file which you have, for which Netgen is quitting with the error that you mentioned?

Usually, such an error appears when the imported STL geometry has topology errors in it, which causes the edge and surface meshing routines to fail.

Also, you might get a faster response, if you post the problem on the Netgen Sourceforge project page.

Have a nice day!

Philippose

[giordy]

Hello Philippose,

Thank you for the reply. I will try the netgen Sourceforge project page. I can also send you the *stl but i am not able to post it.. so i need your private account if possible. thanks.

Stefano

[giordy]

https://download.yousendit.com/Z01QYURLV3JvQnNLSkE9PQ
Stefano

[philippose]

Hello Stefano,

A Good Afternoon to you!

I apologise for the delay in replying to the post. Thanks a lot for the link to the STL data which you sent to my sourceforge account.

It was interesting to note that the STL file was over 13 MB in size..... I opened it in Netgen, and as far as the STL export itself is concerned, it seems to be good. Netgen did not complain when opening the file.

I think the problems in this case are:

1. The vastly different length scales.... the large surfaces of the hull compared to the very small features of the mechanical connection points.

2. The fact that the model is not a surface model but a volume model which is extremely thin. Since the thickness of the model is much much smaller than the other dimensions, creating a pure tetrahedral mesh would result in a huge number of surface and volume elements (because of the quality constraints).

I personally think, that you should consider meshing the geometry either with prismatic elements, or hexahedral elements (because this allows anisotropic meshes to be created).

Purely tetrahedral meshes would be a bad idea in this case.

I shall look a little deeper to see whether I can tweak some of the meshing options in Netgen to come up with a more realistic mesh, but I dont have high hopes.

Have you tried to mesh the geometry with snappyHexMesh (The mesher available within OpenFOAM)? I dont have experience with snappyHexMesh, but there are lot of people on this forum who use it, and would be able to help.

If I remember, snappyHexMesh tries to create a hex dominant mesh from STL geometry.

If I come up with something, shall get back to you.

Have a great weekend!

Philippose

[giordy]

Thank you Philippos.

I will try the snappy tool.

Stefano