[Netgen] Volume mesh instead of surface mesh

phan · November 23, 2008, 22:24

Hello,

I want to mesh a stl file but any time I try Netgen creates a surface mesh.
At the beginning I thought that the volume mesh is just not shown when I used the clipping function because it did only show an empty inside. But I was not able to convert the mesh to the foam format. That's why I guess that the mesh information is not adequate (not a volume).
It always shows the message: "Trying to get back from bad stream"

Is there a way to mesh a volume out of a surface mesh or from a stl file with Netgen or any other Mesher?

Thanks a lot!

nomad · September 2, 2009, 19:16

I use an IGES file in NetGen, then optimize volume in the mesh options. However, the mesh created as is fails in OpenFOAM unless I refine it in gmsh (Mesh-Refine).

ericnutsch · October 17, 2009, 02:46

I have recently attempted to use netgen and cannot mesh volumes either. If I create a surface mesh first it shows elements created but I cannot view them. If i atempt to create a volume mesh before a surface mesh it crashes.

I am using the windows version and it is incredibly unstable. I would like to install the linux version but I strugled with the openfoam install and it was decently documented.

philippose · October 17, 2009, 05:11

Hello Eric,

A Good day to you!!

Nice to see that you have been trying to use Netgen.... I hope I will be able to help you solve the issues you seem to be facing....

Usually, a failure in Volume mesh creation can come from one or a combination of the following situations:

1. First and foremost..... a bad geometry import
-- A message "Cannot visualise face <xxx>" in the console points to a definitely bad geometry
-- If you are working with STEP/IGES files, you can try the geometry healing options in Netgen (Geometry -> IGES/STEP Topology Explorer/Doctor)

2. A bad surface mesh (have you checked in the console whether all surfaces have been meshed without any errors?)

3. Memory limitations.... On 32-bit systems (Windows and linux), you are limited to a maximum memory of 2GB (even if your system has more physical RAM). Trying to create a mesh which requires more memory will result in a crash

4. Trying to make too fine or too coarse a mesh, or using very aggressive mesh grading (> 0.6 for example)

Personally.... I have not seen an open-source tetrahedral mesh generator which is as robust as Netgen :-)

Could you provide me with more details of your particular usage scenarios?

If you require more assistance with Netgen, it might be easier for you to use the Netgen forum on the Sourceforge website.

Have a nice day!

Philippose

ericnutsch · October 18, 2009, 18:17

Thanks Philippose!

I will try the geometry healer and your other recommendations and post back.

It is much easier to be ambitious when you know that your not at a dead end.

Thanks!

November 23, 2008, 22:24	Volume mesh instead of surface mesh	#1
phan New Member Stephan Koerner Join Date: Mar 2009 Posts: 4 Rep Power: 17	Hello, I want to mesh a stl file but any time I try Netgen creates a surface mesh. At the beginning I thought that the volume mesh is just not shown when I used the clipping function because it did only show an empty inside. But I was not able to convert the mesh to the foam format. That's why I guess that the mesh information is not adequate (not a volume). It always shows the message: "Trying to get back from bad stream" Is there a way to mesh a volume out of a surface mesh or from a stl file with Netgen or any other Mesher? Thanks a lot!

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September 2, 2009, 19:16		#2
nomad Member John Join Date: Aug 2009 Posts: 92 Rep Power: 17	I use an IGES file in NetGen, then optimize volume in the mesh options. However, the mesh created as is fails in OpenFOAM unless I refine it in gmsh (Mesh-Refine).

October 17, 2009, 02:46		#3
ericnutsch Senior Member Eric Nutsch Join Date: Sep 2009 Location: Eugene, Oregon USA Posts: 113 Rep Power: 17	I have recently attempted to use netgen and cannot mesh volumes either. If I create a surface mesh first it shows elements created but I cannot view them. If i atempt to create a volume mesh before a surface mesh it crashes. I am using the windows version and it is incredibly unstable. I would like to install the linux version but I strugled with the openfoam install and it was decently documented.

October 17, 2009, 05:11		#4
philippose Senior Member Philippose Rajan Join Date: Mar 2009 Location: Germany Posts: 552 Rep Power: 25	Hello Eric, A Good day to you!! Nice to see that you have been trying to use Netgen.... I hope I will be able to help you solve the issues you seem to be facing.... Usually, a failure in Volume mesh creation can come from one or a combination of the following situations: 1. First and foremost..... a bad geometry import -- A message "Cannot visualise face <xxx>" in the console points to a definitely bad geometry -- If you are working with STEP/IGES files, you can try the geometry healing options in Netgen (Geometry -> IGES/STEP Topology Explorer/Doctor) 2. A bad surface mesh (have you checked in the console whether all surfaces have been meshed without any errors?) 3. Memory limitations.... On 32-bit systems (Windows and linux), you are limited to a maximum memory of 2GB (even if your system has more physical RAM). Trying to create a mesh which requires more memory will result in a crash 4. Trying to make too fine or too coarse a mesh, or using very aggressive mesh grading (> 0.6 for example) Personally.... I have not seen an open-source tetrahedral mesh generator which is as robust as Netgen :-) Could you provide me with more details of your particular usage scenarios? If you require more assistance with Netgen, it might be easier for you to use the Netgen forum on the Sourceforge website. Have a nice day! Philippose

October 18, 2009, 18:17		#5
ericnutsch Senior Member Eric Nutsch Join Date: Sep 2009 Location: Eugene, Oregon USA Posts: 113 Rep Power: 17	Thanks Philippose! I will try the geometry healer and your other recommendations and post back. It is much easier to be ambitious when you know that your not at a dead end. Thanks!