Netgen - Queries Batchmode & Verbose Mode
 

Dear All,

Iam using Netgen in batchmode and verbose mode and iam able to import a Step geometry and perform geometry healing ,Surface mesh generation as well as volume mesh generation.

Here are some queries i have regarding the same:

Healing:

1. Import Step geometry --> Perform geometry healing. After performing healing Save geometry as a Step File. Changes in geometry after healing are not stored in the newly saved step file (For Example Change in the length of short edges)

2. Import Step geometry --> Perform geometry healing. After performing healing Save geometry as a IGES File. Netgen is CRASHING.

Mesh:

Batchmode :

1. When using Netgen in batchmode , there are options to provide local mesh sizes and refinements using two different files i.e, meshsizefile and refinemetinfofile. But there is no sample file or syntax given to write these files.

2. While using netgen in batchmode, As in Verbose mode there is no option provided to generate only surface mesh. By default , netgen batchmode generates volume mesh.

General:

1. I wanted to load a stl surface mesh file and then generate a volume mesh for the same file.
steps:
After generating surface mesh for a geometry , save the mesh in STL mesh format. Now to import this stl mesh file, there is no option provided. Then i tried to use Load geomety option to import this stl file, but the mesh points and surfaces are not loaded.



Thanks in advance.

Regards
M.ShivaPrasad Reddy

Hello Shiva Prasad,

A Good Evening to you!

Sorry for not having replied to your queries before, but I would strongly suggest that in the future, questions related purely to Netgen (without any direct connection to OpenFOAM) be posted on the Netgen Website (in Sourceforge).

As for your questions:

1. Currently, the healing procedure within Netgen is performed directly on the internal data structures, which are not translated back into the OpenCascade geometry structures when exporting it again.


2. The healing option developed so far is very experimental, and it is only meant to be used within Netgen. I would not suggest using Netgen to heal OpenCascade geometry for the purpose of exporting it and using it elsewhere.


3. The batchmode is not meant to be a full-fledged command-line interface for Netgen, and a lot of the features available within the graphical user interface are not available in the batch mode.

As for the refinementinfo file, unfortunately I do not have a sample of the format because I have never used it myself so far. The meshsizefile though, has the following format:

<num of points>
<x1> <y1> <z1> <max_h1>
<x2> <y2> <z2> <max_h2>
<x3> <y3> <z3> <max_h3>
<x4> <y4> <z4> <max_h4>
<x5> <y5> <z5> <max_h5>
.......
.......
.......
<xn> <yn> <zn> <maxh_hn>
<num of lines> <<----- Even if you are not specifying any lines, this number has to be present (if no lines, it will be a "0")
<x11> <y11> <z11> <x12> <y12> <z12> <maxh_h1>
<x21> <y21> <z21> <x22> <y22> <z22> <maxh_h2>
<x31> <y31> <z31> <x32> <y32> <z32> <maxh_h3>
<x41> <y41> <z41> <x42> <y42> <z42> <maxh_h4>
........
........
........
<xn1> <yn1> <zn1> <xn2> <yn2> <zn2> <maxh_hn>

The first set specifies the maximum mesh size at each given point, whereas the second set specifies the maximum mesh size along the specified line.


4. As far as I can remember, in the batchmode you cannot specify that you only want a surface mesh, and no volume mesh...... for such flexibility, the best option other than the graphical user interface is for you to use the library version of Netgen.... "nglib", and write your own code around it to do exactly what you want to achieve.


5. In order to create a volume mesh from an STL file, you do not need to first create a surface mesh file from the STL, save it again as an STL and open it for a second time in Netgen..... why dont you directly generate a volume mesh starting from the STL file?


I hope this helps you come a bit further....

Have a great day ahead!

Philippose