hex mesh

[David]

Dear community,

I need to generate from simple 2D cross sections a rect mesh, that i can then extrude into a hex mesh. Is this a job for OpenCascade or for GMSH or what open source library would you recommend ?

 

[Quaoar]

For meshing, it is definitely not OpenCascade. GMSH, NetGen are some options to build a grid in the 2D section. Then, extrusion is something you can do on your own, but it's very likely that GMSH has this function as well.

 

[synt]

Hi Quaoar,

is it possible to create a script to export all entity of part (point, edge, face, body) then write them in GMSH format?

Regards,

 

[Quaoar]

I don't know, my experience with GMSH does not go farther running its UI and clicking a couple of buttons once in a year.

 

[synt]

i'm a newcomer, Analysis Situs seems complex and advanced inside but look powerful.

my question is related to capability of AS to read CAD files (stp,igs,brp) of geometry e.g by script and save or dump files in plain text format about it's entity (point coordinate, line connection, face definition and surface loop of a body)

is this possible by simple Tcl script or required to digest the C++ codes and develop such as function?

 

[Quaoar]

It is definitely possible to read CAD files using a script function, e.g., `load-part` but dumping them into plain text will require some extra effort. You may want to attach here an example of the output format you'd like to get, and we'll see from there.

 

[synt]

Thanks for informing the possibility, the plain text output may in generic form with prefix for each ID of entity. Later, the user can adapt and modify to their specific needs. An example given below,

Point P1 xi yi zi
Line L1 P1 P2
Arc A1 P1 Pi2 CP
Face F1 L1 L2 L3 L4
Body B1 F1 F2 F3 F4

*edited,
purpose of exporting are to a mesher, but I miss reading an article from development

 

[Quaoar]

We are writing some custom plugins from time to time, e.g., to communicate with ASTRA (which is very specific, but some people needed it), and preparing data for GMSH would be quite similar, at least, in principle. Our preferred way of doing so is writing a function in C++ and then exposing it with Tcl, but sometimes the whole thing can be done entirely in Tcl. If your question is a specific feature request, you may want to formulate it as a ticket in our GitLab.

 

[synt]

Our preferred way of doing so is writing a function in C++ and then exposing it with Tcl, but sometimes the whole thing can be done entirely in Tcl

maybe some documentation required to introduces since STP files is complex format and probably many users interested in extracting the entity properties.

thanks for interesting, actually i'm not know about the future milestone of Analysis Situs. Are partition and meshing is the goals also? if it's yes, so data exchange may less important.

 

[Quaoar]

Initially, the plan was to develop a small & handy tool to inspect geometries, although from day one it was clear that some extensions would shortly come up (some old use cases were listed in this paper, now there are many more). Still, I like the idea of having a small assistant app with powerful scripting abilities (although one might argue how "powerful" Tcl is), and I don't want Analysis Situs to pretend to be a full-fledged CAD system, like FreeCAD. It's just like OpenCascade's DRAW or ACIS' Scheme AIDE which are not real CADs, they are just consoles, and they serve their niches for prototyping.

The main directions of Analysis Situs development haven't been formulated explicitly, but these are definitely our topics of interest:

1. Feature recognition, DFM (manufacturability analysis).
2. Better support for assemblies, possibly just allowing multiple parts like in Catia.
3. Advanced surfacing (Gordon is in progress, least squares fitting + smoothing is on master).
4. Everything for CAE preparation (simplification, idealization, healing).

Some shorter-term tasks, formulated as tickets, are here at GitLab.

Partitioning and meshing are considered, mostly because we have had a customer who was (and, hopefully, still is) willing to keep the results open-sourced. To partition an active part with an existing surface, there's already a context menu command (only on the master branch as of now), but I'd assume you're talking about a somewhat comprehensive partitioning & meshing UI, like in Salome, right?

 

[synt]

To partition an active part with an existing surface, there's already a context menu command (only on the master branch as of now)

great news, it seems more useful when surface is not from existing only but generates internally based on several points or lines

but I'd assume you're talking about a somewhat comprehensive partitioning & meshing UI, like in Salome, right?

not like that, Salome is too advanced and complex. i'm not expected Analysis Situs to do similar interfaces.

 

[Quaoar]

great news, it seems more useful when surface is not from existing only but generates internally based on several points or lines

That was partially doable, at least, in my local experiments. I have to sit down and prepare online docs, as well as the release notes for the upcoming version (it's already insanely behind schedule).