[Gmsh] R: BRL-CAD for Geometry?

Alessandro Vicini alessandro.vicini at sitael.com
Fri Feb 3 15:57:15 CET 2017

Cool…!!  ☺

Da: gmsh [mailto:gmsh-bounces at ace20.montefiore.ulg.ac.be] Per conto di Christophe Geuzaine
Inviato: venerdì 3 febbraio 2017 14.49
A: G. D. McBain
Cc: gmsh at onelab.info
Oggetto: Re: [Gmsh] BRL-CAD for Geometry?

As a little teaser, just to let you know that I'm coding a direct interface to OpenCASCADE CAD creation right in .geo files. This will in particular support automatic creation of conform interfaces when you fuse solids, in order to handle internal boundaries.

Here's what the scripts will look like (not everything is in the SVN trunk yet):


Mesh.Algorithm = 6;
Mesh.CharacteristicLengthMin = 0.4;
Mesh.CharacteristicLengthMax = 0.4;

R = 1.4;
s = .7;
t = 1.25;

Block(1) = {-R,-R,-R, R,R,R};

Sphere(2) = {0,0,0,R*t};

BooleanIntersection(3) = { Volume{1}; Delete; }{ Volume{2}; Delete; };

Cylinder(4) = {-2*R,0,0, 2*R,0,0, R*s};
Cylinder(5) = {0,-2*R,0, 0,2*R,0, R*s};
Cylinder(6) = {0,0,-2*R, 0,0,2*R, R*s};

BooleanUnion(7) = { Volume{4}; Delete; }{ Volume{5}; Delete; };
BooleanUnion(8) = { Volume{6}; Delete; }{ Volume{7}; Delete; };
BooleanSubtraction(9) = { Volume{3}; Delete; }{ Volume{8}; Delete; };

[cid:image001.png at 01D27E36.4943CE80][cid:image002.png at 01D27E36.4943CE80]

On 2 Feb 2017, at 23:28, G. D. McBain <gdmcbain at protonmail.com<mailto:gdmcbain at protonmail.com>> wrote:

Sent from ProtonMail, Swiss-based encrypted email.

-------- Original Message --------
Subject: [Gmsh] BRL-CAD for Geometry?
Local Time: 2 février 2017 4:07 PM
UTC Time: 2 février 2017 05:07
From: toddcpierce at gmail.com<mailto:toddcpierce at gmail.com>
To: gmsh at onelab.info<mailto:gmsh at onelab.info>

Hi All,
It's me again, wondering how I should go about integrating a command-line geometry package into OneLab (or some other chain of multi-physics tools).
As I've mentioned before, although there is no shortage of tools to do meshing, finite element analysis or CFD and so forth, there is no simple way to build geometries from the command line.

Has anybody ever used this BRL-CAD/Mged command line CAD package?  It doesn't look bad, but I do have concerns about it exporting to formats that these meshing and physics programs use.

In the past I have used BRL-CAD's mged command-line tool to create geometries for subsequent CFD simulations.  I used BRL-CAD's g-stl command-line tool to export a triangulation of the bounding surface in STL format.  Gmsh can read this in.

More recently though I'm using FreeCAD which can be scripted in Python and so run from the command-line.  Besides STL, this also outputs IGES, STEP, and BRep, which can contain more information that STL.  Gmsh reads all four formats.

OpenSCAD is an excellent accompaniment to FreeCAD too, especially via Solid Python.

Often my workflow looks like FreeCAD -> Gmsh -> FreeFem++ -> (Gmsh or pandas), with the whole thing run from a single SCons build file.  No GUIs, except for preliminary exploratory work.

I haven't looked into OneLab yet.

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gmsh at onelab.info<mailto:gmsh at onelab.info>

Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science

Free software: http://gmsh.info | http://getdp.info | http://onelab.info

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