[Gmsh] EXTERNAL: Re: Embedded Mesh

Thu Oct 11 21:18:44 CEST 2018

Hi Max,

Thanks for the quick response.  I’m not sure how much time you have for debugging but I’ve attached my input files.  The main file is the geo file of course.  Goal.png shows what I have so far and what I am trying to do.  I have no error messages with the attached files but it’s only meshing the line loop and I would like it to fill in the surface with a 2D mesh.  Any thoughts?

Thanks,
Aaron

From: Max Orok [mailto:morok at mevex.com]
Sent: Thursday, October 11, 2018 3:03 PM
To: Jensen, Aaron J. [US-US]; gmsh at onelab.info
Subject: Re: [Gmsh] EXTERNAL: Re: Embedded Mesh

Hi Aaron,

I might be mistaken, but it looks like your in-file Line Loop stuff is good.
That might mean the Surface Loop command is giving the warning because the two Line Loops don't match up (i.e. form a closed surface)?

Sincerely,
Max

On Thu, Oct 11, 2018 at 1:25 PM, Jensen, Aaron J. <Aaron.J.Jensen at leidos.com<mailto:Aaron.J.Jensen at leidos.com>> wrote:
Christophe,

Thank you for the fast response.  The latest snapshot works great and fixes the crash.

I am still setting up the problem incorrectly.  Here is what I have now:

Merge "square";
Line Loop(1) = {1};

squareWidth = 1.5;
halfSquareWidth = squareWidth/2.0;

lc = 0.3;
Point(1001) = {-halfSquareWidth,-halfSquareWidth,0.0,lc};
Point(1002) = {-halfSquareWidth, halfSquareWidth,0.0,lc};
Point(1003) = { halfSquareWidth, halfSquareWidth,0.0,lc};
Point(1004) = { halfSquareWidth,-halfSquareWidth,0.0,lc};
Line(1001) = {1004,1003};
Line(1002) = {1003,1002};
Line(1003) = {1002,1001};
Line(1004) = {1001,1004};

Line Loop(1005) = {1002,1003,1004,1001};

Surface Loop(1006) = {1005, 1};

I think it is close to working but I get the warning message: "1D mesh not forming a closed loop".

Any help would be greatly appreciated.

Thanks,
Aaron

-----Original Message-----
From: Christophe Geuzaine [mailto:cgeuzaine at uliege.be<mailto:cgeuzaine at uliege.be>]
Sent: Thursday, October 11, 2018 8:11 AM
To: Jensen, Aaron J. [US-US]
Cc: gmsh at onelab.info<mailto:gmsh at onelab.info>
Subject: EXTERNAL: Re: [Gmsh] Embedded Mesh

> On 10 Oct 2018, at 21:12, Jensen, Aaron J. <Aaron.J.Jensen at leidos.com<mailto:Aaron.J.Jensen at leidos.com>> wrote:
>
> Hello,
>
> I would like to merge an existing mesh into a geometry and then mesh the unmeshed region using gmsh (something like a boundary mesh around a pre-existing mesh generated externally by another program).  Ideally, this would result in a mesh that was partially created in gmsh and partially created externally to gmsh.  Ultimately, I would like to do this in both 2D and 3D but am starting with the following in 2D:
>
>
>
> Merge "square";
>
> SetFactory("OpenCASCADE");
>
> Surface Loop(1) = {1};
> //sExternal = news;
> //Rectangle(sExternal) = {0, 0, 0.0, 0.5, 0.5};
>
> s1 = news;
> Rectangle(s1) = {-0.25, -0.25, 0.0, 1.0, 1.0};
>
> //BooleanDifference (2000) = { Surface{s1}; Delete; }{ Surface{sExternal}; };
> BooleanDifference (2000) = { Surface{s1}; Delete; }{ Surface{1}; };
>

This cannot work: boolean operations can only be applied to CAD entities. It should not crash though - and it does not on my machine. Can you try with the latest snapshot?

You can still produce a mesh like the one you want. With the built-in engine, simply

- load the mesh, which should contain the bounding surface mesh

- define the exterior "Surface Loop" where the interior surfaces are the bounding surfaces (discrete)

Christophe

>
>
> OpenCascade doesn’t recognize surface 1 and BooleanDifference causes gmsh to crash.  I assume I am doing something wrong?  Can gmsh embed an existing mesh into a gmsh geometry or CAD model?
>
> Thanks,
> Aaron
> <square>_______________________________________________
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—
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine

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