[Gmsh] listing elements according to which physical volume they belong to

[Abiti Adili]

I  See.

  So if I understand correctly, the high number of points   in and around the ball  and the lesser number of points away from the ball are  inherently determined by the mesher  automatically once I have defined the geomtry.  Does this mean that I don't have to worry about  it as long as I have fine enough mesh for the whole box for my simulation?

Thank you very much.

Adil


________________________________________
From: Max Orok <morok at mevex.com>
Sent: Monday, November 26, 2018 10:06:11 AM
To: Abiti Adili
Cc: gdmcbain at protonmail.com; gmsh at onelab.info
Subject: Re: [Gmsh] listing elements according to which physical volume they belong to

Hello Adil,

I think the mesh is definitely more dense or refined around the spheres.
My first guess is that the mesher makes more points on the spheres because it needs more points to model them accurately.
For the outer box, less points suffice for an accurate mesh.

For a 2D example, if you are trying to discretize a straight line, you can get away with the start and end points and not lose any info.
For a curve however, you'll need more points along it for a good approximation.

For a look at the mesh, you can use a clipping plane: Tools -> Clipping -> (Click mesh in left hand pane) -> Click and drag in D box

Here are some example pictures for a model with a sphere on one side only

The sparser one was done using Tools -> Clipping -> (Check "keep whole elements" and "only draw volume layer")
[image.png]
[image.png]

On Mon, Nov 26, 2018 at 4:22 AM Abiti Adili <aadili1 at lsu.edu<mailto:aadili1 at lsu.edu>> wrote:
Thank you very much. Now I have the lists of the elements with the physical volume tags they belong to.

I have attached a png file of the 3D view of the mesh generated, geomtry.geo and omnibus.geo.

It seems to me that
 when I clicked on 3D in Mesh option  it seems like it started generating more densely around those two balls.

when clicked on "refine by splitting", it still gets dense around those two balls.

You can see it from the attached file of the 3D view of the mesh.

Is there any reason for this mesh to be denser around the ball and not so dense in  the complement of the balls? Or I am just judging this by my eyes while it is not actually like that? Is there any way I can confirm that it is indeed denser around the balls? and If that is true, am I doing something wrong in the geo files?

Thank you very much.

Adil


________________________________________
From: G. D. McBain <gdmcbain at protonmail.com<mailto:gdmcbain at protonmail.com>>
Sent: Sunday, November 25, 2018 11:43:56 PM
To: Abiti Adili
Cc: gmsh at onelab.info<mailto:gmsh at onelab.info>
Subject: Re: [Gmsh] listing elements according to which physical volume they belong to

©\©\©\©\©\©\©\ Original Message ©\©\©\©\©\©\©\
Le lundi, novembre 26, 2018 12:43 PM, Abiti Adili <aadili1 at lsu.edu<mailto:aadili1 at lsu.edu>> a ¨¦crit :

> Hello,
>
> I have a geometry.geo file that creates a box with two small balls in it. I used omnibus.geo file that utilize the geometry.geo. Using this file, I created a 3D mesh over the box(as well as the two balls in it). I need to be able to have a mesh( created over the box) so that the gmsh file lists the tetrahedral elements according which physical volume( ball1, ball2, or the complement of them in the box) they belong to.
>
> The files I currently have are not quite generating what I wanted, it is only listing the elements belong to the complement. I would greatly appreciate if someone can take a look at them and point out the mistakes I made.

The last lines of geometry.geo have:

    Volume(1) = {2};
    Volume(2) = {3};
    Volume(3) = {1, 2};

The last should read

    Volume(3) = {1, 2, 3};

if the second sphere is also to internally bound it.

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Max Orok
Contractor
www.mevex.com<http://www.mevex.com>

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