[Gmsh] mesh size in openCascade units

[Lukas van de Wiel]

Hi Jeremy,

thanks for the help!


With your pointer I managed to make a beautiful smooth transition of
element sizes, by essentially following tutorial 10 :)
I ended up with:

//------------------------------------------------------------------------------------------------------

SetFactory("OpenCASCADE");

lc = 310;

chamberCenterDepth = -2000.0;
chamberMaxRadius = 1000.0;
domainLength = 15000.0;

// start with a sphere
Sphere(1) = {0, 0, -chamberCenterDepth, chamberMaxRadius};

// flatten it  {centerx, centery, centerz} {scale x, scale y, scale z}
Dilate {{0, 0, -chamberCenterDepth}, {1,1,0.1}} { Volume{1}; }

// quarter cylinder
Cylinder(2) =   {0,0,0,0,0,domainLength,domainLength,0.5*Pi};

// remove the cavity
BooleanDifference(10) = { Volume{2}; Delete; }{ Volume{1}; Delete; };

Field[1] = Distance;
Field[1].NodesList = {7,8};
Field[1].NNodesByEdge = 10;
Field[1].EdgesList = {8,9};

Field[2] = Threshold;
Field[2].IField = 1;
Field[2].LcMin = lc / 5;
Field[2].LcMax = lc;
Field[2].DistMin = 3000;
Field[2].DistMax = 10000;

Background Field = 2;

Mesh.CharacteristicLengthExtendFromBoundary = 0;
Mesh.CharacteristicLengthFromPoints = 0;
Mesh.CharacteristicLengthFromCurvature = 0;

//------------------------------------------------------------------------------------------------------

I still have to figure out how to mesh the outer curved surface of the
cylinder, as gmsh does not respond well to RemeshParametrization which I
tried following discussion:
http://onelab.info/pipermail/gmsh/2017/011597.html
But that is something for me to figure out :-)

Best wishes and thanks again

Lukas


On Wed, Apr 24, 2019 at 11:19 PM Jeremy Theler <jeremy at seamplex.com> wrote:

> Hello Lukas
>
> On Wed, 2019-04-24 at 10:46 +0200, Lukas van de Wiel wrote:
> >
> > So far, the geo file looks great.
> > However, I want a mesh that is really fine around the chamber, and
> > that gradually becomes coarser toward the edge of the cylinder.
> >
> > I have of course read
> > http://gmsh.info/doc/texinfo/gmsh.html#Specifying-mesh-element-sizes
> > prior to using this mailing list, which resulted in failed attempts
> > such as:
> >
> > Characteristic Length {Volume{2};} = 500;
> > Characteristic Length {Volume{1};} = 50;
> >
> > How should I go about this?
>
> Read further an use Distance + Threshold fields.
>
> --
> jeremy theler
> www.seamplex.com
>
>
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