# [Gmsh] internal node structure

Trevor Irons trevorirons at gmail.com
Thu Aug 7 18:16:48 CEST 2014

```Thank you again. I tried extruding lines and was able to do so with
straight ones but not Line Loops. I have included as small of an example as
I can think of. This does what I want for the top of the 1/2 cylinder. But
I would like to extend this behaviour to the commented out extrusion step.
Again thanks for any ideas. All I can think of is throw what is written
here into a loop. But I am not sure how well that would work.

lc = 10;   // Target element size
D0 = 10;   // Top
D1 = 11;   // Bottom

// Total Solution Space
X0 = -2.;
X1 =  2.;
Y0 = -2.;
Y1 =  2.;
Z0 =  9.;
Z1 = 12.;

////////////////////////////////////
// North Pole

Point(0) = { 0, 0, D0, lc/10};
Point(1) = { R, 0, D0, lc/10};
Point(2) = { 0, R, D0, lc/10};
Point(3) = {-R, 0, D0, lc/10};

// Connect up the points
Circle(4) = {1, 0, 3};
Line(5) = {3,1};
Line Loop(6) = {4,5};
Plane Surface(7) = {6};

//////////////////////////////////////
// Extrude 1/2 cylinder
//Extrude {0, 0, D1-D0} { Surface{7};  } // I want this *outer surface*
within my final volume

/////////////////////////////////////
// Large Bounding box
Point(116)  = {X0, Y0, Z0};
Point(117)  = {X1, Y0, Z0};
Point(118)  = {X1, Y1, Z0};
Point(119)  = {X0, Y1, Z0};
Line(120) = {116,117};
Line(121) = {117,118};
Line(122) = {118,119};
Line(123) = {119,116};
Line Loop(124) = {120, 121, 122, 123};
Plane Surface(125) = {124};
Extrude {0, 0, Z1-Z0} { Surface{125}; }

// We want the surface in the volume
Surface{7} In Volume{1};
//Surface{8} In Volume{1};

// Don't export internal structure
Physical Volume(1) = {1};

-- Trevor

On 7 August 2014 07:53, jean pierre aubry <jeanpierre at lamachine.fr> wrote:

> without a complete example it is difficult to understand what you want
>
> however extruding the lines that make the borders of Surface{7} you
> should get a Surface which would be bordering the volume along the
> extrusion vector
>
>
> Le Thu, 7 Aug 2014 09:34:36 -0600,
> Trevor Irons <trevorirons at gmail.com> a écrit :
>
> > Thank you. That worked perfectly for a 2D 'plane surface'! Thanks for
> > the tip.
> >
> > would like to do this with a 3D surface, i.e. internal 3D object. But
> > once I extrude it, it becomes a volume and I cannot call Surface In
> > Volume anymore.
> >
> >
> > Line Loop(6) = {4,5};
> > Plane Surface(7) = {6};                           // Define a plane
> > surface Surface{7} In Volume{1};                       // This works
> > for the unextruded surface
> > Extrude {0, 0, D1-D0} { Surface{7};  }  // I want to include the
> > surface of this extrusion in the mesh
> >
> >
> > Surface(8) = CastToSurface{Volume{2}}; // Made up desired
> > functionality Surface{8} In Volume{1};                          // I
> > want to call something like this
> >
> > Is there a way to cast an extrusion back into just a surface, but now
> > just the outer 3D surface?
> >
> > Thanks.
> >
> >
> > -- Trevor
> >
> >
> > On 5 August 2014 05:01, jean pierre aubry <jeanpierre at lamachine.fr>
> > wrote:
> >
> > > hello
> > >
> > > >Is there a way to scrub the internal `surface' but retain the mesh
> > > >structure?
> > >
> > > what about putting the surfaces you want to export into Physical
> > > and to NOT put into Physical the ones you do not want
> > >
> > > i do not know about VTK
> > > but by proceeding this way only the defined Physical are exported
> > > in .msh or .med mesh
> > >
> > > --
> > > jean pierre aubry
> > > 33 688 670 795
> > > jeanpierre [at] lamachine.fr
> > >
>
>
>
> --
> jean pierre aubry
> 33 688 670 795
> jeanpierre [at] lamachine.fr
>
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