Dear Kamil,

Nektar++ is capable of using a mesh comprising of multiple types of elements (e.g. tets, prisms and hexes simultaneously). In many situations this is actually beneficial to the simulation, for example, in resolving boundary layers using prisms, but filling the remainder of the domain using tets.

There is no generic way in gmsh to convert all elements of an existing mesh to be of a specific type. If you want a single type of element you must design your geometry accordingly (e.g. use Recombine/transfinite lines where you want quad faces to enforce prismatic/hex elements).

Cheers,
Chris


On 28/07/14 21:03, Kamil ÖZDEN wrote:

Hi Dr. Moxey,

I also run the script and see the same result. May be it is possible to
write a script for Gmsh to convert the different element types into one
type. However, I want to learn the relation of this issue with Nektar++
before making trials on Gmsh.

So I want to learn the answer of this question: "Is it possible to
generate a problem in Nektar++ with a mesh including different element
types (quads+hexas+prisms etc.) or should I always generate a mesh with
single element type for my problem to convert into .xml and use in
Nektar++?"

Regards,
Kamil


28.07.2014 20:37 tarihinde, David Moxey yazdı:

Hi Kamil,

I have run Sergey's script and get a mesh of various element types --
if you look in the Gmsh statistics it should show 48 tets, 8 hexes and
32 prisms.

Thanks,

Dave

On 2014-07-28 18:51, Kamil ÖZDEN wrote:

Hi Sergey,

 As far as I understood this is an example script to show how
hexahedras are converted to tetrahedras and I have to write like this
kind of a script for each different mesh. Am I right?

 Isn't there any way to directly solve this issue (generate a problem
with a mesh including different element types (quads+hexas+prisms
etc.)) in Nektar++ without doing modifications in Gmsh?

 Regards,
 Kamil

 28.07.2014 07:09 tarihinde, Sergey Yakovlev yazdı:

Hi Kamil,

You can generate a mesh using gmsh that would contain hexes, prisms
and tetrahedrals. You can do transition from
hexahedral layer to tetrahedral layer through the layer of prisms.
Here is an example of gmsh script:

======================================================================

N=2;
Point(1)={-1,-1,0};
bline[]=Extrude{1,0,0}{Point{1};Layers{N};};//prism region boundary
prism_surf[]=Extrude{0,2,0}{Line{bline[1]};Layers{N};};//prism
region base (meshed with triangles)

prism_vol1[]=Extrude{0,0,1}{Surface{prism_surf[1]};Layers{N};Recombine;};//prism

volume
tet_vol[]=Extrude{0,0,1}{Surface{prism_vol1[0]};Layers{N};};//no
recombine, hence getting tet part
h_side[]={prism_vol1[3],tet_vol[3]};

hex_vol[]=Extrude{1,0,0}{Surface{h_side[0]};Layers{N};Recombine;};//recombine

gives us hexes

prism_vol2[]=Extrude{1,0,0}{Surface{h_side[1]};Layers{N};Recombine;};//recombine

gives us prisms
side1[]={prism_vol1[5],tet_vol[5]};//x=1
side2[]={hex_vol[0],prism_vol2[0]};//x=1
side3[]={hex_vol[3],prism_vol2[3],prism_vol1[4],tet_vol[4]};//y=1
side4[]={hex_vol[5],prism_vol2[5],prism_vol1[2],tet_vol[2]};//y=-1
side5[]={prism_vol2[4],tet_vol[0]};//z=1
side6[]={hex_vol[2],prism_surf[1]};//z=-1
Physical Surface(1)={side1[]};
Physical Surface(2)={side2[]};
Physical Surface(3)={side3[]};
Physical Surface(4)={side4[]};
Physical Surface(5)={side5[]};
Physical Surface(6)={side6[]};
//domain[]={hex_vol[1],prism_vol1[1],tet_vol[1],prism_vol2[1]};
Physical Volume(1111)={hex_vol[1]};
Physical Volume(1112)={prism_vol1[1],prism_vol2[1]};
Physical Volume(1113)={tet_vol[1]};

======================================================================

Save the above to the some_name.geo file and run "gmsh -3
some_name.geo". This should give you the mesh file that
you can later convert to Nektar++ xml format. After that you just
need to insert initial/boundary conditions, exact solution, etc.
I've used it for testing with discontinuous Galerkin Helmholtz
solver and it didn't work, but
it maybe that the prisms are better supported in case of continuous
Galerkin.

On Sun, Jul 27, 2014 at 6:26 AM, Kamil ÖZDEN
<kamil.ozden.me@gmail.com> wrote:

Dear All,

Is there any way to generate a problem in Nektar++ with a mesh
including different element types (quads+hexas+prisms etc.)?

Regards,
Kamil

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--
Best regards,
Sergey

Links:
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