[CIG-SHORT] How to mesh an interior small surface?

[Charles Williams]

Hi Tu,

Your first option works for me using Trelis 16.5.  What version of Cubit/Trelis are you using?

Here’s the mesh quality information (I haven’t done any smoothing yet):

 quality volume all condition no. global draw histogram draw mesh

 Tet quality, 40492714 elements:
	Condition No. ranges from 1.000e+00 to 2.776e+00 (40492714 entities)
	     Red ranges from 2.523e+00 to 2.776e+00 (7 entities)
	 Magenta ranges from 2.269e+00 to 2.523e+00 (17 entities)
	DkYellow ranges from 2.015e+00 to 2.269e+00 (164 entities)
	  Yellow ranges from 1.761e+00 to 2.015e+00 (8650 entities)
	   Green ranges from 1.508e+00 to 1.761e+00 (1064716 entities)
	    Cyan ranges from 1.254e+00 to 1.508e+00 (8111154 entities)
	    Blue ranges from 1.000e+00 to 1.254e+00 (31308006 entities)

Volume 1  Tet quality, 40492714 elements:
------------------------------------
   Function Name    Average      Std Dev      Minimum   (id)    Maximum  (id)
 -----------------  ---------    ---------    --------------    -------------
   Condition No.    1.182e+00    1.262e-01    1.000e+00 (24410247)    2.776e+00 (16856351)
------------------------------------

Journaled Command: quality volume all condition no. global draw histogram draw mesh

Of course, this is quite a large mesh.  I think you are eventually going to want to use a sizing function to reduce the mesh size.

Cheers,
Charles

p.s.  In my version of Trelis, the size assigned to surface 7 remains at 10 m; however, depending on your version number, it is possible that the surface 7 size could be overridden by the ‘volume all’ statement.  I would reverse the order of those two commands.


> On 29/04/2018, at 8:34 PM, tu xiang <tuxiang2016 at outlook.com> wrote:
> 
> Hi, 
> I have constructed an ellipsoid magma chamber in a volume:
> # -*- Python -*- (syntax highlighting)
> # ----------------------------------------------------------------------
> # ----------------------------------------------------------------------
> # Set units to SI.
> # ----------------------------------------------------------------------
> #{Units('si')}
> #
> # ----------------------------------------------------------------------
> # Reset geometry and turn undo off.
> # ----------------------------------------------------------------------
> reset
> undo off
> #
> # ----------------------------------------------------------------------
> # Create magma chamber.
> # ----------------------------------------------------------------------
> #{chamber_center_x=0.0*m}
> #{chamber_center_y=0.0*m}
> #{chamber_center_z=-380.0*m}
> #{chamber_radius=50.0*m}
> #{phi=250}
> #{alpha=10}
> 
> # Create sphere, then move it to proper location.
> create sphere radius {chamber_radius}
> volume 1 move x {chamber_center_x} y {chamber_center_y} z {chamber_center_z}
> volume 1 scale x 5 y 1 z 1
> #rotate volume 1 about z {phi}
> body all rotate {alpha} about y
> body all rotate {phi} about z
> 
> # ----------------------------------------------------------------------
> # Create box defining domain.
> # ----------------------------------------------------------------------
> #{domain_x=3.0*km}
> #{domain_y=3.0*km}
> #{domain_z=3.0*km}
> #{domain_center_x=0.0}
> #{domain_center_y=0.0}
> #{domain_center_z=-0.5*domain_z}
> 
> # Create box, then move it to correct position.
> brick x {domain_x} y {domain_y} z {domain_z}
> volume 2 move x {domain_center_x} y {domain_center_y} z {domain_center_z}
> 
> # ----------------------------------------------------------------------
> # Chop cylinder with sphere, then delete sphere.
> # ----------------------------------------------------------------------
> chop volume 2 with volume 1
> delete volume 3
> 
> # ----------------------------------------------------------------------
> # Imprint and merge all volumes.
> # ----------------------------------------------------------------------
> merge all
> 
> # ----------------------------------------------------------------------
> # Compress ID's.
> # ----------------------------------------------------------------------
> compress ids all
> 
> I adopted the following two meshing methods to generate grid mesh.
> First:
> # ----------------------------------------------------------------------
> # Assign sizes to different regions and define meshing scheme.
> # ----------------------------------------------------------------------
> #{min_size=10.0*m}
> #{int_size=20.0*m}
> 
> surface 7 size {min_size}
> volume all size {int_size}
> 
> volume all scheme tetmesh
> 
> # ----------------------------------------------------------------------
> # Generate the mesh.
> # ----------------------------------------------------------------------
> mesh surface all
> mesh volume all
> 
> Second:
> ${dx=15.0*m}
> volume all size {dx}
> volume all scheme tetmesh
> mesh surface all
> mesh volume all
> 
> Although I vary the values of min_size, int_size, dx, the trelis reports that:
> Poor Quality Tet Generated!
> (For example, the shape metric for Tet 1405 is 0.031918 .)
> The threshold for a Tet is 0.200000
> Deleting invalid mesh.
> To retain the invalid mesh next time, set keep invalid mesh on.
> ERROR:  Volume 1 (Volume 1) meshing unsuccessful.
> 
> I also failed to mesh the volume with  Sizing Functions (Skeleton Sizing).
> 
> I would like to know is there any methods to solve the problem?
> 
> Hope someone would give me some help.
> 
> Best regards,
> 
> Tu Xiang
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Charles Williams I Geodynamic Modeler
GNS Science I Te Pῡ Ao
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