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Discrete load on a cube surface

Posted: 16 Feb 2011, 11:08
by thejonesyboy
I've managed to run (mostly using ElmerGUI) a simulation of a fully supported (sides and bottom) cube with a point load vertically downward onto a small area at the centre of the top surface.

I first manually wrote a .grd file to define a cube with 10x10x10 elements and one boundary per side (six boundaries), and then used ElmerGUI to find the element numbers of four elements at the centre of the top surface. I changed the elements' boundary numbers to seven by manually editing the boundary mesh file, reloaded ElmerGUI and applied the force to that boundary. I used ElmerPost to visualise the displacement into the cube.

I was wondering if it would be possible to automatically generate my cube (with the seven boundaries) using just the .grd file? This way I wouldn't have to do any manual edits to the generated mesh files. I have read the ElmerGrid tutorial extensively and I am very lost :-)

I have attached some images of the model to help explain the situation.

Thanks!
3.jpg
3.jpg (159.22 KiB) Viewed 2742 times

Re: Discrete load on a cube surface

Posted: 16 Feb 2011, 11:29
by Juha
Hi,

yes it is possible to define such .grd file. For example, define the "material" structure
in plane as

...
1 1 1
1 2 1
1 1 1
...
Materials intervals = 1 2
...

and the subcell limits or sizes accordingly. If this is the plane strucure it think ElmerGrid will
create different BC numbers for the differing material numbers when extruding. You'll
end up with 8 boundary indices, 2 for both up & down planes.

Also you could just define your "force" as coordinate dependent (assuming force given in x-y plane).

Variable Coordinate; Real MATC "if ( tx(0)>0.4 & tx(0)<0.6 & tx(1)>0.4 & tx(1)<0.6 ) { 1 } else { 0 }"

or whatever your geometry limits are.

BR, Juha

Re: Discrete load on a cube surface

Posted: 16 Feb 2011, 11:33
by raback
Hi, If point load is what you're looking for I would suggest that you use the "Target Coordinates" keyword to define the node closest to that coordinate on-the-fly. That way you don't have to care about defining a small patch. Or you could define a Gaussian force distribution using MATC. -Peter

Re: Discrete load on a cube surface

Posted: 16 Feb 2011, 12:02
by Juha
HI,

just to add , the load for points is given with keywords of style:

Code: Select all

Variable name load = real x
e.g.

Code: Select all

Displacement 3 Load = real 1
The feature might not be available through GUI though....
Juha

Re: Discrete load on a cube surface

Posted: 16 Feb 2011, 12:31
by thejonesyboy
Thank you so much for your quick help Juha and raback. I have learnt much in the last hour.

I went with your suggestion Juha, but slightly modified:

Code: Select all

Variable Coordinate; Real MATC "if ( tx(0)>0.4 & tx(0)<0.6 & tx(2)>0.4 & tx(2)<0.6 & tx(1)>0.99) { -1.0e10 } else { 0 }"
This targets the 0.2 x 0.2 square of nodes (elements) above y = 0.99, which is equivalent to what I need for now. I guess tx(1)==1.0 would be more appropriate. I added this to 'Force 2' in the 'Body Force' section.

Re: Discrete load on a cube surface

Posted: 16 Feb 2011, 12:46
by Juha
Hi,

you could also add that as the "Force 2" in the relevant "Boundary Condition"-section?

Juha

Re: Discrete load on a cube surface

Posted: 21 Jul 2019, 20:04
by TheWonder34
How did you edit that file with cube to get 7 boundaries?