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April 8, 2010 8:12am UTC

How to add roughness on a surface?

Hi all,

I'm simulating a layer with roughness(50nm-100nm), I have read from several comsol papers that this might be solved by using moving mesh. But how exactly I have no idea. Could anyone give me some guidance and hints?

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April 8, 2010 2:41pm UTC in response to Ivar Kjelberg

Re: How to add roughness on a surface?

Ivar, thank you for your reply. Do you have the course slides or manuals may be I can take a look?

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April 9, 2010 5:50am UTC in response to Ivar Kjelberg

Re: How to add roughness on a surface?

Hi

I quickly generate an example, this gives the idea:

Start Comsol in 2D with just a moving mesh ALE mode, draw a rectangle 1 m in x, 0.2 m in y

Define an analytical function "Wave" with argument "x" and expression something like

0.05*sin(2*pi*3.5*x)

I have choosen a half total wavenumber just to make the funtion symmetric between x = 0 and 1, this is no necessity, test it by plotting it in the Function GUI for 0 < x < 1.

Then you define the boundary conditions:

lower edge "2": fixed mesh dx=dy=0
left and right edges "1,4": fixed along dx=0 and dy not selected = free
top edge "3": fixed along dx=0 and dy=Wave(x) forced to the Wave function

You mesh and hit refinement once to get a reasonnable mesh, w.r.t. the wave periode and you solve.

To see the mesh, use "postprocessing - plot parameters - General tab: Element refinement OFF and value "1" its toward the middle-bottom part of the GUI, and in Surface tab: Coloring: FLAT Fill Style Wireframe

there you are.

now you can save this "deformed" mesh as a geometry, but you might need to "remesh it" as the mesh quality might become poor, also if the mesh was rather rough you might not have a very clean geometry, once saved, with a few "spikes, that might need some tweaking.

have fun COMSOLING

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August 25, 2010 12:17pm UTC in response to Ivar Kjelberg

Re: How to add roughness on a surface?

Dear all,

The solution presented above probably refers to version 3.5.
I would like to implement a similar solution in 4.0a how can I do that?
Is it possible to set a similar boundary condition in 4.0a? If so, how?

BR
Mehdi

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September 21, 2010 2:40pm UTC in response to Matthias K

Re: How to add roughness on a surface?

Hi

first be sure you have the latests patch 4.0.0.993 for me today ;)

Then if you rightclick the Moving mesh node you can see the domain and boundary prescribed displacement that allows you to define boundary or point meshing constriants. By dfault everything is fixed, sou you must also add a free mesh domain node and select which are "free" to move

--
Good luck
Ivar

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October 10, 2010 10:33am UTC in response to Steven Wang

Re: How to add roughness on a surface?

Hi

you are right in V4 "ale" is under "Mathematics - Deformed mesh"

Then by default V4 comes with Fixed Mesh "all" for the full/all volume so you must add:
Free Deformation and select domain 1 (the only one or the one you want to deform if several)
Thereafter you might define your boundary Prescribed mesh displacements

in V4 I ususally leave the two default entries Fixed Mesh 1 and Prescribed Mesh Displacement 1 as is and add my own thereafter.
For this example:
1x Free Displacement (on the domain) and
3x Prescribed Mesh Displacements on the Boundaries sa described.

The mesh "size" is in the "SIZE" subnode of the mesh, the first subnode is a global settings (or the one you add to a partial meshing command)
The mesh refinement is somewhat hidden in the sub-node: right-click_on_Mesh + More_Operations + Refine

Then solve, to see the mesh, use a mesh plot (right click under Results - 2D Plot Group)

--
Good luck
Ivar

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October 11, 2010 4:19pm UTC in response to Steven Wang

Re: How to add roughness on a surface?

Hi

normally there is an Export to file as right-click option for the meshing

--
Good luck
Ivar

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October 11, 2010 7:38pm UTC in response to Steven Wang

Re: How to add roughness on a surface?

Hi

Good remark, in V4 I cannot find any saved deformed mesh or make geoemtry of deformed mesh, could be that it is not yet implemented ?

--
Good luck
Ivar

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January 31, 2011 3:26pm UTC in response to Ivar Kjelberg

Re: How to add roughness on a surface?

Hello Ivar,

I have some problems in reconstructing the example you described above. Could you post the file you have created the screenshot from? So I could check out what I have missed in the boundary conditions or somewhere else.

Thanks a lot,
Thomas

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