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3D Symmetry of Model

Posted 1 juil. 2013, 16:41 UTC−4 MEMS & Nanotechnology, MEMS & Piezoelectric Devices, Geometry, Mesh, Results & Visualization Version 4.3 8 Replies

Daniel Livingston
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Good afternoon all,

I am modelling two electrodes (tips facing each other) and the electric field between them. There are two Z-axis layers to each of the electrodes, measured in nanometers, whereas the width of the electrodes are measured in the hundreds of micrometers. Further, the electrode tips are half-cylinders. As you can imagine, this leads to some mesh-compiling problems (where it only compiles when the electrode width is set to a few dozen microns, instead of the desired hundreds), and I'm looking for solutions to be able to create and render a larger mesh.

The best hope to a solution (unless there are any you can recommend) seems to be symmetry, as both electrodes and the environment around them are identical.


I don't think 2D axial symmetry, extruded into 3D, would be able to suit my needs.

How would I do 3D symmetry along an axis? I've scoured the COMSOL forums, and while they are normally very helpful (thank you to everyone who takes the time to respond, you aren't just helping the OP) all the advice on symmetry is very vague and esoteric to a beginner like myself.

Thank you for your help,
Daniel
8 Replies Last Post 16 nov. 2017, 05:33 UTC−5
Josh Thomas Certified Consultant
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Posted: 1 decade ago 1 juil. 2013, 16:54 UTC−4
Daniel-

2D axial symmetry is not extruded into 3D rather it is "revolved" into 3D in the azimuthal direction around the symmetry axis.

Also, what do you mean by 3D symmetry? You can define symmetry planes in 3D where the geometry/physics/results will be mirrored across the plane. Is that what you are referring to? This will result in 1/2 or 1/4 symmetry or maybe even 1/8 depending on how many symmetry planes you define. Also, you can have sector symmetry in 3D where symmetry planes are not orthogonal but still intersect along a common axis.

Best regards,
Josh Thomas
AltaSim Technologies
Daniel- 2D axial symmetry is not extruded into 3D rather it is "revolved" into 3D in the azimuthal direction around the symmetry axis. Also, what do you mean by 3D symmetry? You can define symmetry planes in 3D where the geometry/physics/results will be mirrored across the plane. Is that what you are referring to? This will result in 1/2 or 1/4 symmetry or maybe even 1/8 depending on how many symmetry planes you define. Also, you can have sector symmetry in 3D where symmetry planes are not orthogonal but still intersect along a common axis. Best regards, Josh Thomas AltaSim Technologies
Daniel Livingston
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Posted: 1 decade ago 2 juil. 2013, 12:13 UTC−4
Josh,

Thank you for responding.
It is exactly what you are you referring to in the latter which I am trying to figure out: I'd like a 3D symmetry plane to project 1/2 symmetry for each of what you mentioned: geometry, physics, and results. How might I go about defining this plane, the 1/2-fractional symmetry, and the projection of it into the geometry, physics, and results?
Forgive my ignorance, I have only been working with COMSOL for a few weeks.

Best wishes,
Daniel
Josh, Thank you for responding. It is exactly what you are you referring to in the latter which I am trying to figure out: I'd like a 3D symmetry plane to project 1/2 symmetry for each of what you mentioned: geometry, physics, and results. How might I go about defining this plane, the 1/2-fractional symmetry, and the projection of it into the geometry, physics, and results? Forgive my ignorance, I have only been working with COMSOL for a few weeks. Best wishes, Daniel
Josh Thomas Certified Consultant
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Posted: 1 decade ago 2 juil. 2013, 12:19 UTC−4
Daniel-

Well, you need to build only half the geometry (or build the entire geometry and then delete 1/2 of it).

Then, under the Physics set-up, right-click and define a symmetry boundary condition on the 1/2 symmetry plane. This will constrain the values of any variables with a no-flux condition.

Then, if you want, when post-processing you can visualize in the full 3D model by generating a full, 3D data set that is re-mirrored back across the symmetry plane. This is done using the Mirror 3D data set found under Data sets.

Best regards,
Josh Thomas
AltaSim Technologies
Daniel- Well, you need to build only half the geometry (or build the entire geometry and then delete 1/2 of it). Then, under the Physics set-up, right-click and define a symmetry boundary condition on the 1/2 symmetry plane. This will constrain the values of any variables with a no-flux condition. Then, if you want, when post-processing you can visualize in the full 3D model by generating a full, 3D data set that is re-mirrored back across the symmetry plane. This is done using the Mirror 3D data set found under Data sets. Best regards, Josh Thomas AltaSim Technologies
David Reens
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Posted: 1 decade ago 31 oct. 2013, 14:34 UTC−4
Hi Josh,

Thanks for the helpful comments. I'm looking forward to applying some symmetry planes to my 3D model, but for the life of me I can't find where I can apply boundary conditions. It feels like I've tried right clicking everything under the sun :). What's killing me too is that I feel like I remember seeing it somewhere recently.

Can you be more specific about "under the physics setup right click and define a symmetry boundary condition"?

Thanks,
Dave
Hi Josh, Thanks for the helpful comments. I'm looking forward to applying some symmetry planes to my 3D model, but for the life of me I can't find where I can apply boundary conditions. It feels like I've tried right clicking everything under the sun :). What's killing me too is that I feel like I remember seeing it somewhere recently. Can you be more specific about "under the physics setup right click and define a symmetry boundary condition"? Thanks, Dave
Josh Thomas Certified Consultant
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Posted: 1 decade ago 31 oct. 2013, 14:43 UTC−4
David-

Well, it depends on the physics and the modules that you have available, but if you right-click on the main physics node in the Model Builder window in most cases there is a "Symmetry" option available. For example, if you are modeling Solid Mechanics then you would right click on the Solid Mechanics node and add the Symmetry boundary condition.

--
Best regards,
Josh Thomas
AltaSim Technologies
David- Well, it depends on the physics and the modules that you have available, but if you right-click on the main physics node in the Model Builder window in most cases there is a "Symmetry" option available. For example, if you are modeling Solid Mechanics then you would right click on the Solid Mechanics node and add the Symmetry boundary condition. -- Best regards, Josh Thomas AltaSim Technologies
Ari
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Posted: 9 years ago 10 nov. 2015, 15:00 UTC−5
Hello Josh,

I have a different physics but similar question.
You've mentioned that under the Physics set up there is a possibility for "Symmetry" boundaries. However, it does not exist for "Electrostatics (es)", "Coefficient Form PDE (c)", and "Laplace equation (lpeq)".

My system consists of a few metallic surfaces and some dielectric structures and I'm solving Laplace equation for the surrounding area using Dirichlet Boundary conditions on the metallic surfaces. Therefore use the above-mentioned physics. In this case, what would be a way around this issue?

Best Regards,
Ari


Hello Josh, I have a different physics but similar question. You've mentioned that under the Physics set up there is a possibility for "Symmetry" boundaries. However, it does not exist for "Electrostatics (es)", "Coefficient Form PDE (c)", and "Laplace equation (lpeq)". My system consists of a few metallic surfaces and some dielectric structures and I'm solving Laplace equation for the surrounding area using Dirichlet Boundary conditions on the metallic surfaces. Therefore use the above-mentioned physics. In this case, what would be a way around this issue? Best Regards, Ari
Sagar Deshmukh
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Posted: 7 years ago 26 août 2017, 14:14 UTC−4
Hey have you got any clue to do it? Please let me know if you had, I am too facing same problem
Hey have you got any clue to do it? Please let me know if you had, I am too facing same problem
MG
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Posted: 7 years ago 16 nov. 2017, 05:33 UTC−5
Updated: 7 years ago 16 nov. 2017, 05:34 UTC−5

Dear COMSOL User, I am facing simillar problem, When I go to symmtery under the physics tab, the domain is unable to select the object. I don't know why? domain option and all other options are off thats why unable to select the layer of my object whose symmetry I want to make.

If anyone could give me any idea. I am working on solid mechanics, eigenfrequency module.

Thank you

Dear COMSOL User, I am facing simillar problem, When I go to symmtery under the physics tab, the domain is unable to select the object. I don't know why? domain option and all other options are off thats why unable to select the layer of my object whose symmetry I want to make. If anyone could give me any idea. I am working on solid mechanics, eigenfrequency module. Thank you

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