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simulation of skin

Posted Aug 5, 2009, 12:08 a.m. EDT Bioengineering 6 Replies

Lodge Pun
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Dear all,

i am trying to simulate a human arm (approximate as a cylinder) in Comsol. However, when i trying to introduce the skin into my model (skin thickness = 1mm, diameter of the human arm =25mm) . The computation time increase dramatically. Is there any way to represent this skin layer in Comsol? I have read "thin-layer approximation " , but i am not sure if the approximation valid in the case. Does anyone has any idea about this? Thank you very much

Best Regards,
Lodge
6 Replies Last Post Oct 18, 2010, 6:33 a.m. EDT
Alessandro Ricci
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Posted: 2 decades ago Aug 5, 2009, 11:24 a.m. EDT
Dear Lodge,
if your models involves structural mechanics you can model skin with the aid of shell elements.
You just have to employ Solid-stress strain application mode for the arm and shell for the skin layer. Pay attention that, by default, shell appl. mode is active on all the surfaces. Therefore you have to deactivate it wherever skin is not present.
This combination of application modes saves a lot of computational time since shell elements simply use the "surface" of the mesh of the 3d solid-stress strain appl. mode.
An other way to model the same problem (which works in a more general context) is to couple your 3d module with a weak form contribution (PDE modes/weak form boundary). When you are asked for setting the dependent variables in the model navigator, use the same dependent variables of your 3d module. Then in the boundary settings of you weak form module you have to enter the equation (written in the weak form) which models your skin.
Also this way, is very "cheap" for what concerns the computational cost, since you don't have to mesh thin layers. The effect of your thin layer is taken in account by an equation.
I hope this help.
Hi.

Alessandro
Dear Lodge, if your models involves structural mechanics you can model skin with the aid of shell elements. You just have to employ Solid-stress strain application mode for the arm and shell for the skin layer. Pay attention that, by default, shell appl. mode is active on all the surfaces. Therefore you have to deactivate it wherever skin is not present. This combination of application modes saves a lot of computational time since shell elements simply use the "surface" of the mesh of the 3d solid-stress strain appl. mode. An other way to model the same problem (which works in a more general context) is to couple your 3d module with a weak form contribution (PDE modes/weak form boundary). When you are asked for setting the dependent variables in the model navigator, use the same dependent variables of your 3d module. Then in the boundary settings of you weak form module you have to enter the equation (written in the weak form) which models your skin. Also this way, is very "cheap" for what concerns the computational cost, since you don't have to mesh thin layers. The effect of your thin layer is taken in account by an equation. I hope this help. Hi. Alessandro
Lodge Pun
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Posted: 2 decades ago Aug 6, 2009, 12:38 a.m. EDT
Dear Alessandro,
Thank you very much for your help. I think that i cannot use the shell appl. mode as i am currently using the AC/DC module for simulation the electromagnetic effect to the human limb. I think that i need to read the mannul about the weak form to model the skin layer because i am not new to COMSOL. Your information is quite helpful for me and thank you very much for your help.
Best Regards,
Lodge
Dear Alessandro, Thank you very much for your help. I think that i cannot use the shell appl. mode as i am currently using the AC/DC module for simulation the electromagnetic effect to the human limb. I think that i need to read the mannul about the weak form to model the skin layer because i am not new to COMSOL. Your information is quite helpful for me and thank you very much for your help. Best Regards, Lodge
Alessandro Ricci
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Posted: 2 decades ago Aug 6, 2009, 6:13 a.m. EDT
Dear Lodge,
besides the weak boundary contribution approach, which is always valid, Ac/Dc module contains standard boundary conditions to model "skin effect".
Give a look, for instance, to the tutorial "Ac/Dc module/Tutorial models/coil eddy currents".
I hope this help.

Alessandro
Dear Lodge, besides the weak boundary contribution approach, which is always valid, Ac/Dc module contains standard boundary conditions to model "skin effect". Give a look, for instance, to the tutorial "Ac/Dc module/Tutorial models/coil eddy currents". I hope this help. Alessandro
Lodge Pun
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Posted: 2 decades ago Aug 6, 2009, 6:39 a.m. EDT
Dear Alessandro,
Thanks. I think that i should have a good look about the tutorial of AC/DC module. Thank you very much for your kind help.
Best Regards,
Lodge
Dear Alessandro, Thanks. I think that i should have a good look about the tutorial of AC/DC module. Thank you very much for your kind help. Best Regards, Lodge
Lodge Pun
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Posted: 2 decades ago Aug 6, 2009, 6:50 a.m. EDT
Dear Alessandro,
do you mean the tutorial "Eddy Currents" (p.29 in Ac/Dc user guide")? I have read this and i found that the idea is a bit different from the thin layer. Thank you very much.
Best Regards,
Lodge
Dear Alessandro, do you mean the tutorial "Eddy Currents" (p.29 in Ac/Dc user guide")? I have read this and i found that the idea is a bit different from the thin layer. Thank you very much. Best Regards, Lodge
bushra riaz
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Posted: 1 decade ago Oct 18, 2010, 6:33 a.m. EDT
Dear Lodge Pun
I am a new comsol user and trying to model the same arm and want to use the same modulde Ac dc module
Can you please give me more detials how have u model that?
Thank you
Dear Lodge Pun I am a new comsol user and trying to model the same arm and want to use the same modulde Ac dc module Can you please give me more detials how have u model that? Thank you

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