Menu

Discussion Forum

New Discussion
Filtrer

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

contact resistance with moving parts

Posted 21 janv. 2011, 06:35 UTC−5 Low-Frequency Electromagnetics, MEMS & Nanotechnology, MEMS & Piezoelectric Devices, Structural Mechanics 6 Replies

Federico Moro
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hi,

I am trying to simulate a sphere-cylinder geometry with a contact resistance (thermal or electrical). Voltage and temperature drop at the sphere-cylinder interface due to contact resistances. For instance voltage drops can be simulated with the command "Contact resistance" in COMSOL 4.1.

I would like to simulate a contact model with pressure dependent contact resistances and varying contact area, i.e. an electro-thermo-mechanical contact problem. In the attached model the geometry is finalized as an "assembly" rather than a "union" (contacting boundaries are distinct) and an identity pair is defined. However, the command "Contact resistance" cannot be defined for identity pairs. I can impose only continuity conditions for electric potential and temperature.

Do you know how to simulate contact resistances with disconnected parts and non-overlapping boundaries? How to include surface resistance heating?

Any suggestions will be greatly appreciated!
Thanks a lot,
Federico
6 Replies Last Post 13 mai 2011, 09:28 UTC−4
Ralf Tschiesche
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 28 janv. 2011, 02:43 UTC−5
Hi Federico!

I had a similar problem in Electric Currents, and got an answer form support:
...
This boundary condition has not been
implemented yet, but it is on our todo list.

As a workaround, you can add the boundary condition manually as a weak
contribution, but it is a bit tricky since pair boundary conditions are
special. Here is the procedure:

1) Add a pair boundary condition that does not give a weak contribution,
i.e., electric insulation. This is just so that some special features of
pair boundary conditions are defined.

2) Add a weak contribution to the same boundaries as the electric
insulation pair boundary condition was defined for.

3) Write the following expression for the weak contribution:

if(src2dst_p2,1e7*(src2dst_p2(V)-V)*test(V),0)+if(dst2src_p2,1e7*(dst2src_p2(V)-V)*test(V),0)

In the expression above, src2dst_p2 and dst2src_p2 are functions that map
from source to destination and vice versa. Without arguments, they
determine if the two parts of the pair are in contact. The suffix p2 refers
to the name of the defined pair, which is p2 in your example. The number
1e7 is the conductivity divided by the thickness, which for your example
was 1e-3/1e4.
...

This works for me. Good luck!
Ralf
Hi Federico! I had a similar problem in Electric Currents, and got an answer form support: ... This boundary condition has not been implemented yet, but it is on our todo list. As a workaround, you can add the boundary condition manually as a weak contribution, but it is a bit tricky since pair boundary conditions are special. Here is the procedure: 1) Add a pair boundary condition that does not give a weak contribution, i.e., electric insulation. This is just so that some special features of pair boundary conditions are defined. 2) Add a weak contribution to the same boundaries as the electric insulation pair boundary condition was defined for. 3) Write the following expression for the weak contribution: if(src2dst_p2,1e7*(src2dst_p2(V)-V)*test(V),0)+if(dst2src_p2,1e7*(dst2src_p2(V)-V)*test(V),0) In the expression above, src2dst_p2 and dst2src_p2 are functions that map from source to destination and vice versa. Without arguments, they determine if the two parts of the pair are in contact. The suffix p2 refers to the name of the defined pair, which is p2 in your example. The number 1e7 is the conductivity divided by the thickness, which for your example was 1e-3/1e4. ... This works for me. Good luck! Ralf
Federico Moro
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 28 janv. 2011, 11:24 UTC−5
Thanks a lot for your help! your workaround works fine!!
Federico
Thanks a lot for your help! your workaround works fine!! Federico
Weiching Liao
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 4 mai 2011, 15:32 UTC−4
Hi,

May I ask a question about the expression?
Does if(src2dst_p2,1e7*(src2dst_p2(V)-V)*test(V),0) mean:
if src2dst is "true", the value is 1e7*(src2dst_p2(V)-V)*test(V); otherwise it's 0.

Thank you

Weiching
Hi, May I ask a question about the expression? Does if(src2dst_p2,1e7*(src2dst_p2(V)-V)*test(V),0) mean: if src2dst is "true", the value is 1e7*(src2dst_p2(V)-V)*test(V); otherwise it's 0. Thank you Weiching
Federico Moro
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 5 mai 2011, 04:26 UTC−4
That's true. The command "src2dst " can be used to check if moving parts are in contact. When the if condition is true a voltage step is applied at the contact interface, which depends on the Ohm's law J=sigma*(V1-V2) where sigma is the contact conductance and J is the current density.
That's true. The command "src2dst " can be used to check if moving parts are in contact. When the if condition is true a voltage step is applied at the contact interface, which depends on the Ohm's law J=sigma*(V1-V2) where sigma is the contact conductance and J is the current density.
Weiching Liao
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 12 mai 2011, 13:30 UTC−4
Hi,

I have one more question about how this approach.
First, how does the weak boundary on the identity pair couple with the two adjacent domains since it serves as the boundary condition of current density?
Thanks.

Wei-Ching
Hi, I have one more question about how this approach. First, how does the weak boundary on the identity pair couple with the two adjacent domains since it serves as the boundary condition of current density? Thanks. Wei-Ching
Federico Moro
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 13 mai 2011, 09:28 UTC−4
The identity pair condition cannot be regarded as a boundary condition. Electric potentials and temperatures are projected from the master to the slave domain in order to enforce the field continuity. Voltage and temperatures drops at the contact interface can be modelled by means of electric and thermal contact resistances.
The identity pair condition cannot be regarded as a boundary condition. Electric potentials and temperatures are projected from the master to the slave domain in order to enforce the field continuity. Voltage and temperatures drops at the contact interface can be modelled by means of electric and thermal contact resistances.

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content