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contact resistance with moving parts
Posted Jan 21, 2011, 6:35 a.m. EST Low-Frequency Electromagnetics, MEMS & Nanotechnology, MEMS & Piezoelectric Devices, Structural Mechanics 6 Replies
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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
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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
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Federico
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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
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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
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