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How to get the current from current density
Posted Jan 26, 2011, 10:50 a.m. EST Version 4.0a 5 Replies
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I am simulating a piezo electric transducer in COMSOL Multiphysics 4.0a. In order to get the impedance of the transducer at different frequencies, I need the current flowing at the boundary of piezo ceramic. My model is 2D axisymmetric. Following are my problems:
1. For getting current(I) from the variable current density(J), I have to integrate the expression:
int(J*2*pi*r)dr over the boundary
However, I came to know from my friend that multiplication by (2 *pi *r) is applicable for COMSOL 3.5 but COMSOL 4.0a does this automatically through internal calculations for axisymmetric models. So there is no need to evaluate int(J*2*pi*r)dr. Rather int(J)dr is appropriate. Please confirm if it is correct.
2. How can I get the integration of current density. Using probe option, model coupling etc. Expedite if anyone have an idea
3. If I get the current by above means, then how to plot this impedance (Z=V/I), versus frequency. I mean how to access current value and corresponding frequencies to plot line graph.
Hope to hear anyone soon, Thanking you in anticipation
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User COMSOL
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I'm no longer sure about the 2*pi*r, I though it was only the 2*pi, but is it still there in 4.1 ? Ibelieve not that its back to 3.5a
The best as there are so many "small" things like this to remeber, is to check by estimating the volume from the 2D-axy symmetry:
integrate "1" then "r" and "2*pi*r" over a circle and check analytically.
Compare also the integration of "1" with the the option "Integration settings - Compute volume integral (axial symmetry)
Impedances are typically obtained either through energy calculation or via the lumped ports, or by the ratio imaginary versus real parts, all depends on your physics and what you are doing. Check the doc and the examples of the model library
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Good luck
Ivar
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User COMSOL
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indeed, these checks are so simple and quickly done, that if you have any doubts, its much faster to check it. Just be careful with the default values i.e. 2D thickness = 1[m] mostly then the division by 1 induces you often in error. Or that you have the origin at the CoG bay design, most of the cases, then you have once a part far off and you forget to take the difference of the true CoG i.e. for an inertia evaluation
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Good luck
Ivar
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