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Why the integral of "u",the x componenet of velocity, over a surface parallel to "xy" plane is not zero?!!
Posted 2011年7月29日 GMT-4 16:25 Microfluidics, Results & Visualization Version 4.2 0 Replies
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I ran into a very strange problem. I was checking the mass conservation in my model when I found that COMSOL 4.2 does not take the integration in a way we expect. I have normal velocity as my inlet BC and pressure, no viscous stress as my outlet BC. The integral of "w", the z component of velocity, and velocity magnitude "spf.U", over my inlet surface parallel to "xy" plane were equal which was good. The integral of "u" and "v" over the inlet surface were zero which was reasonable. HOWEVER, for the outlet I have non zero values as the integrals of "u" and "v" over the outlet surface parallel to "xy" plane. The integrals of "w" and "spf.U" are not equal. Integration of "w" gives me the right (equal to inlet) flow rate but integration of "spf.U" gives me a value more than my inlet flow rate, most likely because of accounting for "u" and "v". Everybody knows that the integral of a vector parallel to a surface, over that surface should be zero. How does COMSOL calculate the integral?
by the way, I am using Results/ derived values/ integration to calculate the integral. There is no script involved.
Thanks in advance.
Hello Mahshid Mohammadi
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