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shear stress in microchannel
Posted 2012年5月8日 GMT-4 00:50 Fluid & Heat, Computational Fluid Dynamics (CFD), Parameters, Variables, & Functions, Results & Visualization Version 4.2, Version 5.3 8 Replies
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I am clueless as to how to start the post-process data analysis to get the spatial distribution of shear stress of a micro channel. I have read the few discussion threads but it involves exporting the slice 3D plot of the velocity and then do the calculation of shear stress in Matlab. I would appreciated it if someone can either tell me (a) what Matlab code or equation you used to solve for shear stress from the velocity profile slice or (b) a way to get Comsol to compute shear stress for me and graph it (a much easier way for a newbie like me).
Thank you so much!
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Are you sure you do not have enough COMSOl variables already defined to extract the shear stress directly in the GUI ?
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Good luck
Ivar
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well within a minus sign that is the COMSOL internal stress tensor variable:
spf.K_stress_tensorxy
check your expressions, so I would say its not far away ;)
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Good luck
Ivar
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I am interested in the same problem, have you found an answer?
Thanks in advance,
Gautier
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my comment was just to remind you about all the predefined internal variables of COMSOL, unfortunately I do not know of any exhaustive list, but you can find them in the pull down menus of the Derived Variables, (or with the CNTRL Space) and in the equation view nodes
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Good luck
Ivar
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I know this is an old post, but I wanted to thank you for mentioning the spf.K_stress_tensorxy variable. I never would have found it otherwise.
As a general comment, it seems far more difficult than need be to find some variables. For example, one place I've looked extensively is in the drop-down lists where you can add variables to a probe. Those lists do not seem complete. I checked my "Derived" list also and the only things in there are the probes I defined. Then there is the "Equation View," which sometimes reveals a useful variable, but it does not seem complete either. And finally, there is the documentation -- you can search every manual, and there is no mention of "stress_tensorxy". There is a discussion of the stress tensor, but it doesn't tell you what to call it when you need it.
Any idea why these lists can't be comprehensive? And how does one find these "secret" variables -- is there somewhere I have not looked?
Thanks,
James
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More generally, other than unit differences, it is unclear to me how, at a basic conceptual level, viscous shear stress, traction, and shear rate (since I would think it would be directly proportional to shear stress via dynamic viscosity) really differ. I'm trying to use them as the constraint to set to 0 in a global equation for a stationary study and none of them (plus others I've tried) are giving me answers that make sense. Any insight would be greatly appreciated.