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user-defined functions with strain rate

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Old   May 27, 2009, 12:46
Default user-defined functions with strain rate
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ems
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Eric
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I am trying to model a non-newtonian fluid (blood) that depends on shear rate. I used the equation:

0.026314*pow($StrainRate,(0.47234-1)) + 3.117316

but I get an error that $StrainRate is not recognized. Is this not the correct term for strain rate, or am I using it incorrectly? I haven't been able to find the correct usage in the help or anywhere else. Any help or advice would be appreciated.

Thanks,

Eric
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Old   May 28, 2009, 07:40
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Aroon
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Go into Tools > Field Functions and check the format for Strain Rate. I do not have experience in non-Newtonian fluids, but if the Strain Rate exists it should be listed in the Field Functions. The Function Name should give you the syntax when you use the function.
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Old   May 28, 2009, 14:33
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After talking to support, I understand what I was doing wrong. If anyone has the same problem in the future, you have to check the box for "Temporary Storage Retained" under Solvers->"solver_used," then strain rate appears in the field function list. Thanks for your help.
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Old   May 30, 2010, 07:56
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Quote:
Originally Posted by ems View Post
After talking to support, I understand what I was doing wrong. If anyone has the same problem in the future, you have to check the box for "Temporary Storage Retained" under Solvers->"solver_used," then strain rate appears in the field function list. Thanks for your help.

Hi, how can I use the function Strain Rate magnitude

what is the syntax to follow

thanks
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Old   June 2, 2010, 09:38
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As I had mentioned, you will have to check the box for "Temporary Storage Retained" in the solvers section. On my particular simulation, I had it checked for Lagrangian Multiphase, Segregated Flow, and K-epsilon Turbulence. Then, in your user-defined field function, call strain rate magnitude using the handle $StrainRate

As a note, there is no strain rate for the first iteration. So, you should let your simulation run one or two iterations without calling the $StrainRate function and then stop it and apply the field function. As an example, my program used a strain-rate dependent viscosity. So for the first couple iterations I used a constant viscosity, then paused and changed my viscosity definition to my field function that included $StrainRate. If I had tried to use that field function from the beginning, I would have gotten an error.

Let me know if you are still having trouble.

-Eric
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