How to express strain rate in Comsol

Ahadi · December 9, 2014, 17:10

Hello everyone,

I am relatively new to simulation. I have a question in COMSOL but it is quite general. I am trying to define an analytic function in COMSOL. The equaiton is Carrea_Yasuda fluid model. It is non newtonian fluid model that is function of shear rate. How to write an expression for the shear rate for a 3D problem?

Thank you very much for your help.

Best regads,
hasan.

JBurnham · December 10, 2014, 11:34

Strain rate and shear rate are tensors, and that's how they're solved in 3-D. The lab data you fit to parameterize non-Newtonian models are usually from a testing apparatus that is essentially 1-D, so the tensor has a lot of zeros and can be represented as a single scalar value. That shouldn't stop you from being able to parameterize the fluid; you don't need to know the 3-D characteristics of the flow, you just need to know the lab data.

This is a FLOW-3D forum, not a Comsol forum, so you're not likely to get an answer here that's more detailed than that.

December 9, 2014, 17:10	How to express strain rate in Comsol	#1
Ahadi New Member hassan Join Date: Jun 2014 Posts: 4 Rep Power: 11	Hello everyone, I am relatively new to simulation. I have a question in COMSOL but it is quite general. I am trying to define an analytic function in COMSOL. The equaiton is Carrea_Yasuda fluid model. It is non newtonian fluid model that is function of shear rate. How to write an expression for the shear rate for a 3D problem? Thank you very much for your help. Best regads, hasan.

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December 10, 2014, 11:34		#2
JBurnham Senior Member Jeff Burnham Join Date: Apr 2010 Posts: 204 Rep Power: 17	Strain rate and shear rate are tensors, and that's how they're solved in 3-D. The lab data you fit to parameterize non-Newtonian models are usually from a testing apparatus that is essentially 1-D, so the tensor has a lot of zeros and can be represented as a single scalar value. That shouldn't stop you from being able to parameterize the fluid; you don't need to know the 3-D characteristics of the flow, you just need to know the lab data. This is a FLOW-3D forum, not a Comsol forum, so you're not likely to get an answer here that's more detailed than that.