Field FUnction
 

Hi, I want to create a field function to measure the shear stress in a fluid flow. I have written a field function but it is not giving me proper values.
The function is

($DynamicViscosity*grad($$Velocity[0]))

I want to use the value from this function to refine my mesh - basically I want to refine mesh wherever the value of shear stress is above some threshold value. When I do the refinement, I cant see any change from the previous mesh.
For mesh refinement, my function is

(mag2($DynamicViscosity * grad($$Velocity[0]))>1.0e-6)?0.75:0

What this does is it changes the cell size to 0.75 wherever the value of the function is greater than 1.0e-6. But I dont see any refinement using this function.

Please help.

Have you done a scalar plot of your field function to verify that there are values greater than 1.0e-6? Also verify that the units are correct. That could screw things up as well.