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Old   May 7, 2018, 16:38
Default CFX Post - expressions / math. operations
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Hi,

I need to calculate second derivatives in CFX Post.
I created an expression which works for something like \frac{\partial v_x}{\partial x} with
"Velocity u.Gradient X"

Basically I want to calculate something like \frac{\partial^2}{\partial x_i \partial x_j}u_i u_j

I tried different things like Velocity u.Gradient X.Gradient X, but even (Velocity u * Velocity v).Gradient X doesnt work. Also creating an expression for lets say "grad_x_v_x = Velocity u.Gradient X" and then creating a new expression "grad_x_v_x.Gradient X" doesn't work.

I am using version 18.2.

Can anyone help? Thank you guys so much!
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Old   May 8, 2018, 15:21
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Insert a User Defined variable, select scalar type.

Then, set equal to Velocity u.Gradient X

MyUGradX = Velocity u.Gradient X

Now, insert a new variable (any name)

Select Gradient, and choose you MyUGradX, press Apply

You should get MyUGradX.Gradient which represents

MyUGrad.Gradient X, MyUGrad.Gradient Y, MyUGrad.Gradient Z

Effectively, they should correspond to

d2u/dx2, d2u/dydx, d2u/dzdx
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