Material Derivative: Finding P for Steady State Flow

[cabellos]

material derivative?

I have to find the material derivative of the density P for the following steady state flow:

P = -1-2xy-3z^3 and u = (3x-z, y+3z, x-y)

I have looked at previous examples but I am not sure what i have to do with the density -1-2xy-3z^3 ... ?

please help.

 

[arildno]

What's the DEFINITION of the material derivative?

 

[cabellos]

I think iv got my head round it now. If someone has a spair few minutes could they check my answer of -8xy +8zy -12xz