[petsc-users] ex42 question

Sang pham van pvsang002 at gmail.com
Wed Mar 26 11:55:45 CDT 2014

Hi Dave,
I guess you are the one contributed the ex42 in KSP's examples. I want to
modify the example to solve for stokes flow driven by volume force in 3D
duct. Please help me to understand the code by answering the following

1. Firstly, just for confirmation, the equations you're solving are:
     \nu * \nabla \cdot \nabla U - \nabla P = 0 and
     \nabla \cdot U = 0

      where U = (Ux,Uy,Uz), \nu is variable viscosity?

 2. Are U and P defined at all nodes? (I googled the Q1Q1 element, it looks
like a box element with U and P defined at 8 corners).

 3. Are nodes' coordinate defined though the DA coordinates?

 4. How can I enforce noslip BC, and where should I plug in volume force?

Thank you in advance.
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