[petsc-users] ex42 question

[Sang pham van]

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
questions:

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.
Regards,
Sang
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