As per John’s suggestion, I’m emailing it to the whole users list for some very simple questions on example 13:


·         We are solving the gov. equations for a lid driven cavity in 2D:

rho*(v_i,0 + v_i,j*v_j) + p_i - mu*v_i_jj = 0

v_ii = 0


The FEM formulation of the above equations in example 13 is not clear to me. Can anyone help?


Boundary conditions are implemented using penalty method.


I couldn’t figure out the exact formulation to figure how it’s doing it.


(I’m not very knowledgeable about FEM and trying to relate what I read in a book e.g. for say linearized burger’s equation v_i,0 + vbar_j*v_i,j – nu*v_i,jj – f_i = 0  with generalized galerkin methods leads to the formulation (A + dt/2*(B+K)*V^n+1 = [A-dt/2*9B+K)]v^n + dt*(F + G)). (A  is mass matrix, K is stiffness matrix  etc.

Now this is basically in the form A*u =B . which is then solved for u. The formulation is DST approximation.


So basically how does the ex13 implementation translates to something like above.

The book I’m referring is Computational Fluid Dynamics by T J Chung.

I’m pretty sure it’s quite simple and those who have done it can quickly scribble. I might be able to figure it out eventually as I get proficient in FEM but it would save me a lot of time if you folks can help me here.


·         The above should hopefully also answer how we have a terms like Kuu, Kup , Kuv etc. which are themselves matrices.

·         I wanted to compute Re of the flow but couldn’t find the value of “nu” used in the problem?  (L & u is 1 but don’t know nu, 1/300 ??)


Any help would be greatly appreciated. Unless I understand all this I’m finding it difficult to move on.