Thank you all
1.) I am trying to solve the lid-driven cavity problem for an incompressible Stokes and Navier Stokes equations using the general "Mixed" finite element method. Dirichlet boundary conditions are specified everywhere on the boundary.
When I try to solve these systems of equations, my matrix showing is that it is singular. I doubt whether it is necessary to specify pressure value at some point. Otherwise how to impose the constraint "average pressure over the domain is zero"? in FEM.
2.) I am trying to simulate incompressible flow over a cylinder using the mixed finite element method. Dirichlet boundary conditions are specified at the inlet, top, and bottom on a circle and do nothing on the outlet.
Is it necessary to give pressure value at some point?