Periodic boundary condition and no-slip boundary condition need to be applied in my program for stokes equation.
The result is very strange that some couples of dofs for periodic b.c. are right others are wrong. Also the same with the result of no-slip b.c.
I think the result is relate to the sequence of applying periodic b.c. and no-slip b.c. In my program, the periodic b.c. is applied element by element during the assembling of global stiffness matrix firstly. Then after assembling the global matrix, no-slip b.c. is applied by setting the value on the correspond dof in the global matrix a large number and the correspond value on the right vector Zero.
Maybe it is first to apply no-slip b.c. during assembling global matrix element by element before appling periodic b.c. Is it right?

Best regards,

Yours sincerely
Department of Engineering Mechanics
State Key Laboratory of Structural Analysis for Industrial Equipment
Dalian University of Technology
Dalian, 116023, P. R. China