Dirichlet BC for some components of vector

Question

Hello!

I solve elasticity problem and need to fix only some components of displacement vector $u$ on a boundary:

For example: $u_x = 0$ on one boundary and $u_y = 0$ on another.

I can't find any examples for this case.

Thank you.

Comments

This is a duplicate of this:

http://fenicsproject.org/qa/3412/constraint-component-vector-field-using-boundary-conditions