I figured out what the mistake was. The degrees-of-freedom of the point I want to find through “rd = dolfinx.fem.locate_dofs_geometrical(V=V, marker=lambda x: np.isclose(x[0], 2.0) & np.isclose(x[1], 0.0))” is actually The global index of the node. So if I want to apply a x-direction force on the node, I should use “b.setValue(2*rd, 1)” instead of “b.setValue(rd, 1)”. Still thanks for your reply.