  We discuss the dynamics of a bilayer membrane with partial slip boundary
conditions between the monolayers and the bulk fluid. Using Onsager's
variational principle to account for the associated dissipations, we derive the
coupled dynamic equations for the membrane height and the excess lipid density.
The newly introduced friction coefficients appear in the renormalized fluid
viscosities. For ordinary lipid bilayer membranes, we find that it is generally
justified to ignore the effects of permeation and parallel slip at the membrane
surface.
