  We analytically derive the effective layer elastic energy of smectic-A and
smectic-C liquid crystals by adiabatic elimination of the orientational degree
of freedom from the generalized Chen-Lubensky model. In the smectic-A phase,
the effective layer bending elastic modulus is calculated as a function of the
wavelength of the layer undulation mode. It turns out that an unlocking of the
layer normal and the director reduces the layer bending rigidity for
wavelengths smaller than the director penetration length. In the achiral
smectic-C phase, an anisotropic bending elasticity appears due to the coupling
between the layer displacement and director. The effective layer bending
rigidity is calculated as a function of the angle $\vartheta$ between the layer
undulation wave-vector and the director field. We compute the free energy
minimizer $\vartheta=\theta$. It turns out that $\theta$ varies from $0\deg$ to
$90\deg$ depending on the tilt angle, undulation wave-length and other elastic
constants. We also discover a new important characteristic length and the
discontinuous change of $\theta$. Using the elastic constants of Chen-Lubensky
model, we determine the parameters of the more macroscopic model [Y. Hatwalne
and T. C. Lubensky, Phys. Rev. E {\bf 52}, 6240 (1995)]. We then discuss the
hydrodynamics, and demonstrate the alignment of director and the propagation of
the anisotropic layer displacement wave in the presence of an oscillatory wall
and a vibrating cylindrical source respectively.
