  Several recent studies have suggested that circumstellar disks in young
stellar binaries may be driven into misalignement with their host stars due to
secular gravitational interactions between the star, disk and the binary
companion. The disk in such systems is twisted/warped due to the gravitational
torques from the oblate central star and the external companion. We calculate
the disk warp profile, taking into account of bending wave propagation and
viscosity in the disk. We show that for typical protostellar disk parameters,
the disk warp is small, thereby justifying the "flat-disk" approximation
adopted in previous theoretical studies. However, the viscous dissipation
associated with the small disk warp/twist tends to drive the disk toward
alignment with the binary or the central star. We calculate the relevant
timescales for the alignment. We find the alignment is effective for
sufficiently cold disks with strong external torques, especially for systems
with rapidly rotating stars, but is ineffective for the majority of
star-disk-binary systems. Viscous warp driven alignment may be necessary to
account for the observed spin-orbit alignment in multi-planet systems if these
systems are accompanied by an inclined binary companion.
