  Warped H I gas layers in the outer regions of spiral galaxies usually display
a noticeably twisted structure. This structure almost certainly arises
primarily as a result of differential precession in the H I disk as it settles
toward a preferred orientation in an underlying dark halo potential well that
is not spherically symmetric. In an attempt to better understand the structure
and evolution of these twisted, warped disk structures, we have adopted the
"twist-equation" formalism originally developed by Petterson (1977) to study
accretion onto compact objects. Utilizing more recent treatments of this
formalism, we have generalized the twist-equation to allow for the treatment of
non-Keplerian disks and from it have derived a steady-state structure of
twisted disks that develops from free precession in a nonspherical, logarithmic
halo potential. We have used this steady-state solution to produce H I maps of
five galaxies (M83, NGC 300, NGC 2841, NGC 5033, NGC5055), which match the
general features of the observed maps of these galaxies quite well. In
addition, the model provides an avenue through which the kinematical viscosity
of the H I disk and the quadrupole distortion of the dark halo in each galaxy
can be quantified. This generalized equation can also be used to examine the
time-evolutionary behavior of warped galaxy disks.
