  Interactions between an internal flow and wall deformation occur in many
biological systems. Such interactions can involve a complex and rich dynamical
behavior and a number of peculiarities which depend on the flow parameter
range. The aim of this paper is to present a variant (obtained via a weighted
residual approach) of the averaged one-dimensional model derived by Stewart et
al. "Local and global instabilities of flow in a flexible-walled channel," Eur.
J. Mech. B/Fluids 28, 541-557 (2009)]. The asymptotic expansions for small
Reynolds numbers of these two models, compared to the exact solution obtained
from the lubrication approach, reveal some quantitative difference, even at
higher Reynolds numbers. Qualitatively, the two models give similar results at
least at a linear level. It is shown that for relatively low membrane tension
(T), there are distinct regions in the (T,R) parameter space where steady
bifurcating flows may occur. These flows can also be observed at vanishingly
small Reynolds numbers combined with relatively high membrane tension. At
sufficiently high T and R, the bifurcating flow is rather time periodic. A
weakly nonlinear analysis is then performed in both cases leading to the
derivation of evolution equations for the amplitudes of the bifurcating flows.
The amplitude equations show that the saddle node bifurcation has a
transcritical character while the Hopf bifurcation is either subcritical or
supercritical, depending both on the mode number and membrane tension.
