  The geometric approach to study the dynamics of U(1)-invariant membranes is
developed. The approach reveals an important role of the Abel nonlinear
differential equation of the first type with variable coefficients depending on
time and one of the membrane extendedness parameters. The general solution of
the Abel equation is constructed. Exact solutions of the whole system of
membrane equations in the D=5 Minkowski space-time are found and classified. It
is shown that if the radial component of the membrane world vector is only time
dependent then the dynamics is described by the pendulum equation.
