  We propose a mechanism for the excitation of large-scale quasi-periodic
fast-propagating magnetoacoustic (QFP) waves observed on both sides of the
coronal mass ejection (CME). Through a series of numerical experiments, we
successfully simulated the quasi-static evolution of the equilibrium locations
of the magnetic flux rope in response to the change of the background magnetic
field, as well as the consequent loss of the equilibrium that eventually gives
rise to the eruption. During the eruption, we identified QFP waves propagating
radially outwards the flux rope, and tracing their origin reveals that they
result from the disturbance within the flux rope. Acting as an imperfect
waveguide, the flux rope allows the internal disturbance to escape to the
outside successively via its surface, invoking the observed QFP waves.
Furthermore, we synthesized the images of QFP waves on the basis of the data
given by our simulations, and found the consistence with observations. This
indicates that the leakage of the disturbance outside the flux rope could be a
reasonable mechanism of QFP waves.
