  Large-amplitude longitudinal oscillations (LALOs) in prominences are
spectacular manifestations of the solar activity. In such events nearby
energetic disturbances induce periodic motions on filaments with displacements
comparable to the size of the filaments themselves and with velocities larger
than 20 km/s. The pendulum model, in which the gravity projected along a rigid
magnetic field is the restoring force, was proposed to explain these events.
However, it can be objected that in a realistic situation where the magnetic
field reacts to the mass motion of the heavy prominence, the simplified
pendulum model could be no longer valid. We have performed non-linear
time-dependent numerical simulations of LALOs considering a dipped magnetic
field line structure. In this work we demonstrate that for even relatively weak
magnetic fields the pendulum model works very well. We therefore validate the
pendulum model and show its robustness, with important implications for
prominence seismology purposes. With this model it is possible to infer the
geometry of the dipped field lines that support the prominence.
