  Bars in spiral galaxies can weaken through gas inflow towards the center, and
angular momentum transfer. Several bar episodes can follow one another in the
life of the galaxy, if sufficient gas is accreted from the intergalactic medium
to revive young disks.
  Pattern speeds of the successive bars are different, due to mass
concentration, or increased velocity dispersion of the remaining stellar
component. In the same time, the spiral galaxy evolves in morphological type.
Numerical simulations are presented, trying to correlate type and bar pattern
speeds.
