We generalize the Layzer's bubble model to the cases of two-dimensional and three-dimensional analytical models of an arbitrary interface Atwood number and obtain self-consistent equations. The generalized model provides a continuous bubble evolution from the earlier exponential growth to the nonlinear regime. The asymptotic bubble velocities are obtained for the Rayleigh-Taylor(RT) and Richtmyer-Meshkov(RM) instabilities. We also report on the two-dimensional and the three-dimensional analytical expressions for the evolution of the RT bubble velocity.