Nonlinear Beat Cepheid Models
  The numerical hydrodynamic modelling of beat Cepheid behavior has been a longstanding quest in which purely radiative models have failed miserably. We find that beat pulsations occur naturally when turbulent convection is accounted for in our hydrodynamics codes.   The development of a relaxation code and of a Floquet stability analysis greatly facilitates the search for and analysis of beat Cepheid models.   The conditions for the occurrence of beat behavior can be understood easily and at a fundamental level with the help of amplitude equations. Here a discriminant D arises whose sign decides whether single mode or double mode pulsations can occur in a model, and this D depends only on the values of the nonlinear coupling coefficients between the fundamental and the first overtone modes. For radiative models D is always found to be negative, but with sufficiently strong turbulent convection its sign reverses. 
Z. Kollath, J.P. Beaulieu, J.R. Buchler, P. Yecko