Published online by Cambridge University Press: 12 April 2016
The hydrodynamical modeling of steady double-mode (DM) pulsations has been a long-standing quest. Recent improvements in turbulent-convective pulsation codes provide a natural way to calculate nonlinear DM oscillations. The eddy viscosity plays a crucial role in these models. We present models both for RRd and beat Cepheid variables and for different chemical compositions. Simple nonresonant amplitude equations capture the DM phenomenon, giving an overview of modal selection on the HR diagram.