QUASI-PERIODIC PATTERNS IN RAYLEIGH-BENARD CONVECTION UNDER GRAVITY MODULATION

We investigate nonlinear three-dimensional convection under gravity mo dulation. Depending upon modulation frequency and amplitude, unstable modes in harmonic or subharmonic temporal resonance with the mechanica l drive can be observed. We focus on a situation where both modes comp ete. In non-Boussinesq fluids the dominating interaction mechanism is a nonlinear triad wave-vector resonance. We construct a minimum Galerk in model which describes the competition between several regular conve ction patterns. Our results indicate that squares or quasiperiodic pat terns with a 12-fold rotational axis are the preferred convection stru ctures.