An extended body, free floating near one of the horizontal boundaries in a convective cell heated from below and cooled from above, with a suitable set of control parameters, provides the convective pendulum mode in which the body performs regular oscillatory movements from one sidewall to the other. In this paper we consider numerically, in the simplest two-dimensional formulation, a convective cell at moderate Rayleigh numbers $\mathrm{Ra}\approx (5\times {10}^5)\text{–}(5\times {10}^6)$ with two bodies (plates) floating at different depths. Two convective oscillators in one cell are subject to a complex mutual influence determined by the geometry of the cavity, the size and the depth of immersion of the plates, and the intensity of heating, leading to a wide variety of observed modes. The dynamics of large plates (of the order of half the horizontal size of the cell or more) strongly depends on the depth of immersion and includes a convective pendulum mode with regular antiphase oscillations, irregular fluctuations, full stops, and synchronized periodic movements. The dynamics of two plates of relatively small size is fundamentally different and unexpected. The complex interaction between the small plates leads to modes with a pronounced intermittent character, when intervals of quasiperiodic movements of both plates are replaced by low-amplitude oscillations against the background of random wandering throughout the cell. During full-amplitude oscillations, the plates move quasiperiodically but with a random phase shift. The very specific behavior observed during random walks, in which the plates perform small-scale chaotic oscillations, without breaking away from each other, as if they are on a flexible bundle.

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• Plumes & thermals
• Rayleigh-Bénard convection
• Thermal convection
• Turbulent convection
• Direct numerical simulations
• Immersed boundary methods