Competition between subharmonically generated equilateral triangles and regular hexagons is observed in the Faraday experiment with viscous fluids subjected to a sinusoidal forcing. For kinematic viscosities around 17 ${\mathrm{cm}}^2$/s, all spatially regular patterns—stripes, squares, hexagons, and triangles can be parametrically excited in the same fluid depending on the forcing amplitude and frequency. Close to this value of viscosity, hexagonal and square patterns coexist showing a bicritical point.

• Received 27 June 1994

DOI:https://doi.org/10.1103/PhysRevE.52.R4606