Hexagon Formation as a Compromise Between Squares and Stripes in Vertically Vibrated Granular Layers

We propose a spatially continuous and temporally discrete model for pattern formation in vertically vibrated granular layers. The grain transfer and the grain mobility transitions are introduced qualitatively, but explicitly. This model reproduces experimentally observed f/2 patterns, including squares in high-mobility conditions and stripes in low-mobility conditions. Hexagons are obtained when a high-mobility condition and a low-mobility condition are alternately applied. We discuss this hexagon formation in connection with the formation of squares and stripes. In addition to the experimentally observed localized oscillon structures, this model also exhibits localized hexagonal structures. These localized hexagonal structures grow by nucleating oscillons of equal phase.