The kinematics of wheat struck by a wind gust

A nonlinear model of the kinematics of a wheat stalk struck by a wind gust is developed. Individual stalks were excited from each of many directions a nd observed by videophotography The underdamped flexural response involved anisotropic circling motion that can be reproduced by a nonlinear system of ODEs. In the model, the horizontal path traveled by the grain mass is desc ribed in principal coordinates X-I and X-II. The four required constants ar e stiffnesses k(I)<k(II) in these directions, linear viscous damping <zeta> . and coupling strength beta related to a torque imposed by wind drag. This stem torque can cause nonlinear coupling if both XI and XII are excited an d if k(i) not equal k(II), such that damping can vary by 30 percent over ea ch cycle. The directionality of the single stalk may promote interplant col lision, which could have important integrated effects on crop behavior at l arger size scales.