Dynamics of a droplet-impact-driven cantilever making contact with the ground

Abstract

To understand the mechanical principles of raindrop-based energy-harvesting systems, we experimentally investigate the dynamics of a cantilever, which deforms by a falling droplet and sequentially contacts the ground below. A new dimensionless parameter defined as the ratio of impact force to bending force is used to characterize the droplet–cantilever interaction. The bending stiffness of the cantilever, the impact velocity and size of the droplet, and the gap distance between the cantilever and the ground are varied to find how the transition boundary between contact and non-contact modes is affected by the dimensionless force ratio. The rebound amplitude, contact duration, and contact area of the cantilever are then analyzed. After the contact with the ground occurs, the rebound amplitude monotonically increases with the dimensionless force ratio. The contact duration of the cantilever with the ground is in a linear relation with the maximum contact area. We also examine the effects of the impact location and surface tension of the droplet on the contact responses. While the contact duration and area are changed notably by the impact location, the dynamics of the cantilever show minor variations with respect to the surface tension, despite a dramatic variation in droplet spreading behavior.