Time series analysis based study of a mass-spring-like oscillation and detachment of a metal pendant droplet

•Oscillating metal pendant droplet detachment was studied using time series analysis.•A t–f map of the pendant droplet vertical displacement time series was calculated.•Based on the t–f map, the pendant droplet was described as a mass-spring system.•The t–f map showed the resonant nature of the pendant droplet detachment.•The detached droplet diameter was predicted by an algebraic formula.

The subject of this study is the vertical mass-spring-like oscillation of a pendant droplet and its resonant detachment, which was experimentally observed in the process of laser droplet generation from a metal wire. The process was characterized by various time series, which were generated from a sequence of infrared intensity images of the process. Following a visual inspection of pendant droplet images and an analysis of a wavelet based time-frequency map of the droplet’s vertical displacement time series, the pendant droplet’s oscillation is described by a time-variable mass-spring system. Based on the characteristics of the time-frequency map, the resonant nature of the pendant droplet detachment was demonstrated. Additionally, an algebraic expression was formulated, which can be used to predict the detached droplet’s diameter as a function of the laser pulse frequency.