Dynamics of a piezoelectric energy harvester in a simulated rain environment

Abstract

Rain impact energy harvesting has proven to be a feasible and potent source of alternative energy. This paper presents the development of a dynamical model for rain impact energy harvester using a piezoelectric beam in simulated rain environment. Most of the conducted works in literature were based on single droplet impact with fixed height and drop position. The main contribution of this paper is to extend the single droplet impact dynamical model by incorporating random drop sizes and drop positions. In this work, a rain simulator is used to generate artificial rain of different rain rates. Following our previous works, the water accumulation on the piezoelectric beam is modeled using added mass coefficient, and impact coefficient is integrated into the dynamical model to describe the post-impact dynamics of the droplet impact. The stochastic nature of the artificial rain is described using rain rate and drop size distribution. Two random number generators are integrated into the model, which are lognormally and uniformly distributed, to generate random numbers for droplet diameter and drop position respectively. The accuracy of the theoretical model is validated experimentally by considering four different rain rates.

Development of a Novel Piezoelectric Harvester Excited by Raindrops

“…The damping ratio of the system (ζ) was calculated with the logarithmic decrement method [20], which is based on the assumption of a linear viscous damping. This assumption usually is well verified by a standard harvester in open-circuit condition, but may be less sound for a raindrop harvester due to the motion of water inside the spoon [14]. Actually, the values of ζ calculated using the first part of the signal (t < 0.3 s), which are characterized by the largest amplitudes, are significantly larger than the values obtained, considering the rest of the signal.…”

“…A raindrop harvester is a dynamic system excited by a series of impacts. Experimental results obtained with actual rain [13] and simulated rain [14] show that the rain drops generate series of well-separated force impulses on the harvester. Therefore, the study of the response of a harvester to a single raindrop is meaningful.…”

“…Conversely, the presence of a water layer changes the impact dynamics, since the water layer accumulated on the harvester makes the impact surface softer [16]. The mass of water that accumulates on the surface of the harvester adds to the mass of the harvester itself and lowers the natural frequency of the system [14]. The water that accumulates on the harvester surface and that vibrates with the harvester increases the damping of the dynamic system [16].…”

Dynamic Response of PVDF Cantilever Due to Droplet Impact Using an Electromechanical Model

“…Here, we express the reaction force as a ratio of the impact force, an empirical expression of F reaction is written in Equation (20) where D* (=2.3 mm) is a reference droplet diameter. Therefore, the mechanical equation of motion in modal coordinates for SH cantilever beam becomes Equation (21).…”

“…Therefore, the PVDF is being increasingly used and many available commercial PVDF sensors also provide convenience for conducting impact tests. However, only a prototype of energy harvesters made by a PZT bimorph cantilever was developed and tested in both simulated and actual rain conditions [ 21 , 22 ]. For PVDF harvesters, the electromechanical behaviors as well its superiority to PZT harvesters still need to be further explored before being put into service.…”