Design and experimental analysis of broadband energy harvesting from vortex-induced vibrations L.B. Zhang a , A. Abdelkefi b , H.L. Dai a,n , R. Naseer b , L. Wang a a Department of Mechanics, Huazhong University of Science and Technology, Wuhan 430074, China b Department of Mechanical and Aerospace Engineering, New Mexico State University, Las Cruces, NM 88003, USA article info Article history: Received 6 March 2017 Received in revised form 13 July 2017 Accepted 15 July 2017 Handling Editor: L.G. Tham Keywords: Vortex-induced vibration Energy harvesting Synchronization Softening behavior abstract In this paper, an operable strategy to enhance the output power of piezoelectric energy harvesting from vortex-induced vibration (VIV) using nonlinear magnetic forces is pro- posed for the first time. Two introduced small magnets with a repulsive force are, re- spectively, attached on a lower support and the bottom of a circular cylinder which is subjected to a uniform wind speed. Experiments show that the natural frequency of the VIV-based energy harvester is significantly changed by varying the relative position of the two magnets and hence the synchronization region is shifted. It is observed that the proposed energy harvester displays a softening behavior due to the impact of nonlinear magnetic forces, which greatly increases the performance of the VIV-based energy har- vesting system, showing a wider synchronization region and a higher level of the har- vested power by 138% and 29%, respectively, compared to the classical configuration. This proposed design can provide the groundwork to promote the output power of conven- tional VIV-based piezoelectric generators, further enabling to realize self-powered sys- tems. & 2017 Elsevier Ltd All rights reserved. 1. Introduction In recent years, harnessing kinetic energy from ambient vibrations to generate electricity has attracted considerable attention due to its potential applications in operating portable, wearable, and implantable microelectronic devices [1–3]. For example, based on flow-induced vibrations or base excitations, significant effort has been devoted to create realization about a renewable and sustainable energy harvester using one of the transduction mechanisms, such as piezoelectric [4–8], electromagnetic [9,10], and electrostatic [11]. Among all, the piezoelectricity is one of the most attractive transfer me- chanisms in mechanical energy conversion [12–14]. There are several aeroelastic phenomena that give rise to dynamic responses of the piezoelectric material structures subjected to wind loading, including galloping [15–18], vortex-induced vibration (VIV) [19–23], and flutter [24]. Among them, VIV-based energy harvesting has received increasing concerns due to its unique features of self-excited and self- restricted oscillations in the lock-in (synchronization) region as the vortex shedding frequency is close to one of the natural frequencies of the structure [25]. The concept of VIV-based energy converter was earlier proposed by Bernitsas et al. [26], who designed the device of vortex-induced vibration aquatic clean energy (VIVACE) which consists of a cylinder submerged Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jsvi Journal of Sound and Vibration http://dx.doi.org/10.1016/j.jsv.2017.07.029 0022-460X/& 2017 Elsevier Ltd All rights reserved. n Corresponding author. E-mail address: daihulianglx@hust.edu.cn (H.L. Dai). Journal of Sound and Vibration 408 (2017) 210–219