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This paper proposes a softening nonlinear aeroelastic galloping energy harvester for enhanced energy harvesting from concurrent wind flow and base vibration. Traditional linear aeroelastic energy harvesters have poor performance with quasi-periodic oscillations when the base vibration frequency deviates from the aeroelastic frequency. The softening nonlinearity in the proposed harvester alters the self-excited galloping frequency and simultaneously extends the large-amplitude base-excited oscillation to a wider frequency range, achieving frequency synchronization over a remarkably broadened bandwidth with periodic oscillations for efficient energy conversion from dual sources. A fully coupled aero-electro-mechanical model is built and validated with measurements on a devised prototype. At a wind speed of 5.5 m/s and base acceleration of 0.1 g, the proposed harvester improves the performance by widening the effective bandwidth by 300% compared to the linear counterpart without sacrificing the voltage level. The influences of nonlinearity configuration, excitation magnitude, and electromechanical coupling strength on the mechanical and electrical behavior are examined. The results of this paper form a baseline for future efficiency enhancement of energy harvesting from concurrent wind and base vibration utilizing monostable stiffness nonlinearities.

This paper investigates a dynamic model and behavior of a novel double-beam piezo–magneto–elastic nonlinear wind energy harvester (DBPME-WEH). The DBPME-WEH is a double-beam structure, which contains the magnet-induced bistable nonlinearity to enhance the performance of the galloping-based vibration energy harvesting. The corresponding governing equations of motion are formulated, and the numerical results based on the equations are validated by a series of the wind tunnel experiments. Both the numerical and experimental results show that the DBPME-WEH outperforms the linear double-beam piezoelectric wind energy harvester, significantly reducing the cut-in speed. To understand the nonlinear dynamic behavior of the proposed energy harvester, this study performs the numerical investigations of the time-domain responses, phase portraits and frequency spectrums of the DBPME-WEH under selected wind speeds. The intra-well, chaotic and inter-well oscillations are discovered with respect to low, medium and high wind speeds intervals, respectively. The parametric study is performed to uncover the influences of the beams stiffness ratio, effective mass ratio and the width of the bluff body that help developing the insights of the effective design of the DBPME-WEH.

While there has been a surge of study on nonlinear aeroelastic energy harvesting structures for enhanced wind power extraction, there is a gap in the literature on the integration of advanced power conditioning circuits with these mechanically sophisticated nonlinear structures. This article presents an investigation on the influence of different voltage processing interface circuits on the power generation performance in nonlinear galloping energy harvesting. Cubic hardening, cubic softening, and bistable configurations are studied. Their mechanical and electrical responses associated with the simple ac, standard dc, and synchronous charge extraction (SCE) circuits analyzed and compared. Results show that with the ac and standard dc circuits, the bistable and cubic hardening configurations are superior to the cubic softening configuration, generating comparably high power outputs with beneficially small displacements. The SCE circuit significantly boosts the power generation of the two monostable (cubic hardening and softening) harvester designs, but degrades the performance of the bistable design by trapping the oscillation within a single potential well over a large wind speed range. The findings form a baseline for future enhancement in the design of nonlinear aeroelastic wind power generators.

Studies regarding concurrent wind-flow and base-motion energy harvesting have drawn increasing attention in recent years. However, for conventional wind energy harvesters under such dual excitations, the base-excited inertial vibration and flow-induced aeroelastic vibration supplement with each other only within a narrow range of frequency near the resonance. Within this range, aeroelastic vibration frequency is locked into the base vibration frequency where the two sources are concurrently contributing to power generation; while the concurrent feature is lost outside this range. Internal resonance in multimodal systems has been utilized in recent years for efficiency improvement in pure base vibration energy harvesters. The merit comes from the fact that energy can be pumped from other modes to the power generation bandwidth, broadening the bandwidth toward both lower and higher frequency regions. In this paper, a broadband galloping-based aeroelastic energy harvester with internal resonance is proposed for the purpose of efficiency enhancement in concurrent wind and base vibration energy harvesting. Two-to-one internal resonance is aroused by arranging two sets of magnets symmetrically at the beam connection. Numerical solutions are calculated for the fully coupled aero-electro-mechanical model. A significantly widened lock-in bandwidth with multiple power peaks is achieved for effective concurrent wind and vibration energy harvesting.

This paper presents an analysis of galloping-based wind energy harvesters with piezoelectric and electromagnetic transductions. The lumped parameter models of the galloping-based piezoelectric energy harvester (GPEH) and galloping-based electromagnetic energy harvester (GEMEH) are developed and the approximate analytical solutions of the equations are derived using the harmonic balance method (HBM). The accuracy of the approximate analytical solutions is validated by the numerical solutions. A parametric study is then conducted based on the validated models and solutions to understand the effects of the dimensionless load resistance, r, and electromechanical coupling strength (EMCS) on various quantities indicating the performance of the harvesters, including the dimensionless oscillating frequency, cut-in wind speed, displacement, and average power output. The results show that both r and EMCS can affect the dimensionless oscillating frequencies of the GPEH and GEMEH in a narrow frequency range around the natural frequency. A significant decrease in the displacement around r = 1 for GEPH and at a low r for GEMEH indicates the damping effect induced by the increase in EMCS. There are two optimal r to achieve the maximal power output for GPEH given strong EMCS while there is only one optimal r for GEMEH. Both GPEH and GEMEH show similar characteristics in that the optimal power outputs can reach saturation with an increase of the EMCS. The findings from the parametric study provide useful guidelines for the design of galloping-based energy harvesters with different energy conversion mechanisms.

© 2017 Liya Zhao and Yaowen Yang. The concept of harvesting ambient energy as an alternative power supply for electronic systems like remote sensors to avoid replacement of depleted batteries has been enthusiastically investigated over the past few years. Wind energy is a potential power source which is ubiquitous in both indoor and outdoor environments. The increasing research interests have resulted in numerous techniques on small-scale wind energy harvesting, and a rigorous and quantitative comparison is necessary to provide the academic community a guideline. This paper reviews the recent advances on various wind power harvesting techniques ranging between cm-scaled wind turbines and windmills, harvesters based on aeroelasticities, and those based on turbulence and other types of working principles, mainly from a quantitative perspective. The merits, weaknesses, and applicability of different prototypes are discussed in detail. Also, efficiency enhancing methods are summarized from two aspects, that is, structural modification aspect and interface circuit improvement aspect. Studies on integrating wind energy harvesters with wireless sensors for potential practical uses are also reviewed. The purpose of this paper is to provide useful guidance to researchers from various disciplines interested in small-scale wind energy harvesting and help them build a quantitative understanding of this technique.

© 2019 Copyright SPIE. Concurrent energy harvesting by simultaneously harvesting wind and base vibration energy has received very little attention until recently. Yet a major problem with a traditional wind energy harvester under concurrent loadings is the dramatically reduced efficiency when the base vibration frequency deviates from the resonance. This paper investigates a novel design to enhance concurrent energy harvesting from concurrent base vibrations and wind flows. A piecewiselinear aeroelastic energy harvester is integrated with a stopper which can also work as a complementary generator. In order to fast and accurately characterize the response of the harvester, exact analytical solutions are derived based on the harmonic balance analysis and method of averaging. The interaction of the two coexisting excitation frequencies as well as the impact effects between the aeroelastic energy harvester and the stopper are fully considered. Closed-form expressions for both mechanical and electrical responses are presented and validated numerically. Results show that a greatly widened bandwidth is achieved with the proposed design where both aeroelastic and base vibratory energy are effectively harnessed. The analytical solutions are essential to fully understand the characteristics of this new kind of broadband concurrent energy harvester, and serve as a guideline for efficient performance evaluation and parameter optimization.

© 2018 IEEE. In this paper, using a high frequency mechanical stopper as a complementary energy harvester is proposed to improve the performance of energy harvesting from concurrent wind flows and base vibrations. Galloping aeroelasticity of a square-sectioned bluff body is employed to achieve limit-cycle structural oscillations. The analysis demonstrates that the bandwidth for effectively harnessing both aerodynamic and base vibratory energy is substantially widened, and simultaneously, the total power amplitude is significantly enhanced as compared to the original linear galloping energy harvester. It is concluded that the proposed system is viable solution to enhance energy conversion in situations where wind flows and base vibrations are coexisting.

This paper proposes a novel broadband energy harvester to concurrently harvest energy from base vibrations and wind flows by utilizing a mechanical stopper. A problem for a conventional wind energy harvester is that it can only effectively harness energy from two types of excitations around its resonance frequency. The proposed design consists of a D-shape-sectioned bluff body attached to a piezoelectric cantilever, and a mechanical stopper fixed at the bottom of the cantilever which introduces piecewise linearity through its impact with the bluff body. The quasi-periodic oscillations are converted to periodic vibration due to the introduction of the mechanical stopper, which forces the two excitation frequencies to lock into each other. Broadened bandwidth for effective concurrent energy harvesting is thus achieved, and at the same time, the beam deflection is slightly mitigated and fully utilized for power conversion. The experiment shows that with the stopper-bluff body distance of 19.5 mm, the output power from the proposed harvesting device increases steadily from 3.0 mW at 17.3 Hz to 3.8 mW at 19.1 Hz at a wind speed of 5.5 m/s and a base acceleration of 0.5 g. A guideline for the stopper configuration is also provided for performance enhancement of the broadband concurrent wind and vibration energy harvester.

There has been growing research interest in converting ambient energy in the environment to electricity in order to realize self-powered electronic systems such as wireless sensor networks. This paper targets wind energy as an alternate power source. While structural modification of a wind energy harvester contributes to the power enhancement, the electrical interfacing circuit is also vital for the system optimization. However, despite the enthusiastic investigation on interfacing circuit in the field of base vibration energy harvesting, it has been frequently ignored in wind energy harvesting researches. This paper evaluates and compares the performances of four electrical interfacing circuits in a galloping-based wind energy harvesting system, including the synchronous charge extraction (SCE) circuit, series and parallel synchronized switch harvesting on inductor (SSHI) circuits as well as the standard circuit. Based on the analysis, a guideline is proposed for circuit selection in different circumstances. It is concluded that the SCE circuit is suitable for weak coupling and higher wind speed conditions. The two SSHI circuits are recommended in both weak coupling and medium coupling conditions, especially when a low cut-in wind speed is desired. The series-SSHI circuit is suggested in high terminal load situation while the parallel-SSHI circuit is recommended in small terminal load condition. If strong coupling presents, the standard circuit is recommended considering its simplicity and equally good performance with that of the SSHI interfaces. In special, it is found that the behavior of the ranges of k e 2 for the SCE, S-SSHI and P-SSHI with enhanced power over the standard circuit is different from the case of base vibration energy harvesting.

Copyright © 2017 Techno-Press, Ltd. The interdisciplinary research area of small scale energy harvesting has attracted tremendous interests in the past decades, with a goal of ultimately realizing self-powered electronic systems. Among the various available ambient energy sources which can be converted into electricity, wind energy is a most promising and ubiquitous source in both outdoor and indoor environments. Significant research outcomes have been produced on small scale wind energy harvesting in the literature, mostly based on piezoelectric conversion. Especially, modeling methods of wind energy harvesting techniques plays a greatly important role in accurate performance evaluations as well as efficient parameter optimizations. The purpose of this paper is to present a guideline on the modeling methods of small-scale wind energy harvesters. The mechanisms and characteristics of different types of aeroelastic instabilities are presented first, including the vortex-induced vibration, galloping, flutter, wake galloping and turbulence-induced vibration. Next, the modeling methods are reviewed in detail, which are classified into three categories: the mathematical modeling method, the equivalent circuit modeling method, and the computational fluid dynamics (CFD) method. This paper aims to provide useful guidance to researchers from various disciplines when they want to develop and model a multi-way coupled wind piezoelectric energy harvester.

Galloping phenomenon has attracted extensive research attention for small-scale wind energy harvesting. In the reported literature, the dynamics and harvested power of a galloping-based energy harvesting system are usually evaluated with a resistive AC load; these characteristics might shift when a practical harvesting interface circuit is connected for extracting useful DC power. In the family of piezoelectric energy harvesting interface circuits, synchronized switching harvesting on inductor (SSHI) has demonstrated its advantage for enhancing the harvested power from existing base vibrations. This paper investigates the harvesting capability of a galloping-based wind energy harvester using SSHI interfaces, with a focus on comparing the performances of Series SSHI (S-SSHI) and Parallel SSHI (P-SSHI) with that of a standard DC interface, in terms of power at various wind speeds. The prototyped galloping-based piezoelectric energy harvester (GPEH) comprises a piezoelectric cantilever attached with a square-sectioned bluff body made of foam. Equivalent circuit model (ECM) of the GPEH is established and system-level circuit simulations with SSHI and standard interfaces are performed and validated with wind tunnel tests. The benefits of SSHI compared to standard circuit become more significant when the wind speed gets higher; while SSHI circuits lose the benefits at small wind speeds. In both experiment and simulation, the superiority of P-SSHI is confirmed while S-SSHI demands further investigation. The power output is increased by 43.75% with P-SSHI compared to the standard circuit at a wind speed of 6m/s.

Small-scale wind energy can be harvested for wireless sensing applications by exploiting the galloping phenomenon of a bluff body attached to a piezoelectric cantilever. Certain predictive model is required to understand the behavior of such a galloping-based piezoelectric energy harvester (GPEH). Conventional analytical and numerical models have simplified the interface circuit as a pure resistor. In practice, the energy generated by the harvester should be rectified before delivery to a real application. In such a case, the formulation of analytical or numerical model becomes cumbersome considering the complex coupling between the structure, fluid, piezoelectric transducer and practical interface circuit. This paper proposes an equivalent circuit representation approach to predict the performance of GPEHs, capable of incorporating various interface circuits. The mechanical parameters and piezoelectric coupling in the system are represented by standard electronic components and the aerodynamic force by a user-defined component (non-standard). The entire system is modeled in a circuit simulator for system-level simulation and evaluation. The proposed approach is verified by theoretical solution and experiment. Subsequent parametric study is performed to investigate the influence of standard AC and DC interfaces on the GPEH’s behavior, with a focus on the threshold of galloping, power output and induced electrical damping. Accepted version

Aeroelastic instabilities have been frequently exploited for energy harvesting purpose to power standalone electronic systems, such as wireless sensors. Meanwhile, various energy harvesting interface circuits, such as synchronized charge extraction (SCE) and synchronized switching harvesting on inductor (SSHI), have been widely pursued in the literature for efficiency enhancement of energy harvesting from existing base vibrations. These interfaces, however, have not been applied for aeroelastic energy harvesting. This paper investigates the feasibility of the SCE interface in galloping-based piezoelectric energy harvesting, with a focus on its benefit for performance improvement and influence on the galloping dynamics in different electromechanical coupling regimes. A galloping-based piezoelectric energy harvester (GPEH) is prototyped with an aluminum cantilever bonded with a piezoelectric sheet. Wind tunnel test is conducted with a simple electrical interface composed of a resistive load. Circuit simulation is performed with equivalent circuit representation of the GPEH system and confirmed by experimental results. Consequently, a self-powered SCE interface is implemented with the capability of self peak-detecting and switching. Circuit simulation for various electromechanical coupling cases shows that the harvested power with SCE interface for GPEH is independent of the electrical load, similar to that for a vibration-based piezoelectric energy harvester (VPEH). The SCE interface outperforms the standard interface if the electromechanical coupling is weak, and requires much less piezoelectric material to achieve the maximum power output. Moreover, influence of electromechanical coupling on the dynamics of GPEH with SCE is found sensitive to the wind speed. Published version

This letter presents a comparative study of different tip cross-sections for small scale wind energy harvesting based on galloping phenomenon. A prototype device is fabricated with a piezoelectric cantilever and a tip body with various cross-section profiles (square, rectangle, triangle, and D-shape) and tested in a wind tunnel. Experimental results demonstrate the superiority of the square-sectioned tip for the low cut-in wind speed of 2.5 m/s and the high peak power of 8.4 mW. An analytical model is established and verified by the experimental results. It is recommended that the square section should be used for small wind galloping energy harvesters. Published version

A galloping piezoelectric harvester for small wind energy harvesting usually consists of a cantilever beam clamped at one end and a tip body attached to its free end. The tip body has significant influence on the aeroelastic characteristic of the harvester thus the efficiency of energy harvesting. However, no systematic study on the tip body is available in the literature. This article focuses on the effect of tip body on the performance of the harvester. A prototype device is fabricated with different tip bodies having various cross sections, lengths, and masses. Wind tunnel tests are conducted to determine the influence of these parameters on the power generated. A peak output power of 8.4 mW is achieved at a wind velocity of 8 m/s for the harvester with a tip of square section. An analytical model integrating electromechanical and aerodynamic formulations is established, and the results agree well with the experiments. It is recommended that the tip of square section should be used for galloping energy harvesters.Copyright © 2012 by ASME

Wind energy is ubiquitous in both outdoor and indoor environments, yet small-scale energy harvesting aimed to harness power from wind with low speed (