Amin Bibo

A scalable concept for micropower generation using flow-induced self-excited oscillations

Inspired by music-playing harmonicas that create tones via oscillations of reeds when subjected to air blow, this paper entails a concept for microwind power generation using flow-induced self-excited oscillations of a piezoelectric beam embedded within a cavity. Specifically, when the volumetric flow rate of air past the beam exceeds a certain threshold, the energy pumped into the structure via nonlinear pressure forces offsets the system’s intrinsic damping setting the beam into self-sustained limit-cycle oscillations. The vibratory energy is then converted into electricity through principles of piezoelectricity. Experimental and theoretical results are presented demonstrating the feasibility of the proposed concept.

Investigation of concurrent energy harvesting from ambient vibrations and wind using a single piezoelectric generator

In this letter, a single vibratory energy harvester integrated with an airfoil is proposed to concurrently harness energy from ambient vibrations and wind. In terms of its transduction capabilities and power density, the integrated device is shown to have a superior performance under the combined loading when compared to utilizing two separate devices to harvest energy independently from the two available energy sources. Even below its flutter speed, the proposed device was able to provide 2.5 times the power obtained using two separate harvesters.

Modeling and Characterization of a Piezoelectric Energy Harvester Under Combined Aerodynamic and Base Excitations

This paper develops and validates an aero-electromechanical model which captures the nonlinear response behavior of a piezoelectric cantilever-type energy harvester under combined galloping and base excitations. The harvester consists of a thin piezoelectric cantilever beam clamped at one end and rigidly attached to a bluff body at the other end. In addition to the vibratory base excitations, the beam is also subjected to aerodynamic forces resulting from the separation of the incoming airflow on both sides of the bluff body which gives rise to limit-cycle oscillations when the airflow velocity exceeds a critical value. A nonlinear electromechanical distributed-parameter model of the harvester under the combined excitations is derived using the energy approach and by adopting the nonlinear Euler–Bernoulli beam theory, linear constitutive relations for the piezoelectric transduction, and the quasi-steady assumption for the aerodynamic loading. The resulting partial differential equations of motion are discretized and a reduced-order model is obtained. The mathematical model is validated by conducting a series of experiments at different wind speeds and base excitation amplitudes for excitation frequencies around the primary resonance of the harvester. Results from the model and experiment are presented to characterize the response behavior under the combined loading.

On the optimal performance and universal design curves of galloping energy harvesters

In this letter, we establish a universal relationship between a dimensionless version of the output power and the flow speed for galloping energy harvesters. This relationship yields a unique curve, which is only sensitive to the aerodynamic properties of the bluff body, but is, otherwise, invariant under any changes in the mechanical and electrical design parameters of the harvester. The curve permits a simple and direct comparative analysis of the energy harvesting performance of different bluff bodies so long that the other design parameters are kept constant. The universal curve is also shown to facilitate the optimization analysis, thereby providing significant insight into the optimal performance conditions.

Electromechanical Modeling and Normal Form Analysis of an Aeroelastic Micro-Power Generator

Combining theories in continuous-systems vibrations, piezoelectricity, and fluid dynamics, we develop and experimentally validate an analytical electromechanical model to predict the response behavior of a self-excited micro-power generator. Similar to music-playing harmonica that create tones via oscillations of reeds when subjected to air blow, the proposed device uses flow-induced self-excited oscillations of a piezoelectric beam embedded within a cavity to generate electric power. To obtain the desired model, we adopt the nonlinear Euler-Bernoulli beam’s theory and linear constitutive relationships. We use Hamilton’s principle in conjunction with electric circuits theory and the inextensibility condition to derive the partial differential equation that captures the transversal dynamics of the beam and the ordinary differential equation governing the dynamics of the harvesting circuit. Using the steady Bernoulli equation and the continuity equation, we further relate the exciting pressure at the surface of the beam to the beam’s deflection, and the inflow rate of air. Subsequently, we employ a Galerkin’s descritization to reduce the order of the model and show that a single-mode reduced-order model of the infinite-dimensional system is sufficient to predict the response behavior. Using the method of multiple scales, we develop an approximate analytical solution of the resulting reduced-order model near the stability boundary and study the normal form of the resulting bifurcation. We observe that a Hopf bifurcation of the supercritical nature is responsible for the onset of limit-cycle oscillations.

Exploiting a nonlinear restoring force to improve the performance of flow energy harvesters

This paper investigates employing a nonlinear restoring force to improve the performance of flow energy harvesters (FEHs). To that end, a galloping FEH possessing a quartic potential energy function of the form V=12μy2+14γy4 is considered. This potential function is used to model either a softening (μ > 0, γ   0, γ > 0), or bi-stable (μ   0) restoring force. A physics-based model of the harvester is obtained assuming piezoelectric transduction and a quasi-steady flow field. The model is validated against experimental data and used to obtain a closed-form solution of the response by employing a multiple scaling perturbation analysis using the Jacobi elliptic functions. The attained solution is subsequently used to investigate the influence of the nonlinearity on the performance of the harvester and to illustrate how to optimize the restoring force in order to maximize the output power for given design conditions and airflow parameters. Specifically, it is shown that for similar de...

An analytical framework for the design and comparative analysis of galloping energy harvesters under quasi-steady aerodynamics

This paper presents a generalized formulation, analysis, and optimization of energy harvesters subjected to galloping and base excitations. The harvester consists of a cantilever beam with a bluff body attached at the free end. A nondimensional lumped-parameter model which accounts for the combined loading and different electro-mechanical transduction mechanisms is presented. The aerodynamic loading is modeled using the quasi-steady assumption with polynomial approximation. A nonlinear analysis is carried out and an approximate analytical solution is obtained. A dimensional analysis is performed to identify the important parameters that affect the systems response. The analysis of the response is divided into two parts. The first treats a harvester subjected to only galloping excitations. It is shown that, for a given shape of the bluff body and under quasi-steady flow conditions, the harvesters dimensionless response can be described by a single universal curve irrespective to the geometric, mechanical, and electrical design parameters of the harvester. In the second part, a harvester under concurrent galloping and base excitations is analyzed. It is shown that, the total output power depends on three dimensionless loading parameters; wind speed, base excitation amplitude, and excitation frequency. The response curves of the harvester are generated in terms of the loading parameters. These curves can serve as a complete design guide for scaling and optimizing the performance of galloping-based harvesters.

Performance analysis of a harmonica-type aeroelastic micropower generator

This article investigates the influence of the design parameters on the performance of an aeroelastic micropower generator with the goal of minimizing its cut-in wind speed and maximizing its output power. The generator, which mimics the basic physics of music-playing harmonicas, transforms wind energy into electricity via the self-excited oscillations of a piezoelectric reed embedded within a cavity. Previously, the authors have presented and validated an analytical aeroelectromechanical model describing the response behavior of the generator. By utilizing the proposed model, this study implements a stability analysis and numerical optimization algorithms to delineate the influence of the design parameters on the device’s response. The effect of the electric load, chamber volume, and aperture size on the cut-in wind speed is investigated. The results illustrate that the cut-in wind speed can be reduced significantly if the device is designed with an optimal chamber volume, which is shown to be inversely proportional to the square of the beam’s first modal frequency. Minimizing the aperture width is also shown to significantly reduce the cut-in speed. However, due to the reduced strain rate in the piezoelectric layer, it is observed that minimizing the wind speed does not always yield an increase in the output power. As such, a numerical investigation of the influence of the design parameters on the output power is utilized to generate design charts that assist in the selection of the optimal parameters for a known average wind speed. Several qualitative verifications of the theoretical trends are also presented through an experimental case study.

Sensitivity Enhancement of Cantilever-Based Sensors Using Feedback Delays

This paper entails a novel sensitivity-enhancement mechanism for cantilever-based sensors. The enhancement scheme is based on exciting the sensor at the clamped end using a delayed-feedback signal obtained by measuring the tip deflection of the sensor. The gain and delay of the feedback signal are chosen such that the base excitations set the beam into stable limit-cycle oscillations as a result of a supercritical Hopf bifurcation of the trivial fixed points. The amplitude of these limit-cycles is shown to be ultrasensitive to parameter variations and, hence, can be utilized for the detection of minute changes in the resonant frequency of the sensor. The first part of the manuscript delves into the theoretical understanding of the proposed mechanism and the operation concept. Using the method of multiple scales, an approximate analytical solution for the steady-state limit-cycle amplitude near the stability boundaries is obtained. This solution is then utilized to provide a comprehensive understanding of the effect of small frequency variations on the limit-cycle amplitude and the sensitivity of these limit-cycles to different design parameters. Once a deep theoretical understanding is established, the manuscript provides an experimental study to investigate the proposed concept. Experimental results demonstrate orders of magnitude sensitivity enhancement over the traditional frequency-shift method.

Flow Energy Harvesters With a Nonlinear Restoring Force

This ppppaper examines the performance of a galloping energy harvester possessing a nonlinear restoring force. To achieve this goal, a flow energy harvester consisting of a piezoelectric cantilever beam augmented with a square-sectioned bluff body at the free end is considered. Two magnets located near the tip of the bluff body are used to introduce the nonlinearity which strength and nature can be altered by changing the distance between the magnets. A lumped-parameter aero-electromechanical model adopting the quasi-steady assumption for aerodynamic loading is presented and utilized to numerically simulate the harvester’s response. Wind tunnel tests are also performed to validate the numerical simulations by conducting upward and downward wind velocity sweeps. Results comparing the relative performance of several harvesters with potential functions of different shapes demonstrate that a mono-stable potential function with a hardening restoring force can outperform all other configurations.Copyright