Fluid-solid-electric lock-in of energy-harvesting piezoelectric flags

The spontaneous flapping of a flag in a steady flow can be used to power an output circuit using piezoelectric elements positioned at its surface. Here, we study numerically the effect of inductive circuits on the dynamics of this fluid-solid-electric system and on its energy harvesting efficiency. In particular, a destabilization of the system is identified leading to energy harvesting at lower flow velocities. Also, a frequency lock-in between the flag and the circuit is shown to significantly enhance the system's harvesting efficiency. These results suggest promising efficiency enhancements of such flow energy harvesters through the output circuit optimization.Comment: 8 pages, 8 figures, to appear in Physical Review Applie

Direct Scaling of Measure on Vortex Shedding through a Flapping Flag Device in the Open Channel around a Cylinder at Re ∼ 10^3: Taylor’s Law Approach.

none8noThe problem of vortex shedding, which occurs when an obstacle is placed in a regular flow, is governed by Reynolds and Strouhal numbers, known by dimensional analysis. The present work aims to propose a thin films-based device, consisting of an elastic piezoelectric flapping flag clamped at one end, in order to determine the frequency of vortex shedding downstream an obstacle for a flow field at Reynolds number Re∼103 in the open channel. For these values, Strouhal number obtained in such way is in accordance with the results known in literature. Moreover, the development of the voltage over time, generated by the flapping flag under the load due to flow field, shows a highly fluctuating behavior and satisfies Taylor’s law, observed in several complex systems. This provided useful information about the flow field through the constitutive law of the device.openSamuele De Bartolo, Massimo De Vittorio, Antonio Francone, Francesco Guido, Elisa Leone, Vincenzo Mariano Mastronardi, Andrea Notaro, Giuseppe Roberto TomasicchioDE BARTOLO, Samuele; DE VITTORIO, Massimo; Francone, Antonio; Guido, Francesco; Leone, Elisa; Mariano Mastronardi, Vincenzo; Notaro, Andrea; Tomasicchio, Giusepp

Fluttering energy harvesters in the wind: A review

The growing area of harvesting energy by aerodynamically induced flutter in a fluid stream is reviewed. Numerous approaches were found to understand, demonstrate and [sometimes] optimise harvester performance based on Movement-Induced or Extraneously Induced Excitation. Almost all research was conducted in smooth, unidirectional flow domains; either experimental or computational. The power outputs were found to be very low when compared to conventional wind turbines, but potential advantages could be lower noise levels. A consideration of the likely outdoor environment for fluttering harvesters revealed that the flow would be highly turbulent and having a mean flow angle in the horizontal plane that could approach a harvester from any direction. Whilst some multiple harvester systems in smooth, well-aligned flow found enhanced efficiency (due to beneficial wake interaction) this would require an invariant flow approach angle. It was concluded that further work needs to be performed to find a universally accepted metric for efficiency and to understand the effects of the realities of the outdoors, including the highly variable and turbulent flow conditions likely to be experienced

Review of flexible energy harvesting for bioengineering in alignment with SDG

To cater to the extensive body movements and deformations necessitated by biomedical equipment flexible piezoelectrics emerge as a promising solution for energy harvesting. This review research delves into the potential of Flexible Piezoelectric Materials (FPM) as a sustainable solution for clean and affordable energy, aligning with the United Nations' Sustainable Development Goals (SDGs). By systematically examining the secondary functions of stretchability, hybrid energy harvesting, and self-healing, the study aims to comprehensively understand these materials' mechanisms, strategies, and relationships between structural characteristics and properties. The research highlights the significance of designing piezoelectric materials that can conform to the curvilinear shape of the human body, enabling sustainable and efficient mechanical energy capture for various applications, such as biosensors and actuators. The study identifies critical areas for future investigation, including the commercialization of stretchable piezoelectric systems, prevention of unintended interference in hybrid energy harvesters, development of consistent wearability metrics, and enhancement of the elastic piezoelectric material, electrode circuit, and substrate for improved stretchability and comfort. In conclusion, this review research offers valuable insights into developing and implementing FPM as a promising and innovative approach to harnessing clean, affordable energy in line with the SDGs.</p

Review of flexible energy harvesting for bioengineering in alignment with SDG

To cater to the extensive body movements and deformations necessitated by biomedical equipment flexible piezoelectrics emerge as a promising solution for energy harvesting. This review research delves into the potential of Flexible Piezoelectric Materials (FPM) as a sustainable solution for clean and affordable energy, aligning with the United Nations' Sustainable Development Goals (SDGs). By systematically examining the secondary functions of stretchability, hybrid energy harvesting, and self-healing, the study aims to comprehensively understand these materials' mechanisms, strategies, and relationships between structural characteristics and properties. The research highlights the significance of designing piezoelectric materials that can conform to the curvilinear shape of the human body, enabling sustainable and efficient mechanical energy capture for various applications, such as biosensors and actuators. The study identifies critical areas for future investigation, including the commercialization of stretchable piezoelectric systems, prevention of unintended interference in hybrid energy harvesters, development of consistent wearability metrics, and enhancement of the elastic piezoelectric material, electrode circuit, and substrate for improved stretchability and comfort. In conclusion, this review research offers valuable insights into developing and implementing FPM as a promising and innovative approach to harnessing clean, affordable energy in line with the SDGs.</p

Modelling and control strategies for hydrokinetic energy harnessing

The high prices and depletion of conventional energy resources and the environmental concern due to the high emission of CO2 gases have encouraged many researchers worldwide to explore a new field in renewable energy resources. The hydrokinetic energy harnessing in the river is one of the potential energies to ensure the continuity of clean, reliable, and sustainable energy for the future generation. The conventional hydropower required a special head, lots of coverage area, and some environmental issues. Conversely, the hydrokinetic system based on free stream flowing is one of the best options to provide the decentralised energy for rural and small-scale energy production. Lately, the effort of energy harnessing based on hydrokinetic technology is emerging significantly. Nevertheless, several challenges and issues need to be considered, such as turbine selection for energy conversion, generalised turbine model and control strategies for the grid and non-grid connection. To date, no detailed information on which turbines and turbine model are most suited to be implemented that match Malaysia’s river characteristics. Besides, a large oscillation has occurred on the output current and power during dynamic steady state due to the water variation and fluctuation in the river. Hence, reducing the energy extraction and controller efficiency for stand-alone and grid-connected systems, respectively. Therefore, the study aims to analyse the different turbine's design, proposed the turbine model, and propose the potential control strategies for stand-alone and grid-connected hydrokinetic energy harnessing in the river. In this work, three types of vertical axis turbines, including the H-Darrieus, Darrieus, and Gorlov with twelve different NACA and NREL hydrofoils, were analysed using the QBlade and MATLAB software, respectively. The effect of symmetrical and non-symmetrical geometry profiles, hydrofoils thicknesses, and turbine solidities have been compared to choose one of the best option turbines based on the highest power coefficient (CP) and a torque coefficient (CM), respectively. Subsequently, the turbine power model generalised equation has been proposed to represent the hydrokinetic turbine characteristic using a polynomial estimation equation. On the other hand, the MPPT control strategy is employed for the off-grid system using the sensorless method. The circuit topology based on an uncontrolled rectifier with the DC boost converter is implemented to regulate the rectifier output voltage through duty ratio. Subsequently, the metaheuristic method based on the combination of the Hill-Climbing Search (HCS) MPPT algorithm and the Fuzzy Logic Controller has been proposed to produce a variable step size compared to the fixed step size in conventional HCS algorithm. On the contrary, the dynamic model of the grid-connected hydrokinetic system has been linearised for small-signal stability analysis. The eigenvalues analysis-based approached has been applied to evaluate the system stability due to the small disturbance. The PI controller with the eigenvalues tracing method has been proposed to improve the system stability by reducing the oscillation frequency. The research outcomes indicated that the H-Darrieus with NACA 0018 was the best turbine for energy conversion in the river. Besides, the HCS-Fuzzy MPPT algorithm improved the energy extraction up to 88.30 % as well as reduced 74.47 % the oscillation compared to the SS-HCS MPPT. The stability of grid-connected hydrokinetic energy harnessing was improved up to 63.63 % by removing the oscillation frequency at states of λ8,9,10,11 as well as reducing 40.1 % oscillation of the generator stator current at the rotor side controller (RSC)

Aeroelastic Flutter Vibration Energy Harvesting: Modeling, Testing, And System Design

The rapid proliferation of wireless sensors and microelectronics has spurred considerable interest in developing small scale devices that convert ambient energy sources to electrical power. Such "energy harvesting" devices could thus eliminate the need for hardwired power and extend the useful lifespan of a wireless sensor beyond the finite capacity of a battery. Piezoelectric materials, which directly convert mechanical strain to electrical energy, have been extensively investigated in recent years as a potential means to harvest energy from mechanical vibrations. This research has predominately focused on harvesting energy from preexisting vibrating host structures through base excitation of cantilevered piezoelectric beams. This approach, while simple to implement, inherently restricts the application of piezoelectric energy harvesting technology to environments where suitable vibrations are available. This dissertations proposes and investigates a novel piezoelectric energy harvesting device that simultaneously generates vibrations and harvests energy from an ambient fluid flow by inducing an aeroelastic flutter instability in a simple structure. The proposed device is studied through a combination of analytic modeling and wind tunnel experimentation. A model of this device that captures the three-way coupling between the structural, unsteady aerodynamic, and electrical aspects of the system is developed. The model is applied to predict the flow speed required for energy harvesting using linear stability analysis, and is generalized to account for aerodynamic nonlinearities that lead to flutter limit cycle behavior over a broad range of flow speeds. Wind tunnel test results are presented to determine empirical aerodynamic model coefficients and to characterize the power output and flutter frequency of the harvester as functions of incident wind speed. The model is then used to investigate the key design parameters of the system and determine the sensitivity and effective range of each parameter in affecting the characteristics of the aeroelastic instability driving the energy harvester. Finally, wind tunnel testing and flow visualization investigate the aerodynamic interactions between multiple flutter energy harvesters operating simultaneously. These experiments reveal synergistic wake-structure interactions than can be used to enhance the array performance, allowing the harvesters to produce more power when operating in close proximity than in a steady free stream flow

Exploiting Stiffness Nonlinearities to Improve the Performance of Galloping Flow Energy Harvesters

Fluid-structure coupling mechanisms such as galloping and wake galloping have recently emerged as effective methods to develop scalable flow energy harvesters (FEHs) that can be used to power remote sensors and sensor networks. The oper-ation concept of these devices is based on coupling the pressure forces culminating from the motion of the fluid past a mechanical oscillator to its natural modes of vibration. As a result, the mechanical oscillator undergoes large-amplitude motions that can be transformed into electricity by utilizing an electromechanical transduc-tion mechanism, which is generally piezoelectric or electromagnetic in nature. Due to their scalability and design simplicity, FEHs are believed to be more effective for micro-power generation than their traditional rotary-type counterparts whose efficiency is known to drop significantly as their size decreases. Furthermore, FEHs can be used to harvest energy from unsteady flow patterns which permits targeting a niche market that traditional rotary-type generators do not address. In the open literature, galloping FEHs have always been designed to possess a linear restoring force. This dissertation considers the design and performance analysis of galloping FEHs with a nonlinear restoring force. Specifically, the objective of this dissertation is three fold. First, it assesses the influence of stiffness nonlinearities on the performance of galloping FEHs under steady and laminar flow conditions. Second, it studies the influence of the nonlinearity on the response of a wake gal-loping FEH to single- and multi-frequency Von Karman vortex streets. Third, for known flow characteristics, the dissertation provides directions for how to choose the restoring force of the harvester to maximize the output power. To achieve the objectives of this dissertation, a nonlinear FEH which consists of a thin piezoelectric cantilever beam augmented with a square-sectioned bluff body at the free end is con-sidered. 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. For a steady laminar flow, three types of nonlinear restoring forces are compared: bi-stable, mono-stable hardening, and mono-stable softening. To study the influ-ence of the restoring force on the performance, a physics-based nonlinear lumped-parameter aero-electromechanical model adopting the quasi-steady assumption for aerodynamic loading is developed. A closed-form solution of the nonlinear response is obtained by employing a multiple-scales perturbation analysis using the Jacobi el-liptic functions. The attained solution is validated experimentally using wind tunnel tests performed at different wind speeds for the three types of restoring forces con-sidered. The validated solution is then used to study the influence of the nonlinearity on the harvesters response. In general, it is shown that, under optimal operating conditions, a harvester designed with a bi-stable restoring force outperforms the other designs. For single- and multi-frequency vortex streets, only linear and bi-stable restoring forces were considered and compared. A nonlinear lumped-parameter model adopt-ing the common uncoupled single-frequency force model for aerodynamics loading is developed and solved using the method of multiple scales. The model is validated against experimental data obtained in a wind tunnel. It is demonstrated that when subjected to a single-frequency periodic wake, the broadband characteristics of wake-galloping FEHs can be dramatically improved by incorporating a bi-stable restoring force. This has the influence of reducing the harvester’s sensitivity to variations in the wind speed around the nominal design value. It is also demonstrated that the shape of the potential function has a considerable influence on the performance of the bi-stable wake galloping FEH. Specifically, it is shown that, for shallower poten-tial wells and smaller separation distances between the wells, the harvester starts performing large inter-well motions at lower wind speeds, but the resulting inter-well motions are generally smaller. On the other hand, for deeper potential wells and larger separation distances between the wells, the harvester starts performing large inter-well motions at higher wind speeds, but the magnitude of the resulting inter-well motions are generally larger. The dissertation also compared the performance of linear and bi-stable wake-galloping FEHs under a multi-frequency vortex street. Results demonstrated that the bi-stable system outperforms the linear harvester as long as the vortices have sufficient time to interact and build a multi-frequency vortical structure. Maximum voltage levels were generated at locations where the interacting vortices result in powerful modes close to the harvesters natural frequency

A drifter-based self-powered piezoelectric sensor for ocean wave measurements

In the present research, a drifter-based piezoelectric sensor is proposed to measure ocean waves’ height and period. To analyze the motion principle and the working performance of the proposed drifter-based piezoelectric sensor, a dynamic model is developed. The developed dynamic model investigates the system’s response to an input of ocean waves and provides design insights into the geometrical and material parameters. Next, finite element analysis (FEA) simulations using the commercial software COMSOL-Multiphysics have been carried out with the help of a coupled physics analysis of Solid Mechanics and Electrostatics Modules to achieve the output voltages. An experimental prototype has been fabricated and tested to validate the results of the dynamic model and the FEA simulation. A slider-crank mechanism is used to mimic ocean waves throughout the experiment, and the results show a close match between the proposed dynamic modeling, FEA simulations, and experimental testing. In the end, a short discussion is devoted to interpreting the output results; comparing the results of the simulations and the experimental testing; the sensor’s resolution; and the self-powering functionality of the proposed drifter-based piezoelectric sensor

The design of low-frequency, low-g piezoelectric micro energy harvesters

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 107-112).A low-frequency, low-g piezoelectric MEMS energy harvester has been designed. Theoretically, this new generation energy harvester will generate electric power from ambient vibrations in the frequency range of 200~30OHz at excitation amplitude of 0.5g. Our previous energy harvester successfully resolved the gain-bandwidth dilemma and increased the bandwidth two orders of magnitude. By utilizing a doubly clamed beam resonator, the stretching strain triggered at large deflection stiffens the beam and transforms the dynamics to nonlinear regime, and increases the bandwidth. However, the high resonance frequency (1.3kHz) and the high-g acceleration requirement (4-5g) shown in the testing experiments limited the applications of this technology. To improve the performance of the current energy harvesters by lowering the operating frequency and excitation level, different designs have been generated and investigated. Moreover, a design framework has been formulated to improve the design in a systematic way with higher accuracy. Based on this design framework, parameter optimization has been carried out, and a quantitative design with enhanced performance has been proposed. Preliminary work on fabrication and testing setup has been done to prepare for the future experimental verification of the new design.by Ruize Xu.S.M