Toward Small-Scale Wind Energy Harvesting: Design, Enhancement, Performance Comparison, and Applicability

© 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

Dynamic analysis and fabrication of a bi-stable structure designed for MEMS energy harvesting applications.

Thanks to the rapid growth in demand for power in remote locations, scientists’ attention has been drawn to vibration energy harvesting as an alternative to batteries. Over the past ten years, the energy harvesting community has focused on bistable structures as a means of broadening the working frequency range and, by extension, the effective efficiency of vibration-based power scavenging systems. In the current study, a new method is implemented to statically and dynamically analyze a bistable buckled, multi-component coupled structure designed specifically for low-frequency vibration energy harvesting systems in both macro and MEMS-scale sizes. Furthermore, several micro-fabrication steps using advanced manufacturing technology methods were applied to design and fabricate a micro-scale version of the energy harvester at the University of Louisville Micro/Nano Technology Center. First, previously efforts performed on different aspects of vibration energy harvesting systems are reviewed to show the current challenges associated with such devices. The coupled structure proposed in this project is then introduced and its equations of motion are developed based on nonlinear Euler-Bernoulli beam theory. These governing equations are discretized and solved using a Galerkin method in two different approaches: with some known shape functions which only satisfies the geometrical boundary conditions; with the exact shape functions obtained from solving the linearized coupled structure as a one single system. An experimental setup is also used to verify the advantages of designed structure in capturing bistable motion at low-frequency range. To validate the modeling approaches, the obtained results are compared with the ones captured from both FEA model and the experimental setup, which shows the superiority of the proposed approach in which exact shape functions of the system are used as the basis in the discretization process. After the validation of the proposed approach, it is applied on a micro-scale version of the system in which structural, piezoelectric, and electrode layers are all considered as they exist in an actual device. Furthermore, a different bistable system, which was previously studied by other researchers in the area, is analyzed by this method to show the reliability of the proposed model. For all these cases, the amplitude-frequency response of the system and snap-through regime with the variation of various parameters, including exciting frequency, base vibration, and buckling loads are investigated based on the developed model. It is shown that bisatble motion and other nonlinear phenomena such as super-harmonic behavior in the system can be captured under certain circumstances, which can significantly impact major system functionalities such as output voltage response and is crucial for the performance of energy harvesting devices. As mentioned above, various micro-fabrication techniques were also used to design and fabricate a micro-scale version of the proposed system, which eventually led to the successful fabrication of a MEMS device as a result of experimental efforts performed to overcome the challenges and issues associated with the designed manufacturing process

Bistable energy harvesting backpack:Design, modeling, and experiments

Inspired by the dynamics of the noninertial systems, a novel bistable energy harvesting backpack is proposed that improves biomechanical energy harvesting performance. In contrast to traditional bistable energy harvesters that use an oblique compressed spring, a new bistable backpack is developed that uses the change of a spring torque direction located on a pinion. A detailed nondimensionalized model of the novel bistable energy harvesting backpack is developed and analyzed. Based on the dynamic bistable model, the influence of the carried backpack mass on the symmetry and the bifurcation frequency and amplitude of oscillation is examined to determine the ideal design parameters of the bistable backpack for experimental analysis and prototype manufacture. A comparison is made between the new bistable backpack and a traditional linear backpack under both harmonic and human walking excitation. The new bistable backpack design exhibits an improved frequency bandwidth from 1 Hz to 1.65 Hz at the base harmonic excitation of 2 m/s2 and the harvesting performance is enhanced from 2.34 W to 3.32 W when the walking speed is 5.6 km/h. The bench and treadmill tests verify the theoretical analysis and demonstrate the ability of the bistable energy harvesting backpack for broadband and performance enhancement.</p

Invited Review: Recent developments in vibration control of building and bridge structures

This paper presents a state-of-the-art review of recent articles published on active, passive, semi-active and hybrid vibration control systems for structures under dynamic loadings primarily since 2013. Active control systems include active mass dampers, active tuned mass dampers, distributed mass dampers, and active tendon control. Passive systems include tuned mass dampers (TMD), particle TMD, tuned liquid particle damper, tuned liquid column damper (TLCD), eddy-current TMD, tuned mass generator, tuned-inerter dampers, magnetic negative stiffness device, resetting passive stiffness damper, re-entering shape memory alloy damper, viscous wall dampers, viscoelastic dampers, and friction dampers. Semi-active systems include tuned liquid damper with floating roof, resettable variable stiffness TMD, variable friction dampers, semi-active TMD, magnetorheological dampers, leverage-type stiffness controllable mass damper, semi-active friction tendon. Hybrid systems include shape memory alloys-liquid column damper, shape memory alloy-based damper, and TMD-high damping rubber

Energy Harvesting & Wing Morphing Design Using Piezoelectric Macro Fiber Composites

Energy harvesting from vibration sources was a very promising field of research throughout the last few decades among the engineers and scientist as considering the necessity of renewable/green energy for the welfare of mankind. Unused vibration energy exists in the surrounding or machineries was always tried to be utilized. Since then, by using piezoelectric transduction, researchers started to harvest the vibration energy. However, after the invention of piezo ceramics Macro Fiber Composites (MFC) by NASA, the research in this field augmented a lot due to its high efficiency to convert mechanical strain or vibration to useful electrical power and vice versa. Apart from energy harvesting researcher concentrated to utilize this harvested energy for daily life and hence application of this harvested energy for structural health monitoring inaugurated. Recent study showed that, the vibration energy harvested from the vehicles or aerospace (UAV) structure is good enough to power its onboard structural health monitoring unit though for feeding this power to any other onboard electrical system is still challenging due to low power generation along with its random production. Moreover, Macro Fiber Composites (MFC) can be used as an actuator to change the shape of aircraft wing to enhance aerodynamic performance and hence, application of MFC for wing morphing design has become popular throughout these years. The purpose of this research work is to depict the recent progress & development that took place in the field of energy harvesting & wing morphing research using macro fiber composites and combining the existing knowledge continue the work further, the future of this harvested energy, new design concept & upcoming challenges along with its possible solution. This work investigates the different configuration of macro fiber composites (MFC) for piezoelectric energy harvesting and its contribution for wing morphing design with enhanced aerodynamics. For the first part of this work, uniform MFC configuration was modeled and built up based on the Euler-Bernoulli beam theory. When the governing differential equations of the systems were derived, by applying the harmonic base excitation, coupled vibration response and the voltage response were obtained. The prediction of the mathematical model was at first verified by unimorph MFC with a brass substrate obtained from the state of art and then validation was justified by MFC unimorph along with three different substrate materials (copper, zinc alloy & galvanized steel) and thickness for the first time in this type of research. Computational & analytical solution revealed that, among these three substrates and for same thickness, maximum peak power at resonance excitation was obtained for the copper substrate. For the second part of the study (i) computational analysis was performed and the output was compared with the real time data obtained from the wind tunnel experiment and the conclusion stood that, with the increment of the incoming flow velocity, the power output from the MFC increases with a thin aerofoil made of copper substrates and two MFC on its upper surface (ii) wing morphing design was performed for a NACA 0012 aerofoil for the first time where macro fiber composite actuators were used to change the top and bottom surfaces of the aerofoil with a view to recording the enhanced aerodynamics performance the designed morphing wing. CFD simulation results were compared with the wind tunnel testing data from the state of art for NACA 0014 for all identical parameters. The enhanced aerodynamics performance observed for designed wing morphing can be used for future concepts like maneuvering of the aircraft without the help of ailerons or for the purpose of active flow control over the aircraft wing

Rectifying the output of vibrational piezoelectric energy harvester using quantum dots

Piezoelectric energy harvester scavenges mechanical vibrations and generates electricity. Researchers have strived to optimize the electromechanical structures and to design necessary external power management circuits, aiming to deliver high power and rectified outputs ready for serving as batteries. Complex deformation of the mechanical structure results in charges with opposite polarities appearing on same surface, leading to current loss in the attached metal electrode. External power management circuits such as rectifiers comprise diodes that consume power and have undesirable forward bias. To address the above issues, we devise a novel integrated piezoelectric energy harvesting device that is structured by stacking a layer of quantum dots (QDs) and a layer of piezoelectric material. We find that the QD can rectify electrical charges generated from the piezoelectric material because of its adaptable conductance to the electrochemical potentials of both sides of the QDs layer, so that electrical current causing energy loss on the same surface of the piezoelectric material can be minimized. The QDs layer has the potential to replace external rectification circuits providing a much more compact and less power-consumption solution

Piezoelectric Energy Harvester Technologies: Synthesis, Mechanisms, and Multifunctional Applications.

Piezoelectric energy harvesters have gained significant attention in recent years due to their ability to convert ambient mechanical vibrations into electrical energy, which opens up new possibilities for environmental monitoring, asset tracking, portable technologies and powering remote "Internet of Things (IoT)" nodes and sensors. This review explores various aspects of piezoelectric energy harvesters, discussing the structural designs and fabrication techniques including inorganic-based energy harvesters (i.e., piezoelectric ceramics and ZnO nanostructures) and organic-based energy harvesters (i.e., polyvinylidene difluoride (PVDF) and its copolymers). The factors affecting the performance and several strategies to improve the efficiency of devices have been also explored. In addition, this review also demonstrated the progress in flexible energy harvesters with integration of flexibility and stretchability for next-generation wearable technologies used for body motion and health monitoring devices. The applications of the above devices to harvest various forms of mechanical energy are explored, as well as the discussion on perspectives and challenges in this field

New Advances in Fluid Structure Interaction

Fluid–structure interactions (FSIs) play a crucial role in the design, construction, service and maintenance of many engineering applications, e.g., aircraft, towers, pipes, offshore platforms and long-span bridges. The old Tacoma Narrows Bridge (1940) is probably one of the most infamous examples of serious accidents due to the action of FSIs. Aircraft wings and wind-turbine blades can be broken because of FSI-induced oscillations. To alleviate or eliminate these unfavorable effects, FSIs must be dealt with in ocean, coastal, offshore and marine engineering to design safe and sustainable engineering structures. In addition, the wind effects on plants and the resultant wind-induced motions are examples of FSIs in nature. To meet the objectives of progress and innovation in FSIs in various scenarios of engineering applications and control schemes, this book includes 15 research studies and collects the most recent and cutting-edge developments on these relevant issues. The topics cover different areas associated with FSIs, including wind loads, flow control, energy harvesting, buffeting and flutter, complex flow characteristics, train–bridge interactions and the application of neural networks in related fields. In summary, these complementary contributions in this publication provide a volume of recent knowledge in the growing field of FSIs