Shaikh Faruque Ali

Energy harvesting is a promise to harvest unwanted vibrations from a host structure. Similarly, a dynamic vibration absorber is proved to be a very simple and effective vibration suppression device, with many practical implementations in civil and mechanical engineering. This paper analyzes the prospect of using a vibration absorber for possible energy harvesting. To achieve this goal, a vibration absorber is supplemented with a piezoelectric stack for both vibration confinement and energy harvesting. It is assumed that the original structure is sensitive to vibrations and that the absorber is the element where the vibration energy is confined, which in turn is harvested by means of a piezoelectric stack. The primary goal is to control the vibration of the host structure and the secondary goal is to harvest energy out of the dynamic vibration absorber at the same time. Approximate fixed-point theory is used to find a closed form expression for optimal frequency ratio of the vibration absorber. The changes in the optimal parameters of the vibration absorber due to the addition of the energy harvesting electrical circuit are derived. It is shown that with a proper choice of harvester parameters a broadband energy harvesting can be obtained combined with vibration reduction in the primary structure. Copyright © 2013 by ASME.

This paper presents active vibration control and morphing of thin plates using an array of piezoelectric actuator-sensor system whose locations are determined by optimization. The sudden application of control input for morphing leads to unwanted vibrations which are suppressed using the piezoelectric actuator-sensor couples, which form a feedback control loop. Dynamic Inversion technique is used to determine the control inputs to morph the plate and to suppress the vibrations in the process. The Dynamic Inversion controlled system is compared to uncontrolled system and as a reference, the results are compared with that of Linear Quadratic Controller. The partial differential equations governing the behaviour of plate and piezoelectric actuation are solved using lower dimensional projection method, following Design-then-Approximate (DTA) method, which will reduce spillover effects. Two reference configurations are considered to perform simulations. The actuators are designed for both vibration control and morphing since thin plates have poor damping characteristics and need external damping. The displacement, velocity and error norm time histories are analysed and the configuration achieved by the system by both controllers are compared.

Influence of potential well asymmetry on the dynamics of magneto-elastic and piezo-magneto-elastic harvesters with symmetric and asymmetric bi-stable potential wells are investigated in this article. An autonomous algorithm is developed which categorizes the response obtained under different harmonic excitations and initial conditions into seven unique-primary attractor solutions. Influence of two small and two moderate levels of asymmetry in potential well is visualized at the different excitation frequencies through the attractor basins and largest Lyapunov exponent of the solutions. The results of the numerical investigations prove that small and moderate levels of asymmetry considered in this investigations have insignificant influence on the desirable cross-well periodic solution. Also, under small asymmetry levels, the cross-well periodic solutions preferably transform into other cross-well solutions only, viz. cross-well subharmonic and chaotic solutions, if attainable. In addition, these asymmetry levels are beneficial in restraining the chaos-prone solutions and even boost up the basin areas of the cross-well periodic solution. A reduction in chaos-prone responses not only implies a simplified and efficient energy harvesting circuitry, but also results in an improved life expectancy of the transduction material as the instances of stress reversals are reduced.

Owing to their high energy densities, smart materials like shape memory alloys (SMAs), Macro-Fiber Composites (MFCs) and, electroactive polymers (EAPs) have massive potential as actuators in wing morphing applications. In this article, a detailed numerical model is developed for the shape prediction of an elastic base that is actuated by a combination of a shape memory alloy (SMA) wire and a Macro-Fiber Composite (MFC) bimorph. It has been demonstrated using the model that it is possible to achieve large deflections at low frequencies by virtue of the phase transformations in the SMA wire and rapid actuation with small deflections due to the MFC bimorph. In the developed scheme, the elastic base is modeled using non-linear Euler-Bernoulli beam theory. The influence of the non-linear hysteresis in the SMA wire and the linear actuation characteristics of the MFC is studied by incorporating thermo-mechanical and electro-mechanical constitutive behavior into the non-linear beam theory. The system of coupled equations hence obtained, is solved iteratively to obtain the deflected shape of the elastic base. The results from the developed numerical scheme are validated against the previously available studies in the literature and experiments. Additionally, the synergistic advantage of using the two actuators together has been shown through experiments. As an illustration, a smart trailing edge camber morphing concept is developed by integrating the flexible elastic structure along with the two smart actuators to a NACA 0012 airfoil as the trailing edge.

The study focuses on the design of an energy harvesting nonlinear dynamic vibration absorber (DVA) for possible vibration attenuation and energy generation. As an application vibration mitigation of a base-excited single degree of freedom (SDOF) system is considered. Conventional DVAs are widely used as vibration control devices that undergo large displacements in order to dissipate the energy from the primary structure. For an energy harvester higher the vibration higher is the energy generated. Therefore, if an energy harvester is attached to the DVA, the primary structure DVA interaction can be used for dual purposes. In this study, a duffing-type nonlinear DVA system with a piezo patch is proposed as energy harvesting nonlinear DVA to mitigate the vibration and to obtain electricity. The modeling of the total system is carried out considering the electromechanical interactions between the harvester-DVA and structural system. The formulation is done in time domain and a simulation study is carried out for harmonic base excitation to understand the effect of nonlinearity in voltage generation. A frequency sweep study is carried out to locate the frequency band in which the system responses are consistently higher. Further, the important design parameters are identified. A parametric study to obtain optimal design parameters is also reported. The advantages of nonlinear energy harvesting DVA over the linear ones are many. A nonlinear harvester provides power over a broad range of frequencies and, therefore would be able to dissipate energy from the primary structure over wideband excitations. Finally, the performance of the designed nonlinear DVA system with harvester is examined for vibration mitigation of SDOF primary system.

This study focusses on the development of stochastic reduced order model for probabilistic characterisation of bladed disc systems with random spatial inhomogeneities. High fidelity finite element modelling is used to mathematically model the system. A two step reduction strategy is applied involving reduction in the state space dimension and reduction in the stochastic dimensions. Information of the spatial inhomogeneities are assumed to be available from limited in situ measurements across the spatial extent and are modelled as non-Gaussian random fields. The stochastic version of the finite element matrices are developed using a polynomial chaos based framework, which optimizes the stochastic dimensionality of the problem. The uncertainties in the input propagates through the system into the response, which are also random. Surrogate models for these response quantities are obtained as PCE and are constructed using the method of stochastic collocations. Challenges involved in application of PCE on complex geometrically irregular spatial domains are addressed. The efficacy of the proposed framework is demonstrated through two numerical examples -an academic bladed disc system and an industrial turbine rotor blade.

Small and micro-scale energy harvesting is an essential and viable option for the powering of portable and maintenance free electronic devices, wireless sensor nodes, and similar applications. In this regard, piezoelectric harvesters have presented promising outcomes. This article provides a sequential, comprehensive, and informative survey of potential well based models and studies related to piezoelectric harvesters (PEH). Piezoelectric materials used for energy harvesting are discussed briefly, following which a non-dimensional generalized model is derived to set the discussion on a common platform. Dynamics of various potential well configurations are presented using the generalized model before discussing specific models and related studies. The survey is classified into symmetric and asymmetric potential well categories. Under the symmetric head, lumped and distributed parameter linear models and tuning methods for improving the broadband response are discussed. Subsequently, studies related to nonlinear mono-stable, bi-stable, and tri-stable potentials showing interwell, multi-periodic and chaotic oscillations with improved broadband response are discussed. The asymmetric section studies the influence of asymmetries on the performance of the mono-stable, bi-stable, and tri-stable configurations. Few other configurations outside the cantilever type PEH were mentioned, realizing the widespread research in this field. Important observations and future challenges for performance improvement are also discussed.

Current trend in energy harvesting research is to increase the operating bandwidth of energy harvesters. Multiple harvesters, nonlinear harvesters and hybrid harvesters are suggested to address the issue. In this paper, a system consisting of two electromagnetic harvesters with magnetic and mechanical couplings subjected to harmonic support excitations is proposed. Two pendulums with close resonating frequencies are used to generate power over a broad range of frequencies. The pendulums behave nonlinearly under the influence of magnetic interaction. This nonlinear motion harvests power at broader bandwidth. A mathematical model of the proposed harvester is established. Experiments are performed to validate the theoretical results. It has been observed that the nonlinear responses due to both magnet and mechanical couplings improve individual harvester performance. This is advantageous over harvesters that have magnetically coupling only. Additionally, the dynamics of harvesting system is numerically studied where large amplitude chaotic motion, quasi-periodic oscillations and periodic motions are observed and reported.

An inverted cantilevered beam vibration energy harvester with a tip mass is evaluated for its electromechanical efficiency and power output capacity in the presence of pure harmonic, pure random and various combinations of harmonic and random base excitation cases. The energy harvester employs a composite piezoelectric material device that is bonded near the root of the beam. The tip mass is used to introduce non-linearity to the system by inducing buckling in some configurations and avoiding it in others. The system dynamics include multiple solutions and jumps between the potential wells, and these are exploited in the harvesting device. This configuration exploits the non-linear properties of the system using base excitation in conjunction with the tip mass at the end of the beam. Such nonlinear device has the potential to work well when the input excitation does not have a dominant harmonic component at a fixed frequency. The paper presents an extensive experimental analysis, results and interesting conclusions derived directly from the experiments supported by numerical simulations. Copyright © 2013 by ASME.