M. Thota

Bistable energy harvesting enhancement with an auxiliary linear oscillator

Recent work has indicated that linear vibrational energy harvesters with an appended degree-of-freedom (DOF) may be advantageous for introducing new dynamic forms to extend the operational bandwidth. Given the additional interest in bistable harvester designs, which exhibit a propitious snap through effect from one stable state to the other, it is a logical extension to explore the influence of an added DOF to a bistable system. However, bistable snap through is not a resonant phenomenon, which tempers the presumption that the dynamics induced by an additional DOF on bistable designs would inherently be beneficial as for linear systems. This paper presents two analytical formulations to assess the fundamental and superharmonic steady-state dynamics of an excited bistable energy harvester to which is attached an auxiliary linear oscillator. From an energy harvesting perspective, the model predicts that the additional linear DOF uniformly amplifies the bistable harvester response magnitude and generated power for excitation frequencies less than the attachments resonance while improved power density spans a bandwidth below this frequency. Analyses predict bandwidths having co-existent responses composed of a unique proportion of fundamental and superharmonic dynamics. Experiments validate key analytical predictions and observe the ability for the coupled system to develop an advantageous multi-harmonic interwell response when the initial conditions are insufficient for continuous high-energy orbit at the excitation frequency. Overall, the addition of an auxiliary linear oscillator to a bistable harvester is found to be an effective means of enhancing the energy harvesting performance and robustness.

On achieving high and adaptable damping via a bistable oscillator

This research investigates a bistable oscillator which, through snap through actions, can significantly increase the power dissipated and provide passive damping adaptability with respect to the input amplitude and frequency. The increase in motion generated during high orbit, snap through dynamic response leads to a significant increase in the power dissipated by the embedded damper. The power dissipated can change passively and drastically depending on the response dynamics excited by the input. Both analytical and experimental efforts are pursued to investigate and demonstrate the concept.

Reconfigurable origami sonic barriers with tunable bandgaps for traffic noise mitigation

An origami sonic barrier composed of cylindrical inclusions attached onto an origami sheet is proposed. The idea allows for tunable sound blocking properties for application in attenuating complex traffic noise spectra. Folding of the underlying origami sheet transforms the periodicity of the inclusions between different Bravais lattices, viz. between a square and a hexagonal lattice, and such significant lattice re-configuration leads to drastic tuning of dispersion characteristics. The wave tuning capabilities are corroborated via performing theoretical and numerical investigations using a plane wave expansion method and an acoustic simulation package of COMSOL, while experiments are performed on a one-seventh scaled-down model of origami sonic barrier to demonstrate the lattice re-configuration between different Bravais lattices and the associated bandgap adaptability. Good sound blocking performance in the frequency range of traffic noise spectra combined with less efforts, required for actuating one-...

Harnessing intrinsic localized modes to identify impurities in nonlinear periodic systems

Intrinsic localized modes (ILMs) are concentrations of vibrational energy in periodic systems/lattices due to the combined influences of nonlinearity and discreteness. Moreover, ILMs can move within the system and may strongly interact with an impurity, such as a stiffness change, mass variation, etc. Numerous scientific fields have uncovered examples and evidence of ILMs, motivating a multidisciplinary pursuit to rigorously understand the underlying principles. In spite of the diverse technical studies, a characterization of ILM interaction behaviors with multiple impurities in dissipative lattices remains outstanding. The insights on such behaviors may be broadly useful when dynamic measurements are the only accessible features of the periodic system. For instance, one may guide an ILM within the lattice using a deliberately applied and steered impurity and harness the observed interaction behaviors with a second, static (immovable) impurity/defect to identify how the underlying lattice is different at ...

Origami metastructures for tunable wave propagation

Wave propagation inside a host media with periodically distributed inclusions can exhibit bandgaps. While controlling acoustic wave propagation has large impact on many engineering applications, studies on broadband acoustic bandgap (ABG) adaptation is still outstanding. One of the important properties of periodic structure in ABG design is the lattice-type. It is possible that by reconfiguring the periodic architectures between different lattice-types with fundamentally distinct dispersion relations, we may achieve broadband wave propagation tuning. In this spirit, this research pioneers a new class of reconfigurable periodic structures called origami metastructures (OM) that can achieve ABG adaption via topology reconfiguration by rigid-folding. It is found that origami folding, which can enable significant and precise topology reconfigurations between distinct Bravais lattice-types in underlying periodic architecture, can bring about drastic changes in wave propagation behavior. Such versatile wave transmission control is demonstrated via numerical studies that couple wave propagation theory with origami folding kinematics. Further, we also exploit the novel ABG adaptation feature of OM to design structures that can exhibit unique tunable non-reciprocal behavior. Overall the broadband adaptable wave characteristics of the OM coupled with scale independent rigid-folding mechanism can bring on-demand wave tailoring to a new level.Copyright

A bi-stable oscillator for increasing damping and providing passive adaptability

This research investigates a bi-stable oscillator which, through snap-through actions, can significantly increase energy dissipation loss factor and provide passive damping adaptability with respect to input amplitude and frequency. The increase in motion generated during snap-through leads to a significant increase in the energy dissipated by the embedded damper and the corresponding loss factor. The system parameters can be designed such that the snap-though threshold occurs at different input amplitudes. Overall, the device can be programmed to adjust damping to changes in the loading environment in a passive manner.

Steady-state dynamics of a bistable energy harvester with linear appendage oscillator

Recent interest in bistable devices for vibration energy harvesting has given evidence of their beneficial performance in realistic stochastic or low frequency excitation environments since the snap through effect (high displacement switching from one stable state to another) is a non-resonant dynamic. It has yet to be rigorously determined how adding additional degrees-of-freedom may influence bistable energy harvesting response since the nonlinearities do not allow for a direct analogy from multi-body linear examples. We analytically and experimentally assess the potential for improving energy harvesting dynamics by adding a conventional linear oscillator to a bistable energy harvester. The traditional coupling parameters of mass ratio and tuning ratio are evaluated as means to tune the harvesters response. Advantageous design regimes are classified and explanations for the rich dynamics are provided. Experiments confirm the benefit of appending a linear oscillator to the bistable system as a simple means by which to enhance harvesting performance.