Showing papers by "Ryan L. Harne published in 2012"

Theoretical investigations of energy harvesting efficiency from structural vibrations using piezoelectric and electromagnetic oscillators.

Abstract: Conversion of ambient vibrational energy into electric power has been the impetus of much modern research. The traditional analysis has focused on absolute electrical power output from the harvesting devices and efficiency defined as the convertibility of an infinite resource of vibration excitation into power. This perspective has limited extensibility when applying resonant harvesters to host resonant structures when the inertial influence of the harvester is more significant. Instead, this work pursues a fundamental understanding of the coupled dynamics of a main mass-spring-damper system to which an electromagnetic or piezoelectric mass-spring-damper is attached. The governing equations are derived, a metric of efficiency is presented, and analysis is undertaken. It is found that electromagnetic energy harvesting efficiency and maximum power output is limited by the strength of the coupling such that no split system resonances are induced for a given mass ratio. For piezoelectric harvesters, only the coupling strength and certain design requirements dictate maximum power and efficiency achievable. Since the harvesting circuitry must “follow” the split resonances as the piezoelectric harvesters become more massive, the optimum design of piezoelectric harvesters appears to be more involved than for electromagnetic devices.

Concurrent attenuation of, and energy harvesting from, surface vibrations: experimental verification and model validation

Abstract: Fundamental studies in vibrational energy harvesting consider the electromechanically coupled devices to be excited by uniform base vibration. Since many harvester devices are mass–spring systems, there is a clear opportunity to exploit the mechanical resonance in a fashion identical to tuned mass dampers to simultaneously suppress the vibration of the host structure via reactive forces while converting the ‘absorbed’ vibration into electrical power. This paper presents a general analytical model for the coupled electro-elastic dynamics of a vibrating panel to which distributed energy harvesting devices are attached. One such device is described which employs a corrugated piezoelectric spring layer. The model is validated by comparison to measured elastic and electric frequency response functions. Tests on an excited panel show that the device, contributing 1% additional mass to the structure, concurrently attenuates the lowest panel mode accelerance by >20 dB while generating 0.441 µW for a panel drive acceleration of 3.29 m s−2. Adjustment of the load resistance connected to the piezoelectric spring layer verifies the analogy between the present harvester device and an electromechanically stiffened and damped vibration absorber. The results show that maximum vibration suppression and energy harvesting objectives occur for nearly the same load resistance in the harvester circuit.

Structural-acoustic aspects in the modeling of sandwich structures and computation of equivalent elasticity parameters

Abstract: Small-deflection theory is used along with FE models to compute the equivalent elasticity parameters of sandwich structures. Eigenfrequency and eigenmode analyses, comparing the equivalent 2-D continua with full 3-D models, are utilized to determine how continuous connections and in-vacuo assumptions are influenced as real-world discontinuities and gas- or foam-filled cavities are included. It is found that discrete connections between structural elements reduce stiffnesses and eigenfrequencies of the net structure substantially. The presence of gas or foam in the core cavities is observed to increase the overall damping of the dynamic panel response while also amplifying certain panel resonances.

Modeling of a distributed device for simultaneous reactive vibration suppression and energy harvesting

Abstract: Distributed devices or treatments are a mainstay of passively suppressing structural vibrations. In some cases, piezoelectric materials were included within the devices to utilize them as actuators. Interest in energy harvesting encourages a reassessment of these devices, using the piezoelectric materials as a means to convert input vibrational energy into electrical power. A numerical model of one such device, exhibiting mass-spring-damper dynamics, attached to a vibrating host structure is described and validated against 3D finite element analysis. The model is utilized to evaluate the simultaneous goals of passive vibration attenuation and energy harvesting of devices on a lightweight, clamped panel. The objectives are found to be partly in opposition, particularly when the total mass of the added devices becomes more substantial. This feature is widely neglected in employing mass-spring systems as energy-harvesting devices, where the mass of the device is insubstantial relative to the main structure. ...

The concurrent suppression of an energy harvesting from surface vibrations: experimental investigations

Abstract: Vibrational energy harvesting devices are oftentimes constructed in a manner identical to classical tuned-massdampers used in vibration control applications. However, many applications and models in past work assume that the harvesters will have negligible influence on the host structure (e.g. harvesters on a bridge). In contrast, this work adopts the perspective that the energy harvester is analogous to an electromechanical vibration absorber, attenuating the structural vibrations via a dominant mechanical influence while converting the absorbed energy into electric power. One embodiment of a device serving these two purposes-passive vibration attenuation and energy harvesting-is introduced. The device utilizes a distributed piezoelectric spring layer such that as the spring is strained between the top mass layer and the vibrating host structure the piezoelectric spring generates a voltage potential across its electrodes. Two experimental studies are detailed which investigate the capability for energy harvesting vibration absorbers to meet both goals. It is found that achievement of both objectives may require compromise but with proper device design still yields a viable electrical output.