344 research outputs found
Optimum resistive loads for vibration-based electromagnetic energy harvesters with a stiffening nonlinearity
No full textThe exploitation of nonlinear behavior in vibration-based energy harvesters has received much attention over the last decade. One key motivation is that the presence of nonlinearities can potentially increase the bandwidth over which the excitation is amplified and therefore the efficiency of the device. In the literature, references to resonating energy harvesters featuring nonlinear oscillators are common. In the majority of the reported studies, the harvester powers purely resistive loads. Given the complex behavior of nonlinear energy harvesters, it is difficult to identify the optimum load for this kind of device. In this paper the aim is to find the optimal load for a nonlinear energy harvester in the case of purely resistive loads. This work considers the analysis of a nonlinear energy harvester with hardening compliance and electromagnetic transduction under the assumption of negligible inductance. It also introduces a methodology based on numerical continuation which can be used to find the optimum load for a fixed sinusoidal excitation
A new approach for changing structural properties of a membrane mirror strip for adaptive optics applications
No full text
Overview of piezoelectric impedance-based health monitoring and path forward
No full textIn this paper we summarize the hardware and software issues of impedance-based structural health monitoring based on piezoelectric materials. The basic concept of the method is to use high-frequency structural excitations to monitor the local area of a structure for changes in structural impedance that would indicate imminent damage. A brief overview of research work on experimental and theoretical studies on various structures is considered and several research papers on these topics are cited. This paper concludes with a discussion of future research areas and path forward.This work was sponsored by the Department of Energy
through Laboratory Directed Research Development, entitled
“Damage Prognosis Solution”
Aerodynamic and Aeroelastic Considerations of A Variable-Span Morphing Wing
No full textMorphing concepts for air vehicles such as unmanned air vehicles (UAVs) have been a topic of current research interest in aerospace engineering. A morphing wing is a bird-like wing that has the ability of adapting to obtain better flight performance. One concept of morphing is the variable-span morphing wing (VSMW) in which the wingspan is varied to accommodate multiple flight regimes. In the present study, the advantages and disadvantages of a VSMW for a cruise type missile are discussed. The aerodynamic characteristics and the range of this morphing wing are analyzed as its wingspan is changed. The results of the analysis demonstrate an improvement in the aerodynamic characteristics of the VSMW, in the form of a reduction in the induced drag, resulting in an increase in range. As further discussed, the VSMW also provides an native method of controlling the roll motions of a bank-to-turn cruise missile. Compared to conventional roll control the variable span method provides an increase in roll control authority. Unfortunately, the aeroelastic characteristics of the VSMW become worse because the wing-root bending moment increases due to the wingspan increase
The bandwidth of optimized nonlinear vibration-based energy harvesters
No full textIn an attempt to improve the performance of vibration-based energy harvesters, many authors suggest that nonlinearities can be exploited to increase the bandwidths of linear devices. Nevertheless, the complex dependence of the response upon the input excitation has made a realistic comparison of linear harvesters with nonlinear energy harvesters challenging. In a previous work it has been demonstrated that for a given frequency of excitation, it is possible to achieve the same maximum power for a nonlinear harvester as that for a linear harvester, provided that the resistance and the linear stiffness of both are optimized. This work focuses on the bandwidths of linear and nonlinear harvesters and shows which device is more suitable for harvesting energy from vibrations. The work considers different levels of excitation as well as different frequencies of excitation. In addition, the effect of the mechanical damping of the oscillator on the power bandwidth is shown for both the linear and nonlinear cases.</p
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