1,721,000 research outputs found
A new approach for changing structural properties of a membrane mirror strip for adaptive optics applications
No full textOptimum 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
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
Impedance-based structural health monitoring considering temperature effects
No full textThis paper presents an impedance-based structural health monitoring (SHM) technique considering temperature effects. The temperature variation results in a significant impedance variation, particularly a frequency shift in the impedance, which may lead to erroneous diagnostic results of real structures such as civil, mechanical, and aerospace structures. A new damage detection strategy has been proposed based on the correlation coefficient (CC) between the reference impedance data and a concurrent impedance data with an effective frequency shift which is defined as the shift causing the maximum correlation. The proposed technique was applied to a lab-sized steel truss bridge member under the temperature varying environment. It has been found, however, the CC values are still suffering from the significant fluctuation due to the temperature variation. Therefore, an outlier analysis providing the optimal decision boundary has been carried out for damage detection. From an experimental study, it has been demonstrated that a narrow cut inflicted artificially to the steel structure was successfully detected using the proposed SHM strategy
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