1,721,133 research outputs found
FLEXURAL CAPACITY OF LONG-SPAN TRANSVERSELY LOADED HOLLOW BLOCK MASONRY WALLS
No full textAn experimental programme was carried out on long-span masonry walls made of hollow concrete blocks. Both low-rise unreinforced walls and tall reinforced walls were subjected to four-point bending tests. The tests aim at obtaining indications on the flexural capacity of partially grouted, long-span masonry walls, which basically consist of unreinforced walls laterally supported by reinforced columns, and are mainly subjected to transverse loads. The tests on reinforced walls were also intended to compare the effectiveness of two types of reinforcement (a traditional one and an innovative one in which stirrups are replaced by metal strips welded to the longitudinal rebars) on the flexural capacity. Eurocode 6 is found to strongly underestimate the experimental flexural strength of the unreinforced walls. The traditional reinforcement was found to be more effective than the innovative one. Eventually, a finite element model of the reinforced walls was developed to try and capture their failure modes. Upon a careful calibration, the numerical model is able to match the experimental ultimate load, although the real transverse displacements cannot be correctly captured
The effect of inherent nonlinearities in coupled piezo-magneto-electric vibration energy harvester
Full text linkThis work deals with the experimental observation of inherent material nonlinearities occurring due to the magnetic plucking in a nonlinear piezoelectric vibration energy harvester. A piezoelectric cantilever is actuated via magnetic forces with a robotic arm at different constant velocities, in the range of 0.5 m/s - 2.5 m/s. The Fast Fourier Transforms of the voltage, in open circuit conditions, show that as the impulsiveness of the magnetic force
increases, the peak of the first bending mode of the beam shifts toward lower frequencies. Such
phenomenon should be taken into account for a reliable simulation and thus for the evaluation
of the optimal electrical condition of power extraction
A Review of Nonlinear Mechanisms for Frequency Up-Conversion in Energy Harvesting
Full text linkVibration-based energy harvesting has garnered considerable attention from researchers over the past two decades, using different transduction mechanisms. In this context, the utilization of piezoelectric materials has proven to be highly successful, due to their power density, across a broad range of voltages. A primary challenge in environmental vibration harvesting lies in the frequency mismatch between the devices, which typically exhibit optimal performance at hundreds or thousands of hertz due to their small size (centimeter or millimeter) and the environmental vibration. The latter has considerable energy density around tens of hertz. For this reason, over the last 15 years, the scientific community has concentrated on exploring techniques for band broadening or frequency up-conversion by intentionally introduced (or designed) nonlinearities. This review, following an introduction to the topic of vibration energy harvesting, provides a description of the primarily developed mechanisms, presenting a chronological development for each, from the initial works to the most recent advancements. Additionally, the review touches upon implementation efforts at the micro-electromechanical systems (MEMS) scale for each described technique. Finally, the incorporation of nonlinearities through electronic circuits to enhance performance is briefly discussed
Numerical and experimental evaluation of the magnetic interaction for frequency up-conversion in piezoelectric vibration energy harvesters
Full text linkThe purpose of this work is to improve the modelling process for the application of permanent magnets in a frequency up-conversion (FuC) mechanism for piezoelectric energy harvesters. More specifically, the aim is to avoid the burdensome finite element analyses (FEA) in the framework of electromechanical devices design. The analytical calculations are compared with experimental tests conducted by an ad-hoc set up and with FEA. After investigations on the interaction, an application of FuC mechanism is proposed on a meso-scale case study in which a low frequency seismic mass (LFM) interacts non-linearly, due to magnetic field, with an high frequency piezoelectric vibration energy harvester (PVEH). Numerical simulations have been carried out in the time domain (step-by-step analysis) under a harmonic low-frequency input acceleration signal. The peculiar behavior, due to non-linear dynamics, is investigated in both the repulsive and the attractive configurations of the magnets. The results confirm the effectiveness of magnetic FuC and show that the repulsive case allows the device to recover a larger amount of energy than the attractive configuration
An investigation on the magnetic interaction for frequency up-converting piezoelectric vibration energy harvesters
Full text linkThis work presents an investigation of different approaches for modelling the magnetic force between permanent magnets for realizing the frequency up-conversion (FuC) in piezoelectric vibration energy harvesters (PVEH). Different analytical models are compared with finite element analyses (FEA). After the investigation, the FuC mechanism is applied on a meso-scale case study and dynamic analyses in the time domain are performed in case of harmonic monochromatic acceleration signal on the device at low-frequency. Both the repulsive and the attractive layouts of the magnets are considered and a larger amount of power is recovered in case of repulsive configuration
Edge-selective reconfiguration in polarized lattices with magnet-enabled bistability
No full textThe signature topological feature of Maxwell lattices is their polarization, which manifests as an unbalance in stiffness between opposite edges of a finite domain. The manifestation of this asymmetry is especially dramatic in the case of soft lattices undergoing large nonlinear deformation under concentrated loads, where the excess of softness at the soft edge can result in the activation of sharp indentations. This study explores how this mechanical dichotomy between edges can be tuned and possibly extremized by working with soft magneto-mechanical metamaterials. The magneto-mechanical coupling is obtained by endowing the lattice sites with permanent magnets, which activate a network of magnetic forces that can interact with – either augmenting or competing with – the elasticity of the material. Specifically, under sufficiently large deformation that macroscopically alters the equilibrium positions of the sites, the attractive forces between the magnets can trigger bistable reconfiguration mechanisms. The strength of such mechanisms depends on the landscapes of elastic reaction forces exhibited by the edges, which are different due to the polarization, and is therefore inherently edge-selective. We show that, on the soft edge, the addition of magnets simply enhances the softness of the edge. In contrast, on the stiff edge, the magnets activate snapping mechanisms that locally reconfigure the cells and produce a lattice response reminiscent of plasticity, characterized by residual deformation that persists upon unloading
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Dynamical Behavior of Frequency up-Converted Piezoelectric Vibration Energy Harvesters at Different Velocities of Magnetic Interaction
Full text linkThis work proposes an experimental investigation on the dynamical behavior of a magnetically frequency upconverted piezoelectric energy harvester. The magnetic interaction arises between a tip magnet on a piezoelectric bimorph and a moving magnet. The latter is controlled through a low-frequency shaker at a fixed frequency of 3 Hz ( typical of human motion). The analysis shows that the activation of the first mode of vibration is linked to the velocity of the magnetic interaction. Also, inherent material nonlinearities appear as a frequency shift of the first mode on the Fast Fourier Transforms of the output voltage near short circuit condition
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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