1,721,068 research outputs found
A theoretical model and experimental validation of the oscillations of a para- or dia-magnetic beam subject to the effects of passive magnetic elements
No full textEdge states and topological pumping in stiffness-modulated elastic plates
Full text linkWe demonstrate that modulations of the stiffness properties of an elastic plate along a spatial dimension induce edge states spanning nontrivial gaps characterized by integer-valued Chern numbers. We also show that topological pumping is induced by smooth variations of the phase of the modulation profile along one spatial dimension, which results in adiabatic edge-to-edge transitions of the edge states. The concept is first illustrated numerically for sinusoidal stiffness modulations and then experimentally demonstrated in a plate with square-wave thickness profile. The presented numerical and experimental results show how continuous modulations of properties may be exploited in the quest for topological phases of matter. This opens new possibilities for topology-based waveguiding through slow modulations along a second dimension, spatial or temporal
Adiabatic sound transport in acoustic waveguides with time-varying Helmholtz resonators
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Evaluation of a road bridge dynamic response to ambient excitation by wavelet and other estimation techniques
No full textA dynamic test was performed over a bridge located in northern Italy. The dynamic measures were analyzed by means of four different techniques to seek for the best algorithm within those appropriate for the identification of dynamic systems excited by unknown input. The bridge under test was excited by the flowing traffic and by some other unmeasured excitations as wind or other ground micromovements. A finite element model was set up using eight nodes brick elements based only on a rough sketch of the bridge which was used to optimize the position of the reference accelerometers
Oberst beam test technique
No full textThe definition of the mechanical properties of viscoelastic materials, i.e. the elastic modulus and the loss factor, is carried out, according to many national and international standards, with many different techniques, both of the resonant and non-resonant type. In this paper we focus our attention on the pros and cons of the resonant technique based on the classical Oberst beam method. When the damping material to be tested is not self-supporting, its properties are determined taking start from the measured modal frequencies and loss factors of a laminated beam, constituted by one or two metallic strips, ideally undamped, and one or two viscoelastic layers. The formulae specified on the standards hold valid under the assumptions of the theory developed by Kerwin, Ungar and Ross and we try in this paper to quantify witch deviation of the results should be expected when moving away from their ideal hypotheses
A physical interpretation for broken reciprocity in spatiotemporal modulated periodic rods
No full textPeriodic systems have long been known for their peculiar characteristics in wave propagation and have been studied in many fields over the last century, going from electro-magnetics and optics to elastic structures, which drew an increasing interest in structural and mechanical engineering for vibration suppression and control spanning over broadband frequency ranges. Recently, on the stream of other studies conducted in different fields, spatiotemporal modulated elastic structures have been studied, showing promising results for wave control in that one-way propagation in the so called directional-bands can be achieved, constituting what may be called a mechanical diode. Despite of the fact that mathematical methods for the analysis of such structures have already been developed, often physics behind them is difficult to grasp. In this work, a simplified interpretation of the undergoing phenomena is thus given relating wave propagation in the mean to its physical characteristics as well as to modulation parameters. Exploiting Doppler effect and passive equivalent structures, it is shown that the broken reciprocity is due to the fact that opposite travelling waves effectively see two different periodic structures. To this aim the rod case is analysed for low modulation speeds and low modulation amplitudes; finally, in the light of the previous analysis, an explanation for First Brillouin Zone's asymmetry is given
Identification of the dynamic behavior of bridges under ambient excitation using wavelet transform
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