158 research outputs found
Numerical simulation of real debris-flows events
No full textA one-dimensional model is presented to
predict debris-flow runouts. The model is based on shallow
water type assumptions. The fluid is assumed to be
homogeneous and the original bed of the flow domain to be
unerodible. The fluid is characterized by a rheology of
Bingham type.
A numerical tool able to cope with the nature of debris
flows has been worked out. It represents an extension of a
second order accurate and conservative method of
Godunov type. Special care has been devoted to the
influence of the source terms and of the geometrical
representation of the natural cross sections, which play a
fundamental role.
The application concerns a monitored event in the
Dolomites in Italy, where field analyses allowed a
characterization of the behavior of solid-liquid mixture as a
yield stress material. The comparison between numerical
simulations and field observations highlights the
impossibility of representing all phases of the flow with
constant values of the rheological parameters. Nevertheless
the results show that it is possible to separately represent
the phase of the flow in the upstream reach and the phase of
the deposition in the alluvial fan, with a good agreement
with field observations
Ab initio modeling of 2D and quasi-2D lead organohalide perovskites with divalent organic cations and a tunable band gap
No full textWe describe theoretically the structure and properties of layered lead organohalide perovskites, considering purely bi-dimensional (2D) PbI4 layers, and quasi-2D systems where the inorganic layers are formed by more than one lead iodide sheet. The intercalating organic dications were designed to have low lying virtual orbitals (LUMO), so as to induce in the perovskite the appearance of virtual bands, localized in the organic layer, either close to the inorganic conduction band bottom or valence band top, or in some cases in the middle of the inorganic band gap. Such a feature is quite uncommon for this class of materials, and deserves attention since it allows one to tune the effective band gap of the material, possibly leading to the absorption of visible light and influencing the optical properties deeply. We discuss the effect of functional groups on the organic cations, and of the different symmetries used in geometry optimizations: a careful analysis of the contributions to the dispersion curves and band gaps was performed. The charge carrier mobility is also discussed, computing the conductivity over relaxation time and the effective masses for all the systems, with particular attention to the features related to the unusual organic intra-gap bands. All the structures were optimized at the DFT level, with inclusion of dispersion effects; dispersion curves were computed with full relativistic potentials, and the band gaps corrected for long range coulombic effects at the GW level. A semiempirical approach, based on the integration of charge carrier group velocities over a dense grid of k-points, was used to compute the conductivities and effective masses
Experimental and numerical characterization of a gravitational electromagnetic energy harvester
No full textIn this paper, the dynamic experimental identification of an inductive energy harvester for the conversion of vibration energy into electric power is presented. Recent advances and requirements in structural monitoring and vehicle diagnostic allow defining Autonomous Internet of Things (AIoT) systems that combine wireless sensor nodes with energy harvester devices properly designed considering the specific duty cycle. The proposed generator was based on an asymmetrical magnetic suspension and was addressed to structural monitoring applications on vehicles. The design of the interfaces of the electric, magnetic, and structural coupled systems forming the harvester are described including dynamic modeling and simulation. Finally, the results of laboratory tests were compared with the harvester dynamic response calculated through numerical simulations, and a good correspondence was obtained
Rheological stratification in experimental free-surface flows of granular-liquid mixtures
No full textPiezoelectric energy harvesting for autonomous sensors network on safety-improved railway vehicles
No full text Mechanical vibrations of railway vehicles were converted to electric power by means of a piezoelectric energy harvester, a rectification circuit, and a storage battery. The power harvested is used to supply one node of a sensor network for the structural monitoring and safety improvement on railway vehicles. The dynamic dimensioning of the piezoelectric generator is presented, for the mechanical and electric viewpoints; the resonance tuning is described and the experimental validation of the performances of the node is provided. The tests were conducted on a scaled railway bogie, which is able to simulate the real working conditions of a train. The efficiency and the duty cycle of the autonomous sensing platform are measured. </jats:p
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