The seismic performance of a earth dam by different displacementbased methods

The performance-based design of earth dams and the rehabilitation of existing ones require the evaluation of seismic performance based on permanent displacements caused by expected the earthquake. The paper reports a comparison between different methods with increasing complexity for estimating seismic displacements: simplified rigid block method, based on empirical relationships (Bray and Rathje, 1998; Tropeano et al., 2009); simplified uncoupled method, again based on the sliding block analysis, but accounting for soil deformability; coupled ‘stick-slip’ approach, based on a 1D lumped mass model to calculate together dynamic response of the site and movement of sliding block (Tropeano et al., 2011); 2D finite differences analyses by the FLAC code, reproducing the heterogeneity of soil and topographic effects. The methods were applied to the case of the dam of Marello mountain across the Angitola river (Southern Italy). The parameters for static and dynamic geotechnical characterization of subsoil model have been taken from the results of the site investigation published in technical reports. The spectral shape and peak ground acceleration specified by the Italian Seismic Hazard Map, representative of input motion on outcropping bedrock, allowed to choose a set of spectrum-compatible acceleration time histories to simulate the seismic input. The sliding displacements predicted using simplified method resulted strongly dependent on topographic coefficient. Both uncoupled and coupled approaches have shown conservative permanent displacements compared to Newmark method. The average displacement of the sliding block by two-dimensional finite difference analysis, considering the stiffness variability related to depth, results comparable with values obtained by other methods

Le tecniche di indagine NDT nel processo di restauro e consolidamento di edifici soggetti a tutela

Le attività di restauro e consolidamento di edifici soggetti a tutela sono fortemente ancorate alla conoscenza del bene, alla consistenza geometrico-strutturale e a quella materica, nonché all’analisi del degrado del manufatto e del suo stato di conservazione in tutti i suoi elementi. Altri aspetti tecnici da portare in conto sono ovviamente quelli legati al monitoraggio da attuare eventualmente in fase di diagnosi e obbligatoriamente in fase di esercizio, al fine di disporre di una robusta mole di dati per governare l’attività manutentiva. Un valido supporto all’insieme di queste problematiche è offerto oggi dalle tecniche non distruttive (NDT), le quali si inseriscono sia nel processo di screening conoscitivo del manufatto che nel processo di progettazione, di realizzazione degli interventi e di vita utile del bene. In questo contesto, la presente nota illustra una panoramica di alcune delle moderne tecniche di indagine NDT impiegate nelle attività di rilievo, di valutazione dello stato dei materiali e nelle attività di monitoraggio sia propedeutiche alla redazione del progetto, sia nel corso dell’esercizio. In riferimento a quest’ultimo aspetto, le tecniche illustrate mirano ad essere parte integrante di una metodologia di controllo "routinaria" da esercitare in continuo e con la possibilità di essere interrogabile anche in tempo reale. Alcuni esempi applicativi qui riportati, seppur in forma sintetica, consentiranno di apprezzare i benefici derivanti dall'utilizzo di tecniche NDT, il cui punto di forza risiede soprattutto nel loro essere non invasive e autodiagnosticanti

Innovative 3-D Printing Processing Techniques for Flexible and Wearable Planar Rectennas

This work demonstrates the use of a low-cost, lossy, flexible substrate processed by novel 3-D printing techniques which significantly mitigate its intrinsic losses, thus providing performance comparable to those of traditional substrates. These processing techniques are applied to both microstrip and coplanar waveguide structures; they are first derived theoretically, starting from the electromagnetic theory of modes propagation, then numerically validated by full-wave analysis, and finally experimentally verified. The design of a miniaturized 868 MHz rectenna, adopting a coplanar-fed patch antenna based on the proposed fabrication approach, is presented. By means of nonlinear/electromagnetic co-design, the antenna is directly matched to the rectifier. A 30-dB power range starting from -20 dBm is considered. Direct matching allows to get rid of a dedicated matching network and its associated losses, resulting in a slight efficiency increase and a significant reduction of the overall dimensions. Finally, the 3-Dprinted prototype is presented: the overall rectenna performance proves that design freedom enabled by 3-D printing paves the way to the use of low-cost flexible dielectric materials, even with poor electromagnetic properties, to realize wearable battery-free wireless nodes

Valutazione degli spostamenti permanenti sismoindotti mediante un approccio accoppiato non lineare

Le procedure per valutare lo spostamento che può subire un pendio sotto l’azione sismica tipicamente si riferiscono a tre diverse classi di metodi: 1) relazioni semplificate; 2) metodi degli spostamenti (o analisi dinamica semplificata) e 3) analisi dinamica avanzata. Tali approcci differiscono sostanzialmente dal grado di conoscenza del modello geotecnico del pendio e dell’azione sismica richiesta. In particolare, la seconda classe di metodi presenta un buon compromesso tra la facilità di applicazione, legata a schemi di pendio semplificati, e l’affidabilità dei risultati che rende tali metodi competitivi rispetto alle analisi dinamiche avanzate. I metodi degli spostamenti prendono origine dal modello di blocco rigido di Newmark (1965) e dalla rimozione delle ipotesi che ne stanno alla base. In particolare l’ipotesi stessa di “blocco rigido” può essere rimossa attraverso due approcci: a) approccio “disaccoppiato”, in cui la deformabilità dei terreni che causa la risposta dinamica del sito e gli spostamenti del blocco sono calcolati separatamente o b) approccio “accoppiato” in cui la risposta del sito è valutata contemporaneamente nelle fasi di adesione e scorrimento del pendio. In questa nota, si sintetizzano gli sviluppi del codice ACST, implementato da Ausilio et al. (2008), effettuati nell’ambito del progetto ReLUIS MT 1.2 “Linee guida e codici per analisi di risposta sismica locale”. In particolare, si è introdotta la non linearità nell’analisi della risposta dei terreni attraverso la formulazione modificata dei criteri di Masing secondo la recente formulazione di Phillips & Hashash (2009). Si è, inoltre, implementata una procedura che permette di individuare automaticamente, durante il calcolo, la superficie di scorrimento di prima rottura. I risultati in termini di risposta sismica e spostamenti cumulati sono stati confrontati con quelli ottenuti con la prima versione del codice

Beyond the fundamental noise limit in coherent optical fiber links

It is well known that temperature variations and acoustic noise affect ultrastable frequency dissemination along optical fiber. Active stabilization techniques are in general adopted to compensate for the fiber-induced phase noise. However, despite this compensation, the ultimate link performances remain limited by the so called delay-unsuppressed fiber noise that is related to the propagation delay of the light in the fiber. In this paper, we demonstrate a data post-processing approach which enables us to overcome this limit. We implement a subtraction algorithm between the optical signal delivered at the remote link end and the round-trip signal. In this way, a 6 dB improvement beyond the fundamental limit imposed by delay-unsuppressed noise is obtained. This result enhances the resolution of possible comparisons between remote optical clocks by a factor of 2. We confirm the theoretical prediction with experimental data obtained on a 47 km metropolitan fiber link, and propose how to extend this method for frequency dissemination purposes as well

Application of NASTRAN/COSMIC in the analysis of ship structures to underwater explosion shock

The application of NASTRAN/COSMIC in predicting the transient motion of ship structures to underwater, non-contact explosions is discussed. Examples illustrate the finite element models, mathematical formulations of loading functions and, where available, comparisons between analytical and experimental results

High homogeneity solenoidal magnet for cesium frequency standard

In Cs frequency standards a zone of highly uniform magnetic flux density, lower in value of 0.1 T, is required. The magnetic homogeneity value is tied to the overall accuracy of the standard and, for an accuracy of 10-14, a design value 1 p.p.m. is required. For this purpose a resistive solenoid 700 mm long with a bore radius of 32.5 mm has been designed and built. This paper reports the design process, the measurements on the manufactured magnet and the shimming strategy used to reach the homogeneity target

Tactile sensors for parallel grippers: Design and characterization

Tactile data perception is of paramount importance in today’s robotics applications. This paper describes the latest design of the tactile sensor developed in our laboratory. Both the hardware and firmware concepts are reported in detail in order to allow the research community the sensor reproduction, also according to their needs. The sensor is based on optoelectronic technology and the pad shape can be adapted to various robotics applications. A flat surface, as the one proposed in this paper, can be well exploited if the object sizes are smaller than the pad and/or the shape recognition is needed, while a domed pad can be used to manipulate bigger objects. Compared to the previous version, the novel tactile sensor has a larger sensing area and a more robust electronic, mechanical and software design that yields less noise and higher flexibility. The proposed design exploits standard PCB manufacturing processes and advanced but now commercial 3D printing processes for the realization of all components. A GitHub repository has been prepared with all files needed to allow the reproduction of the sensor for the interested reader. The whole sensor has been tested with a maximum load equal to 15 N, by showing a sensitivity equal to 0.018 V/N. Moreover, a complete and detailed characterization for the single taxel and the whole pad is reported to show the potentialities of the sensor also in terms of response time, repeatability, hysteresis and signal to noise ratio