Platonic crystal with low-frequency locally resonant snail structures. Wave trapping, transmission amplification and shielding

We propose a new type of platonic crystal. The proposed microstructured plate includes snail resonators with low-frequency resonant vibrations. The particular dynamic effect of the resonators are highlighted by a comparative analysis of dispersion properties of homo- geneous and perforated plates. Analytical and numerical estimates of classes of standing waves are given and the analysis on a macrocell shows the possibility to obtain localization, wave trapping and edge waves. Applications include transmission amplification within two plates separated by a small ligament. Finally we proposed a design procedure to suppress low frequency flexural vibration in an elongated plate implementing a by-pass system re- routing waves within the mechanical system.Comment: 11 figures (20 files

A decision support system based on Electre III for safety analysis in a suburban road network

The aim of this paper is to develop a method for supporting decision makers in transport planning. When funds are insufficient to cover the interventions required to ensure safe driving conditions, it is necessary to optimize resources for the most critical sections. In this analysis, the multicriteria ranking method based on the ELECTRE III algorithms is applied to a real case, involving different sections of a motorway. This analysis is based on a comparison of different road sections in regard to safety conditions. The rank of more critical sections identifies intervention priorities

A decision support system for road safety analysis

The aim of this paper is to develop a procedure for supporting public administrations in planning safety interventions on the road network. Road safety conditions depend on several factors, represented by a variety of quantitative and qualitative data, including: number of traffic accidents, traffic flow, lane width, shoulder width, road curvature and grade, access-point density, road markings and road signs (Mooren et al., 2012; OECD, 2002). By analysing a set of given roads or different sections of the same road, each with specific safety conditions, this methodology allows to determine which sections require interventions to improve safe driving conditions. Specifically, the multicriteria analysis technique is used in decision-making processes to support the choice among different alternatives in complex problems (Fadda, 2002). Among the different multicriteria techniques available, the Concordance Analysis will be used here. This paper proposes a unique modelling tool that incorporates the different indicators to calculate safety conditions. The methodology has been applied to a real case study for evaluating road safety on sections of a motorway infrastructur

Drag-free estimation feasibility study

A drag compensation system for solar probes and other spacecraft that require a drag-free capability is presented. Estimation techniques, derived from modern control theory, are proposed

Elastic wave propagation and stop-band generation in strongly damaged solids

In this work, we study the propagation of elastic waves in elongated solids with an array of equallyspaced deep transverse cracks, focusing in particular on the determination of stop-bands. We consider solids with different types of boundary conditions and different lengths, and we show that the eigenfrequencies associated with non-localized modes lie within the pass-bands of the corresponding infinite periodic system, provided that the solids are long enough. In the stop-bands, instead, eigenfrequencies relative to localized modes may be found. Furthermore, we use an asymptotic reduced model, whereby the cracked solid is approximated by a beam with elastic connections. This model allows to derive the dynamic properties of damaged solids through analytical methods. By comparing the theoretical dispersion curves yielded by the asymptotic reduced model with the numerical outcomes obtained from finite element computations, we observe that the asymptotic reduced model provides a better fit to the numerical data as the slenderness ratio increases. Finally, we illustrate how the limits of the stop-bands vary with the depth of the cracks

Forcing the silence of the Lamb waves: Uni-directional propagation in structured gyro-elastic strips and networks

In this paper, we propose an innovative design of an elastic network, which is capable of channelling the energy supplied by an external source towards any of its endpoints, that can be chosen arbitrarily and in advance. This system, named Mechanical Switching Network (MSN), consists of an interconnected array of branches, each of which is represented by a lattice strip endowed with gyroscopic spinners. The latter make the system non-reciprocal and, hence, are responsible for the preferential directionality exhibited by the network. We formulate and solve the forced problem for the gyro-elastic strip in the analytical form and compare the derived solutions with the results of independent finite element simulations, showing an excellent agreement. Additionally, we carry out a parametric analysis to evaluate the influence of the main parameters of the system on the uni-directional wave propagation of Lamb waves. We envisage that the proposed model can have important implications in many engineering applications, where control and tunability of guided waves play a key role

Lamb waves in discrete homogeneous and heterogeneous systems: Dispersion properties, asymptotics and non-symmetric wave propagation

In this paper, we study Lamb waves propagating in a discrete strip, whose microstructure is represented by either a monatomic or a diatomic triangular lattice. In considering the in-plane vector problem, we derive an analytical solution for the dispersion relation of Lamb waves. Additionally, we investigate the main features of the eigenmodes of the system, which describe how the lattice strip vibrates at different frequencies. Further, we discuss how the dispersion properties depend on the number of the lattice's rows and on the chosen boundary conditions. For heterogeneous systems, we focus the attention on the internal stop-band and on the flat bands appearing in the dispersion diagram. Different asymptotic models are employed to approximate the low-frequency behaviour of the lattice strip, starting from the classical Euler–Bernoulli beam. The effective behaviour of a lattice strip with dense microstructure is also investigated, and we present a comparative numerical analysis with the analogous continuum for which the classical Lamb wave problem is posed. The theory developed is exploited here to design a structured medium capable of manipulating wavemodes, and, through conversion and selection, generating uni-directional wave phenomena. We envisage that the present work can fill a gap in the research field related to the analytical study of dispersive waves in microstructured media, whose dynamic performance is influenced by the presence of multiple external boundaries

Aggiornamenti e novità sulla distribuzione del genere Gagea (Liliaceae) in Toscana

Viene confermata la presenza di Gagea bohemica (zauschn.) Scuhlt. & Schult. f. nell’unica località nota per la Toscana (isola d’Elba) e di G. granatellii (Parl.) Parl. all’isola del Giglio, dove da oltre 100 anni la specie non era stata più osservata. Vengono anche segnalate nuove località di G. granatellii nella porzione centrale e orientale dell’isola d’Elba, nonché di G. lutea (L.) Ker-Gawl. e di G. pratensis (Pers.) Dumort. nella Toscana settentrionale (Pracchie di Pontito e Monte Morello, rispettivamente)

Scattering reduction and resonant trapping of flexural waves: Two rings to rule them

In this paper, we discuss two problems concerning scattering and localisation of flexural waves in structured elastic plates. Firstly, we compare the scattering amplitudes of waves in a thin plate, generated by a point source, due to a single mass and to a large number of smaller masses, having the same equivalent mass and located around a circle. We show that in the second case, the scattering can be reduced, in particular in the medium-and high-frequency regimes. Secondly, we develop a homogenised model for a double-ring cluster of spring-mass resonators, connected to an elastic thin plate. We determine the conditions for which the plate exhibits vibration modes trapped between the two rings. Further, we show that the frequencies of the localised modes can be tuned by varying the geometry of the two rings and the characteristics of the resonators. The analytical results are corroborated by numerical simulations performed with independent finite element models