Forecasting high waters at Venice Lagoon using chaotic time series analisys and nonlinear neural netwoks

Time series analysis using nonlinear dynamics systems theory and multilayer neural networks models have been applied to the time sequence of water level data recorded every hour at 'Punta della Salute' from Venice Lagoon during the years 1980-1994. The first method is based on the reconstruction of the state space attractor using time delay embedding vectors and on the characterisation of invariant properties which define its dynamics. The results suggest the existence of a low dimensional chaotic attractor with a Lyapunov dimension, DL, of around 6.6 and a predictability between 8 and 13 hours ahead. Furthermore, once the attractor has been reconstructed it is possible to make predictions by mapping local-neighbourhood to local-neighbourhood in the reconstructed phase space. To compare the prediction results with another nonlinear method, two nonlinear autoregressive models (NAR) based on multilayer feedforward neural networks have been developed. From the study, it can be observed that nonlinear forecasting produces adequate results for the 'normal' dynamic behaviour of the water level of Venice Lagoon, outperforming linear algorithms, however, both methods fail to forecast the 'high water' phenomenon more than 2-3 hours ahead.Publicad

Northern Adriatic general circulation behaviour induced by heat fluxes variations due to possible climatic changes

The thermohaline circulation of the central-north Adriatic basin is investigated by means of a 3D hydrodynamic numerical model. Three different runs — where the surface heat fluxes annual average is respectively negative, slightly positive and slightly negative — are performed; the general circulation patterns are then discussed and depicted, also with the aid of the trajectories of numerical particles released during the integrations. Results confirm that surface heat fluxes can start and trigger the general circulation in the basin (both vertically and horizontally), even without prescribing other forcings. Particularly, when the annual budget of the heat fluxes is negative (i.e. the basin loses heat to the atmosphere)a horizontal cyclonic surface circulation is generated, characterized by a northward flow along the eastern coast and a southward return current system along the western one. From the vertical point of view, an antiestuarine circulation is established. A similar circulation pattern is depicted when the surface fluxes have a slightly negative annual budget. On the other hand, when the annual fluxes balance is positive the vertical circulation switches to estuarine and, as expected, the integrated circulation becomes anticyclonic. A modification in the heat fluxes budget is strictly related to a change in the water column turnover time of the Jabuka pit, the deepest meso-Adriatic depression: when the annual heat fluxes balance is negative but close to zero, the dense-water residence time in the pit becomes minimum and the water has a shorter turnover time, denoting a faster renewal compared to those exhibited in the other experiments

The disastrous storm of 4 November 1966 on Italy

International audienceThis is the first modeling reconstruction of the whole aspects (both meteorological and oceanographic) of the storm which hit Italy on 4 November 1966, producing 118 victims and widespread damages in Tuscany, at the northern Adriatic coast and in the north-eastern Italian Alps. The storm was produced by a cyclone which formed in the western Mediterranean and moved eastward towards Italy, reaching the Thyrrenian Sea, and then northward. The most peculiar characteristic of the storm has been the strong zonal pressure gradient and the consequent intensity and long fetch of the south-easterly sirocco wind, which advected a large amount of warm moist air, and determined exceptional orographic precipitation over Tuscany and the north-eastern Alps. The funneling of the wind between the mountain chains surrounding the Adriatic basin further increased the wind speed and determined the highest ever recorded storm surge along the Venetian coast. This study shows that present models would be able to produce a reasonably accurate simulation of the meteorological event (surface pressure, wind and precipitation fields, and storm surge level). The exceptional intensity of the event is not suggested by single parameters such as the sea level pressure minimum, the wind speed or the total accumulated precipitation. In fact, the precipitation was extreme only in some locations and the pressure minimum was not particularly deep. Moreover, the prediction of the damages produced by the river run-off and landslides would have required other informations concerning soil condition, snow coverage, and storage of water reservoirs before the event. This indicates that an integrated approach is required for assessing the probability of such damages both on a weather forecast and on a climate change perspective

a decoupled numerical procedure for modelling soil interaction in the computation of the dynamic response of a rail track

Abstract The problem of vibration transmitted by train traffic to the soil in the case of railway lines in urban areas is gaining increasing attention in environmental impact analysis. An efficient method to consider both the train-track interaction in detail and the vibration transmitted to the soil nearby with an affordable computational cost is desirable. The paper proposes a numerical procedure based on a substructuring approach, in which the system is divided into three main subdomains: the train running on the track, the rail subjected to the loads coming from the train and the reactions from the sleepers and the "ground" sub-system, composed by the sleepers, the ballast with its subgrade and the actual ground. The overall procedure is divided into subsequent steps: first, the finite element modelling of the sleeper-ballast-subgrade combined system, characterized within the linear elastic field by means of frequency response functions at rail-sleeper interfaces. In a second step, moving loads transmitted to the track are computed by numerical time domain integration of the equations of motion of the train running on a model of the track only, in which the subgrade is modelled as a series of spring-damper elements, whose parameters are tuned according to the results of the FE model used in the first step and therefore consistent with it. Non-linear behavior of the rail-wheel interaction can be accounted for by the time-domain procedure. The track dynamics is finally computed via direct frequency domain analysis; the track is again modelled by Finite Elements, loaded by the forces transmitted by the train wheels and by the supporting sleepers. Finally, the vibrations propagated through the soil to a general receiver point are evaluated. The procedure can exploit favorable properties of frequency domain analysis in treating moving loads; in addition, frequency dependent properties of materials can be introduced

On the correct surface stress for the prediction of the wind wave field and the storm surge in the Northern Adriatic Sea

This paper discusses which formulation of the surface stress over the sea determines the most accurate prediction of the wind wave field and storm surge in the Northern Adriatic Sea. The study shows that the results of the storm surge and wind wave models, when compared to the available observations, can be used for the validation of the surface stress and of the expression adopted for the ssr (sea surface roughness). The results are representative of short fetch and young wind sea conditions. The agreement between the results and the measurements shows the feasibility of the wind wave and storm surge predictions in the Adriatic Sea and supports the dependence of the ssr, and, therefore, of the surface stress, on the spectrum of the surface wave

The effect of the boundary conditions on the simulation of the 4 November 1966 storm over Italy

This study analyses the extreme event which took place on 4 November 1966, when a storm produced intense and persistent precipitation over northern and central Italy and an extreme surge in the northern Adriatic Sea, causing casualties and huge damages. Numerical simulations with a regional atmospheric model have been performed to reconstruct the phenomenology of the event. Results have been compared with observations. This study shows that the choice of the global fields for initial and boundary conditions is crucial for the quality of the reconstruction. The simulation is reasonably accurate if they are extracted from the NCEP re-analysis, while it is not satisfactory if ERA-40 data are used, though fields have a higher resolution in the ERA-40 than in the NCEP set of data. The internal physics of the model plays a smaller role in the reproduction of the dynamics of the event

Quando la ricerca da pubblica si fa privata : innovazioni organizzative in un caso di studio

Lo studio dell'innovazione \ue8 un'area di ricerca in rapida crescita degli studi organizzativi. Tra i diversi punti di attenzione, la distinzione tra organizzazioni pubbliche e private ha rappresentato per lungo tempo uno dei temi maggiormente discussi. All'interno di questo ambito di studio, questo contributo si pone l'obiettivo di comprendere se la trasformazione di un istituto di ricerca da ente pubblico a fondazione privata costituisca di per s\ue9 un'innovazione organizzativa. Gli autori presentano uno studio di caso in cui vengono esplorate le dinamiche di trasformazione a partire da tre specifiche, ma interdipendenti, angolazioni: i processi di governance; l'introduzione del primo contratto collettivo di lavoro privato della ricerca; le procedure amministrative e contabili. L'ultima parte \ue8 dedicata a rispondere in modo complessivo alla domanda di ricerca alla base di questo studio

Forecasting high waters at Venice Lagoon using chaotic time series analysis and nonlinear neural networks

Time series analysis using nonlinear dynamics systems theory and multilayer neural networks models have been applied to the time sequence of water level data recorded every hour at 'Punta della Salute' from Venice Lagoon during the years 1980–1994. The first method is based on the reconstruction of the state space attractor using time delay embedding vectors and on the characterisation of invariant properties which define its dynamics. The results suggest the existence of a low dimensional chaotic attractor with a Lyapunov dimension, DL, of around 6.6 and a predictability between 8 and 13 hours ahead. Furthermore, once the attractor has been reconstructed it is possible to make predictions by mapping local-neighbourhood to local-neighbourhood in the reconstructed phase space. To compare the prediction results with another nonlinear method, two nonlinear autoregressive models (NAR) based on multilayer feedforward neural networks have been developed. From the study, it can be observed that nonlinear forecasting produces adequate results for the 'normal' dynamic behaviour of the water level of Venice Lagoon, outperforming linear algorithms, however, both methods fail to forecast the 'high water' phenomenon more than 2–3 hours ahead

Multibeam scanning antenna system based on beamforming metasurface for fast 5G NR initial access

Fifth-generation (and beyond) networks are characterized by ever more demanding requirements in terms of speed, bandwidth, and number of servable users. Fast and reliable access to the main network is mandatory, requiring technologies and procedures that ensure high performing cell search and initial access (IA). Existing phased array antennas (PAAs) are limited by the single beam scanning approach and complex feeding systems. In this paper, a beamforming metasurface that shifts the field manipulation from an electric level to an electromagnetic one is proposed for speeding up the IA procedure with respect to a traditional system using PAAs. The main advantage is given by the simultaneous transmission of multiple signals in different directions. The numerical results demonstrate that a much faster IA with similar success probability can be reached. Our system provides high gain, parallel computation, and scalability for larger systems, becoming a relevant candidate in the new radio and smart electromagnetic environment context

Aesthetic compatibility assessment of consolidants for wall paintings by means of multivariate analysis of colorimetric data

Background and methods: Wall paintings and architectural surfaces in outdoor environments are exposed to several physical, chemical and biological agents, hence they are often treated with different products to prevent or slow down their deterioration. Among the factors that have to be taken into account in the selection of the most suitable treatment for decorated surfaces, the aesthetic compatibility with the substrate is of great importance in the cultural heritage field; minimizing colour variation after treatment application is a crucial issue in particular for painted surfaces. In the framework of the European Project Nanomatch the color variation induced on wall painting mock-ups by the two innovative consolidants (calcium alkoxides) developed was evaluated using colorimetry in comparison with two traditional products. In this work these innovative consolidants have been also tested in combination with two commercial biocides and the results of colorimetric measurements discussed. Moreover, as the univariate approach didn't allow to draw clear conclusions on the relation between the different sources of data variability, multivariate analysis was performed on colorimetric data. Results: Principal Component Analysis and multi-way Parallel Factor Analysis (PARAFAC) were successfully applied to colorimetric data to investigate the short-term effects of the application of different consolidants on wall painting surfaces, making it possible to study at the same time the different sources of data variability, i.e. treatments, painting techniques, pigments. Finally, a ranking list of the treatments under study in terms of colour variation induced on the surface was established, in function of the painting technique and pigment, taking also in consideration the combination consolidant/biocide. In particular, given the true multi-way nature of the data, PARAFAC model turned out to be extremely useful in the study of the dependence of colour variation on pigments, a critical issue for painted surfaces, that was not clear using univariate approach. Conclusions: Multivariate approach to colorimetric data and especially 3-way PARAFAC method resulted a powerful technique to evaluate in short-term the color compatibility of consolidants for wall paintings, improving data interpretation and visualization, and thus outperforming the univariate statistical analysis