1,720,968 research outputs found
Modello di hindcast del moto ondoso negli ultimi 10 anni: metodo statistico, probabilistico e stocastico applicato al Mar Ligure,
No full textGEMS: underwater spectrometer for long-term radioactivity measurements
No full textGEMS (Gamma Energy Marine Spectrometer) is a prototype of an autonomous radioactivity sensor for underwater measurements, developed in the framework of the KM3NeT Design Study (DS) EC project. The spectrometer is sensitive to gamma rays produced by 40K decays and it is also able to detect other natural (e.g., 238U, 232Th) and anthropogenic radionuclides (e.g. 137Cs). The decay of 40K, contained in sea salt, particulate and sediments, is one of the main sources of photon background in the underwater environment. GEMS was first calibrated in the laboratory using known sources, also in order to evaluate the performance of the instrument. In November 2008 GEMS was deployed at a depth of 3200 m in the area of Capo Passero (in the Ionian Sea) to acquire data autonomously. After recovery of the spectrometer six months later (May 2009) it was found that the instrument had worked within the specifications and acquired data over the full deployment period. These data allowed us to investigate over a long period the possible variations of activity at the Capo Passero site. GEMS is suitable to be used either in autonomous mode or as payload of seafloor observatories or vehicles
Modellistica di previsione e reanalisi per l'ingegneria marittima
No full textLe necessità progettuali e l’avanzamento della ricerca nel campo dell’Ingegneria Marittima hanno fatto sì che nelle ultime decadi ci sia stata una tendenza sempre maggiore a supportare le attività progettuali e di ricerca sia con modelli sperimentali di laboratorio che con simulazioni numeriche. Quest’ultime stanno trovando sempre maggior impiego soprattutto grazie a un aumento significativo delle prestazioni di calcolo e della ricerca nell’ambito della simulazione numerica della meccanica dei fluidi. Inoltre lo sviluppo di sistemi di misura diretti e indiretti di grandezze quali il moto ondoso e le correnti marine, ha messo a disposizioni basi di dati solide e affidabili con cui verificare e validare i modelli numerici.
In quest’ottica presso il Dipartimento di Ingegneria Civile, Chimica e Ambientale (DICCA) dell’Università di Genova è stata sviluppata e validata un catena modellistica per la simulazione della generazione e propagazione del moto ondoso all’interno del bacino del Mediterraneo (www.dicca.unige.it/meteocean). Tale strumento viene impiegato sia a scopo previsionale, quindi per poter fornire informazioni sullo stato del mare a breve termine, sia per attività di reanalisi del clima ondoso, rendendo così possibile la stima delle caratteristiche del moto ondoso a lungo termine
Evaluating third generation wave spectral models performances in coastal areas. An application to Eastern Liguria.
No full textMoto ondoso e valori estremi: una reanalisi lungo le coste italiane.
No full textIl presente lavoro si colloca nell'ambito dell'analisi dei valori estremi (Extreme Value Theory - EVT) applicata all'ingegneria marittima e costiera. Gli aspetti maggiormente critici di tale materia consistono nella disponibilità di dati di qualità relativi al moto ondoso e nella possibilità di utilizzo dei diversi modelli statistici proposti in letteratura. In particolare, nell'ambito della presente ricerca, sono stati passati in rassegna i principali contributi scientifici, partendo dalle teorie più tradizionali, per poi tenere in conto quelle più avanzate (Tancredi et al., 2006; Wadsworth et al., 2010; MacDonald et al., 2011), evidenziandone le principali peculiarità. Inoltre sono state esposte anche alcune considerazioni sull'utilizzo nell'ambito della EVT dei modelli dipendenti da soglia (Méndez et al., 2006; Hawkes et al., 2008) e delle tecniche basate su massimi identicamente distribuiti (Cañellas et al., 2007)
How an optimized meteocean modelling chain provided 30 years of wave hindcast statistics: the case of the Ligurian Sea.
No full textSUB-MESOSCALE WAVE HEIGHT RETURN LEVELS ON THE BASIS OF HINDCAST DATA: THE NORTH TYRRHENIAN SEA
No full textA 32-years wave re-analysis has been employed in order to develop an extreme value analysis for the whole Ligurian Sea (North Tyrrhenian Sea). Wave hindcast data have been obtained through numerical modelling implemented at DICCA, University of Genoa, covering the whole Mediterranean Sea. Model outputs for wave characteristics (wave height, period and direction of propagation) have been extracted on 30 virtual buoys displaced in the area covering the whole temporal domain (32-years) at hourly frequency in order to develop an exhaustive wave climate analysis. A non stationary model is presented and applied in wave climate assessment with the purpose of taking account for the effects of seasonality in providing return level estimates. Time-varying model employed proved to be versatile in modelling different wave fields largely diversified in such kind of area and wave hincast data apply well in order to perform waves statistical downscaling
Wave hindcast resolution reliability for extreme analysis
No full textHere we analyze the wave hindcast reliability for a proper description of wave climate in the Mediterranean Sea. To this aim, 6-hourly 35-years ECMWF (European Center Medium Weather Forecast) wave data at 0.7° resolution grid are compared with those provided by means of a meteocean modelling chain operative at DICCA, University of Genoa (http://www.dicca.unige.it/meteocean/) covering a 34-years temporal span at an hourly frequency on a 0.1° resolution domain. Results reveal not negligible differences in evaluating significant wave heights at peaks; in particular the tendency to underrate values in storm sea conditions performed by ECMWF dataset is here evidenced. This behavior turns directly into not-reliable long-term return level estimates for extreme wave analysis, leading to a weak description of wave climate; conversely, a wave climate robust assessment is of primary importance for maritime design
Wave hindcast resolution reliability for extreme analysis
No full textHere we analyze the wave hindcast reliability for a proper description of wave climate in the Mediterranean Sea. To this aim, 6-hourly 35-years ECMWF (European Center Medium Weather Forecast) wave data at 0.7° resolution grid are compared with those provided by means of a meteocean modelling chain operative at DICCA, University of Genoa (http://www.dicca.unige.it/meteocean/) covering a 34-years temporal span at an hourly frequency on a 0.1° resolution domain. Results reveal not negligible differences in evaluating significant wave heights at peaks; in particular the tendency to underrate values in storm sea conditions performed by ECMWF dataset is here evidenced. This behavior turns directly into not-reliable long-term return level estimates for extreme wave analysis, leading to a weak description of wave climate; conversely, a wave climate robust assessment is of primary importance for maritime design
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No full textA nonstationary model based on a time-dependent version of the Generalized Pareto Distribution (GPD)-Poisson point process model has been implemented and applied to model extreme wave heights in the Mediterranean basin. Thirty-two years of wave hindcast data have been provided by a forecast/hindcast numerical chain model operational at the University of Genoa (www.dicca.unige.it/meteocean). The nonstationary behavior of wave height maxima prompted the modeling of GEV parameters with harmonic functions. Harmonics have been introduced to model seasonal cycles within a year, also taking into account long-term trend and covariates effects. The model has been applied on eight locations corresponding to buoys belonging to the RON (Rete Ondametrica Nazionale), chosen in order to represent best the main features and variability of waves along the Italian coast. The best performing model is chosen among a large set of possible candidates identified by different combinations of wave heights maxima and model parameters. Direct comparison with stationary results has been performed; furthermore, the model has demonstrated a good performance in gathering different seasonal behaviors related to the main meteorological forcing standing on the Mediterranean Sea. Trends related to extreme significant wave heights have also been evaluated in order to offer some insight into decadal-scale wave climate. Results achieved show how the use of a nonstationary statistical model together with the analysis of the main meteorological forcings characterizing the area could prove useful in understanding wave climate related to atmospheric dynamics
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