1,721,273 research outputs found
VISIR-I: small vessels – least-time nautical routes using wave forecasts
Full text linkA new numerical model for the on-demand computation of optimal ship routes based on sea-state forecasts has been developed. The model, named VISIR (discoVerIng Safe and effIcient Routes) is designed to support decision-makers when planning a marine voyage.
The first version of the system, VISIR-I, considers medium and small motor vessels with lengths of up to a few tens of metres and a displacement hull. The model is comprised of three components: a route optimization algorithm, a mechanical model of the ship, and a processor of the environmental fields. The optimization algorithm is based on a graph-search method with time-dependent edge weights. The algorithm is also able to compute a voluntary ship speed reduction. The ship model accounts for calm water and added wave resistance by making use of just the principal particulars of the vessel as input parameters. It also checks the optimal route for parametric roll, pure loss of stability, and surfriding/broaching-to hazard conditions. The processor of the environmental fields employs significant wave height, wave spectrum peak period, and wave direction forecast fields as input. The topological issues of coastal navigation (islands, peninsulas, narrow passages) are addressed.
Examples of VISIR-I routes in the Mediterranean Sea are provided. The optimal route may be longer in terms of miles sailed and yet it is faster and safer than the geodetic route between the same departure and arrival locations. Time savings up to 2.7 % and route lengthening up to 3.2 % are found for the case studies analysed. However, there is no upper bound for the magnitude of the changes of such route metrics, which especially in case of extreme sea states can be much greater. Route diversions result from the safety constraints and the fact that the algorithm takes into account the full temporal evolution and spatial variability of the environmental fields
A General Methodology for Beached Oil Spill Hazard Mapping
Full text linkThe current lack of a standardized approach to compute the coastal oil spill hazard due to maritime traffic accidental releases has hindered an accurate estimate of its global impact, which is paramount to manage and intercompare the associated risks. We propose here a hazard estimation approach that is based on ensemble simulations and the extraction of the relevant distributions. We demonstrate that both open ocean and beached oil concentration distributions fit a Weibull curve, a two-parameter fat-tail probability distribution function. The simulation experiments are carried out in three different areas of the northern Atlantic. An indicator that quantify the coastal oil spill hazard is proposed and applied to the study areas
Storm Surge Ensemble Prediction System for Lagoons and Transitional Environments
Full text linkWe developed a storm surge ensemble prediction system (EPS) for lagoons and transitional environments. Lagoons are often threatened by storm surge events with consequent risks for human life and economic losses. The uncertainties connected with a classic deterministic forecast are many, thus, an ensemble forecast system is required to properly consider them and inform the end-user community accordingly. The technological resources now available allow us to investigate the possibility of operational ensemble forecasting systems that will become increasingly essential for coastal management. We show the advantages and limitations of an EPS applied to a lagoon, using a very high-resolution unstructured grid finite element model and 45 EPS members. For five recent storm surge events, the EPS generally improves the forecast skill on the third forecast day compared to just one deterministic forecast, while they are similar in the first two days. A weighting system is implemented to compute an improved ensemble mean. The uncertainties regarding sea level due to meteorological forcing, river runoff, initial boundaries, and lateral boundaries are evaluated for a special case in the northern Adriatic Sea, and the different forecasts are used to compose the EPS members. We conclude that the largest uncertainty is in the initial and lateral boundary fields at different time and space scales, including the tidal components
Drift simulation of MH370 debris using superensemble techniques
Full text linkOn 7 March 2014 (UTC), Malaysia Airlines flight 370 vanished without a trace.
The aircraft is believed to have crashed in the southern Indian Ocean, but
despite extensive search operations the location of the wreckage is still
unknown. The first tangible evidence of the accident was discovered almost
17 months after the disappearance. On 29 July 2015, a small piece of the right
wing of the aircraft was found washed up on the island of Réunion,
approximately 4000 km from the assumed crash site. Since then a number of
other parts have been found in Mozambique, South Africa and on Rodrigues Island.
This paper presents a numerical simulation using high-resolution
oceanographic and meteorological data to predict the movement of floating
debris from the accident. Multiple model realisations are used with different
starting locations and wind drag parameters. The model realisations are
combined into a superensemble, adjusting the model weights to best represent
the discovered debris. The superensemble is then used to predict the
distribution of marine debris at various moments in time. This approach can
be easily generalised to other drift simulations where observations are
available to constrain unknown input parameters.
The distribution at the time of the accident shows that the discovered debris
most likely originated from the wide search area between 28 and
35° S. This partially overlaps with the current underwater search
area, but extends further towards the north. Results at later times show that
the most probable locations to discover washed-up debris are along the
African east coast, especially in the area around Madagascar. The debris
remaining at sea in 2016 is spread out over a wide area and its distribution
changes only slowly
Coppini and Pinardi are contributing authors
No full textnot availableEuropean Environment Agency and European Topic Centre on WaterPublished4.6. Oceanografia operativa per la valutazione dei rischi in aree marineope
Coppini and Pinardi are contributing authors
No full textnot availableEuropean Environment Agency and European Topic Centre on WaterPublished4.6. Oceanografia operativa per la valutazione dei rischi in aree marineope
IT-OSRA: applying ensemble simulations to estimate the oil spill risk associated to operational and accidental oil spills
Full text linkOil Spill Risk Assessments (OSRAs) are widely employed to support decision making regarding oil spill risks. This article adapts the ISO-compliant OSRA framework developed by Sepp Neves et al. (J Environ Manag 159:158–168, 2015) to estimate risks in a complex scenario where uncertainties related to the meteo-oceanographic conditions, where and how a spill could happen exist and the risk computation methodology is not yet well established (ensemble oil spill modeling). The improved method was applied to the Algarve coast, Portugal. Over 50,000 simulations were performed in 2 ensemble experiments to estimate the risks due to operational and accidental spill scenarios associated with maritime traffic. The level of risk was found to be important for both types of scenarios, with significant seasonal variations due to the the currents and waves variability. Higher frequency variability in the meteo-oceanographic variables were also found to contribute to the level of risk. The ensemble results show that the distribution of oil concentrations found on the coast is not Gaussian, opening up new fields of research on how to deal with oil spill risks and related uncertaintie
Multi-nest high-resolution model of submesoscale circulation features in the Gulf of Taranto
Full text linkRecent oceanographic field measurements and high-resolution numerical modelling studies have revealed intense, transient, submesoscale motions characterised by a horizontal length scale of 100 - 10,000 m. This submesoscale activity increases in the fall and winter when the mixed layer (ML) depth is at its maximum. In this study, the submesoscale motions associated with a large-scale anticyclonic gyre in the central Gulf of Taranto were examined using realistic submesoscale-permitting simulations. We used realistic flow field initial conditions and multiple nesting techniques to perform realistic simulations, with very-high horizontal resolutions (> 200 m) in areas with submesoscale variability. Multiple downscaling was used to increase resolution in areas where instability was active enough to develop multi-scale interactions and produce 5-km-diameter eddies. To generate a submesoscale eddy, a 200-m resolution was required. The submesoscale eddy was formed through small-scale baroclinic instability in the rim of a large-scale anticyclonic gyre leading to large vertical velocities and rapid restratification of the ML in a time-scale of days. The submesoscale eddy was confirmed by observational data from the area and we can say that for the first time we have a proof that the model reproduces a realistic submesoscale vortex, similar in shape and location to the observed one
Very Large Ensemble Ocean Forecasting Experiment Using the Grid Computing Infrastructure
No full textA box model to represent estuarine dynamics in mesoscale resolution ocean models
Full text linkRepresenting the net freshwater flux at river mouths is challenging for global and regional scale ocean modelling. Although rivers are well known to affect both the coastal and basin-wide circulation and dynamics, coarse resolution ocean models cannot resolve the estuarine dynamics and are usually forced at river outlets in a simplistic way, with climatological runoff and zero or constant salinity values. The aim of this study is to provide a more realistic representation of the estuarine water inputs to a coarse but eddy-resolving regional model. First, the river volume transport and salinity values at the outlets are modelled with three different Estuary Box Models (EBMs) for stratified estuaries: the Knudsen relations model, a published EBM, called UCONN-NCAR EBM, which parameterizes the tidal inflow and mixing inside the estuary, and a new model, called CMCC-EBM. The CMCC EBM has been conceived to represent the estuarine processes coupled to a mesoscale resolving hydrodynamic model that resolves the entering flow field at the estuary mouth and it offers a new representation of the tidal inflow and a new salinity tidal mixing parameterization via horizontal diffusive processes. The Ofanto and Po rivers flowing into the Adriatic Sea (northern part of the central Mediterranean Sea) are selected as case studies. The coupling of the eddy resolving ocean model to the CMCC EBM is found to outperform the one with the UCONN-NCAR EBM in the region of freshwater influence on the shelf area
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