1,721,031 research outputs found
A Prediction Technique for the Transverse Vortex-Inuced Oscillations of Tensioned Risers
No full textEvidences of atmospheric pressure drop and sea level alteration in the Ligurian Sea
No full textExtreme weather events have significant impacts on coastal human activities and related economy. In this scenario, the forecast of sea storms and sea level alteration in order to mitigate the effects of waves on shores, piers and coastal structures, is a challenging goal. To this end, we investigated the atmospheric pressure drop and sea level increase as a result of 29-30 October 2018 storm event. The dataset used to analyze these phenomena consists of wind-wave numerical modelling and in-situ measurements, validated with National Mareograph Network (RMN) and Tuscan regional wave network. The results of the numerical model give severe wave heights and a pressure drop at the peak of the storm, which produced many coastal damages with coastal defences collapses, loss of property and infrastructure
Mooring control of semi-submersible structures for wind turbines
No full textThe paper deals with the mooring control of tri-floater support structures for wind turbines; both catenary and vertical tensioned lines are considered. Operational and extreme climate conditions are examined, with reference to three different locations in Southern Mediterranean Sea. Mooring system is dimensioned in such a way that the offset due to environmental actions is restrained within allowable limits. The response of the platform is assessed in terms of: static forces due to turbine thrust, wind and current drag forces and steady drift force; the wave frequency montion RAO curves; the low frequency second order wave motins. Finally, assuming the Dutch tri-floater structure as a test case, a parametric study is carried out to identify the most suitable mooring configurations , varying the water depth in the range between 50 and 200 m
Towards a unified formulation of time and frequency-domain models for point absorbers with single and double-body configuration
No full textPoint absorbers represent an attractive choice to harness the wave power potential, even if relevant technology is still in a pre-commercial phase and is not competitive enough, as regards other renewable sources. In this respect, in the last decade research activities focused on the design and optimization of the floating buoy, in order to increase the device efficiency and reduce the power production costs. Based on actual state of art, it is still necessary to develop a unified formulation for the hydrodynamic behaviour of point absorbers with single and double-body configuration. Hence, the first aim of current research is to develop a unified time-domain model for point absorbers with single and double-body configurations, focusing on the assessment of power production and the strength check of the tensioned line, connecting the floating buoy to a permanent magnet linear generator, lying on the seabed. Subsequently, a new formula for power production, based on frequency-domain analysis, is outlined to account for the heave motion restraint, exerted by the Power Take-Off unit, as well as for the partial overlapping between translator and stator. Current analysis is performed for a reference point absorber, deployed in the western Mediterranean Sea
Ultimate and accidental limit state design for mooring systems of floating offshore wind turbines
No full textThe paper deals with the design of mooring systems for tri-floater offshore wind turbines. Both ultimate (ULS) and accidental (ALS) limit states are examined; correspondingly 50 years and 1 year return period environmental loads are associated with. Two turbine conditions, namely power production and parked wind turbine, are analyzed; to the first condition the ULS is applied, to the second one both ULS and ALS are considered. The platform static demand is assessed in terms of static forces due to turbine thrust, wind and current drag forces and wave steady drift forces. The platform dynamic offset is determined considering both wave-frequency linear and low-frequency second order motions. Mooring patterns with 6, 9 and 12 l9nes are considered; both chain cables and steel wire ropes are assumed for the mooring lines. Water depth incidence is examined in the range between 50 and 300 m. In each case the mooring system is dimensioned in such a way that the mooring system weight is deternined. The Dutch tri-floater design is assumed as reference structure and three candidate sites in Southern Mediterranean Sea are considered. It is found that both platform maximum admissible offset and line pattern significantly influence the overall weight of the mooring system
Coastal sensitivity/vulnerability characterization and adaptation strategies: A review
Full text linkCoastal area constitutes a vulnerable environment and requires special attention to preserve ecosystems and human activities therein. To this aim, many studies have been devoted both in past and recent years to analyzing the main factors affecting coastal vulnerability and susceptibility. Among the most used approaches, the Coastal Vulnerability Index (CVI) accounts for all relevant variables that characterize the coastal environment dealing with: (i) forcing actions (waves, tidal range, sea-level rise, etc.), (ii) morphological characteristics (geomorphology, foreshore slope, dune features, etc.), (iii) socio-economic, ecological and cultural aspects (tourism activities, natural habitats, etc.). Each variable is evaluated at each portion of the investigated coast, and associated with a vulnerability level which usually ranges from 1 (very low vulnerability), to 5 (very high vulnerability). Following a susceptibility/vulnerability analysis of a coastal stretch, specific strategies must be chosen and implemented to favor coastal resilience and adaptation, spanning from hard solutions (e.g., groins, breakwaters, etc.) to soft solutions (e.g., beach and dune nourishment projects), to the relocation option and the establishment of accommodation strategies (e.g., emergency preparedness)
Wave simulations through SAR COSMO-SkyMed wind retrieval and verification with buoy data
No full textIn this paper the use of SAR-derived wind fields is proposed to force surface wave models in a coastal environment, together with their validation with a valuable data set provided by both scatterometer and wave buoys data. The test area is the coastal zone of the Southern Tyrrhenian Sea, including the gulfs of Gaeta, Napoli, Salerno and Policastro, which is of great applicative relevance for both oceanographic and coastalmaritime surveillance purposes. The study can be summarized according to the three following stages. The first one consists of preliminary simulations of the wave fields, accomplished by means of both Wave Watch III (WWIII) and Weather Research and Forecasting (WRS) models, respectively, with forcing provided by ECMWF wind field model data. Once the relevant wave parameters have been evaluated on the calculation grid (i.e. significant wave height, Hs, wave direction, Dw, and peak period, Tp), the wave model validation has been performed with respect to some significant wave storms relevant to the summer and the winter seasons of 2010. A validation step has been accomplished to compare relevant wave parameters gathered by means of SAR-derived wind field estimations with the ones provided by both ASCAT scatterometer wind data and in situ wave buoy observations. The results were quite satisfactory in terms of the storm trend, less satisfactory in terms of the maximum Hs values. So the third stage of the study is about the development of some techniques to improve the model accuracy, in particular the use of blended data, i.e. ECMWF model data and COSMO-SkyMed© SAR-derived wind field retrievals. The use of blended data improves the model accuracy with respect to the COSMOSkyMed © data alone, although the best results have been obtained with ECMWF data, both in terms of Hs values and directions
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