1,721,000 research outputs found
Italian seas wave extremes: a preliminary assessment
No full textOccasional damages occurring to offshore structures and routing ships have brought attention on whether conventional analyses of stormy seas are adequate to represent wave extremes. Indeed, field and laboratory data showed that in short-crested seas (typical of stormy conditions) the maximum wave elevation is rarely retrieved by a single-point observation (a buoy, for example), which tends to underestimate the actual extreme that occurs over an area surrounding the point. Recently, stochastic models for the prediction of maxima of multidimensional Gaussian random fields (e.g. the Piterbarg’s theorem and the Adler and Taylor’s Euler Characteristics approach) have been successfully applied to ocean wave statistics, thus permitting to extend the extreme value analysis from the time to the space–time domain. Results from space–time models are here firstly compared to observations gathered by an optical stereo system, and then used to preliminarily assess wave extremes over the Italian Seas, by using a numerical model analysis covering the period 2007–2013. In particular, space–time maxima are estimated as affecting a fishing boat and a cruise ship, showing that, locally, space–time extremes may exceed time-based values up to about 50 %
The hydro-morphodynamic response of a protected beach subject to sea storms: a numerical study
No full textSea storms are becoming more and more important in the economy of coastal areas, because they heavily affect both maintenance and life of the defense/touristic facilities, especially if they take place during the summer period. In conjunction with this, the design of traditional coastal defense structures is crucial for the protection of such facilities. The present study, based on numerical simulations performed by means of an innovative shallow-water numerical hydro-morphodynamic solver, explores the overall response of a protected beach to sea storms. Numerical tests have been run with the purpose of evaluating both i) the effect of real-life sea storms with different spectral characteristics, and ii) the influence of the positioning of shore-parallel submerged breakwaters on the beach morphology. The results of the simulations have revealed that erosion/accretion patterns depend weakly on the different sea storm conditions here used. On the other hand, the morphodynamics induced around the barriers is strongly influenced by the breakwater positioning: for the forcing here analyzed, the more the structures are offshore located, the more the bed variation is intense. On the opposite, the swash zone morphology is weakly influenced by the positioning of the breakwaters
Improving the assessment of wave energy resources by means of coupled wave-ocean numerical modeling
No full textANTICHE STELLE. MITI DI GLORIA E DI HYBRIS NEL CIELO DEI GRECI E DEI ROMANI
No full textI miti con cui i Greci hanno popolato il cielo attraverso le costellazioni rivelano la collocazione che essi attribuivano agli uomini rispetto alla loro visione dell'universo
Towards an Operational Stereo System for Directional Wave Measurements From Moving PlatformsVolume 8B: Ocean Engineering
No full textStereo video imaging of water surface has become an effective instrumentation to gather wind waves 3-D data from small to medium range spatial scales. Indeed, recent applications of stereo techniques provided new insights of space-time distributions of sea wave elevations, small scale wave statistics, and directional wave spectra. Like most photogrammetric applications, an accurate calibration of the optical acquisition machinery is required to provide a low-noise, precise and reliable surface reconstruction adequate to extract meaningful wavy surfaces. However, for practical open field applications, there is a strong interest to provide a calibration procedure apt to be performed in an uncomfortable environment in which it may be unfeasible to take apart or even physically access the device. Here, we propose a stereo pipeline suitable for 3-D wave measurements from fixed and moving platforms. In particular, within the Wave Acquisition Stereo System (WASS) framework, we contemplated a self-calibration technique for a robust estimation of the stereo extrinsic parameters, a fast dense stereo correspondence algorithm, and a two-step correction of the cameras motion. As for other applications, wave information collected by WASS includes synthetic wave parameters (e.g., significant wave height, wave periods, and directions), wavenumber and frequency-direction spectra, spatial distribution of wave elevations, heights, and lengths. The new pipeline features has been firstly assessed by installing WASS on top of the "Acqua Alta" oceanographic tower in the northern Adriatic Sea (Italy) and comparing WASS measurements against those acquired at the tower with reference instrumentation. Afterwards, the stereo system has been mounted on board the R/V "Urania" during a cruise on April 2013 in the southern Adriatic Sea. During the cruise, to correct for ship's motion, WASS has been synchronized to the motion unit used for the vessel's navigation. For validation, sea wave state gathered by WASS has been compared to theoretical models and results from the numerical wave model SWAN. Results presented show that the accuracy of 3-D waves provided by the new algorithms is comparable to that of other WASS applications, although significantly reducing the installation effort and the computational time by more than one order of magnitude. Additionally, encompassing for ship's motion makes stereo system a perspective instrumentation for operational wave measuring from research and opportunity vessels. The manuscript is completed by a discussion on the limitations and troubleshooting related to the proposed pipeline
Multi-Physics Ensemble versus Atmosphere–Ocean Coupled Model Simulations for a Tropical-Like Cyclone in the Mediterranean Sea
Get PDFBetween 19 and 22 January 2014, a baroclinic wave moving eastward from the Atlantic Ocean generated a cut-off low over the Strait of Gibraltar and was responsible for the subsequent intensification of an extra-tropical cyclone. This system exhibited tropical-like features in the following stages of its life cycle and remained active for approximately 80 h, moving along the Mediterranean Sea from west to east, eventually reaching the Adriatic Sea. Two different modeling approaches, which are comparable in terms of computational cost, are analyzed here to represent the cyclone evolution. First, a multi-physics ensemble using different microphysics and turbulence parameterization schemes available in the WRF (weather research and forecasting) model is employed. Second, the COAWST (coupled ocean–atmosphere wave sediment transport modeling system) suite, including WRF as an atmospheric model, ROMS (regional ocean modeling system) as an ocean model, and SWAN (simulating waves in nearshore) as a wave model, is used. The advantage of using a coupled modeling system is evaluated taking into account air–sea interaction processes at growing levels of complexity. First, a high-resolution sea surface temperature (SST) field, updated every 6 h, is used to force a WRF model stand-alone atmospheric simulation. Later, a two-way atmosphere–ocean coupled configuration is employed using COAWST, where SST is updated using consistent sea surface fluxes in the atmospheric and ocean models. Results show that a 1D ocean model is able to reproduce the evolution of the cyclone rather well, given a high-resolution initial SST field produced by ROMS after a long spin-up time. Additionally, coupled simulations reproduce more accurate (less intense) sea surface heat fluxes and a cyclone track and intensity, compared with a multi-physics ensemble of standalone atmospheric simulations
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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