1,720,974 research outputs found
Oscillatory flow around a sphere resting on a rough bottom: Direct numerical simulations
No full textOscillatory flow around a large sphere resting on a plane and rough bottom is simulated by means of direct numerical simulations of continuity and Navier-Stokes equations. The bottom roughness is provided by a layer of spherical particles, the size of which is much smaller than the radius of the large sphere, arranged in a hexagonal pattern. To investigate the conditions at the bottom of a propagating sea wave, the flow is forced by a spatially uniform and temporally oscillating pressure gradient. The numerical approach will determine the magnitude and spatial distributions of vorticity and bottom stress, which are difficult to measure in an experimental apparatus. Attention is focused on the dynamics of the vortex structures originated by the free shear layer shed by the surface of the large sphere and on the interaction of the vortex structures with the bottom roughness. In particular, the bottom shear stress in the region close to the large sphere was evaluated suggesting the tendency of the small spheres to be moved and transported by the flow. The results show that peaks of the bed stress originate in the lateral regions as an effect of the flow acceleration around the spherical object
Direct numerical simulation of the oscillatory flow around a sphere resting on a rough bottom
No full textThe oscillatory flow around a spherical object lying on a rough bottom is investigated by means of direct numerical simulations of the continuity and Navier–Stokes equations. The rough bottom is simulated by a layer/multiple layers of spherical particles, the size of which is much smaller that the size of the object. The period and amplitude of the velocity oscillations of the free stream are chosen to mimic the flow at the bottom of sea waves and the size of the small spherical particles falls in the range of coarse sand/very fine gravel. Even though the computational costs allow only the simulation of moderate values of the Reynolds number characterizing the bottom boundary layer, the results show that the coherent vortex structures, shed by the spherical object, can break up and generate turbulence, if the Reynolds number of the object is sufficiently large. The knowledge of the velocity field allows the dynamics of the large-scale coherent vortices shed by the object to be determined and turbulence characteristics to be evaluated. Moreover, the forces and torques acting on both the large spherical object and the small particles, simulating sediment grains, can be determined and analysed, thus laying the groundwork for the investigation of sediment dynamics and scour developments.</jats:p
HYDRODYNAMICS OF A MUDDY ESTUARINE ENVIRONMENT: SUMMERTIME VS WINTERTIME CONDITIONS
No full textThe hydrodynamics of an estuarine environment characterized by cohesive sediments, has been studied through a pair of experimental campaigns performed at the mouth of the Misa River. The Misa River flows from the Apennine Mountains and enters the Adriatic Sea in Senigallia, a tourist town located on the Mid-East coast of Italy. The estuary of the Misa River has characteristics of a field-scale laboratory; the final reach is highly engineered with containment structures. Consequently, it was chosen as a suitable site for the experiments undertaken during the EsCoSed (“Estuarine Cohesive Sediment”) Project. The estuarine environment of the Misa River was observed during both summertime and wintertime experiments. The hydrodynamics was monitored using both Eulerian (e.g., bottom moored platforms at both the river-bed and sea-bed with high-resolution ADCPs recording velocity profiles) and Lagrangian (e.g., surface drifters) instrumentation, allowing for the characterization of the flow field during very different flow conditions. The climate occurring before and during the investigated periods has also been analyzed through use of numerical simulations, wave buoy measurements, and tide gauges. A comparative analysis between summertime and wintertime conditions, focused on wave-current forcing and local estuarine hydrodynamics, is underway. The preliminary results highlight the control of wind direction on the observed hydrodynamics. During the summertime the wind frequently changes direction. Conversely, during wintertime the wind direction remains fairly constant leading to severe storms. The extreme wintertime events generate intense sediment transport driving morphologic change
Hydrodynamics at a microtidal inlet: Analysis of propagation of the main wave components
Get PDFThe evolution of different wave components as they propagate within a microtidal inlet during a storm occurring from 24–26 January 2014 is analyzed, in order to improve knowledge on how microtidal river mouths typical of the Adriatic Sea behave. For the first time, the ”low-pass filter” mechanism previously ascertained at several macrotidal oceanic inlets around the world has been observed in the field with remarkably specific hydrodynamic conditions, i.e. low tide excursion, permanent connection with the sea and generally milder wave climate than in the ocean. Sea/swell (SS) waves were strongly dissipated before entering the river mouth, through the combined action of wave breaking due to reducing depths and opposing river currents enhanced by rainfall. Infragravity (IG) waves propagated upstream and significant IG wave heights of up to 0.4 m, about 13% of the local water depth, have been observed 400 m upriver (about 10 times the local SS peak wavelength) during storm climax. The IG wave energy here represented over 4% of the maximum offshore storm energy. IG wave components travelled upriver at estimated velocities between 3.6 m/s and 5.5 m/s (comparable with speeds of nonlinear long waves) during intense storm stages up to 600 m into the river channel (about 15 times the local SS peak wavelength), and are enhanced by tide-induced increase in water depths. It is estimated that tide-induced excursion accounted for about 80% of the total mean water elevation at storm peak at about 400 m into the river. Finally, tidal oscillations are detected up to 1.5 km upstream (about 40 times the local SS peak wavelength). This study highlights the dominance of astronomical tide over both wave setup and storm surge in controlling the upriver propagation of IG waves, even in a microtidal environment
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
