1,720,984 research outputs found
Fractional Stefan problems exhibiting lumped and distributed latent-heat memory effects
No full textWe consider fractional Stefan melting problems which involve a memory of the latent-heat accumulation. We show that the manner in which the memory of the latent-heat accumulation is recorded depends on the assumed nature of the transition between the liquid and the solid phases. When a sharp interface between the liquid and the solid phases is assumed, the memory of the accumulation of the latent heat is "lumped" in the history of the speed of the interface. In contrast, when a diffuse interface is assumed, the memory of the accumulation is "distributed" throughout the liquid phase. By use of an example problem, we demonstrate that the equivalence of the sharp-and diffuse-interface models can only occur when there is no memory in the system. DOI: 10.1103/PhysRevE.87.04240
Exact solutions for the fractional nonlinear Boussinesq equation
No full textWe investigate the existence of exact solutions in closed form to a fractional version of the nonlinear Boussinesq equation for groundwater flow through an unconfined aquifer. We show this fractional equation appears naturally when the classical nonlinear Darcy’s law is replaced by a space-fractional one. After a physical discussion on the fractional model, we give several exact solutions in closed form for special choices of initial and boundary data. We provide solutions for steady andunsteady cases, by considering both classical and fractional derivatives in time.Fil: Ceretani, Andrea Noemí. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Investigaciones Matemáticas "Luis A. Santaló". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Matemáticas "Luis A. Santaló"; ArgentinaFil: Falcini, Federico. Consiglio Nazionale delle Ricerche; ItaliaFil: Garra, Roberto. Consiglio Nazionale delle Ricerche; ItaliaINdAM workshop on fractional differential equations : modeling, discretization, and numerical solversRomaItaliaIstituto Nazionale di Alta Matematica “Francesco Severi”Università di Salern
Diagnostic analysis of contourite drifts and contour currents around small-scale topographic features: some examples from the Italian Seas (Mediterranean Sea),
No full textWe analyse here contourite drifts presumably related to a topographic control given by promontories or seafloor depressions (e.g., slide scars) in some Italian Seas. We therefore investigate the local effect of a topographic unevenness (such as a landslide scar) on flow contouring a cape by applying the classical conservation of marine water potential vorticity (PV). We further analyse the presence of non-linear and/or baroclinic instabilities that may lead to erosive or depositional conditions which, in turn, inhibit or favour the formation of contourites. Such an analysis is performed by applying the classical theory for conservation of potential vorticity (PV) in a cylindrical frame, which is able to describe the fluid properties by means of bathymetric curvatures
Interplay between down-slope and along-slope sedimentary processes during the late Quaternary along the Capo Vaticano margin (southern Tyrrhenian Sea, Italy)
No full textLate Quaternary along-slope and down-slope sedimentary processes and structures in the upper slope-shelf sector of the Calabro-Tyrrhenian continental margin off Capo Vaticano have been investigated using very high-resolution single-channel seismic profiles and multibeam bathymetric data. The results show that a competition among along-slope bottom currents-vs down-slope mass-wasting mostly contributed in shaping the seafloor and controlling deposition of sedimentary units during the Late Quaternary. Along-slope processes mostly formed elongated drifts located on the upper continental slope and outer shelf, between -90 and -300 m. The contourite deposits and associated erosive elements indicate the presence of a northwestward geostrophic flow that can be related to the modified-LIW issued by the Messina Strait. According to the proposed stratigraphic reconstruction it is likely that the activity of bottom-currents off Capo Vaticano was intensified around the LGM period and during the post-glacial sea-level rise, whereas they were less intense during the Holocene. Gravity-driven down-slope processes formed mass-transport deposits and turbidite systems with erosive channels, locally indenting the present-day shelf. Several slide events affected the upper 10-20 m of the stratigraphic record, dismantling considerable volume of contourite sediment. High-resolution seismic profiles indicate that failure processes appear to be dominated by translational sliding with glide plains mainly developed within contourite deposits. The most striking feature is the Capo Vaticano slide complex, which displays a large spatial coverage (area of about 18 km2) and is composed by several intersecting slide scars and overlapping deposits; these characteristics are peculiar for the Tyrrhenian continental margins, where slide events developed in open-slope areas are usually less complex and smaller in size. The presence of high-amplitude reflectors within contourite deposits (representing potential weak layers in the slope stratigraphy) along with high post-glacial sedimentation rates estimated for contourite deposits (about 100 cm/ka) and steep seaward flank of the drifts can act as a relevant predisposing/triggering factor for medium-large scale slope instability on the Tyrrhenian margins. This study highlights how a complex spatial and temporal interplay of along- and across slope processes can occur over a narrow area in a relatively short time-span (the post-glacial period). This is particularly relevant for the Mediterranean Sea, where mixed turbidite-contourite systems are poorly represented because the rare occurrence (or knowledge) of contourite deposits
A general theory for the effect of local topographic unevenness on contourite deposition around marine capes. An inverse problem applied to the Italian continental margin (Cape Suvero)
No full textThe interaction between ocean bottom currents and topographic obstacles often results in sedimentary processes that form intriguing sedimentary deposits. However, without a thorough knowledge of both fluid mechanical processes and oceanographic settings regarding these sedimentary deposits, such an inherited interaction is not easy to understand. We here analyze the interaction between a bottom, geostrophic current and a local topographic depression, a slide scar offshore Cape Suvero, an Italian headland in the southern Tyrrhenian Sea, in order to explain the presence of contourite drifts off this cape. We apply the classical conservation of marine water potential vorticity and demonstrate the presence of a steady cyclonic circulation over the scar, which in turn affects contourite deposition. We thus show that the application of the potential vorticity conservation provides a simple but powerful, general tool for the understanding of the complex relations among ocean current, seafloor morphologies and sedimentary structures. (C) 2016 Elsevier B.V. All rights reserved
Analysis and modeling of contourite drifts and contour currents off promontories in the Italian Seas (Mediterranean Sea)
No full textThe complex relationship between currents flowing around capes and their related contourite deposits is still an interesting topic to confront, both from a sedimentologic and oceanographic perspective. We analyze here recent observations of contourite drifts, located at intermediate depths off promontories in the southern Tyrrhenian and in the southern Adriatic Sea. These contourites are located slightly upstream from the cape tip of Cape Vaticano, while they occur both upstream and downstream, in the lee wave region, of the Gargano Promontory. We therefore analyze and discuss tank and numerical simulations of contour-following flows, with particular attention to the presence of turbulent phenomena occurring in the lee region. Discussing the classical stream-tube model (i.e., a thin vein of dense water flowing around a cape) we moreover provide physical justification for some aspects we recognized in the study experiments. The comparison between bathymetric-stratigraphic data and numerical, tank and analytic results, allows investigation of the possible occurrence of sediment drifts around capes. We found that the presence of turbulence, and thus of erosive conditions for sediments in the lee of a cape, can be detected by using dimensionless numbers related to cape dimension and ocean current features. This work can be seen as a new approach to bridge the gap between marine sedimentology and physical oceanography
Linking mixing processes and climate variability to the heat content distribution of the Eastern Mediterranean abyss
Full text linkThe heat contained in the ocean (OHC) dominates the Earth’s energy budget and hence represents a fundamental parameter for understanding climate changes. However, paucity of observational data hampers our knowledge on OHC variability, particularly in abyssal areas. Here, we analyze water characteristics, observed during the last three decades in the abyssal Ionian Sea (Eastern Mediterranean), where two competing convective sources of bottom water exist. We find a heat storage of ~1.6 W/m2– twice that assessed globally in the same period – exceptionally well-spread throughout the local abyssal layers. Such an OHC accumulation stems from progressive warming and salinification of the Eastern Mediterranean, producing warmer near-bottom waters. We analyze a new process that involves convectively-generated waters reaching the abyss as well as the triggering of a diapycnal mixing due to rough bathymetry, which brings to a warming and thickening of the bottom layer, also influencing water-column potential vorticity. This may affect the prevailing circulation, altering the local cyclonic/anticyclonic long-term variability and hence precondition future water-masses formation and the redistribution of heat along the entire water-column
Remote sensing and coastal morphodynamic modelling: A review of current approaches and future perspectives
No full textWe want to investigate the use of remotely sensed data in shoreline morphodynamic modelling. For this aim, we present a review of current approaches for Total Suspended Matter (TSM) retrieval from satellite data in coastal waters and outline some perspectives for the definition of an operative, satellite-based, alongshore sediment flux. Coastal, turbid and optically complex waters have traditionally posed challenges to remote sensing and space-borne techniques for a variety of reasons: the complexity and variability of their radiative processes on one hand; spatial, temporal and spectral resolution issues on the other. Nevertheless, different sensors/satellites have been used in order to retrieve the main biogeochemical characteristics of these waters. Geostationary satellites (such as SEVIRI for European seas and COMS1 for South Korea) have been recently adopted for their high temporal resolution while classical ocean colour mappers (such as SeaWiFS, MODIS, MERIS, VIIRS) and other Earth observation satellites (like the Landsat series, Envisat, ERS series and Sentinel program) are commonly used because of their finer spatial and spectral resolutions. The immediate future looks promising because of the recent launch of the first satellite of the Sentinel-3 constellation with a new ocean colour instrument (OLCI) (21 spectral bands, 300m spatial resolution and a revisit time of 1.4 days). In the longer term, from 2018 onwards, the launch of Hyper Spectral instruments (e.g., German EnMAP, Italian PRISMA) with much higher spectral resolution capabilities, although at the expenses of a lower time resolution, promises finer water constituents determination and grain size characteristics, based on their spectral signatures. Consequently, a large variety of different methods, empirical or semi-analytical, are used by the scientific community in order to get the most suitable algorithm for the TSM retrieval. Envisaged developments include multi sensor approaches, new algorithms, coupled sea-atmosphere radiative transfer models. We here discuss the best strategy in order to achieve the most suitable regional TSM product for coastal geomorphologic applications and thus to pair it with coastal water velocity fields, allowing for a satellite-based definition of alongshore sediment transport.We also discuss spatial, temporal, and spectral characteristics of different sensors and novel algorithms that might combine these properties together
Numerical and experimental analysis of Lagrangian dispersion in two-dimensional chaotic flows
Full text linkWe present a review and a new assessment of the Lagrangian dispersion properties of a 2D model of chaotic advection and diffusion in a regular lattice of non stationary kinematic eddies. This model represents an ideal case for which it is possible to analyze the same system from three different perspectives: theory, modelling and experiments. At this regard, we examine absolute and relative Lagrangian dispersion for a kinematic flow, a hydrodynamic model (Delft3D), and a laboratory experiment, in terms of established dynamical system techniques, such as the measure of (Lagrangian) finite-scale Lyapunov exponents (FSLE). The new main results concern: (i) an experimental verification of the scale-dependent dispersion properties of the chaotic advection and diffusion model here considered; (ii) a qualitative and quantitative assessment of the hydro-dynamical Lagrangian simulations. The latter, even though obtained for an idealized open flow configuration, contributes to the overall validation of the computational features of the Delft3D model
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