1,721,171 research outputs found
On wave kinematics at steep slopes: second order model
No full textThis paper presents an experimental study investigating the relevant characteristics of the flow field induced by a regular wave acting on a uniform steep slope. Due to their uniqueness, the experimental data are of paramount importance and give a contribution toward the rational definition of wave-structure interaction. In the first part of the paper, attention is focused on the flow field characteristics, i.e., temporal and spatial behavior of surface elevation and vertical distribution of the horizontal component of the local velocity. In the second part, it is shown that the main characteristics of the velocity distributions may be represented by the variance of the distribution itself. Furthermore, it has been verified that the temporal behavior of the variance is well reproduced by a Fourier series truncated to the first three even harmonics. Relationships are presented between the coefficients of the Fourier series and some global quantities of the wave motion. Due to the relationship between the variance of velocity distribution and the momentum flux correction coefficient, the proposed second-order model allows the actual shape of the velocity profiles to be accounted for in onedimensional numerical models describing the flow field due to the action of a wave on a steep slope
DISCUSSION OF "IMPACT OF COEFFICIENTS IN MOMENTUM EQUATION ON SELECTION OF INERTIAL MODELS"
No full textquesto articolo è una discussion e non ha abstrac
Partial standing waves on a steep slope
No full textMeasured free surface elevations and horizontal velocities of non-breaking regular waves on a 1:2 rough permeable
slope are analyzed to examine the cross-shore variations of the incident and reflected waves on the steep slope. The
co-located measurements of the free surface elevation and horizontal velocities at a number of elevations are used to
separate the incident and reflected waves locally. The estimated partial standing waves are then shown to describe
the local free surface elevation and horizontal velocity reasonably well. The incident wave energy flux is found to be
approximatelyc onstant along the 1:2 slope, whereas the data and linear theory are not accuratee nough to detect the
cross-shore variation of the relative small wave reflection coefficient. The measured mean horizontal velocities are
shown to be in qualitative agreement with the return current estimated from the separated incident and reflected
waves
Three-dimensional analysis of local scouring induced by a rotating ship propeller
Full text linkThe jet induced by a rotating ship propeller can cause scouring of the seabed and consequent deposition of the scoured material nearby. Despite these effects are extremely important for the operability of a harbour, there is currently limited work concerning a detailed investigation of the three-dimensional (3D) characteristics of the bed topography changes induced by the ship propeller. Thus, this paper presents laboratory experiments with the aim of analysing the effects induced by a propeller on a mobile bed, in different conditions of submergence depth (h0) and rotational speed (n). The equilibrium bed surface topography was acquired with the photogrammetry technique combined with a 3D Terrestrial Laser Scanner (TLS), in order to analyse, for the first time, bed elevation data obtained from high-resolution Digital Elevation Models (DEMs). As a result, it was demonstrated that the swirling jet produced by a rotating propeller causes the development of a bed topography not symmetrical with respect to the propeller longitudinal axis, with a deeper scour hole on one side and a higher deposition mound on the other side. Therefore, the scour hole induced by a propeller cannot be assimilated to that produced by a water jet and this behaviour can be noted only with a comprehensive and detailed analysis of a 3D model of the bed topography. Furthermore, it was shown that increasing n for the same h0 (or reducing h0 by keeping n constant) causes a longer, deeper and wider scour hole and a higher deposition mound, with a greater volume of sediments eroded from the bed and deposited nearby the scour hole. To be precise, this is the first study aiming at estimating the eroded and deposited sediment volumes by a propeller jet, thanks to the use of the high-resolution DEMs. The relationships between all the involved variables were analysed, providing equations, graphs and an abacus for the prediction of the effects induced by the propeller as a function of h0 and the Froude number
A Multiresolution Filtering Method to Enhance the Circular Pattern of Cherenkov Light Images
No full textNeural network application to traffic shaping architecture for the ESW broadband satellite system
No full textEuroSkyWay (ESW) is a continental broadband data-communication satellite system which has the mission
to provide connectivity services both to telecom operators and servi ce providers serving a wide users
population with the appropriate levei of service. ESW architecture foresees a satellite constellation and it is
organised into ESW sub-networks (ESW-SN) each of them being served by a singie satellite. An advanced
traffic management architecture allows ESW to fully adapt the bandwidth of provided connections to
diversified traffic supported. At this aim, ESW dynamic bandwidth allocation capability, allows to change
dynamically the bandwidth of each connection even though ESW switching mode is based on classica)
circuit switches. ESW traffic management architecture is distributed over three main functionai component:
the Traffic Resource Manager (TRM), hosted on board, which provides the network side of the architecture,
a traffic management agent which, from the ESW user terminaI side inter-operates with the TRM and,
finally, the Usage Parameters Control (UPC) which provides the traffic shaping functionaIity within the
ESW user terminaI itseif. The UPC component covers the set of actions devoted to monitor and contro)
traffic offered for a given ESW connection, at the end-system accesso Its main purpose is to protect network
resources from malicious as well as unintentionai misbehaviour, which can affect the QoS of other aiready
estabIished connections, by deteeting vioiations of negotiated parameters and taking appropriate aetions. In
partieuIar this component monitors the eonformanee of the traffic actually in input against the traffie
descriptors negotiated at eonnection set-up time. In case of a traffic contraet conformanee vioiation, a proper
policing action on the eells sent in excess shall be applied. A eonformance monitoring is provided in term
of the following traffie deseriptor measurement: Peak Cell Rate, Sustainable Celi Rate and Maximum Burst
Size. In order to meet the expectations of network users, in terms of parameters sueh as celI Ioss and eall
bIocking probabiIity, the use of network resources must be carefully eontrolled. On the other hand, resources
should be handied so that the network operator revenue is maximised over time. In generaI, two types of
traffic contro I mechanisms are adopted: preventive traffie eontrol and reactive traffie eontroI. Neurai
Networks (NNs) have severai properties that are vaIuabie when impiementing traffic contro I. NNs can
implement direet adaptive contro I without an anaIytieai representation of the traffie but using a good
representation ofthe probiem. Moreover, the distributed and parallel architecture ofNNs, ean be exploited in
hardware implementations, largeIy availabie on market, which provide short and predietabie response times.
These properties have addressed a neural network solution for the traffic management functionality Iocated
in the ESW user terminaI. In this paper, a study of the traffie shaping funetionality and a dynamic resouree
assignment mechanism for the ESW broadband satellite network is presented. A neurai network architeeture
based on the feed-forward scheme is proposed in the resource management mechanism for an adaptive ondemand
traffie resourees assignment using the Usage Parameters Contro I function
Large-scale offshore wind production in the Mediterranean Sea
No full textIn recent years there has been a growing interest in offshore wind energy thanks to the various advantages it offers. The offshore wind energy is used for the production of electric energy above all in the shallow waters but different research activities and large-scale demonstrations are also under way for the deep waters with scientific and technological advances that open possibilities also for new markets such as the Mediterranean Sea. In this context, the present paper aims to estimate the large-scale offshore wind production of the Mediterranean Sea. The methodology uses an open GIS platform and considers bathymetric data, annual average wind speed data, environmental data, turbines technical characteristics and administrative information. Three depth categories have been considered. The overlap between depth categories and annual average wind speeds ranges has allowed to determine the areas potentially suitable for wind farms allocation. On the basis of optimal wind farm layouts and of the characteristic of the type of turbines considered, the theoretical maximum annual offshore wind production has been estimated for whole Mediterranean area and it is about 742 TWh/year. Moreover, for each depth category, the theoretical annual wind offshore production for each Mediterranean country has been estimated
A Dynamic Bandwidth Resource Allocation based on Neural Networks in EuroSkyWay Multimedia Satellite System
No full textAdvanced traffic management based on the dynamic resource assignment allows a broadband satellite system such as euroskyway (ESW) to dynamically assign the resources of connections. The mechanisms of the dynamic assignment exploit variations of burstiness exhibited by real time and non-real time variable bit rate traffic sources to perform an optimized resource redistribution. The efficiency of the dynamic bandwidth allocation capability (DBAC) depends on the accuracy of the traffic source description; inaccurate assessment of the arrival process will cause an overhead and a degraded utilisation of system resources.
In this paper a flexible traffic burstiness predictor for dynamic bandwidth resource allocation based on neural network is presented. The approach is able to perform an online estimation of expected resource requests implementing traffic resource assignment by using a sub-symbolic adaptive representation of the traffic source. The achieved results prove that the flexible approach is more effective than the ones based on fixed schemes designed using analytical traffic source description when applied on the satellite terminal ESW system component
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