1,721,067 research outputs found
Assessment of hydrodynamics, biochemical parameters and eddy diffusivity in a semi-enclosed Ionian basin
No full textIn the framework of the Italian flagship Project RITMARE, during December 2013 a meteo-oceanographic station was installed in the Mar Grande basin, a semi-enclosed bay in Southern Italy, connected to the Ionian Sea. Due to the presence of coastal heavy industry and anthropic pressure, this marine system has experienced environmental degradation over the last decades. Therefore, much monitoring of hydrodynamics and water quality indicators is required. In fact, this monitoring makes it possible to check the real-time bio-chemical status of the basin and therefore promptly intervene when accidental spills occur, and to create a dataset necessary to calibrate and validate modelling systems providing forecasts. The present paper aims to analyze and discuss the long term and continuous recordings of hydrodynamic and biochemical data collected by this station, available for the period from January 2014 up to December 2014. In detail, hourly measurements of wind, waves, current velocity, water temperature, salinity, chlorophyll and turbidity concentrations were archived in monthly time-series and processed in frequency domain, using the FFT (Fast Fourier Transform), to both delineate the reciprocal effects of drivers and deduce some correlations between parameters (De Serio and Mossa, 2013). Following this, monthly surface current data were processed in order to obtain time-averaged values of the turbulent velocity components, turbulent kinetic energy and turbulent time scales. Based on these calculated turbulent parameters, the horizontal eddy diffusivity was computed with the hypothesis of homogeneous turbulence using two methods, which provided results with the same order of magnitude. These results are of interest for numerical dispersion models. Finally, only referring to the month of December 2014, the time series of the crude oil concentration was available at the station and was examined in depth. The field data enabled us to conclude that the crude oil dispersion process is influenced by the sea turbulence
Environmental monitoring in the Mar Grande basin (Ionian Sea, Southern Italy)
Full text linkHydrodynamic and water quality data has been recorded since February 2014 by a meteo-oceanographic station installed in the inner part of the Gulf of Taranto, in the northeastern part of the Ionian Sea (Southern Italy). This monitoring action, managed by the research unit of the Technical University of Bari, DICATECh Department, could play a pivotal role in a vulnerable and sensitive area, affected by massive chemical and biological pollutant discharges due to the presence of heavy industry and intense maritime traffic. Monthly trends of winds, waves, currents, and biochemical parameters, such as dissolved oxygen, chlorophyll, and turbidity, are analyzed and discussed. The analysis exhibits that the wave regime is slightly controlled by wind forcing; rather, topography strongly affects the wave propagation direction. Surface currents appear wind induced in the measuring station, while near the bottom a quasi-steady current directed towards southwest is formed. The selected water quality indicators show monthly trends consistent with the typical seasonal convective fluxes and mixing
A laboratory study of irregular shoaling waves
No full textThe present research aims to investigate the dynamics of a single laboratory irregular wave, characterized by a narrow-banded spectrum and developing on a sloping sand bottom, in intermediate waters up to the surf zone. Experiments focused on the wave shoaling region, in order to examine how the wave is affected by breaking induced turbulence offshore the surf zone. A 3D acoustic Doppler velocimeter was used to measure the three wave velocity components, which were all processed to evaluate the time-averaged vertical distributions of orbital velocities, wave and turbulent Reynolds shear stresses and turbulent intensities. The vertical distributions of the phase-averaged velocity components, turbulent kinetic energy and transport of turbulence were also analysed. The adopted phase-averaging technique was applied to each investigated measurement point. Therefore, the crucial element of the study is that all the analysed values derive directly from real measurements and are not approximated by any kind of interpolation. The study confirmed some dynamic behaviour in the shoaling zone already known in the literature, such as the typical cell-type flow pattern of the mean flow and the necessity to evaluate the turbulent kinetic energy with all the three velocity components, when available, which would otherwise be underestimated. Referring to the time-averaged wave and Reynolds shear stresses, a contribution was added to the open debate on their order of magnitude. The measured wave Reynolds shear stresses were also compared with the results of the model by Zou et al. (J Geophys Res 111:C09032, 2006), confirming the behaviour typical of dissipative breaking waves. The analysis of turbulence transport in the shoaling zone revealed that it is seaward directed close to the surface and landward directed close to the bottom. The results presented in the paper can be extended only to other analogous flow conditions
Field measurements and monitoring of sea water
No full textMonitoring surveys carried out in winter and spring conditions in the Southern coastal area of Bari, Italy are described in the present paper. Velocity components were measured at different depths, with intervals of 1.5m, by means of a Vessel Mounted Acoustic Doppler Profiler, together with salinity and water temperature data, collected with a CTD recorder system. Wind intensity and air temperature were also recorded for each measurement station. The target area neighbours the eastern wastewater sea outfall system of the city, thus its analysis is necessary for investigating the process of diffusion and transport of the wastewater outfall (taking into account that the sea currents play a pivotal role on physical and microbiological effects), and to validate predictive hydrodynamic models
Assessment of classical and approximated models estimating regular waves kinematics
No full textThe planning and management of many coastal activities require the knowledge of the wave mechanics in a target area. Many theoretical models have been developed to describe the evolution of a regular wave, with different levels of accuracy, but it is hard to evaluate which model is the most suitable one to reproduce a precise marine process.
In this regard, an experimental program, started up at the Technical University of Bari, aims to provide some useful references to practitioners in the field. The present work enriches the existing experimental dataset and analyzes two new experimental regular breaking waves, examined in the shoaling zone. Their cross-shore and vertical velocities have been measured together with their elevations by means of a 2D Laser Doppler Anemometer and a resistive gauge, respectively. Several classical theories and approximate methods have been used to reproduce the waves kinematics, in order to test their validity and applicability. Mainly, the study outlines that i) an increasing error in the reproduction of the wave kinematics is observed while increasing its non linearities; ii) approximate methods tend to better perform in comparison with classical theories, even if in some cases they are more sensitive to the surface boundary conditions
Cylindrical obstacle impacted by long waves: experimental observation of downstream vorticity and coherent structures
No full textStreamwise velocity profiles in coastal currents
No full textThe ability to model marine currents can be a powerful device for many planning activities, for which the knowledge of the velocity field is of pivotal importance, such as the evaluation of current-induced loading on maritime structures or the diffusion and dispersion of polluted flow discharges. Observations of time-averaged velocity profiles, taken with a vessel mounted acoustic Doppler current profiler during a monitoring survey program in the seas of Southern Italy, are analysed in this paper. The measurements were taken under non-breaking conditions, offshore the surf zone, with the aim of reproducing the vertical trends of the streamwise velocity by means of standard theoretical laws. To evaluate also the possible influence of stratification on the current velocity profile shape, together with velocity measurements water temperature and salinity were also measured at the same time and locations, by means of a CTD recorder. The examined surveys referred to different time periods and sites, to guarantee a general validity of deductions. On the basis of the experiments, we verified the actual existence of a log-layer and concluded that the upper limit of the region in which the log law is applicable extends well beyond the inner region. Moreover, the deviations of the measured velocity from the logarithmic profiles above the height of the log layer is consistent with the effects of stratification. The parameters of the log law were estimated, depending on both flow dynamics and stratification in the target area. As a second step, in the most superficial and stratified layer, the velocity profiles were modelled by means of a power law, which fitted the measured data well. According to previous studies, the power law parameters result Reynolds number dependent by means of a new proposed formulation. Finally, the bottom stress and the bottom drag coefficient were investigated
THE FUNWAVE MODEL APPLICATION AND ITS VALIDATION USING LAB DATA
No full textIn this paper, the performance of a Boussinesq model is evaluated for its ability to predict deep waters and shoaling zone velocity and elevation, comparing it with laboratory data. The model evaluation places emphasis on the parameters of the wave field that could be used for the prediction of coastal phenomena. It was found that the model proved its ability to predict regular wave velocity and elevation both in deep waters and shoaling zones right up to the breaking region. In contrast to previous works found in literature, the comparisons in this case are not limited to modelled and
measured wave elevations, but also involve horizontal velocities. As a result, experimental and computed time series of wave elevations and horizontal velocities and their corresponding phaseaveraged values are investigated along the wave channel, showing a good performance of the model
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