196,145 research outputs found
Vegetation effects on vertical jet structures
No full textThis paper deals with measurements of the three-velocity components of a vertical, round, turbulent jet discharged into a vegetated cross flow. Over the last years, a large number of experimental studies and numerical models on turbulent jets discharged into a cross flow have been carried out, as well as several studies on vegetated channels. However, these studies show a lack of data regarding the combination between the vegetated channels and jets. The present study aimed at obtaining a more thorough understanding of the vegetation effects on the jet behaviors. To simulate the vegetation, arrays of emergent, rigid, circular steel cyl-inders were used. The jet source was placed at the centre of the experimental vegetated area. The time-averaged velocity field was investigated in the longitudinal, cross and horizontal planes of the channel. The results show that vegetation has significant effects on the jet structure as compared with the case of non-vegetated channel. Above all, the rigid stems reduce streamwise velocities, giving rise to an increase of the jet penetration height within the ambient flow. Moreover, the familiar pair of counter-rotating vortices and kid-ney shape observed in the cross section of the jet discharged into the non-vegetated channel disappears and transforms under the effects of stems into a complex flow motion structure for the jet discharged into the vegetated flume
Modelling circulation in a Southern Italy coastal basin
No full textThe purpose of the present work is the study of particular hydrodynamic aspects
of Mar Piccolo, a basin located in the Northern side of the Gulf of Taranto in the
Ionio Sea (Italy), by means of mathematical modelling. A first analysis has been
driven, thus realizing a test case with simple hypothesis, referring to data from
the literature, in order to validate two 3D hydrodynamic models, i.e. the
Princeton Ocean Model and the MIKE 3. Once a quite good agreement
wasobserved between the outputs of the tested models, a further comparison was
considered. The results of the two models have been compared with some
circulation structures proposed in the literature, in analogous conditions.
Successively, both models have been forced by a further input, in order to
observe the response of the circulation to input modifications. The direct
comparison between simulation results and field measurements collected during
surveys is the future development of the ongoing research
Physical modelling of buoyant effluents discharged into a cross flow
No full textThis study focuses on physical modelling of turbulent vertical buoyant jets, discharged into a transversal current and interacting with localized background turbulence. The physical model was developed in the Coastal Engineering Laboratory of the Technical University of Bari. The physical model consists of a sophisticated system that allows to monitor and adjust all the characteristic parameters of both the channel flow (e.g. discharge, flow depth) and the buoyant jets (e.g. flow rate, temperature, salinity). Positively and negatively buoyant
jets are realized by discharging water respectively at a temperature and salinity higher than that of the receiving environment. Due to the complexity of the jet-current hydrodynamic phenomena, a set of sophisticated instruments to measure the jet spreading within the cross flow is used. The average jet dilution is measured by (i) four different Resistance Temperature Detectors (RTD) for the positively buoyant jet, and (ii) a MicroScale Conductivity Temperature Instrument (MSCTI) of high resolution for the negatively buoyant jet. Whereas, a Nortek Acoustic Doppler Velocimeter (ADV) system is used to measure the field flow velocities, together with CollectV software for data acquisition and ExploreV software for data analysis. The measured scalar and vector fields will be illustrated in this paper, with the aim to emphasize that a well- set physical model is able to explain the behavior of buoyant jets in an open channel with ambient factors, such as cross flow and vegetation
Experimental study of the impact of rigid vegetation on a buoyant jet in presence of crossflows
No full textThe present study deals with how a uniform cross-stream, with a channel bed surface covered by rigid emergent
stems, affects the behavior of a circular, turbulent buoyant jet. The time-averaged temperature and velocity fields
were investigated along the longitudinal central plane of the channel and across the jet, in order to understand
the jet diffusion and penetration within the ambient fluid. Moreover, an analysis of the jet axis was carried
out and compared with similar results found in literature for a pure jet in a cross flow. The evolution of the jet
was compared in cases both with and without vegetation in the surrounding environment. The examination
and comparison of the results show that the presence of emergent vegetation affects both the average velocity
and temperature fields and the jet structure, with a particular increase in the jet penetration height and dilution,
compared to the test case without vegetation
Two dimensional Lattice Boltzmann numerical simulation of a buoyant jet
No full textSince its introduction (Succi, 2001), the Lattice Boltzmann Method (LBM) has obtained increasing attention in the field of Computational Fluid Dynamics, due to its intrinsic simplicity and ability even in dealing with rather complex flows. This work is aimed at assessing the ability of the two dimensional version of the LBM in simulating a buoyant jet. The latter is a saline jet, entering a uniform flow. The inlet velocity of the jet is perpendicular to the velocity of the flow. The adopted two-dimensional Lattice Boltzmann formulation is equivalent to the Navier-Stokes equation with a Boussinesque gravity force term. Experiments on turbulent negatively buoyant jets into cross flow have been utilized to assess the validity of the numerical simulations. A conductivity probe for high resolution measurement of turbulent density was utilized to measure the mixing of the salt water into the cross current, whereas the Acoustic Doppler Velocimeter (ADV) system was used for the measurement of the instantaneous threeflow velocity components. The comparison of the two dimensional numerical results with the experimental results shows that the former are able to capture the general appearance of the flow, although there are important differences. In particular, two dimensional simulations are characterised by vortices which do not appear in experiments: this is probably due to two-dimensional nature of the numerical simulation and its reduced ability in dissipating turbulent structures
Mathematical modelling as support for planning decisions
No full textThe present work focus on the study of the circulation pattern in the North Bari coast, Italy,
where a waste water discharge from a treatment plant is present. Simulations with a 3D
hydrodynamic mathematical model, which was validate with field measurements, were carried
out in order to analyze (i) the most frequent meteoclimatic conditions and then (ii) two project
hypotheses that could minimize the impact of the discharge on the coast
Spinal changes associated with mechanical hypersensitivity in a model of Guillain-Barré syndrome
No full textGuillain-Barre syndrome (GBS) is an inflammatory disease of the peripheral nervous system which can cause pain via mechanisms that are poorly understood. Here, we show that in rat experimental autoimmune neuritis (EAN) mechanical allodynia developed up to 9 days before the onset of detectable neurological deficits. Allodynia was associated with an increase in the number of microglial cells in the dorsal horn of the spinal cord. The expression of the chemokine CX3CL1 (fractalkine) and its receptor CX3CR1 were also higher in EAN than in control dorsal horns suggesting spinal microglia and CX3CL1/CX3CR1 may play a role in the pain-like behaviour. (c) 2008 Elsevier Ireland Ltd. All rights reserve
Opere costiere per la difesa dei ripascimenti artificiali a basso impatto ambientale
No full textNel presente lavoro si riportano i principali risultati ottenuti durante una campagna sperimentale in corso presso il Laboratorio di Ingegneria Costiera (LIC) del Politecnico di Bari. Le attività sperimentali mirano ad ana-lizzare gli effetti del sistema di drenaggio spiagge (BDS) accoppiato ad una barriera sommersa ad elevata som-mergenza (c.a. - 1.80 m) sull’evoluzione trasversale a breve termine di un ripascimento artificiale, in condizioni ondose erosive. Le prove su modello fisico 2-D in scala geometrica indistorta di Froude 1:10 sono state condotte in condizioni non protette e protette, a partire dallo stesso profilo iniziale sino al raggiungimento del profilo di equilibrio (16-19 ore in scala modello). L’influenza dei due sistemi sui processi sottocosta è stata analizzata os-servando il comportamento del sistema di drenaggio spiagge (BDS) e della barriera sommersa (BW) prima se-paratamente e poi congiuntamente, al fine di poter scindere gli effetti di ciascun intervento sul trasporto dei se-dimenti. In via preliminare, i risultati sperimentali hanno inoltre consentito l’analisi delle capacità predittive del modello numerico XBeach (Roelvink et al., 2009) per lo studio dell’evoluzione del profilo trasversale di un ripa-scimento non protetto, nelle condizioni testate in laboratorio sul modello fisico. La sensitività del modello è sta-ta dapprima valutata in relazione alla discretizzazione spaziale della griglia e alla condizione ondosa al contor-no, consentendo la definizione di un modello base per la successiva fase di calibrazione rispetto all’evoluzione del profilo, considerando alcuni parametri coinvolti nella modellazione dei processi di idrodinamica e morfodi-namica. I primi risultati mostrano come, nonostante il modello restituisca un buon grado di accuratezza per la previsione dell’evoluzione morfodinamica del fondo e dell’idrodinamica, alcune incertezze risiedono nella mo-dellazione della forma della barra sommersa.The development of waterfronts constitutes a highly topical issue that involves large as well as small urban are-as facing the sea. Coastal areas represent the interfaces between the urban fabric and the sea, which is widely recognized as an engine for European economy. In order to exploit the potential that coastal areas offer, the planning and management strategies must be aimed at recovering the environmental quality which has seen its gradual decline, especially in recent years since the effects induced by climate changes exacerbate natural and anthropic pressures.
In agreement with Horizon 2020 and recently highlighted by the Blue Growth strategy undertaken by the Euro-pean Commission, it is necessary to encourage and support sustainable long-term growth in the marine and maritime sectors, through the strengthening of the seas, oceans and coasts in order to create new job opportuni-ties and companies in the Blue Economy productive sectors. Indeed, the protection of coasts and maintenance of a good quality of marine environments become a priority, to guarantee their sustainable use and reduce the ex-posure against erosion and flood phenomena that alter their stability, environmental quality and economical value.
In such a context, the rehabilitation of coastal areas often translates into the creation of artificial nourishments, which allow to restore an adequate extension of the emerged beach and the dune system, without compromis-ing the landscape and bathing activities. These interventions require an accurate management plan aimed at defining the financial sustainability of the work, mainly linked to its life-time.
In the present work, an alternative approach for protecting sandy beach nourishment is proposed. The short-term morphological evolution of beach nourishment profile under erosive wave conditions is investigated in presence of a mixed defence system composed by a drain pipe placed inside the beach in the swash zone, paral-lel to the shoreline, and a submerged rubble mound breakwater characterized by a high freeboard, namely equal to 90% of the offshore significant wave height below the mean water level.
A new experimental campaign is underway at the Coastal Engineering Laboratory of the Polytechnic University of Bari (Bari, Italy). The tests on 2-D small scale physical model (according to Froude analogy, 1:10) have been conducted in both unprotected and protected conditions starting from the same initial profile up to equilibrium conditions (16-19 hours in model scale). The drainage system (BDS) and the submerged barrier (BW) have been tested firstly separately and deployed together, in order to be able to separate the effects of each intervention on sediment transport. The experimental measurements have also allowed a preliminary calibration of the XBeach numerical model in reproducing the evolution of the nourishment profile in unprotected conditions
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