1,721,167 research outputs found
Caisson Foundations for Competitive Offshore wind Farms in ITALY
No full textAbstractThe research presented in the paper moves from the results of a feasibility study recently carried out for the development of an offshore wind farm off the cost of Rimini, in the Northern Adriatic Sea. The work, based on in-situ measurements of the environmental conditions, assessed the suitability of the considered area for the development of a relatively large wind farm, although at the profitability limit. The study has considered 60 offshore wind turbines installed on monopiles, as they are, at present, the most common solution and a quantification of the investment costs could be reliably completed. With reference to such case, the paper addresses the use of caisson foundations, a convenient alternative to monopiles in water of shallow to intermediate depth, with the final aim of improving the overall cost-effectiveness of the investment
Investigation of environmental conditions: Current statistics including tidal, bathymetric an wave generated currents, residual large currents.
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Field measurements of hydrodynamics around a beach defence system
No full textAn extensive program of field measurements of currents around a beach defence system is described and results are shown. The monitoring program was carried out in the last three years around a semi-submerged breakwater built in Lido di Dante, Italy to protect a beach nourishment and prevent erosion. The monitoring aims to study the complex hydrodynamics of Low-Crested Structures (LCS). Drifter tracks surveyed in the study area together with current and wave measurements through an ADCP provide a better comprehension of the hydrodynamics during typical wave storms and a tool for the calibration of numerical models
Coastal flooding: A copula based approach for estimating the joint probability of water levels and waves
No full textAn accurate joint probability assessment of water levels and waves is of primary importance for effective coastal flooding management even in microtidal environments subjected to severe storm surge events. A copula based approach is presented for modeling the joint distribution derived from almost six years of sea levels and waves at a site suffering from coastal flooding. The evaluation of the upper tail dependence coefficient represents an unavoidable step in the copula selection process since it provides indications on extreme dependence that cannot be neglected to reliably estimate the probability of marine inundation. Based on the results of various statistical tests and estimation of the upper tail dependence coefficient, a one-parameter extreme value copula is selected to model the dependence structure of events representing conditions at peak water levels, including wave height, incoming wave direction and season of occurrence. The joint distribution obtained is subsequently used for reliability analysis. A particular simplified application case is described for the Ravenna coast (Italy) and the probability of failure/inundation is estimated through the direct integration method. Since the failure function employed involves the wave runup depending on wave period, the joint distribution of wave height and wave period is also assessed. The study highlights the importance of taking into account all the variables involved in the flooding phenomenon for a reliable flood probability estimate. The presented methodology can be applied to the assessment of flood probability at coastal sites at risk of inundation due to the combined impact of waves and water levels
Application of a new OpenFOAM tool to design a pilot floating wind farm offshore mazara del vallo (Italy)
No full textA new Computational Fluid Dynamic tool, based on OpenFOAM, was implemented to reproduce a physical wave tank for offshore applications. The code has new boundary conditions for deep water wave generation, a new turbulent model and a new numerical restraint to represent realistic mooring lines in OpenFOAM. A real study case application of this tool is shown hereby: a preliminary analysis of a floating wind turbine offshore Mazara del Vallo, (Italy). The application demonstrated the usefulness and capability of the model. Moreover, with active absorption, the dimension of the numerical domain, computational costs and time of the simulations are reduced
Design of multipurpose coastal protection measures at the reno river mouth (Italy)
No full textThis work presents the approach strategy for the optimization of the coastal defence at a specific site in the Northern Adriatic Sea, the Reno river mouth (Italy). The area is extremely dynamic and vulnerable since exposed to several climate change related effects and in the last decades has suffered strong erosion processes. A rocky revetment covered by a superficial bituminous layer protects this coastal area, but the bad state of conservation makes this defense technique inadequate also during ordinary events. In addition, important morphological variations at the mouth (i.e., the human demolishing of the final part of the right riverside) affected the stability of the protection works and compromised the inland safety. The analysis of multipurpose coastal schemes for flood mitigation and coastal defence of the area is carried out by means of the well-known commercial software MIKE21, that was implemented to simulate waves (SW), currents and levels (HD) and sediment transport (ST). Different sea events from NW (Bora) and SE (Scirocco) were reproduced in the site, also including tidal level, storm surge and river discharge associated to the reproduced storm. Current configuration of the area and alternative defence schemes (i.e. breakwater, groins) to improve coastal protection were simulated and the numerical results were compared in terms of wave load, inundation rate and bed level change. The condition of Bora with the simultaneous presence of high tidal level results to be the most severe event, since the developed longshore current contrasts the river outflow, leading to a high probability of fluvial flooding of the area. The comparative numerical analysis of the different scenarios and configurations allows estimating the optimal coastal protection scheme both in terms of flooding mitigation and erosion reduction and the implemented model can be a useful tool for future studies regarding a so vulnerable and dynamic area
Sediment fluidization system for nautical depth maintenance under monitored environmental currents
No full textOceanic ships are getting larger and costs of dredging are increasing, which largely justify the research on new practices for harbour entrance maintenance. In fact, the sedimentation of sands transported along coast reduces the navigable depth and requires a continuous dredging to ensure the entry of the vessels in secure conditions.
As new practice for reducing the dredging operations it is proposed a sediment fluidization system, which can maintain the required water depth by pumping water under the bed of the port entrance. Conditions to cause the sediment/fluid mixture to behave as a fluid could be achieved by the introduction of pressurized sea water through the sediment deposition. This results in heavily loaded fluid that can be removed by environmental currents. In this way erosion and deposition can be driven to maintain nautical depth and on the basis of monitored environmental currents.
Sand fluidization as opposite to sediment dewatering could be applied to mobilize depositions in the intertidal zones, when suitable currents take place to remove low depths barrier to navigation and harbour entrance. In the chemical industry the fluidization is usually realized within reactors, while, in the case of nautical depth maintenance, pump systems similar to dewatering system could be applied and controlled by means of Acoustic Doppler Current Profilers (ADCP) to monitor tidal and long shore currents.
A first application of the fluidization system was made on the commercial harbour of Ravenna (Italy), by means of the numerical code Mik21, to study the sediment transport near the port entrance. Ravenna represents the only commercial port of the Emilia Romagna Region and, thanks to its geographical position, is a leader in Italy for trade with the East Mediterranean Sea and the Black Sea, and also plays an important role for trade with the Middle and Far East. A first analysis indicates that the fluidization system can be used instead of dredging operations for removing the clean sediments from the entrance of the harbour by means of coastal currents
CFD investigations of OXYFLUX device, an innovative wave pump technology for artificial downwelling of surface water
No full textNo other environmental variable of such ecological importance to estuarine and coastal marine ecosystems around the world has changed so drastically, in such a short period of time, as dissolved oxygen in coastal waters. The prevalent methods for counteracting anoxic sea events are indirect measures which aim to cut-down anthropic loads introduced in river and marine environments. To date, no direct approaches, like artificial devices have been investigated except the WEBAP and OXYFLUX devices. The present paper adopts a numerical approach to the analysis of the pumped surface water as well as the analysis of the dynamic response of the OXYFLUX device. By means of a CFD-RANS code and through the application of overset grid method, the 1/16 OXYFLUX model's dynamic response and pumping performance are evaluated. The appropriate grid is selected after an extensive sensitivity analysis carried out on 9 different grids. The CFD model is validated by comparing numerical and physical results of heave decay test, heave response, and surface water discharge under the action of regular waves. The extensive comparison with experimental results shows consistently accurate predictions. The main findings of the study show that nonlinear effects remarkable reduce the dynamic behaviour of the OXYFLUX and generate an unexpected second harmonic for pitch response intensifying the overtopping discharge also for small waves caused by the summer's low intensity winds
3D-numerical analysis of wave-floating structure interaction with OpenFOAM
No full textModelling of floating structures is a challenging task for offshore and coastal engineering purposes. Their design requires detailed knowledge in forces, flow velocities, rotations, displacements and loads. Highresolution numerical modelling allows for the study of their behavior under sea forcings, giving necessary information on the turbulent multiphase processes and induced loads. OpenFOAM is one of the code that offers a possibility to include Computational Fluid Dynamics approach into the design processing. In the present study, a floating vertical cylinder was chosen to evaluate the code capability to simulate moving bodies under waves. Tests reproducing the free decay were performed. Then, the wave generation tool, IHFOAM, was included to analyze the dynamics of a cylinder, moored to the bottom, under regular waves. This innovative application with OpenFOAM® represents the first step to develop a numerical wave tank where to study wave-structure interaction
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