New large-scale laboratory data are presented on a physical model of a spar buoy wind turbine with angular motion of control surfaces implemented (pitch control). The peculiarity of this type of rotating blade represents an essential aspect when studying floating offshore wind structures. Experiments were designed specifically to compare different operational environmental conditions in terms of wave steepness and wind speed. Results discussed here were derived from an analysis of only a part of the whole dataset. Consistent with recent small-scale experiments, data clearly show that the waves contributed to most of the model motions and mooring loads. A significant nonlinear behavior for sway, roll and yaw has been detected, whereas an increase in the wave period makes the wind speed less influential for surge, heave and pitch. In general, as the steepness increases, the oscillations decrease. However, higher wind speed does not mean greater platform motions. Data also indicate a significant role of the blade rotation in the turbine thrust, nacelle dynamic forces and power in six degrees of freedom. Certain pairs of wind speed-wave steepness are particularly unfavorable, since the first harmonic of the rotor (coupled to the first wave harmonic) causes the thrust force to be larger than that in more energetic sea states. The experiments suggest that the inclusion of pitch-controlled, variable-speed blades in physical (and numerical) tests on such types of structures is crucial, highlighting the importance of pitch motion as an important design factor.
Dune restoration projects that integrate vegetation efforts with natural, sustainable, and soft solutions have become increasingly popular in coastal communities. Eco-restored dunes have high aesthetic value and are likely to be more resilient to near-surface wind effects and/or minor storms events. However, environmental-friendly restoration strategies still lack scientific insight from systematic research and the role of eco-restoration in dune erosion resistance and resilience has not yet been rigorously investigated. The question is: how can we optimize eco-friendly solutions in dune ecosystem restoration to maximize the resistance and resilience of coastal dunes against erosion from wind, wave, and storm surge attack? The present paper proposes an innovative colloidal silica-based consolidation technique for coastal sand dunes. A special focus is placed on the description of the experience gained from two pilot field studies started in Salento coastal area, in the south of Italy. The preliminary observations clearly show that mineral colloidal silica increases the mechanical strength of non-cohesive sediments allowing the adopted solution to reduce the volume of dune erosion and the dune scarp retreat rate, thus improving the resistance and resilience of the dune system. Besides furthering our knowledge of coastal erosion, the results of these and future studies will be of value to coastal managers and policy makers responsible for dune restoration projects.
Beach–dune system morphodynamics is probably one of the most classical coastal engineering problems. While the topic has been studied extensively and literature is plentiful of considerable research contributions, from the authors’ knowledge the subject is still challenging for coastal and environmental sciences. As a part of the Special Issue entitled “Beach–dune system morphodynamics” of this Journal, the present paper reviews traditional issues and design advances building bridges between potential risks and adaptation measures. The benefits of nature-based and hybrid solutions and the need for multidisciplinary studies and approaches to promote sustainable and resilient conservation of the coastal environment are emphasized. Considering the importance and complexity of the subject, this work cannot be fully complete. It is limited to providing a general overview and outlining some important directions intending to serve as a springboard for further research in the field of beach–dune system morphodynamics.
Dune recovery interventions that integrate natural, sustainable, and soft solutions have become increasingly popular in coastal communities. In the present study, the reliability of an innovative non-toxic colloidal silica-based solution for coastal sand dunes has been verified for the first time by means of laboratory experiments. An extensive experimental campaign aimed at studying the effectiveness of the use of nanosilica has been conducted in the 2D wave flume of the EUMER laboratory at the University of Salento (Italy). The study was first based on a horizontal seabed and then a cross-shore beach-dune profile was drawn similar to those generally observed in nature. Detailed measurements of wave characteristics and observed bed and cross-shore beach-dune profiles were analyzed for a wide range of wave conditions. In both cases, two sets of experiments were carried out. After the first set of experiments performed resembling the native conditions of the models composed with natural sand, the effects of the injection of the mineral colloidal silica-based grout were investigated. The observations show that mineral colloidal silica increases the mechanical strength of non-cohesive sediments reducing the volume of dune erosion, thus improving the resistance and longevity of the beach-dune system.
Submerged and low-crested breakwaters are nearshore barriers with an underwater or slightly emergent crest, designed to reduce the energy of wave attacks and, consequently, to protect the coast from erosion and flooding. Their performance in reducing the wave energy can be evaluated by the value of the wave transmission coefficient, which thus requires accurate prediction. In the last few decades, several experimental investigations allowed the development of several formulae to predict this coefficient that agreed well within the given range of validity. In the present study, a comprehensive review of the existing formulae has been reported and the influence of input design variables has been highlighted. Moreover, an extensive set of experimental data has been collected and critically examined and re-analyzed to obtain a homogenous up-to-date database. Special attention has been addressed to the assessment of the reliability of each existing formula for and to evaluate its performance beyond the validity limits for which it was developed.
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