1,721,030 research outputs found
Hydrodynamics and morphodynamics in the swash zone: hydralab III large-scale experiments
No full textThe modelling of swash zone hydrodynamics and sediment transport and the resulting morphodynamics has been an area of very active research over the last decade. However, many details are still to be understood, whose knowledge will be greatly advanced by the collection of high quality data under controlled large-scale laboratory conditions. The advantage of using a large wave flume is that scale effects that affected previous laboratory experiments are minimized.
In this work new large-scale laboratory data from two sets of experiments are presented. Physical model tests were performed in the large-scale wave flumes at the Grosser Wellen Kanal (GWK) in Hannover and at the Catalonia University of Technology (UPC) in Barcelona, within the Hydralab III program.
The tests carried out at the GWK aimed at improving the knowledge of the hydrodynamic and morphodynamic behaviour of a beach containing a buried drainage system. Experiments were undertaken using a set of multiple drains, up to three working simultaneously, located within the beach and at variable distances from the shoreline. The experimental program was organized in series of tests with variable wave energy. While a positive effect was observed under low energy conditions, for medium and high energy conditions the benefit of having the drains operative was not always clear. In any case, it was evident that any positive effect of the drains on the beachface was confined by the position of the cone of depression in the aquifer’s surface.
The tests carried out in the large wave flume at UPC had the intent to investigate swash zone under storm conditions. The main aim was to compare beach profile response for monochromatic waves, monochromatic waves plus free long waves, bichromatic waves and random waves. Both erosive and accretive conditions were considered. The experiments suggest that the inclusion of long wave and wave group sediment transport is important for improved nearshore morphological modelling of cross-shore beach profile evolution, and provide a very comprehensive and controlled series of tests for evaluating numerical models. It is suggested that the large change in the beach response between monochromatic conditions and wave group conditions is a result of the increased significant and maximum wave heights in the wave groups, as much as the presence of the forced and free long waves induced by the groupiness. The equilibrium state model concept can provide a heuristic explanation of the influence of the wave groups on the bulk beach profile response if their effective relative fall velocity is larger than that of monochromatic waves with the same incident energy flux
Idro-morfodinamica di una spiaggia sottoposta a mareggiate caratterizzate da differente raggruppamento delle onde: esperimenti in larga scala
No full textLa zona di battigia presenta un delicato equilibrio idro-morfodinamico, per cui a modeste variazioni delle condizioni
idrodinamiche al contorno possono corrispondere sensibili effetti morfologici. Negli ultimi anni si sono
osservati grandi progressi per quanto concerne la modellazione del trasporto sedimentario in questa regione.
Tuttavia, molti elementi concettuali sono ben lontani dall’essere nitidamente definiti e, certamente, misurazioni
di campo risultano alquanto complesse e perturbate. In un quadro siffatto appare evidente come disporre
di dati di alta qualità ottenuti in condizioni controllate, giochi un ruolo cruciale. Il presente articolo descrive
gli esperimenti condotti presso il canale a larga scala dell’Università Politecnica della Catalogna. L’obiettivo era
studiare la risposta di una spiaggia a mareggiate caratterizzate da differente raggruppamento delle onde
Analisi dei carichi su un nuovo tipo di diga marittima per la conversione dell’energia ondosa in energia elettrica
No full textBeach sediment mixing under drained and undrained conditions
No full textThe paper describes a set of experiments undertaken at the Grosser Wellen Kanal (GWK) in Hannover on sediment
mixing on a beachface exposed to the action of a buried drainage system. Experiments were performed using a set of
drains (up to three working simultaneously), located at variable distance from the shoreline. Wave energy during the
tests ranged from medium (0.59 m < Hs < 0.61 m) to high (0.76 m < Hs < 0.83 m). Beach profiles were measured at the
end of each test. Further validation came from measurements using a grid of rods that were monitored at the same time
as the beach profiles were surveyed. While some beach stabilization was observed for low energy conditions, for
medium and high energy conditions the benefit of having the drains operative was not so clear. The comparison
between beach profiler and rods showed good agreement regarding relative vertical accretion and erosion events. In any
case, it was evident that the sedimentary effect on the beachface was confined to a narrow area above the drains. The
drained area showed slightly lower values of sediment mixing under drained conditions, but evidently this factor was
not important enough to trigger a widespread beach stabilization. Values of sediment mixing averaged across the whole
beachface ranged between 2-4 % and 4-6 % of the breaking wave height respectively for high and medium energy wave
conditions. Grain size, beach slope and drain configurations used here are fully comparable to field installations present
in the literature
Laboratory study on a beach drainage system
No full textIn recent years Beach Drainage Systems (BDS) have been considered as an innovative approach to stabilize the
beachface even if it still has to be proven to what extent they are effective in stabilizing the beach or causing accretion.
This paper describes tests carried out at the “GrosserWellenKanal” in Hannover aimed at improving the knowledge
of the hydrodynamic and morphodynamic behaviour of a beach containing a buried drainage system. Scale
effects that affected previous BDS laboratory experiments are minimized by the large scale. The morphodynamic response
of the undrained beach compared to a beach drained under the same type of wave action is reported. Experiments
were undertaken using a set of multiple drains, up to three working simultaneously, located below the beach
and at variable distances from the shoreline. The experimental program was organized in a series of tests with variable wave
energy.While a positive effect was observed under low energy conditions, for medium and high energy
conditions, the benefit of having the drains operative was not always clear. In any case, it was evident that any positive
effect of the drains on the beachface was limited to the position of the cone of depression represented by the
lowering of the hydraulic head
Dynamic Model of the Seawater Low-Head Turbine for Wave Energy Conversion
No full textIn this paper, a dynamic model of a seawater low-head turbine for an Overtopping BReakwater Energy Conversion (OBREC) system is presented. The model is not based on the physical similarity of hydraulic machines, as classical models are, and is easy to tune and lightweight to execute. These characteristics make the model ideal for preliminary control simulations or hardware-in-the-loop tests because it removes the necessity of depicting a particular turbine before starting the control design. This study pro- vides the static characteristics of the developed models in terms of torque and power as a function of speed and water height. These diagrams agree with the experimental studies conducted on physical turbines of similar characteristics as reported in other studies. In addition, the models were dy- namically tested for energy conversion and power exchange with a power grid. The perturb and observe method was adopted for the test, and it was observed that its tuning depended on the water wavelength
Test Reference Year for wave energy studies: Generation and validation
No full textIn a perspective of impoverishment of the fossil fuel and preservation of the natural environment, the sea wave energy is being increasingly regarded as alternative and promising resource. A key aspect to take in consideration for the deployment of Wave Energy Converters is the local characterization of the wave climate. In this contribute, a methodology for the calculation and validation of a site-specific Test Reference Year (TRY), from a multiyear dataset such ERA-Interim and ERA-5, to be used in wave energy conversion studies is proposed. Comparison of the two datasets with observed data gives ERA-5 as the best dataset.The methodology applied for the TRY generation has proven to be very effective, with the daily sum of H-s and T-m being the most effective indices for the TRY generation and in general T-m about twice more important than T-m. Once obtained, the TRY is applied in order to force an implementation of the Simulating WAves Nearshore (SWAN) model in an area of the central Adriatic Sea to characterize the area
Improved methodology for the optimal mixing of renewable energy sources and application to a multi-use offshore platform
Full text linkThe increase of Renewable Energy (RE) production to fight the climate crisis is posing new technological and financial challenges, due to the availability and variability of RE Sources (RES). These challenges can be addressed by selecting the most suitable mix of RES to optimise power production, to assure grid resilience and to promote local energy use. To facilitate the selection of such combination, this paper presents an original methodology that allows to compare mixing scenarios with different RES, also in presence of batteries and backup system. It simultaneously optimises the energy surplus with respect to the eventual external electrical load and the missing energy with respect to the same electrical load. This method, which can cope with isolated or plugged-to-grid systems, is here applied to a novel case study, an oil&gas platform under decommissioning, located in the Adriatic Sea (Italy). The RE production from wind, wave and solar panels is supposed to support other activities for the platform reuse, such as aquaculture, monitoring and mineral deposition. In this case, solar energy is providing the greatest contribution to the optimal mix in terms of production, while wave energy assures the most relevant contribution in terms of continuity
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