1,721,219 research outputs found
Coastal development under the threat of floods and climate change: risk assessment and sustainable decision making
No full textAnalysis of debris wave development with one-dimensional shallow water equations
No full textThe objective of this contribution is to analyse the formation of debris waves in natural channels.
Numerical simulations are carried out with a 1D code, based on shallow water equations and on the Weighted Averaged Flux method. The numerical code represents the incised channel geometry with a power-law relation between local width and flow depth and accounts for all source terms in the momentum equation. The debris mixture is treated as a homogeneous fluid over a fixed bottom, whose rheological behaviour alternatively follows Herschel-Bulkley, Bingham or Generalised Visco-Plastic models.
The code is first validated by applying it to dam-break tests on mudflows down a laboratory chute and verifying its efficiency in the simulation of rapid transients.
Then, following the analytical method developed by Trowbridge, the stability of a uniform flow for a Generalised Visco-Plastic fluid is examined, showing that debris flows become unstable for Froude numbers well below 1.
Applications of the code to real debris flow events in the Cortina d’Ampezzo area (Dolomites) are presented and compared with available measured hydrographs. A statistical analysis of debris waves shows that a good representation of wave statistics can be obtained with a proper calibration of rheological parameters.
Finally, it is shown that a minimum duration of debris event and channel length are required for waves showing-up and an explanation, confirmed both by field data and numerical simulations, is provided
Statistical Analysis of the Wave Runup at Walls in a Changing Climate by Means of Image Clustering
Full text linkThis contribution builds on an existing methodology of image clustering analysis, conceived for modelling the wave overtopping at dikes from video records of laboratory experiments. It presents new procedures and algorithms developed to extend this methodology to the representation of the wave runup at crown walls on top of smooth berms. The upgraded methodology overcomes the perspective distortion of the native images and deals with the unsteady, turbulent and bi-phase flow dynamics characterizing the wave impacts at the walls. It accurately reconstructs the free surface along the whole structure profile and allows for a statistical analysis of the wave runup in the time and spatial domain. The effects of different structural configurations are investigated to provide key information for the design of coastal defences. In particular, the effects of increased sea levels in climate change scenarios are analysed. Innovative results, such as profiling of the envelopes of the runup along the wall cross and front sections, and the evidencing of 3D effects on the runup are presented. The extreme runup is estimated for the definition of the design conditions, while the envelopes of the average and minimum runup heights are calculated to assess the normal exercise conditions of existing structures
Transmission of wave energy at permeable low crested structures
No full textThis paper presents a conceptual model for the prediction of energy transmission in presence of emergent permeable low crested structures. The transmitted wave is reconstructed from the superposition of perturbations generated leeward the structure by filtration and overtopped volumes. The model requires only structure geometry and incident wave conditions (wave height, period). A fair agreement is obtained by comparing the predicted transmission coefficients and wave spectra with measurements performed in wave flume and wave basin
MODELLO ANALITICO PER LA RICOSTRUZIONE DELLO SPETTRO D’ONDA TRASMESSA A TERGO DI SCOGLIERE A CRESTA BASSA
No full textQuesto contributo presenta un modello concettuale per la previsione dell’energia trasmessa a tergo di scogliere emergenti in condizioni 2D. L’onda trasmessa viene ricostruita dalla sovrapposizione lineare di due componenti: l’onda trasmessa per
filtrazione e l’onda generata dai volumi d’acqua tracimati che ricadono sul corpo d’acqua a tergo dell’opera. Il modello necessita solo della conoscenza della geometria della struttura e delle condizioni d’onda incidente (altezza, periodo)
Minimum channel length for roll wave generation
No full textThe initial phase of roll-wave development is investigated by means of spatial linear stability analysis using the St. Venant equations, subject to a pointwise time-varying oscillating disturbance. The predicted spatial growth is compared with both Vedernikov’s results and those computed with a fully non-linear model. It is shown that for large values of the channel slope Vedernikov’s theory systematically overpredicts the roll waves spatial growth rate, whereas the present analysis yields significant improvements. A modification of Montuori’s criterion for the minimum channel length prediction is finally proposed, which agrees with available experimental data independently of the channel slope
Influence of relative roughness and Reynolds number on the roll waves spatial evolution
No full texthttps://doi.org/10.1061/(ASCE)HY.1943-7900.000013
Frangiflutti galleggianti soggetti ad onde oblique
No full textI moderni frangiflutti galleggianti sono costituiti da elementi prefabbricati e inaffondabili, ancorati al fondo con catene e connessi fra loro da tiranti che ne vincolano il movimento relativo. Il vincolo agisce in modo sostanzialmente diverso dove i moduli sono allineati e dove formano un eventuale angolo in pianta perché il fronte d'onda investe le diverse parti della struttura con un certo sfasamento.
Questa lavoro si propone di esaminare, su generici frangiflutti soggetti ad onde oblique, la trasmissione ondosa, il tiro applicato agli ancoraggi e ai connettori.
Nella vasca ad onde (3.8m x 20.6 m x 0.8 m) del laboratorio di Costruzioni Marittime dell'Università di Padova, è stato esaminato un frangiflutti di sezione trasversale tipica disposto secondo due schemi planimetrici (ad I e a J), in presenza di onde a cresta larga con tre diverse obliquità (0°, 30°, 60°). Alcune prove sono state ripetute con nuovi strumenti per verificare l'attendibilità dei risultati.
All'aumentare dell'obliquità dell'onda il molo appare più efficiente grazie alla diminuzione della trasmissione e della forza su ancoraggi e connettori. L'effetto della presenza di un angolo fra due moduli dà un modesto beneficio in termini di trasmissione, le forze sugli ancoraggi sono fortemente ridotte e le forze sui connettori aumentano solo leggermente
Wave overtopping and transmission: an interpretation of spectral changes at low-crested rubble mound structures
No full textThis paper analyses wave transformation in presence of low crested permeable structures aiming to develop a simple, physically based model for the interpretation of the shape of transmitted wave spectra. The transmitted wave is reconstructed as the sum of the overtopped and filtered components of the incident wave. Incident waves transform seawards the structure into overtopping events and then regenerate, leewards the structure, due to perturbations caused by impulsive overtopping volumes. The overtopping and filtration discharge are added and converted into displacements of an ideal wave maker placed leewards the structure. This scheme is verified by means of 2D and 3D experimental data, obtaining a fair agreement between simulated and measured spectra, in particular when overtopping is prevailing on filtration
Experimental analysis of piling-up and filtration in presence of low crested structures
No full textIn the recent years, interest in Low Crested Structures (LCSs) has been growing up together
with the sensitivity to environmental impacts produced by coastal defences. Both a national PRIN 2001 and
EC project DELOS allowed to achieve a deeper knowledge of such structure type. Overtopping however,
which is a crucial aspect of LCSs, has not been completely characterised yet. The aim of this contribution is
to experimentally analyse in a wave flume, equipped with a recirculation system, the filtration discharge
(and thus the overtopping) in presence of permeable LCSs, characterised by different submergence, berm
slope and width. Different wave conditions are tested with varying recirculation discharge, till null piling-up
is reached. For the limited range of tested waves, results obtained so far show that overtopping is roughly
proportional to piling-up in confined conditions (absence of filtration), and piling-up is proportional to filtration.
The comparison of available piling-up dataset with existing formulae show poor agreement
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