1,721,047 research outputs found
L’influenza delle opere sommerse nella morfodinamica costiera: uno studio numerico
No full textNegli ultimi anni, le mareggiate risultano avere un impatto sempre più importante sull’economia dei litorali, incidendo pesantemente anche sul mantenimento delle strutture ricettive/turistiche, specialmente
se hanno luogo nel periodo estivo. La progettazione delle tradizionali opere di difesa della costa risulta determinante nella protezione di tali strutture. Per questo motivo sono state effettuate alcune simulazioni
mediante un solutore numerico idro-morfodinamico che risolve le equazioni delle acque basse e l’equazione di Exner. Sono stati realizzati test numerici con lo scopo di valutare i) l’effetto di mareggiate reali con
diverse caratteristiche spettrali e ii) l’influenza della distanza da riva di una coppia di scogliere sommerse sulla morfologia della spiaggia. I risultati delle simulazioni hanno evidenziato una variazione minima nelle
forme di erosione/accrescimento al variare delle caratteristiche spettrali delle mareggiate. La morfodinamica che si realizza intorno alle scogliere e nel varco è invece fortemente influenzata dalla posizione delle opere: le
variazioni del fondale sono tanto maggiori, quanto più lontane sono le opere da terra. La zona di battigia, invece, è poco influenzata dalla distanza da riva delle scogliere
Scour depth under pipelines placed on weakly cohesive soils
Full text linkWe here study the scouring processes that evolve around a submarine pipeline placed on a weakly cohesive seabed. We first analyze some laboratory tests carried out by Vijaya Kumar et al. [21], Xu et al. [25] and Zhou et al. [28] that focused on the scouring around a horizontal cylinder lying on a cohesive bed, subject to waves and currents. The specific purpose is that of finding a new formula for the prediction of the equilibrium scour depth under submarine pipelines. After a theoretical analysis of the main parameters, the sought formula has been found to be a function of: (i) the hydrodynamic forces acting on the cylinder (through the Keulegan-Carpenter parameter KC), (ii) the clay content of the soil C-c, and (iii) the burial depth eo ID. In the presence of small amounts of clay (C-c< 5%), the scour depth depends directly on KC (as confirmed by many literature works for pipelines lying on sandy soils, e.g.[18]) and inversely on C-c (as already seen for bridge abutments on cohesive soils, e.g. [1]), the best-fit law being characterized by a coefficient of determination R-2 = 0.62. If some burial depth is accounted for, this being a novelty of the present work, a more general formulation can be used, valid in the presence of weakly-cohesive soils and with burial depths of the pipe smaller than 0.5 (R-2 = 0.79). For large clay-content ranges (2% <C-c < 75 %), the scour depth depends directly on both KC and C-c, this giving R-2 = 0.79 (no burial depth) and 0.91 (some burial depth). However, this finding is at odds with the main literature, because, for large amounts of clay, it is fundamental to consider the liquidity index LI, which accounts for some important clay properties, like the plasticity. We argue that the absence of LI is balanced by the direct dependence of the scour depth on C-c. Notwithstanding the small number of available data, a formula for the prediction of the scour depth under pipelines lying on cohesive soils is fundamental for several engineering applications. The present contribution represents the first attempt to build such a formula, when the pipeline is subject to the wave-current forcing and the seabed is characterized by a relatively small clay content. (C) 2015 Elsevier Ltd. All rights reserved.II
A wave-by-wave analysis for the evaluation of the breaking-wave celerity
No full textThe paper gives an overall description of the breaking-wave celerity on the basis of a wave-by-wave analysis that has been performed by using field data collected during the ECORS Project (Truc Vert Beach, France, 2008). Data coming from two pressure sensors have been analyzed with the aim to correlate, after a zero-crossing analysis, each wave of both signals. The method is based on a first correlation between 10 ' time windows of both signals and, then, on the individuation of the correct time lag for each wave. Such data, which reveals a quasi-gaussian behavior of the breaking wave celerity, have also been used to relate the wave celerity with suitable wave characteristics, and comparisons are made with the most common formulas that can be found in the literature. The wave-by-wave method, validated by means of suitable laboratory test data, gives good results in the evaluation of the celerity, especially when it is made to depend on both a velocity scale and the wave non-linearity parameter. Further, a comparison with literature models used for the prediction of breaking wave celerity suggests good performances of both solitary-wave (correlation coefficient R-2 = 0.79) and shock-wave (R-2 = 0.71) theories, that give results well matched to the field data
Numerical Hydro-morphodinamic 2DH model for the shallow waters
No full textNella presente tesi viene descritto un solutore numerico idro-morfodinamico, quale contributo innovativo nello studio e previsione dei flussi sotto-costa e delle variazioni di fondale indotte da onde e correnti. Il modello include un robusto solutore idrodinamico per l'integrazione delle Non-Linear Shallow Water Equations (NSWE) ed un solutore piuttosto flessibile per la risoluzione dell'equazione di Exner (utilizzato per valutare l'evoluzione morfologica del fondale marino). L’accoppiamento delle NSWE con l’equazione di Exner e l'aggiornamento della soluzione vengono effettuati mediante uno schema di splitting sequenziale.
Il modello è stato validato mediante la riproduzione sia di test numerici/analitici, presenti nella letteratura degli ultimi anni, sia delle esperienze di laboratorio eseguite nel Laboratorio di Idraulica dell’Università Politecnica delle Marche (AN). La simulazione delle soluzioni teoriche esistenti ha portato a risultati coerenti sia per quanto riguarda l'idrodinamica sia la morfodinamica, soprattutto nella previsione dell’evoluzione dei fondali marini dovuta al trasporto solido al fondo o a quello in sospensione, in seguito a eventi di dam-break e di swash. Il confronto tra risultati numerici del solutore e dati sperimentali è parzialmente soddisfacente. Infatti, il solutore riproduce abbastanza bene le caratteristiche principali del fondo in presenza di onde spettrali, ma fallisce quando vengono riprodotte onde regolari, a causa di “effetti di laboratorio”, verificatisi in canaletta
Morphodynamic shoreline boundary conditions: A preliminary validation from laboratory experiments
No full textAt present the processes occurring in the Swash Zone (SZ) are
disregarded by all available wave-averaged nearshore circulation
models. Only recently a series of studies has proposed an approach to
solve this problem by means of Shoreline Boundary Conditions (SBCs)
obtained from integrating the Nonlinear Shallow Water Equations over
the SZ width. While hydrodynamic conditions are a consolidated and
validated theoretical tool, morphodynamic conditions (MSBCs) still
require theoretical inspection and experimental validation. We here
focus on a theoretical analysis of the problem, which, on the basis of
available experimental data, aims at clarifying the role of short- and
long-wave contributions to the mentioned MSBCs
Condizioni al Contorno di Riva Morfodinamiche: Alcuni Aspetti della Metodologia di Validazione
No full textLong waves approaching the coast: Green’s law generalization
No full textThe original Green’s relationship provides the amplitude of a long wave at a given water depth as a function of the amplitude in deeper waters, accounting for the wave shoaling, taken as a one-dimensional process, and neglecting both diffraction and refraction effects. An analytical application of Green’s law can only be made in case of simple bathymetries, monotonically increasing in the cross-shore direction and being longshore uniform. In the present work, a new formulation is proposed, based on Green’s law, for the direct calculation of the change in amplitude of a long wave that approaches the coast while traveling over a natural bathymetry, characterized by a general shape. Hence, the effects due to the ray curvature provided by the refraction/diffraction phenomena are accounted for. In detail, a generalization of Green’s law is proposed by introducing a numerically computed coefficient. Comparisons have been provided between the wave amplitude evolution, reconstructed using the proposed law, and the results of numerical simulations, run using a solver based on the solution of the shallow water equations. Although local effects due to obstacles are not properly captured, such comparisons reveal that the generalized Green’s law works well in the far field under different wave and complex morphological conditions
Un'analisi preliminare sul ruolo della vegetazione nell'idrodinamica dei canali a sezione composta
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