1,721,118 research outputs found
Transient response of harbours to long waves under resonance conditions
No full textThis paper presents the results of a study aimed at quantifying the time-response of harbour basins to long waves under resonance conditions. On the basis of numerical simulations reproducing long waves in the yacht harbour of Rome (Ostia, Italy), it shows that the results valid for periodic forcing waves, acting for an infinitely long time, as those provided by models based on elliptic equations like the Helmoltz and the mildslope equations, can be misleading with respect to the more realistic ones that can be obtained using time-varying wave equations. Taking advantage of the similarity between the processes studied here and a simple one-dimensional resonator, a method is also proposed to roughly estimate a time-response parameter of each mode of the harbour, using results from steady-state numerical model results, commonly applied for studying harbour resonance in engineering practice. On the basis of further numerical simulations, aimed at reproducing schematic harbour layouts, the effect on resonance of the position of the entrance and of an outer harbour is studied. The results indicate that the effects of design solutions to reduce resonance, by placing the entrance at the middle of the harbour, or using the outer harbour as a resonator, can be correctly evaluated only when considering the time needed for the oscillations to fully develop. (c) 2007 Elsevier B.V. All rights reserved
Un semplice modello per il calcolo della velocita' delle correnti di rip e del sovralzo nell’intorno di barriere sommerse discontinue per la difesa delle spiagge
No full textAn improved analytical model for estimating water level set-up and currents induced by waves over submerged low crested coastal defence structures
No full textA simplified model for estimating rip currents flow parameters: application to a study case
No full textA simplified model of rip currents systems around discontinuous submerged breakwaters
No full textAlthough in the last years, several numerical models have been shown to be able to reproduce rip currents around discontinuous submerged barriers, only few simple methods of practical use are available for estimating main flow parameters, like the current intensity and the mean water levels, in terms of geometrical (barrier and gap dimensions) parameters and wave characteristics. The aim of this paper is to present a simplified model to be used for an easy estimate of these important rip currents parameters. The model, which is based on rough simplifications, considers the area between the shoreline and the barrier as a reservoir in which water is pumped by breaking short waves across the barrier and from which water flows out at the gap. Four equations (mass and momentum conservation across the barrier, free discharge at the gap and balance of water pumped towards the shore and freely flowing offshore) are used to derive one single model equation that can be solved for the wave set-up and subsequently used for rip current velocity calculation. Two free parameters appear in this equation which respectively account for energy losses at the gap (C-v) and bed friction (mu). The proposed model is validated against available laboratory experiments to show its ability in providing reasonable estimates of the desired parameters, that may be considered by engineers adequate at the preliminary design stage of submerged breakwaters and that can be used for evaluating hydrodynamics on barred beaches. (C) 2004 Elsevier B.V. All rights reserved
Un nuovo modello numerico per la simulazione di batterie di convertitori di energia ondosa
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