QUALITATIVE AND QUANTITATIVE FEATURES OF WAVE BREAKING OVER A SUBMERGED BREAKWATER, AND EFFECTS ON NONLINEAR WAVE- … (original) (raw)
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Experimental tests on interaction between a wave and a submerged rubble-mound breakwater were performed in wave flume at University of Napoli Federico II. Different incident wave conditions were tested, including both non-breaking and breaking waves over the barrier. In cases of breaking, different breaker types at structure were described and classified according to hydraulic-morphological criteria. Experimental results show, according to early literature, that wave breaking induces a saturation in non-linear processes that characterize wave-structure interaction. Effect of saturation on 2 nd order transmitted free waves amplitude was investigated, and a best-fit formula was derived. A simple approximate method for wave profile prediction leeward of the barrier is finally proposed.
Wave Transmission over Rubble-Mound Submerged Breakwaters
Journal of Marine Science and Engineering
This study focuses on the prediction of technical efficiency of narrow-crested submerged permeable rubble-mound breakwaters, in terms of wave attenuation. A number of existing formulae for estimating wave transmission coefficient for submerged breakwaters can be found in the literature, whereas in this work further improvement for that estimation has been achieved mainly through physical modelling. A series of 2D experiments under scale were conducted for regular and random waves providing data on wave transmission coefficient and respective wave breaking characteristics. A Boussinesq-type wave model capable of simulating wave propagation for regular waves over porous submerged breakwaters was also used in order to provide additional wave transmission information. Data analysis showed that wave breaking mechanism significantly affects wave energy dissipation and, therefore, wave breaking occurrence and type can be directly linked to wave transmission coefficient for a given structur...
Analysis of the wave-flow interaction with submerged breakwaters
WIT transactions on modelling and simulation, 2007
The use of submerged breakwaters against coastal erosion problems has some advantages when compared, for example, with the use of similar emerged coastal protection structures and for that reason their use in coastal protection is becoming popular all over the world. Their effect in the wave field and especially in the wave-induced velocities has been analysed by several authors though there is still a lack of knowledge on the wave-flow interaction. The aim of this study was to analyse the behaviour of submerged breakwaters and especially the wave induced velocity field, which can have great impact in the stability of the structures and in the sediment circulation. Two-dimensional scaled physical tests were carried out in the Hydraulics Laboratory wave tank of the University of Porto, in order to understand with more accuracy the influence of the permeability and of the submergence of the breakwaters in the wave-structure interaction. For that reason, tests were performed with the same wave conditions (regular waves), with two different models with the same geometry, one with permeable and one with impermeable rough slopes, and with two water depths (leading to two different freeboards of the structure).
COASTAL …, 2002
Functional design of low crested breakwaters requires an accurate prediction of wave transmission in the protected areas. Nevertheless, commonly used formulae do not appear to be reliable enough, especially for structures located in shallow waters. The paper describes results from large-scale model tests conducted on rubble mound breakwaters exposed to breaking waves. Tests were carried out at the "Grosser WellenKanal" of Hannover, Germany. The model dimension, near to prototype, allowed minimizing scale effects connected to wave breaking. Existing formulas on wave transmission have been verified and influence of crest width and breaker index have been highlighted.
Permeability effects on breaking waves over submerged rubble mound breakwaters
In the present study the effect of breakwater permeability on breaking, regular waves over submerged permeable breakwaters is investigated numerically. The COBRAS, Liu et al. (1999), wave model is used for the numerical simulation of waves propagation. It is calibrated and validated against experiments from the DELOS project conducted in the Cantabria University wave flume. Structure porosities from 0.3 to 0.8 are examined resulting in permeabilities from 6.92*10-9 m 2 to 2.57*10-5 m 2 for various wave conditions. The freeboard of the structure is 5 cm in a total water depth of 40 cm. It is revealed that structure permeability affects wave breaking and therefore surface evolution on the seaward slope, the crest and the landward slope, of the structure. The spectra undergo significant changes under the combined effects on non-linear energy transfer and dissipation for lower structure permeabilities. On the contrary these phenomena are milder in the case of higher permeabilities. The phenomena of higher frequency harmonics generation is more evident in the first case. Energy considerations reveal that permeability affects significantly transmission, reflection and dissipation, of wave energy mainly due to the change of friction and wave breaking characteristics. 2DV turbulence kinetic energy fields reveal that turbulence kinetic energy intensity in the case of lower permeabilities is much lower than in the case of higher permeabilities. In the first case maximum turbulence kinetic energy intensity is observed in the porous body of the structure while in the second case maximum turbulence kinetic energy intensity is observed over the crest of the breakwater.
Laboratory Tests on the Interaction Between Nonlinear Long Waves and Submerged Breakwaters
Coastal Engineering 1992, 1993
This paper deals with the use of submerged detached breakwaters as beach protection, a use that today has become quite popular. This type of structure has been largely studied both theoretically and through experimental analyses in recent years, however its behaviour has not been completely understood, specially if related to the real irregular wave attacks. In particular some laboratory studies carried out by the authors have pointed out some interesting phenomena associated with the interaction between the nonlinearities of wave transformations in shallow water and submerged breakwaters. Aiming at discerning between the phenomena related to the structure (beach and breakwater) and flume geometry, a new series of laboratory tests have been carried out in a 50 m long wave flume; these tests and the results obtained are described in this work. Besides the study of the behaviour of submerged structures related to the bounded-long-waves, some current velocities have also been measured during this research through directional micro-propeller fluid meters.
Oblique wave transmission through rough impermeable rubble mound submerged breakwaters
2010
There is a growing interest in the application of submerged rubble mound breakwaters as coastal defence structures. As their defensive ability highly depends on the amount of wave energy remaining at their lee side, the accurate prediction of the energy in the lee of such structures is of utmost importance. Past experiments have shown that the behaviour of rough permeable rubble mound structures under oblique wave attack was found to be significantly different from that of smooth impermeable low crested structures. This behavioural difference has led to the research objective of this present study which is to investigate oblique wave transmission by rough impermeable rubble mound submerged breakwaters using 3D physical model tests. This study intentionally uncouples two parameters, being the permeability of the core and the roughness of the breakwater. Analysing the data of this study shows that the permeability of the core has no visible influence on the structure's behaviour with respect to the influence of oblique wave attack. The fully permeable rough rubble mound breakwater behaves analogous to the fully impermeable rough rubble mound breakwater.
Wave breaking macrofeatures on a submerged rubble mound breakwater
Journal of Hydro-environment Research, 2008
Results of an extensive experimental study on the interaction between waves and submerged barriers are presented. In particular, the present paper deals with identification of breaking conditions and morphological description of breaker types occurring on a submerged rubble mound breakwater. Barriers with varying geometry and permeability were used for tests. Video data were collected and analyzed and, in case of breaking, different classes and subclasses of breaker types were described and classified, considering: (a) the features of the incipient mechanism of wave rupture, (b) the shape of wave profile at breaking and (c) the evolution of breaker travelling above and leeward of the barrier. The breaker index, i.e. wave height to crest freeboard ratio at incipient breaking was studied as a function of the structure layout and wave parameters; experimental results were found to reasonably agree with Goda and Morinobu (1998) findings and a best-fit expression for scale parameter in Goda breaking formula was derived. A first parameterization of breaker types was then proposed, considering both wave and structure characteristics, described by appropriate non-dimensional numbers.
Wave Transmission and Water Setup Behind an Emergent Rubble-Mound Breakwater
Journal of Coastal Research, 2013
Wave transmission and water setup landward of emergent detached breakwaters play a major role in altering nearshore hydrodynamics, circulation, and morphodynamics and influencing the safety of recreational bathers. These phenomena have been extensively studied by means of small-scale laboratory experiments and numerical simulation, but field measurements have been extremely limited. In this work, wave transmission and setup were measured landward of a detached, emergent rubble-mound breakwater at Marina di Pisa, Italy. Water-surface elevations were measured with pressure transducers onshore and offshore of the breakwater. Measurements were made for 14 hours during a storm with significant wave heights up to 3.5 m and mean periods of 8.5 s. In the present work, the data were used to quantify and develop statistical relationships describing wave transmission and water setup and to evaluate the performance of empirical models of transmission and setup for emergent breakwaters. We found that the incident wave height explained (statistically) 94% of the variability in wave transmission and 96% of the variability in setup for the Marina di Pisa breakwater. There was a 99% coefficient of determination when explaining variation in setup using incident wave height and transmissivity. Of the empirical models we tested, those that best predicted observed wave transmission landward of the breakwater had root mean square (RMS) errors of 33%. The best available models to predict observed setup had RMS errors of 66%.
Overtopping of Rubble-Mound Breakwaters by Irregular Waves
Proceedings of ... Conference on Coastal Engineering, 1976
This paper describes the results of an experimental study on the effect of waves on rubble-mound breakwaters, wave transmission subsequent to wave overtopping, the stability of the three sides subjected to wave action and the effect of the breakwaters on waves. Two different rubble-mound breakwaters were tested, i. e. one with a rigid impermeable crest and the other with a flexible permeable crest. Tests were performed with both regular and irregular wave train systems. To obtain the simulated irregular wave trains, four theoretical spectra were chosen: Neumann, Bretschneider, Moskowitz, and Scott. Results obtained from tests with irregular wave trains were compared to those obtained from tests with regular wave trains. It was found that more information was obtained on the behaviour of the structure when it was submitted to the attack of irregular waves than when submitted to regular waves, and that the use of irregular wave trains gave more interesting results.