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Abstract: This article presents a field study of the bed response near linear reflective structures under wind wave-dominated conditions at the Motril harbor (Spain) on the Mediterranean coast. In 1999 the harbor breakwater was enlarged 600 m by adding vertical caissons. Before this enlargement took place, no significant bed features had been observed in the area. However, at the end of 2004 high resolution bathymetry showed the existence of 3–4 bars parallel to the structure with lengths between crests of 0(70 m) in the cross-shore direction and heights of 0(25 cm). Toe erosion with an amplitude up to 25 cm was also observed along the structure. The necessary conditions for the appearance of the bar system are: (1) a standing wave pattern in front of the structure; (2) local satisfaction of the wave-height and wave-period threshold limits for sediment mobility. Using an energy-based approach, we analyze the time series of sea states with sediment transport capacity after breakwater construction. The cumulative distributions of the shear velocities related to WSW–SW sea states show that all the bars have a greater probability of being N-type features (predominant bed load) under generalized sediment transport conditions. These conclusions were verified by matching nodal lines of standing WSW–SW wave patterns with the bar locations. The results suggest that the Motril bar system of Motril is possibly generated by the standing wave patterns induced by several sea states with peak periods of O(10 s) and significant sediment transport capacity resulting from WSW–SW severe storm events that occurred in Motril after breakwater construction. This article highlights the need to verify in field conditions the present threshold limits for sediment transport mobility. [Copyright &y& Elsevier]

A simple method is proposed for the experimental calculation of the mode conversion coefficients in multimode optical fibers. It only requires observing the far-field output pattern from a fixed length of fiber as the launching angle changes, as well as the intersection point between two far-field output patterns corresponding to two different input angles. The results obtained with this method are quite insensitive to small variations of the experimental parameters. A good agreement between theoretical and experimental results is also found. [ABSTRACT FROM PUBLISHER]

We have studied the optical power losses due to multiple curvatures in polymethylmetacrylate (PMMA) plastic optical fibers (POFs) of different numerical apertures (NAs) and attenuation. The fibers were tested for several configurations in order to assess the influence of different types of curved-to-straight fiber transitions in the amount of power radiation. We found that losses are below the standards for all tested fiber types, and thus, they are a suitable choice for local area network (LAN) applications. In addition, our results revealed the presence of modal interactions as confirmed using an experimental procedure to estimate the mode coupling strength for the same fibers. [ABSTRACT FROM PUBLISHER]

In this work, an intensity modulation/frequency-shift keying (IM/FSK) orthogonal modulation scheme is achieved by direct modulation of a distributed feedback laser source using its adiabatic chirp characteristics. Optical frequencies for "1" and "0" bits are separated only 0.7 GHz, obtaining a narrow-FSK modulation and, accordingly, a low residual intensity modulation. Ethernet frames at 1.25 Gb/s (GbE) are transmitted with a label inserted using coded mark inversion codification at a 155-Mb/s rate. Error rates for the Ethernet payload and for the label have been measured for different payload extinction ratios, showing the viability of this scheme for distances up to 25 km [ABSTRACT FROM PUBLISHER]

The performance of a colourless WDM PON architecture based on frequency-shift keying (FSK) by direct modulation of a DFB laser diode for the downstream and intensity modulation by means of a reflective semiconductor optical amplifier for the upstream channel is assessed. The operation of the architecture is demonstrated, showing excellent performance for distances up to 25 km. [ABSTRACT FROM AUTHOR]

In the present experiments a volumetric particle-tracking system (V3V from TSI Inc.) allowed the measurement of the velocity fields generated by regular breaking waves past a fixed bar on a 1:10 rigid plane slope. The measurement volume extended from the wave crest to a portion of the domain below the wave trough, with two sets of monochromatic wave trains with different periods and heights. The aim of the present work is the quantification of the terms in the vorticity balance equation by including all the terms in a fully 3D approach. A possible new vorticity generation mechanism is revealed, that is amplified by the geometry of the laboratory flume and that awaits experimental validation in 3D wave tanks and in the field. The results are new and original and represent a data set for the comprehension of the effects of a submerged berm, for developing conceptual models of vorticity and for the calibration of numerical codes. [ABSTRACT FROM AUTHOR]

Wind–waves play a relevant role in the downward flux of mass, momentum and heat, and in their balances. Thus, they are quite significant in small- and large-scale processes like global warming, especially in continental shelf. There is still no consensus on the effectiveness of different mechanisms in enhancing, e.g., the carbon dioxide ( CO 2 ) uptake in the continental shelves with respect to the open ocean. To our best knowledge, the role of partial reflections of short and long waves in the budget has been largely neglected without a specific justification, even though reflection in water waves is a recurring phenomenon. Presumably, this is a consequence of the difficulties in performing experiments with variable reflection coefficient and phase shift of the waves approaching coastal structures. We report experiments on the vertical momentum transfer in partially reflecting waves propagating on a flat horizontal bottom. We measured the free surface level and the fluid velocity, and estimated the Reynolds wave–generated shear stress. A set of experiments using paddle waves or a paddle plus wind waves and a reflection coefficient ranging from 0.10 − 0.75 , with a phase shift of π / 4 − π rad, confirms the theoretical model. The results indicate that reflection must be carefully considered in the correct interpretation of data, particularly when considering momentum transfer in the vertical. The new contributions in the paper are (i) the adoption of a generation–absorption system that controls the reflection coefficient and phase shift between incident and reflected waves; (ii) the quantification of the phase shift influence on the vertical momentum transfer and its horizontal variability; (iii) the consequences for locally–generated wind–waves and wind generated surface currents. To our knowledge, these are the first experiments where the characteristics of the reflected waves have been imposed, allowing a thoroughly analysis of their effects on the flow field. [ABSTRACT FROM AUTHOR]

This research is an experimental study of ripple and sandbar dynamics under regular and random waves in partially reflective conditions. As part of this study, a series of small-scale flume experiments were performed that reproduced the growth and migration of the bedforms, starting from a flat bed or rippled bed, with sediment transport in the bedload regime. The results showed that the evolution and dynamics of sandbar geometry were slower processes than the evolution of ripples. Moreover, they were governed by the wave field, reflective conditions, and sediment characteristics. Sandbar generation was controlled by the intensity of reflection, whereas the location of the crests (or deposition and erosion areas) was constrained by the phase shift of the reflected waves. Significant differences were also found between sandbars under regular and random waves. Sandbars under regular waves showed flat or practically flat troughs. In contrast, sandbars under random waves were almost uniformly covered by ripples. The experimental results showed that the concurrence of ripples and sandbars under partially reflected waves has a spatially modulating effect on ripple characteristics (i.e. growth, shape and migration celerity), which could not be consistently interpreted by using the classical formulas valid for ripples under progressive waves and/or without large-scale bedforms. This variability was more pronounced for regular waves than for random wave trains. Larger ripples develop in the nodes of the free surface envelope (more or less corresponding to the sandbars crests), whereas smaller ripples occurred in the antinodes (or sandbars troughs). The statistics of ripples geometry and celerity were computed with a sample stratification, based on their position in reference to the sandbars. In addition, they were compared in two energetically equivalent tests with regular and random waves, respectively. Although ripples under random waves had a larger wavelength and height than ripples under regular waves, the celerity of migration was comparable. Our results showed that the sandbars modified the equilibrium geometry of ripples. Furthermore, because of roughness, streaming was induced by the highest and longest ripples in the sandbar crests. The spatial modulation of the ripple celerity was found to be related to the local Lagrangian mass transport velocity, which was produced by the quasi-standing wave inside the bottom boundary layer at the grain-diameter scale. [ABSTRACT FROM AUTHOR]

Abstract: A beach sedimentation problem is presented. This problem involves assessing the impact and importance of land-based sediment sources (erosion from gullies during intense rainfall, and directly from cliffs by wave action) on morphodynamic changes at a beach. The site motivating the study is La Barrosa beach, Spain. The location is described and a discussion of possible approaches presented. A schematized representation of a gully and beach is used. A hybrid approach is adopted, in which sediment deposition by run-off (and to a lesser extent cliff erosion) is modelled using wave-resolving hydrodynamic models. It is found that significant amounts of sediment can be supplied by gully run-off during storms. For small run-offs the swash can be involved in determining the region of deposition within the gully area, with longer period motions favouring increased sediment deposition at gully sides. Simulations also show that swash motions can erode gully sides, and the presence of a cross-shore jet associated with the swash and gullies can also impact on sediment movement. Longer term, wave-averaged morphodynamic modelling (without a swash zone) indicates that run-off deposits subsequently diffuse laterally, whether under normal or oblique incidence. These simulations also reveal the possibility of underlying crescentic bar-shedding dynamics that may pertain during changes of wave conditions. [Copyright &y& Elsevier]

Abstract: The paper introduces a new approach to composite breakwater design based on minimizing initial/construction costs subject to yearly failure rate bounds for all failure modes, and presents a technique for sensitivity analysis. The solution of the resulting optimization problem becomes complex because the evaluation of failure rates involves one optimization problem per failure mode (FORM), so that a decomposition method is used to solve the problem. In addition, a sensitivity analysis is performed, which makes it possible to determine how the cost and yearly failure rates of the optimal solution are affected by small changes in the input data values. The proposed method is illustrated by its application to the design of a composite wall under breaking and non-breaking wave conditions. The storms are assumed to be stochastic processes characterized by their maximum significant wave heights, their maximum wave heights and the associated zero-up-crossing mean periods. [Copyright &y& Elsevier]

Air-sea interaction is a relevant topic with still many open questions, also in consideration of the numerous and complex scenarios that occur in nature. In this manuscript we report an experimental study of partially-reflected regular (long) waves under the action of an opposite wind, which generates short wind-waves (wind generated water waves, WGW). Wind blows against the incident wave, and therefore it is in the same direction as the reflected wave. Regular waves are generated by a paddle and are defined as mechanically generated water waves (MGW). MGW and WGW are separated by a spectral filtering technique, and free surface statistics of wave height, period and steepness are studied. The spatial variation induced by partial reflection of MGW (generated by paddles) is experimentally observed and theoretically described, and the effects of wind on reflection parameters are observed and examined. A phase-conditional analysis of wind-waves statistics, separating crest and trough, and upwind and downwind sides, reveals the importance of the local wind forcing, and captures features of the wind-waves modulated by the longer waves which are not detected with standard statistical analyses. The phase celerity of the wind-waves is analysed including the effects of the wind-induced shear current and the non-inertial effects of the MGW; to the best of our knowledge, this last effect experimental analysis is novel. The study is relevant to characterize the wave field in front of coastal structures and beaches under swell and wind waves (co-linear in the same, and in the opposite direction) conditions, affecting run-up, overtopping and mean quantities modulated by the dynamics of group of waves. • Experiments on opposite wind waves riding long waves have been analysed. • Variations induced by varying reflection coefficients are analysed, for log waves and for short wind waves. • Phase celerity of wind waves are computed and corrected according to the phase position in the long waves. • An original model for correction relies also on the vertical acceleration in the non-inertial frame of the short waves. [ABSTRACT FROM AUTHOR]

We present the experimental analysis of the interaction between wind waves and currents, during the generation process, through laboratory experiments in a wind-waves-current tunnel. The objective is the quantification of the effects of a co-/counter-current on the main characteristics and statistical estimators of the wave field. Twenty-two experiments were performed with two different wind speed values and eleven different current speed values (including zero value, absence of current), with a ratio of current speed to group celerity u c / c g ∈ − 0.47 , + 0.30 , measuring the instantaneous water level in different sections with ultrasonic probes. The collected data allow the characterization of the free surface statistics, the calculation of the phase and group celerity of the waves, the analysis of the grouping. The aim is the description of the complex interaction between different forcing terms effective during wave generation. We found that (i) spectral shape and evolution is extremely sensitive to tiny counter-currents, with a fast grows of a second peak, (ii) grouping and the statistics of the free surface reflect the action of the current; (iii) energy transfer and breaking are significantly affected by the currents. The results are new and original and represent a set of data for understanding the generation of waves by the wind in all conditions in which the currents are not negligible, for example in the surf zone, lagoons, estuaries, swamps, shallow lakes and shallow reservoirs. • The interaction between wind waves and currents, during the generation process, is studied. • Several laboratory experiments were performed, with different combination of wind and current velocities. • The collected data allow free surface statistics analysis, phase and group celerity of the waves and grouping evaluation. • In the presence of counter-currents, the spectral evolution from a single peak towards a two-peak shape is observed. • The results are new and original for understanding the generation of wind waves in the presence of currents. [ABSTRACT FROM AUTHOR]