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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: 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]