Papers by Miguel A Losada
Coastal Engineering 2006 - Proceedings of the 30th International Conference, 2007
Scientia Marina, 2010
Large beach cusps (LBC, wavelength of ~ 30 m) are intertidal features that can alternately exist ... more Large beach cusps (LBC, wavelength of ~ 30 m) are intertidal features that can alternately exist in the swash and in the inner surf zone due to tidal sea level changes. They have a larger cross-shore extent (up to 50 m) than traditional cusps. This extent has been explained by a shift of the swash zone during falling tide. The cusps immerse at rising tide and previous studies indicate that surf zone processes are exclusively destructive. Here, the behaviour of large beach cusps in the inner surf zone is investigated by using a 2DH morphological numerical model applied to Trafalgar Beach (Cádiz, Spain). The model results indicate that the inner surf zone processes do not always destroy the cusps but can in fact reinforce them by considering neither the swash processes nor the tidal changes. More generally, in conditions favouring the presence of the LBC the surf zone of a beach can be unstable, leading to the formation of transverse/oblique sand bars that can have characteristics similar to the LBC. Thus, in principle, the LBC could emerge not only due to swash zone morphodynamics but also due to surf zone morphodynamics or a combination of both.
The velocity fields induced by regular breaking waves past a fixed bar on a 1:10 rigid plane slop... more The velocity fields induced by regular breaking waves past a fixed bar on a 1:10 rigid plane slope were measured and analysed using a volumetric particle-tracking velocimetry system. Under specific conditions, the wave-mophological features interaction steepens the waves which eventually breaks. The geometry of the boundaries of the present experiments is common in natural environments, where reefs, sand and gravel bars, and submerged coastal structures, interact with the incoming wave field 'affecting' the transport budget of substances (sediment, nutrients and pollutants), with relevant consequences on the water quality. The aims of the present work are the analysis of the flow field in the breaker, the quantification of the terms in the equations usually adopted for modelling the flow and the turbulence. Two sets of attacking monochromatic wave trains with different periods and heights were used to generate a dataset of instantaneous velocity, which was further analysed to extract turbulence. The measurement volume extended from the wave crest to a portion of the domain below the wave trough. The balance of linear momentum for the average field and the balance of turbulence, were scrutinised and included all the terms in a 3D approach. The analysed data and results are original and novel because they include all the contributions derived from the 3D structure of a real flow field, and constitute a huge data set for calibration of numerical codes.
Coastal Structures 2011, 2012
ABSTRACT This paper presents an analysis of measured data of pressures and subpressures, as well ... more ABSTRACT This paper presents an analysis of measured data of pressures and subpressures, as well as horizontal and vertical forces exerted by waves on a non-overtopping vertical breakwater during storm events. The breakwater studied was the North Breakwater of the Port of Gijón (Spain). The forces were obtained by integrating the measured pressures from 17 sensors spread across the central body, the superstructure and the bottom of the caisson. The results show the influence of the distribution of energy flows on the pressure laws due to the wave-breakwater interaction. The maximum sea-level reference pressure is directly proportional to the free surface at that instant. The simultaneity of the maximum horizontal and vertical forces in a given sea state was also analyzed, concluding that these forces are not always in phase.
Coastal Engineering Proceedings, 2012
This work studies the interaction of a composite breakwater and irregular waves as a function of ... more This work studies the interaction of a composite breakwater and irregular waves as a function of the breakwater geometry and wave characteristics. For this, tests in a flume wave were carried out. The model consisted of a composite breakwater with rectangular cross section and with the width, foundation depth and stone diameter varying in order to know their influence in the breakwater behavior. Results show that reflection coefficient increase with B/L (where B is the width of the dike and L is the wave length) until a maximum value (saturation point) from which it is constant or decreases slightly. Before this point, reflection coefficient depends on breakwater geometry and wave characteristics and when the dike reaches the saturation regime, it only depends on stone diameter or porosity. The value of the sea water elevation at the wall and the horizontal pressure depends on the reflection coefficient. Finally, the relationship between horizontal and vertical forces is linear depending on the reflection regime. This analysis shows that energy distribution is the main variable to know the structural behavior of a dike. Based on these results, a methodology to obtain the loads over the composite breakwater is proposed.
Coastal Engineering Proceedings, 2014
Seabed instability has been cited as the cause of failure for a number of coastal structures in r... more Seabed instability has been cited as the cause of failure for a number of coastal structures in recent years, stimulating an interest in understanding the interaction between waves, marine structures and the seabed upon which they are built. A series of experimental tests were carried out in a wave flume at the Engineering Institute of the National University of Mexico, to investigate the failure of seabeds with a high mud content and the interaction of the seabed with a scaled structure (vertical breakwater) and regular waves (T = 0.6, 0.8 and 1.0 s; H = 6, 8 and 10 cm), through the analysis of pore pressure distribution. Three different materials were tested: 100, 90 and 85 % mud content, mixed with natural sand and water. Pore pressure build-up was registered in the tests with 85 % of mud content, and knowing that a buildup precedes soil liquefaction, failure may have occurred. But in these cases the maximum pressure in the tests did not exceed the critical value and no liquefaction was observed. For soils of 90 and 100 % mud content, the pore pressure shows a homogeneous vertical behaviour and only pore pressure falls were registered. This phenomenon may be attributed to the cohesion effect in the mud particles and to the consolidation process.
Coastal Engineering Proceedings, 2011
This work studies the horizontal and uplift pressure distributions over a caisson founded on poro... more This work studies the horizontal and uplift pressure distributions over a caisson founded on porous materials, and their dependence on the stone diameter and the height of the foundation. For this, tests at a wave flume with an idealized composite breakwater of rectangular section, varying the depth of the foundation of the caisson and the diameter of the stones, were carried on. Eight resistive gauges and eight pressures sensors were used to measure free surface elevations and horizontal and uplift pressure variation, respectively. Results show that: 1) there exist a "saturation" of the reflection coefficient for B/L>0.4, being B the width of the dike and L the wave length, 2) by using the total wave height measured at the toe of the dike in the analysis, the dispersion of the results is significantly reduced; 3) dimensionless run-up and pressures obtained using total wave height mainly depends on the reflection regime and on the relative height of the foundation; 4) maximum uplift and horizontal forces are not always in phase, and three regimes are identified depending on which force dominates; and 5) the relation between the dimensionless forces with the total wave height at the toe of the dike depends mainly on the reflection regime and on the relative foundation height.
Coastal Engineering 2006 - Proceedings of the 30th International Conference, 2007
In this paper, laboratory data of breakwater damage, profile evolution and energy fluxes over an ... more In this paper, laboratory data of breakwater damage, profile evolution and energy fluxes over an homogeneous mound breakwater are presented and discussed. The experiments were done over two models, consisting on a mound breakwater composed of cubes of the same size, ...
Coastal Structures 2007 - Proceedings of the 5th Coastal Structures International Conference, CST07, 2009
Renewable Energy, 2016
Oscillating water column (OWC) are devices for wave energy extraction equipped with turbines for ... more Oscillating water column (OWC) are devices for wave energy extraction equipped with turbines for energy conversion. The purpose of the present work is to study the thermodynamic of a real gas flow through the turbine and its differences with respect to the ideal gas hypothesis, with the final goal to be applied to OWC systems. The effect of moisture in the air chamber of the OWC entails variations on the atmospheric conditions near the turbine, modifying its performance and efficiency. In this work we study the influence of humid air in the performance of the turbine. Experimental work is carried out and a real gas model is asserted, in order to take a first approach to quantify the extent of influence of the airewater vapour mixture in the turbine performance. The application of a real gas model and the experimental study confirmed the deviations of the turbine performance from the expected values depending on flow rate, moisture and temperature.
Coastal Engineering Proceedings, Feb 1, 2011
This work studies the horizontal and uplift pressure distributions over a caisson founded on poro... more This work studies the horizontal and uplift pressure distributions over a caisson founded on porous materials, and their dependence on the stone diameter and the height of the foundation. For this, tests at a wave flume with an idealized composite breakwater of rectangular section, varying the depth of the foundation of the caisson and the diameter of the stones, were carried on. Eight resistive gauges and eight pressures sensors were used to measure free surface elevations and horizontal and uplift pressure variation, respectively. Results show that: 1) there exist a "saturation" of the reflection coefficient for B/L>0.4, being B the width of the dike and L the wave length, 2) by using the total wave height measured at the toe of the dike in the analysis, the dispersion of the results is significantly reduced; 3) dimensionless run-up and pressures obtained using total wave height mainly depends on the reflection regime and on the relative height of the foundation; 4) maximum uplift and horizontal forces are not always in phase, and three regimes are identified depending on which force dominates; and 5) the relation between the dimensionless forces with the total wave height at the toe of the dike depends mainly on the reflection regime and on the relative foundation height.
Revista da Gestão Costeira Integrada, 2012
Journal of Geophysical Research, 2009
1] In this paper, the oscillatory contributions to the steady shear stress of regular wave groups... more 1] In this paper, the oscillatory contributions to the steady shear stress of regular wave groups propagating over plane beds in the laminar regime are investigated theoretically and experimentally. Assuming weak nonlinearity, it was found that weak-unsteady motions induced by regular wave groups and second-order harmonics induced by nonlinear bottom boundary layer (BBL) dynamics contribute to the same order. Wave reflection was found to be an additional mechanism to generate high-order contributions to the steady shear stress. High-order oscillatory contributions to the steady shear stress generate small-amplitude perturbations to the steady streaming through the BBL. As a result, steady secondary circulation cells can be distinguished in the wave group-induced BBL. The magnitude and length scale of the measured small-amplitude perturbations are consistent with the theoretical predictions. Moreover, it is shown that the oscillatory contributions are selected according to their characteristic timescale with distance to the bed. The results could have important implications for understanding BBL dynamics and transport and the transition to the perturbed laminar regime in multiple-scale oscillatory flows.
Journal of Hydraulic Engineering, 2011
This study presents field observations and numerical modeling of surface seiche formations on a s... more This study presents field observations and numerical modeling of surface seiche formations on a shallow reservoir in a complex terrain (Rules Reservoir, Spain). The influence of the surrounding topography on the atmospheric loading (barometric pressure and wind speed) is investigated, with the associated atmospheric-hydrodynamic coupling. During a 13-day field study, maximum free surface oscillations of 4 cm were recorded after the passing of a short duration storm (< 5 min), which included a peak wind gust of 22 m=s. Observations also present evidence of resonant excitation of the free surface caused by high-frequency microscale harmonics (< 10 min) in the atmospheric forcing. Resonant excitation caused by harmonics in the atmospheric forcing is significant for small reservoirs situated in regions of complex terrain where topographical obstacles modify the flow patterns in the near-surface boundary layer, generating eddies with harmonics in the microscale range of the atmospheric forcing spectrum. Harmonics in the atmospheric forcing are observed for a range of periods (200-700 s) during the survey. Surface oscillations of 2 cm are generated when the frequency of the forcing matches the fundamental reservoir modal frequency, even for low wind speeds. A two-dimensional depth-integrated numerical model predicted the observed surface seiche formation in both cases.
Coastal Engineering 2006 - Proceedings of the 30th International Conference, 2007
BOTTOM BOUNDARY LAYER UNDER STANDING WAVE GROUPS:
Coastal Engineering, 1998
The time-and depth-averaged equations in a porous medium are used to analyse how Ž . dissipation ... more The time-and depth-averaged equations in a porous medium are used to analyse how Ž . dissipation inside an infinitely long vertical breakwater generates an alongbreakwater AB current inside the structure. This mean current is transferred seawards and leewards by turbulent diffusion. Based on a theoretical eddy viscosity law, an analytical solution is obtained. The mean current velocity profile depends on characteristics such as water depth, wave height, wave period and angle of incidence and on porous medium properties including porosity and friction. In the neighbourhood of the structure, the simultaneous action of waves and the AB current are taken into account to study the potential sediment transport patterns. Seawards of the structure, the obtained results may help to explain the formation of bars almost parallel to the breakwater. Under certain circumstances the presence of the breakwater enhances the sediment transport in the zone closest to the seaward face, which may induce scouring at the toe of the structure. q 1998 Elsevier Science B.V. All rights reserved. 0378-3839r98r$ -see front matter q 1998 Elsevier Science B.V. All rights reserved.
Ingeniería del agua, 1994
RESUMEN: Uno de los factores determinantes del diseño de los diques rompeolas es el relativo al t... more RESUMEN: Uno de los factores determinantes del diseño de los diques rompeolas es el relativo al tipo y peso de las piezas del manto principal, que con un talud determinado, son capaces de resistir las solicitaciones debidas al oleaje. En este artículo se realiza una revisión del estado del arte de los métodos de cálculo de la estabilidad hidrodinámica de las piezas del manto principal de los diques rompeolas. A lo largo de los diferentes apartados se analizan la estabilidad de las piezas del manto exterior y de los morros de los diques no rebasables, de los diferentes mantos de los diques rebasables y de los diques berma. Junto al análisis anterior se acompañan las tablas y gráficos que permiten el cálculo del peso de las piezas artificiales y naturales más utilizadas. Por último se dedica un breve apartado al problema de la determinación de la solicitación de cálculo.
Uploads
Papers by Miguel A Losada