Symbiosis numerical - hydraulic models

Peer Reviewe

A ferrofluid-based sensor to measure bottom shear stresses under currents and waves

This is an Accepted Manuscript of an article published by Taylor & Francis Group in Journal of Hydraulic Research on 2018, available online at: http://www.tandfonline.com/10.1080/00221686.2017.1397779The measurement of the near-bottom flow characteristics is crucial to correctly understand coastal processes. To overcome some of the limits of present state-of-the-art measuring instruments, we propose a novel approach to measure bottom shear stress under currents and waves based on the exploitation of magneto-rheological fluids, named ferrofluids. In particular, the deformation of a magnetically controlled ferrofluid drop O(0.01 ml) is transformed by a conditioning circuit into an output voltage which is proportional to the bottom shear stress. Calibration curves are presented for both steady-current and regular wave conditions, over fixed and weakly mobile beds, showing that the behaviour of the proposed measuring system can be assumed linear. In the range of the investigated parameters, it is shown that the working range is comprised between 0.08 N m-2 and an upper limit which is a function of the controlling magnetic field and the flow type.Peer ReviewedPostprint (author's final draft

Lad_3D: modelo 3D de simulación de la dispersión en campo cercano y lejano de contaminantes en aguas costeras

Los modelos numéricos bidimensionales que resuelven la hidrodinámica y el transporte de contaminantes asociado han sido ampliamente utilizados en el caflpo lejano, pero pueden dar lugar a resultados poco realistas en el campo cercano o en situaciones en las cuales la hidrodinámica es esencialmente tridimensional. Este es el caso por ejemplo de las corrientes inducidas por viento cerca de la costa o inducidas por oleaje en la zona de rompientes. Con el objetivo de resolver la ecuación de convección-difusión en tres dimensiones y simular el transporte de contaminantes eii flujos no uniformes y estratificados se ha desarrollado un inodelo numérico basado en una formulación lagratigiana del problema tridimensional. El modelo es descrito en detalle y se aplica al caso del emisario submarino de Barceloiia en el Mediterráneo español.Two-diineiisional numerical models have been extensively used the far field to solve hydrodynaniics aiid tlie associated pollutant transport; however tlie obtained from these models may not be valid wlien used in the lzear field or in areas where tlie hydrodynanlics is inainly 3D, as in tlie case of wind-induced currents in the nearshore region, or wave-induce currents in tlie surf-zone. A 3D lagrangian numerical model has been developed to solve tlie three-dimensional convection-diffusion equation, aild therefore to simulate pollutant transport in non-uniform and stratified hydrodynamic flows. In this paper the model is described in detail and it is applied to the real case of the Besos sea outfall, near Barcelona city (Spanish Mediterraiiean coast).Peer Reviewe

An analysis of nearshore profile and bar development under large scale erosive and accretive waves

This is an Accepted Manuscript of an article published by Taylor & Francis Group in Journal of Hydraulic Research on 2018, available online at: http://www.tandfonline.com/10.1080/00221686.2017.1315748Typical morphodynamic laboratory tests have been carried out at small scales and without sufficient coverage or resolution. These limitations, applying particularly to accretive tests, have obstructed reliable observations and restricted modelling capabilities. Here we present experiments with erosive/accretive waves acting on a large scale flume bed profile. The paper reports a set of high-quality hydro-morphodynamic data. The analysis is focused on net transport rates and how these patterns change between different accretive conditions. The measured velocity and acceleration skewness are presented and discussed, linking the net transport over the bar to the measured hydrodynamics and sediment concentrations. The resulting profile behaviour is discussed as a function of hydro-morphodynamic settings to facilitate comparisons with other datasets.Peer ReviewedPostprint (author's final draft

Un modelo numérico para la simulación de la evolución del fondo marino en la zona cercana a la costa

En este artículo se presenta un modelo numérico que simula la evolución del fondo marino en la zona cercana a la costa. El modelo está dividido en tres módulos que calculan la propagación del oleaje, las corrientes inducidas por oleaje y viento y el transporte de sedimentos y los cambios morfodinámnicos asociados al mismo. Para calibrar y validar el modelo se han utilizado algunos ejemplos extraídos de la literatura, así como datos de campo. Los resultados del modelo muestran que éste estima adecuadamente tanto las magnitudes como las tendencias de la evolución del fondo marino bajo distintas condiciones hidrodinámicas, por lo que puede ser considerada una herramienta útil para propósitos ingenieriles.Peer Reviewe

Circulación baroclínica e inducida por viento en el puerto de Tarragona (España)

The sustainability of harbour management from an environmental standpoint is a current concern for port authorities. It includes dealing with problems that may affect the quality of in-harbour waters. In semi-enclosed basins, the characteristics of the circulation pattern are one of the main factors influencing the water quality, since they determine the residence time of pollutants inside the basin and govern the interaction between inside waters and the cleaner outside waters. Although harbour hydrodynamics are affected by the constant traffic of vessels and the physical constraints imposed by harbour structures, the water dynamics in ports are generally governed by three mechanisms: tidal forcing, wind surface stress, and baroclinic effects. This study presents the characterisation of winter circulation features in Tarragona harbour (northeast Spain), based on both field data and numerical simulations. Due to the microtidal nature of the Mediterranean Sea, three-dimensional water density distribution and local wind are expected to be the most relevant driving mechanisms. The results obtained suggest that, although wind effects may be important in determining the water flow in and out of the harbour for small time-scales, in the long term the most important water exchange mechanism is related to the waterbody’s baroclinic structure, with wind forcing playing only a second-order role. La gestión sostenible de los puertos desde un punto de vista ambiental es un tema de interés actual y un objetivo para las autoridades portuarias. Este tipo de administración incluye el tratamiento de problemas que pueden afectar a la calidad de las aguas interiores del puerto. En cuerpos de agua semicerrados, uno de los factores que más influye en la calidad del agua son las características del patrón de circulación, puesto que gobiernan la interacción entre aguas interiores y aguas exteriores más limpias, y determinan el tiempo de residencia de contaminantes dentro del recinto. Si bien las corrientes dentro de los puertos se ven afectadas continuamente por el tráfico de buques y por las restricciones físicas impuestas por las propias estructuras portuarias, la hidrodinámica general está dominada por tres mecanismos distintos: mareas, tensión de viento, y efectos baroclínicos. Este estudio presenta la caracterización de la circulación invernal en el Puerto de Tarragona (España), basada en datos de campo y en simulaciones numéricas. Debido al carácter micromareal del Mediterráneo, se espera que los forzamientos más relevantes sean el viento local y la distribución tridimensional de la densidad del agua. Los resultados obtenidos sugieren que, si bien los efectos del viento pueden ser importantes para determinar el flujo de agua hacia el interior del puerto para escalas de tiempo reducidas, a largo plazo el mecanismo más importante de intercambio de agua con el exterior está asociado a la estructura baroclínica del cuerpo de agua, siendo el forzamiento por viento un agente secundario

Comparison between nested grids and unstructured grids for a high-resolution wave forecasting system in the western Mediterranean sea

This is an Accepted Manuscript of an article published by Taylor & Francis Group in Journal of Operational Oceanography on 2017, available online at: http://www.tandfonline.com/10.1080/1755876X.2016.1260389Traditionally wave modelling uses a downscaling process by means of successive nested grids to obtain high-resolution wave fields near the coast. This supposes an uncertain error due to internal boundary conditions and a long computational time. Unstructured grids avoid multiple meshes and thus the problem of internal boundary conditions. In the present study high resolution wave simulations are analysed for a full year where high-resolution meteorological models were available in the Catalan coast. This coastal case presents sharp gradients in bathymetry and orography and therefore correspondingly sharp variations in the wind and wave fields. Simulations with SWAN v.4091A using a traditional nested sequence and a regional unstructured grid have been compared. Also a local unstructured grid nested in an operational forecast system is included in the analysis. The obtained simulations are compared to wave observations from buoys near the coast; almost no differences are found between the unstructured grids and the regular grids. Simultaneously, tests have been carried out in order to analyse the computational time required for each of the alternatives, showing a decrease to less than half the time when working with regional unstructured grids and maintaining the forecast accuracy and coastal resolution with respect to the downscaling system.Peer ReviewedPostprint (author's final draft

Study of the efflux velocity induced by two propellers

Present analysis is related with seabed erosion caused during docking and undocking maneuvering. Twin propellers without rudder were studied using a physical model with a fixed clearance distance and three different rotating velocities. Experimental results were compared to theoretical expressions of the efflux velocity, axial velocity and finally maximum bed velocity. Efflux velocity equations overestimate the experimental results, whereas axial velocity computed using the Dutch method fits reasonably well the experimental data. However, when maximum bed velocity expressions are compared to experimental results, German method behaves better with an over estimation if a quadratic superposition of the single jets is used.Postprint (published version

Adaptation under extreme events: predictive maintenance for risk reduction

Increasing human and climatic pressures on coastal systems and their infrastructure has resulted in cumulative loses for ecosystem services (e.g. Sanchez-Arcilla et al, 2022) and increasing degradation of coastal and harbour structures (e.g. Kong and Frangopol, 2004; Speijker et al 2000). The result has been a steady increase in risk levels, both for infrastructures (Al-Najjar, 2007) and coastal habitats (Coanda et al., 2020), compounded by a lack of bespoke predictive maintenance (Hermans et al., 2013). A predictive maintenance programme, linking observations and inspections with numerical and/or experimental analyses of water-sediment-structure-ecosystem interactions, specially under extreme conditions, would reduce coastal risks during the life cycle of coastal structures or habitats (Yang et al 2004; Yang et al 2006; Okasha and Frangopol, 2009).This project has received funding from the MCIN / AEI /10.13039/501100011033 and from the “Next Generation EU”/PRTR”, with contract number PLEC2021-007810 (PI-BREAK project). It has also benefitted from the EU Horizon 2020 research and innovation programme under grant agreement No 101037097 (REST-COAST project).Postprint (published version