Estabilización de la superfície libre en la solución de ecuaciones shallow -water por elementos finitos. Aplicaciones oceanográficas

El movimiento del mar (corrientes, olas...) es un factor determinante de las condiciones ambientales del medio marino. Estas condiciones son alteradas por las actuaciones humanas mediante la construcción de diques o espigones, el tendido de tuberías submarinas, la ejecución de planes de ordenación de playas, etc...Para evaluar y predecir los efectos de las actuaciones humanas en la zona litoral (e.g. alteraciones de la línea de orilla, contaminación debida a la emisión de efluentes químicos o térmicos, etc...) es necesario simular el flujo marino mediante un modelo matemático que nos permita abordar este cometido con total generalidad, aunque introduciendo por economía computacional, todas las simplificaciones que la naturaleza física del problema permita. En el estudio de la circulación marina en áreas de plataforma continental, bahías y estuarios poco estratificados, etc, es frecuente el uso de una versión simplificada de las ecuaciones de Navier-Stokes para aguas someras, comúnmente denominadas ecuaciones de Shallow-Water (SWE) (ver e.g. Abbot, 1979).Entre 1987 y 1990, se desarrolló en el Laboratorio de Ingeniería Marítima de la Universitat Politècnica de Catalunya un modelo quasi-3D en elementos finitos (ANASTASE) para resolver las SWE en régimen estacionario, encaminado al estudio oceanógrafico de la circulación en las zonas de rompientes y de plataforma continental a bajo coste computacional. El esquema numérico del modelo se basaba en una versión modificada del método de la función de penalización (García, 1990). Su uso práctico puso de manifiesto un conjunto de problemas característicos de códigos similares a éste (García et al., 1990; Espino et al.; 1992), cuyo denominador común es el no cumplimiento de la condición de incompresibilidad (Pelletier et al., 1989). Por otro lado, la elección de elementos Ql/PO para "abaratar" el coste de las soluciones numéricas planteaba, además de inconvenientes de tipo teórico, restricciones en cuanto a la bondad de los campos de presión (o altura de la superficie libre) calculadas por el modelo. En esta memoria se pretende desarrollar um modelo quasi-3D en elementos finitos que elimine los problemas que limitan la aplicabilidad/de ANASTASE. En segundo lugar, se investigan, haciendo uso del nuevo código, rasgos de la circulación general inducida por el viento en dos regiones con interés oceanógrafico: El Golfo de St. Jordi (Mediterráneo Occidental) y el Estrecho de Bransfield (Antártida).Postprint (published version

Modeling circulation patterns induced by spatial cross-shore wind variability in a small-size coastal embayment

This contribution shows the importance of the cross-shore spatial wind variability in the water circulation in a small-sized micro-tidal bay. The hydrodynamic wind response at Alfacs Bay (Ebro River delta, NW Mediterranean Sea) is investigated with a numerical model (ROMS) supported by in situ observations. The wind variability observed in meteorological measurements is characterized with meteorological model (WRF) outputs. From the hydrodynamic simulations of the bay, the water circulation response is affected by the cross-shore wind variability, leading to water current structures not observed in the homogeneous-wind case. If the wind heterogeneity response is considered, the water exchange in the longitudinal direction increases significantly, reducing the water exchange time by around 20%. Wind resolutions half the size of the bay (in our case around 9 km) inhibit cross-shore wind variability, which significantly affects the resultant circulation pattern. The characteristic response is also investigated using idealized test cases. These results show how the wind curl contributes to the hydrodynamic response in shallow areas and promotes the exchange between the bay and the open sea. Negative wind curl is related to the formation of an anti-cyclonic gyre at the bay's mouth. Our results highlight the importance of considering appropriate wind resolution even in small-scale domains (such as bays or harbors) to characterize the hydrodynamics, with relevant implications in the water exchange time and the consequent water quality and ecological parameters.Peer ReviewedPostprint (author's final draft

Estabilización de la superficie libre en la solución de ecuaciones Shallow-Water por elementos finitos

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Estabilización de la superfície libre en la solución de ecuaciones shallow -water por elementos finitos. Aplicaciones oceanográficas

El movimiento del mar (corrientes, olas...) es un factor determinante de las condiciones ambientales del medio marino. Estas condiciones son alteradas por las actuaciones humanas mediante la construcción de diques o espigones, el tendido de tuberías submarinas, la ejecución de planes de ordenación de playas, etc...Para evaluar y predecir los efectos de las actuaciones humanas en la zona litoral (e.g. alteraciones de la línea de orilla, contaminación debida a la emisión de efluentes químicos o térmicos, etc...) es necesario simular el flujo marino mediante un modelo matemático que nos permita abordar este cometido con total generalidad, aunque introduciendo por economía computacional, todas las simplificaciones que la naturaleza física del problema permita. En el estudio de la circulación marina en áreas de plataforma continental, bahías y estuarios poco estratificados, etc, es frecuente el uso de una versión simplificada de las ecuaciones de Navier-Stokes para aguas someras, comúnmente denominadas ecuaciones de Shallow-Water (SWE) (ver e.g. Abbot, 1979).Entre 1987 y 1990, se desarrolló en el Laboratorio de Ingeniería Marítima de la Universitat Politècnica de Catalunya un modelo quasi-3D en elementos finitos (ANASTASE) para resolver las SWE en régimen estacionario, encaminado al estudio oceanógrafico de la circulación en las zonas de rompientes y de plataforma continental a bajo coste computacional. El esquema numérico del modelo se basaba en una versión modificada del método de la función de penalización (García, 1990). Su uso práctico puso de manifiesto un conjunto de problemas característicos de códigos similares a éste (García et al., 1990; Espino et al.; 1992), cuyo denominador común es el no cumplimiento de la condición de incompresibilidad (Pelletier et al., 1989). Por otro lado, la elección de elementos Ql/PO para "abaratar" el coste de las soluciones numéricas planteaba, además de inconvenientes de tipo teórico, restricciones en cuanto a la bondad de los campos de presión (o altura de la superficie libre) calculadas por el modelo. En esta memoria se pretende desarrollar um modelo quasi-3D en elementos finitos que elimine los problemas que limitan la aplicabilidad/de ANASTASE. En segundo lugar, se investigan, haciendo uso del nuevo código, rasgos de la circulación general inducida por el viento en dos regiones con interés oceanógrafico: El Golfo de St. Jordi (Mediterráneo Occidental) y el Estrecho de Bransfield (Antártida)

An implicit finite-element model for 3D non-hydrostatic mesoscale ocean flows

We present in this paper a pressure stabilized, finite element method for the numerical approximation of three-dimensional, non-hydrostatic mesoscale ocean flows. The model considered here incorporates surface wind stress, bottom friction and Coriolis acceleration, and it is applicable to irregular bottom topographies. An implicit unconditionally stable scheme is employed for the time advancement and an anisotropic stabilization technique is used for the spatial finite element discretization. The numerical results obtained on test cases demonstrate the robustness and accuracy of the method proposed here

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

Wave–current interactions in a wind-jet region

Wave–current interactions (WCIs) are investigated. The study area is located at the northern margin of the Ebro shelf (northwestern Mediterranean Sea), where episodes of strong cross-shelf wind (wind jets) occur. The aim of this study is to validate the implemented coupled system and investigate the impact of WCIs on the hydrodynamics of a wind-jet region. The Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) modeling system, which uses the Regional Ocean Model System (ROMS) and Simulating WAves Nearshore (SWAN) models, is used in a high-resolution domain (350 m). Results from uncoupled numerical models are compared with a two-way coupling simulation. The results do not show substantial differences in the water current field between the coupled and the uncoupled runs. The main effect observed when the models are coupled is in the water column stratification, due to the turbulent kinetic energy injection and the enhanced surface stress, leading to a larger mixed-layer depth. Regarding the effects on the wave fields, the comparison between the coupled and the uncoupled runs shows that, when the models are coupled, the agreement of the modeled wave period significantly improves and the wave energy (and thus the significant wave height) decreases when the current flows in the same direction as the waves propagate.Peer ReviewedPostprint (published version

Enhanced mixing in heterogeneous Buckley Leverett flow due to temporal fluctuations

Peer ReviewedPostprint (published version

Finite element approximation of 3D non-hydrostatic turbulent coastal ocean flows using a LES model

In this paper we present a stabilized finite element method for three-dimensional, non-hydrostatic, turbulent coastal ocean flows. The model we have developed, named HELIKE, incorporates also surface wind stress, bottom friction, Coriolis forces and several closure models for both the horizontal and the vertical turbulent eddy vis- cosity coefficients. Unstructured meshes are employed so that complex geometries can be accurately approximated, and implicit time stepping allows to use large time steps. Numerical results are presented in various test cases, in which comparisons between different turbulence models are provided

Numerical simulation of the dispersion of contaminants by a characteristic-based method with applications to the Ebro delta and the Huelva estuary

In this paper we consider an explicit, characteristic-based method for the numerical simulation of the dispersion of contaminants in a fluid medium. A quasi-3D formulation is employed for the spatial approximation. Two real-life applications of the model developed are presented: the dispersion of the plume of the Ebro river and the thermal outflow of power plants in the Huelva estuary