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Author: Elena Pallarès López Publisher: ISBN: Category : Languages : en Pages : 194
Book Description
It is widely known that wind and wave predictions in the nearshore are less precise for semi enclosed domains than in the open ocean. The Catalan coast is a clear example of this situation, with a wave climate controlled by short fetches, complex bathymetry, high wind field variability in time and space, and sea and swell waves combined that generate bimodal spectra. These characteristics, typical for a semi-enclosed basin, limit the reliability of wave predictions in the area, with errors on the significant wave height around 10% and a clear under-prediction of the wave period with errors around 30%. The motivation of this work is to improve the actual wave forecasting abilities for the Catalan Coast using the SWAN v.4091 wave model. In order to achieve this goal, three working lines are considered: (1)adapting the model to the Catalan coast conditions, tuning the wave growth rates included in the model to better reproduce the observed values, (2) evaluate the effect of the currents and wind into the wave field by using a coupled system and (3) consider the use of unstructured grids as an alternative to the traditionally nested systems in order to obtain high resolution wave forecasts in coastal areas reducing the computational time and avoiding the use of internal boundary conditions with their associated errors. The results obtained support previous studies where the limited ability of the models to reproduce wave growth rates in young seas have been detected. The whitecapping term correction proposed in this document helps reducing under-prediction of the wave period observed with almost no effect on the significant wave height. This correction can be applied to similar environments. However, the proposed formulation is only suitable for the early stages of generation and should be discontinued after waves reach a certain maturity. Two coupling strategies are considered, a one-way coupling where current fields are directly introduced into the wave model, and a two-way coupling where the waves, currents and winds models run in parallel. The effects of the coupling are evaluated during calm periods but also during energetic events. The results show that during calm conditions the coupling does hardly improve the results while during energetic events, such as superficial currents intensifications or wind jet events, the coupling has greater importance. However, the two-way coupling has extremely high computational requirements, not always available. In this sense, the use of unstructured grids as an alternative to the traditional nested systems is presented. The main benefit of unstructured grids is that allows working with a single grid with different resolutions in each sub-domain, improving the resolution in coastal areas. Other advantage is the capacity to better reproduce the sharp coastline and the areas around the islands. The design of unstructured grids has been shown as one of the most delicate parts of this methodology, requiring special attention for the grid generation criteria. The validation of the results, performed with buoy measurements in the nearshore but also for the entire domain with altimetry measurements, allows stating that unstructured grids perform correctly in the study area. Finally, the proposed work suitability for an operational forecasting system has been considered. The whitecapping term modification is proven to be decisive in the quality of the wave forecast, while the coupling is not always recommended depending on computational capabilities. The use of unstructured grids with a regional triangular mesh covering the entire Western Mediterranean sea is considered as the first option, providing accurate high resolution wave conditions near the coast with a clear reduction of the computational time in comparison with a traditional nested system.
Author: Elena Pallarès López Publisher: ISBN: Category : Languages : en Pages : 194
Book Description
It is widely known that wind and wave predictions in the nearshore are less precise for semi enclosed domains than in the open ocean. The Catalan coast is a clear example of this situation, with a wave climate controlled by short fetches, complex bathymetry, high wind field variability in time and space, and sea and swell waves combined that generate bimodal spectra. These characteristics, typical for a semi-enclosed basin, limit the reliability of wave predictions in the area, with errors on the significant wave height around 10% and a clear under-prediction of the wave period with errors around 30%. The motivation of this work is to improve the actual wave forecasting abilities for the Catalan Coast using the SWAN v.4091 wave model. In order to achieve this goal, three working lines are considered: (1)adapting the model to the Catalan coast conditions, tuning the wave growth rates included in the model to better reproduce the observed values, (2) evaluate the effect of the currents and wind into the wave field by using a coupled system and (3) consider the use of unstructured grids as an alternative to the traditionally nested systems in order to obtain high resolution wave forecasts in coastal areas reducing the computational time and avoiding the use of internal boundary conditions with their associated errors. The results obtained support previous studies where the limited ability of the models to reproduce wave growth rates in young seas have been detected. The whitecapping term correction proposed in this document helps reducing under-prediction of the wave period observed with almost no effect on the significant wave height. This correction can be applied to similar environments. However, the proposed formulation is only suitable for the early stages of generation and should be discontinued after waves reach a certain maturity. Two coupling strategies are considered, a one-way coupling where current fields are directly introduced into the wave model, and a two-way coupling where the waves, currents and winds models run in parallel. The effects of the coupling are evaluated during calm periods but also during energetic events. The results show that during calm conditions the coupling does hardly improve the results while during energetic events, such as superficial currents intensifications or wind jet events, the coupling has greater importance. However, the two-way coupling has extremely high computational requirements, not always available. In this sense, the use of unstructured grids as an alternative to the traditional nested systems is presented. The main benefit of unstructured grids is that allows working with a single grid with different resolutions in each sub-domain, improving the resolution in coastal areas. Other advantage is the capacity to better reproduce the sharp coastline and the areas around the islands. The design of unstructured grids has been shown as one of the most delicate parts of this methodology, requiring special attention for the grid generation criteria. The validation of the results, performed with buoy measurements in the nearshore but also for the entire domain with altimetry measurements, allows stating that unstructured grids perform correctly in the study area. Finally, the proposed work suitability for an operational forecasting system has been considered. The whitecapping term modification is proven to be decisive in the quality of the wave forecast, while the coupling is not always recommended depending on computational capabilities. The use of unstructured grids with a regional triangular mesh covering the entire Western Mediterranean sea is considered as the first option, providing accurate high resolution wave conditions near the coast with a clear reduction of the computational time in comparison with a traditional nested system.
Author: Antonio Navarra Publisher: Springer Science & Business Media ISBN: 9400757697 Category : Science Languages : en Pages : 245
Book Description
This is the third volume of a three-volume final report, which thoroughly describes, synthesizes and analyzes the results of the four-year Integrated Research Project CIRCE – Climate Change and Impact Research: Mediterranean Environment, funded by the EU 6th Framework Programme. Conducted under the auspices of the National Institute of Geophysics and Volcanology in Rome, Italy, the study was designed to predict and to quantify the physical impacts of climate change in the Mediterranean, and to assess the most influential consequences for the population of the region.
Author: Laura Ràfols Bundó Publisher: ISBN: Category : Languages : en Pages : 179
Book Description
The water currents and the wave field at the Catalan coast (in the Northwestern Mediterranean Sea) are investigated. However, the main research is focused at the northern margin of the Ebro Shelf, where there is a relatively high amount of data for study purposes and where episodes of strong northwesterly wind occur. In such cases, the wind is channeled through the Ebro Valley and intensifies upon reaching the sea, resulting in a wind jet. The research has been divided into four parts: (1) the study of the water circulation induced by a wind jet, by means of the Regional Ocean Modeling System (ROMS) numerical model; (2) the study of the waves dynamics induced by a wind jet, using the Simulating WAves Nearshore (SWAN) numerical model; (3) the study of the wave-current interactions during wind-jet events, coupling the numerical models used formerly; and (4) the implementation and validation of a waves and currents forecasting system at the Catalan coast, based on the knowledge gained during the research performed in the previous parts.
Author: Susana Sellés Valls Publisher: ISBN: Category : Languages : en Pages :
Book Description
Coastal zones are home to more than half of the world's population. Due to increasing human activity and the presence of varied and rich ecosystems in coastal regions, there is increased awareness of the importance of knowledge concerning the surrounding environment which is acquired through observation and modeling of coastal processes. The aim of this study is to determine the wave propagation patterns along the northern coast of Catalonia on the basis of the wave data recorded by the existing oceanographic network. The study area contains the two most representative coastal layouts in the northern Catalan littoral: El Maresme, with homogeneous and open coasts and La Costa Brava, encompassing cliffs and rocky coasts. The purpose of such analysis is to perform the coastal clustering based on the wave exposure and to identify the most vulnerable coastal stretches. SWAN has been used as the software to carry out the simulations of the wave propagation from deep waters all the way to the coastline. The mean wave regime (study cases) and the digital terrain model (bathymetry) are the necessary inputs to run SWAN. This software propagates the information read on the boundary (wave-height, period and wave direction ) and generates a file in a matrix format and then it is post-processed with Matlab to achieve the graphic results. The process is repeated twice. It computes the waves on a coarse grid for a larger region first and then on a finer grid for a smaller region to achieve a higher resolution. The final results show that as expected, the wave propagation patterns found are governed by the wave-period, offshore direction, shorelines orientation and bathymetry. A non-homogeneous distribution of the wave energy along the coastal area has been found. However, both of the zones, La Costa Brava and El Maresme, exhibit similar wave propagation patterns within their own borders. Moreover, several coastal sections within both regions present locations where the wave energy is highly concentrated and therefore higher wave-heights are achieved. However, the areas within La Costa Brava manifest a higher wave exposure than the unsheltered regions of El Maresme.
Author: Mercè Casas Prat Publisher: ISBN: Category : Languages : en Pages : 229
Book Description
Climate change is a hot research topic due to the consequent impacts on our environment in the near future. The last report of the International Panel on Climate Change¿the leading international body for assessment of climate change¿highlights a lack of information on the potential changes in wave climate and, consequently, on their coastal impacts. The problem is largely complicated because wave forcing is affected by a number of uncertainty factors, being the choice of the climate model one of the most relevant. The main purpose of this thesis is to provide a better understanding of the future wave climate in the area of interest: the Catalan coast, which is located in the NW part of the Mediterranean Sea, a basin particularly exposed to climate change. Based on previous studies, three methodological approaches are explored to address this issue: trend analysis, dynamical modelling and statistical modelling. The thesis work results in the generation and analysis, for the first time in this area, of a high temporal and spatial resolution database of future wave projections. The use in this thesis of atmospheric projections obtained by five combinations of regional-global climate models enables the study of the inter-model variability in terms of wave parameters. The results illustrate, for the winter season, the large variability associated to the parent global circulation model (particularly for the wave direction, a wave variable that seems to be especially affected by climate change in this area). In most of the domain, wave height and wave period tend to generally decrease for both mean and stormy conditions but extremes are associated to a large uncertainty. As expected, these changes are closely related to those of the (wave forcing) surface wind speed but fetch also plays an important role. For favourable fetch conditions (waves coming from east) wave climate changes are more accentuated and to the percentage of mixed sea states tends to increase. The second important contribution of this thesis is related with the methodology. New approaches of trend analysis that take into consideration the nature of the data are presented. Also, especial emphasis is given to the uncertainty analysis in order to detect statistically significant changes. In this regard, bootstrapping is shown to be a simple but effective method if adequately modified. Nevertheless, the most significant methodological contribution is perhaps the development of a new (computationally inexpensive) statistical method to model wave heights, that greatly improves the model performance at nearshore areas. The frequency and directional dispersion theory of wave propagation is used to explicitly model swell waves, making use of the principal component analysis to simplify the forcing into a set of representative atmospheric patterns. Finally, from an engineering perspective, this thesis reviews and quantifies the main physical impacts that changes in ocean wave patterns can have on coastal areas. It is found that mild variations of forcing wave conditions can greatly affect coastal processes, due to their non-linear relation. For example, longshore sediment transport can vary at a rate higher than 100% caused by a rotation of the mean wave direction of only 10o. Getting into more detail, a couple of case studies on the Catalan coast analyse the affectation on harbour agitation and longshore sediment transport on beaches.
Author: Elena Pallarès López
Author: Elena Pallarès López
Author: Elena Pallarès López
Author: Marta Alomar
Author: Marta Alomar Domínguez
Author: Agustin Sanchez-Arcilla
Author: Antonio Navarra
Author: Laura Ràfols Bundó
Author: Susana Sellés Valls
Author: Adrian Moya Ortiz
Author: Mercè Casas Prat