Estudio sobre la capacidad de resuspensión de las corrientes de densidad. Aplicación al caso del embalse de Flix.

Estudio sobre el fenómeno de las corrientes de densidad y su capacidad de resuspensión del sedimiento en el fondo de una masa de agua. El anális se cotextualiza en Flix en diciembre de 2001, en el que murieron varios miles de peces y el agua de abastecimiento de Tarragona quedó contaminada. Se realiza un estudio sobre las hipótesis que se dieron como explicación y se plantea una nueva basada en las corrientes de densidad. Se tratan también diferentes técnicas de gestión y remediación de sedimientos contaminados en fondos de masas de agua

Inundabilitat i camps de cultiu

Postprint (published version

Experimental and theoretical analysis of flow and sediment transport in 90-degree fluvial diversions.

Fluvial bifurcations are systems that have a great influence on human society. Their formation and evolution can affect to activities as agriculture or industry and a good knowledge of the mechanisms that affect the processes involved can be determinant for a proper land management. From a geometrical point of view, diversions or lateral intakes are a particular case of fluvial bifurcations in which one of the downstream branches exits laterally while the other follows the same direction as the incoming channel. Diversions are characterized by a significant trend of sediment to deviate towards the lateral branch. The first part of this document describes the experimental work performed in the Fluvial Morphodynamic Laboratory in BarcelonaTech University. Water and solid discharge distributions, as well as bed and water surface levels are measured along the model, during tests with different total water discharges. Results confirm the sediment distributions reported in the literature and but also highlight the influence of bed bathymetry evolution and three-dimensional flow patterns in the local sediment transport of the diversion area. A threshold value is found for total discharge, above which a vortex is formed in front of the diversion entrance and a scour hole is formed in the first stretch of the main channel downstream of the diversion. An energy balance equation is proposed between upstream and downstream of the diversion taking into account the energy losses associated with the vortex, and a good comparison is found when tested against the experimental results. A nodal equation that relates water discharge to sediment discharge distribution is developed considering separately bed load and suspended sediment transport. Calculated values of sediment discharge ratio compare reasonably well with experimental values. Joining these equations, uniform flow, transport capacity and mass continuity equations for water and sediment, a theoretical model is proposed to evaluate the equilibrium situation of a fluvial diversion in terms of water discharge, sediment discharge, water depth and bed slope in both downstream branches.Les bifurcacions fluvials son sistemes amb una gran influència a la societat. La seva formació i evolució pot afectar a activitats com l’agricultura i la indústria, i un bon coneixement dels mecanismes que afecten els processos involucrats pot ser determinant per una correcta gestió del territori. Des d’un punt de vis ta geom ètric, les derivacions o pres es d’aigua laterals són un cas particular de les bifurcacions fluvials , en el qual un dels ramals s urt lateralment i l’altre s egueix la mateixa direcció que el canal entrant. Les derivacions es caracteritzen per una tendència significativa del sediment a ser desviat cap al ramal lateral. La primera part d’aquest document descriu el treball experimental portat a terme al Laboratori de Morfodinàmica Fluvial de la Universitat Politècnica de Catalunya. S’han realitzat experiments amb diferents cabals totals d’aigua, durant els quals s’han pres mesures de la distribució de cabal líquid i sòlid, així com dels nivells del fons i la superfície de l’aigua al llarg de tot el model. Els resultats confirmen el desequilibri de cabals s òlids reportat en estudis anteriors, però també posen de manifest la influència de l’evolució de la batimetria i les característiques tridimensionals del flux en la dinàmica local del transport dels ediments . S’ha trobat un valor límit pel cabal líquid total, per sobre del qual es genera un vòrtex davant de l’entrada del ramal lateral i es form a un fos s at d’eros ió al tram inicial del ramal recte, aigües avall de la derivació. Es proposa una equació de balanç d’energia entre aigües amunt i aigües avall de la derivació tenint en compte les pèrdues d’energia associades al vòrtex, que reprodueix de forma bastant bona els resultats experimentals. Es desenvolupa una equació nodal que relaciona les distribucions de cabal líquid i sòlid, considerant per separat el transport de fons i el transport en suspensió. Els valors del rati de cabal sòlid calculat es corresponen raonablement bé amb els obtinguts experimentalment. Unint aquestes equacions amb les de flux uniforme i transport s òlid a cada ramal, i continuïtat de massa per aigua i sediment, es proposa un model teòric per avaluar la situació d’equilibri d’una derivació fluvial en termes de cabal líquid, cabal sòlid, calat d’aigua i pendent de la llera en cadas cun dels ramals d’aigües avall

Cracking assessment in concrete structures by distributed optical fiber

In this paper, a method to obtain crack initiation, location and width in concrete structures subjected to bending and instrumented with an optical backscattered reflectometer (OBR) system is proposed. Continuous strain data with high spatial resolution and accuracy are the main advantages of the OBR system. These characteristics make this structural health monitoring technique a useful tool in early damage detection in important structural problems. In the specific case of reinforced concrete structures, which exhibit cracks even in-service loading, the possibility to obtain strain data with high spatial resolution is a main issue. In this way, this information is of paramount importance concerning the durability and long performance and management of concrete structures. The proposed method is based on the results of a test up to failure carried out on a reinforced concrete slab. Using test data and different crack modeling criteria in concrete structures, simple nonlinear finite element models were elaborated to validate its use in the localization and appraisal of the crack width in the testing slab.Peer ReviewedPostprint (author’s final draft

Application of distributed optical fiber sensors for the health monitoring of two real structures in Barcelona

This is an Accepted Manuscript of an article published by Taylor & Francis Group in Structure and Infrastructure Engineering on 2018, available online at: http://www.tandfonline.com/10.1080/15732479.2018.1438479The versatility and ease of installation of Distributed Optical Fibre Sensors (DOFS) compared with traditional monitoring systems are important characteristics to consider when facing the Structural Health Monitoring (SHM) of real world structures. The DOFS used in this study provide continuous (in space) strain data along the optical fibre with high spatial resolution. The main issues and results of two different existing structures monitored with DOFS, are described in this paper. The main SHM results of the rehabilitation of an historical building used as hospital and the enlargement of a pre-stressed concrete bridge are presented. The results are obtained using a novel DOFS based on an Optical Backscattered Reflectometry (OBR) technique. The application of the optical fibre monitoring system to two different materials (masonry and concrete) provides also important insights on the great possibilities of this technique when monitoring existing structures. In fact, the influence of strain transfer between the DOFS and the bonding surface is one of the principal effects that should be considered in the application of the OBR technique to real structures. Moreover, and because structural surfaces generally present considerable roughness, the procedure to attach the optical fibre to the two monitored structures is described.Peer ReviewedPostprint (author's final draft

Stellar activity in exoplanet hosts

[cat] Actualment, la major part dels esforços per la cerca i caracterització d’exoplanetes de tipus terrestre es centren en aquells que orbiten estrelles de baixa massa. Algunes de les característiques importants de l’estructura i els processos d’aquest tipus d’estrelles són encara poc coneguts, i per tant és important fer-ne un estudi acurat com un dels següents passos en el camp de l’exoplanetologia. En concret, el senyal produïit pels fenòmens d’activitat estel•lar, degut a la presència de taques i fàcules, introdueix variacions en les mesures fotomètriques i espectroscòpiques amb una periodicitat modulada per la rotació de l’estrella. En aquesta tesi s’ha realitzat un estudi dels fenòmens d’activitat a la fotosfera d’estrelles de baixa massa a través de diverses tècniques que ens han permès modelitzar o bé simular les relacions entre les propietats estel•lars i les dades observables. La simulació de mostres estadístiques d’estrelles basada en les relacions conegudes entre l’activitat estel•lar i la rotació ha permés implementar una tècnica per estimar la inclinació de l’eix de les estrelles a partir de mesures espectroscòpiques, resultant en un catàleg amb les millors candidates per una cerca de planetes amb trànsits. Per a la caracterització dels fenòmens relacionats amb l’activitat i un estudi acurat dels seus efectes sobre les mesures i cerques d’exoplanetes, s’ha aprofitat la disponibilitat de dades fotomètriques de Kepler juntament amb tècniques de modelització de taques, centrant-nos particularment en l’estudi de LHS 6343 A per obtenir informació d’activitat en la seva superfície. A més, s’ha dissenyat un simulador dels efectes d’activitat a la fotosfera basat en tècniques d’integració de superfície i models d’atmosfera Phoenix, que permet obtenir sèries temporals de dades sintètiques i estudiar els efectes de les regions actives sobre les mesures de trànsits de planetes. En particular, s’ha modelat el cas de HD189733. Els resultats d’aquest treball conclouen que és essencial una correcta modelització del senyal de l’activitat estel•lar en el camp de l’exoplanetologia, i es proporcionen algunes eines i estratègies per tal de caracteritzar i corregir aquests efectes i obtenir-ne informació astrofísica.[eng] Most of the efforts on the search and characterization of Earth-like exoplanets are currently focused on low mass stars. Some important properties related to the structure and processes in this type of stars are still unknown, so a careful characterization is essential as one of the next steps in exoplanet sciences. The characterization of stellar activity in low mass stars was carried out through several techniques that allowed us both to model and to simulate the relationships between the observational data and the stellar properties. Several empyrical relations for low mass stars allow to find correlations between certain activity indicators and the rotation period. These have permitted us to generate synthetic samples of stars with stochastic distributions of stellar and geometric properties allowing to estimate the inclination of the rotation axis from the distribution in the activity-vsini diagram. The methodology was applied to a sample of 1200 observed low mass stars and the best candidates for a targeted transit search were selected. Spot modelling techniques allow to obtain physical information about the stellar surface from time series photometric and spectroscopic data. In this work we analyse Kepler photometry of LHS 6343 A, an M-dwarf being eclipsed by a brown dwarf companion every 12.718 days, and showing photometric oscillations with the same periodicity and a phase lag of 100º from the eclipses. The accurate modeling of the Kepler data allowed to explain these oscillations with the presence of active regions appearing at a fixed longitude, thus suggesting a possible magnetic connection between both components. On the other hand, we also studied an alternative explanation for the photometric oscillations in LHS 6343 A in terms of the Doppler beaming effect, showing that this could be the main cause of the observed oscillations. Stellar activity effects are responsible for the noise observed at different amplitude and timescales on time series data. Such noise represents one of the main limitations for exoplanetary sciences. In order to characterize it, we designed a methodology to simulate the photosphere of an active rotating star through the integration of small surface elements from Phoenix atmosphere models. This allows to characterize the signal produced by activity and further study its relationship with the stellar properties, as well as the possible effects produced on exoplanet measurements. The methodology allowed us to present several strategies in order to correct or reduce the effects of spots on the photometry of exoplanet transits, as these may induce significant variations on the measurement of the planetary radius. We focused on a comprehensive analysis of HD 189733, a K5 star hosting a giant planet, which has simultaneous photometric (MOST) and spectroscopic (SOPHIE) data available. An accurate surface map was obtained using the methodology above, accurately reproducing the light curve and radial velocity observations. Such map was used in order to study the effects of activity on the exoplanet transits. We showed that the effects of spot-crossing events are significant even for mid-infrared wavelengths. Moreover, the chromatic effects of spots not occulted by the planet show a signal with a wavelength dependence and amplitude that are very similar to the signature of the atmosphere of a planet dom- inated by dust. The radial velocity theoretical curve is in agreement with the observations up to the typical instrumental systematics of SOPHIE. The results from this work conclude that it is essential to correctly model the stellar activity signals for exoplanetary sciences, and we provide some tools and strategies to characterize and reduce such effects and extract astrophysical information