Public display of deposited theses

DOCTORAL DEGREE IN AEROSPACE SCIENCE AND TECHNOLOGY

• KHALEDIAN, HOMEYRA: Aircraft Trajectory Estimation and Guidance Mode Identification using Bayesian Filtering Techniques
  
  Author: KHALEDIAN, HOMEYRA
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN AEROSPACE SCIENCE AND TECHNOLOGY
  Department: Department of Physics (FIS)
  Mode: Normal
  Deposit date: 06/09/2024
  Deposit END date: 20/09/2024
  Thesis director: PRATS MENENDEZ, XAVIER | VILÀ VALLS, JORDI
  Committee:
       PRESIDENT: UIJT DE HAAG, MAARTEN
       SECRETARI: LÓPEZ LEONÉS, JAVIER
       VOCAL: SUN, JUNZI
  Thesis abstract: The dissertation explores advanced methods for aircraft trajectory estimation and trajectory prediction (TP), which are critical for the next generation of Air Traffic Management (ATM) systems operating under the Trajectory-Based Operations (TBO) paradigm. As ATM systems evolve, more responsibilities like flight plan adjustments and separation management are expected to shift from ground-based controllers to aircraft, emphasizing the need for precise trajectory estimation. The research primarily focuses on improving single-aircraft trajectory estimation and guidance mode identification, important for safe and efficient operations of both ground-based and airborne Decision Support Tools (DSTs). The core of the work is the development of sophisticated Interacting Multiple Model (IMM) algorithms enhanced with advanced filtering techniques, including Kalman filters and Sequential Monte Carlo (SMC) methods. These enhancements address challenges such as managing uncertainties, potential model mismatches, and identifying hidden guidance modes, all of which significantly impact TP. A dynamic model for trajectory estimation and TP requires various inputs, including measurement data, weather forecasts, aircraft performance models, and operational constraints. However, a key challenge is the availability of aircraft intent, which includes operational instructions and guidance modes that are required for accurately predicting trajectories. Identifying guidance modes is essential for improving TP performance, as it directly influences how the aircraft is controlled during flight. The main objectives of this dissertation are to characterize the estimation and guidance mode identification problem and enhance existing filtering methodologies using Bayesian techniques that rely on multiple-model approaches. The work proposes an optimal IMM approach that uses Kalman filter-based methods, particularly the Extended Kalman Filter (EKF), to manage the nonlinear dynamics predominant in vertical trajectory profiles, which are typically more uncertain than lateral paths. However, the research identifies limitations in the optimal method, particularly in tracking hybrid jumps— simultaneous changes in the state component and a mode switch. To overcome these limitations, the research introduces an enhanced IMM, named generalized IMM (GIMM), framework that better predicts transitions between guidance modes and tracks hybrid jumps more accurately. Additionally, SMC-based methods, i.e., Particle Filter (PF), is proposed as an alternative to manage complex flight dynamics and improve robustness in state estimation and mode identification. The effectiveness of these methodologies is validated through extensive testing with synthetic and real-flight data. Results show that the maximum percentage error in aircraft mass estimation is minimal, and other state variables are also accurately estimated with low delays in tracking hybrid jumps and identifying guidance modes. This research not only addresses the immediate needs of ATM systems under the TBO framework but also lays the groundwork for future advancements. Potential future directions include integrating lateral navigational maneuvers into system models, expanding the state vector to include additional flight parameters, and adapting these methodologies for multi-aircraft tracking scenarios. These enhancements aim to further refine TP capabilities, advancing ATM systems towards greater efficiency and safety.
  

DOCTORAL DEGREE IN COMPUTATIONAL AND APPLIED PHYSICS

• NABAHAT, MEHRAN: Dynamic Heterogeneity in Metallic Glasses: Study of Structural Relaxation, Aging, and Mechanical Properties of Vit4 alloy
  
  Author: NABAHAT, MEHRAN
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN COMPUTATIONAL AND APPLIED PHYSICS
  Department: Department of Physics (FIS)
  Mode: Normal
  Deposit date: 12/09/2024
  Deposit END date: 25/09/2024
  Thesis director: PINEDA SOLER, ELOY
  Committee:
       PRESIDENT: SUÑOL MARTÍNEZ, JUAN JOSÉ
       SECRETARI: BRUNA ESCUER, PERE
       VOCAL NO PRESENCIAL: LYU, GUOJIAN
  Thesis abstract: Metallic glasses (MGs), distinguished by their unique microstructural features and exceptional mechanical properties, offer compelling materials for exploring relaxation dynamics and related phenomena within glass science. This doctoral thesis provides an in-depth examination of the dynamic and structural heterogeneity of Zr46.8Ti8.2Cu7.5Ni10Be27.5 (Vit4) glass-forming alloy, investigating the intricate relationships between its structural dynamics, thermal behavior and mechanical properties. The overarching objective is to advance in theoretical knowledge while also exploring innovative techniques for material manipulation and optimization of MGs.Firstly, a thorough examination of the viscoelastic and anelastic behavior of MGs is conducted, focusing on the spectrum of structural dynamic processes and characteristic times under small stress in the linear regime. This analysis highlights the reversible nature of most processes, where thermally activated anelastic particle rearrangements can be frozen by quenching after creep experiments, revealing new configurations of the potential energy landscape. This comprehensive approach significantly deepens our understanding of the viscoelastic properties of MGs.Secondly, the study critically evaluates the limitations of existing microscopic models, such as shear transformation zones, in explaining the anelastic recoverable strain of MGs. By analyzing experimental data, particularly recovery curves, the research isolates the pure anelastic response, minimizing the influence of the viscous component. This method uncovers the dependence of anelastic relaxation timescales on prior loading duration, providing crucial insights for interpreting mechanical probe results and refining assessments of MG properties.Lastly, the investigation delves into the dynamic heterogeneity and aging effects in MGs. In the supercooled liquid state, time-temperature superposition of α-relaxation and coherence between experimental and mechanical observations indicate a stable dynamic heterogeneity. However, transitioning to the glass state reveals an intensifying dynamic heterogeneity with aging, leading to inconsistencies between microscopic and mechanical studies. At the micrometer scale, significant changes in local hardness due to aging are observed, emphasizing the intricate nature of relaxation processes and their impact on the mechanical properties of Vit4. This detailed study advances our comprehension of the aging and dynamic behaviors in MGs.
  

DOCTORAL DEGREE IN ELECTRONIC ENGINEERING

• CAÑO PRADES, IVAN: New synthesis methodologies to develop emerging chalcogenides and chalcohalides for photovoltaic applications
  
  Author: CAÑO PRADES, IVAN
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN ELECTRONIC ENGINEERING
  Department: Department of Electronic Engineering (EEL)
  Mode: Article-based thesis
  Deposit date: 05/09/2024
  Deposit END date: 19/09/2024
  Thesis director: SAUCEDO SILVA, EDGARDO ADEMAR | PLACIDI, MARCEL JOSE
  Committee:
       PRESIDENT: PÉREZ RODRÍGUEZ, ALEJANDRO
       SECRETARI: VOZ SANCHEZ, CRISTOBAL
       VOCAL: HOYE, ROBERT LIANQI ZHAO
  Thesis abstract: Chalcogenide materials have been central to some of the most significant events in the history of photovoltaic energy, includingthe fabrication of the first solar cell in 1883 by Charles Fritts, which was based on selenium. However, the rapid development ofcrystalline silicon starting in 1954, and the lack of knowledge on their most attractive properties, led to various chalcogenidebasedmaterials to being largely overlooked despite the technological efforts to advance solar energy from the 1960s onward.Only in the last 10 to 20 years have these materials garnered renewed interest in the scientific community, driven by newadvances in structure simulation and advanced characterization techniques in materials science.In particular, antimony and bismuth chalcogenides have garnered considerable interest, as they are constituted by earthabundantelements, which can be easily extracted from the refinement of natural ores. Also, they are mostly harmless to thehuman health and the environment, they exhibit optimal properties for photovoltaic technology (such as a high absorptioncoefficient and bandgap in the visible spectrum range), and their optical properties can be tuned through doping strategies,chemical substitution or solid solution fabrication. They also exhibit structural and electronic characteristics similar to other highperformancephotovoltaic compounds (e.g., hybrid perovskites), and their quasi-1D crystalline structure based on covalentlybonded ribbons linked by Van der Waals interactions leads to unique anisotropic properties, such as enhanced electronictransport in the direction of the covalent chains. Therefore, by adjusting the structure, crystalline orientation, and composition, it ispossible to develop new materials with a clear potential for next-generation photovoltaic technologies. Furthermore, their highabsorption coefficient and adjustable bandgap open the door to exploring new application avenues, such as flexible, semitransparentsolar cells, or compatible devices with the Internet of Things.In the context of this effort directed towards the development of chalcogenide compounds for photovoltaics, this thesis focuses onthree groups of chalcogenide and chalcohalide materials (i.e., including chalcogenide and/or halide anions), which exhibit thefollowing common features: they present properties analogous to hybrid perovskites – either structurally or electronically –, havea low-dimensional crystalline structure, are composed of abundant elements without toxicity risk, and they have been scarcelystudied, leaving many unanswered questions regarding their chemical nature, behavior as semiconductors, and performance inphotovoltaic prototypes.The work has several objectives. First, we study the effects of synthesizing Sb2Se3 under non-stoichiometric conditions, as wellas adjusting its optical properties by incorporating bismuth via thermal evaporation processes. Secondly, we develop aninnovative and versatile methodology for the fabrication of antimony chalcohalides (SbSeI and SbSeBr), based on a combinationof co-evaporation and high-temperature and high-pressure annealing, which enables the fabrication of a wide range ofcompounds that could not be effectively synthesized with the previous techniques. Finally, we investigate a new solutionprocessing methodology based on molecular precursor ink deposition which allows obtaining chalcohalide anti-perovskites(Ag3SBr and Ag3SI) at very low temperatures, opening the door for these compounds to also be manufactured using adaptableand low-cost chemical techniques. All materials have been studied using structural and optoelectronic characterizationtechniques, showing their potential as photovoltaic absorbers, and demonstrating that chalcogenides still have much to offer inthe field of solar energy.
  

DOCTORAL DEGREE IN GEOTECHNICAL ENGINEERING

• ZENG, HAO: Multi-scale hydro-mechanical and gas transport characterisation of granular bentonite
  
  Author: ZENG, HAO
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN GEOTECHNICAL ENGINEERING
  Department: Department of Civil and Environmental Engineering (DECA)
  Mode: Normal
  Deposit date: 04/09/2024
  Deposit END date: 18/09/2024
  Thesis director: ROMERO MORALES, ENRIQUE EDGAR | GONZÁLEZ BLANCO, LAURA
  Committee:
       PRESIDENT: VILLAR GALICIA, MARÍA VICTORIA
       SECRETARI: LLORET MORANCHO, ANTONIO
       VOCAL: JOMMI, CRISTINA
  Thesis abstract: Bentonite-based materials with low permeability, great water retention and self-sealing properties have been extensively used for engineered barriers in waste disposal facilities. Several typologies of bentonites exist. On the one hand, during installation, powder bentonites can release and disperse fine particles, while pouring bentonites in the form of pellet/powder mixtures can lead to particle segregation. On the other hand, sand/bentonite mixtures have a lower swelling potential compared to pure bentonites. Highly compacted bentonite blocks are more laborious to install and their use could hinder the release of gases formed in long-term operational facilities. These technological challenges could be addressed by using granular bentonite (GB), which has millimetre-sized granules and micrometre-sized grains, along with an extended particle size distribution (PaSD) (Fuller) that improves workability and pourability. Additionally, GB contains numerous macropores that allow gas release at low pressures. Consequently, GB is emerging as a reference material for engineering barriers. However, the geotechnical properties of GB remain poorly understood, particularly in terms of sample preparation, particle size and microstructural evolution and its correlations to hydro-mechanical (HM) and gas transport behaviour and self-sealing capacity. The Thesis provides robust, systematic, multi-scale experimental and theoretical frameworks for studying these aspects. The outcomes offer new particle-scale insights into the preparation technique of GB samples and how it affects the HM behaviour (e.g. compressibility on loading, volumetric expansion/collapse and swelling pressure on wetting under different stress and displacement boundary conditions) and its microstructure. A straightforward methodology combining Mercury Intrusion Porosimetry (MIP) and X-ray Micro-Computed Tomography (Micro-CT) has been proposed to improve the characterisation of compacted GB’s granular-type microstructure. Based on this methodology, compacted GB’s HM behaviour (e.g. swelling pressure, water permeability) can be further analysed from the pore-scale perspective, which displays a wide range of sizes. This microstructural information has also served as the basis for developing a multi-scale and multi-physics constitutive model of water retention behaviour. Moreover, the granular-type fabric with numerous and large interconnected macropores has been found to limit entrapped gas accumulation under partially saturated states while its gas transport properties also depend on how the initial microstructure evolves in response to gas pressurisation. The gas migration pathways at different HM states have been tracked by imaging techniques, which have subsequently used to define a model that incorporates this unique microstructure and its evolution to predict gas permeability. Furthermore, the granular-type microstructure with many high-density granules influences the sealing of technological gaps during loading and saturation. After gap-sealing, the HM behaviour of compacted GB is governed by the microstructure of the matrix set on compaction (the artificial gap insertion affected the compaction). The geometry of residual gaps after loading and saturation paths determines whether they could serve as preferential pathways for water and gas flow. In conclusion, this Thesis contributes meaningful information for evaluating the short- and long-term behaviour of GB as a geomaterial for engineered barriers.
  

DOCTORAL DEGREE IN MECHANICAL, FLUIDS AND AEROSPACE ENGINEERING

• BETRIU ROURE, PAULA: Optimization Techniques in Science Planning for Planetary Exploration missions
  
  Author: BETRIU ROURE, PAULA
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN MECHANICAL, FLUIDS AND AEROSPACE ENGINEERING
  Department: Department of Physics (FIS)
  Mode: Normal
  Deposit date: 06/09/2024
  Deposit END date: 20/09/2024
  Thesis director: SORIA GUERRERO, MANUEL | GUTIERREZ CABELLO, JORGE LUIS
  Committee:
       PRESIDENT: HUESO ALONSO, RICARDO
       SECRETARI: ROVIRA GARCIA, ADRIÀ
       VOCAL: CARDESIN MOINELO, ALEJANDRO
  Thesis abstract: Solar System robotic missions explore objects in space to elicit key information that contributes to our understanding of the origins and evolution of the Solar System as well as of life. Noticeably, such an ambitious purpose demands an equally challenging endeavor from the scientific and engineering perspectives—an effort that compels to procure high scientific revenues. In this context, science planning plays a key part to guarantee that the mission obtains as large an information harvest as possible to ultimately fulfill a set of scientific objectives. This list of mission objectives can be very extensive and diverse; from the search for life to the identification of planetary resources or the geomorphological analysis, many disciplines come together in this quest. To meet these objectives, spacecraft are equipped with a varied suite of instruments capable of conducting a wide range of experiments. Thorough planning is required to conciliate the instruments' operations while concurrently guaranteeing the spacecraft performance and safety, ensuring a good management of the available resources, as well as the feasibility to forward this information to Earth. These requirements and constraints often result in trade-offs among spacecraft subsystems, including the payload. All in all, the activity plan of a mission constitutes a complex problem that needs to account for a wide spectrum of agents in order to draw a suitable mission program that effectively fulfills the scientific objectives. Within this context, observation and mission planning software tools have played an important role in space missions—and their relevance is only expected to grow in the near future. From designing the instrumental observational activities to overall management of spacecraft resources and activity scheduling, various software tools have greatly assisted in the planning process of missions like Cassini, Dawn or Rosetta. Drawing upon these, this work presents the development and validation of a software prototype designed to streamline science planning processes for planetary exploration missions. Our study focuses on devising an optimized activity plan for a camera instrument, aiming to maximize its scientific return while ensuring efficient mission operations. This software prototype tool, named Observation Planning Tool for Instrument and Mission Analysis (OPTIMA), consists of two consecutive stages. The first one utilizes spacecraft trajectory and, possibly, attitude data to identify feasible observational opportunities based on geometric constraints derived from instrument measurement requirements. These opportunities, defined as science opportunity windows, are used to constrain the exploration space in the subsequent stage. The second phase applies optimization heuristics to develop potential activity plans that maximize scientific returns while adhering to both geometric and operational constraints. The tool's modularity allows for the application of various optimization heuristics tailored to the specific problem. Additionally, OPTIMA includes a component for simulating the camera's observation through mosaic heuristics that aim to achieve maximum coverage of Regions of Interest (ROIs) with minimal make-span. Finally, the methodology's efficacy is demonstrated through hypothetical case studies set in realistic mission scenarios, including a validation case study on Galileo's flybys over Europa and two others during different phases of the JUICE mission. These cases focus on optimizing coverage and/or resolution across various ROIs, considering additional adjustments such as downlink windows allocation and data compression. The algorithm successfully identifies nearly-optimal activity plans that comply with the specified constraints in all cases, showcasing the tool's efficiency and adaptability across different mission scenarios. This makes OPTIMA a valuable asset for multi-mission science planning in planetary exploration.
  
• GUANCHEZ REYES, EDINSON ASDRUBAL: ESTUDIO DE LA INFLUENCIA DE LOS FENÓMENOS DE INTERACCIÓN SUELO-ESTRUCTURA EN LA RESPUESTA SÍSMICA DE ESTRUCTURAS TÍPICAS DE ACERO CON ARRIOSTRAMIENTOS CONCÉNTRICOS
  
  Author: GUANCHEZ REYES, EDINSON ASDRUBAL
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN MECHANICAL, FLUIDS AND AEROSPACE ENGINEERING
  Department: Department of Strength of Materials and Structural Engineering (RMEE)
  Mode: Normal
  Deposit date: 10/09/2024
  Deposit END date: 25/09/2024
  Thesis director: SANCHEZ ROMERO, MONTSERRAT | WEYLER PEREZ, RAFAEL
  Committee:
       PRESIDENT: DEL COZ DÍAZ, JUAN JOSÉ
       SECRETARI: VELAZQUEZ AMEIJIDE, JUAN
       VOCAL: DE LA FLOR LÓPEZ, SILVIA
  Thesis abstract: Steel concentrically braced frames (CBF) are considered efficient in resisting lateral forces because they provide high lateral strength and stiffness, which is particularly beneficial in seismic zones. However, this type of structure has a significant overstrength that is not considered during foundation design, which can lead to uplift of the footings under the braced members and to rocking mechanisms. On the other hand, soil-structure interaction (SSI) phenomena and foundation flexibility are generally not considered in performance-based analyses of new or existing structures.In this research, the influence of SSI phenomena on the seismic response of CBF is evaluated by considering the nonlinear response of embedded footings using the BNWF (Beam on Nonlinear Winkler Foundation) approach. To model the vertical stress-displacement behaviour of the footings, it is possible to define a backbone curve by combining the response of the compression zone in series with that of the tension zone.When uplift of the footing is allowed, it is shown that it is necessary to consider the horizontal stresses of the native soil in situ and the degree of compaction of the soil above the footing to avoid significant deviations between the analysis results and the real response. The tension zone in the response curves has been calibrated to take these parameters into account and, given the difficulty associated with their calibration, an estimate is reported which could also be used for practical applications.The implementation has been validated by various pushover analyses on a steel CBF archetype originally tested in the fixed base condition, and predictions for the flexible base condition have been made considering different soil types and footing embedment depths (Df). The results show a direct relationship between the nonlinear response of steel CBF and the uplift mechanism of embedded footings, with the embedment depth (Df) and the shape of the tension-displacement curve being the most important variables that influence the response.The model has been incorporated in various nonlinear time-history analyses considering a set of seismic records on a well-known steel CBF archetype. The results obtained suggest that, when analysing the response of steel CBF on a nonlinear flexible base condition, it is possible to report variations in the yielding sequence of the superstructure with respect to the fixed base condition. It is reported that the embedment depth (Df) of the footing, and hence its uplift stiffness, is able to modify the overall response of the superstructure. On the other hand, the cyclic response of the foundation determines a process of energy dissipation which is reflected in a reduction of the seismic force on the bracing system of the structure. The energy dissipation mechanism due to vertical response is more efficient for the supports located under the braced frames compared to those footings located under unbraced columns, and the effect is much more pronounced in soft or loose soils. The proposed model can be implemented as part of both static and dynamic analyses to have a more realistic prediction of the seismic response during performance-based designs of structures supported on embedded footings, particularly for the case of steel CBF.
  

DOCTORAL DEGREE IN NATURAL RESOURCES AND THE ENVIRONMENT

• MASSAGUÉ OBRADORS, JORDI: Tendencias y dinámica de los episodios de contaminación por ozono troposférico en España.
  
  Author: MASSAGUÉ OBRADORS, JORDI
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN NATURAL RESOURCES AND THE ENVIRONMENT
  Department: Department of Mining, Industrial and ICT Engineering (EMIT)
  Mode: Article-based thesis
  Deposit date: 12/09/2024
  Deposit END date: 25/09/2024
  Thesis director: QUEROL CARCELLER, XAVIER | ESCUDERO TELLECHEA, MIGUEL
  Committee:
       PRESIDENT: DOS ANJOS ALVES, CÉLIA
       SECRETARI: GAMISANS NOGUERA, XAVIER
       VOCAL: MUÑOZ CINTAS, AMALIA
  Thesis abstract: Tropospheric ozone (O3) is a secondary gaseous photochemical pollutant with adverse effects on health, ecosystems, and materials, and it contributes to the greenhouse effect. 94% of the urban population in Europe is exposed to harmful levels of O3, especially in the south and Mediterranean countries like Spain, where regulatory values are systematically exceeded. The abatement of O3 concentrations is complex due to the nonlinear reactions between its key precursors - nitrogen oxides (NOx) and volatile organic compounds (VOCs)- , and the influence of meteorology and atmospheric transport processes at various scales. The aim of this thesis is to enhance the understanding of O3 dynamics in Spain and contribute to the future National Ozone Plan aimed at reducing its levels. This research is based on the analysis of experimental air quality and meteorological data. A regionalization of the territory has been proposed according to the severity of O3 pollution. Critical zones (hotspots) are those with the highest O3 levels and should therefore be prioritized in implementing reduction policies. These include: the Madrid basin, the north of Barcelona (NoB), the closed basin of Puertollano, the interior of the Valencian Community, and the Guadalquivir basin (GB). In these hotspots, external contributions of O3 to Spain and Europe add to the considerable O3 production generated from intense local/regional precursor emissions, causing exceedances of regulatory values. Proper management of these emissions could significantly reduce O3 levels during episodes.Two hotspots have been studied in depth: (i) the GB, where some O3 contributions have been estimated. Controlling local/regional emissions could reduce O3 levels by up to ~50% during acute episodes. (ii) Barcelona - NoB axis, where three exceptional O3 episodes in the city have been analyzed, identifying their causes (mostly common): prior accumulation of O3, weekend effect, specific meteorological conditions, with Tramontana at altitude and very high temperatures, and multiregional convergence of air masses. The evolution of O3 levels has been analyzed in three phases: before (2008- 2019), during (2020- 2021), and after (2022- 2023) the COVID-19 pandemic, due to its impact on precursor emissions. Between 2008-2019, O3 levels in the hotspots showed divergent trends. In the Madrid basin, they increased generally due to meteorology, reduced NOx emissions from road traffic, and a slight increase in VOCs, in a VOC-limited O3 formation regime. In contrast, Seville recorded decreases in O3, attributed to an atypical urban O3 formation regime (more limited by NOx). Other hotspots showed no clear trends, due to slight variations in precursor emissions and the absence of meteorological variations. During the pandemic, O3 levels decreased widely across the country, especially on the Mediterranean littoral, where for the first time regulatory values were not exceeded, due to the unprecedented reduction in precursor emissions at various scales (local, regional, European, and hemispheric), and unfavorable meteorological conditions for O3 production/accumulation. During the post-pandemic period, O3 levels increased compared to the pandemic, although they generally did not reach pre-pandemic levels, despite multiple and intense heat waves conducive to O3. In all three periods, O3 levels increased in urban areas affected by traffic emissions, indicating various causes. The results suggest a long-term convergence between O3 levels in rural and urban environments. Additionally, they highlight the importance of analyzing O3 dynamics at the local/regional scale and applying differentiated management for the various hotspots.
  

DOCTORAL DEGREE IN STRUCTURAL ANALYSIS

• WIERNA QUIROGA, PABLO NICOLÁS: A Novel Computational Homogenization Theory for Multilayered Plates: The Multiscale 2D+ Approach.
  
  Author: WIERNA QUIROGA, PABLO NICOLÁS
  Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
  Programme: DOCTORAL DEGREE IN STRUCTURAL ANALYSIS
  Department: Department of Civil and Environmental Engineering (DECA)
  Mode: Normal
  Deposit date: 06/09/2024
  Deposit END date: 20/09/2024
  Thesis director: OLIVER OLIVELLA, FRANCISCO JAVIER | LLOBERAS VALLS, ORIOL
  Committee:
       PRESIDENT: ARTEIRO, ALBERTINO
       SECRETARI: CANTE TERAN, JUAN CARLOS
       VOCAL NO PRESENCIAL: SANCHEZ, PABLO JAVIER
  Thesis abstract: This doctoral thesis presents a novel multiscale theory for the analysis of multilayered plate structures, termed the "Multiscale 2D+ approach" or, simply, "2D+". Based on the formalism of computational homogenization theory, this approach is specifically tailored to account for the mechanical behaviour of multilayered materials, which contain a heterogeneous distribution of thin layers across the thickness and often exhibit substantial non-linear material behavior. After identifying the macroscopic scale as the (2D) reference plane of the plate, the strategy models the through-the-thickness heterogeneity by means of a (1D) meso-scale filament, orthogonal to such plane and spanning the plate depth. At the macro-scale level, classical First Order Shear Deformation Theory (FSDT) kinematics is adopted. At the fine-scale level, the Representative Volume Element (RVE) kinematics is initially derived through the linearization of the macro-scale displacement field along the thickness, in accordance with the first-order computational homogenization theory. The RVE is then endowed with a fluctuating displacement field, which aims to capture the well-known (higher-order) zig-zag displacements observed across the thickness of composite laminates. The Hill-Mandel principle is used to establish the mechanical energy balance across both scales, resulting in a one-dimensional Boundary Value Problem (BVP) to be solved at the meso-scale level in terms of the fluctuating displacement field. Furthermore, the variational RVE-problem allows for the enforcement of an additional condition: the fulfillment of the linear momentum balance (equilibrium) equations at every point across the thickness. This yields a physically meaningful computational setting, in which both scales are represented through simple (degenerated) kinematic descriptions, accounting for the essential mechanical behavior observed at each level yet remaining computationally inexpensive. The Multiscale 2D+ approach can therefore be seen as a modern plate theory, where the through-the-thickness mechanical behavior of the plate is obtained upon the solution of the equilibrium problem of a meso-scale filament. Particularly well-suited for bending-dominated scenarios, it provides accurate stress distributions at the ply-level in non-linear simulations, close to those of full-3D models, at a computational cost similar to that of 2D models. The thesis comprises the development of both the formulation and the corresponding numerical multiscale model within the context of the finite element method. Through a series of representative simulations−including assessments of accuracy, computational performance, and non-linear material modeling− the merits of the 2D+ approach in successfully accounting for the mechanical behavior of multilayered plates are clearly evidenced in this contribution.