Doctoral School

Reading date: 30/09/2026

• DURÁN CABALLERO, DIEGO ENRIQUE: Applications of the Geotechnical Particle Finite Element Method to CPTu and Statnamic Pile Load test interpretation
  
  Author: DURÁN CABALLERO, DIEGO ENRIQUE
  Programme: DOCTORAL DEGREE IN GEOTECHNICAL ENGINEERING
  Department: Department of Civil and Environmental Engineering (DECA)
  Mode: Normal
  Deposit date: 04/09/2026
  Reading date: 30/09/2026
  Reading time: 11:00
  Reading place: ETSECCPB.UPC, Campus NordBuilding C1. Classroom: 002C/Jordi Girona, 1-308034 Barcelona
  Thesis director: ARROYO ALVAREZ DE TOLEDO, MARCOS | MONFORTE VILA, LLUÍS
  Thesis abstract: This thesis exploits and extends the Geotechnical Particle Finite Element Method (G-PFEM) to model complex coupled problems in geotechnical engineering, particularly those involving the insertion of solid objects into soil, such as cone penetration testing (CPTu) or pile installation. The insertion of solid objects into soil is the operating principle of several in-situ tests, whose measurements are used later to infer geotechnical design parameters. These inference methods remain largely empirical and carry significant uncertainty, particularly when they are applied beyond the conditions for which they were originally developed. This uncertainty is transferred directly to geotechnical design and may, in some cases, lead to unsafe designs. Part of it arises from the complexity of the insertion process itself, which mobilises several soil mechanisms simultaneously and is therefore only partially represented by the simplified analyses underlying existing correlations.This problem is addressed by reproducing the full mechanics of two in-situ tests: CPTu and the Statnamic pile load test. The tests are analysed across different soil types, drainage conditions and loading rates. In each application, the constitutive model is selected according to the features governing the response: SCLAY-1 is used to represent fabric anisotropy in clay, CASM and SIMSAND to describe the critical-state behaviour of sands and silty sands, and CASM-Visco to capture the viscous response mobilised during rapid loading.For undrained cone penetration in clay, the study identifies the shearing mode governing the response beneath the cone tip and determines which undrained shear strength should be used as the reference for normalising cone resistance. It also evaluates how fabric anisotropy affects the resulting cone factors. For Statnamic testing, the experimental programme carried out at the University of Sheffield is back-analysed reproducing complex sequences of pile penetration, consolidation and rapid loading, providing further insight into the mechanisms governing the measured response. For CPTu in sands, the study examines how the use of a log-linear representation of the critical state line affects the inference of the state parameter. For silty sands, the influence of partial drainage and fines content on the cone response is investigated by mapping their effects onto the constitutive behaviour of a reference clean sand.Overall, the thesis extends the application of G-PFEM to the interpretation of CPTu and Statnamic pile load tests under different governing conditions. The results clarify the soil mechanisms controlling the measured response and contribute to the assessment and development of more accurate test interpretation procedures.
  

• KHAN, AHMAD KAMAL: Cell Geometrical Configurations and Extrusion at Mechanical Equilibrium in Vertex Models
  
  Author: KHAN, AHMAD KAMAL
  Programme: DOCTORAL DEGREE IN APPLIED MATHEMATICS
  Department: School of Mathematics and Statistics (FME)
  Mode: Normal
  Deposit date: 03/09/2026
  Reading date: 30/09/2026
  Reading time: 11:00
  Reading place: Sala de Juntes de l'FME, Edifici U, Campus SudEnllaç videoconferència: https://meet.google.com/dfu-hsdt-chv
  Thesis director: MUÑOZ ROMERO, JOSE JAVIER
  Thesis abstract: Epithelial tissues maintain their structural integrity and undergo controlled shape changes through a precise balance of mechanical forces at the cellular scale. These forces, arising from cortical contractility, cell-cell adhesion, and cell-substrate adhesion determine both the equilibrium geometry of individual cells and the collective mechanical stability of the tissue. Vertex models, in which cells are represented as polygons or polyhedra whose shapes are governed by an energy functional, provide a natural mathematical framework for studying this force balance. Despite their widespread use in computational epithelial biology, analytical solutions for three-dimensional vertex models remain scarce, the quantitative consequences of the choice between linear and quadratic surface energy terms are poorly understood, and a rigorous energy-based description of basal cell extrusion incorporating substrate adhesion has not previously been developed.This thesis addresses these gaps through two interconnected contributions. The first concerns the analytical study of cell shape in three-dimensional vertex models. Closed-form expressions are derived for the equilibrium radius of a single isolated cell and for the shape factor of symmetric and unsymmetric two-cell systems, for both linear and quadratic surface energy functionals in two and three dimensions. A key result is that linear functionals give identical shape predictions in two and three dimensions, consistent with the Young-Laplace relation of classical capillarity theory, while quadratic functionals yield systematically different predictions in the two geometries. This establishes that two-dimensional vertex models with quadratic surface energy terms cannot serve as quantitative surrogates for three-dimensional configurations, a finding with direct implications for model selection and experimental parameter calibration. A variational derivation of the spherical cap solution confirms that the sphere is the energy-minimising shape for a volume-constrained cell, providing the geometric foundation for the parameterisation used throughout. All analytical results are validated against a three-dimensional discrete vertex model based on triangulated cell surfaces and Newton-Raphson energy minimisation. These results have been published in the International Journal for Numerical Methods in Biomedical Engineering.The second contribution concerns the mechanical basis of basal cell extrusion in epithelial monolayers. A two-dimensional vertex model is developed that incorporates substrate adhesion as a mechanically distinct boundary type with its own line tension coefficient, separate from the cell-cell junction tension and the external cortical tension. Simulations of a tissue of cells resting on a substrate reveal that basal extrusion of the central cell can emerge as a spontaneous, continuous mechanical instability from the competition between substrate adhesion, junction tension, and cortical contractility, without any prescribed topological transitions or biochemical signalling. A mechanical phase map is constructed in the space of dimensionless tension ratios, and its phase boundary is confirmed to correspond to configurations of lower total mechanical energy on the extruded side. Extended parametric studies show that the extrusion threshold is lowered by stronger substrate adhesion of the extruding cell, by reduced external cortical tension, by localised dipole forces mimicking basal actomyosin contraction, and by tissue-level boundary compression mimicking proliferative crowding. A non-monotonic dependence of the extrusion threshold on tissue size is identified, reflecting a competition between local mechanical confinement by immediate neighbours and long-range stress accumulation through the tissue. This work will be submitted in the following weeks after the thesis submission.Together, these results establish a minimal mechanical framework in which both the equilibrium ...
  

Reading date: 01/10/2026

• VILELLA I CROSAS, TÀNIA: Biocompatible superelastic TiNb-based alloys produced by additive manufacturing
  
  Author: VILELLA I CROSAS, TÀNIA
  Programme: DOCTORAL DEGREE IN MATERIALS SCIENCE AND ENGINEERING
  Department: Department of Materials Science and Engineering (CEM)
  Mode: Normal
  Deposit date: 02/09/2026
  Reading date: 01/10/2026
  Reading time: 12:00
  Reading place: ESCOLA D'ENGINYERIA BARCELONA ESTC/Eduard Maristany, 16 (08019 Barcelona)EDIFICI A planta 0, SALA D'ACTEShttps://meet.google.com/hzr-ymub-uum
  Thesis director: FARGAS RIBAS, GEMMA | RODRÍGUEZ RIUS, DANIEL
  Thesis abstract: The clinical success of load-bearing orthopaedic implants is fundamentally constrained by two major mechanical and biological limitations: the stress-shielding phenomenon induced by the high elastic modulus mismatch between standard titanium alloys (e.g Ti-6Al-4V) and human cortical bone, and the long-term risk of systemic toxicity or hypersensitivity associated with superelastic shape memory alloys like NiTi. Ni-free, β-type TiNb systems offer an ideal biocompatible alternative due to their inherently low stiffness and capacity for superelastic behaviour. However, conventional processing methods (casting and forging) lead to severe phase segregation, while conventional additive manufacturing (AM) routes remain restricted by the high cost and processing rigidity of pre-alloyed spherical feedstocks. To address this gap, this Thesis establishes novel, cost-effective AM pathways to fabricate complex, bone-mimetic architectures directly from irregular elemental powder blends using two distinct approaches: Direct Ink Writing (DIW) combined with vacuum sintering, and high-energy Electron Beam Powder Bed Fusion (PBF-EB).The first part of this work optimizes the extrusion-based DIW route for binary TiNb configurations. Rheological screening identified an optimal solid powder loading of 75 wt.%. This concentration maximizes green metallic density. It also maintains the shear-thinning behaviour and yield stress needed for shape retention post-printing. Pushing the loading to 80 wt.% triggers a micro-rheological jamming transition. This jamming is driven by internal friction between the irregular elemental particles. Vacuum sintering cycles were mapped to control the evolution of densification and porosity. Open, tubular pore networks successfully consolidated into isolated internal porosity. The macro-porous architecture was preserved. Nb acts as a β-stabilizer and suppresses α-phase formation. This results in a compliant body-centered cubic (bcc) β-matrix. Instrumented micro- and nanoindentation profiling evaluated the local mechanics. The macro-apparent stiffness of the porous scaffolds successfully matched human cortical boneIn the second part of this Thesis, ink formulation was expanded to ternary (TiNbZr, TiNbTa) and and quaternary (TiNbTaZr) systems. This approach achieved successful in-situ alloying. The third part of the thesis investigates single-step liquid-state consolidation via high-energy PBF-EB. A narrow process window was developed. The intense hydrodynamic mixing overcomes the large melting temperature gap between Ti and refractory Nb. The high vacuum and in-situ thermal annealing eliminate macro-segregation. This process results in homogeneous, single β-phase or metastable α’’-phases.The compliant β-phase was integrated with advanced Triply Periodic Minimal Surface (TPMS gyroid) designs to mitigate stress-shielding. Finally, in vitro biological validation using SaOs-2 osteoblast-like cells was performed across the three parts of this Thesis, demonstrating outstanding cytocompatibility in all cases.Conclusively, this Thesis demonstrates flexible, cost-effective, and versatile manufacturing strategies that bridge the gap between low-cost elemental feedstocks and high-performance functional materials. By integrating architectural complexity with precise microstructural control, this work establishes a robust pathway for the development of the next generation of bone-mimetic, superelastic implants, ultimately enhancing patient safety and long-term clinical reliability.
  

Reading date: 02/10/2026

• GARCÍA CARRASCO, VÍCTOR: El nexe aigua-energia de Catalunya davant la transició energètica: simulació horària, dessalinització oportunista i optimització multi-objectiu
  
  Author: GARCÍA CARRASCO, VÍCTOR
  Programme: DOCTORAL DEGREE IN STATISTICS AND OPERATIONS RESEARCH
  Department: Department of Statistics and Operations Research (EIO)
  Mode: Normal
  Deposit date: 02/09/2026
  Reading date: 02/10/2026
  Reading time: 11:00
  Reading place: FIB Sala d'actes Manuel Martí Recober B6-planta 0
  Thesis director: FONSECA CASAS, PAU
  Thesis abstract: Catalonia simultaneously faces two structural crises: the transition towards a decarbonised electricity system and the worsening of water stress under climate change. The 2021-2024 drought, which brought Ter-Llobregat system reservoirs to emergency levels, and the accelerated renewable deployment envisaged by the PROENCAT plan highlight the need for planning tools that integrate both subsystems. This thesis provides the tools to develop the first digital twin of Catalonia's coupled water-energy system at hourly resolution, formally specified using the SDL (Specification and Description Language) framework following the DT = DM + DS paradigm.The model integrates electricity generation (nuclear, wind, solar PV, hydropower, storage and combined cycles), water management (reservoirs, desalination, reclaimed water) and drought policies (progressive restriction phases) within a single simulation framework. It has been validated retrospectively against the 2024 electricity mix (errors < 2%), prospectively against PROENCAT projections for the 2030 and 2040 horizons, and under stress through 5 hydrological perturbation scenarios. The solution space, with until 14 decision variables, has been explored using Random Grid Search and NSGA-II, enabling a methodological comparison of both multi-objective optimisation approaches.Results demonstrate that the planned desalination capacity of 160 hm³/year is necessary but insufficient under severe climate change scenarios, and that 240 hm³/year effectively provides a robust safety margin. An opportunistic desalination strategy is proposed and evaluated, linking plant operation to renewable surplus availability and achieving 49-75% of water production during surplus hours, with a 20-34% reduction in gas consumption. The model confirms the viability of PROENCAT targets for 2040 and identifies 14.8 TWh of renewable surpluses as a fundamental synergy between the energy transition and water security.This thesis contributes in three areas: the formal integration of the water-energy nexus at regional basin scale, the formulation of an opportunistic desalination strategy without precedent in the literature, and a comparative multi-objective optimisation methodology transferable to other Mediterranean basins.
  

• HURTÁN DÍAZ, ENRIQUE: Experimental Characterization of Microconfined High-Pressure Transcritical Fluid Turbulence
  
  Author: HURTÁN DÍAZ, ENRIQUE
  Programme: DOCTORAL DEGREE IN MECHANICAL, FLUIDS AND AEROSPACE ENGINEERING
  Department: Department of Mechanical Engineering (EM)
  Mode: Normal
  Deposit date: 04/09/2026
  Reading date: 02/10/2026
  Reading time: 09:00
  Reading place: Sala de conferències/polivalent de l'edifici I del Campus Diagonal-Besòs, EEBE.
  Thesis director: JOFRE CRUANYES, LLUÍS | CASALS TERRE, JASMINA
  Thesis abstract: Microfluidic systems have emerged as a key enabling technology for compact and highly integrated devices across biomedical and chemical applications. However, their performance remains fundamentally constrained in energy-related applications due to the predominance of laminar flow regimes at small scales, where transport processes are governed primarily by molecular diffusion. This thesis investigates the emergence of turbulent-like flow regimes in microconfined high-pressure transcritical fluids as a novel pathway to overcome these limitations. In particular, the work focuses on the role of strong thermophysical property gradients generated near the critical point and while crossing the pseudo-boiling line in destabilizing microscale flows, enhancing mass and heat transport.The research begins by establishing the experimental and methodological framework required to investigate transcritical microflows under extreme thermodynamic conditions. A dedicated high-pressure microfluidic facility is developed, integrating advanced thermal control and high-speed optical diagnostics based on two-dimensional time-resolved micro-particle image velocimetry (2D TR-μPIV). Particular attention is devoted to identifying the characteristic spatio-temporal scales governing these flows and to assessing the limitations of conventional techniques in resolving the smallest turbulent scales. The analysis reveals that thermophysical scales associated with density gradients become comparable to the smallest hydrodynamic scales of the flow, leading to strong thermodynamic–hydrodynamic coupling and fundamentally altering the interpretation of microscale transport.Building upon this framework, the thesis experimentally demonstrates the existence of instability-driven turbulent-like regimes in microchannels operating under transcritical conditions. The results show that sharp density gradients generate baroclinic torque and variable-density effects that help to trigger and amplify flow perturbations, developing highly unsteady multiscale flow structures even at Reynolds numbers significantly below the transition thresholds of classical incompressible flows. Flow visualizations reveal the presence of fluctuations represented by optical distortions and turbophoretic particle migration, providing direct experimental evidence of turbulent-like dynamics previously predicted by direct numerical simulations.The impact of these regimes on transport processes is subsequently investigated through the development of a microchannel heat exchanger platform. To support these experiments, a novel hybrid custom-fabricated platform based on Ostemer–copper bonding is developed, enabling high-pressure operation while preserving optical accessibility and thermal control. Heat transfer measurements demonstrate substantial enhancement of convective transport under transcritical conditions, directly linked to the emergence of multiscale flow structures and instability-driven mixing. These results establish a direct connection between the underlying flow physics and the observed macroscopic thermofluid performance.Taken together, the findings in this thesis demonstrate that turbulent-like transport in microfluidic systems can be achieved not by increasing inertial forces, but by exploiting the thermodynamic behavior of fluids near the critical point. This work establishes a new paradigm for microscale transport enhancement based on thermodynamic–hydrodynamic coupling, and opens new opportunities for the development of high-performance microfluidic technologies for thermal management, energy conversion, and process intensification applications.