Doctoral School

Reading date: 24/04/2024

• FERNÁNDEZ BOSMAN, DAVID: PyMCGPU-IR: a new tool for patient dose monitoring in interventional radiology procedures
  
  Author: FERNÁNDEZ BOSMAN, DAVID
  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 BIOMEDICAL ENGINEERING
  Department: Institute of Energy Technologies (INTE)
  Mode: Normal
  Deposit date: 27/02/2024
  Reading date: 24/04/2024
  Reading time: 11:30
  Reading place: Aula Capella, Escola Tècnica Superior d'Enginyeria Industrial de Barcelona (ETSEIB), Av. Diagonal, 647. 08028 Barcelona
  Thesis director: GINJAUME EGIDO, MERCE | DUCH GUILLEN, MARIA AMOR
  Committee:
       PRESIDENT: SANS MERCE, MARTA
       SECRETARI: SEMPAU ROMA, JOSEP
       VOCAL: SÁNCHEZ CASANUEVA, ROBERTO MARIANO
  Thesis abstract: Interventional radiology procedures are associated with potentially high radiation doses to the skin. The 2013/59/EURATOM Directive establishes that the equipment used for interventional radiology must have a device or a feature informing the practitioner of relevant parameters for assessing patient dose at the end of the procedure. Monte Carlo codes of radiation transport are considered to be one of the most reliable tools available to assess doses. However, they are usually too time consuming for use in clinical practice. This thesis has been developed at the Institute of Energy Technologies of the Universitat Politècnica de Catalunya within the framework of the European project "Implications of Medical Low Dose Radiation Exposure" (MEDIRAD). The main objective of this work is to develop a software tool based on the Monte Carlo program MC-GPU for assessing the skin dose in patients undergoing interventional radiology (IR) procedures. The achievement of this objective can be divided into two main blocks: the validation of MC-GPU and the development and validation of PyMCGPUIR, a skin dose calculation tool for IR procedures based on MC-GPU. For the validation of MC-GPU, simulations were conducted and compared with the well-validated code PENELOPE/penEasy and then compared against thermoluminescent measurements performed on slab phantoms, both in a calibration laboratory and at a hospital. MC-GPU demonstrated excellent agreement in organ dose distribution, with differences below 1%, despite reducing the calculation time by a factor of 2500. Comparisons with thermoluminescent measurements indicated agreements within 10%, validating MC-GPU¿s ability to provide accurate dose estimates in real clinical setups in very short times. In this work we have also developed PyMCGPU-IR, a new software tool based on the Monte Carlo program MC-GPU for assessing skin dose and organ doses in patients undergoing an interventional radiology (IR) procedure. PyMCGPU-IR has been validated through skin and organ dose measurements in an anthropomorphicphantom and showed differences below 6% in skin dose measurements and mostly below 20% in organ doses in clinical procedures. PyMCGPU-IR offers both, high performance and accuracy for dose assessment when compared with skin and organ dose measurements. It also allows the calculation of dose values at specific positions and organs, the dose distribution and the location of the maximum dose per organ. In addition, PyMCGPU-IR overcomes the time limitations of CPU-based MC codes.In this thesis we have shown that PyMCGPU-IR is an innovative Skin Dose Calculation (SDC) tool that offers higher performance and accuracy for skin dose calculations compared to most available SDCs. Currently, PyMCGPU-IR provides dose values only after the procedure has finished. In the future, PyMCGPU-IR could be adapted to provide real-time dose calculation if real-time radiation source information is available.
  

• RAKHSH MAHPOUR, ALI: Suitability of new lime nonwoven layered flax fiber composite as a reinforcement masonry historical structures system: Microstructural, mechanical, durability and sustainability assessment
  
  Author: RAKHSH MAHPOUR, ALI
  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 ARCHITECTURAL, BUILDING CONSTRUCTION AND URBANISM TECHNOLOGY
  Department: Department of Architectural Technology (TA)
  Mode: Article-based thesis
  Deposit date: 27/03/2024
  Reading date: pending
  Reading time: pending
  Reading place: pending
  Thesis director: CLARAMUNT BLANES, JOSE | ROSELL AMIGÓ, JUAN RAMON
  Committee:
       PRESIDENT: DE ANDRADE SILVA, FLAVIO
       SECRETARI: CORNADÓ BARDÓN, CÒSSIMA
       VOCAL: SANZ ARAUZ, DAVID
  Thesis abstract: This thesis investigates the feasibility and potential applications of flax fiber-reinforced lime mortars in masonry construction, particularly focusing on the seismic retrofitting of Unreinforced Masonry (URM) buildings. The composite material, featuring a non-woven structure of flax fiber layers within the lime mortar matrix, undergoes a comprehensive examination with a specific emphasis on mechanical properties, durability, and consistency. Structured as a collection of articles, the thesis covers various dimensions to provide a holistic understanding of the material's capabilities and applications. The first article delves into the mechanical characterization of Flax Fiber Reinforced Lime Mortars. This involves a rigorous assessment of properties such as tensile strength, compressive strength, flexural strength, and toughness. These mechanical attributes are crucial for determining the material's structural integrity and its potential effectiveness in retrofitting applications.In addition to mechanical properties, the thesis explores the durability of flax fiber-reinforced lime mortars. Durability tests are designed to simulate long-term exposure to environmental conditions, including moisture, temperature changes, and other potential stressors. Evaluating the material's resistance to these factors is essential for ensuring its performance and longevity in real-world applications. An integral part of the research involves investigating the optimal configuration of flax fiber layers within the lime mortar. This aspect aims to optimize the composite's flexibility, crack resistance, and chemical compatibility with historic masonry materials. The layered composition is a critical consideration for achieving the desired structural enhancements while maintaining the material's compatibility with historical structures. Furthermore, the thesis contributes to the understanding of the adhesion between flax fiber-reinforced lime mortars and masonry materials. The adhesion characteristics play a pivotal role in determining the effectiveness of the material as a retrofitting solution for URM buildings. The study aims to provide valuable insights into the mechanical properties, durability, and adhesion to ensure a comprehensive understanding of the material's suitability for historical masonry structures.In conclusion, this research, encapsulated in a series of articles, offers a thorough exploration of flax fiber-reinforced lime mortars for masonry construction. The emphasis on mechanical properties, durability, and adhesion positions the material as a potential innovative solution for retrofitting URM buildings. This not only aligns with sustainability goals but also ensures the preservation of cultural heritage. Looking forward, the thesis provides a foundation for further research, suggesting avenues such as numerical modeling and additive manufacturing for a more nuanced understanding and practical application of the developed materials in the construction industry.
  

Reading date: 26/04/2024

• COLL VALENTÍ, ARNAU: Advanced c-Si solar cell structures: application of laser processes and optical nanostructures
  
  Author: COLL VALENTÍ, ARNAU
  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: 08/03/2024
  Reading date: 26/04/2024
  Reading time: 11:00
  Reading place: Defensa: Aula de Postgrau, edifici C5-116, ETSETB
  Thesis director: BERMEJO BROTO, ALEXANDRA | MARTIN GARCIA, ISIDRO
  Committee:
       PRESIDENT: VOZ SANCHEZ, CRISTOBAL
       SECRETARI: GARIN ESCRIVA, MOISES
       VOCAL: HERNÁNDEZ GARCÍA, DAVID
  Thesis abstract: This thesis works towards efficient and cost-effective methods to improve the performance of thin silicon solar cells. Focusing on two principal objectives, the Thesis develops novel techniques to enhance the production of colloidal crystals and the possibility to apply these crystals to improve the light trapping efficiency, as well as creating a unique structure for lased doped solar cells. Both advancements focus on improving the production solar cells using low-temperature processes and thin wafers, thus circumventing the dependences of high temperature procedures, while bolstering light trapping capabilities. This approach is motivated by the restarting trend to reduce silicon wafer thickness, therefore this work is pushed by the need to overcome the actual technical and physical constrains. The initial part of the Thesis focuses on the implementation of an electrospray system for the creation of colloidal crystals. These colloidal crystals are intended for application as photonic light trapping structures in solar cells. Afterwards, these structures are tested within a laser firing process to double check the viability to be used within the laser firing technique commonly used in solar cell fabrication.The main achievements within the electrospray deposition technique are the development of polystyrene and SiO2 colloidal crystals with areas in the range of 1-2cm2 and up to 17 layers of ordered particles while keep good optical quality. These layers are created at room temperature and with a process that could be adapted to batch processing and parallelized to increase the area. The technique has also been adapted to be used in non-even surfaces like C-Si pyramids or black silicon. At the same time, these structures had been used to create inverse colloidal crystals from Al2O3 and Al2O3 /TiO2 shells while getting rid of polystyrene nanoparticles. The final Al2O3 /TiO2 structure obtains high reflectivity values up to 98.2%. Finally, these inverse opals are created on top of Al2O3 passivated C-Si wafers. These structures are able to withstand a laser firing process while keeping the passivation, demonstrating the capability to be used with in the solar cells fabrication process.The second part of the thesis focuses in the creation of a process to achieve low temperature solar cells by means of highly-doped regions that are punctually defined through laser processed dielectric films. This technique call ¿DopLaCell¿ stand for doped by laser solar cell. In the initial stages of the process and as a proof of concept, 1x1 cm2 solar cells were created on both p- and n-type substrates with efficiencies of 11.6% and 12.8% respectively. In a second step, 1x1 cm2 n-type c-Si solar cells are created using the ¿cold¿ p+ emitters used in the ¿DopLaCell¿ structure. This second batch of solar cells uses a Heterojunction with Intrinsic Thin layer (HIT) in the front face. This approach avoids the use of Transparent Conductive Oxide (TCO) on the back side of the cell thus improving the reflectivity especially with IR photons. These cells reach efficiencies up to 18.1%. Finally the process is being improved towards a pure texturized ¿DopLaCell¿. In this final step, totally ¿cold¿ 2x2 cm2 solar cells are fabricated with and efficiency up to 17.0 % .This work represents a one big step forward towards a future path of thin silicon solar cells fabrication, addressing the actual technology limitations and enabling the possibility to overcome the principal issues. This research lays the ground towards thin, affordable and efficient solar cells improving the path towards a more viable and eco-friendly energy future
  

Reading date: 30/04/2024

• MARTÍ SAUMELL, JOSEP: Agile aerial manipulation: an approach based on full-body dynamics and model predictive control
  
  Author: MARTÍ SAUMELL, JOSEP
  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 AUTOMATIC CONTROL, ROBOTICS AND VISION
  Department: Institute of Robotics and Industrial Informatics (IRI)
  Mode: Normal
  Deposit date: 26/03/2024
  Reading date: 30/04/2024
  Reading time: 11:00
  Reading place: Sala de Juntes de la Facultat Matemàtiques i Estadística (FME) de la UPC, C/Pau Gargallo, 14, 08028 Barcelona
  Thesis director: SANTAMARIA NAVARRO, ANGEL | SOLÀ ORTEGA, JOAN
  Committee:
       PRESIDENT: MANSARD, NICOLAS
       SECRETARI: MORCEGO SEIX, BERNARDO
       VOCAL: LIPPIELLO, VINCENZO
  Thesis abstract: Aerial manipulators, which commonly take the form of multirotors with attached robotic limbs, primarily employ their limbs for pure manipulation tasks and do not rely on them during aerial locomotion. Besides, their movement tends to be slow. This thesis aims to enhance an aerial manipulator¿s agility by harnessing its limb¿s capabilities to augment its overall motion. This objective involves investigating various modes of utilizing the limb: as a tail for aerial locomotion, as an arm for aerial manipulation, or as a leg for hybrid aerial-contact locomotion. The present thesis contributes to two specific domains: 1. Generation and control of agile motions for aerial manipulators, 2. Design and construction of a specialized aerial manipulator for executing agile motions.Generating agile motions requires predicting the movement of the robot considering its dynamics so that these dynamics can be used to favor the robot¿s motion. Hence, we can achieve complex maneuvers with relative ease. Optimal control is a trajectory-generation technique that meets these requirements, and that is central to this thesis. We encode the robot¿s tasks as cost functions of the optimal control problem (OCP) and use the whole-body dynamics as the constraints of the dynamic system. On the control side, to deploy such trajectories in a real robot, we use model predictive control (MPC) techniques, which is the closed-loop control extension of optimal control. To get the control command, an MPC controller solves the OCP in which we have encoded the agile trajectory, and then the controller applies the first command of the solution control trajectory. Thus, MPC requires solving an OCP at the control rate, i.e., within a few milliseconds. This forces us to use fast, specialized solvers based on the dynamic programming principle, such as differential dynamic programming (DDP). In their original form, these solvers cannot consider the control bounds. These bounds are important to create trajectories compatible with the real robot. To tackle this problem, in this thesis, we propose two DDP-based methods to consider the control bounds: one is based on a squashing function, and the other is based on a projection method. Even with these solvers, we face challenges in meeting the solving rate and are forced to reduce the MPC horizon. Reducing the MPC horizon implies that the MPC can only see a portion of the original OCP, possibly leaving out some of the tasks. This affects the predictive capability of the controller and compromises the accomplishment of the tasks, especially those that require an elaborate and dynamic maneuver. To overcome this difficulty, in this thesis, we propose to update, at each MPC iteration, the terminal cost function in the MPC with a function that encodes the part of the trajectory that remains unseen by the controller.Regarding robot design, deploying agile motions becomes difficult with existing aerial manipulators, which are generally big-size multirotor platforms with non-compliant, high-gear ratio limbs. In this thesis, we present Borinot, an open-source aerial robotic platform designed to research hybrid agile locomotion and manipulation using flight and contacts. This platform features an agile and powerful hexarotor that can be outfitted with torque-actuated limbs of diverse architecture, allowing for whole-body dynamic control. We present experiments with this robot showcasing different agile motions.In addition to the stated contributions, this thesis contributes in other areas required to operate the robot, such as a procedure for identifying the dynamical parameters based on factor-graph estimation or a hardware enhancement that allows for direct thrust control of Borinot¿s rotors.
  

Reading date: 02/05/2024

• GASPARINO FERREIRA DA SILVA, LUCAS: High-performance low-dissipation algorithms for simulation of turbulent compressible flows
  
  Author: GASPARINO FERREIRA DA SILVA, LUCAS
  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: 03/04/2024
  Reading date: pending
  Reading time: pending
  Reading place: pending
  Thesis director: LEHMKUHL BARBA, ORIOL | MIRA MARTÍNEZ, DANIEL
  Committee:
       PRESIDENT: RUBIO CALZADO, GONZALO
       SECRETARI: JOFRE CRUANYES, LLUÍS
       VOCAL: COLOMBO, ALESSANDRO
  Thesis abstract: Motivated by recent advances in computational technology aiming at exascale capabilities, which implies a need for applicationscapable of taking advantage of these new supercomputing architectures, this work will present two algorithms aimed at implementing an efficient and low-dissipation algorithm focused on LESand DNS of turbulent compressible flows.The basis for the algorithms is the Continuous Galerkin method applied to elements whose nodes and quadrature points areformed from the Gauss-Lobatto-Legendre roots, resulting in a SpectralElements Method. Throughout this work, it will be evidenced that this formulation leads to highly efficient kernels for discretizingthe convective and diffusive terms of the compressible Navier-Stokes equations, with the added benefit that the order of the scheme is coupled with the order of the shape functionpolynomials employed by the elements themselves, significantly simplifying the process of increasing the order of the scheme.To achieve a stable Total Variational Diminishing algorithm, the \acrshort{sem} scheme will be paired with an EntropyViscosity-based stabilization model and a suitable splitting of the nonlinear convective terms will be employed to eliminate aliasing issues that occur in the \acrshort{sem} formulation.This spatial discretization is then coupled with both an explicit and a semi-implicit scheme to account for the temporal nature ofthe flow equations. The explicit version of the algorithm is expected to be simple and efficient per time step, but due to its \acrshort{cfl} condition limitation, the semi-implicit version is alsoproposed to allow for better overall performance incases where the time-step becomes overly limited, such as in wall-bounded flows.Considering the focus on producing a \acrshort{cfd} application towards the exascale future, an important aspect of this work isthat both algorithms are proposed with a full \acrshort{gpu}implementation in mind: the use of accelerators is expected to be a key aspect of future supercomputing architectures, and thus itis important to design these algorithms with this in mind.Examples detailing the performance of both algorithms will be presented both in the case of a single device and when distributedarchitectures using multiple devices are employed.