Doctoral School

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.
  

• LIPA CUSI, LEONEL: Metodología numérica automatizada para la evaluación de la respuesta dinámica de construcciones prehispánicas de piedra de junta seca en el Perú.
  
  Author: LIPA CUSI, LEONEL
  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 CONSTRUCTION ENGINEERING
  Department: (DECA)
  Mode: Change of supervisor
  Deposit date: 03/04/2024
  Reading date: pending
  Reading time: pending
  Reading place: pending
  Thesis director: PELA, LUCA | TARQUE, SABINO NICOLA
  Committee:
       PRESIDENT: GOICOLEA RUIGÓMEZ, JOSÉ MARÍA
       SECRETARI: ROCA FABREGAT, PEDRO
       VOCAL NO PRESENCIAL: SALOUSTROS, SAVVAS
       VOCAL NO PRESENCIAL: SANTA CRUZ HIDALGO, SANDRA CECILIA
       VOCAL NO PRESENCIAL: SANDOVAL MANDUJANO, CRISTIAN
  Thesis abstract: The study and the conservation of stone heritage is a global concern, mainly when these constructions are in seismic zones. Due to its great cultural and historical diversity, Peru has many stone constructions in different archaeological sites, covering different construction typologies. Unfortunately, many of these constructions have not yet been structurally evaluated, so their structural behaviour is unknown. In addition, there is no classification of the stone structural typologies (taxonomy), so the different characteristics of existing constructions are unknown. One way to study the non-linear dynamic behaviour of these stone structures is to use a rigorous -but fast- numerical methodology to adequately reproduce the different failure mechanisms based on the dynamics of rigid bodies within the finite element method.Then, this work presents a taxonomic classification of prehispanic stone constructions in Peru, derived from a field study, as the first contribution. Based on this taxonomy, several archaeological sites in Puno and Cusco were classified, and the most common typologies of these regions were identified. The research also proposes novel algorithms developed in Python to obtain the geometric model of dry-joint stone structures using images taken by a camera, a mobile phone, or an existing photograph (including identification of stones and joints, named image segmentation). These routines allow the creation of a 3D model of each block (stone), assembling them, and exporting them to a finite element program for further evaluation.Regarding developing a numerical methodology, the dynamic of rigid bodies within the finite element method is proposed here. Each stone block is considered a rigid body interconnected with other blocks through nonlinear interfaces. This methodology was validated using Abaqus, based on the results of experimental tests developed in this thesis. The experimental campaign was carried out on three walls built with concrete blocks, simulating the geometry of the Inca structures. The walls were built on a tilting table and tested by rotating them out of the plane of the wall. Then, numerical models of the tests were developed by considering each stone as a rigid body and calibrating the contact properties to simulate the experimental behaviour correctly. The numerical results in weight, collapse angle, relative displacements at different points of the structure and collapse mechanisms were very similar to those obtained in the experimental campaign.As a case study, a section of an Inca stone wall from Sacsayhuaman, Cusco, was numerically evaluated using various seismic records. The complete geometric model of the stone wall was automatically obtained using the Python routines. Furthermore, discrete element particles represented the soil behind the wall. The properties of the numerical model were obtained from the experimental campaign, and the predominant frequencies of the structure were obtained using the vibration approach. As a result, the structure can adequately support these seismic records scaled up to a peak acceleration of 0.1 g. However, it suffers significant residual displacements for scaled records greater than 0.2 g.The proposed numerical methodology allows the rigorous evaluation of dry-jointed stone structures, knowing if the structure should be intervened to ensure its functionality. Therefore, it is expected that the results of this research will be used to study other stone constructions, opening possibilities for improving the methodology for different structural configurations.
  

• MAJORAL RAMONEDA, MARC: A Flexible System-on-Chip FPGA Architecture for Prototyping Experimental GNSS Receivers
  
  Author: MAJORAL RAMONEDA, MARC
  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 SIGNAL THEORY AND COMMUNICATIONS
  Department: Department of Signal Theory and Communications (TSC)
  Mode: Normal
  Deposit date: 03/04/2024
  Reading date: pending
  Reading time: pending
  Reading place: pending
  Thesis director: FERNANDEZ PRADES, CARLOS | ARRIBAS LÁZARO, JAVIER
  Committee:
       PRESIDENT: CAPARRA, GIANLUCA
       SECRETARI: BARTZOUDIS, NIKOLAOS
       VOCAL: FONT BACH, JOSEP ORIOL
  Thesis abstract: The rapid evolution in satellite navigation technology (GNSS) requires advanced prototyping tools for exploring new signals and developing innovative systems. Prototyping is essential in the design and development process, as it allows researchers to test and refine their ideas before implementing them on a large scale.Prototyping using commercial GNSS receivers poses several challenges. Currently, these receivers are primarily based on application-specific integrated circuits (ASICs), which are characterized by low power consumption, compact dimensions, and low cost, but offer limited flexibility. Although some commercial devices incorporate software-defined radio (SDR) techniques, they often contain proprietary code that restricts reconfiguration through an application programming interface (API) established by the manufacturer.GNSS receivers based on free and open-source software have become very valuable resources in the field of research and development, especially in satellite navigation. These receivers are highly valued for their adaptability and flexibility, allowing researchers to tailor the software to specific experimental needs or develop new signal processing algorithms. However, software-defined receivers tend to be less energy-efficient compared to hardware-based receivers, as they operate on general-purpose processors, which are not optimized for low power consumption.This thesis focuses on the design and development of a low-cost architecture for prototyping experimental GNSS receivers, based on System-on-Chip Field Programmable Gate Arrays (SoC FPGAs). This architecture overcomes the limitations of commercial GNSS receivers in terms of adaptability, flexibility, and reprogramming capacity, and offers improved energy efficiency compared to software-based receivers that rely on general-purpose processors. The strategy consists of combining the versatility of software-defined radio with the intensive parallelism and optimized energy consumption of programmable logic devices, providing the best of both worlds. This fusion allows the development of compact, portable GNSS receivers, thus facilitating the prototyping of embedded devices suitable for field testing. In addition, the GNSS processing core is based on a free and open-source software implementation, which provides detailed access to the signal processing chain and allows unrestricted exploration and modification of the algorithms used.This thesis also presents a design methodology for the development of new prototypes and new GNSS signal processing algorithms based on the proposed SoC FPGA architecture. This methodology places special emphasis on code reuse, a key aspect for reducing development costs and time.The practical applications of this architecture have been demonstrated through three prototypes: a GNSS receiver for low Earth orbit (LEO), a GNSS signal repeater, and a high-sensitivity GNSS receiver.The innovative approach presented in this thesis facilitates the development of experimental prototypes of flexible and portable GNSS receivers and signal generators, suitable for both laboratory experiments and field testing.