Doctoral School

Reading date: 16/04/2024

• ELIZALDE HUITRÓN, SERGIO ALBERTO: Study on the forming limit on shear spinning process
  
  Author: ELIZALDE HUITRÓN, SERGIO ALBERTO
  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 MATERIALS SCIENCE AND ENGINEERING
  Department: (CEM)
  Mode: Normal
  Deposit date: 27/02/2024
  Reading date: 16/04/2024
  Reading time: 11:00
  Reading place: EEBE (Escola d'Enginyeria Barcelona Est), Sala Polivalent de l'Edifici A, planta baixa, Campus Diagonal-Besòs
  Thesis director: CABRERA MARRERO, JOSE MARIA
  Committee:
       PRESIDENT: GARCÍA CANO, IRENE
       SECRETARI: CALVO MUÑOZ, JESICA
       VOCAL: SORGENTE, DONATO
  Thesis abstract: Shear spinning is an incremental sheet metal forming process where a flat metal blank or pre-form is usually converted into an axisymmetric hollow part. Several ductile metals and alloys can be shear formed either at cold and hot conditions, and the most common include steel, aluminum, copper, and nickel alloys. The shape of the shear-formed parts may be conical, concave, convex, or a combination, with wide-ranging applications across industries like aerospace, automotive, and more.The main focus of this research was the study of the forming limit at room temperature in the shear spinning process through experimental trials and finite element simulations. Traditionally, a successful part produced by shear forming is highly dependent on the operator's experience, and usually, the right conditions are found after several trials.The forming limit of any metal forming process is essential data that helps to predict defects appearance in advance, guaranteeing product quality. Accordingly, processing maps to failure were derived for a mild steel DC04, stainless steel AISI 420, precipitation hardening aluminum alloys AA2024 and AA7075, in which the failure limits were found as a function of the thickness reduction, roller attack angle, spindle speed, and feed rate. The experimental findings revealed a convincing relationship between the maximum allowable thickness reduction and the feed rate ratio with the roller nose radius. As the feed rate increased, the maximum allowable thickness reduction exhibited an exponential decrease, described by a parametric equation. Also, it was found that the maximum allowable thickness reduction was 84% for the DC04 and 80% for the rest of the materials.Furthermore, numerical simulations based on the finite element method have been demonstrated as an efficient tool to accurately predict the mechanical response and appearance of defects in metal forming operations. The prediction capabilities of the numerical simulation are based on the evolution of field variables through the operation, i.e., displacements, strain, strain rate, stresses, and ductile damage. Different models of shear spinning were built with the ABAQUS commercial software. First, the efficiency of the different kinematic strategies and solving methods used to model the shear spinning were compared. An efficient segment model was proposed that reduces the computing time up to 300 times compared to conventional models.Further, different uncoupled ductile damage models were implemented via the user materials subroutine (VUMAT). It was found that the ductile damage models can accurately predict failure conditions using a non-linear damage evolution formulation.This research enhances the understanding of material deformation in the shear spinning process and provides a framework for improving operational efficiency in incremental forming processes.
  

Reading date: 17/04/2024

• LORENTE GARCÍA, ESTER: A Simulation-based intermodal assignment accounting for public transport and ride-pooling services
  
  Author: LORENTE GARCÍA, ESTER
  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 STATISTICS AND OPERATIONS RESEARCH
  Department: Department of Statistics and Operations Research (EIO)
  Mode: Normal
  Deposit date: 13/02/2024
  Reading date: 17/04/2024
  Reading time: 15:00
  Reading place: Sala de reunions C5202. Campus NORD, Dep. Estadística i Investigació Operativa. Ed. C5 2 planta
  Thesis director: CODINA SANCHO, ESTEVE | BARCELÓ BUGEDA, JAIME
  Committee:
       PRESIDENT: FAULIN FAJARDO, FRANCISCO
       SECRETARI: MONTERO MERCADÉ, LIDIA
       VOCAL NO PRESENCIAL: FRIEDRICH, BERNHARD
  Thesis abstract: Shared mobility, including Mobility as a Service (MaaS), has emerged as a potential solution for city congestion. However, recent studies have revealed unintended con-sequences such as increased travel times and reduced public transport usage. The International Association of Public Transport (UITP) emphasises the need for a complementary integration of shared mobility and public transportation to achieve positive outcomes. This thesis focuses on the intermodal integration of a ride-pooling service (RP) as a feeder to public transport (PT) stops, enabling combined trips with multiple legs. Unlike previous studies, it explores all the intermodal types, considers a wide range of intermodal combinations beyond the constraints of the closest vehicle and stop, and analyses the performance in a large metropolitan area with an extensive transit network. In this thesis, a dispatching strategy is developed that significantly improves the performance of a ride-pooling system in intermodal combination with public trans-port. It is implemented within the intermodal dispatcher, the key component of the system. The most important characteristics of the strategy are that it uses a batch dispatching approach for optimising requests-to-transport vehicles (RP and/or PT) assignment, and introduces delayed dispatching, which postpones request dispatching until their time window approaches. This strategy enables precise vehicle selection, avoiding premature choices when most vehicle tours are empty. In particular, this affects trips with a last leg (LL) of ride-pooling, which are divided into two parts and treated in two separate iterations. The first part excludes the ending RP leg and is dispatched initially using an estimate for the LL. The second part of the trip is momentarily left pending and is dispatched with a given anticipation to the time window of the LL. To guarantee the availability of vehicles in this second part, the system implements a vehicle reservation mechanism.In order to evaluate the performance of the proposed dispatching strategy, a simulation-based system has been developed that accurately models both the operation of the ride-pooling system in the field (the movement of vehicles and customer request reception) and the processing of requests and vehicle location updates by the dispatcher. Compared to actual field experiments, the simulation allows experiments in which all parameters of the dispatching strategy and of the demand are systematically varied. This simulator is the second significant result of the thesis. The simulation results indicate that implementing a delayed dispatching strategy plus vehicle reservation can lead to higher served demand and improved profitability out-comes compared to a non-delayed strategy, particularly in fleet-saturated scenarios. This strategy optimises the allocation of system resources, specifically the limited fleet of vehicles, as these are more properly selected. As a result, the system may efficiently identify and include alternatives with a high shared proportion of en-route passengers without imposing excessive restrictions on future requests.
  

Reading date: 18/04/2024

• MATSUMURA, KAZUAKI: Advancing the state of the art of directive-based programming for GPUs: runtime and compilation
  
  Author: MATSUMURA, KAZUAKI
  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 COMPUTER ARCHITECTURE
  Department: (DAC)
  Mode: Normal
  Deposit date: 20/03/2024
  Reading date: pending
  Reading time: pending
  Reading place: pending
  Thesis director: PEÑA MONFERRER, ANTONIO JOSE
  Committee:
       PRESIDENT: CASTELLÓ GIMENO, ADRIÁN
       SECRETARI: AYGUADÉ PARRA, EDUARD
       VOCAL: EL HAJJ, IZZAT
  Thesis abstract: The rapid development in computing technology has paved the way for directive-based programming models towards a principal role in maintaining software portability of performance-critical applications. Efforts on such models involve a least engineering cost for enabling computational acceleration on multiple architectures, while programmers are only required to add meta information upon sequential code. Optimizations for obtaining the best possible efficiency, however, are often challenging. The insertions of directives by the programmer can lead to side-effects that limit the available compiler optimization possible, which could result in performance degradation. This is exacerbated when targeting asynchronous execution or multi-GPU systems, as pragmas do not automatically adapt to such mechanisms, and require expensive and time consuming code adjustment by programmers. Moreover, directive-based programming models such as OpenACC and OpenMP often prevent programmers from making additional optimizations to take advantage of the advanced architectural features of GPUs because the actual generated computation is hidden from the application developer.This dissertation explores new possibilities for optimizing directive-based code from both runtime and compilation perspectives. First, we introduce a runtime framework for OpenACC to facilitate dynamic analysis and compilation. Especially, our framework realizes automatic asynchronous execution and multi-GPU use based on the status of kernel execution and data availability while taking advantage of an on-the-fly mechanism for compilation and program optimization. We add a versatile code-translation method for multi-device utilization by which manually-optimized applications can be distributed automatically while keeping original code structure and parallelism. Second, we implement a novel flexible optimization technique that operates by inserting a code emulator phase to the tail-end of the compilation pipeline. Our tool emulates the generated code using symbolic analysis by substituting dynamic information and thus allowing for further low-level code optimizations to be applied. We implement our tool to support both CUDA and OpenACC directives as the frontend of the compilation pipeline, thus enabling low-level GPUoptimizations for OpenACC that were not previously possible. Third, we propose the use of a modern optimization technique, equality saturation, to optimize sequential code utilized in directive-based programming for GPUs. Our approach realizes less computation, less memory access, and high memory throughput simultaneously. Our fully-automated framework constructs single-assignment forms from inputs to be entirely rewritten while keeping dependencies and extracts optimal cases. Overall, we cover runtime techniques and optimization methods based on dynamic information, low-level operations, and user-level opportunities.We evaluate our proposals on the state-of-the-art GPUs and provide detailed analysis for each technique. For multi-GPU use, we show in some cases nearly linear scaling on the part of kernel execution with the NVIDIA V100 GPUs. While adaptively using multi-GPUs, the resulting performance improvements amortize the latency of GPU-to-GPU communications. Regarding low-level optimization, we demonstrate the capabilities of our tool by automating warp-level shuffle instructions that are difficult to use by even advanced GPU programmers. While evaluating our tool with a benchmark suite and complex application code, we provide a detailed study to assess the benefits of shuffle instructions across four generations of GPU architectures. Lastly, with sequential code optimization, we demonstrate a significant performance improvement on several compilers through practical benchmarks.Then, we highlight the advantages of computational reordering and emphasize the significance of memory-access order for modern GPUs.
  

Reading date: 19/04/2024

• ARNAIZ MARTÍNEZ, DAVID MARIANO: Bringing Self-Awareness to the Extreme Edge - A Distributed Approach for Adaptive Energy Management in WSNs Applied to Structural Health Monitoring
  
  Author: ARNAIZ MARTÍNEZ, DAVID MARIANO
  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: Normal
  Deposit date: 21/03/2024
  Reading date: pending
  Reading time: pending
  Reading place: pending
  Thesis director: ALARCON COT, EDUARDO JOSE | MOLL ECHETO, FRANCESC DE BORJA | VILAJOSANA GUILLEN, XAVIER
  Committee:
       PRESIDENT: CHOWDHURY, KAUSHIK ROY
       SECRETARI: ABADAL CAVALLÉ, SERGI
       VOCAL: DINI, PAOLO
  Thesis abstract: In today's landscape, data are increasingly becoming an invaluable resource to enhance decision-making, enable predictive insights, improving operational efficiency, among numerous other applications. Within the current data-centric mindset, wireless sensors play a facilitator role, allowing the collection of data in a flexible, low-cost, and simple-to-deploy way.One of the ever-pending challenges of wireless sensor node technologies is their limited energy availability, particularly their limited battery life. To extend their battery life, sensor nodes need to use their energy as frugally as possible. The optimal behavior for a sensor node is highly dependent on the varying operation conditions. Thus, to operate optimally, sensor nodes need to incorporate adaptive mechanisms to dynamically adjust their behavior at runtime. These adaptive mechanisms are commonly referred to as Dynamic Energy Management (DEM).Despite the progress made in DEM, commercial sensor nodes continue to mostly operate using static behaviors, wasting energy. The main limitation impeding the widespread adoption of DEM is that it renders the node's behavior dependent on the operating conditions, thereby making the node's behavior unpredictable. In recent years, self-awareness has been proposed as a promising solution to this challenge. Self-aware systems autonomously adjust their behavior at runtime based on their internal and external operating conditions to achieve their operational goals as efficiently as possible. Consequently, while the behavior of a self-aware system may not be known at a given time, these systems provide some level of predictability by complying with their operational goals.This thesis delves into the use of self-awareness at the sensor node level to guide the node's adaptive behavior. The main objective of this thesis is to provide a solid foundation to support future progress in self-aware sensor nodes. In pursuit of this goal, it presents a reference architecture of a self-aware sensor node solving the existing lack of standardization in their design. Additionally, it proposes two self-aware monitoring methods enabling the node to comply with its battery lifetime target while optimizing its energy allocation to maximize its monitoring accuracy. Another key aspect that limits the adoption of self-awareness at the sensor node level is the node's lack of information and computing capabilities to model complex environments, as is usually the case in Structural Health Monitoring (SHM) applications. This thesis tackles this issue by proposing an anomaly-aware monitoring method tailored for SHM applications, which models the local vibration patterns measured by the node to determine the current monitoring requirements for the node. Finally, the thesis ends by exploring how the concept of self-awareness can be extended through the network, enabling the interaction between self-aware sensor nodes and a self-managing monitoring application running in the cloud.
  

• FAKHRAEI, JAVAD: Contributions to meshless methodologies for the simulation of acoustic radiation and scattering problems
  
  Author: FAKHRAEI, JAVAD
  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 Mechanical Engineering (EM)
  Mode: Normal
  Deposit date: 16/02/2024
  Reading date: 19/04/2024
  Reading time: 11:30
  Reading place: Sala de conferències del TR5 de l'ESEIAAT (Terrassa)
  Thesis director: ARCOS VILLAMARÍN, ROBERT | PÀMIES GÓMEZ, TERESA
  Committee:
       PRESIDENT: CORTESÃO GODINHO, LUIS MANUEL
       SECRETARI: CLOT RAZQUIN, ARNAU
       VOCAL: DENIA GUZMÁN, FRANCISCO DAVID
  Thesis abstract: Meshless methodologies have emerged as a valuable tool in the field of computational acoustics, offering an efficientapproach to model complex acoustic phenomena. These innovative numerical techniques offer a promising alternative totraditional mesh-based methods to deal with scattering and radiation acoustic wave propagation problems. Unlikeconventional mesh-based approaches, meshless methods do not rely on structured grids of the domain or its boundary,enabling more flexible and adaptive discretisation. The absence of a mesh eliminates the need for time-consuming gridgeneration and refinement, simplifying the simulation process and reducing the computational effort. This efficiency isespecially valuable in addressing large-scale acoustic simulations, such as those encountered in environmental noiseassessments and underwater acoustics.This dissertation is particularly centred on the study and development of a novel group of numerical meshless methodsrelated to boundary collocation approaches. These methods are employed to address problems involving the propagation ofacoustic waves in unbounded domains. The novel approaches presented in this research offer several benefits with respectto existing methodologies, in terms of robustness, accuracy and computational efficiency. Furthermore, in contrast to a fullythree-dimensional analysis, the approaches presented in this dissertation are formulated in the two-and-a-half-dimensionaldomain. This domain is particularly suited for scenarios where the system is subjected to longitudinally moving loads orsources and where the geometry of the system remains longitudinally invariant.The meshless methodologies developed in this thesis mainly rely on two of the most well-established meshless methods inthe field: the singular boundary method and the method of fundamental solutions. In the first instance, an approach based ona two-and-a-half-dimensional version of the singular boundary method is proposed and studied to address acousticradiation and scattering problems. Subsequently, its applicability for real case acoustic scenarios is evaluated throughsimulations involving point source diffraction in the presence of thin noise barriers. As probably representing the mostsignificant novelty of this dissertation, a hybrid method that combines the singular boundary method and the method offundamental solutions is introduced. It is specifically devised to tackle acoustic wave propagation problems featuringcomplex boundary geometries with corners and sharp edges. Finally, two modification techniques are proposed to enhancethe previously mentioned approach based on the two-and-a-half-dimensional sin- gular boundary method. The Burton¿Millerformulation in a first instance, and a dual surface scheme in the second. These modifications aim to overcome the issue ofspurious eigensolutions, which arises from the non-uniqueness solution problem associated with boundary collocationmethods. To comprehensively assess the capabilities and performance of the proposed meshless methods, the availableanalytical solutions and alternative numerical strategies such as the well-known boundary element method are also utilisedin various designed benchmark problems.