ECATI - Atas de Conferências Internacionais
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Item Model-based fault diagnosis and tolerant control: the ESA’s e.Deorbit mission(European Control Conference (ECC19), 2019) Henry, David; Cieslak, Jérôme; Zenteno, J.; Colmenarejo, Pablo; Branco, João; Santos, Nuno; Serra, Pedro; Telaar, Jüergen; Strauch, Hans; Giordano, Alessandro; Ott, Christian; Reiner, Matthias; Jaworski, Jaroslaw; Papadopoulos, Evangelos; Visentin, Gianfranco; Ankersen, Finn; Gil-Fernandez, Jesus; Escola de Comunicação, Arquitetura, Artes e Tecnologias da InformaçãoThe ESA (European Space Agency) is currently pursuing the development of the e.Deorbit mission that will remove a large defunct satellite from Earth orbit: ENVISAT. To fulfil the mission autonomy requirements, ESA has decided to embed in the GNC (Guidance, Navigation, Control) software, fault tolerance capacities against actuator faults. The aim of this paper is to present the development and validation of a model-based fault diagnosis and tolerant control solution for such faults. The proposed solution is based on a new class of nonlinear unknown input observers, optimal in the L2-gain sense, and a modified version of the nonlinear inverse pseudo control allocation technique. An intensive simulation campaign conducted within a high-fidelity nonlinear industrial simulator, demonstrates the efficiency of the approach.Item Methods and outcomes of the COMRADE project - Design of robust Combined control for robotic spacecraft and manipulator in servicing missions: comparison between between Hinf and nonlinear Lyapunov-based approaches(69th International Astronautical Congress (IAC), 2018-10-01) Colmenarejo, Pablo; Branco, João; Santos, Nuno; Serra, Pedro; Telaar, Juergen; Strauch, Hans; Fruhnert, Michael; Giordano, Alessandro; Stefano, Marco; Ott, Christian; Reiner, Matthias; Henry, David; Jaworski, Jaroslaw; Papadopoulos, Evangelos; Visentin, Gianfranco; Ankersen, Finn; Gil-Fernandez, Jesus; Escola de Comunicação, Arquitetura, Artes e Tecnologias da InformaçãoExtending life or repairing damaged on-orbit assets is not only a very attractive economic option for satellite operators as it could potentially increase margins for commercial services or increasing delivered value of scientific missions, but it would also help reducing the number of debris objects in space. These types of servicing missions pose technical challenges never faced until now. Of utmost relevance is the autonomous control of several movable devices, whose dynamics are inter-coupled (e.g., spacecraft platform, robotic manipulator, and end-effector), needed to safely and effectively achieve the mission objective. In the frame of ESA-supported COMRADE study, fully combined control (single control system controlling simultaneously all movable devices) is proposed due to its higher improvement potential (propellant saving, performances increase, safety) w.r.t. tele-operation, decoupled and/or collaborative control (the last one characterized by the use of two different control systems for the spacecraft platform and robotic manipulator respectively but, differently to the decoupled version, with information/feedback about what the other control system intends to do). Two independent combined control designs are developed in COMRADE (H∞ and nonlinear Lyapunov-based), and tested. Each of them is applied for both Active Debris Removal (ADR) and servicing/re-fuelling mission scenarios. This paper presents: the processes of scenario analysis and derivation of COMRADE system requirements; a description of the design and setup for a Simulator, which included at its core the selection, prototyping and integration of algorithms for Guidance, Navigation and Control (GNC), Modes Management (AMM) and Failures Detection, Isolation and Recovery (FDIR) (all three together compose the COMRADE system) and the outcomes of the simulation phase of the Verification & Validation process.Item Assessment of a Supervisory Fault-Hiding Scheme in a Classical Guidance, Navigation and Control Setup: the e.Deorbit mission(4th International Conference on Control and Fault-Tolerant Systems (SYSTOL), 2019-09-18) Cieslak, Jérôme; Henry, David; Colmenarejo, Pablo; Branco, João; Santos, Nuno; Serra, Pedro; Telaar, Jüergen; Strauch, Hans; Giordano, Alessandro; Stefano, Marco; Ott, Christian; Reiner, Matthias; Jaworski, Jaroslaw; Papadopoulos, Evangelos; Visentin, Gianfranco; Ankersen, Finn; Gil-Fernandez, Jesus; Escola de Comunicação, Arquitetura, Artes e Tecnologias da InformaçãoThe design of a model-based Fault Tolerant Control (FTC) strategy based on Virtual Actuators (VA) in a built-in Guidance, Navigation and Control (GNC) setup is addressed for the e.Deorbit space mission. This mission, initiated by the European Space Agency (ESA), aims at removing a large defunct satellite from Earth orbit: ENVISAT. The goal of this paper is to promote academic solutions to add fault tolerance capacities against thruster faults without any change or new tuning of the already in-place GNC solution. The validation of the proposed FTC solution is assessed by a simulation campaign based on a high-fidelity nonlinear industrial simulator.Item Particle swarm and population structure(ACM, 2018) Fernandes, Carlos M.; Rosa, Agostinho C.; Fachada, Nuno; Laredo, Juan L. J.; Merelo, J. J.; Escola de Comunicação, Arquitetura, Artes e Tecnologias da InformaçãoWe investigate the convergence speed, accuracy, robustness and scalability of PSOs structured by regular and random graphs with 3 ≤ k ≤ n. The main conclusion is that regular and random graphs with the same averaged connectivity k may result in significantly different performance, namely when k is low.Item Fun Maths for All Game Development Students(ACM, 2020-06) Andrade, Diogo de; Fachada, Nuno; Escola de Comunicação, Arquitetura, Artes e Tecnologias da InformaçãoWe present an approach for teaching maths to game development undergraduates from a wide variety of backgrounds. We discuss the concepts behind an introductory maths course, its assessment and put forward some preliminary results on a practical implementation.Item A method for detecting statistically significant differences in EEG data(OHBM, 2017) Fachada, Nuno; Cruz, Janir R. da; Herzog, Michael H.; Figueiredo, Patrícia; Rosa, Agostinho C.; Escola de Comunicação, Arquitetura, Artes e Tecnologias da InformaçãoThe highly multivariate nature of EEG data often limits the search for statistically significant differences in data collected from two or more groups of subjects. We have recently developed a new technique for assessing whether two or more multidimensional samples are drawn from the same distribution. Here, we apply this to EEG data collected from schizophrenia patients and healthy controls while performing a Visual Backward Masking (VBM) task.Item Assessing the feasibility of OpenCL CPU implementations for agent-based simulations(AGENT-BASED MODELING, 2017-05) Fachada, Nuno; Rosa, Agostinho C.; Escola de Comunicação, Arquitetura, Artes e Tecnologias da InformaçãoAgent-based modeling (ABM) is a bottom-up modeling approach, where each entity of the system being modeled is uniquely represented as a self-determining agent. Large scale emergent behavior in ABMs is population sensitive. As such, it is advisable that the number of agents in a simulation is able to reflect the reality of the system being modeled. This means that in domains such as social modeling, ecology, and biology, systems can contain millions or billions of individuals. Such large scale simulations are only feasible in non-distributed scenarios when the computational power of commodity processors, such as GPUs and multi-core CPUs, is fully exploited. In this paper we evaluate the feasibility of using CPU-oriented OpenCL for high-performance simulations of agent-based models. We compare a CPU-oriented OpenCL implementation of a reference ABM against a parallel Java version of the same model. We show that there are considerable gains in using CPU-based OpenCL for developing and implementing ABMs, with speedups up to 10x over the parallel Java version on a 10-core hyper-threaded CPU.Item Model-independent comparison of simulation output(Elsevier, 2017) Fachada, Nuno; Lopes, Vitor V.; Martins, Rui C.; Rosa, Agostinho C.; Escola de Comunicação, Arquitetura, Artes e Tecnologias da InformaçãoComputational models of complex systems are usually elaborate and sensitive to implementation details, characteristics which often affect their verification and validation. Model replication is a possible solution to this issue. It avoids biases associated with the language or toolkit used to develop the original model, not only promoting its verification and validation, but also fostering the credibility of the underlying conceptual model. However, different model implementations must be compared to assess their equivalence. The problem is, given two or more implementations of a stochastic model, how to prove that they display similar behavior? In this paper, we present a model comparison technique, which uses principal component analysis to convert simulation output into a set of linearly uncorrelated statistical measures, analyzable in a consistent, model-independent fashion. It is appropriate for ascertaining distributional equivalence of a model replication with its original implementation. Besides model-independence, this technique has three other desirable properties: a) it automatically selects output features that best explain implementation differences; b) it does not depend on the distributional properties of simulation output; and, c) it simplifies the modelers’ work, as it can be used directly on simulation outputs. The proposed technique is shown to produce similar results to the manual or empirical selection of output features when applied to a well-studied reference model.Item micompm: A MATLAB/Octave toolbox for multivariate independent comparison of observations(JOSS, 2018) Fachada, Nuno; Rosa, Agostinho C.; Escola de Comunicação, Arquitetura, Artes e Tecnologias da Informaçãomicompm is a MATLAB / GNU Octave port of the original micompr R package for comparing multivariate samples associated with different groups. Its purpose is to determine if the compared samples are significantly different from a statistical point of view. This method uses principal component analysis to convert multivariate observations into a set of linearly uncorrelated statistical measures, which are then compared using statistical tests and score plots. This technique is independent of the distributional properties of samples and automatically selects features that best explain their differences, avoiding manual selection of specific points or summary statistics. The procedure is appropriate for comparing samples of time series, images, spectrometric measures or similar multivariate observations. It is aimed at researchers from all fields of science, although it requires some knowledge on design of experiments, statistical testing and multidimensional data analysis.Item Revisiting Population Structure and Particle Swarm Performance(SciTePress, Science and Technology Publications, 2018) Fernandes, Carlos M.; Fachada, Nuno; Laredo, Juan L. J.; Merelo, J. J.; Castillo, P. A.; Rosa, Agostinho C.; Escola de Comunicação, Arquitetura, Artes e Tecnologias da InformaçãoPopulation structure strongly affects the dynamic behavior and performance of the particle swarm optimization (PSO) algorithm. Most of PSOs use one of two simple sociometric principles for defining the structure. One connects all the members of the swarm to one another. This strategy is often called gbest and results in a connectivity degree k = n, where n is the population size. The other connects the population in a ring with k = 3. Between these upper and lower bounds there are a vast number of strategies that can be explored for enhancing the performance and adaptability of the algorithm. This paper investigates the convergence speed, accuracy, robustness and scalability of PSOs structured by regular and random graphs with 3≤k≤n. The main conclusion is that regular and random graphs with the same averaged connectivity k may result in significantly different performance, namely when k is low.Item Alterações e Contributo no Comportamento dos Utilizadores de Dispositivos Móveis Com Respeito aos Hábitos de Leitura(2016) Ferreira, Katiane Miranda; Escola de Comunicação, Arquitetura, Artes e Tecnologias da InformaçãoAs tecnologias da Informação (TICs) têm vindo a assumir um papel cada vez mais relevante no quotidiano dos consumidores. Busca por informação, leitura e realização de atividades profissionais são campos nos quais as tecnologias podem dar seu contributo. Através de estudo exploratório investigamos a influência dos dispositivos móveis no comportamento dos utilizadores. Foi também utilizada a metodologia de natureza quantitativa e qualitativa, desenho descritivo suportado num questionário. Amostragem probabilística aleatória simples foi utilizada para a recolha dos dados, os quais foram posteriormente tratados no SPSS. Os resultados sugerem que os utilizadores com maior adesão às tecnologias passaram a ter novos hábitos referentes a leitura, bem como desenvolvimento de atividade profissional. Foi constatado, que os adeptos às tecnologias fazem dos dispositivos um objeto de utilização imprescindível nas mais diversas atividades que desenvolvemItem Biofeedback Game Design(2018) Luz, Filipe Costa; Fachada, Nuno; Junior, Roberto; Escola de Comunicação, Arquitetura, Artes e Tecnologias da InformaçãoThis project aims to explore the psychological effect of the player during gaming and how reciprocally game designers can manipulate the sensations of the player through biofeedback information (physiological sensors) and implementation of certain game mechanics.Item cf4ocl: A C framework for OpenCL(Elsevier, 2017) Fachada, Nuno; Lopes, Vitor V.; Martins, Rui C.; Rosa, Agostinho C.; Escola de Comunicação, Arquitetura, Artes e Tecnologias da InformaçãoOpenCL is an open standard for parallel programming of heterogeneous compute devices, such as GPUs, CPUs, DSPs or FPGAs. However, the verbosity of its C host API can hinder application development. In this paper we present cf4ocl, a software library for rapid development of OpenCL programs in pure C. It aims to reduce the verbosity of the OpenCL API, offering straightforward memory management, integrated profiling of events (e.g., kernel execution and data transfers), simple but extensible device selection mechanism and user-friendly error management. We compare two versions of a conceptual application example, one based on cf4ocl, the other developed directly with the OpenCL host API. Results show that the former is simpler to implement and offers more features, at the cost of an effectively negligible computational overhead. Additionally, the tools provided with cf4ocl allowed for a quick analysis on how to optimize the application.