Clustering of Gaussian Random Vector Fields in Multiple Trajectory Modelling

This paper concerns the estimation of multiple dynamical models from a set of observed trajectories. It proposes vector valued gaussian random fields, representing dynamical models and their vector fields, combined with a modified k- means clustering algorithm to assign observed trajectories to models. The assignment is done according to a likelihood function obtained from applying the random field associated to a cluster, to the data. The algorithm is shown to have several advantages when compared with others: 1) it does not depend on a grid, region of interest, grid resolution or interpolation method; 2) the estimated vector fields has an associated uncertainty which is given by the algorithm and taken into account. The paper presents results obtained on synthetic trajectories that illustrate the performance of the proposed algorithm

Controlo Interno

Lição Sumário apresentada à Universidade Fernando Pessoa como parte dos requisitos para obtenção do título de agregado em Ciências Empresariais, especialidade em Gestã

Numerical simulation of torsional response control of a plan-eccentric mass distribution building by using magnetorheological dampers

Wind and earthquake loads can cause coupled lateral-torsional deformations in building structures due to stiffness and/or mass eccentricities. Simple and regular structural configurations are usually recommended in designing seismic resistant systems to ensure optimal distribution of mass and stiffness in order to reduce torsional effects. However, these structures generally present irregular geometry due to other design requirements resulting in a complex three-dimensional dynamic behavior. In this regard, structural control has become a novel approach to reduce torsional seismic effects in asymmetric-plan building systems. Smart structures based on semi-active control systems are capable to improve significantly the seismic response of these structures with low power requirements, which represent a significant advantage over active systems. This paper presents a numerical simulation of a semi-active based control system using MagnetoRheological (MR) dampers to minimize the coupled lateral-torsional seismic response of a two-story framed building. A parametric study is carried out to evaluate the seismic behavior of the structure taking into account the effect of different mass eccentricities. The results show that it is possible to evaluate and validate the effectiveness of the semi-active control approach to reduce the structural seismic response for planeccentric or irregular mass distributions.info:eu-repo/semantics/publishedVersio

Fast cosine transform for FCC lattices

Voxel representation and processing is an important issue in a broad spectrum of applications. E.g., 3D imaging in biomedical engineering applications, video game development and volumetric displays are often based on data representation by voxels. By replacing the standard sampling lattice with a face-centered lattice one can obtain the same sampling density with less sampling points and reduce aliasing error, as well. We introduce an analog of the discrete cosine transform for the facecentered lattice relying on multivariate Chebyshev polynomials. A fast algorithm for this transform is deduced based on algebraic signal processing theory and the rich geometry of the special unitary Lie group of degree four.Comment: Presented at 13th APCA International Conference on Automatic Control and Soft Computing (CONTROLO 2018); 9 figure

Aplicação do Controlo Numérico BIVAL a um Canal Experimental

O controlo local monovariável em que o órgão de controlo (comporta ou descarregador) controla a profundidade do escoamento imediatamente a montante (controlo local por montante) ou a jusante (controlo local por jusante) são as técnicas mais usuais (sobretudo a primeira) uma vez que são fáceis de calibrar e implementar. Apresenta-se neste artigo um estudo sobre uma das várias alternativas de controlo digital existentes em canais de distribuição de água para rega, o controlo BIVAL, sendo este o controlo que oferece maior flexibilidade na distribuição. Os modelos de simulação hidráulica, em regime variável, são ferramentas indispensáveis na modernização dos sistemas de distribuição de água para rega, uma vez que estes poderão prever o comportamento dos seus órgãos reguladores (comportas ou descarregadores), se bem calibrados e validados. A calibração e validação do modelo BIVAL são realizadas para o Canal Experimental do Núcleo de Hidráulica e Controlo de Canais do Departamento de Engenharia Rural da Universidade de Évora, recorrendo, para o efeito, a um modelo hidráulico de simulação adequadamente calibrado para o canal objecto de estudo

Predictive data mining in nutrition therapy

The assessment and measurement of health status in communities throughput the world is a massive information technology challenge. Data mining, plays a vital role in health care industry since it really has the potential to generate a knowledge-rich environment that reduces medical errors, decreases costs by increasing efficiency, improves the quality of clinical decisions and significantly enhances patient's outcomes and quality of life. This study falls within the context of nutrition evaluation and its main goal is to apply classification algorithms in order to predict if a patient needs to be followed by a nutrition specialist. One of the tools resorted in this study was the Waikato Environment for Knowledge Analysis (Weka in advance) Workbench since it allows to quickly try out and compare different machine learning solutions. The tasks involved in the development of this project included data preparation, data preprocessing, data transformation and cleaning, application of several classifiers and its respective evaluation through performance measures that include the confusion matrix, accuracy, error rate, and others. The accomplished results showed to be quite optimistic presenting promising values of performance measures. specifically an accuracy around 91 %.This work has been supported by Compete: POCI-01-0145-FEDER-007043 and FCT within the Project Scope UID/CEC/00319/2013

A novel control strategy based on predictive control for a bidirectional interleaved three-phase converter

An experimental confirmation of predictive control applied to a bidirectional interleaved three-phase (BIT) converter is presented. The BIT converter is a powerful solution for numerous applications, mainly, renewables interface, motor drivers, active rectifiers, and active power filters. However, a precise and robust digital control strategy is required, maintaining a low computational effort. In this paper, a predictive control based on continuous control set is proposed as a new control scheme for the BIT converter, permitting the control of the ac side current with fixed switching frequency and with a faster response. The predictive control scheme applied to the BIT converter is defined along the paper, evidencing in detail the digital employment aspects according to the discrete-time model of the BIT converter. An explicit experimental validation under realistic operating conditions is presented using a developed laboratorial prototype, highlighting the convenience of the control applied to the BIT converter.This work has been supported by FCT – Fundação para a Ciência e Tecnologia in the scope of the project: PEstUID/CEC/00319/2013. This work has been supported by COMPETE: POCI-01-0145-FEDER-007043 and FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2013. This work is financed by the ERDF – European Regional Development Fund through the Operational Programme for Competitiveness and Internationalisation < COMPETE 2020 Programme, and by National Funds through the Portuguese funding agency, FCT < Fundação para a Ciência e a Tecnologia, within project SAICTPAC/0004/2015< POCI< 01<0145<FEDER<016434. Mr. Tiago Sousa is supported by the doctoral scholarship SFRH/BD/134353/2017 granted by the Portuguese FCT agency.info:eu-repo/semantics/publishedVersio

Path planning trajectories in fluid environments

This paper deals with the problem of finding a mission path that minimizes acceleration and drag while a vehicle moves from an initial position to a final target in fluid environments. A variational problem will be formulated in the general context of manifolds, where the energy functional depends on acceleration and drag forces. The corresponding Euler-Lagrange equations will be derived. Questions regarding the integrability of the Euler-Lagrange equations are the main challenge of this problem even when the geometry of the configuration space is not taken into consideration. This is mainly due to the fact that the power needed to overcome the drag forces is proportional to the cube of the speed. A numerical optimization approach will be presented in order to obtain approximate solutions for the problem in some particular configuration spaces.The first two authors acknowledge “Fundação para a Ciência e a Tecnologia” (FCT−Portugal) and COMPETE 2020 Program for financial support through project UID-EEA-00048-2013. The third author was supported by ALGORITMI R&D Center under the project PEst-UID/CEC/00319/2013 financed by “Fundação para a Ciência e a Tecnologia” (FCT−Portugal)

Fuzzy controller optimization using a genetic algorithm for non-collocated semi-active MR based control of a three-DOF framed struture

This paper aims to explore the usefulness of a simple genetic algorithm (GA) optimized Fuzzy Logic Controller (FLC) to reduce the response of a three-DOF framed structure equipped with a MagnetoRheological (MR) damper. These actuators can be controlled in bi-state control mode and/or in a semi-active configuration by continuously adjusting the amount of damping according to the actual response. Generally, model based controllers are designed to determine the actuator output. In recent years, soft computing techniques have been implemented to deal with the highly non-linear nature of structural systems. Among others, fuzzy based controllers seem to be adequate approach for these cases due to the inherent ability to deal with uncertain systems. However, a FLC design requires a wide experience in operating the system. This can be very difficult to implement in complex systems and several optimization techniques have been suggested to enhance the design process of fuzzy controllers. In this paper, a genetic algorithm (GA) optimized semi-active fuzzy based controller is proposed to reduce the seismic response of a three degree-offreedom (DOF) structure using a MR damper at the first DOF. The uncontrolled and controlled structural responses are compared to evaluate the effectiveness of the semi-active fuzzy based controller.info:eu-repo/semantics/publishedVersio

Controlo de Sistemas Pneumáticos

Neste artigo apresenta-se várias abordagens aos problemas de controlo de sistemas industriais tendo como base de atuação a pneumática. São apresentadas as metodologias de controlo de sistemas pneumáticos mais correntes como sejam o método de Cascata, de Memórias e dos Mapas de Karnaugh quer ao nível do controlo pneumático quer elétrico. Apresentam-se diversas abordagens de controlo destes mesmos sistemas recorrendo a autómatos programáveis (PLC)