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Artificial Neural Network Models: Data Selection and Online Adaptation HAMID REZA KHOSRAVANI ARTIFICIAL NEURAL NETWORK MODELS: DATA SELECTION AND ONLINE ADAPTATION UNIVERSIDADE DO ALGARVE Faculdade de Ciências e Tecnologia 2017 HAMID REZA KHOSRAVANI ARTIFICIAL NEURAL NETWORK MODELS: DATA SELECTION AND ONLINE ADAPTATION Doutoramento em Engenheira Informática (Especialidade em Inteligência Artificial) Trabalho efeuado sob a orientação de: António Eduardo de Barros Ruano e Pedro Miguel Frazão F. Ferreira UNIVERSIDADE DO ALGARVE Faculdade de Ciências e Tecnologia 2017 ARTIFICIAL NEURAL NETWORK MODELS: DATA SELECTION AND ONLINE ADAPTATION Declaração de autoria de trabalho Declaro ser o autor deste trabalho, que é original e inédito. Autores e trabalhos consultados estão devidamente citados no texto e constam da listagem de referências incluída. _________________________________________________ Hamid Reza Khosravani Copyright: Hamid Reza Khosravani A Universidade do Algarve reserva para si o direito, em conformidade com o disposto no Código do Direito de Autor e dos Direitos Conexos, de arquivar, reproduzir e publicar a obra, independentemente do meio utilizado, bem como de a divulgar através de repositórios científicos e de admitir a sua cópia e distribuição para fins meramente educacionais ou de investigação e não comerciais, conquanto seja dado o devido crédito ao autor e editor respetivos. To my love, Elmira To my parents, Parvin and Mehdi To my brother, Ehsan Acknowledgements Undoubtedly doing this PhD would have not been possible without the sincere support and guidance that I received from many people throughout four years studying at the University of Algarve. First of all, I would like to express my special thanks to my supervisors Prof. Antonio Ruano and Prof. Pedro Ferreira for all their precious advices and encouragements allowing me to grow as a research scientist. They were not only continuously supporting me but also gave me a chance to find myself in academic atmosphere. I greatly appreciate the Erasmus Mundus SALAM scholarship program for kindly funding me towards this PhD. I also would like to particularly acknowledge Prof. Hamid Shahbazkia as the coordinator of SALAM scholarship program for all his supports during these years. Many thanks also to my friend, Sergio Silva, as the CSI laboratory’s administrator for his non-stop help and support in providing all stuffs that I needed to proceed my PhD. I also would like to appreciate Prof. Eslam Nazemi who was one the most influent people in my academic life for his great guidance towards my PhD. My deepest acknowledgement goes to my beloved, resilient and patient wife Elmira for bearing and accompanying me shoulder to shoulder in ups and downs throughout last four years. Last but not least, I would like to express my special appreciate to my parents and my brother Ehsan for their ever support and encouragement during my life that enabled me to achieve this goal. Abstract Energy consumption has been increasing steadily due to globalization and industrialization. Studies have shown that buildings have the biggest proportion in energy consumption; for example in European Union countries, energy consumption in buildings represents around 40% of the total energy consumption. Hence this PhD was intended towards managing the energy consumed by Heating, Ventilating and Air Conditioning (HVAC) systems in buildings benefiting from Model Predictive Control (MPC) technique. To achieve this goal, artificial intelligence models such as neural networks and Support Vector Machines (SVM) have been proposed because of their high potential capabilities of performing accurate nonlinear mappings between inputs and outputs in real environments which are not noise-free. In this PhD, Radial Basis Function Neural Networks (RBFNN) as a promising class of Artificial Neural Networks (ANN) were considered to model a sequence of time series processes where the RBFNN models were built using Multi Objective Genetic Algorithm (MOGA) as a design platform. Regarding the design of such models, two main challenges were tackled; data selection and model adaptation. Since RBFNNs are data driven models, the performance of such models relies, to a good extent, on selecting proper data throughout the design phase, covering the whole input-output range in which they will be employed. The convex hull algorithms can be applied as methods for data selection; however the use of conventional implementations of these methods in high dimensions, due to their high complexity, is not feasible. As the first phase of this PhD, a new randomized approximation convex hull algorithm called ApproxHull was proposed for high dimensions so that it can be used in an acceptable execution time, and with low memory requirements. Simulation results showed that applying ApproxHull as a filter data selection method (i.e., unsupervised data selection method) could improve the performance of the classification and regression models, in comparison with random data selection method. In addition, ApproxHull was employed in real applications in terms of three case studies. The first two were in association with applying predictive models for energy saving. The last case study was related to segmentation of lesion areas in brain Computed Tomography (CT) images. The evaluation results showed that applying ApproxHull in MOGA could result in models with an acceptable level of accuracy. Specifically, the results obtained from the third case study demonstrated that ApproxHull is capable of being applied on large size data sets in high dimensions. Besides the random selection method, it was also compared with an entropy based unsupervised data selection method and a hybrid method involving ApproxHull and the I entropy based method. Based on the simulation results, for most cases, ApproxHull and the hybrid method achieved a better performance than the others. In the second phase of this PhD, a new convex-hull-based sliding window online adaptation method was proposed. The goal was to update the offline predictive RBFNN models used in HVAC MPC technique, where these models are applied to processes in which the data input- output range changes over time. The idea behind the proposed method is capturing a new arriving point at each time instant which reflects a new range of data by comparing the point with current convex hull presented via ApproxHull. In this situation the underlying model’s parameters are updated based on the new point and a sliding window of some past points. The simulation results showed that not only the proposed method could efficiently update the model while a good level of accuracy is kept but also it was comparable with other methods. Keywords: Neural Networks; Multi-Objective Genetic Algorithm; Data Selection; Online Adaptation. II Resumo Devido aos processos de industrialização e globalização o consumo de energia tem aumentado de forma contínua. A investigação sobre o consumo mostra que os edifícios consomem a maior fatia de energia. Por exemplo nos países da União Europeia essa fatia corresponde a cerca de 40% de toda a energia consumida. Assim, esta tese de Doutoramento tem um objetivo prático de contribuir para melhorar a gestão da energia consumida por sistemas Heating, Ventilating and Air Conditioning (HVAC) em edifícios, no âmbito de uma estratégia de controlo preditivo baseado em modelos. Neste contexto foram já propostos modelos baseados em redes neuronais artificiais e máquinas de vetores de suporte, para mencionar apenas alguns. Estas técnicas têm uma grande capacidade de modelar relações não- lineares entre entradas e saídas de sistemas, e são aplicáveis em ambientes de operação, que, como sabemos, estão sujeitos a várias formas de ruído. Nesta tese foram consideradas redes neuronais de função de base radial, uma técnica consolidada no contexto da modelação de séries temporais. Para desenhar essas redes foi utilizada uma ferramenta baseada num algoritmo genético multi-objectivo. Relativamente ao processo de desenho destes modelos, esta tese versa sobre dois aspetos menos estudados: a seleção de dados e a adaptação em linha dos modelos. Uma vez que as redes neuronais artificiais são modelos baseados em dados, a sua performance depende em boa medida da existência de dados apropriados e representativos do sistema/processo, que cubram toda a gama de valores que a representação entrada/saída do processo/sistema gera. Os algoritmos que determinam a figura geométrica que envolve todos os dados, denominados algoritmos convex hull, podem ser aplicados à tarefa de seleção de dados. Contudo a utilização das implementações convencionais destes algoritmos em problemas de grane dimensionalidade não é viável do ponto de vista prático. Numa primeira fase deste trabalho foi proposto um novo método randomizado de aproximação ao convex hull, cunhado com o nome ApproxHull, apropriado para conjuntos de dados de grande dimensão, de forma a ser viável do ponto de vista das aplicações práticas. Os resultados experimentais mostraram que a aplicação do ApproxHull como método de seleção de dados do tipo filtro, ou seja, não supervisionado, pode melhorar o desempenho de modelos em problemas de classificação e regressão, quando comparado com a seleção aleatória de dados. O ApproxHull foi também aplicado em três casos de estudo relativos a aplicações reais. Nos dois primeiros casos no contexto do desenvolvimento de modelos preditivos para sistemas na área da eficiência energética. O terceiro caso de estudo consiste no desenvolvimento de III modelos de classificação para uma aplicação na área da segmentação
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