Discrete fractional order system vibrations

A theory of free vibrations of discrete fractional order (FO) systems with a finite number of degrees of freedom (dof) is developed. A FO system with a finite number of dof is defined by means of three matrices: mass inertia, system rigidity and FO elements. By adopting a matrix formulation, a mathematical description of FO discrete system free vibrations is determined in the form of coupled fractional order differential equations (FODE). The corresponding solutions in analytical form, for the special case of the matrix of FO properties elements, are determined and expressed as a polynomial series along time. For the eigen characteristic numbers, the system eigen main coordinates and the independent eigen FO modes are determined. A generalized function of visoelastic creep FO dissipation of energy and generalized forces of system with no ideal visoelastic creep FO dissipation of energy for generalized coordinates are formulated. Extended Lagrange FODE of second kind, for FO system dynamics, are also introduced. Two examples of FO chain systems are analyzed and the corresponding eigen characteristic numbers determined. It is shown that the oscillatory phenomena of a FO mechanical chain have analogies to electrical FO circuits. A FO electrical resistor is introduced and its constitutive voltage–current is formulated. Also a function of thermal energy FO dissipation of a FO electrical relation is discussed.

An Extension of Estimation of Domain of Attraction for Fractional Order Linear System Subject to Saturation Control

This paper employs the Lyapunov direct method for the stability analysis of fractional order linear systems subject to input saturation. A new stability condition based on saturation function is adopted for estimating the domain of attraction via ellipsoid approach. To further improve this estimation, the auxiliary feedback is also supported by the concept of stability region. The advantages of the proposed method are twofold: (1) it is straightforward to handle the problem both in analysis and design because of using Lyapunov method, (2) the estimation leads to less conservative results. A numerical example illustrates the feasibility of the proposed method.

Formulação fisicamente não - linear da teoria generalizada de vigas

Dissertação para obtenção do grau de Mestre em Engenharia Civil

Optimização estrutural na análise não linear dos modelos de escoras e tirantes

Dissertação para obtenção do Grau de Mestre em Engenharia Civil - Perfil Estruturas

Contributo para a modelização de magnetos supercondutores de fluxo residual: aplicação a um motor linear todo supercondutor

Dissertação para obtenção do Grau de Mestre em Engenharia Electrotécnica e de Computadores

Mathematical modelling of shallow flows: closure models drawn from grain-scale mechanics of sediment transport and flow hydrodynamics

Canadian Journal of Civil Engineering 36(10) 1605–16

On the analysis of data emerging in non-linear and complex systemscomparison of two X-Ray prony spectra

New arguments proving that successive (repeated) measurements have a memory and actually remember each other are presented. The recognition of this peculiarity can change essentially the existing paradigm associated with conventional observation in behavior of different complex systems and lead towards the application of an intermediate model (IM). This IM can provide a very accurate fit of the measured data in terms of the Prony's decomposition. This decomposition, in turn, contains a small set of the fitting parameters relatively to the number of initial data points and allows comparing the measured data in cases where the “best fit” model based on some specific physical principles is absent. As an example, we consider two X-ray diffractometers (defined in paper as A- (“cheap”) and B- (“expensive”) that are used after their proper calibration for the measuring of the same substance (corundum a-Al2O3). The amplitude-frequency response (AFR) obtained in the frame of the Prony's decomposition can be used for comparison of the spectra recorded from (A) and (B) - X-ray diffractometers (XRDs) for calibration and other practical purposes. We prove also that the Fourier decomposition can be adapted to “ideal” experiment without memory while the Prony's decomposition corresponds to real measurement and can be fitted in the frame of the IM in this case. New statistical parameters describing the properties of experimental equipment (irrespective to their internal “filling”) are found. The suggested approach is rather general and can be used for calibration and comparison of different complex dynamical systems in practical purposes.

Contributo para o estudo do motor linear síncrono supercondutor

Dissertação para obtenção do Grau de Mestre em Engenharia Electrotécnica e de Computadores

Non-linear time series models

The last three decades have seen quite dramatic changes the way we modeled time dependent data. Linear processes have been in the center stage in modeling time series. As far as the second order properties are concerned, the theory and the methodology are very adequate.However, there are more and more evidences that linear models are not sufficiently flexible and rich enough for modeling purposes and that failure to account for non-linearities can be very misleading and have undesired consequences.

Analyzing Multiple Outcomes: Is it Really Worth the use of Multivariate Linear Regression?

In health related research it is common to have multiple outcomes of interest in a single study. These outcomes are often analysed separately, ignoring the correlation between them. One would expect that a multivariate approach would be a more efficient alternative to individual analyses of each outcome. Surprisingly, this is not always the case. In this article we discuss different settings of linear models and compare the multivariate and univariate approaches. We show that for linear regression models, the estimates of the regression parameters associated with covariates that are shared across the outcomes are the same for the multivariate and univariate models while for outcome-specific covariates the multivariate model performs better in terms of efficiency.

Kalman tracking linear predictor for vowel intelligibility enhancement on european portuguese HMM based speech synthesis

The recent developments on Hidden Markov Models (HMM) based speech synthesis showed that this is a promising technology fully capable of competing with other established techniques. However some issues still lack a solution. Several authors report an over-smoothing phenomenon on both time and frequencies which decreases naturalness and sometimes intelligibility. In this work we present a new vowel intelligibility enhancement algorithm that uses a discrete Kalman filter (DKF) for tracking frame based parameters. The inter-frame correlations are modelled by an autoregressive structure which provides an underlying time frame dependency and can improve time-frequency resolution. The system’s performance has been evaluated using objective and subjective tests and the proposed methodology has led to improved results.

Hydrogeomechanics for rock engineering: coupling subsurface hydrogeomechanical assessement and hydrogeotechnical mapping on fracturated rock masses

The present work aims to achieve and further develop a hydrogeomechanical approach in Caldas da Cavaca hydromineral system rock mass (Aguiar da Beira, NW Portugal), and contribute to a better understanding of the hydrogeological conceptual site model. A collection of several data, namely geology, hydrogeology, rock and soil geotechnics, borehole hydraulics and hydrogeomechanics, was retrieved from three rock slopes (Lagoa, Amores and Cancela). To accomplish a comprehensive analysis and rock engineering conceptualisation of the site, a multi‐technical approach were used, such as, field and laboratory techniques, hydrogeotechnical mapping, hydrogeomechanical zoning and hydrogeomechanical scheme classifications and indexes. In addition, a hydrogeomechanical data analysis and assessment, such as Hydro‐Potential (HP)‐Value technique, JW Joint Water Reduction index, Hydraulic Classification (HC) System were applied on rock slopes. The hydrogeomechanical zone HGMZ 1 of Lagoa slope achieved higher hydraulic conductivities with poorer rock mass quality results, followed by the hydrogeomechanical zone HGMZ 2 of Lagoa slope, with poor to fair rock mass quality and lower hydraulic parameters. In addition, Amores slope had a fair to good rock mass quality and the lowest hydraulic conductivity. The hydrogeomechanical zone HGMZ 3 of Lagoa slope, and the hydrogeomechanical zones HGMZ 1 and HGMZ 2 of Cancela slope had a fair to poor rock mass quality but were completely dry. Geographical Information Systems (GIS) mapping technologies was used in overall hydrogeological and hydrogeomechanical data integration in order to improve the hydrogeological conceptual site model.

Correlação entre a Extensão Linear do Tronco e o Alinhamento Segmentar do Membro Inferior Contralesional na Posição de Pé em Indivíduos Pós-AVE

O controlo postural (CP) do tronco é um pré-requisito para o movimento tendo como objetivo prevenir e minimizar as perturbações. Um CP adequado pressupõe estabilidade e orientação dos segmentos, sendo necessária uma orientação do tronco com componente de extensão linear para as atividades sentado e pé. Num acidente vascular encefálico (AVE), pode existir comprometimento do CP do tronco quer contralesional (CONTRA) como ipsilesional (IPSI). Neurofisiologicamente, parece haver uma projecção predominantemente ipsilateral para garantir um CP do tronco contralateralmente ao movimento, tornando-se importante perceber a correlação entre componentes do CP do tronco e o alinhamento do membro CONTRA. Contudo, atualmente são poucos os estudos direcionados para a o membro inferior (MI). Assim, uma vez que nesta população, assumir a posição de pé e realizar marcha constitui muitas vezes o seu principal objetivo, considerou-se relevante avaliar a correlação entre a extensão linear do tronco e o alinhamento segmentar do MI CONTRA na posição de pé. Participantes e Métodos: Estudo observacional, transversal, analítico com 11 indivíduos (idade média 70+10 anos, 54,5% homens). Como critérios de inclusão definiram-se AVE isquémico da artéria cerebral média, único e unilateral, em fase crónica. Recorrendo a um software de avaliação postural (SAPo) avaliou-se a extensão linear do tronco (alinhamento dos acrómios, alinhamento das espinhas ilíacas ântero-superiores (EIAS), ângulo formado entre os dois e o alinhamento vertical do tronco) e o alinhamento segmentar do MI (ângulo do joelho e ângulo entre o tronco e MI). Para a análise estatística inferencial utilizou-se o coeficiente de correlação de Pearson entre o ângulo dos acrómios e as EIAS, o alinhamento vertical do tronco e o alinhamento horizontal da pélvis IPSI com as variáveis de alinhamento do MI, para uma significância de 0,05. Resultados: Algumas correlações mostraram ser quase nulas (com valores entre -0,02 a 0,02) ou fracas como o alinhamento horizontal da pélvis IPSI com o ângulo do tronco e MI CONTRA (0,29 com p=0,39). O alinhamento do tronco e o ângulo do joelho apresentou moderada correlação (0,642), estatisticamente significativa (p=0,03). Conclusão: Os resultados deste estudo sugerem a existência de uma correlação positiva entre o alinhamento vertical do tronco e a extensão do joelho do MI CONTRA na posição de pé em indivíduos pós-AVE.

Linear amplification with multiple nonlinear devices

Dissertação para obtenção do Grau de Mestre em Engenharia Electrotécnica e Computadores

Estudo de avaliação de emissões de nanopartículas na soldadura por fricção linear de ligas de alumínio

Dissertação para obtenção do Grau de Mestre em Engenharia Mecânica