On the fractional order control of heat systems

The differentiation of non-integer order has its origin in the seventeenth century, but only in the last two decades appeared the first applications in the area of control theory. In this paper we consider the study of a heat diffusion system based on the application of the fractional calculus concepts. In this perspective, several control methodologies are investigated namely the fractional PID and the Smith predictor. Extensive simulations are presented assessing the performance of the proposed fractional-order algorithms.

Tuning and application of integer and fractional order PID controllers

Fractional calculus (FC) is widely used in most areas of science and engineering, being recognized its ability to yield a superior modeling and control in many dynamical systems. In this perspective, this article illustrates two applications of FC in the area of control systems. Firstly, is presented a methodology of tuning PID controllers that gives closed-loop systems robust to gain variations. After, a fractional-order PID controller is proposed for the control of an hexapod robot with three dof legs. In both cases, it is demonstrated the system's superior performance by using the FC concepts.

A Qualidade na administração pública e a CAF – Common assessment framework

Apresentação no âmbito da Dissertação de Mestrado Orientador: Doutora Alcina Dias

SketchyDynamics apoio à produção de sistemas baseados em interfaces caligráficas para a simulação da dinâmica de corpos rígidos

Mestrado em Engenharia Informática - Área de Especialização em Sistemas Gráficos e Multimédia

Gestão de stocks e a sua envolvente – estudo de caso de uma PME da indústria de calçado ortopédico

Dissertação apresentada ao Instituto Superior de Contabilidade para a obtenção do Grau de Mestre em Auditoria Professor orientador: Mestre Manuel Gregório

Mode III interlaminar fracture of carbon/epoxy laminates using the edge crack torsion (ECT) test

The mode III interlaminar fracture of carbon/epoxy laminates was evaluated with the edge crack torsion (ECT) test. Three-dimensional finite element analyses were performed in order to select two specimen geometries and an experimental data reduction scheme. Test results showed considerable non-linearity before the maximum load point and a significant R-curve effect. These features prevented an accurate definition of the initiation point. Nevertheless, analyses of non-linearity zones showed two likely initiation points corresponding to GIIIc values between 850 and 1100 J/m2 for both specimen geometries. Although any of these values is realistic, the range is too broad, thus showing the limitations of the ECT test and the need for further research.

Modelização de equivalente eléctrico para rede de nervuras de folhas vegetais

A tese tem como objectivo principal a criação de um modelo equivalente eléctrico da rede de nervuras de algumas folhas vegetais e analisar o seu comportamento a estímulos eléctricos, analisando-se também a respectiva resposta em frequência. A motivação desta tese passa pela observação dos sistemas existentes na natureza. Neste caso, as folhas vegetais e analisar se são sistemas de ordem fraccionária ou não. Para a sua elaboração, fez-se uma breve abordagem à estrutura das plantas, sob o ponto de vista da botânica e elaborou-se um método de fotografia das amostras, mapeamento da rede de nervuras e medição dos segmentos que compõem essa mesma rede. A tese termina com um capítulo de resultados experimentais.

Economia energética por medição de cor em linha do açúcar à saída das centrífugas no processo de refinação da rama de açúcar

Mestrado em Engenharia Química

Integer vs. fractional order control of a hexapod robot

This paper studies the performance of integer and fractional order controllers in a hexapod robot with joints at the legs having viscous friction and flexibility. For that objective the robot prescribed motion is characterized in terms of several locomotion variables. The controller performance is analised through the Nyquist stability criterion. A set of model-based experiments reveals the influence of the different controller implementations upon the proposed metrics.

Development of fractional order capacitors based on electrolyte processes

In recent years, significant research in the field of electrochemistry was developed. The performance of electrical devices, depending on the processes of the electrolytes, was described and the physical origin of each parameter was established. However, the influence of the irregularity of the electrodes was not a subject of study and only recently this problem became relevant in the viewpoint of fractional calculus. This paper describes an electrolytic process in the perspective of fractional order capacitors. In this line of thought, are developed several experiments for measuring the electrical impedance of the devices. The results are analyzed through the frequency response, revealing capacitances of fractional order that can constitute an alternative to the classical integer order elements. Fractional order electric circuits are used to model and study the performance of the electrolyte processes.

Discretization of complex-order algorithms for control applications

In this article we describe several methods for the discretization of the differintegral operator sa, where α = u + jv is a complex value. The concept of the conjugated-order differintegral is also introduced, which enables the use of complex-order differintegrals while still producing real-valued time responses and transfer functions. The performance of the resulting approximations is analysed in both the time and frequency domains. Several results are presented that demonstrate its utility in control system design.

Analysis of the Van der Pol oscillator containing derivatives of fractional order

In this paper a modified version of the classical Van der Pol oscillator is proposed, introducing fractional-order time derivatives into the state-space model. The resulting fractional-order Van der Pol oscillator is analyzed in the time and frequency domains, using phase portraits, spectral analysis and bifurcation diagrams. The fractional-order dynamics is illustrated through numerical simulations of the proposed schemes using approximations to fractional-order operators. Finally, the analysis is extended to the forced Van der Pol oscillator.

Complex-order dynamics in hexapod locomotion

This paper studies the dynamics of foot–ground interaction in hexapod locomotion systems. For that objective the robot motion is characterized in terms of several locomotion variables and the ground is modelled through a non-linear spring-dashpot system, with parameters based on the studies of soil mechanics. Moreover, it is adopted an algorithm with foot-force feedback to control the robot locomotion. A set of model-based experiments reveals the influence of the locomotion velocity on the foot–ground transfer function, which presents complex-order dynamics.

Fractional order electromagnetics

The Maxwell equations constitute a formalism for the development of models describing electromagnetic phenomena. The four Maxwell laws have been adopted successfully in many applications and involve only the integer order differential calculus. Recently, a closer look for the cases of transmission lines, electrical motors and transformers, that reveal the so-called skin effect, motivated a new perspective towards the replacement of classical models by fractional-order mathematical descriptions. Bearing these facts in mind this paper addresses the concept of static fractional electric potential. The fractional potential was suggested some years ago. However, the idea was not fully explored and practical methods of implementation were not proposed. In this line of thought, this paper develops a new approximation algorithm for establishing the fractional order electrical potential and analyzes its characteristics.

A pré-fabricação em betão em edifícios

No presente trabalho apresenta-se um levantamento com base na literatura especializada, das diversas soluções estruturais em betão pré-fabricado existentes, aplicadas em edifícios correntes, mais especificamente as soluções ao nível dos elementos que as constituem, nomeadamente no que respeita a ligações estruturais dos elementos, com combinações in situ, das estruturas préfabricadas e as moldadas em obra, aproveitando o que de melhor se pode obter de ambas as técnicas, com vista a obter um melhor resultado final. Apesar do setor da construção civil estar em crise, tal como vários outros setores, as empresas de pré-fabricação apresentam soluções que poderão contrariar esta tendência, nomeadamente através da diversificação e flexibilização da sua produção, com inovação, criatividade e elevada qualidade. Num mercado em que a construção de edifícios de raiz sofreu um grande abrandamento, começa a surgir no mercado a necessidade de se reabilitar as construções existentes, nomeadamente nos grandes centros das cidades que foram perdendo população ao longo dos tempos. Esta requalificação do espaço urbano permite o desenvolvimento de soluções estruturais pré-fabricadas, no que respeita à reabilitação dos elementos existentes, quer por justaposição para reforço das estruturas, quer por inserção de elementos novos para efetuar correções. Os baixos custos de mão de obra, equipamentos e estaleiro, assim como a redução dos prazos de construção e entrega ao cliente final, dado que a produção não está dependente das condições existentes in situ para se desenvolver, destacam-se da construção civil tradicional. A produção integral dos elementos pré-fabricados de betão em fábrica tem outras vantagens, entre as quais, um melhor planeamento e controle da segurança, um controle rigoroso de qualidade, a redução dos custos de reparação e manutenção, melhor sustentabilidade com redução da quantidade de resíduos produzidos.