Percorrer por autor "Barbosa, Ramiro S."
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- Analysis of Systems with Backlash and Impacts through the Describing FunctionPublication . Barbosa, Ramiro S.; Machado, J. A. TenreiroThis paper analyses the dynamical properties of systems with backlash and impact phenomena based on the describing function method. The dynamics is illustrated using the Nyquist and Bode plots and the results are compared with those of standard models.
- Analysis of the Van der Pol oscillator containing derivatives of fractional orderPublication . Barbosa, Ramiro S.; Machado, J. A. Tenreiro; Vinagre, B. M.; Calderón, A. J.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.
- Application of fractional calculus in engineeringPublication . Machado, J. A. Tenreiro; Jesus, Isabel S.; Barbosa, Ramiro S.; Silva, Manuel F.; Reis, CecíliaFractional Calculus (FC) goes back to the beginning of the theory of differential calculus. Nevertheless, the application of FC just emerged in the last two decades. It has been recognized the advantageous use of this mathematical tool in the modelling and control of many dynamical systems. Having these ideas in mind, this paper discusses a FC perspective in the study of the dynamics and control of several systems. The paper investigates the use of FC in the fields of controller tuning, legged robots, electrical systems and digital circuit synthesis.
- Application of Fractional Calculus in MechatronicsPublication . Machado, J. A. Tenreiro; Barbosa, Ramiro S.; Duarte, Fernando; Ferreira, NunoFractional Calculus (FC) goes back to the beginning of the theory of differential calculus. Nevertheless, the application of FC just emerged in the last two decades. In the field of dynamical systems theory some work has been carried out but the proposed models and algorithms are still in a preliminary stage of establishment. Having these ideas in mind, the paper discusses a FC perspective in the study of the dynamics and control of mechanical systems.
- Application of genetic algorithms in the design of an electrical potential of fractional orderPublication . Jesus, Isabel S.; Machado, J. A. Tenreiro; Barbosa, Ramiro S.Fractional calculus (FC) is currently being applied in many areas of science and technology. In fact, this mathematical concept helps the researches to have a deeper insight about several phenomena that integer order models overlook. Genetic algorithms (GA) are an important tool to solve optimization problems that occur in engineering. This methodology applies the concepts that describe biological evolution to obtain optimal solution in many different applications. In this line of thought, in this work we use the FC and the GA concepts to implement the electrical fractional order potential. The performance of the GA scheme, and the convergence of the resulting approximation, are analyzed. The results are analyzed for different number of charges and several fractional orders.
- Complex-order dynamics in hexapod locomotionPublication . Silva, Manuel F.; Machado, J. A. Tenreiro; Barbosa, Ramiro S.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.
- Control and Dynamics of Fractional Order SystemsPublication . Machado, J. A. Tenreiro; Jesus, Isabel; Barbosa, Ramiro S.; Silva, ManuelFractional Calculus (FC) goes back to the beginning of the theory of differential calculus. Nevertheless, the application of FC just emerged in the last two decades due to the progress in the area of nonlinear dynamics. This article discusses several applications of fractional calculus in science and engineering, namely: the control of heat systems, the tuning of PID controllers based on fractional calculus concepts and the dynamics in hexapod locomotion.
- Control and dynamics of fractional order systemsPublication . Machado, J. A. Tenreiro; Jesus, Isabel S.; Barbosa, Ramiro S.; Silva, Manuel F.Fractional Calculus (FC) goes back to the beginning of the theory of differential calculus. Nevertheless, the application of FC just emerged in the last two decades due to the progress in the area of nonlinear dynamics. This article discusses several applications of fractional calculus in science and engineering, namely: the control of heat systems, the tuning of PID controllers based on fractional calculus concepts and the dynamics in hexapod locomotion.
- Design of Digital Fractional-Order Integrators and Differentiators by Least SquaresPublication . Barbosa, Ramiro S.; Machado, J. A. Tenreiro; Ferreira, Isabel M.In this paper we develop a method for obtaining digital rational approximations (IIR filters) to fractional-order operators of type sα, where α ∈ . The proposed method is based on the least-squares (LS) minimization between the impulse responses of the digital fractional-order integrator/differentiator and of the rational-fraction approximation. The results reveal that the LS approach gives similar or superior approximations in comparison with other methods. The effectiveness of the method is demonstrated both in the time and frequency domains through an illustrative example.
- Discretization of complex-order algorithms for control applicationsPublication . Barbosa, Ramiro S.; Machado, J. A. Tenreiro; Silva, Manuel F.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.
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