Rato, RT, Ortigueira M, Batista A.
2008.
On the HHT, its problems, and some solutions, August. Mechanical Systems and Signal Processing. 22:1374–1394., Number 6: Elsevier
AbstractThe empirical mode decomposition (EMD) is reviewed and some questions related to its effective performance are discussed. Its interpretation in terms of AM?FM modulation is done. Solutions for its drawbacks are proposed. Numerical simulations are carried out to empirically evaluate the proposed modified EMD.
Valério, D, Ortigueira MD, da Costa JSá.
2008.
Identifying a Transfer Function From a Frequency Response, April. Journal of Computational and Nonlinear Dynamics. 3:021207., Number 2
AbstractIn this paper, the classic Levy identification method is reviewed and reformulated using a complex representation. This new formulation addresses the well known bias of the classic method at low frequencies. The formulation is generic, coping with both integer order and fractional order transfer functions. A new algorithm based on a stacked matrix and its pseudoinverse is proposed to accommodate the data over a wide range of frequencies. Several simulation results are presented, together with a real system identification. This system is the Archimedes Wave Swing, a prototype of a device to convert the energy of sea waves into electricity.
Ortigueira, MD.
2008.
Fractional Central Differences and Derivatives. Journal of Vibration and Control. 14:1255–1266., Number 9-10
AbstractFractional central differences and derivatives are studied in this article. These are generalisations to real orders of the ordinary positive (even and odd) integer order differences and derivatives, and also coincide with the well known Riesz potentials. The coherence of these definitions is studied by applying the definitions to functions with Fourier transformable functions. Some properties of these derivatives are presented and particular cases studied.