Research Papers: Modeling

Identifying a Transfer Function From a Frequency Response

[+] Author and Article Information
Duarte Valério

IDMEC/IST, Technical University of Lisbon, Avenida Rovisco Pais, 1049-001 Lisboa, Portugaldvalerio@dem.ist.utl.pt

Manuel Duarte Ortigueira

 UNINOVA and DEE of Faculdade de Ciências e Tecnologia of UNL, Campus da FCT da UNL, Quinta da Torre, 2825-114 Monte da Caparica, Portugalmdortigueira@uninova.pt

José Sá da Costa

IDMEC/IST, Technical University of Lisbon, Avenida Rovisco Pais, 1049-001 Lisboa, Portugalsadacosta@dem.ist.utl.pt

The AWS was tested 5km offshore Leixões. The data on wave climate were obtained from the ONDATLAS software (13). The location for which ONDATLAS has wave climate data is called Leixões buoy (41°12.2N, 9°5.3W).

J. Comput. Nonlinear Dynam 3(2), 021207 (Feb 04, 2008) (7 pages) doi:10.1115/1.2833906 History: Received June 06, 2007; Revised November 30, 2007; Published February 04, 2008

In 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.

Copyright © 2008 by American Society of Mechanical Engineers
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Grahic Jump Location
Figure 1

The AWS before submersion and its working principle

Grahic Jump Location
Figure 2

Top: Bode diagram of the chosen AWS model; the dots mark the points of Table 4; bottom: output of the chosen AWS model compared with the output of the nonlinear model of the AWS, the input being part of a wave typical for the month of January



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