A time-varying parameter model of a body oscillating in pitch

A. P. McCabe, G. A. Aggidis, T. J. Stallard

    Research output: Contribution to journalArticlepeer-review


    Among the assumptions upon which linear time-invariant models of floating bodies are based is that the body motions are so small that any change in the body's angular position can be disregarded. However, it is often a major design requirement of a wave energy conversion device that the response amplitude is large, thereby invalidating one of the assumptions of the linear model. In particular, the immersed geometry of a body undergoes considerable variation when it is moved in pitch. With regard to this we investigate the difference in performance between a quasi-linear model in which the change of immersed surface is modelled by time-varying parameters and a basic linear model in which the immersed surface is time-invariant. The time-varying parameter model is realized by interpolation between the appropriate parameter values of a set of linear time-invariant (LTI) models derived for the different immersed surfaces that occur at discrete body displacements. It is shown that the responses predicted using the time-varying parameter model are closer to those measured experimentally than those of a standard frequency-domain model. Particular improvement occurs when the responses are large, such as at or near the resonance frequency. A problem which may limit the general use of the model is also discussed. © 2007 Elsevier Ltd. All rights reserved.
    Original languageEnglish
    Pages (from-to)359-370
    Number of pages11
    JournalApplied Ocean Research
    Issue number6
    Publication statusPublished - Dec 2006


    • Potential-flow hydrodynamics
    • Time-domain model
    • Time-varying parameter model


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