Time-frequency Analysis Of Spar Motions
Author(s)
A. E. Altenberg, J. M. Niedzwecki & J. M. Roësset
Abstract
In the study of the dynamic response of spars to wave excitation it is normal to
look not only at the time histories and maximum amplitudes but also at the
frequency content of the motions in order to isolate various nonlinear effects.
When dealing with wave basin tests or the results of dynamic analyses of
relatively small duration the response may not have reached a steady state
condition over most of the duration and it is necessary to look also at the
variation of the frequency content with time. In this paper data from wave basin
tests on a Spar are analyzed using a time-frequency decomposition with a
continuous wavelet transform in order to show their evolutionary nature.
Keywords: spars, wavelets, evolutionary response to waves.
1 Introduction
The dynamic response of Spars has been an area of considerable interest in the
past decade. Extensive experimental studies were carried out at the Offshore
Technology Research Center's (OTRC's) wave model basin [1] on two models
tested under regular monochromatic and bichromatic waves, as well as irregular
waves. Numerical studies were conducted by Mekha et al. [2, 3] and Johnson et
al. [4] using an extension of Morison’s equation in the time domain, commonly
known as slender body theory. Niedzwecki et al. [5] showed that some nonlinear
effects are of similar magnitude but act in opposite directions and thus need to be
carefully considered in the analysis. Including some of these terms while
neglecting others may lead to widely varying and incorrect numerical
predictions. Another approach for the dynamic analysis of floating structures is
the use of nonlinear (usually second order) diffraction-radiation theory. Weggel
and Roësset [6, 7] carried out analyses with this procedure in the frequency
domain. Ran et al. [8] investigated the behavior of spars using second order
diffraction in the time domain. This effort was further extended by Ran and Kim
Keywords
spars, wavelets, evolutionary response to waves.
Related Book
Other papers in this volume
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