For offshore structures with slender elements, the modelling of random wave loads by the Morison equation yields an equation of motion which admits no analytical solution except in few limit cases. This also holds for response moments. If polynomial approximations of the Morison drag loads are introduced, some procedures are available to obtain the stationary moments of the approximate response. These procedures result in large computer codes and time consuming computations if accurate approximations and large structural models are considered. If the response process is fitted by non-Gaussian models such as proposed by Winterstein (1988), the first four statistical moments of the response are necessary. In this paper the authors investigate how many terms should be included in the polynomial approximation of the Morison drag loading to accurately estimate the first four response moments. Analysis is performed in the time domain for a standardized form of the equation of motion. It is shown that a cubic approximation of the drag loading is necessary to accurately predict response variance for any excitation. For the fit of the first four response moments, at least a fifth-order approximation appears necessary. It is concluded that practical fatigue or reliability analyses can require much effort if the influence of nonlinearities in Morison loading needs to be accurately accounted for.

  • Supplemental Notes:
    • OMAE 1995, 14th Intl Conf on Offshore Mechanics & Arctic Engng; 18-22 June 1995; Copenhagen, Denmark. Sponsored by ASME et al. Procs. Publ by ASME, ISBN 0-7918-1308-8. Vol II, p 91 [8 p, 19 ref, 7 fig]
  • Authors:
    • Bouyssy, V
  • Publication Date: 1995


  • English

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Filing Info

  • Accession Number: 00718745
  • Record Type: Publication
  • Source Agency: British Maritime Technology
  • Files: TRIS
  • Created Date: Mar 27 1996 12:00AM