SPECTRAL FATIGUE ANALYSIS OF SHALLOW WATER JACKET PLATFORMS

The spectral analysis approach is a very elegant and computationally efficient method of analysing the fatigue life of offshore jacket platforms. The primary limitation of the approach is that is assumes linearity of both the structural system and the wave loading mechanism. Various methods have been proposed to enable the spectral method to be used for some non-linear situations, including a new approach which uses Longuet-Higgins wave height-period joint probability density function in order to obtain a better linearization technique. This linearization process is associated with the particular wave heights chosen for producing the transfer functions. The new approach provides a better method for choosing the appropriate height of each so called base wave case. In order to verify the new approach a time series analysis, including wave loading nonlinearities, has been adopted to obtain a reference fatigue life. The sea surface elevation spectrum has been decomposed into a set of equivalent harmonic components. The water particle velocities and accelerations were then individually evaluated and the appropriate (Morison's) wave loading was computed for each time step in the sea surface time history. The structural stress response time history was then calculated, from which a fatigue life estimate was obtained. This paper presents the results obtained using this new approach, as well as comparative results obtained using the deterministic, spectral and time domain approaches applied with a representative sea state. The results show that the deterministic-spectral potential, especially for new design work where weight savings and/or increased confidence levels may be achieved.

  • 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 0-7918-1307-X. Vol I, Pt B, p 519 [9 p, 11 ref, 3 tab, 12 fig]
  • Authors:
    • Bishop, N W
    • Feng, Q
  • Publication Date: 1995

Language

  • English

Subject/Index Terms

Filing Info

  • Accession Number: 00718541
  • Record Type: Publication
  • Source Agency: British Maritime Technology
  • Files: TRIS
  • Created Date: Mar 27 1996 12:00AM