By adopting different numbers discrete frequencies as well as making the frequency spacing with uneven distances as the wave energy inputs and calculating the nonlinear dynamic response in time domain, the current paper presents a procedure for calculating the fatigue damage of offshore structures due to wave loading. By applying this approach into the fatigue calculation of a typical jacket structure, the directional effects and the peak enhancement of waves on the fatigue damage of the jacket structure were first identified. Furthermore, the parameters such as the number of sample points of the adopted wave spectrum, and, the length of time steps in the HHT-alpha time integration algorithm were also investigated. It is found that, in the reasonable range of wave peak enhancement, both the total and directional wave induced fatigue damage are not sensitive to the variation of wave enhancement amplitude in JONSWAP wave spectrum. The fatigue damage of selected positions on the jacket structure is mainly caused by the waves from certain directions. It is not sensitive to the variation of the number of wave spectrum input as well as the time step length below certain limits. It is not only dominated by the wave height, but also highly influenced by the waves with low modal period and the locations of the members relative to the sea surface. The free vibration of the jacket contributes significantly to the fatigue damage. The time step length should be carefully chosen to save the computation time as well as the computer memory without losing sufficient accuracy. Compare to the traditional wave energy spectrum input (the frequency spacing Delta omega in the wave energy spectrum has equal distance), the new wave spectrum input approach is more efficient for calculating the fatigue damage. The nonlinear dynamic analysis approach presented in the current paper has been successfully applied in several industry projects for the life time extension of offshore installations subject to dynamic wave and wind loads.
Practical fatigue calculation for offshore structures based on efficient wave spectrum inputs
Praktische Ermüdungsberechnung für Offshore-Konstruktionen auf Basis effizienter Wellenspektrumeingaben
2008
8 Seiten, 11 Bilder, 8 Tabellen, 9 Quellen
Aufsatz (Konferenz)
Datenträger
Englisch
Fatigue analysis - Offshore structures
Tema Archiv | 1986
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