The nonlinear soil model recently incorporated in the OrcaFlex software for dynamic analysis of risers was used to conduct a parametric study to investigate the influence of three key soil parameters on the fatigue response of a typical deepwater SCR. The key soil parameters explored were: the normalised maximum stiffness, the suction ratio that determines the maximum uplift resistance, and the soil shear strength gradient. Results of the sensitivity analysis show that the normalised maximum stiffness has no significant effect on the maximum fatigue damage or its location along the riser. Increasing the suction ratio or shear strength gradient lead to a decrease in fatigue life. Fatigue life is more sensitive to the soil shear strength gradient than to the suction ratio. And increasing the suction ratio shifts the point of maximum fatigue damage towards the floating platform whereas increasing the shear strength gradient shifts it away from the floating platform. It was also found that, while the ordering of the wave packets had some effect on the fatigue life, this was of secondary importance (less than 15%). Analyses using linear seabed stiffness showed that a low stiffness, in the range 10 to 50 kPa,was required to obtain a similar range of fatigue life to that predicted using the nonlinear pipe-soil model. The results from this fatigue parametric study confirm that the soil parameters in the nonlinear soil model can have a significant effect on the SCR fatigue damage in the touchdown zone. However, the fatigue life obtained for typical soil parameters is rather greater than would be obtained using typical linear seabed stiffness values as currently adopted in design. It is recommended that nonlinear pipe-soil interaction should be taken into account in order to allow reliable, but economic, fatigue design of SCRs.


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    Title :

    Advanced nonlinear hysteretic seabed model for dynamic fatigue analysis of steel catenary risers


    Additional title:

    Ein fortgeschrittenes nichtlineares hysteretisches Modell zut dynamischen Ermüdungsanalyse von Stahl-Steigrohren


    Contributors:
    Ting, I.H.Y. (author) / Kimiaei, M. (author) / Randolph, M.F. (author)


    Publication date :

    2011


    Size :

    6 Seiten, 9 Bilder, 3 Tabellen, 10 Quellen



    Type of media :

    Conference paper


    Type of material :

    Storage medium


    Language :

    English




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