Reliability estimate sensitivity to multi-peaked random seas
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abstract
This study compares the reliability estimates of a flexible cylinder for seastates generated using single- and multi-peaked wave amplitude spectra. The horizontal response of a long, flexible cylinder that is representative of a riser or tendon was used for illustrative purposes. A method that characterizes the offshore loading environment independently of the structure, known as the environmental contour technique, was used to compute the reliability estimates for the cylinder. This technique allows one to identify the critical seastate for the structure being examined. The selection of this critical seastate for extreme response and reliability estimates is becoming a necessity as the offshore industry moves to probabilistic-based design codes. Two different simulation scenarios are examined that expand upon established procedures for single-peaked wave spectrum environmental contour. In the first scenario, the primary spectral peak is varied along the environmental contour while the secondary peak is held constant at the first harmonic of the flexible cylinder. For the second scenario, the most probable location of the secondary spectral peak given the significant wave height is used in the analysis. The environmental contour technique for investigation of the sensitivity of reliability estimates can easily be extended to address more complex behavior of a spar or tension leg platform. Conventional techniques for establishing a limit state function and estimating the system reliability could also be implemented.
