You are hereProbability-Based Design Loads and Responses of Floating Structures: Extreme Slow Drift and Tether Tension

Probability-Based Design Loads and Responses of Floating Structures: Extreme Slow Drift and Tether Tension

Report No. : 
K. Engebretsen
S.R. Winterstein
June 1998
RMS30.pdf4 MB

Procedures are described to define design loads and responses of ocean structures. While these methods can be used for both fixed and floating structures, this report focuses on applications to floating structures; specifically, extreme motions of both
a tension-leg platform (TLP) and a spar buoy, and the extreme tether tension of a TLP. This report thus generalizes a recent OMAE paper by the authors [18], which considers mainly t he ext reme motion problem.

To capture the important sensitivity of floating structures to wave period as well as height, joint contours of significant wave height and peak spectral period are derived. Because these contours are structure-independent, they provide a useful means to specify important combinations of environmental parameters for design and wave tank experiments.

New methods are also developed to predict the effect of response variability. These quantify both the response variability in a given seastate, and the background variability in the median response (over all seastates). The result suggests that slow drift
motions may provide a particular modelling challenge: they combine relatively large response variability with rather low background variability levels, the latter due to the limiting steepness behavior of their critical seastates.

The main work has considered Northern North Seas wave environment using the Jonswap wave spectrum. Sensitivity cases including alternative spectrum formulation (bi-modal) and Gulf of Mexico wave climate are also included. These sensitivity
studies also represent extensions to the original OMAE paper cited above.