Ocean Current Profiles for Subsea Installation and Design Analysis

The paper describes different strategies for establishing current design profiles from sea bed to water surface, for use in analysis of subsea installation activities, e.g. during a pipe laying process or for dynamic analysis of risers. Measured data covering a period of 3–4 years for more than 20 measurement depths are used in the study. We investigate 4 strategies for depth profiles: General Purpose Profile: an envelope of the set of n-year speeds for individual depths, with unidirectional current at all depths. Empirical Event Profile: essentially a measured current profile which is deemed to be “serious,” i.e. potentially governing for design, scaled to adequately reflect a required return period. Whether a profile is “serious” or not would depend on the application. Response Based Profile: defined as the most probable profile causing an extreme response. It is obtained from design point current speeds from a reliability analysis of a selected response, while applying a detailed stochastic current model. Alternatively, an envelope of most probable profiles might be used.