No abstract

The wave climate of the Southern Ocean is investigated using a combined dataset from 33 years of altimeter data, in situ buoy measurements at five locations, and numerical wave model hindcasts. The analysis defines the seasonal variation in wind speed and significant wave height, as well as wind speed and significant wave height for a 1-in-100-year return period. The buoy data include an individual wave with a trough to crest height of 26.4 m and suggest that waves in excess of 30 m would occur in the region. The extremely long fetches, persistent westerly winds, and procession of low pressure systems that traverse the region generate wave spectra that are unique. These spectra are unimodal but with peak frequencies that propagate much faster than the local wind. This situation results in a unique energy balance in which waves at the spectra peak grow as a result of nonlinear transfer without any input from the local wind.

The present study is an attempt to re-assess the level of reliability of the mooring system of an existing Floating Production Storage and Offloading (FPSO) unit in West Africa. The study made use of field data for the environment including wind, waves and current together with simultaneous measurements of the FPSO offset and of the mooring line tensions. Three different approaches to predict the extreme response are compared. More specifically, the traditional design method is compared with Response Based Design (RBD) and First Order Reliability Method (FORM) analysis associated with Response Surface Models (RSM) of the moored FPSO. The results of this case study allow assessing the level of conservatism that is currently embedded in classical design rules. Highlights► A reliability analysis of an FPSO mooring system is proposed. ► Field data including wind, waves and current are used. ► Models for FPSO offset and the mooring line tensions were benchmarked. ► The traditional design method is compared with Response Based Design (RBD) and First Order Reliability Method (FORM) analysis associated with Response Surface Models (RSM). ► The level of conservatism currently embedded in design rules for moored structures is assessed.

The behaviour of the flow near the bow of a slender ship is studied. The fluid is assumed to be perfect and incompressible and the flow to be irrotational. The formalism of matched asymptotic expansion is used to provide a consistent perturbation procedure for the simplification of the initial problem. The resulting nonlinear free surface problem describing the flow in the inner domain close to the bow is solved numerically. Examples of solutions are given for the flows around a wedge shaped bow and a prismatic planing hull.