Wave Conditions Inducing Extreme Mooring Loads on a Dynamically Responding Moored Structure

Abstract

The aim of this paper is to determine which wave conditions are inducing extreme mooring loads on a highly dynamically responding moored structure. Currently, the design of a mooring system for a typical oil and gas offshore structure is based on the prediction of the extreme mooring loads for a limited number of wave conditions along the envelope of a wave scatter diagram. During the design process, an inappropriate choice of wave conditions could lead to an incorrect estimation of extreme mooring loads, which may result either in the loss of the mooring system or in a costly overdesign. This paper draws on mooring tensions and wave conditions that have been recorded at a mooring test facility using a multi-leg catenary mooring system. The mooring loads have been assessed to identify extreme mooring loads, which have been analysed in respect to the corresponding wave conditions. Further, joint probability distributions of wave conditions that results in extreme mooring loads have been determined. The most important finding is that extreme mooring loads were not necessarily identified to occur on the envelope of the wave climate parameter scatter diagram.