Guidance for Performing Time-Domain Mooring Analysis of Floating Systems in Squall Environments

Abstract This paper describes a methodology for the design and analysis of offshore floating systems governed by squall wind events. A clear methodology on this subject currently does not exist in industry codes and standards. A well-defined methodology is necessary because squalls govern the strength-based design of moored systems in areas such as offshore West Africa. This work focuses on the identification of load cases for time-domain analysis of wind squall events for spread and turret moored vessels. This paper also proposes a method for determining the characteristic design value of extreme line tension and presents various approaches for characterizing extreme vessel offsets. These recommendations are supported and illustrated using results from time-domain analyses of three different offshore systems: two turret-moored ships and one spread-moored ship. This work identifies the conditions that determine maximum offsets and mooring line tensions. These correspond to (1) the relative heading between the vessel and the squall, and (2) the characteristics of the squall. This paper highlights:Modeling details, sensitivity cases, and convergence studies used to establish confidence in characteristic design values that result from the analyses;The number and type of squalls to be considered and identifies topics requiring further research The recommendations in this paper can provide a basis for updates to industry codes and standards related to the design of mooring systems governed by squall events. Prior to the updating of codes and standards, the recommendations included here can be applied to future analyses of moored systems governed by squall events.