Effects of mooring line design parameters on the line dynamics and fatigue response of subsea mooring lines

Dynamic characteristics of mooring lines play an important role in overall structural response and fatigue design of mooring systems. Full dynamic analysis including line dynamics is a vital part of fatigue design process although in time domain it needs excessive computational efforts. For fatigue analysis of mooring lines where hundreds of different environmental loads have to be checked, alternative analysis approach such as quasi-dynamic analysis with implicit inclusion of the line dynamic effects are used widely in engineering practice. This paper presents the results of series of case studies on the effects of various mooring line design parameters on the line dynamics as well as the mooring line dynamic fatigue response. Various mooring line composition types (all chain and chain-polyester-chain) used in different mooring configurations (catenary, semi-taut and taut) with variable range of mooring line pretensions connected to a floater in shallow and deep water depths are studied. Ratios of fatigue damage results between dynamic and quasi-dynamic results as well as the relation between fatigue damage and statistical characteristics of the line dynamic responses for different line configurations and load cases are investigated in detail.