Dynamic Analysis of Splash-zone Crossing Operation for a Subsea Template

Abstract

Subsea templates are steel structures used to support subsea well components. Normally, offshore crane vessels are employed to install them to the target location on the seabed. Crossing the splash-zone during the lowering of a subsea template is considered the most critical phase during the installation due to slamming loads and needs to be studied to provide the operational weather criterion during the planning phase. In this study, dynamic response analysis has been carried out to evaluate the allowable sea states for the plash-zone crossing phase of the subsea templates. The numerical model of the lifting system, including the crane vessel and the subsea template, is firstly built in the state-of-the-art numerical program SIMA-SIMO. Then, dynamic analysis with time-domain simulations is carried out for the lifting system under various sea states. The disturbed wave field due to the shielding effects from the installation vessel is considered when calculating the hydrodynamic forces on the template. Statistical modelling of the dynamic responses from different wave realizations is used to estimate the extreme responses of various sea states. The application of the generalized extreme value distribution and Gumbel distribution in fitting the extreme responses is discussed. Moreover, the influence of the shielding effects from the vessel, as well as the influence of the changing size of the suction anchor on the hydrodynamic responses and the allowable sea states are studied.