The installation of subsea equipment represents an increasing challenge with respect to safety and costs as water depth increases. Detailed planning is required in order to establish safe and cost-effective operational procedures for the deep water installation. This includes numerical modelling and analysis of dynamic loads on the lifted object and on the installation equipment. This paper presents a simplified approach to establish dynamic loads and limiting sea-states for deepwater lifting, as developed for the new recommended practice DNV-RP-H103 (2009).
The dynamics of the lifted object, in response to wave-induced motion of the vessel crane tip, are of great importance when lifting in deepwater. The resonance period of the lifting system increases with the length of the cable and resonant amplification due to vertical crane tip motion may arise. The most accurate calculation of the dynamic response in the cable is obtained by a time-domain analysis applying a nonlinear FE computer program.
