Advantages of Using a Time-Domain Approach for Dynamic Positioning (DP) Pipelay Studies

Abstract

Normally, the DP capability of a vessel is calculated through the use of static force equilibrium programs in which the dynamic effects are either not taken into account or taken into account by empirical load amplification factors. However, competitive and safe S-laying of large diameter pipelines in deep waters lead to large and long pipe lay vessels for which DP requirements are demanding. The power/propulsion requirement of the vessel needs to be considered from an early stage especially when accounting for the pipe laying equipment demands. This imposes a need for detailed dynamic analysis of the lay vessel. This analysis needs to include the slow drift oscillations counteracted by DP and the analysis in entirety needs to ensure the pipe string integrity is maintained. To this purpose Saipem developed in-house a time-domain simulator (FIPLA – Fully Integrated Pipe LAying) that employs all environmental forces (i.e. wind, wave, current) as well as the pipe tension on the vessel. It is used to assess the DP performances and laying capabilities of pipe lay vessels in harsh dynamic environments as well as critical areas for operations. The software can also be used to assess the performance of the vessel in case of failure of thrusters, power generators or bus bars, study DP Control System improvements, and assess the interaction between vessel, tensioner and pipe in deep and shallow waters. This paper focuses on the advantages of using dynamic simulations as an enhancement to the static DP capability charts, to produce detailed information for the DP Operator (DPO) in terms of setting of the DP parameters and to analyze critical laying events. This information can be used together with the weather forecast and can help getting the best performance out of the DP system in harsh environments, reducing downtime, improving operability and ensuring a safe operation.