Comparison of DP performance prediction techniques for scaled models

Abstract

Utilization of Dynamic Positioning (DP) systems for offshore exploration and production of hydrocarbons is increasing due to the need to exploit deeper water depths, where mooring becomes less feasible. In conducting analysis or predictions for DP System performance, there are three common techniques: experimental investigations at reduced scale, using a simplified mooring system without thrusters; similarly scaled experiments using active DP thrusters; or, time or frequency domain numerical simulations. This paper identifies differences in DP system performance estimates, provided by each of the three methods, by using each method to analyze the same system, in identical wind and wave environments. Experiments were completed using a 1:40 scale model of a typical 99,000t monohull drillship equipped with an active DP system consisting of six azimuthing thrusters. These experiments were repeated with the vessel unpowered on two mooring systems with different stiffnesses. Physical experimental results are then compared to time-domain numerical simulations completed using Oceanic Consulting Corporation's DP simulation program. A comparison of system performance predictions provided by each method is presented.