| As for the design of DP system, it poses a great challenge for engineers to meet new requirements including sorts of analysis and design methodology, which are different from that of traditional positioning system. There are mainly two methods for DP capability analysis, i.e. DP capability polar plot and DP dynamic simulation. At first, frame and operational principle of DP system are presented, including position-measuring system, thrust system and control system, and so on. Then,taking a deepwater semi-submersible drilling platform as an example, the external loads due to wind, current and wave are calculated theoretically firstly, the wave drift force is mainly discussed. Then the DP capability polar plots including of failure modes were finished on the results of the DP thruster system and environmental loads to verify the security of the DP system. Also, DP dynamic simulation are referred to analyze the performance of DP system of the platform; the total power consumed by the DP system in time domain under different water depths and working conditions were calculated to find safe and energy saving strategies to control the DP system. Based on the results of DP dynamic simulations, the limiting water depth of the DP system was determined to ensure the safety of the platform including pipe lines and other important equipments. Finally DP tests at scale 1:50 were completed, the offset of the platform and rpm of the 8 azimuth thrusters were mainly measured and analyzed; also all thrusters intact mode and a pair of thrusters failure mode are included in model tests, the reliability of the DP system was verified. The results from calculation and experiment are compared to make sure that DP thrust system could produce the thrust as designed. All these work provide valuable reference for practical engineering application and technical methodology for DP capability analysis and evaluation as well.
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