Study On Time Domain Analysis For Dynamic Positioning Simulations Of Deepwater Drillship

As the offshore industry is developing into deeper and deeper waters, Dynamic Positioning(DP) techniques are applied to more and more offshore engineering vessels. Especially fordrillship being able to operate in ultra deepwater, DP has been the key techniques for successfuldesign, building and services of it. With the support of national research project “IndependentResearch and Design of3000m Deepwater Drillship”, the paper carries out the research oftime domain analysis of drillship DP simulation. In the research process, the paper mainlyimplements the studying on numerical calculation methods of environmental loads and timedomain for DP simulation of drillship based on SIMO.Firstly, the paper begins with the calculation of wind loads and current loads of thedrillship. The paper makes a in-depth analysis of the principles of time domain analysis of DPsimulation, and studies the establishment of motion function, simulation of environmental loadsand controlling method of thruster system. On that basis, the paper analyzes the simulationprocess of time domain DP analysis in SIMO, and the effect of riser loads on DP capability isanalyzed. Through the analysis of application of SIMO, the paper establishes the simulationmethod and process of time domain analysis of DP capability which applicable to deepwaterdrillship.Secondly, beginning with the wind loads and current loads which having great effects onDP capability, the paper studies the numerical computation method of them. Through theintroduction of CFD principles, the turbulent model and wall functions used in numericalcomputation of the environmental loads of drillship are analyzed. After calculation of currentloads and wind loads of the drillship in CFD methods, the paper compares the CFD results withthe results of model tests and empirical formula. The effectiveness and reliability of the CFDmethod is proved. Meanwhile, as to the drillship, the influence of moonpool is analyzed, andthe shielding effect of wind loads between upper modules is studied.Finally, based on above research methods, the paper implements time domain analysis ofDP simulation for a drillship using SIMO. Through the analysis, the effects of controllingcoefficients and Kalman gains on the capability of DP system are studied. The method of tuning of gains coefficients under different environmental conditions is also summarized and studied.Through the analysis of ERN numbers referenced in DNV rules, the paper analyzes the DPcapability under the worst environment conditions. At last, the effect of riser loads on the DPcapability of the drillship is discussed.Through the above research contents, the paper establishes the process of time domainanalysis for DP simulation of drillship, and makes the methods of analysis of DP capabilitymore applicable.