Abstract No.C180227-242
Author name(s): Jinhui HE1,2, Haibin ZHANG2, Renchuan ZHU1, Baohe YANG 2
Company: 1. State Key Laboratory of Ocean Engineering, Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, Shanghai Jiaotong University, China; 2. Marine Design & Research Institute of China, China
Methods of calculating environmental loads are introduced, including wave loads, current loads and wind loads. A method considered wind force direction correction and shielding coefficient among different parts of drillship is introduced specially for wind load calculation. In this wind load calculation method, three correction coefficients determined by wind tunnel test are brought in to improve the precision of wind load calculation. To maintain the position, thrusters should generate enough force to balance the environmental loads. But in capacity calculation for a DP3 drillship, DP system normally with no less than six azimuth thrusters provides countless solutions of thruster force distribution. To find out the best solution with minimum power consumption, a nonlinear constrained optimization problem is solved by SQP method (Sequence Quadratic Programming). Calculation of a DP3 deepwater drillship with no less than six thrusters is carried out based on the environmental load calculation method and capacity calculation method. According to DP3-class requirement, DP capacity of intact mode, single-thruster-failure mode and one-switchboard-failure mode are estimated. To verify the DP capacity calculation, a time-domain simulation of DP is carried out at the end of the paper to obtain the drillship positioning precision, motion track, and also the time signal of all thrusters including force signal and direction signal. And then the verification is carried out by comparing the average value of the signal and DP capacity calculation result.
KEY WORDS: DP3 drillship; dynamic positioning; time-domain simulation
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