Workspace optimization of azimuth thrusters applied by dynamic positioning
【Abstract】[Objectives] In order to make the dynamic positioning of azimuth thrusters respond to external environmental force in time, avoid the large-scale rotation of the thrusters, and achieve high-precision dynamic fixed-point positioning control, we carried out the research on optimal workspaces of azimuth thrusters. [Methods] Taking the dynamic positioning self-driven model with two azimuth thrusters and a lateral thruster as the research object, we analyzed the problem of the current thrust-allocation singularity optimization index and considered the thrust limits of the thrusters. The method of traversing the thrust and azimuth angles of the thrusters to establish an axial maximum capability matrix is applied. According to the mean and variance of external environmental force, the minimum axial capability requirements are calculated; the optimal workspaces of the thrusters in different external environments are determined in combination with the prohibition angle, and a new thrust-allocation logic framework is proposed. The fixed-point positioning experiments of a dynamic-positioning ship model based on the traditional singularity index and the optimal workspace are carried out. [Results] The experimental results show that the proposed method can overcome the shortcomings of the previous singularity index and achieve the control accuracy of 0.1 m in radii and that of 0.5° in heading angles under the thruster azimuth within a range of 50°. [Conclusions] This method can replace the singularity index; it also satisfies the requirements of the ship-model dynamic positioning experiment and has certain practical engineering values.
【Keywords】 dynamic positioning; azimuth thruster; thrust allocation; optimal workspace; singularity;
(Translated by HAN R)
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