Peculiarities of Torsional Vibrations in Electrically Driven Azimuth Thrusters

The article presents the research results of the peculiarities of torsional vibrations development and calculation in electrically driven azimuth thrusters and proves the efficiency and generality of the new MATHCAD program being specially worked out for the calculation expertise performed by the Register.
Preceeding from the review of “Vulkan” company reports it has been ascertained that the critical parameters of torsional vibrations for azimuth thrusters are not stresses in shafts, but elastic moments in flexible coupling and toothing, as well as power loss for heating the flexible coupling rubber. Besides, the harmonic disturbance torques of the first and second blade order coming from the propeller and reduced to the electric motor speed shall be considered.

Other peculiarities of azimuth thruster calculations are as follows: introducing of zero masses and infinite liquids (zero compliance) to the scheme of gyrating mass system to evaluate the load on spline drives and toothing; algebraic vector summation of oscillations of different orders at zero values of phase displacement, free motion calculation using HOLZER analysis, etc. 
The said peculiarities were considered in the development of a new program using HOLZER analysis carried out in MATHCAD. Comparison of calculation results provided by this program with data submitted by the firms have demonstrated a satisfactory agreement not only between free motion parameters, but also between load amplitudes in the system elements due to cavity and forced oscillations of blade orders. This indirectly proves the correctness and universality of the damping accounting concept for system elements, as stipulated by the new program.

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UDC:  629/12-233/12
Author(s):  L.V. Efremov, M.Yu. Ivanov
Pages:  234 - 244