Вестник МГТУ. 2018, №4.

Вестник МГТУ. 2018. Т. 21, № 4. С. 566-576. DOI: 10.21443/1560-9278-2018-21-4-566-576 these moments of time, namely: 880-1 780 s. They clearly demonstrate the behavior of accelerations in the zone of the paralysis modes. Fig. 9. The linear acceleration of the ship and the angular acceleration of the screw in the interval 380-920 s (the paralysis mode) Рис. 9. Ускорения: линейное судна и угловое винта в интервале времени 380-920 с (паральный режим) Results and discussions The answer to the question whether the paralysis mode generates oscillations with higher frequencies than the base frequency f 0 of the engine torque change (here it is equal to f 0 = 1 / 1200 s) seems to be the most notable one. For this purpose, the fast Fourier transform has been performed using the built-in function fft() included in MathCad. We have applied it to the vessel's velocity v, and to the linear acceleration of the vessel and the angular one of the propeller: Fig. 10. The spectra of the ship's velocity, accelerations of the linear ship and angular screw Рис. 10. Спектры скорости хода, ускорений линейного судна и углового винта The obtained spectra are represented by the curves in Fig. 10. The upper graph of the figure reveals that the both accelerations have almost the same frequency composition, i. e. the paralysis mode does not lead to a special behavior of the screw revolutions. In the graph, three harmonics - multiples of the base frequency: 10х/ 0 , 17xf and 24xf o - can be noted as significant. The fact is that the high frequencies occur, but they are found both in linear and angular accelerations. The bottom graph of Fig. 10 presents the spectrum of the angular acceleration DN f and spectrum V f of the vessel velocity to be compared. It clearly shows that the velocity spectrum has only two harmonics - base and 10-fold. At the same time, the angular acceleration has a number of harmonics of small amplitudes, where speed fluctuations are practically absent. 573