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is found that signals in these bands are uncorrelated, and the damage changes mainly

the properties of the signals in the high-frequency band. These changes are the result

of narrow-band high-frequency modulation of the rotational harmonics of the motor

shaft, the most powerful of which is the first harmonic. In the spectrum of the high-

frequency component, two sets of sharp peaks are distinguished. The frequencies of

the peak values are separated by an interval equal to twice the shaft rotation

frequency. It was established that this spectrum is mixed. The deterministic

component is extracted and it is shown that its power is close to the power of the

stochastic component. Using band filtering, each stochastic component is selected

and it is shown that their correlation functions do not depend on time, but the jointly

correlation functions change periodically, and their time-averaged value is equal to

zero. The quadrature components of both high-frequency sets of peaks were extracted

and their correlation analysis was carried out using the Hilbert transform. It is shown

that the auto- and cross-correlation functions of the quadratures are monotonically

decaying functions of lag. It was established that the values of the correlation

components of the signal calculated on the basis of the correlation functions of the

quadratures, and the values calculated directly from the high-frequency part of the

signal spectrum practically coincide. This fact can be considered as a confirmation of

a model, which was proposed to describe the correlation structure of vibrations.

Establishing this structure made it possible to make a conclusion about the source of

increased vibration of the mechanism.

In the Fourth Chapter the results of experimental studies of vibrations, caused

by friction during the rotation of bodies according to the disc-pad scheme are

presented. Equipment and methods for investigations of the tribological properties of

materials are described. The tests with a samples made of 40 KHN steel under dry

and liquid friction (lubricant I-20) under various loads were performed. The analysis

of time series was carried out using PNRP methods with an unknown period. At the

initial stages of experiment, the general properties of the correlation functions of the

stationary approximation of the PNRP and the spectral components of vibrations

were established. Quasi-optimal quadratic functionals were used to detect of the
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