In practical engineering, the rotor's response to the balanced mass varies not only in the x and y directions, but also in the phase difference of 90° due to the different stiffness of the shaft in each direction, especially the different bearing stiffness in each direction. Therefore, the axis track of the rotor is not a circle but an ellipse, as shown in FIG. 1-1.
According to the above analysis, the main vibration characteristics of rotor unbalance fault are as follows.
(1) the time domain waveform of vibration is approximately sinusoidal wave (figure 1-1).
(2) in the spectrum diagram, harmonic energy is concentrated in the fundamental frequency.And smaller higher harmonics occur, giving the entire spectrum a so-called fir-tree shape, as shown in figure 1-2.
FIG. 1-1 axis track of rotor imbalance
FIG. 1-2 rotor imbalance fault spectrum
(3) when ohm < ohm n, that is, below the critical speed, the amplitude increases with the increase of the speed;When ohm > ohm n, above the critical speed, the amplitude tends to a smaller stable value as the speed increases;When omega is close to omega n, that is, when the speed is close to the critical speed, resonance occurs and the amplitude has the maximum peak value.The vibration amplitude is sensitive to the change of rotation speed, as shown in figure 1-3.
(4) when the working speed is constant, the phase is stable.
(4) the axis trajectory of the rotor is elliptic.
(5) the precession characteristic observed from the axis trajectory is synchronous positive precession.
FIG. 1-3 main characteristics of rotor imbalance