In the forced vibration analysis, it is assumed that there are eccentric masses distributed on the cast rotor, the eccentricity is Δ E1 = 0.03mm ‘, and the azimuth angles of eccentric masses are different. Fig. 1 shows the forced vibration characteristics of the rotor with and without considering the foundation characteristics. Because the stress of the whole rotor is asymmetric, the vibration mode of the rotor is asymmetric without considering the characteristics of the foundation. However, after considering the characteristics of the foundation, the asymmetry degree of the vibration mode of the rotor changes to a certain extent because the rotation of the foundation around the horizontal axis is considered.
From the comparison of amplitude frequency characteristics, it can be seen that the number of resonance points of the rotor increases after considering the foundation characteristics, and the increased resonance points correspond to the second order natural frequency of the system, and the resonance amplitude of the rotor considering the foundation characteristics is less than that without considering the foundation characteristics, which is because the foundation damping plays a role in reducing the amplitude. In addition, the resonance amplitude of the rotor is significantly larger than that of the foundation when considering the earth secrecy characteristics.
Fig. 2-fig. 4 show the influence of the foundation height h on the forced vibration of the rotor. It can be seen from the amplitude frequency response (Fig. 2) that when the foundation height increases, the resonance speed of the same order will decrease. Fig. 3 shows the variation curve of each resonance amplitude with the foundation height H. it can be seen that the resonance amplitude of each order increases nonlinearly with the increase of H. Figure 4 shows the vibration mode of the rotor at different h speeds. The larger the H value is, the closer the shape of the rotor is to that without considering the characteristics of the foundation and the earth.
Fig.5-fig.7 shows the influence of the embedded depth e of the foundation on the forced vibration of the rotor. It can be seen from the amplitude frequency response (Fig. 5) that with the increase of the embedded depth of the foundation, the resonance speed of the same order will increase, especially the first resonance speed. Fig. 6 shows the variation curve of the resonance amplitude of each order with the embedded depth e of the foundation. It can be seen that the resonance amplitude of each order decreases nonlinearly with the increase of the embedded depth, because the damping ratio increases with the increase of the embedded depth. Figure 7 shows the vibration mode of the rotor at different working speeds when e is larger. When e is larger, the shape of the rotor is closer to that without considering the characteristics of the foundation and foundation. This is because with the increase of E, the stiffness of the foundation increases, and the larger the stiffness of the foundation is, the closer it is to that when the foundation is regarded as rigid.
Figure 8 and Figure 9 show the influence of foundation bottom size on amplitude frequency response and mode shape of rotor respectively. It can be seen that with the increase of foundation width b, the amplitude frequency response and vibration mode are closer to those without considering foundation characteristics. When the foundation width increases to B = 3M, the amplitude frequency curve is almost the same as that without considering foundation and foundation characteristics. That is to say, when the foundation size is large enough, the foundation can be regarded as rigid in vibration analysis.