Abstract: Structural resonance is one of the common fault types that may induce the large scale structure vibration. Generally, the problem is solved by improving the structure to adjust its own natural frequencies. Due to the difficulty of structural modification, the damping scheme is often used to suppress the vibration. Unfortunately, the resonance property still remains unchanged. In this paper, a new technical thought is proposed, which can change the natural frequencies of the structure by virtue of bottom load adjustment without any structural alteration or extra damping addition. By using the finite element method, the generator model is established and both the static and the modal analyses are carried out. The impacts of different bottom load distribution on the nature frequencies are calculated. Then, the experimental test is conducted. With the stepped gaskets adjusted to change the bottom load distribution, the natural frequencies are obtained through vibration modal testing. Both the theoretical analysis and the experimental results indicate that by altering the bottom load distribution the natural frequencies can be adjusted effectively and kept away from the working frequency such that structural resonance is avoided. This method has been applied for the generator of Qinshan No.2 Nuclear Power Plant, where the problem of structural resonance is successfully solved.

Key words: generator, vibration, structure, finite element, bottom load distribution, nature frequency