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Rotating Machinery Vibration 2011 Part 15

Tham khảo tài liệu 'rotating machinery vibration 2011 part 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Additional Rotor Vibration Problem Cases 333 duced by the two correction masses has the magnitude ìndrđla 2 of the initial dynamic unbalance but 180 out of angular position with the corotational moment produced by the initial dynamic unbalance. Since a static unbalance can be negated by two in-phase correction weights appropriately placed in the same two planes as the dynamic unbalance correction masses it is clear that a complete rotor balance static dynamic of a rigid rotor can be accomplished by adding correction masses in only two planes. Since a general state of rotor unbalance is a combination of both static and dynamic unbalance the correction weights at different axial locations will generally be neither at the same angular position nor separated exactly by 180 in their relative angular positions. The defining property for so-called rigid rotors is that rotor flexibility is not a significant factor to unbalance vibration response. Therefore the two-plane balance procedure for a rigid rotor can be performed at a speed lower than the operating speed of the rotor. In practical terms this means the rotor may be balanced using vibration or dynamic force measurements at balancing spin speeds substantially lower than the rotor s in-service operating speed. 10.2. Flexible Rotors As all inclusively stated by Dr. Neville Rieger 24 A flexible rotor is defined as being any rotor that can not be effectively balanced throughout its speed range by placing suitable correction weights in two separate planes along its length. Synonymous with this definition is that a so-called flexible rotor has an operating speed range which closely approaches or encompasses one or more bending critical speeds whose rotor flexural bending contributes significantly to the corresponding critical speed mode shape s and unbalance vibration responses. Table 1 in Chapter 2 provides an introductory composite description of the increased rotor dynamic complexity produced when rotor flexibility is .