Modal Balancing of Flexible Rotors with Distributed Unbalance

One of the major causes for rotor vibration is unbalance. Concentrated lumped mass models are adopted in most of the finite element approach for modeling unbalances and subsequent balancing in rotating systems. But this assumption may not be appropriate for long slender rotors with unbalances distributed along the length of the rotor. A polynomial curve for eccentricity distribution with finite element modeling is used to identify the distributed unbalance. The unbalance distributions are estimated by measuring the vibration responses at a low speed. These eccentricity distribution functions are used to balance the rotor at its first bending critical speed using modal balancing method in a single trial run and using a single balancing plane. The method thus avoids multiple trial runs required for modal balancing of flexible rotors. Experiments are carried out on a test rig to verify the balancing method.