A Magnetic Damper for First Mode Vibration Reduction in Multimass Flexible Rotors

Abstract

Many r o t a t i n g machines such as compressors, t u r b i n e s and pumps have l o n t h i n s h a f t s with r e s u l t i n g v i b r a t i o n problems. They would b e n e f i t from a d d i t i o n a f damping n e a r t h e c e n t e r of t h e s h a f t . t h e s e machines because t h e y can o p e r a t e i n t h e working f l u i d environment u n l i k e conventional b e a r i n g s . This paper d e s c r i b e s an experimental test r i g which was set up with a long t h i n s h a f t and s e v e r a l masses t o r e p r e s e n t a f l e x i b l e s h a f t machine.An active m a n e t i c damper was placed i n t h r e e l o c a t i o n s : n e a r t h e midspan, n e a r one midspan l o c a t i o n reduced t h e f i r s t mode v i b r a t i o n 82X, t h e d i s k l o c a t i o n reduced it75% and t h e b e a r i n g l o c a t i o n a t t a i n e d a 74% reduction. Magnetic damper s t i f f n e s s and damping v a l u e s used t o o b t a i n t h e s e reductions were only a few percent of t h e bearing s t i f f n e s s and damping v a l u e s . A t h e o r e t i c a l model of both t h e r o t o r and t h e damper was developed and compared t o t h e measured r e s u l t s . Magnetic dampers have t h e p o t e n t i a l t o be employed i n end d i s k , an 8 c l o s e t o t h e bearing. With t y p i c a l c o n t r o l parameter s e t t i n g s , t h eThe agreement was good.

Reduction of subsynchronous vibrations in a single-disk rotor using an active magnetic damper

“…Nikolajsen et al (1979) demonstrated the use of AMDs for the suppression of vibrations in long transmission shafts. Kasarda et al (1990) demonstrated experimentally that the location of the damper in a multimass rotor plays an important role in its effectiveness because of the rotor mode shapes, and reported that significant reductions of up to 88% in synchronous vibrations at the first and second critical speeds were attainable. The work presented in this paper expands on previous studies and shows experimental results demonstrating the effectiveness of an AMD to reduce subsynchronous vibrations, such as those caused by instability mechanisms, in a single-disk flexible rotor.…”

Magnetic Bearing Control of Flexible Shaft Vibrations Based on Multiaccess Velocity-Displacement Feedback

“…Some of the fundamental work done by Alliare, Humphris et al, [1,2,3,4,7,8,9,11], gave useful experimental insight into the contribution of the bearing stiffness and damping to the general rortor dynamic behaviour. Results of their experimental work with different circuit band widths were also compared in terms of the achieved stability regions.…”

Vibration reduction in a hollow-shaft rotor using flexibly-mounted internal-stator magnetic bearings

“…It was found in this work (Kasarda et al, 1990;Nikolajsen et al, 1979) that a very substantial reduction in vibration amplitudes could be achieved through the used of these "Active Magnetic Dampers" (AMDs).…”