Influence of Delayed Yielding of Magnetorheological Oils in Squeeze Film Dampers on the Vibration Attenuation of Rotors

Unbalance is the main cause of increase of time varying forces transmitted between the rotor and its frame. A flexible suspension with added damping devices is a frequently used technological solution making it possible to reduce their magnitudes. To achieve optimum performance of the damping elements, their damping effect must be controllable. This is offered by magnetorheological squeeze film dampers. Magnetorheological oils are suspensions that under influence of magnetic field behave as liquids with a yielding shear stress. This is caused by forming a chain structure of particles dispersed in carrying liquid induced by magnetic field. Even if this process is rapid, it is not instantaneous. To investigate this phenomenon and its influence on performance of the damping devices a new enhanced mathematical model of a short magnetorheological squeeze film damper has been established. The magnetorheological oil is represented by Bingham material. The steady state yielding shear stress of the magnetorheological liquid is approximated by a power function of magnetic induction. Its dependence on time is described by a differential equation of the first order. The developed mathematical model has been implemented in the computational model of a flexibly supported rigid rotor. In accordance with the theory predictions, the results of the computational simulations showed a strong influence of the delayed yielding effect on performance of the studied damping devices.