Executive Summary : | Many rotating systems such as the driveline of an automobile, railway axle, airplanes and helicopter, etc. are examples where rotors are indispensable. These shaft-rotors are encased in bearings supported by structure and rotate over a wide range of angular speed. Hence, the rotor imitating an axle becomes a critical component for ease of locomotion. During the operation of a rotor-bearing assembly, analysis of torsional vibrations and critical speed are of prime importance to monitor. Usually, rotors operating in different locomotive applications run over their first critical speed, even second and third critical speed too. When passing over these critical speeds, amplitude builds up and reaches the maximum at resonance. This excessive amplitude of vibrations will then be transmitted to the entire structure and the possibility of structural damage becomes very high. A generic rotor bearing assembly has a fixed value of stiffness and damping; consequently, the attenuation of the high amplitude vibrations is difficult (if not possible) when a rotor operates close to critical speed. Thus, if damping and stiffness of a rotor bearing system can be changed, the risk of failure of the rotor or bearing will be minimized. For the active control of such vibrations, either the natural frequency is required to be shifted to avoid the condition of resonance or the amplitude of vibrations is required to be attenuated. The natural frequencies are governed by the mass of the rotating element and the equivalent stiffness of rotor-bearing, which are non-tunable parameters. Both shifting of natural frequency and enhancing damping can be possible by using shape memory alloy (SMA). Components made of SMA exhibit different stiffness upon heating and cooling due to phase change transformation, i.e., the stiffness of SMA is temperature dependent. Underlying this physics, development of novel smart bearing systems for vibration isolation based on SMA is proposed for vibration isolation. These novel smart bearings will be capable of dynamically changing its stiffness during acceleration or deceleration, thereby keeping its critical speed far from natural frequency to avoid any possible resonance causing structural damage. The pseudoelastic property of the SMA will be used to enhance the passive damping. Experimental investigations will be carried out upon the development of smart bearing to analyze the performance related to SMA characteristics and vibration level reduction. In addition, a comparative analysis will also be conducted to showcase the performance of smart bearings for vibration isolation in locomotives. |