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Rotating machinery can often generate undesirable tonal noise. This is typically attributed to structure borne noise which originates from the vibration generated by the motor. In order to understand and therefore better control the structure borne noise generated the dynamics of the system must be characterised. This paper addresses the use of a subsystem based analytical approach to give insight into the system response. Subsequently the influence of different mounting conditions on the vibro-acoustic response is evaluated.

Initially the modelling technique is applied to the motor assembly in isolation by dividing it into three subassemblies; the rotor, the stator and the housing as shown in Figure 1. The model has been validated by comparison with experimental results obtained as shown in Figure 2 and gives valuable insight into the modal response of the motor assembly in isolation.

The model is then extended to account for the coupling of the motor subassembly to an external frame representing the product body. In practice this was done using resilient rubber elements to mount the motor to a rigid chassis. A measurement of the in-situ mount stiffness was then performed for model updating purposes. Subsequently the model and further experimentation gave additional insights into the influence of different mounting conditions on the vibro-acoustic response of the system. The work demonstrates the benefit of using low fidelity analytical models to build an understanding of the system dynamics and insights into the vibro-acoustic response of the system and its sensitivity to design changes.