MODELLING THE DYNAMIC BEHAVIOUR OF A SUPERCRITICAL ROTOR ON A FLEXIBLE FOUNDATION USING THE MECHANICAL IMPEDANCE TECHNIQUE

Rotating machinery in industry is usually placed on foundation structures that are flexible over the operational speed range and thus influence the dynamics of the coupled system. The mechanical impedance method offers a computationally efficient means of developing simple, but sufficiently accurate analytical linear models of such systems, for most practical purposes. The technique facilitates a modelling approach where a mixture of theoretical and experimental models can be incorporated into a model of the complete system. This is particularly useful when modifying existing machinery, where, for example, it may be easier and cheaper to measure the dynamics of a foundation rather than model it. In this paper a composite linear model of a super-critical rotor supported on a foundation through ball-bearings is developed using the mechanical impedance technique. Experimental results are presented to validate the model. Gyroscopic effects, although included in the model, were not investigated due to the limitations of the test rig.