Active control of periodic machinery vibrations

Jenkins, Michael David (1989) Active control of periodic machinery vibrations. University of Southampton, Doctoral Thesis.

Abstract

In many engineering applications the reduction of unwanted vibrations is required and therefore vibration control techniques are employed. These may be classified into `passive' and `active' methods. The fundamental difference between the two is that traditional passive methods cannot supply energy to a system whereas active methods can. In practice these methods are often applied concurrently and a particular control scheme may use a combination of the two. The question of how active elements may best be used to supplement passive systems for vibration isolation is addressed in this thesis. A theoretical and experimental assessment is presented of a combined active/passive system designed specifically for the isolation of periodic machinery vibrations. A theoretical analysis is first presented of how ideal sources of vibration combine on infinite structures, this highlights the important parameters and likely effects of various combinations of primary and secondary source. Finite element models and quadratic optimisation theory are used in order to predict the likely effect of supplementing passive isolators with active elements in order to isolate a discrete vertical primary disturbance in a more realistic source - isolation - receiver system. The frequency limits of the usefulness of the active/passive combination compared with purely passive isolation are investigated. Particular reference is given to the parameters governing the performance of the active systems', such as the finite size of the passive isolators and the number and spatial location of the error sensors used by the controller. Experimental work is presented which (i) validates the finite element techniques used to predict the performance of the active/passive isolation systems and (ii) investigates a simple active/passive mount design which can be used in practical situations to isolate a primary disturbance which is not constrained to act in the purely vertical plane. Some experimental results are presented which demonstrate the successful practical implementation on a real engine installation of a novel design of hybrid active/passive isolator. (D89636)

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