Abstract
In experiments aimed at structural dynamics testing, it is often required to precisely control a multi-shaker system in order to replicate the conditions a machine experiences during typical operation mode. For that purpose one seeks to create a specific pattern of responses or forces motivated by actual measured data. Another use of such tuning is for diagnostic purposes where certain forcing patterns amplify hidden features of the dynamic response. For lightly-damped structures that are normally excited by magnetic or electro-magnetic shakers, this task appears to be difficult, especially when high accuracy is desired. The excitation system, under certain conditions, creates an inherent feedback between the force and the response and often some non-linearity exist in the force path. In this paper, a systematic approach for automatic tuning the amplitude and phase of a multi-shaker in an experimental system is developed. The method is particularly useful in the presence of feedback, mild non-linearity and coupling between the force and response. The usual approach is to use a linear model and to assumed that the non-linearity is small, an approach that is valid for identification of slightly non-linear structures, but which fails when precise tuning of forces is based on this identified model. It is therefore suggested to use a general linearized model, rather than a linear one, so that any irregularities attributed to the non-linearity can be handled. Throughout the paper some simulated and experimental examples of tuning are shown. The interaction mechanism between the shakers and the structure is discussed and modeled and an appropriate strategy allowing us to overcome the demonstrated difficulties, is presented.
Design and Testing of a Co-Rotating Vibration Excitation System
