Search

Output-only modal analysis allows the estimation of modal models for structures in their real in-operation conditions. One of the main drawbacks of this approach is that a part of the modal model can no longer be estimated. As a result, the operational mode shape estimates remain incorrectly scaled, dependent on the unknown level of ambient excitation. This incompleteness somewhat restricts the applicability of in-operation modal models. No techniques were previously available for the normalisation of operational mode shapes purely based on experimental output-only data. Recently, a sensitivity-based normalisation approach, that can be used for output-only data, was proposed and successfully tested on simple laboratory structures. The principle behind the normalisation technique is the interpretation of the shifts in modal parameters induced by well-known structural modifications. In this contribution, the sensitivity-based normalisation approach was experimentally validated on a basis of vibration experiments performed on a tractor-sprayer combination. (C) 2003 Silsoe Research Institute. All rights reserved Published by Elsevier Science Ltd.

It is a well-known fact that the linear dynamic behaviour of mechanical structures can be studied by modelling the relation between force(s) input(s)], acting on the structure, and their resulting structural vibration response(s) [output(s)]. For industrial structures, in their real in-operation conditions, it often becomes hard (or impossible) to experimentally measure the excitation. For this reason, attention has been paid to the development of system identification techniques that work on a basis of response data only. The use of such techniques allows the identification of modal models for structures excited by unknown ambient noise and vibration. In this contribution, controlled vibration experiments were conducted on a sprayer boom that was mounted on a tractor. A comparison was made between the results of a classic input-output and output-only modal analysis based on maximum likelihood system identification techniques. Due to the interaction between the dynamic artificial excitation device and the test structure, the output-only approach modelled the excitation device together with the test structure. The identified output-only modal parameters were validated by direct comparison to the identification results obtained on a classic input-output transfer function data set between the generator input signal and the structural responses. (C) 2003 Silsoe Research Institute. All rights reserved Published by Elsevier Science Ltd.