Identification Of Vibrating Structures

INTERNATIONAL CENTRE FOR MECHANICAL SCIENCES COURSES AND LECTURES - No. 272 IDENTIFICATION OF VIBRATING STRUCTURES EDITED BY H.G. NATKE UNIVERSITY OF HANNOVER SPRINGER-VERLAG WIEN GMBH This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned specifically those of translation, reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machine or similar means, and storage in data banks. © 1982 by Springer-Verlag Wien Originally published by Springer-Verlag Wien New York in 1982 ISBN 978-3-211-81651-6 DOI 10.1007/978-3-7091-2896-1 ISBN 978-3-7091-2896-1 (eBook) PREFACE The dynamic behaviour of novel and complicated structures often needs to be investigated by system analysis and system identification, since it usually has to meet certain requirements. A priori knowledge concerning the real system is gained by system analysis and/or previous tests, and it results in a non-parametric and/or in a parametric mathematical model. The identification of system parameters, i.e. experimental system analysis, is performed using measured quantities and taking into account deterministic and stochastic errors. If results of the identification have to be compared with the results of the system analysis, and if certain error bounds are exceeded, the model has to be improved. System identification has to take into account random aspects (errors, test signals), the real dynamic behaviour (damping coupling, non-linearities) and questions concerning practical handling (including large systems, economics). A broad understanding of system identification needs as its basis an extended theory of structural vibrations and estimation (stochastic processes), and must be coupled with practical aspects including experience and validated software. The course on Identification of Vibrating Structures, the lecture notes of which are collected in this volume, deals with the topics mentioned above. First an introduction into the subject is given, and the theoretical background of vibrating structures and parameter estimation methods is dealt with. The following lectures deal with several identification methods including applications. The next papers discuss the indirect identification, that means the adjustment of theoretical models (results of system analysis) by the results of vibration tests (estimated values). These parts are supplemented by a presentation of an example of commercially available hard- and software including applications. For the practical application of system identification concerning large and complicated structures synthesizing techniques (substructure techniques) including error analysis are necessary, which are the subject of the following two papers, followed by identification of non-linear systems. The closing lectures deal with modern developments, firstly from the point of view of control theory, and secondly by coming from the theory of stochastic systems. The last three lectures deal with theoretical aspects, including examples of (simple) systems mainly with regard to non-deterministic system analysis. This seems to be a flexible and far-reaching tool worthwhile studying, because several applications with regard to early failure detection are possible, and it may give impulses towards the identification of linear and non-linear structures. I wish to express my thanks to the coauthors, who made a very successful course possible at Udine, and I hope this volume will be equally well received by the reader. H.G. Natke CONTENTS Page Identification of vibrating structures: an introduction by H.G. Natke . . . . . . . . . . . . . . . . . . . . 1 Multi-degree-of-freedom systems - a review by H.G. Natke . . . . .