TY - THES A1 - Zabel, Volkmar ED - Könke, Carsten ED - Lahmer, Tom ED - Rabczuk, Timon T1 - Operational modal analysis - Theory and aspects of application in civil engineering N2 - In recent years the demand on dynamic analyses of existing structures in civil engineering has remarkably increased. These analyses are mainly based on numerical models. Accordingly, the generated results depend on the quality of the used models. Therefore it is very important that the models describe the considered systems such that the behaviour of the physical structure is realistically represented. As any model is based on assumptions, there is always a certain degree of uncertainty present in the results of a simulation based on the respective numerical model. To minimise these uncertainties in the prediction of the response of a structure to a certain loading, it has become common practice to update or calibrate the parameters of a numerical model based on observations of the structural behaviour of the respective existing system. The determination of the behaviour of an existing structure requires experimental investigations. If the numerical analyses concern the dynamic response of a structure it is sensible to direct the experimental investigations towards the identification of the dynamic structural behaviour which is determined by the modal parameters of the system. In consequence, several methods for the experimental identification of modal parameters have been developed since the 1980ies. Due to various technical restraints in civil engineering which limit the possibilities to excitate a structure with economically reasonable effort, several methods have been developed that allow a modal identification form tests with an ambient excitation. The approach of identifying modal parameters only from measurements of the structural response without precise knowledge of the excitation is known as output-only or operational modal analysis. Since operational modal analysis (OMA) can be considered as a link between numerical modelling and simulation on the one hand and the dynamic behaviour of an existing structure on the other hand, the respective algorithms connect both the concepts of structural dynamics and mathematical tools applied within the processing of experimental data. Accordingly, the related theoretical topics are revised after an introduction into the topic. Several OMA methods have been developed over the last decades. The most established algorithms are presented here and their application is illustrated by means of both a small numerical and an experimental example. Since experimentally obtained results always underly manifold influences, an appropriate postprocessing of the results is necessary for a respective quality assessment. This quality assessment does not only require respective indicators but should also include the quantification of uncertainties. One special feature in modal testing is that it is common to instrument the structure in different sensor setups to improve the spacial resolution of identified mode shapes. The modal information identified from tests in several setups needs to be merged a posteriori. Algorithms to cope with this problem are also presented. Due to the fact that the amount of data generated in modal tests can become very large, manual processing can become extremely expensive or even impossible, for example in the case of a long-term continuous structural monitoring. In these situations an automated analysis and postprocessing are essential. Descriptions of respective methodologies are therefore also included in this work. Every structural system in civil engineering is unique and so also every identification of modal parameters has its specific challenges. Some aspects that can be faced in practical applications of operational modal analysis are presented and discussed in a chapter that is dedicated specific problems that an analyst may have to overcome. Case studies of systems with very close modes, with limited accessibility as well as the application of different OMA methods are described and discussed. In this context the focus is put on several types of uncertainty that may occur in the multiple stages of an operational modal analysis. In literature only very specific uncertainties at certain stages of the analysis are addressed. Here, the topic of uncertainties has been considered in a broader sense and approaches for treating respective problems are suggested. Eventually, it is concluded that the methodologies of operatinal modal analysis and related technical solutions have been well-engineered already. However, as in any discipline that includes experiments, a certain degree of uncertainty always remains in the results. From these conclusions has been derived a demand for further research and development that should be directed towards the minimisation of these uncertainties and to a respective optimisation of the steps and corresponding parameters included in an operational modal analysis. T3 - ISM-Bericht // Institut für Strukturmechanik, Bauhaus-Universität Weimar - 2019,5 KW - Modalanalyse KW - Strukturdynamik KW - Operational modal analysis KW - modal analysis KW - structural dynamics Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20191030-40061 ER - TY - THES A1 - Zabel, Volkmar T1 - Anwendungen der Wavelet-Transformation in der Systemidentifikation T1 - Applications of Wavelet Analysis in System Identification N2 - Die meisten traditionellen Methoden der Systemidentifikation beruhen auf der Abbildung der Meßwerte entweder im Zeit- oder im Frequenzbereich. In jüngerer Zeit wurden im Zusammenhang mit der Systemidentifikation Verfahren entwicklet, die auf der Anwendung der Wavelet-Transformation beruhen. Das Ziel dieser Arbeit war, einen Algorithmus zu entwickeln, der die Identifikation von Parametern eines Finite-Elemente-Modells, das ein experimentell untersuchtes mechanisches System beschreibt, ermöglicht. Es wurde eine Methode erarbeitet, mit deren Hilfe die gesuchten Parameter durch Lösen eines Systems von Bewegungsgleichungen im Zeit-Skalen-Bereich ermittelt werden. Durch die Anwendung dieser Darstellung können Probleme, die durch Rauschanteile in den Meßdaten entstehen, reduziert werden. Die Ergebnisse numerischer Simulation und einer experimentellen Studie bestätigen die Vorteile einer Anwendung der Wavelet-Transformation in der vorgeschlagenen Weise. ... N2 - Most traditional methods in system identification are based on the analysis of measured data in either the time or frequency domain. In recent years some procedures were developed that apply wavelet analysis in the context of system identification. The purpose of this study was to develop an algorithm that allows for identifying the parameters of a finite element model that describes a tested mechanical system. A method has been derived that determines the desired parameters by solving a system of equations of motion in the time-scale domain. ... KW - Wavelet KW - Systemidentifikation KW - Verbindungskoeffizienten KW - Schädigungsindikator KW - Dynamik KW - Strukturdynamik KW - wavelet KW - system identification KW - connection coefficients KW - damage indicator KW - dynamics Y1 - 2003 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20040202-66 ER -