Dynamic Uncoupling of a System Model for Component Identification David Cloutier, Dr. Peter Avitabile Structural Dynamics and Acoustic Systems Laboratory University of Massachusetts Lowell One University Avenue Lowell, Massachusetts 01854 ABSTRACT System model description from component modes is a common approach for model development. Dynamic uncoupling of a system model to obtain component information is very useful and currently under significant research. Uncoupling can be performed different ways and several approaches are considered for the evaluation of component uncoupling from the system. These approaches are compared with several models to better understand the strengths and weaknesses of each of the techniques often employed. Several cases using both analytical models and experimental data sets are studied and shown in the paper. INTRODUCTION While system assembly modeling has been a valuable tool for many years [1-6], current efforts have also shifted to include decoupling of system models for component identification [7-17]. System assembly is typically performed using frequency response functions of two components, such as Frequency Based Substructuring, or by using modal information of the two components to obtain the fully assembled system characteristics. Dynamic uncoupling of a system presents the inverse problem, where an individual component’s characteristics are desired while measurements are only available on the fully assembled system. Very similar problems found in system assembly are also present in uncoupling. These problems include measurement inaccuracies inherent in test data, inability to measure all coupling degrees of freedom (ie. rotational degrees of freedom) and modal truncation. This paper presents several decoupling techniques performed on analytical and experimental models to determine their sensitivities to measurement inaccuracies. THEORY In general, two components A and B can be used to form a system representation AB. The two components are coupled at a connection point(s), and external forces may be applied at coupling degrees of freedom (DOF) ({f}c), or internal DOF ({f}i). For the work presented in this paper, the general system coupling equations are presented first, followed by the three separate decoupling approaches investigated. General System Modeling Equations response of the system AB can then be written as, T. Proulx (ed.), Linking Models and Experiments, Volume 2, Conference Proceedings of the Society for Experimental Mechanics Series 5, 173 Frequency response functions (FRF) of a structure can be portioned into coupling DOF (c) and internal DOF (i). The DOI 10.1007/978-1-4419-9305-2_12, © The Society for Experimental Mechanics, Inc. 2011
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