Chapter 4 Implementing Experimental Substructuring in Abaqus Benjamin Moldenhauer, Matt Allen, Daniel Roettgen, and Brian Owens Abstract In many applications, components that are difficult or inconvenient to represent as a finite element model (FEM) are instead experimentally characterized to capture their contribution to the overall dynamics of an assembly. A recent advance in experimental substructuring, the Transmission Simulator method, has proven promising for coupling an experimentally identified model to analytical FEMs. While in typical applications all experimental and FEM data is imported into MATLAB and assembled in modal coordinates, it would be preferable to perform equivalent operations in finite element software where large models are readily handled and results are easily visualized and post-processed. This work details a process for importing experimental modal models into the Dassault Systèmes® SIMULIA™ Abaqus finite element analysis software suite through an application of the Transmission Simulator method. In this approach, after decoupling the TS from the experimental subsystem in MATLAB, the result is represented as single degree-of-freedom (DOF) spring-mass oscillators in Abaqus. These are coupled to the native Abaqus FEM by implementing the substructuring constraint equations as linear equation multipoint constraints between the necessary DOF. This approach is shown to perform very well in an analytical test case and reasonably well in an experimental test case. The limiting factors appear to be the quality of measured data and curve fitting used in defining the modal properties of the experimental subsystem, the quantity and location of constraint DOF, and the selection of modes used to represent each subsystem. These determine the quality of the decoupled experimental model, which dictates how accurate the result will be after coupling it to the FEM subsystem. Keywords Experimental substructuring · Transmission simulator · Abaqus · Decoupling · Finite element analysis 4.1 Introduction When creating a finite element model (FEM) of a structure, it is common practice to simplify intricate geometries and interfaces, such as removing fillets and threads and assuming bonded contacts. It is appropriate to make these generalizations when doing so reduces model complexity and solution time without significantly degrading the accuracy of the results. In cases where an intricate component cannot be simplified it may be more efficient to instead conduct a modal test on the part and capture its dynamic response experimentally. This physically based model can then be constrained to the adjacent FEMs with experimental substructuring techniques, allowing for the dynamics of the complete structure to be evaluated. Experimental substructuring has been an active area of structural dynamics research for several decades, the highlights of which can be seen in [1]. A recent development by Allen et al. [2], the Transmission Simulator (TS) method, allows for very efficient coupling of experimental and analytical substructures with excellent accuracy. Usually the modal properties of each subsystem are passed into MATLAB, where performing the necessary calculations is trivial. However, for the uninitiated, using MATLAB to import and handle each component’s data and post-process results can be cumbersome, error prone, and time consuming. The accessibility and usefulness of the TS method could be vastly improved if the experimental data could be imported into finite element software and the substructuring calculations equivalently performed within. This would allow the analyst to leverage the capabilities of that software, where large models are managed efficiently, and extensive capabilities exist for visualizing and processing results. This paper presents a framework for performing TS method experimental B. Moldenhauer ( ) ·M. Allen University of Wisconsin – Madison, Madison, Wisconsin, USA e-mail: bmoldenhauer@wisc.edu D. Roettgen · B. Owens Sandia National Laboratories, Albuquerque, NM, USA © The Society for Experimental Mechanics, Inc. 2021 A. Linderholt et al. (eds.), Dynamic Substructures, Volume 4, Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-47630-4_4 43
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