Structural Dynamics and Modal Analysis
Structural dynamics is an area of research that studies the response of structures to applied loads. The hard disk drive in your laptop, a car driving down the road, and an office building subjected to an earthquake, are all examples of dynamic systems subjected to time-varying loading conditions. Experimental modal analysis is the process of characterizing the dynamic behavior of a structure in terms of its modal parameters, namely natural frequency, damping and mode shapes. These characteristics can be defined independently from the loads applied to the system and the response of the system. Modal analysis is used to develop a dynamic model of a structure which can be used for: troubleshooting, simulation and prediction, optimization, and diagnostics, and health monitoring.
This research involves developing techniques for improved modal test measurements. Impact hammer and shaker testing are two commonly used excitation techniques in experimental modal analysis. The Vibration & Acoustics Laboratory is outfitted with state-of-the-art vibration testing equipment including piezoelectric accelerometers, impact hammers, electrodynamic shakers, National Instrument data acquisition hardware and a 16-channel LMS SCADAS data acquisition system. Current work aims to more accurately develop test specifications (as in selecting the desired frequency range), to better define instrumentation (as in selecting measurement locations and excitation techniques), and to more realistically simulate boundary conditions with proper supports.
One area of research involves testing of structures that exhibit the pseudo-repeated root phenomena. Repeated roots refer to the situation where one of the complex roots (modal frequency, eigenvalue, pole, etc.) occurs more than once in the characteristic equation. Repeated roots or pseudo-repeated roots (when two modal frequencies are close together) exhibit unique modal vectors but these can be difficult to detect unless the test reference points are properly selected. This situation presents an unresolved research question since how does one select the proper reference points without knowledge of the dynamic model in advance.
- Allemang, R. J., 2008, Vibrations: Experimental Modal Analysis. Univ of Cincinnati.
- Avitable, P., 2008, Basic Modal Analysis Seminar, LMS International, Troy, MI.
- Craig, R.R., Kurdila, 2006, A.J., Fundamentals of Structural Dynamics, 2nd Ed. Wiley, NJ.
- Ewins, D.J., Inman, D.J., 2001, Structural Dynamics @ 2000: current status and future directions, Research Studies Press Ltd., England.