Response-Controlled Stepped-Sine Test (RCT): A New Approach in Measuring Frequency Responses of Nonlinear Systems

Date

2020-2-10

Author

Özgüven, Hasan Nevzat
Karaağaçlı, Taylan

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As a result of being widely used in linear experimental modal analysis for many years, force-controlled stepped-sine test approach is the first method that comes to mind in measuring frequency responses of nonlinear systems as well. However, in testing structures showing strong nonlinearity, force-control test strategy is not capable of capturing unstable branch of a nonlinear frequency response, which results in jump phenomenon in stepped-sine testing. On the other hand, experimental continuation methods capable of tracing unstable branches rely on sophisticated control algorithms by giving up industrial standards. Moreover, determination of nonlinear modal damping ratio is a considerable issue in these methods. This paper presents a novel approach called Response-Controlled stepped-sine Test (RCT). By combining RCT with a new concept called Harmonic Force Surface (HFS), unstable branches of frequency responses of nonlinear systems can be measured employing standard equipment, i.e. commercial hardware and software, which makes it very attractive especially for industrial applications. Furthermore, determination of nonlinear modal damping ratio in RCT is quite straightforward by making use of quasi-linearization of frequency responses of nonlinear structures. This approach has successfully been used by the authors in two recent works: In developing new methods for experimental modal analysis of nonlinear structures, and for nonparametric identification of nonlinearity. In this paper, the capability of RCT to capture unstable branches of frequency response curves in strongly nonlinear structures is demonstrated on a bench mark test setup and on a control fin actuation mechanism of a real missile.

Subject Keywords

Harmonic force surface, Nonlinear frequency response, Unstable branch, Nonlinear system identification, Response-controlled stepped-sine testing

URI

https://hdl.handle.net/11511/105237

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Department of Mechanical Engineering, Conference / Seminar