Experimental assessment of polynomial nonlinear state-space and nonlinear-mode models for near-resonant vibrations

• Published in: Mechanical systems and signal processing Vol. 143; p. 106796
• Main Authors: Scheel, Maren, Kleyman, Gleb, Tatar, Ali, Brake, Matthew R.W., Peter, Simon, Noël, Jean-Philippe, Allen, Matthew S., Krack, Malte
• Format: Journal Article
• Language: English
• Published: Berlin Elsevier Ltd 01.09.2020; Elsevier BV
• Subjects: Basis functions; Broadband; Cantilever beams; Excitation; Identification methods; Jointed structures; Lap joints; Modal testing; Nonlinear modal analysis; Nonlinear normal modes; Nonlinear system identification; Nonlinear systems; Phase locked loops; Polynomial nonlinear state-space identification; Polynomials; Resonance; State space models; System identification; Modal testing; Nonlinear normal modes; Nonlinear modal analysis; Jointed structures; Polynomial nonlinear state-space identification; Nonlinear system identification
• ISSN: 0888-3270; 1096-1216
• DOI: 10.1016/j.ymssp.2020.106796

•Two different nonlinear models are identified for two experimental test rigs.•The models are used to predict dynamic behavior under sine (-sweep) excitations.•The modal model is accurate for sine excitation close to resonance.•The modal model is sensitive for uncontrolled sweeps if the excitation force drops.•Polynomial nonlinear state-space models highly depend on the used training data. In the present paper, two existing nonlinear system identification methodologies are used to identify data-driven models. The first methodology focuses on identifying the system using steady-state excitations. To accomplish this, a phase-locked loop controller is implemented to acquire periodic oscillations near resonance and construct a nonlinear-mode model. This model is based on amplitude-dependent modal properties, i.e. does not require nonlinear basis functions. The second methodology exploits uncontrolled experiments with broadband random inputs to build polynomial nonlinear state-space models using advanced system identification tools. The methods are applied to two experimental test rigs, a magnetic cantilever beam and a free-free beam with a lap joint. The respective models obtained by either method for both specimens are then challenged to predict dynamic, near-resonant behavior observed under different sine and sine-sweep excitations. The vibration prediction of the nonlinear-mode and state-space models clearly highlight capabilities and limitations. The nonlinear-mode model, by design, yields a perfect match at resonance peaks and high accuracy in close vicinity. However, it is limited to well-spaced modes and sinusoidal excitation. The state-space model covers a wider dynamic range, including transient excitations. However, the real-life nonlinearities considered in this study can only be approximated by polynomial basis functions. Consequently, the identified state-space models are found to be highly input-dependent, in particular for sinusoidal excitations where they are found to lead to a low predictive capability.