https://popups.uliege.be/2684-6500/index.php?id=218 Publications of Auteurs H. Nevzat Özgüven fr 0 https://popups.uliege.be/2684-6500/index.php?id=367 Decoupling methods based on measured Frequency Response Functions (FRFs) are well established for linear systems, yet their extension to nonlinear systems remains in its infancy. Existing frequency-based decoupling techniques for nonlinear systems are limited to localized nonlinearities and specific configurations that require prior knowledge of the nonlinearity location; a general decoupling method for nonlinear systems does not yet exist. This paper introduces a general nonlinear decoupling framework. The proposed Nonlinear Frequency-Based Decoupling (NL-FBD) framework uses quasi-linear FRFs of the coupled system via response-controlled testing (RCT), and measured or calculated FRFs of the known substructure; and then applies a linear decoupling formulation, to calculate the quasi-linear FRFs of the unknown nonlinear structure at several response levels. Subsequent linear modal identification yields response-dependent nonlinear modal parameters, which are then used to synthesize constant-force FRFs of the unknown nonlinear substructure. The proposed approach is capable of; i) handling multiple nonlinear elements located arbitrarily within the structure, ii) addressing systems even with distributed nonlinearities, iii) accommodating nonlinearities in both substructures, and iv) achieving decoupling at multiple degrees of freedom. The applicability limits of the proposed approach are examined in detail, together with an assessment of its accuracy through numerical case studies. In particular, nonlinearities in both substructures are demonstrated for the single degree-of-freedom connection case, whereas multiple-degree-of-freedom connections are investigated for systems with a known linear substructure. Experimental validation on a nonlinear beam--linear beam assembly confirms that NL-FBD accurately decouples the unknown nonlinear beam, yields a reliable nonlinear modal model, and predicts the forced response of a new assembly incorporating the decoupled nonlinear beam, with excellent agreement to measurements even at high forcing levels. Tue, 06 Oct 2026 14:26:21 +0200 Wed, 07 Oct 2026 09:03:29 +0200 https://popups.uliege.be/2684-6500/index.php?id=367 https://popups.uliege.be/2684-6500/index.php?id=206 The Tribomechadynamics Research Challenge (TRC) was a blind prediction of the vibration behavior of a thin plate clamped on two sides using bolted joints. Specifically, the natural frequency and damping ratio of the fundamental bending mode were requested as function of the amplitude, starting from the linear regime until high levels, where both frictional contact and nonlinear bending-stretching coupling become relevant. The predictions were confronted with experimental results in a companion paper; the present article addresses the experimental analysis of this benchmark system. Amplitude-dependent modal data was obtained from phase resonance and response controlled tests. In the phase resonance test, a resonant phase lag between response and excitation was ensured via feedback control, and the excitation level was step-wise in-/decreased. In the response controlled test, the response level was kept fixed via feedback control. An original variant of response controlled testing is proposed: Instead of a fixed frequency interval, a fixed phase interval is analyzed. This way, the high excitation levels required outside resonance, which could activate unwanted exciter nonlinearity, are avoided. The consistency of the nonlinear modal testing methods, with each other, and with conventional linear tests at low amplitudes, is carefully analyzed. Comparisons of nonlinear-mode based predictions with direct frequency response curve measurements (at fixed excitation level) serve as additional cross-validation. Overall, these measures have enabled a high confidence in the acquired modal data. The different sources of the remaining uncertainty were further analyzed. A low reassembly-variability but a moderate time-variability were identified. The latter is attributed to some thermal sensitivity of the system. Two nominally identical plates were analyzed, which both have an appreciable initial curvature, and a significant effect on the vibration behavior was found depending on whether the plate is aligned/misaligned with the support structure. Further, a 1:2 nonlinear modal interaction with the first torsion mode was observed, which only occurs in the aligned configurations. All data (time series of nonlinear tests; linear modal properties) and post-processing methods are publicly available. Mon, 07 Oct 2024 10:32:51 +0200 Fri, 08 Nov 2024 11:39:05 +0100 https://popups.uliege.be/2684-6500/index.php?id=206