Challenging an experimental nonlinear modal analysis method with a new strongly friction-damped structure

Abstract

In this work, we show that a recently proposed method for experimental nonlinear modal analysis based on the extended periodic motion concept is well suited to extract modal properties for strongly nonlinear systems (i.e. in the presence of large frequency shifts, high and nonlinear damping, changes of the mode shape, and higher harmonics). To this end, we design a new test rig that exhibits a large extent of friction-induced damping (modal damping ratio up to 15 %) and frequency shift by 36 %. The specimen, called RubBeR, is a cantilevered beam under the influence of dry friction, ranging from full stick to mainly sliding. With the specimen's design, the measurements are well repeatable for a system subjected to dry frictional force. Then, we apply the method to the specimen and show that singlepoint excitation is sufficient to track the modal properties even though the deflection shape changes with amplitude. Computed frequency responses using a single nonlinear-modal oscillator with the identified modal properties agree well with measured reference curves of different excitation levels, indicating the modal properties' significance and accuracy.

A Critical Review of Nonlinear Damping Identification in Structural Dynamics: Methods, Applications, and Challenges

“…It also has high resistance against measurement noise and does not require much prior knowledge of the tested systems or special equipment. In another related work, Scheel et al [ 134 ] designed a new test rig named rubbing beam resonator for experimental nonlinear modal analysis. The proposed method performs the analysis based on the concept of the extended periodic motion in order to obtain the modal characteristics.…”

A consistency analysis of phase-locked-loop testing and control-based continuation for a geometrically nonlinear frictional system

“…5b that consists in an online Fourier decomposition using linear low-pass (LP) filters. It has been successfully applied in other PLL tests [29,33,30,19] and is used in this work. A promising alternative is the use of adaptive filters [26] to perform the online Fourier decomposition.…”

“…Backbone curves can also be identified by imposing phase quadrature, linking directly the method to the identification of NNMs. PLL testing has been successfully applied for the characterization of NNMs in many experiments including a blade [31] and a joint [32] with frictional nonlinearities, a circular plate [19] exhibiting hardening and modal interaction, and a cantilever beam with magnetic nonlinearity [33].…”

Stepped and swept control-based continuation using adaptive filtering

“…In those applications, PLLs relied on the unique parameterization of the response manifold in terms of the phase lag. PLLs were also used to identify backbone curves on a number of systems including stiffness and friction nonlinearities [22,23,24,25]. FRCs were synthesized from the measured backbones in [21].…”