Project 1: Handling Shaker Structure Interactions in Nonlinear Dynamic Testing
Patrick Hippold, University of Stuttgart
Tong Wei, Imperial College London
Tong Zhou, Université de Liège
When testing structures with vibration exciters, the structural response may distort the applied forcing. This unwanted interaction compromises the quality of the test results. This project addresses a particular form of distortion, namely the occurrence of higher harmonics in the applied excitation for nominally sinusoidal excitation. An existing test rig comprising a clamped clamped beam, undergoing nonlinear bending stretching coupling, mounted via a stiff frame on a shaker will be modified to tune the system into a 1:3 internal resonance, making the response highly sensitive to higher harmonics generated by shaker structure interaction. A new method to compensate the higher harmonics and achieve a purely harmonic excitation will be implemented, tested and compared to existing alternatives. To further analyze the deterioration of the modal properties induced by shaker structure interaction, the system will also be tested without shaker with impact testing using an automatic hammer.
Project 2: Project 2: Masing Manifolds
Ahmed Morsy, ETH Zurich
Valeria Pinto, Politecnico di Torino
Rafael Teloli, University of Franche-Comté
The Masing conditions have been a highly efficient tool for quantifying hysterestic properties of jointed structures. However, when applied to real systems, the assumptions governing the Masing conditions become invalid, which results in either non-physical models that must be calibrated to match the system’s behavior at the cost of neither being predictive nor being able to fit multiple modes or the requirement of computationally intensive non Masing models. To address this shortcoming, the Masing Manifold is proposed, in which an additional set of constraints is introduced to account for variations in the normal force across a joint. This results in an efficient way to model the hysteretic behavior of a system with a time varying normal force. Preliminary work shows that the Masing Manifold is valid for simple hysteretic elements (e.g., elastic dry friction). In this project, we will seek to understand how effective the Masing Manifold hypothesis is for more complex hysteretic elements (e.g., an Iwan element) as well as more complex system responses (e.g., multi harmonic excitations).
Project 3: TRChallenge 2021 – Obtaining experimental data using advanced nonlinear testing
Arati Bhattu, Rice University
Svenja Hermann, University of Franche-Comté
Nidhal Jamia, Swansea University
In 2021 different research groups around the globe were invited to predicting the nonlinear dynamic response of a system with two inherent nonlinearities, a geometric and a frictional one. A detailed design of the test structure was provided, and the participants were asked to provide their “Best Shot” at a blind prediction of the linear natural frequencies and the modal properties (natural frequency, damping ratio) of the fundamental mode in a certain amplitude range. The aim of this year’s project is to identify the actual behavior of the manufactured structure. The nature of the structure makes it necessary to provide the dynamic loading in the form of base excitation via a large shaker. Thus, the excitation forces cannot be directly measured, which makes it impossible to quantify the damping directly from backbone curves. Recently developed nonlinear testing techniques will be used and compared against amplitude controlled frequency response tests to obtain high quality validation data to be shared within the community.