Development of Experimental Nonlinear Modal Analysis methods under special consideration of exciter-structure interaction

• Applicant: Professor Dr.-Ing. Malte Krack
• Subject Area: Mechanics
• Term: from 2018 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 402813361

The present project has the ambitious goal to extend modal testing, which is a quintessential technique in the linear case, to the nonlinear case. With the methods developed in this project, one will be able to extract the natural frequency, modal damping ratio and vibrational deflection shape (including harmonics), for each mode of interest, as a function of the vibration level. The extracted modal properties will be useful for data-driven modeling of complicated nonlinear behavior, for validating, updating and upgrading nonlinear physics-driven modeling approaches.The ongoing project part revealed a major challenge, the exciter-structure interaction. This challenge will be a focus of the method developments in the proposed project part. The goal of WP1 is to extend the Nonlinear Mode Theory to incorporate an exciter model. The development will be sufficiently general that models of linear attachments can be considered, which are described by linear differential equations with time-invariant coefficients. The attachments do not need to be of purely mechanical nature, but may contain, for instance, electric, magnetic or aerodynamic models, which extends the range of utility of nonlinear modes to applications as diverse as structural modification, smart structures or energy harvesting. With an appropriate exciter model, the extended nonlinear-mode model is expected to provide an accurate prediction of the well-known near-resonant force drop and the response of the coupled exciter-structure system. In WP2, the phase control scheme developed in the ongoing project part will be extended to higher harmonics. Besides extending the range and accuracy of the nonlinear modal testing method, the control scheme will also be useful to achieve a purely harmonic excitation during frequency response tests, and will thus greatly facilitate structural dynamic model validation in general. In WP3, an alternative to phase-resonant testing will be developed, based on velocity feedback. This is expected to considerably simplify the control task, and therefore to be more robust. Finally, in WP4, a nonlinear modal testing method will be developed for the common case of base excitation, as opposed to the shaker-stinger excitation considered so far. Assuming that the dynamics of a large shaker with heavy slip table is not significantly affected by the dynamics of a light specimen, base excitation has the potential to reduce exciter-structure interaction.

• DFG Programme: Research Grants
• International Connection: United Kingdom
• Cooperation Partner: Dr. Ludovic Renson