Exploiting impact-induced Intermodal Targeted Energy Transfer (IMTET) for passive mitigation of resonant vibrations of rotationally periodic structures

• Applicant: Professor Dr.-Ing. Malte Krack
• Subject Area: Mechanics
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 514021014

It is the current predominant engineering practice to avoid nonlinearities whenever possible and to rely mostly on linear analysis. The proposed research stands in polar opposite to the current conventional view, as it exploits intentional strong nonlinearity to enable passive cross-scale energy transfers (having no counterpart in the linear regime) in order to reach unprecedented vibration mitigation performance in a passive, robust and predictable way. To induce such intense energy transfers, a small impactor is placed freely into a cavity of the structure whose vibrations are to be mitigated. In complete contrast to the impact damper, the goal here is to avoid local dissipation in the contact region. This has the important advantages that damage is avoided, and the system behavior can be much better predicted since empirical laws to describe the inelastic impacts and plastic contact damage are not needed. Instead, passive vibration mitigation is achieved by intermodal targeted energy transfer (IMTET), i.e., irreversible energy transfer from low-frequency modes to high frequency ones, with a dual benefit: First, the overall vibration amplitude decreases as the frequency of vibration increases, and, second, vibration energy is dissipated much more effectively and rapidly by the high frequency modes. IMTET across frequencies (scales), as proposed in the present proposal for the purpose of vibration mitigation, is inspired by analogous irreversible energy cascades that occur commonly in natural systems (e.g., turbulence). The concept of IMTET has been developed quite recently and analyzed so far only for the case of isolated structures with well-separated natural frequencies. In this project, IMTET is analyzed, for the first time, for the case of rotationally periodic structures (which inherently have closely-spaced modes due to near symmetry). Many examples of such structures can be found in engineering, including bladed turbine disks, generators with end windings, and cooling towers with legs. A focus is placed on resonant vibrations, for which the mitigation efficacy of IMTET and, more specifically, impact energy scattering is to be investigated using appropriate analytical, computational and experimental methods. The sensitivity of inter-sector and intra-sector IMTET to disorder/mistuning, strength of the inter-sector coupling, centrifugal loading and different dissipation mechanisms (aerodynamic vs. material vs. dry frictional) is to be analyzed for the first time. The project will be carried out in close collaboration with Prof. A. F. Vakakis as Mercator Fellow.

• DFG Programme: Research Grants