Extreme Intermodal Energy Transfers through Vibro-impacts for Highly Effective and Rapid Blast Mitigation

This work investigates intermodal targeted energy transfers (IMTET) for passive mitigation of a large-scale nine-story structure subjected to blast excitation. This is achieved by inducing extreme, fast time scale energy transfers from lower-frequency structural modes which are mainly excited by the blast to higher-frequency ones. These targeted (directed) energy transfers are governed by a non-resonant nonlinear dynamical mechanism induced by inelastic Hertzian vibro-impacts between the nine-story structure (referred to “primary structure”) and an internal secondary “core structure” assumed to be rigid. The clearance distribution between the primary structure and the core structure is optimized using a multi-objective genetic algorithm by minimizing both the characteristic damping time of the transient response of the primary structure, and the energy redistributed from the lowest-frequency (fundamental) structural mode to higher modes. The results show that the IMTET mechanism enables extremely rapid and nearly irreversible low-to-high frequency scattering of the blast energy in the primary structure. In turn, this nonlinear energy scattering rapidly reduces the overall amplitude of the transient structural response, even in the case of purely elastic Hertzian contacts. The mitigation performance is substantially enhanced when more realistic inelastic vibro-impact nonlinearities are considered. In the studied example with the realistic model of a nine-story structure, the synergy between extremely rapid low-to-high frequency energy redistribution and dissipation due to inelastic vibro-impacts yields a reduction of the characteristic damping time by a factor of 20 compared to the linear case. We envision that the proposed concept of rapid nonlinear IMTET is of broad applicability to general classes of dynamical and acoustical systems.