Single and multiple nonlinear energy sinks configurations in 3D civil structures with random excitations

The Nonlinear Energy Sink (NES) is a passive dynamic vibration absorber able to resonate with all the modes of the controlled primary structure. This peculiarity makes it more robust than the most widespread tuned mass damper. For this reason, the scientific community has devoted great attention to the investigation of its features and design [1]. The strong nonlinear nature of the NES allows the triggering of the so-called nonlinear targeted energy transfer, i.e. a passive and irreversible energy flow from the primary structure to the nonlinear device. However, for the same reason, the NES optimal design is significantly affected by variations in load conditions. The NES effectiveness has been mostly studied using deterministic approaches and considering shear type frames. Closed-form solutions to determine the optimal NES nonlinear stiffness have been proposed in past studies for transient, harmonic and white noise excitations [2-5]. The aim of this work is to analyse the performance of ungrounded NESs attached to a three degree-of-freedom, three-dimensional linear structure subjected to random Gaussian white noise base excitations, extending the work presented by the authors in [4]. Two distinct NES configurations have been considered. The first one consists of a single NES located at the centre of mass of the structure, whereas the second one employs two NESs acting independently in the two orthogonal directions x and y. For each of them, numerical analyses have been carried out examining the behaviour of the nonlinear devices by varying the epicentral direction of the ground motion. For the case of a single NES, the analysis has been performed by varying its orientation.