Dynamic disturbance substructuring: identifying localized nonlinear vibrations

In this work, the novel approach Dynamic disturbance (Dydis) substructuring is introduced, and the concept is demonstrated, first on a linear system and then on a simple nonlinear system. Dydis is a means to characterize nonlinear interfaces in complex dynamic engineering structures. It can be any known slight change in the system affecting the vibrational response, as a change in stiffness, mass, inertia, or pre-loading. By measuring the vibrations of systems with and without Dydis, two sets of independent data is obtained, allowing robust estimation of interface dynamics. Nonlinear systems' natural frequencies are amplitude-dependent. Adding mass will change the frequencies and the forcing level, thus enhancing amplitude-dependent nonlinear effects. This work takes the first steps towards a nonlinear Dydis substructuring approach by applying nonlinear frequency response functions and adapting an estimation procedure to work for a simple nonlinear case. Results are promising: in a situation polluted by noise, Dydis halves the error compared to not using it.