Local nonlinear stores induce global modal interactions in the steady-state dynamics of a model airplane

Local nonlinear attachments can affect the global dynamics of their linear host structures through modal interactions. This was shown previously in experimental and computational studies of a model airplane with local nonlinear attachments at its wings, under impulsive forcing. Here we study nonlinear modal interactions in the model airplane subject to harmonic excitation. We consider the case of both attachments locked (L-L – baseline linear system), and compare it to two nonlinear cases, i.e., left-wing attachment unlocked (U-L), and both attachments unlocked (U-U). Nonlinear output response functions are used to study the nonlinear modal interactions due to the local attachments in the frequency domain; these are detected only in a certain frequency band. Proper orthogonal decomposition, in conjunction with a weighted modal assurance criterion, are used to quantify these modal interactions. At some frequency bands the nonlinearities facilitate energy transfer to non-resonant airplane modes, despite being widely separated in frequency from resonant modes. Our findings apply to general linear systems with local nonlinear attachments.