Finite Element Model Upgrading of an Airplane Mockup with Nonlinear Attachments

Abstract

Nonlinear dynamic simulations of complex structures can have very high computational costs. In this work, a nonlinear modeling procedure is applied to an airplane mockup with two localized nonlinearities, connected to its wings. In order to reduce the simulation computational burden, the experimentally validated linear Finite Element Model (FEM) of the airplane is condensed into a Reduced Order Model (ROM). Only the modes with a relevant importance in the frequency range of interest are kept in the ROM. The linear ROM is then coupled with a local nonlinear data-driven model of the nonlinearities, obtaining a nonlinear ROM with relatively low computational weight. After using it for a nonlinear transient simulation, the physical answer in a desired node or point of interest can be obtained performing the inverse coordinate transformation. The local nonlinear data-driven model is based on the nonlinear attachments Restoring Force Surface (RFS), estimated through the Acceleration Surface Method (ASM). The nonlinear stiffness restoring force is modeled as a polynomial, estimated with a least square fitting of the experimental restoring force. The possibility to use this approach in case of multiple nonlinear modes is evaluated and the predictions of the model are compared with measured response.