5 Investigating Nonlinearities in a Demo Aircraft Structure Under Sine Excitation 55 Fig. 5.21 Nonparametric FRFs and total distortions for two different output sensors on the assembly based on measured sine-sweep data for frequency range 6–100 Hz 5.5.4 Nonlinear Characterisation Nonlinear characterisation helps in determining the type of nonlinearity in the structure and in addition seeks to provide answers to some major questions that arise when dealing with nonlinear system. Some of the typical questions that arises are listed below: (a) What is the strength of the nonlinearity? i.e. is it weak or strong nonlinearity (b) What is the source of the nonlinearity? i.e. is it stiffness or damping nonlinearity or both (c) What is the nonlinear stiffness characteristic? i.e. is it hardening or softening (d) What is the characteristic of the restoring force? i.e. is it symmetric or asymmetric Of all the characterization methods available in the literature, the Acceleration Surface Method has proven its ability to characterize the stiffness and damping properties of a nonlinear structure due to its in-built characterization competences. By presenting the restoring force surface results for a nonlinear structure as a function of the displacement, velocity and acceleration in a three-dimensional plot, it is possible to visualize the type of nonlinearity in the system. The stiffness and damping properties of the nonlinearity can also be visualized by taking a slice of the three-dimensional plot at zero values of the corresponding velocity and displacements.
RkJQdWJsaXNoZXIy MTMzNzEzMQ==