M. F. Platten

Identification of a Nonlinear Wing Structure Using an Extended Modal Model

The nonlinear resonant decay method identifies a nonlinear dynamic system using a model based in linear modal space comprising the underlying linear system and a small number of additional terms that represent the nonlinear behavior. In this work, the method is applied to an aircraftlike wing/store/pylon experimental structure that consists of a rectangular wing with two stores suspended beneath it by means of nonlinear pylons with a nominally hardening characteristic in the store rotation degree of freedom. The nonlinear resonant decay method is applied to the system using multishaker excitation. The resulting identified mathematical model features five modes, two of which are strongly nonlinear, one is mildly nonlinear, and two are completely linear. The restoring force surfaces obtained from the mathematical model are in close agreement with those measured from the system. This experimental application of the nonlinear resonant decay method indicates that the method could be suitable for the identification of nonlinear models of aircraft in ground vibration testing.

Identification of Multi-Degree of Freedom Systems With Nonproportional Damping Using the Resonant Decay Method

This paper describes an extension of the force appropriation approach which permits the identification of the modal mass, damping and stiffness matrices of nonproportionally damped systems using multiple exciters. Appropriated excitation bursts are applied to the system at each natural frequency, followed by a regression analysis in modal space. The approach is illustrated on a simulated model of a plate with discrete dampers positioned to introduce significant damping nonproportionality. The influence of out-of-band flexible and rigid body modes, imperfect appropriation, measurement noise and impure mode shapes is considered. The method is shown to provide adequate estimates of the modal damping matrix.

Identification of a Simulated Continuous Structure With Discrete Non-Linear Components Using an Extended Modal Model

In this paper a method capable of the identification of non-linear structures with many degrees of freedom is presented. The Non-Linear Resonant Decay Method achieves this by identifying an underlying linear modal model for the system. Force appropriation is then used to apply sinusoidal bursts to the structure at high levels of force. The system responses to these bursts are used in a regression analysis in modal space to yield a limited number of additional non-linear terms. The method is applied to a simulated continuous system representing a wing/engine structure with discrete non-linear components at the engine attachment points. The resulting identified non-linear modal model is used to generate response data which are compared with responses from the original system.Copyright