Effects of Burst Length Inaccuracies on Non-Linear System Identification

摘要

In practice, most structures exhibit some non-linear behaviour and there is considerable interest in the identification of non-linear dynamic systems with multiple degrees of freedom. Structures may contain several different types of non-linearity, including stiffness or damping, of different order, or friction non-linearity. The Non-Linear Resonant decay Method (NL-RDM) was introduced to identify non-linear multi-degree of freedom systems. The method takes advantage of the transformation to modal space, which allows for the estimation of non-linear models. It also comprises elements of the Phase Separation, Resonant Decay Method (RDM), Force Appropriation of Non-linear System (FANS) and Restoring Force Surface (RFS) methods. The criteria for an ideal method are detailed in the some earlier papers, but the reality creates a limitation. The excitation signal applied as part of the NL-RDM is designed to have a duration that is less than the total length of data acquired. This is to allow the system to decay following the so-called burst; then, because the excitation and response signals will start and end at zero, there should be no leakage errors. However, if the burst length is not chosen carefully, then leakage errors could occur in the differentiation / integration via the frequency domain. So, the effect of burst length and the importance of leakage are highlighted. Then, the sensitivities to the inaccuracy which could be encountered in practical applications, are discussed in concept, generated, applied and analyzed through simulation program for two degree of freedom examples.