Analysis of Nonlinear structures using the Response Controlled Stepped-Sine Testing (RCT) method

Abstract

Dynamic analysis and characterization of structures which contain multiple nonlinearities is challenging and complicated. Despite the rapid technological development, it is still considered that most structures designed and tested exhibit a linear response when subjected to external dynamic loading. However, this leads to unreliable results due to the nonlinear phenomena that can occur. The aim of this thesis is to identify and analyze nonlinear complex dynamic systems. For this reason, it was necessary to find from the literature different techniques that have been developed and examined to deal with this problem. Recently, methodologies such as Response Control Stepped-Sine Testing (RCT) and Harmonic Force Surface (HFS) have been successfully implemented, allowing the easy calculation of nonlinear response curves including all unstable branches that could not be calculated experimentally using the traditional method. These methods were applied to nonlinear structures and computational problems with combined nonlinearities at different locations, which had not been previously investigated by the new methods. Experimental nonlinearity was generated using electromagnetic fields and bolt friction. In addition, several nonlinear MDOF computational problems containing multiple nonlinearities such as Coulomb friction, nonlinear spring and nonlinear damping were analyzed by the arc length continuation method and by using the Describing Functions. Comparing the results of Analytical RCT and HFS with those of the traditional Force Control Method, it is observed that the new method can be successfully applied experimentally and computationally, as the unstable branches of the nonlinear response curves were calculated without additional effort and in less time.