Real-time dynamic substructuring for mechanical and aerospace applications : control techniques and experimental methods

• Main Author: Wallace, Max Ian
• Published: University of Bristol 2005
• Subjects: 621.8
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431834

Real-time dynamic substructuring is an experimental technique for testing the dynamic behaviour of complex structures. It involves creating a hybrid model of the entire structure by combining experimental test piece(s) - the substructure(s) - with a set of numerical model(s) describing the remainder of the system. By employing real-time control techniques to "glue" the numerical and experimental parts together, we create a virtual testing environment that if performed correctly will emulate the dynamic behaviour of the complete structure exactly. In this thesis, we focus on the experimental side of substructuring, specifically concentrating on the influence of delays within the substructured system. These are introduced by the inherent dynamics of the actuation device(s) involved - it is impossible for any controlled transfer system(s) (as they are known) to react instantaneously to a state change in demand. We study the stability of the substructured system in direct relation to the magnitude of this delay error and present two methods for identifying the critical limit of stability; firstly, using a delay differential equation approach by approximating the transfer system to a delayed unit response of the numerical model, and secondly, by observing the magnitude of permissible phase margin of the substructured system. We discuss two different formulations of a compensation scheme; one achieving adaptive forward prediction using polynomial extrapolation and the second achieving lag compensation via the inversion of an identified model of the transfer system. We then extend this control strategy to include the concept of robustness which leads us to develop a four stage testing methodology that can be applied to any substructured system to help ensure successful testing. We build on these fundamental concepts to demonstrate the "proof of concept" of real-time dynamic substructuring for an industrial aerospace application - a helicopter lag damper connected to numerical model of an individual blade excited by flight test data.