Transfer Dynamics Cancellation in Real-Time Dynamic Substructuring

Real-time dynamic substructuring, also referred to as mechanical hardware in the loop, model in the loop, or hybrid numerical-physical testing, is gaining increasing interest from industrial sectors as a practical means of testing components of large structures under realistic operating conditions. Such tests commonly employ hydraulic actuation with force or displacement feedback to couple the physical substructure to the numerical model of the system being tested. A significant challenge in this type of configuration lies in the cancellation of the transfer system dynamics. The control electronics and hydraulics as well as the measurement equipment and feedback mechanisms all introduce their own dynamics to the system which need to be compensated for in order to provide meaningful results. This paper details efforts that have been made to model the transfer dynamics of a hydraulic actuator and its controllers and to employ these models in the cancellation of the transfer dynamics. Several models are proposed, ranging from first order transfer functions to more complete process models, and their performance is assessed in qualification tests as well as simple substructuring exercises.