1. An arrangement for controlling simulation of a coupled hybrid dynamic system, comprising: a physical test rig configured to drive a physical structural component of the system and to generate a test rig response comprising a first component and a second component as a result of applying a drive signal input to the test rig; and a processor configured with a virtual model of the system, the processor receiving the first component of the test rig response and generating a model response of the system based on using the first component of the received test rig response and a virtual drive as inputs; the processor further configured to compare the second component of the test rig response with the model response corresponding to the second component to form a difference, the difference being used by the processor to form a system dynamic response model for generating the test rig drive signal.