Inverse simulation and analysis of underwater vehicle dynamics using feedback principles

Inverse simulation is a technique used in the modelling of dynamic systems that allows time histories of input variables to be found that generate required model output responses and provide inverse solutions in cases where analytical approaches to model inversion can present difficulties. This paper describes the application of inverse simulation to a nonlinear dynamic model of an unmanned underwater vehicle (UUV) and the determination of vehicle control inputs for specified manoeuvres. The approach to inverse simulation used in this application is based on the principles of feedback. Design issues relating to the UUV control surfaces and propeller thrust are highlighted through this procedure. The paper includes an outline of the nonlinear model of the UUV and typical sets of experimental conditions. Feedback loops are designed around the model for selected output variables and the inverse solutions are generated through simulation of this multi-input multi-output closed-loop system. It is shown that the feedback approach can provide inverse solutions for an appropriate choice of loop-gain factors and integration time step using a fixed-step integration algorithm. Inverse solutions generated in this way are shown to provide insight concerning issues of vehicle handling and manoeuvrability in a more direct fashion than is possible using conventional simulation methods.