Characterization, Modeling, and Simulation of an ROV Thruster using a Six Degree-of-Freedom Load Cell

This paper presents the modeling and simulation of a remotely operated vehicle (ROV) thruster. Empirical testing of deep diving ROVs is costly, time-consuming, and risky, creating practical limitations on the application of such testing during the design process. The use of computer-based modeling and simulation of a vehicle's dynamic behavior reduces the need for testing and is therefore a powerful design tool. The ROV and its associated control system are heavily dependent on the performance and response of the vehicle's actuators, which are typically an array of fixed, variable speed marine thrusters. In this work, an accurate dynamic model was created for a commercially available fixed-pitch variable speed thruster using a process of system identification. The thruster's dynamic force and moment response to its control input (throttle) was captured using a novel 6 degree-of-freedom (DOF) Gough-Stewart platform load cell. Numerical optimization was then applied to fit a dynamic model to the response data. Also described is the construction and theory of operation for the load cell. The process for determining thruster model parameters from load cell measured throttle response data is also shown as well as a comparison of the measured data to the simulated thruster model.