Representation of an Autonomous Underwater Vehicle and Trajectory Controller design for in-water ship hull inspection

This paper presents a trajectory controller for a Hovering type Autonomous Underwater (HAUV) Vehicle to meet the demands of in-water ship hull inspection. Accomplishing this task can just be done by a vehicle that has all special requirements like high maneuverability, precise controllability and especially Hovering Capability, utility of such vehicle causes increasing precision, saving more time and money and less health hazard of divers. Thruster's configuration in terms of number of the thrusters, position and the thrust direction of each thruster is presented to provide the most suitable formation in terms of less energy consuming, reducing complexity of control strategies and control the most degrees of freedom. In this paper, roll degree of freedom is just constrained. The controller is demonstrated, was designed upon the linearized dynamic model and then applied to the non-linear model to validate the controller's practicality. This controller consist of 3 different loops, one for horizontal plane another for the vertical plane, both where designed in state space and the last one is a PID controller which is developed to control the forward speed. In the next step, the robustness of the controller is investigated in the presence of underwater disturbance and uncertainty of the hydrodynamic coefficients. State feedback controllers have the advantages such as being suitable for non-linear models, useful for MIMO system and simplicity in application development.