Trajectory Following of a Tethered Underwater Robot With Multiple Control Techniques

A three-dimensional hydrodynamics and control model to simulate a tethered underwater robot system is proposed. The fluid motion around the robot main body with control ducted propellers is governed by the Navier–Stokes equations, and multiple sliding mesh technique is applied for the numerical solution of the equations. The governing equation of umbilical cable is based on the Ablow and Schechter method. The six degrees-of-freedom equations of motion for underwater vehicle simulations are adopted to estimate the hydrodynamic performance of the underwater robot. In the model, a hybrid feed-forward and feedback control technique is applied to adjust the length of the umbilical cable, and the incremental proportional-integral-derivative (PID) control algorithm is adopted to regulate the rotating speeds of the ducted propellers. The numerical results indicate that the multiple control techniques applied in this paper are feasible and effective, and adjusting the length of the umbilical cable is largely responsible for the vertical trajectory control to the robot, while regulating the rotating speeds of the propellers plays a leading role in the horizontal trajectory manipulation, the deviation between the designated trajectory and the controlled one is acceptable.