Numerical Estimation of Base Reactions of an Underwater Manipulator with Variable Drag Coefficients

Underwater vehicles play an essential role in marine geosciences, resource exploration, and strategic applications. The addition of a manipulator to the underwater vehicles extends their capabilities for underwater intervention, object handling, and sample collection. When the manipulator interacts with the underwater environment, it experiences different reaction forces, including hydrodynamic forces. These reaction forces may cause destabilization of the vehicle, which would make it difficult to perform the manipulation task. It is important to ensure the stability of the underwater vehicle while the manipulator is interacting with the subsea environment. This paper presents a study of manipulator hydrodynamic forces and base reaction forces, which would be transferred to the underwater vehicle. These reaction forces need to be compensated by the thrusters of the vehicle to achieve stability. In this work, the variation of drag coefficient with velocity and along the length of the manipulator is considered first time in the dynamic modeling of a two-link underwater manipulator. These results would provide input to the design of suitable controllers for the stability of the vehicle.