Abstract
Underwater vehicles (UVs) are subjected to various environmental disturbances due to ocean currents, propulsion systems, and un-modeled disturbances. In practice, it is very challenging to design a control system to maintain UVs stayed at the desired static position permanently under these conditions. Therefore, in this study, a nonlinear dynamics and robust positioning control of the over-actuated autonomous underwater vehicle (AUV) under the effects of ocean current and model uncertainties are presented. First, a motion equation of the over-actuated AUV under the effects of ocean current disturbances is established, and a trajectory generation of the over-actuated AUV heading angle is constructed based on the line of sight (LOS) algorithm. Second, a dynamic positioning (DP) control system based on motion control and an allocation control is proposed. For this, motion control of the over-actuated AUV based on the dynamic sliding mode control (DSMC) theory is adopted to improve the system robustness under the effects of the ocean current and model uncertainties. In addition, the stability of the system is proved based on Lyapunov criteria. Then, using the generalized forces generated from the motion control module, two different methods for optimal allocation control module: the least square (LS) method and quadratic programming (QP) method are developed to distribute a proper thrust to each thruster of the over-actuated AUV. Simulation studies are conducted to examine the effectiveness and robustness of the proposed DP controller. The results show that the proposed DP controller using the QP algorithm provides higher stability with smaller steady-state error and stronger robustness.
Highlights
The ocean covers approximately 70% of the Earth’s surface and provides us many natural and mineral resources
Motivated by the above challenging issues, this paper investigates a trajectory generation and position control for a hovering autonomous underwater vehicle (AUV) with four horizontal and three vertical thrusters taking the effects of the model uncertainties and the ocean current into consideration
Because the dynamic model of an AUV in the presence of model uncertainties and ocean current disturbances is complex and unstable, it is challenging to simulate the behaviors of the AUV under the input of a new controller
Summary
The ocean covers approximately 70% of the Earth’s surface and provides us many natural and mineral resources. Resources on land are being steadily depleted, and exploring the resources in the ocean such as oil, gas, and minerals under the seabed has been increasingly focused in recent years. It is difficult to explore and investigate very wide underwater environments in usual ways using manned systems and human divers. The UVs are utilized in a variety of applications such as scientific surveying, underwater surveillance, oceanographic research, environment monitoring, natural resource exploration, subsea structure inspection and maintenance, anti-submarine warfare, mine-field operation, and industrial fields, etc. Several studies for the ROV have been conducted by many engineers and researchers with a number of different designs proposed [10,11,12,13,14]
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