This paper presents a comparative study of docking algorithms intended for non-holonomic autonomous underwater vehicles, docking in funnel-shaped docking stations, operating under the influence of ocean currents. While descriptive surveys have been already reported in the literature, our goal is to compare the most relevant algorithms through realistic Monte Carlo simulations to provide an insight into their performance. To this aim, a new numerical performance indicator is proposed, which, based on the geometry of the manoeuvre, is able to characterize a successful or unsuccessful docking, providing a metric for comparison. The experimental study is carried out using hardware-in-the-loop simulation by means of the Stonefish simulator, including the dynamic/hydrodynamic model of the Sparus II AUV, models of all internal and external sensors, and the collision geometry representing the docking station.

Offshore wind farms are a crucial source of renewable energy, but maintenance and repair can be challenging due to their remote locations and harsh environmental conditions. Professional divers or Remotely Operated Vehicles (ROVs) are commonly used to conduct maintenance operations, but they come with high daily operational costs. Autonomous Underwater Vehicles (AUVs) have the potential to improve the efficiency, safety, and costs of maintenance operations. This project evaluates the feasibility of using an AUV to conduct a cathodic protection (CP) survey, which involves measuring the corrosion potential of underwater structures to prevent deterioration. The AUV is equipped with a manipulator that has a CP probe with a sharp tip to puncture through the structure’s coating and make contact with the steel underneath. To ensure high accuracy and reduce environmental perturbances, the AUV attaches to the structure while conducting the survey. The technology and methods used in this project are demonstrated in a water tank using a Girona1000 AUV. Task Priority kinematic control is combined with a custom force control strategy based on admittance control to enable tracking of the end-effector configuration and contact force during the probing operation. The mission flow control is implemented using behavior trees. The results show that the use of AUVs for CP surveys is feasible and has the potential to significantly improve the efficiency, safety, and costs of maintenance operations in offshore wind farms.

This paper presents the design and development of a funnel‐shaped Sparus Docking Station intended for the non‐holonomic torpedo‐shaped Sparus II Autonomous Underwater Vehicle. The Sparus Docking Station is equipped with sensors and batteries, allowing for a stand‐alone long‐term deployment of the vehicle. An inverted Ultra Short Base‐Line system is used to locate the Docking Station as well as to provide long‐term drift‐less vehicle navigation. The Sparus Docking Station is able to observe the ocean currents using a Doppler Velocity Log, being motorized to allow its self‐alignment with the current. Moreover, a docking algorithm accounting for the current is used to guide the robot during the docking maneuver. The paper reports consecutive successful experimental results of the docking maneuver in sea trials in two different countries.