Compliant Manipulation With Quasi-Rigid Docking for Underwater Structure Inspection

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.