Offshore inspection mission modelling for an ASV/ROV system

Abstract

To reduce the human exposure risk during the offshore structure inspection, the Remotely Operated underwater Vehicle (ROV) is a widely used solution. This paper couples an inspection class ROV with an autonomous surface vehicle (ASV) via a launch and recovery system (LARS) in a nonlinear numerical model. Operational inspection missions with both static and moving targets are modelled for this ASV/ROV system. The paper reports the following distinctive mission profiles: i) pipeline inspection, ii) floating offshore wind turbine (FOWT) mooring line inspection and iii) circumferential weld surface scan at the FOWT spar. The results provide important parameters to design and implement autonomous inspection missions. During the scan/check stage, the distance between the ROV and the target will be varying, due to the relative motion between the ASV and ROV. Important model results are that missions with following ASV will allow to reduce the ROV umbilical tension for a given mission profile. Results also determined that the net buoyancy of the ROV will lead to a position offset. In the surface scan cases, it is found that the drag force caused by the tidal current can contribute to ROV rotation and should be considered in detail ahead of any mission.