Evaluation of Moving Capability of Crawler Driven ROV Considering Cable Tension

Abstract

A ROV (Remotely Operated Vehicle) which has a crawler based driving system is considered to be one of the appropriate underwater vehicles for seafloor exploration or seabed resources development [1][2][3][4][5][6][7]. The crawler driven ROV is able to move on sea floor, stay on a fixed sea bottom location and is capable to do heavy works such as digging the seafloor. In order to utilize those capabilities, it is important to know the fundamental moving capability of crawler driven ROV. According to the previous investigations [8][9], the crawler driven ROVs are easy to run in bow-up attitude in some running conditions due to the buoyancy and the hydrodynamic forces acting on the ROV. This irregular running sometimes causes a turning over. Therefore, we have to know the restrictions on the design parameters of the ROV not to run in bow-up attitude to design the ROV. The authors have been investigating the moving capability of crawler driven ROV and showed a method to estimate the restrictions of design parameters to avoid the bow-up running, which is called normal running condition [10][11][12][13]. This method is based on a simple dynamic model which considers the forces acting on ROV as concentrated loads; those are gravity, buoyancy, reaction from the ground, thrust and hydrodynamic drag. The loading position of ground reaction in steady running is obtained from the balance condition of forces. We consider that the loading point of ground reaction should be inside between the fore and rear wheels for the normal running. This constrained condition indicates the relation between gravity and buoyancy center locations for the normal run of ROV under the given body geometry, weight, displacement and running speed. This method estimates the ROV’s running capability in acceptable accuracy compared with the model experiments. However, this method does not consider the tension of the cable which is connected to the ROV. As you can easily imagine, the cable tension has a big influence on the movable area of the ROV. If the ROV keeps going forward, it will turn over due to the tension of the cable at a certain point. We must know the movable area of the crawler driven ROV for the operation planning. The present study shows a method to estimate the movable area of the crawler driven ROV under the restriction of the cable by extending the previous method to estimate the normal running condition.