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.
Seafloor exploration and seabed resources development are important missions for solving international energy issues. The crawler driven ROV which is capable to do heavy works is considered as one of the probable systems for those missions and some have been developed already [1][2][3][4][5][6][7]. It is well known that the movability of actual ROVs on the sea floor is worse compared with the terrestrial crawlers [8][9][10][11][12]. Therefore it is important to make clear what conditions have to be satisfied for the stable running of a ROV on the sea bottom. The experimental investigation on the crawler based ROV’s movability suggests that light weight ROVs are easy to run in bow up condition and sometimes turn over. The authors have shown the condition for the normal running of the ROV which moves on the horizontal and inclined flat water bottom by means of a simple dynamic model [13][14][15]. This normal running condition is represented by the relation between the locations of gravity and buoyancy centers to be satisfied, in case of the weight, displacement, geometry and speed of the ROV are fixed. The model experiments have shown the validity of this normal running condition. However, the sea bottom is not flat and it is very important to know the moving performance of ROV over the bumps for the practical design point of view. In this paper, a method to estimate the ROVs’ ability to climb up the bumps is shown and it is validated by model experiments. The ROV model has two sets of crawlers; the rear crawlers are set horizontally and fore ones are inclined to climb up the bumps. The requirements to climb up the bumps for the design parameters of ROV such as crawler length, weight and displacement of ROV, location of gravity and buoyancy center, derived from present method agreed with the experimental results qualitatively.
Remotely Operated vehicle, so called ROV is widely used for the seafloor explorations. The most of the existing ROVs are the hover type ones which is suspended in the sea. However, the hover type ROV is not suitable for the operations such as moving along the seafloor, stopping at a certain location on the seafloor and doing the heavy works like digging the seafloor. The crawler driven ROV is considered to be an applicable system for those operations. It is known that the crawler driven ROV is easy to run in unsteady attitude due to the buoyancy and the hydrodynamic force acting on the ROV and sometimes causes a turn over. Therefore, we have to know the precise moving capability to design the crawler ROV. Additionally, as the ROV is under the restrictions of the cable, it is necessary to know the movable area of the crawler ROV considering the cable tension. The authors have developed a simple method to estimate the movable area of the ROV based on the simple statics. The cable of the crawler driven ROV sometimes touches the seafloor. Therefore, the cable tension should be calculated considering the contact of the cable with the seafloor. However, in the previous research, the effects of the cable contact with the seafloor was not taken into accounted. The present study shows a numerical procedure to estimate the cable tension considering the contact of the cable with the seafloor and also the bending stiffness of the cable. Adapting this procedure, a method to estimate the movable area of the crawler ROV is shown. The model experiments are conducted to validate this method. Case 1-1 (Cal.) Case 1-2 (Cal.) Case 1-3 (Cal.) Case 1-1 (Exp.) Case 1-2 (Exp.) Case 1-3 (Exp.) Case 1-1 (Cal.) Case 1-2 (Cal.) Case 1-3 (Cal.) Case 1-3 (Exp.) Case 1-2 (Exp.) Case 1-1 (Exp.) Case 2-1 (Cal.) Case 2-2 (Cal.) Case 2-3 (Cal.) Case 2-1 (Exp.) Case 2-2 (Exp.) Case 2-3 (Exp.) Case 2-3 (Cal.) Case 2-2 (Cal.) Case 2-1 (Cal.) Case 2-1 (Exp.) Case 2-2 (Exp.) Case 2-3 (Exp.
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