The Remotely Operated Vehicle, so called “ROV” which has crawler based moving system is considered as one of the appropriate underwater vehicles for seafloor exploration or seabed resources development [1][2][3][4][5][6][7]. The advantages of crawler driven ROV are to be able to stay on a fixed sea bottom location and to be capable to do heavy works such as digging the seafloor. However, the ROV moving on the sea bottom with crawler based driving system easily turn over due to the buoyancy and hydrodynamic forces [8][9][10][11][12]. Therefore, it is important to know the moving capability of the ROV on the sea bottom for the design point of view. The authors have shown the condition for the normal running of the ROV which moves on horizontal and inclined flat sea bottom by means of a simple dynamic model [11]. Normal running means that the ROV runs without bow-up or stern-up situations and the crawlers touch the ground normally. The normal running condition of ROV indicates the constrained condition of the relation between gravity and buoyancy center locations for any given design parameters such as geometry, weight, displacement and running speed of the ROV. Though this method estimates the ROVs’ moving capability with acceptable accuracy, the hydrodynamic forces on the ROV and its application point are required for accurate estimation. In the previous research, those quantities are roughly estimated from the past experimental investigations. The present study investigated the flow around the crawler driven ROV which runs on seafloor with CFD (Computational Fluid Dynamics) analysis to evaluate the characteristics of hydrodynamic forces acting on the ROV. The open source CFD code, OpenFOAM [13] was applied for flow calculation and the results were validated with model experiments. By using the calculated hydrodynamic forces on ROV, the moving capability of ROV was evaluated with a method the authors had shown. The estimates of the running capability of the ROV by using the CFD calculations are quite different from past estimations in some running conditions.
The crawler driven ROV is considered as one of the probable systems for seafloor exploration or seabed resources development [1][2][3][4]. However the movability of crawler driven ROV on the sea bottom is not explained clearly compared with the ones on the land [5][6][7][8][9]. The experimental investigation on the crawler based ROV’s movability suggests that light weight ROV are easy to run in bow up condition and sometimes are possible to turn over. Therefore it is important to make it clear what kind of condition is to be satisfied for the normal run when the ROV moves on the sea bottom with crawlers. In this study, a simple dynamic model for the ROV which runs steadily on the inclined smooth sea bottom has been developed and the condition which should be satisfied for normal running has been derived. We consider that the forces acting on ROV are gravity, buoyancy, reaction from sea bottom, thrust and hydrodynamic resistance and treat them as concentrated loads. From the balance condition of forces for longitudinal and vertical direction and pitching moment, three kinds of relation are obtained. We consider that force reaction point from sea bottom should be inside between the fore and rear wheels for the normal operation. With this condition, the relation to be satisfied between the location of gravity center and center of buoyancy is obtained. To validate this conditional equation, the model experiments are carried out. The ROV model contains several weights and floating materials so that the longitudinal center of gravity and buoyancy can be changed by moving the weights and floats. Changing the longitudinal location of buoyancy center of the model from backward to forward, the limiting normal running condition for each longitudinal location of gravity center are measured. The obtained experimental results agree well with the theoretical ones. The presented conditional equation to be satisfied for normal running is considered to support the basic planning of a crawler driven ROV.
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.
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