Moving Performance of Crawler Driven ROV on the Inclined Sea Bottom

Abstract

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.