Tokihiro Katsui

Preliminary research on the thruster assisted crawler system for a deep sea ROV

In order to reduce a tension on a cable, a deep sea ROV is designed to minimize the weight. However, the ROV having a lightweight is apt to wheelie when running by means of a crawler system. In order to run stably in counterpoise the combination of the center of gravity and the center of buoyancy should be in an adequate area called “stable area” which can be obtained corresponding to the weight and the buoyancy by the theory described in previous papers. The stable area becomes small as the weight is light. The center of gravity and the center of buoyancy is designed to be in the stable area. However, one of the important matters is that the ROV runs forward and also backward. It results in changing the discrimination of the stable area. And it sometimes makes the center of the gravity and the center of buoyancy sometimes to be outside of stable area. So, it is advantageous to increase the weight only when running by crawler system and to change the center of gravity meaningly. This paper proposes a method to virtually increase the weight and to change the center of gravity by using thrusters. And we conducted preliminary experiments using a small-size ROV having four thrusters and crawler system in a water tank to confirm the advantageous effect.

Experimental research on movability characteristic of crawler driven ROV

In order to reduce a tension on a cable, a deep sea ROV is designed to minimize the weight. However, such a light weight will influence on the movability of crawlers. As an initial investigation experiments were conducted in a water tank using a vehicle of ROV ABISMO changing the weight, the buoyancy, the center of gravity and the center of buoyancy. It was observed that the ROV ran unstably in some cases in spite of the fact that the ROV could run stably on land. Especially when the weight in water of was less, the stability of the ROV got worse. It seemed that the ROV could not run on the sea floor in such cases. On the other hand, the ROV ran stably when the ROV had an adequate weight in water and adequate center of gravity as well as center of buoyancy. This paper describes the experiment results of motion of the ROV running in water by means of crawler system. This paper also describes a fundamental theoretical investigation for ROV running in water. A discrimination chart of stable running is presented for the center of gravity and the center of buoyancy. The discrimination line is obtained with the weight and the buoyancy of ROV, the water residence, the point of its application and the dimension of crawlers.

Research on Stability of Crawler System for Deep Sea ROV

A deep sea ROV is desired to be light from the viewpoints of reducing a tension on an underwater cable and possessing the adequate movability by thrusters in water. On the other hand, when moving by a crawler system on the seabed, such a lightweight will influence on its movability characteristics. As an initial investigation experiments using an actual ROV were conducted in a water tank. And it was observed that the ROV ran in wheelie in some cases and almost fell down in extreme case in spite of the fact that it could run stably on land. In order to clarify the results fundamental theory of stability of the ROV in steady running is presented. The theory gives the discriminant chart of stable running for the combination of the center of gravity and the center of buoyancy. Experiments using a model were conducted to verify the theory. In order to increase the stable area and also to change meaningly the center of gravity, this paper proposes a method to virtually increase the weight and to change the center of gravity by using thrusters. And preliminary experiments were conducted to confirm its advantageous effect.Copyright