ABSTRACT

Hydrodynamic coefficients are presented based on ¼ scale model testing of a Super Scorpio ROB, a design typical of many workboat vehicles. Since subsea intervention often requires ROVs to carry a variety of tools and equipments, force and moment measurements were also taken for the model carrying two representative work packages : a pipeline survey skid an a control pod replacement module, the latter being of similar size to the ROB itself. These results should prove useful in assisting powering calculations and operating assessments, as well as supplying input data for control simulators.

Introduction

Remotely Operated Vehicles (ROVs) have made an increasingly important contribution to subsea operati.ons in the offshore oil industry. ROV's have been used in support of activities ranging from drilling and construction to inspection and maintenance, and are ideally suited to such tasks as pipeline surveys. A number of recent proposals depend critically on ROV capabilities (e.g. BP's DISPS and Esso's EOIPS projects). Efficient intervention depends partly on the ability of an ROV to have "good" transit speeds, a high degree of maneuverability and no tendency to instabilities, particularly at the worksite. Papers dealing with the design of ROVs, however, generally provide little information on the methods used to determine an ROV's hydrodynamic characteristics. Rogers et al (1982) outline what appears to be a common approach, the drag coefficient Cd for their streamlined ROV being estimated in relation to the known coefficients of similar bodies. They state that open-frame bodies have Cd between 1.2 and 1.4;. however no information on the geometry of the open frame bodies is given, nor is any mention made as to whether these values include any allowance for drag due to thruster interactions with the ROV hull.

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