MODUS: Space Shuttle for Deepwater Interventions
Authors: Clauss G.F. , Hoog S. , Vannahme M. , Gerber H. , Gasparoni F. , Calore D. 
Published: October 2008

This paper presents MODUS (Mobile Docker for Underwater Sciences), a specialized ROV for deployment, recovery and servicing of heavy sea bottom stations, e.g. scientific observatories for deepwater application (depth rated 4000 m). Developed, built and tested as part of the EC funded project GEOSTAR (Geophysical and Oceanographic Station for Abyssal Research), the new ROV-system includes the operating vessel with winch and umbilical and the versatile 'space shuttle' MODUS for handling the bottom station with modularized payload.

The paper focuses on aspects of the development as well as open water trials and missions. Results from hydrodynamic analyses are presented to illustrate design studies for minimized structure drag and therefore minimized power requirements for thruster driven horizontal movements. Motion analyses comprise the dynamic behavior of the ship and the entire deep dived system considering hydroelastic effects. Due to the direct coupling, vertical excitations of the ship in the prevailing sea are substantially transmitted along the submerged umbilical to the ROV, causing potentially harmful slack cable situations. Results from numerical simulations illustrate the dynamic response of the system due to ship oscillations in random seas and the associated downtime of MODUS operations.

The paper presents the latest technological and scientific applications of MODUS during its first cruises: Reaching depths of 3700 m within the EC funded projects GEOSTAR and BIODEEP (BIOtechnology from the DEEP) in the Mediterranean Sea demonstrates its high availability with reliable performance and low costs.

Introduction

The conquering of deepwater "or inner space" is technologically mainly driven by exploration and exploitation activities of the Offshore Oil and Gas industry. Key tools permitting and supporting these interventions are Unmanned Underwater Vehicles (UUV) comprising both Autonomous Underwater Vehicles (AUV) and Remotely Operated Vehicles (ROV). Consequently, during the last 25 years standard ROV technology evolved to a reliable everyday tool, used in all fields of oceanographic engineering [1]. This growing ROV market initiated numerous theoretical investigations and sea trials covering the entire scheme of static and dynamic problems during operation. Vertically tethered as well as towed body systems are characterized by hydroelastic effects, influencing the safe and reliable overall performance. These systems consist, in general, of an operating vessel, a tether, umbilical or towing cable and the suspended or towed sensor carrier, respectively. The tethers or umbilicals connecting the ship with the submerged sensor carrier enable the system to stay underwater almost without time restrictions. Because MODUS as a flexible inner space shuttle can operate various sea bottom stations and support deep sea missions the system opens a wide spectrum of activities, fully controlled by the operator on board the ship.

Fig. 1-GEOSTAR main components: Vessel with winch and A-frame, multifunctional umbilical, MODUS and Bottom Station(Available in full paper)

A major problem is the coupling of heave and pitch motions of the vessel and the subsequent oscillations of the suspended carrier system. Due to the transmission of wave induced ship motions along the submarine umbilical, the dynamic behavior and stability of the towed or suspended carrier becomes a critical aspect during operation.