Autonomous Underwater Vehicle for Subsea Intervention
With the growing trend to develop deepwater fields, the offshore oil and gas industry is constantly demanding tools for cost-effective, as well as reliable exploitation and maintenance of subsea equipment. Although, conventionally used Remotely Operated Vehicles (ROVs) have proven to be very efficient and versatile, they require a great amount of electrical energy as well as constant control from a support ship to underwater systems. A promising alternative is autonomous underwater vehicles (AUVs). These are free-swimming marine tools that require little or no human intervention. The work of ALIVE project was focused on broadening the scope of tasks carried out by AUVs. In specific, it addressed the issue of economically carrying out light intervention tasks on standard, un-modified underwater structures without the need or long and heavy umbilicals and costly support vessels. The ALIVE vehicle can be launched from any suitable vessel of opportunity and proceed independent under the supervision of an operator. It uses on-board computers, power packs and vehicle payloads for automatic control, navigation and guidance. The key technical contribution of the project was the development of a novel hybrid navigation system based on dead-reckoning as well as speed vector/altitude/depth. For dead-reckoning navigation, the system has been designed to rely on on-board sensors, and on external acoustic positioning system to periodically reset it. Corrections are made based on Global Positioning System (GPS) during surface navigation, and when it is underwater, corrections are provided by GIB system, which sometimes is referred to as "underwater GPS". What binds all these systems together is the amount of intelligence in the software created for the ALIVE vehicle. Following a set of tank and shallow water tests, sea trials of ALIVE navigation system have been successfully performed under severe open sea and wind conditions. Now, additional applications of ALIVE vehicle are being envisaged that include assistance in rescue operations, archaeological missions and hazardous materials collection.