Improvement to date of the multi-goal AUV by ECA has culminated in a ten-day deepwater pipeline inspection trial for BP America Production Co. in the King field in the Gulf of Mexico. In mid-2006, the completed a pre-programmed inspection mission with no physical hyperlink to the surface.
The trials had been supported by ECA’s US companion Harvey Lynch Inc. from an Oceaneering vessel hired by BP. The runs integrated numerous missions at 1,356 m (four,450 ft) on a 229 mm x 330 mm (9 in. x 13 in.) flowline. The car capabilities had been confirmed for the following:
- Precise repositioning close to seabed right after the descent phase
- Maintaining an acoustic supervision from the surface all through the mission
- Validating a sophisticated mission management method
- Discovering and “locking” onto a pipeline right after a browsing phase
- Tracking and closely following a pipeline among 1 and two m (three.28 and six.56 ft) above the pipe enabling recording of higher good quality video photos of the pipeline
- Detecting and carrying out close inspection of an anomaly making use of committed patterns
- Safely getting recovered to the surface.
The ’s major traits are a length of five m (16 ft), a maximum physique diameter of 1.two m (four ft), an all round height of 1.five m (four.9 ft), total weight of two,one hundred kg (four,630 lb) which includes up to 200 kg (441 lb) payload, and an operating depth of -three,000 m (-9,842 ft).
Fig 1. Alistar 3000 maneuverability advantages from longitudinal, lateral and vertical thrusters.
It is equipped with 4 longitudinal, two lateral and two vertical thrusters. The actuators layout delivers maneuverability, in particular at zero speed, providing the autos the capacity to hover. An active ballast method enables the car to operate from to three,000 m (9,842 ft) devoid of the want to manually adjust the ballasting ahead of launch. Alistar is in a position to operate at knots when hovering and can attain a maximum speed of six knots by means of water.
The car has pitch and roll stability due to its mechanical architecture, decreasing the power consumption for stabilizing the car, which is of paramount significance for an AUV.
Fig two. This reduce-away of the AUV shows the removable payload skid front section and bottom section.
A removable lithium ion secondary battery, housed in a stress hull, delivers 25 kW of embarked power with a maximum recharge time of eight hours. This battery delivers 24-hr autonomy at cruise speed. A computer system-primarily based battery management method monitors the battery status.
Precise positioning, tracking, and monitoring are accomplished making use of the following gear: Navigation sensors such as Inertial Navigation Program (INS), Doppler Velocity Log (DVL) and Kalman Filter higher accuracy depth sensor altimeter obstacle avoidance method GPS and, acoustic localization transponder.
The AUV has numerous communication systems, which includes a fiber optic hyperlink, a radio Ethernet hyperlink and underwater acoustic communications. The fiber optic hyperlink is made use of when the car is onboard the ship to download the mission ahead of launch and to retrieve information at the finish of the mission. This hyperlink also can be made use of to get actual-time information such as video and sonar photos from the car. The radio hyperlink is made use of on surface, to transfer information among the car and the surface ship and to operate the AUV from either the major console or a transportable remote console throughout launch and recovery. The underwater acoustic communication method consists of a bi-directional, low information price hyperlink to monitor and to send orders to the car and a higher-price information hyperlink to send video or sonar photos to a surface vessel to monitor the good quality of the information recorded by the car.
Car security is offered by a wellness monitoring method, integrated security weights, security beacon, radio and ARGOS beacons, flasher, and water ingress sensors.
The Autonomy Management Program (AMS) of the AUV has to execute a mission, that can be modified in an uncertain atmosphere. Execution should take into account the external elements (a surface ship, a target) with which the AUV may well communicate. There are other elements to think about as effectively, such as the internal Wellness Management that is not necessarily coupled to the mission.
For this function, the AMS should handle information coming from sensors (depth meter, sonars, communication receivers) and should produce orders to actuators (propellers, communication transducers) so the mission can be executed.
Fig three. The assistance vessel for BP’s Gulf of Mexico tests.
The AMS has a dual-function structure:
1. “Awareness making” utilizes sensor information to produce a numerical state of the car and its atmosphere, and some symbolical events (by detection and classification).
two. “Decision making” utilizes the previously gathered information to produce the preferred behavior by indicates of actuators. Guidance and autopilot are the low-level component of choice creating.
Fig four. The AUV launch for BP’s Gulf of Mexico tests.
The AMS utilizes a dual “living” database structure. The “World Model” is an a priori numerical model of the car, the atmosphere, and their interactions. This model is initialized at the starting of the mission and can be modified throughout the mission. The “Vehicle Behavior” describes (in coherence with the initial Planet Model) perfect anticipated car behavior.
The Mission Management Program is component of the all round AMS, which delivers the operating group with full functions for arranging, monitoring, and post-processing by means of its Mission screen and Information Vision screen.
The mission screen delivers enhanced uncomplicated-to-use interactive tools to generate fundamental AUV behaviors primarily based on pre-defined models. A mission model is composed of “phases” linked with behaviors and “chaining links” that specify how mission phases are linked. Safety parameters also are defined to full mission information (operating region, intended duration of mission, thresholds). Models are managed by means of a database method to make mission information persistent.
Fig five. Mission management gear is carried out onboard an help vessel.
An integrated simulation function permits verification of the coherence and feasibility of the programmed mission.
Mission information can be uploaded to the AUV by means of Ethernet radio hyperlink in the widespread XML format.
The Information Vision screen shows video/sonar information from AUV cameras, plus navigational parameters, to assist the operator manually manage the robot to get it into the appropriate orientation to start out autonomous operations. The screen is also made use of later for recovery at the finish of the mission.
Fig six. Mission management gear is carried out onboard an help vessel.
The mission is monitored making use of a USBL method and by information received from the AUV by means of acoustic transmission. Optionally, operations can be supervised by sending single orders to the AUV according to the programmed mission or for safety causes.
Immediately after downloading the onboard information, recorded payload information are processed and analyzed making use of manufacturer offered tools. Recorded navigational information can be re-played (Mission screen) synchronized with recorded video/sonar information (Information Vision screen) below the manage of the operator in a “Video Player” way. They also can be processed particularly for transfer to an external evaluation method.
Distributed computer software architecture of the method, primarily based on a “publish-subscribe” information server, offers it scalability and AUV behavior enrichment capacities.
Fig 7. This artist’s rendering illustrates kinds of missions for the Alistar 3000.
Due to its higher stability, maneuverability, and hovering capability, is a multi-goal car. Even so, the method is developed mostly to inspect underwater structures such as pipes, risers, mooring lines, wellheads, manifolds and so forth. It also delivers pipelay help by carrying out TDP monitoring. The method can execute numerous missions such as basic web page survey, pre- and post-lay survey.
Payloads are installed on skids in two sections of the car, 1 at the front and the other underneath. The method has been developed for interface with diverse manufacturer gear.
Every year, thousands of kilometers of pipelines are inspected with towed fish or ROVs fitted with sonars, video, and magnetic sensors, opening a industry for inspection variety AUVs.
The difficulty for pipeline inspection with an AUV mostly lies in the truth that as-constructed reports providing the position of these pipelines are not precise adequate to be in a position to pre-system a trajectory with waypoints above the pipeline. Video inspection of a pipeline also indicates the AUV is straight above the pipeline with a tolerance of about 508 mm (20 in.) either side and at about 1 m (three ft) above it.
The AUV made use of for performing this variety of process needs the car to be really close to the pipe. This indicates a car with higher maneuverability to preserve its relative position to the pipe and to stay clear of a collision with the seabed. The is fitted with thrusters to present numerous degrees of freedom.
The car also requires to have a particular set of sensors (in addition to the video method made use of to record the pipe video photos) to discover the pipe and to comply with it even when sections are partially or entirely buried.
To create pipeline inspection for the , numerous actions had been followed and trials performed given that 2004. The 1st tests made use of . These trials had been in July 2004 with the inspection of a 508-mm (20-in.) diameter, 500-m (1,640-ft) extended pipe in shallow water in Toulon, France. In the course of these tests, was “locked” onto the pipe by the operator. After locked, the car followed the pipe autonomously, making use of its acoustic sensor, 1-two m (three-six ft) above it, recording video photos.
Then, this 1st version of Autonomous Inspection Capability was transferred to when testing numerous kinds of sensors that could be made use of for pipe and underwater inspection. Amongst the sensors tested had been: side scan sonar, multi beam echo-sounder, magnetometer, acoustic profiler, and CP sensors. This assessment phase was concluded in 2004. The choice of a set of acoustic and magnetic sensors was then integrated and tested with .
The Alistar 3000 AUV getting retrieved following a test run.
The suite of sensors chosen with each other with the algorithms created allow the vessel to search for the pipeline automatically detect and ‘lock’ onto the pipe comply with the pipe, detect and inspect CP anodes method and inspect a structure with a committed pattern and, record video and sonar photos of the pipe.
These capabilities had been demonstrated in sea trials in France in 2005 and 2006.
“Sea trials prove AUV pipeline inspection value”. January 2007.