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Optical System for Underwater Positioning of Observation Class Remotely Operated Vehicle
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Vågkraft)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2016 (English)Conference paper, Published paper (Refereed)
Abstract [en]

To make wave power a viable energy source, large clusters of wave energy converters (WECs) will be deployed into large farms. For most of these farms, the output power of the WECs will be aggregated in a marine substation and then transmitted to the grid. The need for cost effective underwater connection operations is one of the main challenges with this kind of offshore installation. Our research is related to underwater connection with help of Observation Class Remotely Operated Vehicles (OC ROVs). The main idea is to use a docking system in order for the small and light ROV to perform the connection, using the reaction force from its docking point instead of the motors propulsion, the latter being too little. This docking operation has to be very accurate and needs both an autopilot and a good positioning tool. In this paper we present an optical positioning system made of green lasers that together with the ROV’s camera measure the distances to the docking point. This is obtained by tracking the laser beams on the images captured from the camera and using triangulation of the points extracted. The tool has been implemented into an OCROV and tested in a tank.

Place, publisher, year, edition, pages
2016.
Keyword [en]
ROV, positioning, underwater connections, wave energy converters
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:uu:diva-302641OAI: oai:DiVA.org:uu-302641DiVA: diva2:963000
Conference
3rd Asian Wave and Tidal Energy Conference, AWTEC, Singapore
Available from: 2016-09-07 Created: 2016-09-07 Last updated: 2016-09-08Bibliographically approved
In thesis
1. Underwater Electrical Connections and Remotely Operated Vehicles
Open this publication in new window or tab >>Underwater Electrical Connections and Remotely Operated Vehicles
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Remotely Operated Vehicles (ROVs) are underwater robots that perform different kind of operations, from observation to heavier tasks like drilling, carrying and pulling cables, etc. Those ROVs are costly and require skilled personal to operate it as well as equipment for transportation and deployment (boats, cranes, etc.).

The division for electricity at Uppsala University, is developing a wave energy converter (WEC) concept. The concept is based on a point-absorbing buoy with a directly driven linear generator placed on the seabed. Several units are connected to a marine substation that is located on the seabed, whose role is to collect and smooth the power absorbed from the waves and then bring it to the shore through one single cable.

Cable connection is a big challenge in the project because the WEC concept is small and many units are necessary to create a rentable farm. Nowadays this operation is performed by divers but using Observation Class ROV (OCROV) could be an interesting alternative since they are affordable at lower costs and easier to operate. Cable connection is however a heavy task and requires force that an OCROV does not have. It will need a docking system from which the vehicle will take its force. It would then go to the station, dock itself to this support plate, grab the cables and connect them together. This procedure cannot be done by the ROV operator because it requires accurate displacement and quick adjustment of the robot’s behavior.

An autopilot was created in Matlab Simulink that consists of three units: the path following, the ROV, and the positioning unit. The first one uses the vehicle’s position and computes the speed and heading to be applied on the ROV in order to guide it on the desired path. The second one contains a controller that will adapt the thrust of each propeller to the force needed to reach the desired heading and speed from the path following unit. It also contains the model of the ROV that computes its position and speed. The last unit consists of a Kalman filter that estimates the ROV position and will be used in case of delay or failure in the communication with the positioning sensors.

The autopilot model is used with a positioning system that utilizes green lasers and image processing. Two green lasers are used as fixed points in each camera picture and from their distance on the image, the actual distance between the ROV and the docking platform can be computed. In addition, optical odometry is used. The idea behind is to estimate how the ROV is behaving by evaluating the changes between two pictures of the camera. Those two systems, laser and odometry, work together in order to get more accurate results.

The laser system has so far been tested in air. The distance measurements gave interesting results with an error inferior to 3%, and angle measurements gave less than 10% error for a distance of one meter. One advantage with the system is that it gets more accurate as the vehicle gets closer to the docking point.

In addition to the ROV project, a review study was conducted on the variability of wave energy compared with other resources such as tidal, solar, and wind power. An analysis of the different tools and models that are used to forecast the power generation of those sources was done. There is a need for collaboration between the different areas because the future will aggregate those different sources to the grid and requires a unification of the models and methods.

Place, publisher, year, edition, pages
Uppsala: Department of Engineering Sciences, 2016. 66 p.
Series
UURIE / Uppsala University, Department of Engineering Sciences, ISSN 0349-8352 ; 349-16L
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-302644 (URN)
Presentation
2016-09-30, 16:08 (English)
Opponent
Supervisors
Projects
Lysekil project
Available from: 2016-10-18 Created: 2016-09-07 Last updated: 2016-10-18Bibliographically approved

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