13 research outputs found
Automation of underwater operations on wave energy converters using remotely operated vehicles
No full textIn the last fifteen years, the Division of Electricity at Uppsala University has been 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, whose role is to collect and smooth the power absorbed from the waves and then bring it to the shore through one single cable. A big challenge in the project is to reduce the costs related to the deployment and maintenance of the WECs and substation. Currently, those operations are performed by divers, which is costly and entail considerable risks. A possibility is to replace divers with automated solutions using small robots called remotely operated vehicles (ROVs). This PhD thesis proposes and analyses a method for deployment and maintenance of underwater devices with no use of diving operations. Existing ROVs need additional modules and equipment in order to carry out operations with the required force and precision. Typical missions are inspection, shackles or slings removal, valve closing, and cable connection. The latter demands especially high precision in the positioning: 5 mm in distance and 5◦ in heading angle. In addition, this operation involves forces up to 200 N. This combination power-precision is not reached by existing ROVs. This PhD thesis presents a positioning system for underwater robot to enable autonomous positioning of the vehicle before cable connection. The positioning system is composed of two green lasers and a monocular camera, and is based on image processing. Experimental results from laboratory testing show that the mean absolute error in distance measurement is as low as 6 mm at 0.7 m from the target, whereas the heading is minimized to 2◦. The computational time for the image processing is 13.6 ms per image, meaning the possibility of a 30 Hz measurement system. Used together with a closed-loop path-following unit, this positioning system can support autonomous docking. This PhD thesis presents the model of an autopilot and results from docking simulations, showing the performance of the positioning system used in closed-loop
Underwater Electrical Connections and Remotely Operated Vehicles
No full textRemotely 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.Lysekil projec
Autonomous docking based on optical positioning system for remotely operated vehicle
No full textUnderwater docking is of high interest as it could be used to chargeunderwater robots while on a mission, thus extending their range of ac-tion, or to upload data without retrieving the vehicle, thus increasing itsmemory capacity. In this paper, the purpose of the docking system is toperform cable connections using remotely operated vehicles. The modelof an autopilot for autonomous docking is presented and the performancesof its components are analysed. This autopilot is based on measurementsfrom an optical positioning system which localizes the vehicle based onfeature detection from image processing. It shows that this positioning system could be integrated to the modelled autopilot and used in closed-loop for autonomous docking.</p
Electrical Connectors for Underwater Applications
No full textPublisher Copyright: © 2021 John Wiley & Sons, Ltd.Nowadays, numerous companies offer a large choice of underwater connectors and assemblies, and it can be complex to distinguish the different technologies employed for each of them. This chapter provides an overview of the types of connectors that exist for underwater and subsea electrical connections. It presents different types of commercial-off-the-shelf electrical connectors, and lists their performances and defaults, as well as typical failure modes and their known causes. Although each manufacturer has its own designs and technologies, underwater connectors can be grouped into five main categories: rubber-molded, rigid-shell or bulkhead assemblies, fluid-filled underwater mateable, inductive coupling, and assemblies (non-unmateable). The chapter contains the theory on sealing and on connectors’ thermal, electrical, and mechanical properties. It provides information on connection procedures and other details about connecting subsea cables with a focus on the connection of offshore renewable energy farms.Peer reviewe
Automation of underwater operations on wave energy converters using remotely operated vehicles [Elektronisk resurs]
No full textIn the last fifteen years, the Division of Electricity at Uppsala University has been 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, whose role is to collect and smooth the power absorbed from the waves and then bring it to the shore through one single cable.A big challenge in the project is to reduce the costs related to the deployment and maintenance of the WECs and substation. Currently, those operations are performed by divers, which is costly and entail considerable risks. A possibility is to replace divers with automated solutions using small robots called remotely operated vehicles (ROVs). This PhD thesis proposes and analyses a method for deployment and maintenance of underwater devices with no use of diving operations.Existing ROVs need additional modules and equipment in order to carry out operations with the required force and precision. Typical missions are inspection, shackles or slings removal, valve closing, and cable connection. The latter demands especially high precision in the positioning: 5 mm in distance and 5◦ in heading angle. In addition, this operation involves forces up to 200 N. This combination power-precision is not reached by existing ROVs. This PhD thesis presents a positioning system for underwater robot to enable autonomous positioning of the vehicle before cable connection.The positioning system is composed of two green lasers and a monocular camera, and is based on image processing. Experimental results from laboratory testing show that the mean absolute error in distance measurement is as low as 6 mm at 0.7 m from the target, whereas the heading is minimized to 2◦. The computational time for the image processing is 13.6 ms per image, meaning the possibility of a 30 Hz measurement system. Used together with a closed-loop path-following unit, this positioning system can support autonomous docking. This PhD thesis presents the model of an autopilot and results from docking simulations, showing the performance of the positioning system used in closed-loop.</p
Review of Electrical Connectors for Underwater Applications
No full textThe history of underwater electrical connectors is relativelynew: In 1858, the first transatlantic communication cable was created. Sincethen, the need for subsea electrical connectors has been growing very fastin the offshore industry. Today numerous companies offer a large choiceof underwater connectors and assemblies, and it can be intricate to distinguish the different technologies employed for each of them. However theuse, deployment, maintenance, and lifetime of any subsea equipment, froma simple sonar to a wave energy converter, relies on its connectors. Hencethe design of an underwater electrical connector is to be carefully lookedat, and especially for tailor-made applications that have more specific requirements. To produce a good connector, it is necessary to account for thermal, electrical, and mechanical properties, as well as to determine thebest materials that should be used for the application. Finally, connector issues go hand in hand with the deployment and operation of any electrical equipment, and it is of interest to review the different techniques for cable connection, as well as the challenges related to cable layout. Those challenges can be of different nature, but they should all be taken into account for any subsea connection
Automation of subsea connections for clusters of wave energy converters
No full textTo make wave power a viable energy source, large clusters of wave energy converters should be deployed. For most of the farms the output power of the WECs should be aggregated in a marine substation and then transmitted to the grid. The need for cost effective underwater cable connection operations is one of the main issues in offshore operations. Underwater connections can be conducted with wet- or dry-mateable connectors, performed by divers or ROVs. Although there are existing solutions used by the oil and gas industry that could be employed, the capital expenditure needed is not compatible with the offshore renewable energy industry. The objective of this research is to decrease costs and minimize working hazards associated with sub-sea work when performing these underwater electrical connections. This article presents a solution using small ROV’s instead of divers to execute the task. The main idea is to perform the connection underwater, but using dry-mateable connectors. A solution to make this possible is to install air pockets at the substation enclosing the connectors. These boxes are meant to be filled with air and hence create a dry environment in which to perform the connections. This is achieved with help of two tools. First a docking system allows the operator to fix the ROV at the substation before doing the connection. Then a gripper tool added to the ROV grasps the cable and connects it to the substation in the air pocket. The procedure and design of this low-cost solution are described, and the different prototypes that have been tested for offshore operation are also shown.</p
Underwater Electrical Connections and Remotely Operated Vehicles [Elektronisk resurs]
No full textRemotely 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.</p
