A Wave Simulator and Active Heave Compensation Framework for Demanding Offshore Crane Operations

Abstract-In this work, a framework is presented that makes it possible to reproduce the challenging operational scenario of controlling offshore cranes via a laboratory setup. This framework can be used for testing different control methods and for training purposes. The system consists of an industrial robot, the Kuka KR 6 R900 SIXX (KR AGILUS) manipulator and a motion platform with three degrees of freedom. This work focuses on the system integration. The motion platform is used to simulate the wave effects, while the robotic arm is controlled by the user with a joystick. The wave contribution is monitored by means of an accelerometer mounted on the platform and it is used as a negative input to the manipulator's control algorithm so that active heave compensation methods can be achieved. Concerning the system architecture, the presented framework is built on open-source software and hardware. The control software is realised by applying strict multi-threading criteria to meet demanding real-time requirements. Related simulations and experimental results are carried out to validate the efficiency of the proposed framework. In particular, it can be certified that this approach allows for an effective risk reduction from both an individual as well as an overall evaluation of the potential harm

ALTERNATIVE AND FLEXIBLE CONTROL METHODS FOR ROBOTIC MANIPULATORS: On the challenge of developing a flexible control architecture that allows for controlling different manipulators

Robotic arms and cranes show some similarities in the way they operate and in the way they are designed. Both have a number of links serially attached to each other by means of joints that can be moved by some type of actuator. In both systems, the end-effector of the manipulator can be moved in space and be placed in any desired location within the system’s workspace and can carry a certain amount of load. However, traditional cranes are usually relatively big, stiff and heavy because they normally need to move heavy loads at low speeds, while industrial robots are ordinarily smaller, they usually move small masses and operate at relatively higher velocities. This is the reason why cranes are commonly actuated by hydraulic valves, while robotic arms are driven by servo motors, pneumatic or servo-pneumatic actuators. Most importantly, the fundamental difference between the two kinds of systems is that cranes are usually controlled by a human operator, joint by joint, using simple joysticks where each axis operates only one specific actuator, while robotic arms are commonly controlled by a central controller that controls and coordinates the actuators according to some specific algorithm. In other words, the controller of a crane is usually a human while the controller of a robotic arm is normally a computer program that is able to determine the joint values that provide a desired position or velocity for the end-effector. If we especially consider maritime cranes, compared with robotic arms, they rely on a much more complex model of the environment with which they interact. These kinds of cranes are in fact widely used to handle and transfer objects from large container ships to smaller lighters or to the quays of the harbours. Therefore, their control is always a challenging task, which involves many problems such as load sway, positioning accuracy, wave motion compensation and collision avoidance. Some of the similarities between robotic arms and cranes can also be extended to robotic hands. Indeed, from a kinematic point of view, a robotic hand consists of one or more kinematic chains fixed on a base. However, robotic hands usually present a higher number of degrees of freedom (DOFs) and consequentially a higher dexterity compared to robotic arms. Nevertheless, several commonalities can be found from a design and control point of views. Particularly, modular robotic hands are studied in this thesis from a design and control point of view. Emphasising these similarities, the general term of robotic manipulator is thereby used to refer to robotic arms, cranes and hands. In this work, efficient design methods for robotic manipulators are initially investigated. Successively, the possibility of developing a flexible control architecture that allows for controlling different manipulators by using a universal input device is outlined. The main challenge of doing this consists of finding a flexible way to map the normally fixed DOFs of the input controller to the variable DOFs of the specific manipulator to be controlled. This process has to be realised regardless of the differences in size, kinematic structure, body morphology, constraints and affordances. Different alternative control algorithms are investigated including effective approaches that do not assume a priori knowledge for the Inverse Kinematic (IK) models. These algorithms derive the kinematic properties from biologically-inspired approaches, machine learning procedures or optimisation methods. In this way, the system is able to automatically learn the kinematic properties of different manipulators. Finally, a methodology for performing experimental activities in the area of maritime cranes and robotic arm control is outlined. By combining the rapid-prototyping approach with the concept of interchangeable interfaces, a simulation and benchmarking framework for advanced control methods of maritime cranes and robotic arms is presented. From a control point of view, the advantages of releasing such a flexible control system rely on the possibility of controlling different manipulators by using the same framework and on the opportunity of testing different control approaches. Moreover, from a design point of view, rapidprototyping methods can be applied to fast develop new manipulators and to analyse different properties before making a physical prototype

Variable buoyancy anchor deployment analysis for floating wind applications using a Marine Simulator

The research presented in this paper has been primarily sponsored by EPSRC’s Supergen ORE Hub & ORE Catapult Floating Offshore Wind Centre of Excellence (grant number FF2021-1040). The authors acknowledge funding received from Energy Technology Partnership Knowledge Exchange Network scheme (grant number PR057-ME) that provided additional funding to support this work. The authors wish to thank Oceanetics Inc. and Aubin Group for their support towards this project. This work has benefited from the support and funding received from Net Zero Technology Centre and The University of Aberdeen through their partnership in The National Decommissioning Centre (NDC) and The Scottish Government’s Decommissioning Challenge Fund in part-funding the establishment of the Marine Simulator research facility at the NDC.Peer reviewedPublisher PD

Real-Time Motion Compensation in Ship-to-Ship Load Handling

DoktorgradsavhandlingLike the automotive industry, the maritime industry is facing a higher demand for autonomous offshore operations. It is therefore in the author’s belief that the marine industry has to develop and implement new technology for both existing and new products to meet the increased autonomy demand. This thesis aims at presenting a unified understanding of the motions and the accompanying load handling issue in ship-to-ship operations. The ship-to-ship kinematics is modeled and a crane operator assistant is developed as a possible solution to increase the so-called weather window of ship-to-ship load transfers. The weather window is today determined by the significant wave height, and the current limitation of such operations is at 2.5m significant wave height. Proposing new methods capable of assisting the crane operator when transferring the load from one ship onto another is believed to further relax the weather window criteria, as well as increasing both the safety and efficiency of the operation itself. A novel ship-to-ship estimation algorithm using the well known Extended Kalman Filter (EKF) is developed and experimentally investigated in the Norwegian Motion Laboratory. In addition to the ship-to-ship observer, an observer for measuring the suspended load motions is developed. These estimators are used to form the novel crane operator assistant presented at the end of this thesis. The presented assistant consists of a wire-length assistant and an anti-swing assistant, which both aim at assisting the crane operator in ship-to-ship load transfers by adjusting the crane operator inputs slightly in real-time. The expected outcome is increased repeatability and efficiency, as well as reduced risk in general. The developed methods are described using a common and consistent mathematical notation for both the observers and the kinematic control systems. The appended papers at the end of this thesis have experimentally investigated and validated the proposed methods using several experiments which have been carried out in the Norwegian Motion Laborator

Relating onshore wind turbine reliability to offshore application

With the award of the latest Round 3 offshore wind farm sites around the UK coast the wind industry is moving from the operation of near inshore to truly offshore wind farms. This has two major implications, the first being that wind turbines are now being specifically designed for offshore deployment, a key feature being that the new wind turbines are likely to be two to four times the size of the largest current onshore machines. The second is that due to the limitations of access to offshore wind turbines, their availability needs to be in the order of 98% or greater if reasonable costs of energy are to be achieved. The distance of the wind turbines from shore means that more attention needs to be given to the availability, reliability and maintainability of these offshore wind turbines. The research discussed in this report set out to examine these factors in more depth, using the reliability data of Clipper Windpower’s onshore 2.5 MW Liberty machine as the practical evidence for doing so. In analysing the data the primary aim was to build a picture of typical fault type and duration and more specifically alarm type, distribution and alarm quantity. These results were then compared with an external data source to identify common trends or major divergences and the findings used to identify potential improvements in availability, reliability and maintainability for the design of Clipper Windpower’s offshore Britannia 10 MW machine. The key conclusions of the research are that: The Britannia wind turbine pitch system needs dramatic improvement on that of the Liberty wind turbine and this requires further detailed investigation. The ability to access the wind farms quickly and cost effectively will be critical to maintaining the required levels of wind turbine availability. The Britannia wind turbine needs to be designed for reliability and availability not simply for keeping the wind turbine in a safe mode. The number and classification of alarms built into the wind turbine monitoring system needs to be critically reviewed with the aim of reducing and rationalising responses where possible

Advancing Climate Change Research and Hydrocarbon Leak Detection : by Combining Dissolved Carbon Dioxide and Methane Measurements with ADCP Data

With the emergence of largescale, comprehensive environmental monitoring projects, there is an increased need to combine state-of-the art technologies to address complicated problems such as ocean acidifi cation and hydrocarbon leak detection

Committee V.4 - Offshore Renewable Energy

This is the author accepted manuscript. The final version is available from CRC Press via the DOI in this recordProceedings of the 19th International Ship and Offshore Structures Congress, Cascais, Portugal, 7 - 10 September 201

Annual General Assembly of the International Association of Maritime Universities

978-84-947311-7-

Improving Energy Efficiency and Motion Control in Load-Carrying Applications using Self-Contained Cylinders

Because of an increasing focus on environmental impact, including CO2 emissions and fluid spill pollution, inefficient hydraulic systems are being replaced by more environmentally friendly alternatives in several industries. For instance, in some offshore applications that have multiple diesel generators continuously running to produce electricity, all hydraulic rotating actuators supplied from a central hydraulic power unit have been replaced with AC induction motors containing a variable frequency drive and gearbox. However, hydraulic linear actuators are still needed in most load-carrying applications mainly because of their high reliability associated with external impact shocks. Moreover, their force capacity is higher than that of their linear electromechanical counterparts. Valve-controlled linear actuators (cylinders) supplied from a centralized hydraulic power unit are standard in offshore load-carrying applications. In addition to the advantages mentioned above of hydraulic linear actuators, they have, nevertheless, a number of important drawbacks, which include: 1) a high level of energy consumption due to significant power losses caused by flow throttling in both the pipelines and valves, 2) reduced motion performance due to the influence of load-holding valves, 3) high CO2 emissions and fuel costs related to the diesel generator that supplies electricity to the hydraulic power unit, 4) significant potential for hydraulic fluid leakage because of many leakage points, 5) demanding efforts with respect to installation and maintenance, as well as 6) costly piping due to the centralized hydraulic power supply. The work presented in this dissertation and the appended papers are devoted to replacing inefficient hydraulic linear actuation systems traditionally used in offshore load-carrying applications with more environmentally friendly solutions. Two alternative technologies are identified, namely electro-mechanical and electro-hydraulic self-contained cylinders. The feasibility of replacing conventional valve-controlled cylinders with self-contained cylinder concepts is investigated in two relevant case studies.publishedVersio