Optimal control of the heave motion of marine cable subsea-unit systems

One of the key problems associated with subsea operations involving tethered subsea units is the motions of support vessels on the ocean surface which can be transmitted to the subsea unit through the cable and increase the tension. In this paper, a theoretical approach for heave compensation is developed. After proper modelling of each element of the system, which includes the cable/subsea-unit, the onboard winch, control theory is applied to design an optimal control law. Numerical simulations are carried out, and it is found that the proposed active control scheme appears to be a promising solution to the problem of heave compensation

Robotic Digital X-ray Scanning System for Deep Water Flexible Riser Inspection

Flexible subsea risers are highly complex structures with multiple layers and varying material types. They are being used worldwide for oil and gas extraction in deep water. The complexity of these flexible risers and the hostile conditions in a deep-water environment present major challenges for non-intrusive, in-service inspection. This paper presents a novel automated radiography inspection system to detect defects from X-ray images of such flexible risers. The concept of a robotic digital X-ray scanning system which addresses the needs and challenges of deepwater flexible riser inspections has been studied. The proposed radiography inspection system is an ideal solution for flexible risers as it penetrates through all the layers in the riser structure, providing detailed information on any damage to the various layers. The system integrates the advanced technologies of image processing, machine learning, and robot crawlers to automatically detect abnormal textures such as erosion, corrosion and strand damage, foreign objects and other critical features from flexible risers. The performance of feature extraction, feature normalization, image processing, and machine learning for the purpose of defect detection have been tested and analysed. With smart integration and enhancement of different techniques, the limitations of each algorithms have been mitigated while the overall performance has been improved significantly. The detailed stages of the implementation are also discussed. The key features of the subsea riser inspection system are: (i) Real-time radiographic inspection result, (ii) Robotic system adaptable to various pipe types and sizes, (iii) High accuracy and reliability.Innovate UK grant agreement No 10408

Sustainable seabed mining: guidelines and a new concept for Atlantis II Deep

The feasibility of exploiting seabed resources is subject to the engineering solutions, and economic prospects. Due to rising metal prices, predicted mineral scarcities and unequal allocations of resources in the world, vast research programmes on the exploration and exploitation of seabed minerals are presented in 1970s. Very few studies have been published after the 1980s, when predictions were not fulfilled. The attention grew back in the last decade with marine mineral mining being in research and commercial focus again and the first seabed mining license for massive sulphides being granted in Papua New Guinea’s Exclusive Economic Zone.Research on seabed exploitation and seabed mining is a complex transdisciplinary field that demands for further attention and development. Since the field links engineering, economics, environmental, legal and supply chain research, it demands for research from a systems point of view. This implies the application of a holistic sustainability framework of to analyse the feasibility of engineering systems. The research at hand aims to close this gap by developing such a framework and providing a review of seabed resources. Based on this review it identifies a significant potential for massive sulphides in inactive hydrothermal vents and sediments to solve global resource scarcities. The research aims to provide background on seabed exploitation and to apply a holistic systems engineering approach to develop general guidelines for sustainable seabed mining of polymetallic sulphides and a new concept and solutions for the Atlantis II Deep deposit in the Red Sea.The research methodology will start with acquiring a broader academic and industrial view on sustainable seabed mining through an online survey and expert interviews on seabed mining. In addition, the Nautilus Minerals case is reviewed for lessons learned and identification of challenges. Thereafter, a new concept for Atlantis II Deep is developed that based on a site specific assessment.The research undertaken in this study provides a new perspective regarding sustainable seabed mining. The main contributions of this research are the development of extensive guidelines for key issues in sustainable seabed mining as well as a new concept for seabed mining involving engineering systems, environmental risk mitigation, economic feasibility, logistics and legal aspects

Plenary keynote: Monitoring Safety Critical Infrastructure with Mobile Robots

Reliable Non Destructive Testing (NDT) is vital to the integrity and performance management of capital assets in safety critical industries such as aerospace, transportation, pipelines, petro-chemical processing, and power generation [ ]. The structures that are to be inspected are usually very large and located in remote and hazardous environments. The NDT system has to be deployed by first providing very expensive access, requiring the erection of scaffolding and lengthy preparation before NDT can start. In addition the system must be capable of finding and characterizing component and structural defects to a high probability of detection thereby decreasing the probability of failure. Another priority is to reduce outage time as the cost of loss of production runs into millions. This presentation describes recent developments in mobile wall climbing, swimming and pipe crawling robots that provide the means to perform NDT on difficult to access structures and provide the possibility of carrying out the NDT in-service thus preventing costly outages. In confined and hazardous environments they are the only means to reach a test site and perform the NDT. Our research, funded by the European Commission and Industry, is developing mobile NDT Robots to go inside petro-chemical storage tanks (while full of product) to inspect floors for pitting and corrosion [ ], to climb on the hulls of steel ships to inspect hundreds of kilometres of weld [ ], to inspect mooring chains securing off-shore oil and gas platforms in both air and underwater, to inspect the walls of petro-chemical storage tanks for corrosion and weld integrity, to inspect nozzle welds inside nuclear pressure vessels, to inspect concrete structures such as dams and buildings, to internally inspect buried pipelines that are currently not reachable by intelligent pigs, to climb up off-shore wind turbine towers to inspect the blades[ ], and to climb on aircraft wings and fuselage to detect for cracks and loose rivets

Non Destructive Testing With Mobile Wall Climbing And Swimming Robots (Abstract)

This keynote paper will describe the application of mobile climbing and swimming robots to perform Non Destructive Testing (NDT) of large safety critical infrastructure. Tools are required for the integrity management of structures such as storage tanks, pressure vessels, aircraft, ships, mooring chains, wind and tidal turbine towers/blades, subsea oil and gas pipelines and flexible risers, etc.[1, 2, 3]. The mobile robots are designed to provide access and deploy a variety of NDT techniques to test sites located on these structures. They obviate the need to carry out lengthy and expensive preparation such as the erection of scaffolding or the dangerous deployment of rope abseiling and platform systems. The aim is to reduce planned outage times by speeding up inspection and wherever possible to perform the NDT on-line thus preventing costly outages. In addition, intrusive robotic inspection systems are usually the only means to perform NDT of structures located in hazardous or difficult to access environments

Non Destructive Testing With Mobile Wall Climbing And Swimming Robots (Abstract)

This keynote paper will describe the application of mobile climbing and swimming robots to perform Non Destructive Testing (NDT) of large safety critical infrastructure. Tools are required for the integrity management of structures such as storage tanks, pressure vessels, aircraft, ships, mooring chains, wind and tidal turbine towers/blades, subsea oil and gas pipelines and flexible risers, etc.[1, 2, 3]. The mobile robots are designed to provide access and deploy a variety of NDT techniques to test sites located on these structures. They obviate the need to carry out lengthy and expensive preparation such as the erection of scaffolding or the dangerous deployment of rope abseiling and platform systems. The aim is to reduce planned outage times by speeding up inspection and wherever possible to perform the NDT on-line thus preventing costly outages. In addition, intrusive robotic inspection systems are usually the only means to perform NDT of structures located in hazardous or difficult to access environments

Application of Fieldbus Technology to Enable Enhanced Actuator Control of Automated Inspection for Offshore Structures

Due to extreme environmental loadings and aging conditions, maintaining structural integrity for offshore structures is critical to their safety. Non-destructive testing of risers plays a key role in identifying defects developing within the structure, allowing repair in a timely manner to mitigate against failures which cause damage to the environment and pose a hazard to human operators. However, in order to be cost effective the inspection must be carried out in situ, and this poses significant safety risks if undertaken manually. Therefore, enabled by advancements in automation and communication technologies, efforts are being made to deploy inspection systems using robotic platforms. This paper proposes a distributed networked communication system to meet the control requirements of a precision rotary scanner for inspection of underwater structures aimed at providing a robotic inspection system for structural integrity in an offshore environment. The system is configured around local control units, a fieldbus network, and a supervisory control system accounting for the environment conditions to provide enhanced control of actuators for automated inspection of offshore structures

Reconstruction of Riser Profiles by an Underwater Robot Using Inertial Navigation

This paper proposes a kinematic model and an inertial localization system architecture for a riser inspecting robot. The robot scrolls outside the catenary riser, used for underwater petroleum exploration, and is designed to perform several nondestructive tests. It can also be used to reconstruct the riser profile. Here, a realistic simulation model of robot kinematics and its environment is proposed, using different sources of data: oil platform characteristics, riser static configuration, sea currents and waves, vortex-induced vibrations, and instrumentation model. A dynamic finite element model of the riser generates a nominal riser profile. When the robot kinematic model virtually scrolls the simulated riser profile, a robot kinematic pattern is calculated. This pattern feeds error models of a strapdown inertial measurement unit (IMU) and of a depth sensor. A Kalman filter fuses the simulated accelerometers data with simulated external measurements. Along the riser vertical part, the estimated localization error between the simulated nominal and Kalman filter reconstructed robot paths was about 2 m. When the robot model approaches the seabed it assumes a more horizontal trajectory and the localization error increases significantly

Review of Composite Marine Risers for Deep-Water Applications: Design, Development and Mechanics

In recent times, the utilisation of marine composites in tubular structures has grown in popularity. These applications include composite risers and related SURF (subsea umbilicals, risers and flowlines) units. The composite industry has evolved in the development of advanced composites, such as thermoplastic composite pipes (TCP) and hybrid composite structures. However, there are gaps in the understanding of its performance in composite risers, hence the need for this review on the design, hydrodynamics and mechanics of composite risers. The review covers both the structure of the composite production riser (CPR) and its end-fittings for offshore marine applications. It also reviews the mechanical behaviour of composite risers, their microstructure and strength/stress profiles. In principle, designers now have a greater grasp of composite materials. It was concluded that composites differ from standard materials such as steel. Basically, composites have weight savings and a comparative stiffness-to-strength ratio, which are advantageous in marine composites. Also, the offshore sector has grown in response to newer innovations in composite structures such as composite risers, thereby providing new cost-effective techniques. This comprehensive review shows the necessity of optimising existing designs of composite risers. Conclusions drawn portray issues facing composite riser research. Recommendations were made to encourage composite riser developments, including elaboration of necessary standards and specifications

Design study of composite repair system for offshore riser applications

Risers in offshore operations are subjected to corrosion during their service life cycle. The use of relatively inexpensive, high strength to weight ratio fibre reinforced polymer composite (FRPC) as a load bearing pipe repair sleeve is an emerging technology that is becoming common for offshore applications. Risers experience complex loading profiles and experimental investigations often incur substantial time, complicated instrumentation and setup costs. The main aim of this research is to develop a design tool for the repair of offshore riser that suffers from external corrosion damage on its surface using FRPC material. The simplest configuration of a fixed platform riser in the form of a vertical single-wall pipe is being considered. Characterization of the stress-strain behaviour of the FRPC laminate in the composite repair system subjected to various load profiles of a common riser is performed. The means of composite repair takes into account the ease of automated installation. The final repair method considers the use of unidirectional pre-impregnated (prepreg) FRPC that is assumed to be helically wounded around the riser. Finite element models of the composite repair system were developed via ABAQUS. Global analysis of the entire length of the riser was omitted as external corrosions usually occurs in a localised manner on the surface of the riser. Instead, local analyses were conducted where boundary conditions were applied to mimic an infinitely long cylindrical structure such as the riser. The local analyses FEA models were made to capture the stress-strain behaviour of the FRPC laminate subjected to different load profiles including static loadings such as internal pressure, tensile load and bending load. The design loads were calculated based on a limit analysis known as Double-Elastic Curve method developed by Alexander (2008). Proper element selection and mesh convergence were carried out to determine the FE model that can minimize the time and CPU memory needed for the simulation without compromising the accuracy of the results. The second part of this research integrated experimental tests to validate the FE model developed using the ABAQUS general purpose code. Due to constraints on cost and supply of materials and equipment, small-scale tests were conducted. Similitude relations were used to determine the scale properties between the model and the prototype. The final results showed that the FE model can represent the real-life tests of corroded riser repaired with off-axis FRPC laminate with great accuracy of more than 85%. Hence can be a useful tool for design and parametric study of the composite repair system. Using the validated FE model, an extensive parametric study of the composite repair system with respect to varying corrosion defects was conducted. The thickness and length of the repair laminate were compared to the ASME PCC-2 standard. Optimum thickness and length of the composite laminate were determined based on the maximum allowable strains computed using the Double-Elastic Curve method. In addition, varying fibre angle orientation of the unidirectional prepreg was considered as it is one of the main factors in helical winding. Based on the results from the parametric study, a simple relation was developed to predict the required thickness of the composite repair system subjected to combined loading. This relation combined with the developed FE model can be used to provide a quick design and performance validation of a composite repair system for offshore riser, which is the main novelty aspect of this research