Maritime Autonomous Surface Ships (MASS) currently have no formal regulations developed specifically for their operation, as their regulatory framework is still under development. Rasmussen's Risk Management Framework has been used to develop an actor map of the current MASS system in the UK, to show who the actors, decision-makers, and planners are within the wider sociotechnical system and the level at which they sit. From the actor map, two social networks were created, one to show the connections that currently exist between the actors within the MASS system and another to show what a future MASS system could look like if regulations and standards were put in place for MASS. Social Network Analysis was then used to investigate the wider MASS system's dynamics, to understand which actors currently have a high degree of influence within the UK MASS system, and where the shortfalls are in the current MASS system. The analysis showed that the industry and end user levels lacked support from the higher system levels, and the addition of formal regulations and standards in the future MASS system would increase the MASS system's resilience. System recommendations for each level in the Risk Management Framework were then made to suggest ways to increase the influence of the regulators and promote the safe operation of MASS.

It is expected that a key part of a future with increasing use of maritime autonomous systems, will require collaborative and integrated approaches to working. How such approaches can be developed and tested was the focus of the Integrated Mission Management System 2019 (IMMS2019) project. The immediate objective was to experimentally demonstrate the ability of a single mission management system to control a fleet of heterogeneous, multi-domain autonomous platforms whereby their collaborative mission could be planned, verified, and delivered. To challenge the various spatial-temporal-energetic-communication-environmental constraints when operating such a fleet, real-world demonstration trials were carried out in Plymouth sound deployed from the Thales Maritime Autonomy Centre at Turnchapel Wharf. The trials were focussed on providing essential information into how such collaborations can be best executed, alongside invaluable lessons as to how existing platforms need to enhance their interoperability and in particular, robustness of communications and mission plans.

Increasing demand for versatile and long-endurance autonomous underwater vehicles puts significant design pressure on all aspects of AUV design and operation, including that of the propulsive system. The present study discusses testing of a thruster unit and several propellers developed to propel a hybrid glider/flight-style underwater vehicle. Due to the AUV being required to operate at largely different speeds and thrust levels between the two configurations, the propulsive subsystem needs to be capable of remaining efficient and effective across a wide range of operating conditions. Thus, the current results focus on quantifying all of the factors affecting the drive train, ranging from open-water performance of the propeller up to electro-mechanical efficiency of the magnetic coupling and geared electric motor. It is shown that, depending on the required operating point, total efficiency of the vehicle is primarily affected by non-linear low Reynolds number effects, sudden drop of gearbox efficiency at low revolutions and applied torques, as well as blade deformation, aside of the baseline propeller efficiency.

A key risk with autonomous systems (AS) is the trustworthiness of the decision-making and control mechanisms that replace human control. To be trustworthy, systems need to remain safe while being resilient to unpredictable changes, functional/operational failures and cybersecurity threats. Rigorous validation and verification are essential to ensure trustworthiness of AS. Current engineering practice relies heavily on Verification and Validation (V&V) test-and-fix of system characteristics which is very time-consuming and expensive, limiting the possibilities for exploration of alternatives in system design. Instead, we focus on building a correct-by-construction system. In this paper, we present an approach to identifying and analysing mission requirements for squads of autonomous missions. Clear definition of requirements is an important pre-requisite for mission planning and for V&V of mission management. We use a structured approach to requirements identification and use formal modelling to help remove ambiguities in the requirements and to specify formal properties that should be satisfied by the missions. Our approach use a combination of analysis techniques based on Systems Theoretic Process Analysis (STPA) and formal modelling to generate critical requirements that ensure the safety and security of the system. We also suggest a compositional approach for formal modelling to enhance re-usability and address the complexity of formal modelling. Our approach is being evaluated through consideration of a combined mission of an Unmanned Surface Vehicle (USV) with deployment/recovery of small Unmanned Underwater Vehicles (UUV) within a shipping channel whereby the USV has to safely maintain station for a long period and then proceed to recover the UUV, while maintaining a communication link to an Unmanned Aerial Vehicle (UAV).

Two models of underwater gliders were tested in a wind tunnel: one corresponding to a legacy shape commonly used in contemporary vehicles and the other a scaled down version of a new design. Performance of the two vehicles was characterized over a range of speeds and angles of attack. Particular attention was paid to the effect of sharp features along the hulls of the two vehicles and how they affect the observed flow regime. It has been shown that the new design, which uses a bow shape designed to encourage natural laminar flow, benefits from a 10% reduction of parasitic drag and 13% increase in lift-to-drag when the hull surface is smooth. The legacy glider, made up of a faired bow and a cylindrical hull, suffers from laminar separation and up to 100% increase in induced drag if the flow over its bow is prevented from transitioning to a turbulent state before encountering adverse pressure gradient at lower Reynolds numbers. This results in lowering of attainable speed at shallow glide path angles, whereas the associated parasitic drag reduction is demonstrated to increase the maximum velocity of the glider when moving at glide slopes greater than approximately 30°. 1. Introduction Underwater gliders are autonomous underwater vehicles (AUVs) that rely on using a buoyancy engine to ascend or descend through the water column, and by adjusting their pitch, they can use this vertical motion to develop forward thrust from their hydrofoils. This propulsion method allows them to undertake long-endurance missions, often several months long (Eriksen 2003; Rudnick et al. 2004; Graver 2005). Hydrodynamic performance of an underwater glider is primarily governed by its lift-to-drag (L/D) ratio, which dictates the minimum glide path angle the vehicle may adopt, and drag coefficient, which affects the maximum forward speed the glider may achieve for a fixed amount of vertical force developed (Graver 2005). It is thus important to minimize the drag of the AUV to allow it to perform longer deployments and gather more science data without increasing the size of the engine. Because of the typical Reynolds numbers on the vehicle hulls being less than 106 and of the order of 104–5 on the appendages, laminar and transitional flow regions may occur. Correctly identifying these is critical to achieve a robust performance prediction.

Hydrodynamic design of an underwater glider is an act of balancing the requirement for a streamlined hydrodynamically effective shape and the consideration of the practical aspects of the intended operational envelope of the vehicle, such as its ability to deploy a wide range of sensors across the water column. Key challenges in arriving at a successful glider design are discussed and put in the context of existing autonomous underwater vehicles (AUV) of this type. The design cycle of a new vehicle shape is then described. The discussed AUV will operate both as a buoyancy-propelled glider and a flight-style propeller-driven submersible, utilizing its large size to deliver substantial scientific payloads to remote locations to perform environmental monitoring, seabed survey, and exploration for subsea oil, gas, and material deposits. Emphasis is put on using computational fluid dynamic (CFD) methods capable of predicting laminar-turbulent transition of the flow to estimate the performance of candidate designs and thus inform and guide the evolution of the vehicle. A range of considered shapes is therefore described and their hydrodynamic characteristics predicted using CFD are summarized. A final shape for the new glider is then proposed. This is then subject to an in-depth flow-field analysis, which points out how natural laminar flow may be used as a means of drag reduction without compromising the practical aspects of the design, such as its ability to carry sufficient payload. Finally, the obtained data are used to project the expected glide paths, as well as give preliminary estimates of its range. These show the benefits of minimizing the vehicle drag, as well as highlight the possible tradeoffs between maximizing speed and endurance of the AUV.

Ships and offshore structures operate in harsh and corrosive environments and they are subject to high hydrodynamic and inertial loads. Thus it is important to accurately predict the mechanical response of thin-walled marine structures subject to corrosion damage in loaded conditions. This paper present a transition study to investigate in depth the usage of shell and solid elements in nonlinear finite element structural analysis with localised corrosion features. An experimental, stereo full field imaging technique, 3D digital image correlation is used to verify both the shell and solid modelling results. The solid-to-shell coupling techniques were subsequently assessed based on a deck plate model. Models containing a localised section using either the second-order hexahedral element C3D20 or tetrahedral element C3D10I show a similar performance that is compatible with the model using only shell element. The proposed coupling method works well for localised electrochemical or mechanical-electrochemical analysis with subsequent geometrical updates.

The experimental procedures developed to measure small forces generated by underwater vehicle appendages in a wind tunnel are described. These involve using precision load cell sensors arranged into a bespoke dynamometer, that has been integrated into a stand-alone wind tunnel rig. The set up is used to quantify performance of a scaled underwater glider hydrofoil, with particular care being paid to the effects of laminar and transitional flow features. Present data are benchmarked against similar measurements and simulations and it is shown that satisfactory results may be obtained with the current approach despite its simplicity and low cost. The apparatus is then used to show that the presence of laminar flow significantly affects performance of the considered foil at Reynolds numbers corresponding to a typical regime in which underwater gliders operate.

Hydrodynamic design of an underwater glider is an act of balancing the requirement for a streamlined, hydrodynamically effective shape and the consideration of the practical aspects of the intended operational envelope of the vehicle, such as its ability to deploy a wide range of sensors across the water column. Key challenges in arriving at a successful glider design are discussed and put them in the context of existing autonomous underwater vehicles (AUV) of this type. The design cycle of a new vehicle shape is then described. The discussed AUV will operate both as an buoyancy-propelled glider and a flight-style, propeller-driven submersible, utilising its large size to deliver substantial scientific payloads to remote locations to perform environmental monitoring, seabed survey, and exploration for sub-sea oil, gas and material deposits. Emphasis is put on using computational fluid dynamic (CFD) methods capable of predicting laminar-turbulent transition of the flow in order to estimate the performance of candidate designs and thus inform and guide the evolution of the vehicle. A range of considered shapes are therefore described and their hydrodynamic characteristics predicted using CFD are summarised. A final shape for the new glider is then proposed. This is then subject to an in-depth flowfield analysis which points out how natural laminar flow may be used as a means of drag reduction without compromising the practical aspects of the design, such as its ability to carry sufficient payload. Finally, the obtained data are used to project the expected glide paths, as well as give preliminary estimates of its range. These show the benefits of minimising the vehicle drag, as well as highlight the possible trade-offs between maximising speed and endurance of the AUV.

For marine platforms, assessing the structural resilience in a corroded condition is vital for both design and maintenance practices. With the development of computational and experimental methods for structural analysis, the accuracy of the structural response prediction relies on a better understanding of the material degradation process. However, a realistic estimate of corrosion is inherently a complex undertaking. Corrosion of even a single form can often involve multiple stages, each of which has different steps across several geometric scales; corrosion systems are often multi-layered and involve geometric complexities; the mechanical factors (stress/strain distributions) could affect the corrosion initiation and kinetics. These complexities have resulted in scientific barriers to the advancement of a corrosion prognosis that forecasts damage accumulation, as well as a computational realization of the corrosion-structural analysis. This paper reviews the numerical and experimental work that the authors have done, including the development of nonlinear finite element models to assess the behavior of damaged steel ship structures, full-field experimental verifications, application of the mechano-electrochemical theory and in situ tensile-corrosion tests. It is intended that the outcome of this research will be the establishment of a systematic multi-scale multi-physics experimental and numerical protocol for predicting aged structural resilience.

Underwater vehicles are increasingly important tools for use in science and engineering, but maneuverability and mission life seem to be mutually exclusive goals. Inspired by the unique swimming method of the plesiosaur, which used four flippers of essentially equal size and musculature, we analyzed designed and built an underwater vehicle with the potential for both gliding and active maneuvering modes. Using 2D simulations and strip theory approximation to account for the changing arc length along the flipper span, we studied the wake and forces on the foils and determined the optimum flipper geometry, spacing and kinematics. To reduce mechanical and control complexity and cost, we next studied the impact of under-actuated kinematics. Even after optimizing pivot location and range of motion, leaving the foils free to pitch was found to reduce efficiency by approximately 50%. Based on these specifications, the vehicle was built and tested over a range of free swimming and maneuvering cases using motion tracking equipment. The excellent maneuverability of the under-actuated vehicle validates the concept, and the new platform should enable further detailed experimental measurements in the future.

Carbon steel marine platforms, including ships and offshore structures, are at high risk of corrosion due to the combination of aggressive seawater environment, corrosive cargoes and constantly changing loading conditions. In particular, the combined influence of mechanical and electrochemical effects (which is often termed mechano-electrochemistry) has gained increasing attention over the last decade. Although various experiments, along with theoretical/empirical expressions, have been proposed to establish the relationship between stress/strain and the corrosion behavior, there are few in situ measurements of corrosion and the mechanical properties. Moreover, such corrosion mechanisms have not been incorporated for large scale ship or offshore structural members. This work has developed an experimental protocol including in situ potentiostat and quasi-static tensile tests to provide an improved understanding of the corrosion behavior of UNS G10210 steel at different stress levels. A novel local-global finite element method has been proposed to model a steel plate at a ship compartment scale under uniaxial quasi-static tensile/compressive loading. The stress distributions together with the experimental measurements were utilized to simulate a local mechano-electrochemical corrosion process and predict the stress-induced corrosion rate change. The modeling results demonstrate a more realistic approach to estimate marine structural integrity considering stress-induced localized corrosion.

Progressive Collapse Method (PCM) has been broadly applied to predict moment-carrying capacity of a hull girder, however accuracy of PCM has not been much studied. Accuracy of PCM is known to be dependent on how Load-Shortening and -Elongation (LSE) curve of a structural units are well predicted. This paper presents a new procedure to determine LSE datum based on box girder Finite Element Analyses (FEAs) instead of using finite element model of stiffened panels. To verify reliability of FEA results, the simple box girder collapse test results are compared with FEA results of same box girders. It reveals one frame-based box girder model is sufficiently accurate in terms of ultimate strengths of the box girders. After extracting LSE data from the box girders, PCM-based moment-carrying capacities are compared with those from FEAs of the box girders. PCM results are found to be equivalent to FEAs in terms of moment-carrying capacity if accurate LSE data are secured. The new procedure is applied to well-known 1/3 scaled frigate full section. Very excellent moment-carrying capacity of frigate hull section is obtained from PCM with LSE data from box girder FEAs.

The process of designing an apt hydrodynamic shape for a new underwater glider is discussed. Intermediate stages include selecting a suitable axi-symmetric hull shape, adding hydrofoils and appendages, and evaluating the performance of the final design. All of the hydrodynamic characteristics are obtained using computational fluid dynamics using the kT - kL - ω transition model. It is shown that drag reduction of the main glider hull is of crucial importance to the ultimate performance. Suggested steps for achieving this are the encouragement of natural laminar flow, integration of sensors into the streamlined hull shape, and sound operational practice.

The ultimate longitudinal bending strength of thin plated steel structures such as box girder bridges and ship hulls can be determined using an incremental-iterative procedure known as the Smith progressive collapse method. The Smith method first calculates the response of stiffened panel sub-structures in the girder and then integrates over the cross section of interest to calculate a moment-curvature response curve. A suitable technique to determine the strength behaviour of stiffened panels within the Smith method is therefore of critical importance. A fundamental assumption of the established progressive collapse method is that the buckling and collapse behaviour of the compressed panels within the girder occurs between adjacent transverse frames. However, interframe buckling may not always be the dominant collapse mode, especially for lightweight stiffened panels such as are found in naval ships and aluminium high speed craft. In these cases overall failure modes, where the buckling mode extends over several frame spaces, may dominate the buckling and collapse response. To account for this possibility, an adaptation to large deflection orthotropic plate theory is presented. The adapted orthotropic method is able to calculate panel stress-strain response curves accounting for both interframe and overall collapse. The method is validated with equivalent nonlinear finite element analyses for a range of regular stiffened panel geometries. It is shown how the adapted orthotropic method is implemented into an extended progressive collapse method, which enhances the capability for determining the ultimate strength of a lightweight stiffened box girder. (C) 2014 Elsevier Ltd. All rights reserved.

To date hydroelastic towing tank models are generally segmented, flexible backbone or hinged models which provide an extremely limited representation of the ship structure and record loads only at a finite number of locations between segments. Fully flexible “hydro-structural” models, whilst providing a more accurate structural representation are rarely used due to expense and the complicated nature of their construction. Rapid prototyping is a powerful tool the potential of which is yet to be exploited in the marine industry. By using it to manufacture a realistic ship structure from materials of different properties, new model manufacturing paradigms may be explored. The focus of this paper is the initial findings from an investigation of the use of three-dimensional (3D) printing technologies for manufacturing structurally accurate flexible towing tank models. A detailed assessment is carried out of the material properties of 3D printed materials and their ability to model the scaled structural behaviour of a ship. Scaling implications when considering the realistic ship structure are presented and practical considerations for the construction of 3D printed towing tank models are discussed.