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Ship manoeuvrability is closely related to the safety of ship operation in a real seaway; therefore, predicting a ship's manoeuvring performance is of great importance. However, an accurate prediction of ship manoeuvrability in a real seaway is one of the most challenging problems in ship hydrodynamics, attributed to the complexity of the flow arising from the hydrodynamic interactions between the hull, propeller, rudder, and external disturbances during manoeuvres. To date, theoretical methods have been widely used for the prediction of ship manoeuvring behaviours in real sea states. These approaches rely on assumptions from the potential flow theory. However, the reliability of the potential flow theory is limited due to the lack of physics associated with viscous and turbulent effects and the free surface resolution, which are significant for manoeuvring problems. Hence, such effects which are ignored in the potential flow theory should be incorporated in the numerical codes. In light of this, Reynolds-Averaged Navier-Stokes (RANS) approaches are very attractive alternatives to the theoretical methods since they are capable of directly accounting for viscous effects in their calculations. Free-running Computational Fluid Dynamics (CFD) simulations are progressively gaining popularity for manoeuvring prediction since they are capable of incorporating viscous and turbulent effects being important on ship manoeuvring as well as do not use any consumables (as opposed to experiments). However, due to its brevity, there are no definite guidelines and recommendations regarding the numerical setup of the free-running CFD simulation in different environmental conditions such as waves, shallow waters, and currents. Given this, in this thesis, the general framework is proposed for the analysis of ship manoeuvrability, course-keeping control, and seakeeping using the unsteady RANS computation coupled with the equations of rigid body motion with full six degrees of freedom (6DOF), with a particular focus on the numerical modelling for a free-running CFD model. Ships are exposed to various environmental loads such as waves, wind, and currents during their operations at sea. Such external disturbances can lead to substantial changes in the behaviour of a ship during manoeuvring when compared to its inherent behaviour in calm water. Nevertheless, to date, the vast majority of studies in the field of ship manoeuvrability have been devoted to analysing the inherent manoeuvrability of a ship in calm water in conformity with the recommendation of ITTC. Their findings are not able to provide general observations on the relationship between external disturbances and manoeuvring behaviours. This thesis, therefore, aims to systematically carry out hydrodynamic analyses of a ship's manoeuvring performance in different environmental conditions (including deep unrestricted water, regular waves, irregular waves, shallow water, and ocean currents) in order to provide an in-depth understanding of a ship's manoeuvrability for navigational safety at sea. Firstly, a literature review of previous publications on all aspects of ship manoeuvrability is performed. The literature survey presents an overview of current standards and guidelines regarding the assessment of ship manoeuvrability, and then outlines a classification of the methods widely applied to manoeuvring problems. The research gaps detected during the literature review are also listed, which are addressed in detail in this PhD. thesis. Following this, free-running CFD models are developed for the prediction of the ship's manoeuvring performance by means of an unsteady RANS solver. These models are validated against the available experimental results from a free-running test. The numerical results are found to be in good agreement with available experimental data, which demonstrates that the numerical approach proposed in the present thesis is reliable in estimating ship manoeuvrability in various environmental conditions. Afterwards, a series of free-running CFD simulations are carried out to analyse the manoeuvrability of the ship characterised by a traditional single rudder / single propeller configuration in different environmental conditions. It is revealed that the environmental conditions applied in this thesis have a strong effect on the manoeuvring performance of the ship, including the hydrodynamic loads, kinematic parameters, turning indices, and trajectories through comparative analyses. Finally, the main results obtained from each chapter of this thesis are summarised and discussed, and recommendations for future work are made. It is highly believed that the general framework presented in this thesis could encourage academic researchers to participate in research on manoeuvring problems by performing free-running CFD simulations without much difficulty. It is also expected that the numerical results drawn from the hydrodynamic analyses in this thesis will provide navigators with a deeper insight into the ship manoeuvrability in real sea states as well as support them in proper decision-making for ship handling actions to avoid collision. In addition to this, the high-fidelity CFD model developed in this thesis can easily be combined with a path following algorithm for maritime autonomous surface ships (MASS), providing a valuable contribution to enhancing the safety of autonomous marine navigation.

The inclusion of steps presents an attractive solution to improving the efficiency of high-speed planing vessels, yet analysis tools and the available knowledge for improving stepped hulls are considerably under-developed. The research presented in this thesis addresses these issues, seeking answers to the question: "How can we enhance and accelerate analysis techniques for stepped hulls through knowledge developed from numerical simulations and can hydrodynamic performance be improved through the application of these tools." The studies in this thesis apply state-of-the-art Fluid Dynamics (CFD) to examine the impact that the addition of steps has to a planning hull, investigating the mechanisms through which efficiency is improved. The fluid flow is analysed as it separates at each step and interacts with the remainder of the hull, with existing methods of modelling this behaviour being evaluated and novel modelling strategies being proposed. The knowledge established through these investigations is applied to develop mathematical models for the performance prediction of single and double-stepped planing hulls, aiming to address the limitations and enhance the accuracy of those currently available. The proposed models displayed high degrees of accuracy, calculated the resistance with an average error of 2.50% and 1.29% respectively for single and double stepped hulls. The enhanced analysis techniques are applied to investigate how the hydrodynamic performance of single and double stepped hulls may be improved. This was successfully achieved, identifying design trends and establishing relationships between design parameters that may be universally applied by designers to lower the resistance of stepped hulls.

Over the past two decades the marine industry has been facing ever more stringent and radical environmental aims. These are not only been defined by the International Maritime Organisation (IMO), but also by individual countries defining limitations to greenhouse gases emitted by vessels. To combat this the industry has turned towards the use of more complex fluid analysis tools, both model scale tests and computational simulations. This analysis has not only focused on hull design, but also on hull roughness, hull propeller rudder interaction and the marine environment. The focus of this PhD research is to develop methodologies that can be utilised within the industry to optimise vessel performance. With this research optimisation aimed towards improving vessel manoeuvring, with focus away from the traditional nondimensional methodologies. To do so, this research aims to lean heavily on the utilisation of Reynolds Averaged Navier Stokes (RANS) method within Computational Fluid Dynamics (CFD). Towing tests have been considered the primary means of evaluating designs, not only for resistance but also for vessel motions. This includes the analysis forces and motions from both waves and manoeuvring tests. These tests however can be time consuming and financially costly. Therefore, the industry has begun to utilise CFD analysis at the early design stage as a low-cost and fast alternative. Not only this, but in recent years CFD has begun to achieve a level of accuracy matching towing tank tests. Due to these factors this research has a focus on the use of such computational means to improve vessel performance, with extensive validation against multiple towing tank tests. The research has a focus on developing and understanding that can be used to quickly evaluate a potential ship design's manoeuvring characteristics. The methodology for simulating a captive harmonic test is presented, which has been validated against towing tank data conducted for the SIMMAN 2014 conference. This methodology is used in conjunction with a fully parametric hull form, developed within this research, to create and evolve equations used for ranking the hull forms manoeuvring performance. These unique equations are used in two optimisations cycles, one on the NPL hull and a further one on a custom hull to improve the vessels performance and efficiency. The optimum NPL hull forms are evaluated through a virtual turning circle manoeuvring simulation in CFD to quantify the improvements made through optimisation. This research developed a novel methodology for ranking manoeuvring characteristics that significantly reduced the overall optimisation time, as well as producing manoeuvring gains over 20% when evaluated in a simulated turning circle manoeuvre. In addition, the research has also presented best practice approaches for developing such a scheme and how to create a parametric setup that enables quick and accurate CFD simulations for complex manoeuvring simulations. This has been extensively validated against benchmark studies of the DTMB hull form from the SIMMAN 14 towing tank data.

Marine renewable energies, including wave and tidal are considered part of the solution to decarbonise electricity generation and contribute to meeting widely agreed Greenhouse Gas emission reduction targets. Differences in the development phase of each sector result in the existence of different barriers that hinder this contribution. This thesis adopts a portfolio approach, initially addressing a challenge facing the wave energy sector, the lack of experience in the operation and maintenance of wave energy converters. Part two of the portfolio addresses the challenge facing the tidal stream energy sector of flow measurement in complex flow environments, an accurate assessment of which enhances evaluation of forces and loads exerted on tidal devices, predictions of resource availability and operations and maintenance planning. In collaboration with the wave energy developer CorPower Ocean Ltd during ocean testing of a half scale wave energy converter, this thesis portfolio commences with the critical evaluation of prototype operations and maintenance activity relating to an operations and maintenance model, a failure modes effects analysis and half-scale wave energy converter ocean testing. The evaluation improves tools available for risk reduction, cost modelling and operations and maintenance planning at prototype testing stage, facilitating device development and deployment by CorPower Ocean and developers across the sector. In collaboration with the European Horizon 2020 RealTide project, the second part of the portfolio presents the development of modular and high-resolution acoustic measurement technology for use in high energy marine environments. A hardware/software test bed is deployed in the FloWave Ocean Energy Research Facility, testing and proving subsystems of the high resolution sensor, the convergent acoustic Doppler profiler (C-ADP). A collaboration with PNNL, a Department of Energy funded laboratory in the USA, designed, constructed, commissioned and ocean tested a C-ADP, novelly with an actuated measurement location. This work generates key outputs to de-risk activity underway on the RealTide project and contributes to the phased development of acoustic measurement technology to reduce uncertainty in flow measurement and characterisation for the tidal energy sector. Resultant reliability improvements and cost reductions are critical elements in ensuring tidal energy's contribution to our future energy mix.

Floating offshore wind turbine technology is progressing from the research stages to commercial projects. It will be an increasing source of renewable energy over the next few years. The better quality of the wind resource and environmental considerations will encourage developers further offshore, if commercially viable. This research work presents the initial development of the Deep Turbine Installation-Floating (DTI-F) concept. The DTI-F concept is a hybrid spar buoy-based floating offshore substructure capable of supporting a 7 MW wind turbine with the uniqueness of being able to raise and lower the tower and nacelle, which simplifies construction, installation, maintenance, and de-commissioning. The research proceeds in three parts; the first part is a compilation of the background of floating wind turbines and the DTI-F concept. A novel construction method and the installation and assembly processes are outlined, as well as the parametric approach used to perform the preliminary design of the floater. The second part presents both the aerodynamic and hydrodynamic modelling techniques applied during this research. It covers the aeroelastic analysis of the Levenmouth wind turbine (WT) and the experimental and numerical hydrodynamic analysis of the DTI-F concept holding the Levenmouth WT. The Levenmouth (Samsung Heavy Industries - S7.0-171) offshore wind turbine owned by the Offshore Renewable Energy Catapult (ORE Catapult) is a real, operating demonstration wind turbine. The aeroelastic model of the Levenmouth WT has provided the load-matrix of a real, operating seven megawatts WT. The results of the aeroelastic analysis have been integrated parametrically into the design of the DTI-F floater. The hydrodynamic analysis of the floating system undertaken for this research is based on experimental and numerical modelling work. A 1:45 Froude scale model of the DTI-F wind concept was tested using three different mooring configurations: i) three mooring lines, ii) four mooring lines, and iii) three mooring lines with a delta connection. Free decay and stiffness decay tests were carried out together with regular and irregular wave tests. The numerical study comprises diffraction analysis (ANSYS AQWA) and time-domain modelling (OrcaFlex) of the system, and it has been validated against the aforementioned experimental results. The outcome of this research has demonstrated the good practice of the DTI-F concept and has increased the Technology Readiness Level of the studied concept from 1 to 3 while proving that the DTI-F concept has a high degree of technical feasibility. The concluding part of the research provides a discussion of the overall work along with conclusions, recommendations, and future work suggestions.

Historically, the prediction of ship resistance has received its fair share of attention by the scientific community. Although there is a significant body of literature devoted to the study of ship hydrodynamics, several open research questions of great practical relevance remain unanswered. Among these are the extrapolation of ship resistance from model to full-scale in restricted, and unrestricted waters, as well as shallow water ship flows. Most approaches used to predict the performance of a ship have typically relied on the assumptions inherent in potential flow theories, namely, the fluid is treated as inviscid and irrotational. In many cases, these are justifiable assumptions, yielding accurate predictions. However, there are equally many occasions, in which the analyst may not obtain a correct picture of the performance of a ship when relying on the assumptions of potential flow theory. Predicting scale effects, and shallow water influences on ship performance are prime examples of such cases. Numerical techniques based on the Navier-Stokes equations can be thought of as a solution in cases where it is important to model a greater proportion of the physical phenomena. The numerical simulation of ship flows has evolved into a highly practical approach in naval architecture. The main advantages of using such an approach relate to the fact that it accounts for the action of viscosity and turbulence, and can therefore model scale effects and shallow water ship flows. However, with the rapid advent of computational methods in all fields of engineering, several areas have emerged as significant sources of ambiguity. Amongst these are the best approach to modelling turbulence, the numerical uncertainty induced as a result of mapping the continuous governing equations onto a discrete grid, and boundary conditions within the computational domain. This thesis aims to address all of these issues using a commercially available Reynolds averaged Navier-Stokes solver. Firstly, a detailed literature review on the current methods and approaches to circumventing the problems mentioned above, both numerically and through the use of potential flow theory, is given. Then, studies on scale effects in deep and shallow waters are performed, supplemented by investigations into turbulence modelling and numerical uncertainty. Following these, the thesis’ focus shifts towards shallow water phenomena. In particular, the modelling of ship flows without the use of Galilean relativity, and the determination of the Kelvin half-angle in restricted waters. Abrupt changes in the cross-section of the canal in which a ship propagates are also explored, with focus on ship resistance and the properties of the wave field. Finally, the main results obtained from each chapter are summarised and compared against the aims and objectives of this thesis, before recommendations for future work are suggested.

When a ship is sailing in shallow and restricted waters such as harbours and canals, it is usually accompanied by obvious sinkage and trim, called squat. The ship squat has important influences on ship hydrodynamic performance in shallow and restricted water such as ship resistance. Squat is caused by the drop in pressure under the bottom of the ship, where the relative speed of the water is higher. Due to the squat effect, the hydrodynamic forces on the ship will increase largely, ship control will become difficult and risks of grounding may increase. A new division of the Suez Canal is called New Suez Canal, recently opened for international navigation. It is important to obtain accurate prediction data for ship squat to minimise the risk of grounding in this canal. Accurate prediction of the squat is of great significance to correctly evaluate ship hydrodynamic performance and to ensure navigation safety in the New Suez Canal. In this study, various methods for prediction of shi p squat were conducted and introduced. A series of experiments were conducted with a model scale of the KRISO Container Ship (KCS) at 1:75 scale. The squat of the KCS was examined by measuring its sinkage, trim and resistance. The influences of ship speed, water depth, ship-bank distance on the squat and blockage effect were analysed. The results indicated that for Froude's number based on depth (Fnh) below 0.4, measured squat values do not change with either Fnh or depth to draft ratio (H/T). The squat increases with H/T values for the depth Froude numbers higher than 0.4. Moreover, a ship's speed can be increased to up to 9 knots inside the New Suez Canal with no adverse effects, thus significantly reducing the time for a ship to pass through the Canal. Next, the study of reduced the Canal width to 62.5% of its real-life cross sectional area, no significant effect was observed on ship squat. Moreover, a series of experimental tests were conducted at loading conditions under different trimming angles to examine the range of ship trim for safe and efficient sailing in canals. to detect the best trim angle for ships during sailing in restricted waters to reduce resistance and therefore fuel consumption. The results show that for depth Froude's numbers higher than 0.4, the ship model sinkage is less for aft trim than for level trim or forward trim. Concurrently, it can be observed that there is less water resistance for aft trim than for forward trim, albeit level trim shows the least resistance. Furthermore, the present study combines numerical, analytical and empirical methods for a holistic approach in calm water. As a case-study, the KCS hullform is adopted, and analysed experimentally, via Computational Fluid Dynamics, using the slender body theory, and empirical formulae. The results reveal strong effect between the canal's cross section and all examined parameters. In addition, CFD calculations proved to be a reliable tool for predicting ship performance while navigating shallow and restricted waters. CFD simulations in multiphase and double body regime are performed to reveal the form factor and wave resistance of the KCS. This is performed in two different canals while varying the depth Froude number. The results suggest a dependency of the form factor on ship speed. Analytical and empirical methods were used for comparison, the slender body theory, provided good predictions in the low speed range, but did not agree well with the experimental data at high speeds. To model the sloping canal sides of the Suez Canal via the slender body theory, a rectangular canal with equivalent blockage was constructed, which may have influenced the accuracy of the theory.

The development and implementation process of a complete numerical framework for high-fidelity Fluid–Structure Interaction (FSI) simulations of moored floating bodies using Computational Fluid Dynamics (CFD) with the Finite Element Method (FEM) is presented here. For this purpose, the following three main aspects are coupled together: Two-Phase Flow (TPF), Multibody Dynamics (MBD), and mooring dynamics. The fluid–structure problem is two-way and fully partitioned, allowing for high modularity of the coupling and computational efficiency. The Arbitrary Lagrangian–Eulerian (ALE) formulation is used for describing the motion of the mesh-conforming fluid–solid interface, and mesh deformation is achieved with linear elastostatics. Mooring dynamics is performed using gradient deficient Absolute Nodal Coordinate Formulation (ANCF) elements with a two-way mooring–structure coupling and a one-way fluid–mooring coupling. Hydrodynamic loads are applied accurately along mooring cables using the solution of the fluid velocity provided by the TPF solver. For this purpose, fluid mesh elements containing cable nodes that do not conform to the fluid mesh are located with a computationally efficient particle-localisation algorithm. As it is common for partitioned FSI simulations of solids moving within a relatively dense fluid to experience unconditional instability from the added mass effect in CFD, a non-iterative stabilisation scheme is developed here. This is achieved with an accurate and dynamic estimation of the added mass for arbitrarily shaped structures that is then applied as a penalty term to the equations of motion of the solid. It is shown that this stabilisation scheme ensures stability of FSI simulations that are otherwise prone to strong added mass effect without affecting the expected response of structures significantly, even when using fully partitioned fluid–structure coupling schemes. Thorough verification and validation for all aspects of the FSI framework ultimately show that the produced numerical results are in good agreement with experimental data and other inherently stable numerical models, even when complex nonlinear events occur such as vortices forming around sharp corners or extreme wave loads and overtopping on moving structures. It is also shown that the mooring dynamics model can successfully reproduce nonlinearities from high frequency fairlead motions and hydrodynamic loads. The large-scale 3D simulation of a floating semi-submersible structure moored with three catenary lines ties all the models and tools developed here together and shows the capability of the high-fidelity FSI framework to model complex systems robustly and accurately.