In recent years, more and more research attention has been paid to the NOx emissions caused by marine diesel engines. Selective catalytic reduction (SCR) system has been proven to be an effective technology for the removal of NOx emitted from marine diesel engines. In order to comply with stringent International Maritime Organization (IMO) Tier III NOx emission regulations, a number of engine manufacturers have developed their own SCR systems with an option of installing SCR reactors before or after the turbines of engine turbochargers. This thesis focuses on modelling of evaporation and decomposition of urea-water-solution (UWS) droplets, design and optimisation of static mixers, modelling of an SCR reactor and developing model-based urea dosing control strategy. The amount of ammonia converted from UWS has a significant effect on the NOx removal efficiency of SCR systems. Due to a limited installation space for SCR systems on board, choosing the location of urea injection nozzle appropriately has become a critical issue for SCR system design. An evaporation and decomposition model of UWS droplets has been developed in this research in order to determine the total depletion time of a UWS droplet, which is helpful to calculate the proper length between the urea nozzle and reactor of an SCR system. In order to achieve a high NOx removal rate and reduce the quantity of NH₃ slip, static mixers are commonly used before SCR reactors to improve the mixing between ammonia and exhaust gases. 4 novel static mixers have been designed and the performance of the mixers is compared in the study. An experiment has been conducted to validate the mixing performance and pressure loss of the static mixers developed. It shows that there is a satisfied agreement between the simulation and experiment results. A mathematical model of SCR reactors has been established. The unknown parameters of the model are identified by minimising the error between the model predicted and measured values of both the temperature and the species concentration after the SCR reactor. The SCR reactor model is further used in a simulation for the purpose of developing model-based urea dosing control strategies. A state observer is used to determine the actual states in the reactor which supplies the mandatory information for developing model-based urea dosing control strategies. The NH₃ cross-sensitivity of NOx sensors can be described by a linear equation. The simulation results of the observer show that the NH₃ cross-sensitivity of NOx sensors can be neglected when estimating the actual states of the reactor if NH₃ is of a low concentration in the exhaust.

Concept design is the initial stage of the ship design process during which design alternatives are developed to study their cost and performance trade-offs. Traditional design approaches are capable of exploring only a small region of the design space around a chosen parent. Alternative approaches have not received widespread acceptance because of their "black-box" nature, whereby they try to provide prescriptive solutions rather than assist the designer in comparing available design alternatives. This thesis proposes a new design approach that avoids these drawbacks. Central to the proposed design approach is a multi-objective optimisation tool using genetic algorithms, capable of generating the Tareto-front' consisting of designs optimised to a set of objectives. The novelty in the proposed design approach lies in the analysis of the Pareto-front, which helps to provide design insights about the whole Pareto-front and about the individual designs. This thesis describes and illustrates the proposed design approach with example ship designs. To demonstrate the approach, it is used to re-design three naval combatants that were originally designed using a traditional design approach. These applications illustrate how the analysis of the Pareto-front can potentially assist in the concept design process. For example, it may reveal interesting regions of the performance space, such as discontinuities. Multiple Pareto-fronts with varying constraints or design inputs may identify designs not traditionally examined. Such results may help the designer to have a more informed dialogue with the customer about the design requirements and the potential solutions. It is hoped that the transparent and interactive nature of the proposed design approach will make it useful to practising designers and thus improve the applicability of multi-objective optimisation during preliminary ship design. This may improve the quality of the ships designed, albeit within the limited objectives considered for optimisation, and reduce the total time taken for concept design.

A methodology for the assessment of global wave load combinations on a container ship is developed taking into account load modelling uncertainties such as the sea state, the speed with and direction in which the ship travels etc. Data from wave statistics are used to determine the sea state which is required for specifying the sea spectrum associated with a given sea state. The sea spectrum together with the response amplitude operators (RAOs) of the ship are used to determine the stochastic responses of the ship in waves. This load combination methodology employs stochastic analysis in conjunction with cross-spectral analysis to determine a given wave-induced load that is associated with a principal wave-induced load which have been determined a priori via common spectral methods. All the global wave-induced loads are assumed to be random variables that are Gaussian distributions with zero means and variances obtained from their respective zeroth spectral moments. The peaks of the responses are modelled as Rayleigh distributions and the combination of any two responses modelled by a copula function which is a bivariate Rayleigh distribution with parameters such as the zeroth spectral moments of the responses concerned and their interactions in form of a correlation parameter obtained via a cross-spectral analysis of the given responses. Load combinations are obtained with respect to any given design extreme global wave-induced load as the principal load whose effects may be a source for concern at the design stage of the ship. The results were compared to results obtained from existing methods of load combinations. A Spearman’s rank correlation test shows a very good covariation between the compared methods. Nonlinear finite element modelling and analyses on the midship section of a 10,000 TEU container ship are used to assess its ultimate strength under combined loads such as the vertical bending moment, horizontal bending moment and torsional moment. The primary loads that act on an actual ship hull girder are of different modes corresponding to the six degrees of freedom hence it is more realistic to consider the ii E. Alfred Mohammed effects of loads in other modes other than the dominant vertical bending moment in the determination of the longitudinal strength of the hull girder. Torsional moment is particularly important because it can be a serious problem for container ships which have wide open hatches and hence low torsional rigidity. A three-compartment finite element model for the container ship OL185 is developed from the transverse section detail of the ship. A progressive collapse analyses are performed on it using the Abaqus finite element code to determine the ultimate strength of the container ship under combined vertical bending, horizontal bending and torsional moments. These provide a basis for load interaction and combination studies via interaction relationships featuring the relevant load combinations. Finally, the interaction relationships are used to show the hull girder safety margin via a comparison with a predetermined global wave-induced load combination for the midship section of OL185 container ship obtained using the cross-spectral probabilistic methodology.

The phenomenon of low cycle fatigue (LCF) is characterised by high stress range, close to or above yield, and relatively low number of cycles to failure, typically below 104. In the case of tankers and Floating, Production, Storage and Offloading units (FPSO), nominal stress amplitudes lower than the yield stress may result in plastic strains due to the high stress concentrations that are typical in many of the hulls’ structural details. FPSOs are more susceptible to damage due to LCF compared to tankers, cargo and other ocean going ships. The main reasons are; the unique structure of FPSO in terms of the presence of internal turret and topsides load which affects the structural response of FPSO to dynamic and quasi-static loads, the frequent loading and unloading patterns of FPSO (i.e. unlike oil tankers which are either in full load or ballast condition) which causes the FPSO to experience the maximum hogging and sagging still water bending moment every single cycle and the condition of the sea at which the FPSO is operating (site specific environment) where even benign condition may subject the FPSO to extremely diverse wave induced loads. An increasing number of FPSOs are being used in the oil and gas industry due to the practical advantages they offer as compared to fixed installations, however, many FPSO show signs of cracks at critical locations in the first five years of service. It is believed that this is primarily due to LCF. It is therefore imperative to address LCF at the design stage. Finite Element Analysis (FEA) has been used to demonstrate that extremely high stress levels, exceeding three times the yield stress of the material, may occur at some critical locations during FPSO operations. Due to this ‘new’ form of damage in ship structures classification societies, shipyards and other organizations are addressing the issue of LCF by issuing various guidance notes and recommended practices in order to assess the damage due to LCF. This research contains a very extensive and useful literature review of the state-of-theart in LCF assessment methods available in literature and various class societies. Representative operational loading conditions (most onerous) have been presented for LCF Assessment of FPSO. LCF tests of typical longitudinal attachment were performed. This important structural element is seldom tested compared to the transverse attachment or cruciform. Experimental and numerical results compare well. A novel method of predicting LCF life has been proposed and a new S-N curve is proposed to be used for LCF assessment.

Over the last few years, there has been a rising demand for sub-metre accuracy (and higher) for navigation and surveying using signals from Global Navigation Satellite Systems (GNSS). To meet this rising demand, many precise positioning techniques and algorithms using the carrier-phase observable have been developed. Currently, high accuracy Real-Time Kinematic (RTK) positioning is possible using relative or differential techniques which require one GNSS user receiver and at least one other as the reference (known) station within a certain distance from the user. Unlike these conventional differential positioning techniques, Precise Point Positioning (PPP) is based on processing carrier phase observations from only one GNSS receiver. This is more cost-effective as it removes the need for reference receivers and therefore, is not limited by baseline length. However, errors mitigated by ‘differencing’ in conventional methods must be modelled accurately and reliably for PPP. This thesis develops a PPP software platform in Matlab code and uses it to investigate the state-of-the-art PPP algorithms and develop enhancements. Specifically, it is well documented that conventional PPP algorithms suffer from long convergence periods ranging from thirty minutes (for static users) to hours (for dynamic users). Therefore, to achieve fast convergence, two approaches are developed in this thesis. Firstly, a combination of the state-of-the-art GNSS error models and new algorithms for measurement weighting, management of receiver clock jumps and assignment of a dynamic covariance factor, are exploited. Secondly, based on the results of the analysis of the quantitative relationships between the PPP convergence and each of the residual measurement noise level and satellite geometry, a strategy for the selection of satellites (GPS and GALILEO) for PPP is developed and exploited. Tests using 24 hours of real data show that the two developments above contribute to the realisation of static PPP positioning accuracies of 40 cm (3D, 100%) within a convergence time of 20 minutes. Furthermore, based on simulated data, the same accuracy is achieved in kinematic mode but within a convergence time of one hour. These levels of performance represent significant improvements over the state-of-the-art (i.e. convergence time of twenty minutes instead of thirty for static users and one hour instead of hours for dynamic users). The potential of the use of multiple frequencies from modernised GPS and GALILEO on float ambiguity PPP is demonstrated with simulated data, and shown to have the potential to offer significant improvement in the availability of PPP in difficult user environments such as urban areas. Finally, the thesis addresses the potential application of PPP for mission (e.g. safety critical) applications and the need for integrity monitoring. An existing Carrier-phase Receiver Autonomous Integrity Monitoring (CRAIM) algorithm is implemented and shown to have the potential to protect PPP users against abnormally large errors.

Prediction of fracture and failure is a challenging research area. There are various methods available in the literature for this purpose including well-known finite element (FE) method. FE method is a powerful technique for deformation and stress analysis of structures. However, it has various disadvantageous in predicting failure due to its mathematical structure since it is based on classical continuum mechanics (CCM). CCM has governing equations in the form of partial differential equations. These equations are not valid if the displacement field is discontinuous as a result of crack occurance. In order to overcome this problem, a new continuum mechanics formulation was introduced and named as Peridynamics. Peridynamics uses integrals equations as opposed to partial differential equations of CCM. Moreover, it does not contain any spatial derivatives. Hence, its equations are always valid regardless of discontinuities. In this thesis, the applications of Peridynamics for marine structues are demonstrated. Particularly, the Peridynamic equations are rederived for simplified structures commonly used in marine structures including beams and plates. Furthermore, underwater shock response of marine composites is investigated. Finally, the peridynamic formulation for contact analysis which can be used for collision and grounding of ship structures is demonstrated. In order to reduce the computational time, several solution strategies are explained.

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Experimental investigations of the velocity characteristics related to turbulent propeller-jet flow were carried out. Laser Doppler Anemometry (LDA) was used as the measurement technique. The investigations were performed in a free-surface tank, large enough to allow the unhindered expansion of unconfined propeller jets at bollard-pull. Comprehensive time-averaged (mean) and instantaneous real-time (blade-to- blade) velocity measurements were taken to assess the magnitude and location of the velocities that produce serious seabed scour. The results identify that the propeller blades play an important role in the development of the instantaneous velocity fields up to a downstream distance of two propeller diameters. Beyond this distance, the time-averaged form of measurement resolved all necessary information regarding the axial, radial and rotational velocity components. Establishing methods through which the characteristics of all three-velocity components can be determined using linear regression techniques has been carried out to extend the applications of existing semi-empirical equations. In the absence of suitable linear approximations of the main velocity characteristics, Artificial Neural Network (ANN) programmes were developed as an alternative method of determining the three-dimensional flow fields of a diffusing propeller jet produced in the confines of a harbour basin.