In recent years, the Air Supported Vessels (ASVs) has received some interest due to increasing oil prices and the stricter regulations on emissions. The ASVs have the potential of reducing fuel consumption with less drag by adopting air cavity underneath its hull surface. Research so far has been mainly focused on the mechanism and effectiveness of the air cavity for drag reduction, i.e., the resistance in calm water condition. Other hydrodynamic performances of the ASVs are rarely studied. In this thesis, it is attempted to address some of the other hydrodynamic problems for the ASV, namely, wash wave field, motion response in waves and the stability. New mathematical models have been proposed to tackle these problems. The models cover the steady flow, frequency domain analysis (seakeeping) and time domain analysis (the dynamic stability). Emphases are placed on numerical calculation of the flow field generated by the excess pressure inside the cavity. Although the analytic expressions of the potential flow field by a pressure patch moving on the free surface are well known, the numerical calculations remain challenging. The singularities and highly oscillatory behaviour of the velocity potentials and the free surface elevations will cause numerical instability problem. In this study, new numerical schemes are proposed and the irregularities have been successfully removed. A number of case studies have been carried out to verify the proposed mathematical models and numerical methods. Satisfactory agreements have been found as far as there are other computations or measurements for comparison; or reasonable results are obtained. It is expected that the mathematical model, the numerical methods and tools established in the present study can be a supplementary means for developing the ASV at both design and operational stages.

As part of the ongoing development of Flapping-Wing Micro Air Vehicle (FMAV) prototypes at RMCS Shrivenham,a model of insect-like wing aerodynamics in hover has been developed, and implemented as MATLAB code.The model is intended to give better insight into the various aerodynamic effects on the wing, so is as close to purely analytical as possible. The model is modular, with the various effects treated separately.This modularity aids analysis and insight, and will allow future refinement of individual parts. However,it comes at the expense of considerable simplification,which requires empirical verification. The model starts from quasi-steady inviscid flow around a thin 2D rigid flat wing section,accounting for viscosity with the Kutta-Joukowski condition,and the leading edge suction analogy of Polhamus. Wake effects are modelled using the models of Kussner and Wagner on a prescribed wake shape,as initially used by Loewy. The model has been validated against experimental data of Dickinson's Robofly, and found to give acceptable accuracy.Some empirically inspired refinements of the Polhamus effect are outlined, but need further empirical validation. This thesis comprises of six main parts: Part I is introductory material, and definitions, including an overview of what insect-like Rapping flight actually entails, and detailed definitions of the variables and terms used later. Part 2 describes the new theoretical model, and a simple scaling analysis of the forces and moments predicted. Part 3 deals with the MATLAB implementation of the above theory, and the considerations re-quired when adapting the theory for computational use. Part4 shows and discusses the results of the above code, against experimental measurements on Dickinson's Robofly. Part 5 is the conclusions, including a comprehensive list of all assumptions made in the theory. Part6 , the appendices, contain useful mathematical identities,and a copy of the code that was developed.

The rapid development of hovercraft during the past decade has involved a concentrated effort on research and development to overcome the problems associated with a new form of transport. Some of the problems have not yet been solved and, in particular, the question of ride and stability characteristics is most important. An experimental and theoretical study has been made to achieve a method of prediction of stiffness and damping parameters through the change of cushion pressure during forcing of the cushion.

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Road vehicles are still largely a consumer product and as such the styling of a vehicle becomes a significant factor in how commercially successful a vehicle will become. The influence of styling combined with the numerous other factors to consider in a vehicle development programme means that the optimum aerodynamic package is not possible in real world applications. Aerodynamicists are continually looking for more discrete and innovative ways to reduce the drag of a vehicle. The current thesis adds to this work by investigating the influence of active flow control devices on the aerodynamic drag of square back style road vehicles. A number of different types of flow control are reviewed and the performance of synthetic jets and pulsed jets are investigated on a simple 2D cylinder flow case experimentally. A simplified ¼ scale vehicle model is equipped with active flow control actuators and their effects on the body drag investigated. The influence of the global wake size and the smaller scale in-wake structures on vehicle drag is investigated and discussed. Modification of a large vortex structure in the lower half of the wake is found to be a dominant mechanism by which model base pressure can be influenced. The total gains in power available are calculated and the potential for incorporating active flow control devices in current road vehicles is reviewed. Due to practicality limitations the active flow control devices are currently ruled out for implementation on a road vehicle. The knowledge gained about the vehicle model wake flow topology is later used to create drag reductions using a simple and discrete passive device. The passive modifications act to support claims made about the influence of in wake structures on the global base pressures and vehicle drag. The devices are also tested at full scale where modifications to the vehicle body forces were also observed.