In the light of global warming, the associated socio economical consequences, and the projected shortage of natural energy resources and ever rising oil prices, this thesis examines the potential for unconventional aero engine architectures to reduce fuel consumption of passenger aircraft. Current aircraft engines are based on the Brayton cycle, where the working fluid successively experiences isentropic compression, isobaric combustion, and isentropic expansion. Deviations from the ideal cycle in real engines occur through component inefficiencies. The maximum achievable thermodynamic efficiency of the Brayton cycle increases hand in hand with its peak cycle temperature. Since the peak cycle temperature is limited by material properties of the turbine, the maximum cycle efficiency of current jet engines is limited by the laws of thermodynamics. Hence, efficiency improvements of jet engines beyond what is possible with conventional turbofan designs are only feasible through unconventional engine architecture. Several technologies enabling unconventional engine architectures for aircraft propulsion have been identified. They include wave rotor, pulse detonation and internal combustion. These technologies are merged with conventional jet engine technology to form hybrid designs. A one dimensional engine performance model was developed to calculate the performance and allow a comparison of the hybrid cycles with a conventional turbofan cycle. Gradient optimisation techniques were applied to the allow comparison of the best possible designs. Results suggest that of the examined cycles, the hybrid internal combustion cycle has the best potential for fuel savings compared to conventional turbofan cycles.

Hazards on accident sites are such that investigators must balance personal safety against the risks involved in collecting evidence intended to prevent future loss of life. Better knowledge of hazards and their mitigation could reconcile these conflicting objectives to a point at which risk might be no greater than in other workplaces. Nevertheless, the magnitude and nature of the hazards at any accident site cannot be determined in advance. The perceptions of novice accident investigators of potential hazards are not greatly different from the realities encountered by experienced investigators, although the former tend to focus on general health and safety issues, while experienced investigators are more aware of hazards arising from aircraft systems and materials. Experienced investigators reported most of the hazards they encountered over six years as arising within a narrow range of hazard categories - yet they must be prepared to carry out thorough investigations while protecting themselves against all hazards, including those encountered very infrequently. Both generic and dynamic risk assessments are important in protecting investigators and the integrity of evidence. The ongoing management of an investigation in the field involves a continuous and iterative cycle: identification of hazards, determination of exposure, assessment of risk, introduction of controls, review and assessment of remaining risk, and identification and management of residual hazard. Lives and evidence depend upon the quality of this process. At present, great reliance is placed on personal protection equipment as a control on hazards. Observation of participants in training programmes has identified instances of poor selection and ineffective use of such equipment to the extent that it has provided no protection. The thesis points to required further directions in the training of investigators - an investment which will yield its dividend in the prevention of future accidents and loss of life.

From molecules to living organisms and from atoms to planets a variety of physical phe- nomena operate at different temporal and spatial scales. Understanding the nature of those phenomena is crucial for advancing new technologies in many disciplines. In micro and nanofluidics as the operational dimensions are downsized to smaller scales the surface-to- volume ratio increases and the surface phenomena become dominant. Numerical modelling is the key for obtaining a better insight into the processes involved. The Achilles heel of fine grain microscopic numerical simulations is their computational cost. Simulating a multiscale phenomenon with an accurate microscopic description is extremely demand- ing computationally. On the contrary, simulations of multiscale phenomena based only on macroscopic descriptions cannot fully capture the physics of the multiscale systems. In order to confront this dilemma multiscale frameworks, called hybrid codes, have been de- veloped to couple the microscopic and macroscopic description of a system and to facilitate the exchange of information. The aim of this research project is to establish and implement a robust hybrid molecular- continuum method for micro- and nano-scale fluid flows. Towards that direction a hybrid multiscale method named as Point Wise Coupling (PWC) has been developed. PWC aims to circumvent the limitations of the existing hybrid continuum/atomistic approaches and deliver a modular and applicable methodology. In the PWC, the whole domain is covered with the macroscopic solver and the microscale model enters as a local refinement. Ad- ditionally, numerical techniques based on neural networks are employed to minimise the cost of the molecular solver and reduce the outcomes’ variability induced by the fluctuating nature of the atomistic data. Molecular studies have been performed (i) to obtain a better insight of the interfacial phenomena in the solid/liquid interfaces, and (ii) to study the parametrisation of the molec- ular models and mapping of atomistic information to hybrid frameworks. Specifically, the impact of parameters, such as surface roughness and stiffness, to slip process is studied. PWC framework has been employed to study a number of fundamental test cases in- cluding Poiseuille flow of polymeric fluids, isothermal slip Couette flow and slip Couette flow with heat transfer. Attention is drawn to the boundary condition transfer from the continuum solver to the atomistic description. In the performed hybrid studies the effects of the numerical optimisation techniques (linear interpolation, neural networks) to simu- lations’ accuracy, stability and efficiency are studied. The outcomes of the simulations suggest that the neural networks scheme enhance the simulation’s efficiency by minimising the number of atomistic simulations and at the same time act as a smoothing operator for reducing the oscillations’ strength of the atomistic outputs.

Trends in aircraft design and manufacture are towards the reduction of manufacturing cost and structural weight while maintaining high level of safety. These reductions can be achieved by using integral structures. However, integral structures lack redundant structural members, hence fail safety is not guaranteed. Bonded selective reinforcements (straps) can obviate this problem and improve the damage tolerance capability of integral structures, although increase the design di±culties. The objective of this research is to develop an effective analysis method to predict the fatigue crack growth (FCG) life of integral structures reinforced by bonded crack retarders, determine the effectiveness of the reinforcements, and assess the important strap design parameters. The main mechanisms that influence the crack propagation have been identified, modelled, and discussed. When a crack propagates in the panel skin, bonded straps delay the fracture growth by exerting bridging forces at the crack tip. Nevertheless damage also affects the strap due to the stiffness mismatch and high stress concentration, and the strap/substrate interface is affected by a progressive delamination that advances together with the substrate crack and limits the strap bridging action. Tensile thermal residual stresses (TRS) in the cracked substrate, caused by the adhesive cure process, act to open the crack and hence increase the growth rate. Last but not least, secondary bending caused by the non-symmetric configurations induces a stress gradient along the crack front. This reduces the effectiveness of the bridging action and causes a curved crack front. An enhanced 2D FE modelling technique that takes into account of these mechanisms and their interactions has been developed and implemented in a computerprogram that interfaces the commercial code NASTRAN. This program is used to calculate the stress intensity factors and the FCG life of bonded strap reinforced integral structures. This modelling technique has been validated for a wide range of test samples in terms of TRS and their redistribution with crack propagation, disbond areas, and FCG lives. The FCG life of a large scale integral skin-stringer panel reinforced by various bonded straps has also been predicted and compared with the experiments. Numerical predictions have shown good agreement with the experimental measurements. Parametric studies have been conducted to understand the effectiveness of different strap configurations on crack growth retardation; these include different strap materials, strap dimensions and locations on the substrate. A design tool has been developed aimed at achieving optimal crack retarder design in terms of prescribed fatigue life target and minimum structural weight. In conclusion, a novel modelling tool has been developed, the effectiveness of bonded straps in retarding fatigue crack growth has been demonstrated and, following the parametric analysis, the most important parameters in the design of bonded straps have been identified.

With the market introduction of both the Airbus A350XWB and the Boeing 787, Carbon Fibre Reinforced Plastics (CFRP) has been applied to primary structure of large commercial aircraft, as a means of enhancing overall performance. Both these aircraft are being developed and produced in a unique way where Airbus and Boeing are acting as System Integrators and using Risk Sharing Partners to develop the majority of the principal components. To support this new business and technological model it is necessary that the System Integrator has sufficient knowledge and tools to support the development of the components. Of particular interest are items such as the wing covers, as they are both heavy and expensive items, thus offering large opportunities for optimisation, in particular when the benefits of applying CFRP are considered. This creates the forum for this thesis, i.e. to thoroughly understand all factors that influence a CFRP wing cover, from which an optimisation methodology is developed, incorporating design constraints, while seeking the lightest weight solution, with a resultant Life Cycle Cost (LCC). Based on this, different solutions can be compared based on weight and LCC. In general stringer-stiffened panels are, from a weight perspective, the optimal configuration for wing covers, and thus are solely considered. Serendipitously, due to their prismatic shapes, buckling calculations of stringer-stiffened panels can be solved with reasonable accuracy and ease using the Finite Strip Method (FSM), as opposed to more time consuming methods such as the Finite Element Method. A suitable FSM program is available from ESDU, which when used in combination with a configured Excel spreadsheet can take into consideration constraints established from the extensive literature review. Once the lowest weight solution is obtained under buckling constraints, the solution is then checked for in-plane and if desired out-of-plane strength. Based on the structurally optimised wing cover, the manufacturing cost is calculated using a Process Based Cost Model (PBCM), which has been developed based on different CFRP materials for the skin and stringer fabrication, as well as suitable manufacturing and integration methods. In order to consider the LCC, i.e. all costs from cradle to grave, the PBCM factors in both the cost of recycling scrap material during manufacture and after retirement. Furthermore, when more than one solution is compared then the Economic Value of Weight Saving, which is based on the range equation, can be factored in to consider the financial benefit of weight saving. The optimisation methodology and PBCM has been evaluated on diverse wing cover examples, which has considered both uni-directional prepreg, non-crimp fabric and braids materials in combination with autoclave and liquid composite moulding techniques. The results demonstrated a trend which can be considered realistic, although the cost estimation is very much dependent on the assumptions made. In conclusion, the thesis and the optimisation methodology can be used to compare different configurations.

The future of the civil aeronautics industry will be determined by the decreasing oil supplies around the world and by more environmentally friendly aircraft designs. Future Gas Turbine engines are being designed focusing on the fuel economy reducing emissions and noise. This project is on the application of Computational Fluid Dynamics (CFD) techniques to the computation and parametric analysis of drag produced by the nacelle of Very High By-pass Ratio (VHBR) engines as integrated into the airframe. Engines based on VHBR concept are consistent with the objectives of VITAL which is an EU project for creating environmentally friendly engine without SFC penalties or impairing other benefits. Three main architectures for the fan were considered for the task, a geared turbofan, contra rotating turbofan and direct drive turbofan. The long range geared turbofan is the one considered in this project. Increasing the BPR for turbofan engines is one of the best options for decreasing the SFC and noise produced by the power plant, unfortunately there are some issues to be considered. One of the major drawbacks when the BPR reaches very high values (VHBR) is the integration to the airframe because of the very large size of the fan. The drag produced by the nacelle has to be countered with propulsive force and therefore decreasing the propulsive efficiency and increasing the SFC. CFD can be used for parametric analysis of drag produced by turbofan nacelles. The analysis was carried out in 3 basic stages. 2D geometry analyses of the afterbody and forebody are the first stage. Small changes to the basic geometry parameters were made in order to form conclusions about which parameters are more significant for drag generation in each section of the nacelle. In the second stage of the project a 3D geometric analysis was carried out with the whole nacelle. The important parameters from the 2D simulations and some of the parameters required for 3D geometry were varied in the analysis. Conclusions were made about the influence of each of the parameters in drag generation and their influence on the interaction between forebody and afterbody. In the third stage of the project, the influence on drag of the positioning of the engine relative to the wing is analyzed. No geometry changes were made and no pylon was used. Conclusions were made from the changes of pressure distribution and supersonic zones and their impact on the drag.

The impact of noise on civil aviation is not just a localised airport problem, but a global concern, due to the ever-increasing demands for passenger travel. The challenge of designing a ‘Silent Aircraft’ lies within the development, integration, and optimisation of efficient airframe-engine technologies. This research study investigates the design of novel airframes with the aim of producing a methodology that incorporates airframe noise. Studies investigating the design of Broad Deltas (BD), Blended Wing Bodies (BWB), and Joined Wing airframe configurations are integrated with innovative propulsion systems designs to identify key parameters in order to design a Silent Aircraft. The airframe configuration plays an important role in the total aircraft noise, where the novel airframes that are analysed, are compared to a datum ‘baseline’ aircraft. All novel configurations show significant improvements in airframe noise reduction, enhanced by the addition of ultra-efficient propulsion systems, for which integration studies are discussed. The research into novel airframes uses a developed design methodology which integrates design considerations such as aerodynamics, performance, and cost models to complement the noise analysis and identify the most silent airframe configuration. The research goal was to identify a silent airframe solution for a future viable short-medium range airliner, where the final solutions described suggest proposals for the future development of aviation. The proposals suggested describe a short-term solution to the noise challenge, with a longer-term solution to aid the development of technologies, maturity in technology release levels (TRLs), and development of a future 2050 medium capacity civil airliner.

Thermal and dynamic soaring are two techniques commonly used by birds to extract energy from the atmosphere. This enables them to reduce, energy used during flight and increases their endurance. The thermal soaring technique involves extraction of energy from thermal updrafts and in dynamic soaring energy is extracted from wind shear. These techniques are investigated in this thesis using point mass and non-linear 6DoF models of an unmanned powered sailplane. The key challenges of autonomous thermal soaring are the ability to identify remote thermal activity using on-board sensors and to position correctly in a thermal. In dynamic soaring, a real-time fuel saving trajectory generation technique along with a trajectory following control system is needed. A hand held IR camera was used to assess the feasibility to observe hot spots associated with thermals. The thermal positioning capability was demonstrated in a 6DoF model using a positioning algorithm. The inverse Dynamics Virtual Domain (IDVD) technique was used to generate real-time trajectories for dynamic soaring applications using a point mass model of a powered unmanned sailplane and the fuel saving trajectories were validated using a high fidelity 6DoF model and a classical controller. An important outcome of the research is the fact that energy saved during dynamic soaring flight was also realized due to a sinusoidal manoeuvre using reduced thrust. In this manoeuvre the kinetic energy is converted into potential energy by gaining altitude and by reducing airspeed. Then initial values of altitude and speed are gained by loosing the altitude. In this process a horizontal distance is travelled by using reduced thrust.

Robust high precision control of spacecraft formation flying is one of the most important techniques required for high-resolution interferometry missions in the complex deep-space environment. The thesis is focussed on the design of an invariant stringent performance controller for the Sun-Earth L2 point formation flying system over a wide range of conditions while maintaining system robust stability in the presence of parametric uncertainties. A Quasi-Linear Parameter-Varying (QLPV) model, generated without approximation from the exact nonlinear model, is developed in this study. With this QLPV form, the model preserves the transparency of linear controller design while reflecting the nonlinearity of the system dynamics. The Polynomial Eigenstructure Assignment (PEA) approach used for Linear Time-Invariant (LTI) and Linear Parameter-Varying (LPV ) models is extended to use the QLPV model to perform a form of dynamic inversion for a broader class of nonlinear systems which guarantees specific system performance. The resulting approach is applied to the formation flying QLPV model to design a PEA controller which ensures that the closed-loop performance is independent of the operating point. Due to variation in system parameters, the performance of most closed-loop systems are subject to model uncertainties. This leads naturally to the need to assess the robust stability of nonlinear and uncertain systems. This thesis presents two approaches to this problem, in the first approach, a polynomial matrix method to analyse the robustness of Multiple-Input and Multiple-Output (MIMO) systems for an intersectingD-region,which can copewith time-invariant uncertain systems is developed. In the second approach, an affine parameterdependent Lyapunov function based Linear Matrix Inequality (LMI) condition is developed to check the robust D-stability of QLPV uncertain systems.

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