This thesis focuses on the micro/nanoparticle size measurement by using Diffusing-wave Spectroscopy, investigating the laser power and concentration effect on the measurement and researching the measuring method for particles in shear flow. A DWS-CCD backscattering experiment set-up was used in this project. By using this set-up, in all about 2000 experiments were performed during the project, including system testing, laser power influence study, concentration effect study and shear flow study. In the beginning, a detailed analysis of the particle sizing for particles in static condition was carried out by summarising the principles and procedures. The results revealed that the experimental set-up in this work was reliable and repeatable. A calibration process was still required for the CCD’s frame rate and resolution, the light absorption and the CCD’s position in the set-up. After determining some important parameters, the research was extended to laser power and concentration influence study. The autocorrelation functions were produced under different laser power and for different concentration of particle solution. Analysis confirmed the influences, and the results were expressed in formulas to describe specific effects for laser power and solution concentration. Based on the formulas, new equations for particle sizing were derived for different concentration ranges. After that, particle’s motion and light scattering in shear flow were investigated. It was concluded that three regions could be used to describe the particle’s movement under shear force; in different regions, the autocorrelation functions were different due to the variation of the characteristic time scales. The Brownian motion and shear strain dominated particle’s movement under specific flow velocities. Therefore, for particles subjected to high flow velocities, a new particle sizing formula was produced to distinguish the general formula which was only valid for particles under Brownian motion. Contributions made by this research are applying DWS application to micro/nanoparticle sizing in different conditions. In static condition, the laser power and concentration influence were described in formulas; new equations were produced for particle sizing for different concentration range. In shear flow, the thresholds of Brownian motion domination and shear flow domination were found; a new particle sizing equation was derived for particles only controlled by shear force.

Laser forming (LF) offers industry the promise of controlled shaping of metallic and nonmetallic components in prototyping, correction of design shape or distortion and precision adjustment applications. In order to fulfil this promise in a manufacturing environment the process must have a high degree of controllability, which can be achieved through a better understanding of its underlying mechanisms. The work presented in this thesis is primarily concerned with the use of modelling of the LF process at macro and micro scales as a means of process development. At the macro scale, finite element (FE), finite difference (FD) and analytical modelling were used to gain a better understanding of the complex interrelation between the various process parameters for specific geometries, reducing the need for extensive empirical investigations. A particular focus of the investigation was ascertaining which of these parameters influenced the fall off in bend angle per pass in multiple pass LF, along with the magnitude of their influence. The development of a full thermal-mechanical model of the LF process is detailed, as well as its application in a feasibility study into the forming of square section mild steel tubes for the automotive industry. Using this model, experimental observations were rationalized and novel scan strategies were developed which optimized the efficiency and accuracy of the process, something hitherto not possible using empirical methods alone. At the micro-scale, FE modelling was used to determine the mechanism of deformation in a novel laser micro-forming (LμF) technique, in conjunction with a full empirical study. The technique combined short pulse durations (20 ps) with high repetition rates (500 kHz) to generate localized heat build-up on the top surface of micro-scale stainless steel components, allowing for controlled and repeatable micro-adjustment. Modelling results suggest the mechanism works by confining the heating effect to the surface of the material, thereby selectively inducing thermal stresses and avoiding thermal damage of the component.

The Laser Assisted Direct Write (LADW) method can be used to generate electrical circuitry on a substrate by depositing metallic ink and curing the ink thermally by a laser. Laser curing has emerged over recent years as a novel yet efficient alternative to oven curing. This method can be used in-situ, over complicated 3D contours of large parts (eg. aircraft wings) and selectively cure over heat sensitive substrates, with little or no thermal damage. In previous studies, empirical methods have been used to generate processing windows for this technique, relating to the several interdependent processing parameters on which the curing quality and efficiency strongly depend. Incorrect parameters can result a track that is cured in some areas and uncured in others, or in damaged substrates. This thesis addresses the strong need for a quantitative model which can systematically output the processing conditions for a given combination of ink, substrate and laser source; transforming the LADW technique from a purely empirical approach, to a simple, repeatable, mathematically sound, efficient and predictable process. This thesis describes in detail a novel and generic Finite Element Method (FEM) model that for the first time predicts the evolution of the thermal profile of the ink track during laser curing and thus generates a parametric map which indicates the most suitable combination of parameters for process optimisation. Experimental data is compared with simulation results to verify the accuracy of the model. This study also theoretically and experimentally investigates the curing process under different intensity profiles obtained with the SunShaper, a novel beam shaping device invented by Dr Wellburn, and thus predicts the performance of curing with various circular shaped beams.

In this thesis, the exploitation of computational fluid dynamics (CFD) methods for the flight dynamics of manoeuvring aircraft is investigated. It is demonstrated that CFD can now be used in a reasonably routine fashion to generate stability and control databases. Different strategies to create CFD-derived simulation models across the flight envelope are explored, ranging from combined low-fidelity/high-fidelity methods to reduced-order modelling. For the representation of the unsteady aerodynamic loads, a model based on aerodynamic derivatives is considered. Static contributions are obtained from steady-state CFD calculations in a routine manner. To more fully account for the aircraft motion, dynamic derivatives are used to update the steady-state predictions with additional contributions. These terms are extracted from small-amplitude oscillatory tests. The numerical simulation of the flow around a moving airframe for the prediction of dynamic derivatives is a computationally expensive task. Results presented are in good agreement with available experimental data for complex geometries. A generic fighter configuration and a transonic cruiser wind tunnel model are the test cases. In the presence of aerodynamic non-linearities, dynamic derivatives exhibit significant dependency on flow and motion parameters, which cannot be reconciled with the model formulation. An approach to evaluate the sensitivity of the non-linear flight simulation model to variations in dynamic derivatives is described. The use of reduced models, based on the manipulation of the full-order model to reduce the cost of calculations, is discussed for the fast prediction of dynamic derivatives. A linearized solution of the unsteady problem, with an attendant loss of generality, is inadequate for studies of flight dynamics because the aircraft may experience large excursions from the reference point. The harmonic balance technique, which approximates the flow solution in a Fourier series sense, retains a more general validity. The model truncation, resolving only a small subset of frequencies typically restricted to include one Fourier mode at the frequency at which dynamic derivatives are desired, provides accurate predictions over a range of two- and three-dimensional test cases. While retaining the high fidelity of the full-order model, the cost of calculations is a fraction of the cost for solving the original unsteady problem. An important consideration is the limitation of the conventional model based on aerodynamic derivatives when applied to conditions of practical interest (transonic speeds and high angles of attack). There is a definite need for models with more realism to be used in flight dynamics. To address this demand, various reduced models based on system-identification methods are investigated for a model case. A non-linear model based on aerodynamic derivatives, a multi-input discrete-time Volterra model, a surrogate-based recurrence-framework model, linear indicial functions and radial basis functions trained with neural networks are evaluated. For the flow conditions considered, predictions based on the conventional model are the least accurate. While requiring similar computational resources, improved predictions are achieved using the alternative models investigated. Furthermore, an approach for the automatic generation of aerodynamic tables using CFD is described. To efficiently reduce the number of high-fidelity (physics-based) analyses required, a kriging-based surrogate model is used. The framework is applied to a variety of test cases, and it is illustrated that the approach proposed can handle changes in aircraft geometry. The aerodynamic tables can also be used in real-time to fly the aircraft through the database. This is representative of the role played by CFD simulations and the potential impact that high-fidelity analyses might have to reduce overall costs and design cycle time.

Computational fluid dynamics methods to simulate flows around geometries in relative motion are important for the aerospace industry. Traditional methods like finite-volume techniques are better suited for static simulations where the geometry of the problem does not change, or where only small movements are found. The meshless method can provide a solution for these problems where the geometry changes significantly and different bodies can move in relation to one another. A meshless method to select stencils from overlapping and moving point distributions, and a corresponding ow solver capable of solving the Euler equations on those stencils, have been developed previously. This work expands the existing meshless formulation by including the capabilities to simulate viscous ows in laminar and turbulent regimes and by implementing different parallel computing techniques in an effort to improve the computational efficiency. The treatment of viscous and turbulent flows is performed by augmenting the original Euler meshless scheme by using central-differences to discretise the viscous terms in the Navier-Stokes equations. The Spalart-Allmaras turbulence model is used to model the turbulent viscosity term and complete the closure of the system of equations to be solved. Validation of the method was carried out by calculating several well-known test cases and comparing the results to published data. The parallel implementation of the flow solver follows a distributed approach with asynchronous communications using message-passing standards. The parallel flow solver method is tested with two three-dimensional geometries, running in dedicated parallel machines with processor numbers ranging in the thousands. Results show good agreement to published data and very good parallel scalability. Preliminary testing of the stencil selection method, showed that the computational cost of the operations needed to find stencils for each point in the domain can vary dramatically for all points. Furthermore, this cost cannot be predicted a-priori, making it very difficult to perform an appropriate domain decomposition. With this in mind, three types of implementation are used for the parallel stencil selection scheme: a distributed memory approach, a shared memory approach and hybrid method combining the two previous ones. Using the shared and hybrid implementations, the negative effects of using a poor domain decomposition are reduced. Four test cases are studied using the parallel stencil selection procedure coupled with the parallel flow solver. Two of these cases are static, and two of them are simulations over moving geometries. The fourth case introduces a 6 degree-of-freedom simulation to calculate the movement of a store being released from an aircraft and showcases the full capabilities of the method. These parallel tests show important reductions in the calculation times and open the door for the meshless scheme to be used in the future for more realistic cases.

Demand for renewable energy resources to reduce greenhouse gases for EU targets, has led to a recent rapid development of Offshore Wind Farms (OWF). As OWFs become larger and multiple sites are developed, it becomes increasingly important to determine the wind farms impact on the coastal environment for design and planning. It is well established that the wind turbine monopiles at OWFs modify the flow in the localised area of the structure, to create a complex 3D flow structure, which ultimately results in scour hole formation. This present research aims to determine the impact of an OWF at both the localised and coastal scale through large scale modelling with the structures represented as islands in the mesh. This method is thought to be an improvement on the typical method of representing the structures as a resistance term in the grid, as it is able to capture some of the complex flow at the structure. The TELEMAC modelling package is used, with the hydrodynamics determined by the TELEMAC-3D module, the waves by the TOMAWAC module, and sediment transport by the SISYPHE module. Validation of the model at the structure showed good agreement with empirical data in the near field of the structure. Tidal flows are well predicted across the water depth, whilst scour formation is well predicted in front of the pile, there are areas of accretion in the wake which are unexpected. The large scale impact of the wind farm on coastal processes was assessed and compared over two wind farm sites, representing different coastal environments. The Burbo Bank wind farm is situated in a coastal bay, whereas Scroby Sands OWF is an open coast site. In both cases the wind farm was seen to block the flow and influence the large scale coastal sediment pathways. At Burbo Bank the wind farm enabled stirring of sediment into suspension, and influenced the sediment transport over the south east corner of Liverpool Bay. The Scroby Sands wind farm was found to reduce the sediment flux magnitude in the vicinity of the array. The long term morphological impact is also determined for the Burbo Bank OWF over a year period, with a morphological acceleration factor. Two methods are compared for generation of a set of representative waves, based on frequency of occurrence and wave energy. Both methods indicate that over a year period the wind farm has a large influence on sediment transport pathways, and increases sediment flux across the Great Burbo Flats. Maximum scour depth predictions at the structures showed good agreement with empirical formula. The pattern of scour for the representative waves based on frequency of occurrence, fits well with measured scour at the wind farm array.

In civil engineering, steel cables are widely used in the construction of bridges and sports stadia. However, their robustness and resilience against explosively formed fragment impact, whether accidental or malicious, remains largely unknown and very little research has been carried out on this subject to date. The concern is that small fragments projected from the explosion and travelling at high velocity may induce significant damage to the cables. This damage could rupture a cable releasing large amounts of kinetic energy into the surrounding structure and other damaged cables resulting in multiple cable loss and possible disproportionate collapse of the structure. To begin investigating this problem a good understanding of the localised damage sustained by the cables on impact is required. The work described within this thesis begins to address this problem by use of both physical tests and detailed finite element analysis. The tests involved firing fragment simulating projectiles at velocities ranging from 200 – 1400 m/s at un-tensioned spiral strand cables. Detailed finite element models have been developed for the spiral strand cables, with careful considerations given to the geometry of the cables, inter-wire contact mechanics, cable end boundary conditions and material modelling. The numerical results have been verified by comparison with the test results, with particular attention paid to the localised damage area, the fragment penetration depth, and the number of heavily damaged and totally broken wires. A global response study has also been undertaken on a case study structure to assess the effects of sudden cable loss. The work contained with this thesis forms part of larger research programme studying the robustness and resilience of cable supported structures subjected to highly transient loading conditions.

Multibody systems, which consist of several separate or interconnected, rigid or flexible bodies, occur frequently in problems of aerospace engineering. Such problems can be difficult to solve using conventional finite volume methods in computational fluid dynamics. This is particularly so if the bodies are required to undergo translational or rotational displacements during time-dependent simulations, which occur, for example, with cases involving store release or control surface deflection. These problems are generally limited to those when the movements are small or known a-priori. This thesis investigates the use of the meshless method to solve these difficult multibody systems using computational fluid dynamics, with the aim of performing moving-body simulations involving large scale motions, with no restrictions on the movement. An implicit meshless scheme is developed to solve the Euler, laminar and Reynolds-Averaged Navier-Stokes equations. Spatial derivatives are approximated using a least squares method on clouds of points. The resultant system of equations is linearised and solved implicitly using approximate, analytical Jacobian matrices and a preconditioned Krylov subspace iterative method. The details of the spatial discretisation, linear solver and construction of the Jacobian matrix are discussed, and results which demonstrate the performance of the scheme are presented for steady and unsteady flows in two and three-dimensions. The selection of the stencils over the computational domain for the meshless solver is vital for the method to be used to solve problems involving multibody systems accurately and efficiently. The computational domain is obtained using overlapping point distributions associated with each body in the system. Stencil selection is relatively straight forward if the point distributions are isotropic in nature; however, this is rarely the case in computations that solve the Navier-Stokes equations. A fully automatic method of selecting the stencils is outlined, in which the original connectivity and the concept of a resolving direction are used to help construct good quality stencils with limited user input. The methodology is described, and results, that are solutions to the Navier-Stokes equations in two-dimensions and the Euler equations in three-dimensions, are presented for various systems.

The starting point for this research was the viability of the Selective Laser Melted (SLM) titanium alloy Ti-6Al-4V micro-lattice structure for applications in Foreign Object Impact (FOI) situations in aerospace sandwich constructions. To this end, the mechanical behaviour of single struts and the compression behaviour of micro-lattice blocks were studied. Detailed characterizations of dimensional accuracy, circularity and microstructure, as well as clarifications of deformation behaviour and failure of single manufactured struts under tensile loading were done. The variability in stress-strain curve of struts which was derived using compliance correction method was found to arise from the variations in strut diameters, due to outer surface roughness of the material. Post-manufacture heat-treatment processes improved the surface roughness and variations of strut diameters as well as the microstructure of the α/β titanium alloy, hence reduced the scatter in the stress-strain curve of single struts. The deformation of the SLM Ti-6Al-4V micro-lattice blocks with Body Centred Cubic (BCC) structure was elucidated using combined experimental studies and computational analysis. Detailed analysis of geometry and diameter variations in struts of the micro-lattice blocks were done and compared to that of single manufactured struts. Node formation and manufactured quality of the micro-lattice structure were revealed from a 45° angle diagonal plane of sectioned block. The compressive deformation behaviour of the BCC micro-lattice block structures was then studied. Effects of different manufacturing routes and parameters as well as post-manufacture treatments in the compressed micro-lattice structures were discussed. Finite element analysis was performed using a validated model of BCC micro-lattice unit cell. The progressive collapse of the micro-lattice block structure was shown to be comparable with the prediction from the finite element model of a unit cell. The numerical simulation was then used to quantify the effect of parent material properties on block collapse. In this way, the relations between SLM manufacturing route, material properties and structural performance are highlighted.

To maximise the amount of energy extracted from wind turbines, the rotor diameter has increased, reaching values of 160m in some cases. Large scale wind turbines are working at high Reynolds numbers and a wide range of flow conditions, with virtually incompressible flow present at the root and mildly compressible near the blade tips, where the Mach numbers can reach locally 0.48 for the largest wind turbines employed to date. In traditional aerodynamics, most CFD methods were designed to cope with high Mach number flows and consequently solve the compressible Navier-Stokes equations. This is the case of the Helicopter Multi-Block (HMB2) CFD method from Liverpool University. The present PhD thesis aims to provide an all-Mach-number capability to the HMB2 method, by implementing modified Roe schemes to account for low-Mach flows. For 2D cases, the modified Roe schemes showed great improvement in the convergence and the quality of the solution, when compared with the Original Roe and Osher schemes, and the Low-Mach Roe scheme showed the best performance. With the low-Mach capability included in the compressible solver, both MEXICO and NREL Annex XX experiments were simulated. A detailed analysis of the velocity field behind the MEXICO rotor was performed, where the low-Mach scheme (LM-Roe) showed less sensitivity on the grid size than the Osher scheme. Accurate prediction of wind turbine wake breakdown is also important for the performance analysis of the turbines and their optimal positioning within tightly-spaced wind farms. Using a fine mesh able to preserve the vortices up to 8R downstream the MEXICO rotor plane, the instabilities on the wake leading to vortex pairing were captured. FFTs of the axial velocity component enabled to identify the main harmonics in the wake. In the stable region, the wake was a perfect spiral and the main frequency was the bladepassing one. An approximate exponential growth was then observed and in the region where instabilities were present, higher frequencies dominated, leading an oscillatory pattern. Simple wake models were also investigated and a combination between a kinematic model to account for the wake initial expansion and a field model to account for the far wake decay was proposed, showing good agreement with the CFD solution. With the correct set of constants, it was proved that this simple model can be used to approximate the behaviour of wind turbine wakes with minimal computational cost. Another consequence of the increased size of wind turbines is that their stiffness lowers and aeroelasticity therefore plays an important role, since the blades can suffer great deformations. To account for the blade deformations, a tightly coupled CFD-CSD method was employed to analyse the MEXICO and NREL Annex XX wind turbines. For the latter, the tower and nacelle were considered as stiff bodies and the blades were allowed to deform. As a result of the aeroelastic calculations, the blades showed deformation in bending (towards the tower). The maximum deflections were present after the blades had passed in front of the tower, and maximum amplitudes of 0.59%R, at 20m/s were observed.