The influence of the Ara on the hot ductility of steels was examined. Tensile samples were heated to 1603K, cooled at 60Kmin" and tested in the temperature range 1323-873K at a strain rate of 3x10-3S-1. The Ara was altered by variations in C, (0.1 to 0.15%C), Mn, (0.6 to 1.4%Mn), Si (0.1 to 0.5%Si) and P, (0.001 to 0.025%P). Elements that raise the Ara e. g. Si and P were found to lead to recovery in ductility at slightly higher temperatures at the low temperature end of the trough. However, reducing C levels to <0.1C had the most pronounced influence on hot ductility since ductility was then observed to recover just below the Ae3 and the trough was very narrow. The lower C level allowed large amounts of deformation-induced ferrite (equilibrium amounts) to form, ferrite having excellent ductility. mThe influence of both S in solution and elongated sulphides on hot ductility was also examined. Although elongated sulphides encouraged ferrite formation, this was a relatively minor improvement. In these steels, low C levels (<0.1%) i. e. high Ae3 temperatures, ensured ductility recovered rapidly just below the Ae3 obscuring the effect of S. Similar behaviour was noted with as-cast steel, increasing the S level from 0.004 to 0.019% had little influence on the hot ductility. Increasing the cooling rate after solidification, from conventional continuous casting to that pertaining to thin slab casting, results in worse ductility. This can be ascribed to finer precipitation and/or a finer inclusion distribution at the y grain boundaries. A model was devised for predicting the hot ductility curve for simple plain C-Mn steels. However, this model has limited application and further development is needed to take into account the influence of grain boundary sliding on the reduction of area values. Columnar grains were found to be very detrimental to hot ductility and to avoid transverse cracking, it is suggested magnetic stirring be used in the mould to break up the columnar structure.

This thesis presents two types of alternating current (ac) generators that are becoming popular for use in small-scale distributed generation and in autonomous (or standalone) power systems. For the induction generator (IG), two modes of operation are identified, namely operation on the power grid and operation in the isolated mode. Single-phase operation is emphasized due to its applicability in remote rural regions where electrification is both costly and difficult to carry out. In the case of gridconnected operation, a number of practical phase-balancing schemes for a three-phase IG are proposed and analyzed. The method of symmetrical components is found to be a versatile tool for analyzing all the circuit configurations to be studied, including the Smith connection. Microcontroller-based multi-mode operation of an IG with the Smith connection is also investigated. When operated in the stand-alone mode, the IG is more commonly known as the selfexcited induction generator (SEIG). In this thesis, a unified approach that combines the method of symmetrical components and the pattern search method of Hooke and Jeeves is used to analyze a three-phase SEIG which supplies asymmetrical or single-phase loads. Its applicability is tested on various SEIG schemes, including the Steinmetz connection, modified Steinmetz connection (MSC), the simplified Steinmetz connection (SSC), the self-regulated self-excited induction generator (SRSEIG), and SEIG with the Smith connection (SMSEIG). For certain studies, the above approach is used in association with an iterative procedure in order to obtain the solution. A coupled circuit and field approach based on a two-dimensional finite element method (2-D FEM) is proposed for analyzing a grid-connected IG with the Steinmetz connection. The technique of coupling the single-phase circuit equations to the field domain equations is set forth and a rotor circuit model that accounts for the nonuniform current distribution in the rotor winding is also presented. A voltage and frequency control scheme that employs an SEIG with slip-ring rotor, namely the SESRIG, is also proposed and investigated. The feasibility of using an external rotor resistance as a control parameter is demonstrated theoretically and experimentally. The study on the permanent-magnet synchronous generator (PMSG) is focused on autonomous power system applications. A PMSG with inset rotor, which possesses an inverse saliency characteristic, is found to give satisfactory performance when supplying isolated loads. Zero voltage regulation and other extremum conditions are deduced based on the two-axis model. A saturated two-axis model that gives a more accurate prediction of the load characteristic is developed. For a more rigorous analysis, a coupled circuit and field, time-stepping 2-D FEM is also proposed.

Increasingly stringent equipment performance and reliability requirements are being specified to the aerospace industry by aircraft manufacturers, driven by the expectations of both certification authorities and operators. The reality is that aircraft system and equipment reliability in service can fail to meet the design expectations. This thesis details the problem areas within the current analysis process, describing the procedures currently in use and showing what can go wrong. It goes on to propose action that can be taken to ensure safety levels are maintained and details a new approach that is unique to this thesis. The author has devised a new System Safety Compliance Model (SSCM) for ensuring that aircraft system safety standards can be better maintained. Evolved from his earlier highly successful database system at TRW Lucas Aerospace, SSCM will be: - Demonstrably cost effective - A step change in process capability, offering "something new" - Instantly accessible at shop floor level to everyone in the business - Easy to use and as automated as possible to minimise staff training requirement - Capable of performing instant re-assessment of safety performance down to system level and including consideration of a variety of operating environments and conditions - The industry standard repository of component reliability data - "Centrally" owned by a world-wide recognised industry body SSCM is the first system to operate in such a way, and will ensure that the original system safety analysis performed at the design stage, is continually assessed for accuracy throughout its in-service life. If the new methods detailed in this thesis are adopted and acted upon, there is a high probability of a reduction in the risk of aircraft systematic failure in service, leading to increased safety in aviation. The model can be equally applied to other areas of transportations uch as railways.

High-pressure multi-hole nozzles, carrying a Diesel-derived technology, are believed to be promising Fuel Injection Equipment (FIE) for Direct-Injection (DI) Spark Ignition (SI) gasoline engines. Having explored thoroughly swirl pressure atomisers and their spray behaviour, multi-hole nozzles represent the second-generation injectors. Thus, complete investigation of multi-hole nozzle flow, spray characteristics and their engine performance is a vital part of development of future DI gasoline engines. The internal nozzle flow of an enlarged transparent multi-hole injector was investigated for different flow rates and needle lifts under steady state flow conditions. High-resolution CCD camera and high speed digital video systems were employed to visualize the nozzle flow patterns and cavitation development. The images identified the onset of cavitation in multi-hole gasoline nozzles and revealed the transition from pre-film to film stage cavitation. Cavitation strings were also visualized inside the injection hole that could extend to the needle face. However, these structures are highly unstable and directly affected by needle lift and cavitation number, although it appeared to be independent of the Re, in a behaviour similar to that of multi-hole diesel injectors. The sprays from various high-pressure multi-hole nozzle designs injected into a high-pressure/temperature constant-volume chamber have been visualised and quantified in terms of droplet velocity and diameter with a two-component phase-Doppler Anemometry (PDA) system at injection pressures up to 200bar and chamber pressures varying from atmospheric to 12bar. The overall spray angles relative to the axis of the injector were found to be almost independent of injection and chamber pressure, a significant advantage relative to swirl pressure atomisers. Within the measured range, the effect of injection pressure on droplet size was rather small while the increase in chamber pressure from atmospheric to 12bar resulted in much smaller droplet velocities, by up to fourfold, and larger droplet sizes by up to 40%. The effect of chamber temperature on multi-hole sprays confirmed the expected trends that dictate smaller droplet size distributions as temperature rise from 50 to 90 and 120°C. Additionally, multiple-injection proved to have similar dependencies to the single injection with certain operating limits. Laser-induced fluorescence has been mainly used to characterise the two-dimensional fuel vapour concentration inside the cylinder of a multi-valve twin-spark ignition engine equipped with high-pressure multi-hole injectors. The effects of injection timing, in-cylinder charge motion and injector tip layout have been quantified. The flexibility in nozzle design of the multi-hole injectors has proven to be a powerful tool in terms of matching overall spray cone angle and number of holes to specific engine configurations. Injection timing was found to control spray impingement on the piston and cylinder wall, thus contributing to quick and efficient fuel evaporation. Multipleinjection performed well under certain operating conditions and proved to be a powerful tool in the hands of engine manufacturers. It was confirmed that in-cylinder charge motion plays a major role in engine's stable operation by assisting in the transportation of the air-fuel mixture towards the ignition locations (i.e. spark-plugs) in the way of a uniformly distributed charge or by preserving stratification of the charge depending on operating mode of the engine.

This thesis presents a newly developed Quasi Arbitrary Lagrangian-Eulerian Finite Element Method (QALE-FEM) for numerically simulating wave-body interaction problems based on the fully nonlinear potential theory. The boundary value problem in this model is solved by a finite element method (FEM). The main difference between this method and the conventional FEM is that the complex mesh is generated only once at the beginning of the calculation and is moved at all other time steps in order to conform to the motion of the free surface and structures. This feature allows one to use an unstructured mesh with any degree of complexity without the need of regenerating it every time step, which is generally inevitable and very costly. Due to this feature, the QALE-FEM has high computational efficiency when applied to problems associated with the complex interaction between large steep waves and structures since the use of an unstructured mesh in such a case is likely to be necessary. In order to achieve overall high efficiency, some numerical techniques, including the method to move interior nodes, the technique to redistribute the nodes on the free surface, the scheme to calculate velocities, are developed. To overcome the difficulty associated with the force and acceleration of freeresponse floating bodies, an ISITIMFB (Iterative Semi-Implicit Time Integration Method for Floating Bodies) iterative procedure is developed. The developed QALE-FEM method is applied to simulate the waves generated by a wavemaker and their interaction with sandbars on the seabed, waves generated by a floating body in forced motion, the response of a 2D or 3D freely floating body to a steep wave. Some of the results have been validated by analytical solutions, experimental data and numerical results from other methods. Satisfactory agreements are achieved. The convergence properties of this model in cases with or without floating bodies are all investigated. The nonlinearities associated with different cases are investigated. The mesh quality is also investigated using either qualitative or quantitative methods. The results show the mesh quality during long-period simulation is retained. The efficiency of the QALE-FEM method is finally discussed and compared with other methods. It is concluded that the QALE-FEM method is 10 times faster than the conventional FEM method in case with unstructured mesh and at least 7 times faster than the fast BEM methods for the fully nonlinear waves.

This research, which was begun as part of the now defunct CargoLifter project, concerns the ground handling and support systems of the large rigid airships (commonly known as "Zeppelins") that were built between 1900 and 1940. The intention was to assess the value of such historical information as has survived from the previous generation of very large airships in order to minimise the physical and financial risks inherent in the development of any future generations of such aircraft. The idea was to isolate and understand the fundamental issues that were actually encountered by the ground based personnel responsible for looking after the various British, German, American and Italian airships of the previous generation, and to gather as much information as possible about the techniques and operational procedures that were devised, tried and tested in the field. This information would then be used to establish guidelines for future projects that are based on real experience rather than on prediction, assumption or theory. Sadly, the CargoLifter project foundered in 2002; however the author had by then amassed sufficient research material for him to complete the study independently and to present it as a guide for the ground handling of hitherto unrealised concepts such as the proposed new "Transport category" or "CargoLifter" type large airships. Such practical skills as those required by airship ground crew personnel are normally passed on by firsthand instruction from one experienced practitioner to the trainee. This option is not available for the next generation of very large airships because there are no personnel alive today with any operational experience of the previous generation of really large airships. The problem therefore is to examine the historical records and to evaluate the written information in order to interpret it and pass on knowledge that will reduce the risk of future generations wasting their time in "re-inventing the wheel. " In the course of the study it was found that historical research (HR) enabled the results of the pre-war prototype projects to be usefully assessed despite the fact that very little of the material was written with that end in view. More specifically the analysis of historical airship activities (AHAA) revealed that it was possible to retrieve a considerable amount of lost or forgotten knowledge concerning the ground handling of very large airships, also to unearth ideas that were ahead of their time, which might be applicable today or in the future; and in addition to identify several areas worthy of further investigation (e. g. ideas that were rejected at the time but which may now be feasible due to technological progress). The research and analysis also uncovered some ideas and suggested solutions which are fundamentally flawed and that should be avoided by designers of large airships and their support systems. The work includes a detailed analysis of the tasks involved in the ground handling of very large airships and concludes with a suggested strategy for all those intent upon the design and planning of ground support infrastructures for any further large airship development projects either today or in the future.

In recent years supply chains have gained the attention of both academia and industry. In this thesis, a novel state-space model of a multi-node supply chain is presented, controlled via local proportional inventory-replenishment policies. The model is driven by a stochastic sequence representing customer demand. The model is analysed under stationarity conditions, guaranteed to arise if the control parameters lie in a certain range which is identified and a simple recursive scheme is further developed for updating the covariance matrix of the system in closed form, i. e., as an explicit function of the control parameters. This allows us to analyse the effect of inventory policies on the "bullwhip effect" (demand amplification) for chains with an arbitrary number of nodes. The three-node model is subsequently analysed in detail under information sharing and the optimal policy is derived, which minimises inventory fluctuations (and inventory mean) under a probabilistic constraint related to downstream demand. It is shown that this policy can never lead to demand amplification in the chain, as long as the gain parameter of the downstream node lies in the stability region. Finally, issues related to estimation schemes based on local historical data are discussed. The main results and conclusions are illustrated via numerous examples and simulations. An alternative model of the supply chain is also developed using timed Hierarchical Coloured Petri Nets (HCPN). This approach considers supply chains as event-driven systems and studies decentralised control structures by analysing the impact of various continuous inventory policies and known forecasting methods followed by supply chain participants. CPN-Tools [fCPN] are used for the design of decision-making policies and simulation results are presented to highlight the main issues arising in real systems and to provide insights for future modelling and simulation work. Finally, a detailed case study is undertaken, for the production line of the "Bridngorth Aluminium Ltd" company which produces high quality rolled aluminium lithographic strips. An efficient representation for such production processes is provided and subsequently used for an extensive analysis and performance evaluation through appropriate metrics. In particular, the work addresses the implementation of an overall model in a simulation environment, capable of integrating the various aspects of the specific production management processes.

No description available.

This thesis presents a rational and unified approach for determining the strength of reinforced and prestressed concrete rectangular beams subjected to combined bending, torsion and shear. In this study failures have been classified into three broad categories: 1) yield modes (3 cases) 2) partial yield modes (6 cases) 3) over-reinforced modes (3 cases). The effect of dowel action, aggregate interlock, uncracked concrete and spacing of stirrups on the resistance of applied torque have been examined. The predictions of the proposed theories have been compared with more than a thousand test results available in literature. In general the agreement is good. A method for predicting cracking strength for reinforced and prestressed concrete beams subjected to bending, torsion and shear is given. The results of tests on 25 thin-walled prestressed concrete box-beams subjected to torsion, bending and shear are presented. Experimental and theoretical investigations on the behaviour and strength of dowels in concrete are given.

This thesis deals with the influence of fire on the behaviour of steel concrete composite floors. A theory has been developed to calculate deflections during the fire and the ultimate strength of the composite floor under such conditions. The solution is based on the finite difference method. It takes temperature-dependent material properties into account. The method of analysis comprises two parts; the first is thermal analysis, enabling temperatures to be calculated as a function of fire exposure time. The second is strength analysis for calculating the strength of composite floor with material properties affected by temperature. For the heat flow analysis, the cross-section is divided into mainly rectangular elements. Sloping boundaries are approximated by triangular elements. The heat transfer from the fire to the surface is considered as well as heat conduction to the neighbouring points. At internal points, heat conduction to all the neighbouring points is considered. To calculate the deflections, the floor is divided into a two-dimensional mesh. The deflections are calculated for each mesh point based on orthotropic plate theory. The differential operators are replaced by the finite difference formulae. This reduces the governing differential equation into a system of linear algebraic equations. To calculate the plate rigidities, it is necessary to find curvatures for all mesh points in the two planes using finite difference operators. The thermal strains are superimposed on the mechanical strains associated with curvatures to find the net strains, and then stresses are calculated using the non-linear temperature dependent stress-strain curves. Integrating the stresses, the internal stress resultants are calculated. The above method has been programmed in Visual Basic. To validate this method, a comparison with a number of fire tests has been carried out, for both thermal and mechanical behaviour. The temperatures at comparable points are generally close to each other. Comparisons have also been carried out for calculated mid-span deflections by this method and the published test results. The results show excellent correlation between the tests and the new method. A parametric study has been carried out on floors with different boundary conditions when subjected to in-plane forces for two fixed and simple ends. Comparison of mid-span deflections between the fixed and simple end conditions has shown that fixed edges have better fire resistance than simply supported when not subjected to in-plane forces. It has found that in-plane forces had little effect on deflection rates at initial stages of the fire. These only appeared at later stages. When subjected to in-plane forces in one direction only the floor showed better response. The conclusion from the parametric study is that in-plane forces at different edges play a significant role in the behaviour, as the surrounding structure provides restraint increasing the fire resistance of the structure within the fire compartment.