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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Material characterisation using nonlinear ultrasound

Best, Steven R. January 2014 (has links)
Accurate monitoring of creep- and fatigue-based degradation in engineering components has become increasingly important within the power generation industry in recent years. One feature associated with the presence of such degradation, particularly in its early stages, is a certain amount of 'nonlinearity' in the ultrasonic response of a component. This nonlinear response is known to be sensitive to microstructural changes in the propagation medium, even before the stage where larger-scale features of damage may produce a measurable linear response. Measuring changes in signal nonlinearity therefore represents a promising means of material characterisation during the onset stages of component deterioration. The work in this thesis is based on the second hannonic generation method - an ultrasonic inspection technique which exploits the generation of higher harmonics in a nonlinearly propagating sinusoidal signal. Many recent experimental studies have found second harmonic measurements to be a strong indicator of increasing levels of creep and fatigue damage in laboratory specimens. However, while the theoretical aspects of harmonic generation in solids are generally quite well understood, the practical implementation of the technique is still at a relatively early stage in its development. Because of this, damage assessment experiments have generally only been qualitative in their estimations of nonlinearity. A large part of the work here is aimed at exploring improvements to the ways in which harmonic generation measurements are made and interpreted. Firstly, by developing a model representative of a typical measurement, the effects of various experimental parameters on the accuracy of the outcome are assessed. Here, theoretical and experimental results show that significant improvements in measurement interpretation can be made by including factors which are generally overlooked. The model is then used to explore alternative practical methods of implementation of the technique. Here a single-sided measurement configuration is explored, the feasibility of which is confirmed experimentally. Finally, a method is proposed to provide an increased level of detail regarding the distribution of nonlinearity within a component.

An investigation of the separated flow induced by a sharp bend in a pipe

Tunstall, Michael John January 1967 (has links)
An experimental investigation into the flow field associated with n fully developed turbulent flow passing through a 90° mitred pipe bend is described. The results of flow visualisation in both air and water and other techniques are presented, demonstrating that the downstream secondary flow does not conform to the anticipated twin-circulatory type, but consists of a single unsteady circulation. The circulation can assume either a clockwise or an anticlockwise sense and switches between these at a low, apparently random frequency. The resultant asymmetry and unsteadiness affects the majority of the flow field and severely complicates it. A suggested reason for this behaviour is given, based on the structure of turbulent pipe flow. Details of the strongly peaked spectra and high. intensities of the fluctuating wall pressure field generated by the separation are presented.

Pre-emptive infrared countermeasures

Jackman, J. January 2012 (has links)
The aim of this PhD is to investigate pre-emptive flare release compared to reactive flare release and their efficacy as a countermeasure device in the protection of fast jet and transport aircraft against the MANPAD threat. Implicit in this is to study the optimum release time of the flare decoy. Consequently, this also raises the question of whether flares of reduced payload size can be as effective as standard flares when released at this optimum time. To achieve these aims the initial step is to develop models for the different types of Man-Portable Air-Defence (MANPAD) systems and the IR seekers they utilise. This also requires the simulation of the full pre-launch process, namely the acquisition of the target to obtain lock-on then the application of lead and super elevation to give a more realistic model of the firing sequence. Two target models are also developed, a fast jet (AMX-A1) and a transport aircraft (C130), with realistic positions and ejection characteristics for the countermeasure (CM) dispensers. The next stage includes a counter-countermeasure (CCM) capability in the IR seekers. The first is a track angle bias with values optimised for the two aircraft models. Second is the development of a two-colour seeker with signal processors designed for both a spinscan and a conscan system. Using all MANPAD models flares are released at intervals throughout the engagements to find the optimum firing time and the simulations repeated for flares with reduced peak intensity and burn time. The results show that flare release around the time of missile launch is effective against most threats, even the more advanced MANPADs with CCMs. Also, that for reduced performance flares maintaining the burn time is perhaps more important than the peak intensity.

The history of roads in the Highlands

Stephen, James Souter January 1936 (has links)
Too often the name of General Wade is the only one mentioned in the History of Military Road-making in Scotland. It is true that he was the originator of the scheme, but what is perhaps more important is the fact that he had the faculty of choosing the best men to carry out his purpose. It was indeed fortunate for Wade that Ireland produced such a fine organiser and administrator as William Caulfield at this time. Wade was a General with ideas; Caulfield a man of action. In reality the one was the complement of the other. Wade's fame to a large extent rests upon Caulfield's labour, and Caulfield was dependent upon Wade for the idea and the opportunity of putting that idea into practice. Together they were responsible for building up a system of Military Roads which played an important part in the pacification of the Highlands. All Wade Roads are Military Roads, but the converse is far from true. Wade himself was responsible for 245 miles, while the total mileage under Military control in 1779 was 1,103. The/ The History of Scottish Military Roads may be divided into three periods:- The Early Georgian or Pre-Rebellion Period - 1725-40 -- Wade. The Mid Georgian or Post-Rebellion Period 1746-67 -- Caulfield. The Late Georgian or Peace Period 1770-1814 -- Skene - Anstruther. WADE. The work in the first period was definitely influenced by Wade who often inspected the roads. 1725 was an experimental year. The experiment was successful and as a result two great lines of road were laid down. The roads from Fort William and Dunkeld (with its Crieff-Dalnacardoch branch) converged at Inverness, while they were also con-nected by the Mountain road between Fort Augustus and Ruthven Barrack called the Corrieyairack Pass. This scheme includes all the roads definitely known to have been made by Wade. Others, such as the Glen Roy Road, may have been made by him. CAULFIELD. William Caulfield became Inspector of Roads in 1732, and it is most important to note that in 1732 bridge building first became a prominent feature of Military Road-making. In that year St./ St. George's Bridge - a double arched bridge - was constructed on the Corrieyairack Pass, and a new road made from Inverness to Fort Augustus. This route was only made possible by bridging the Faragaig. In the following year the famous Tay Bridge at Aberfeldy was begun and so on. Was it merely a coincidence that Caulfield was made In-spector in 1732, and that bridge building began (l) in that year Before he died in 1767, Caulfield had laid out all the remaining Military Routes in the Highlands - over 800 miles of road. SKENE-ANSTRUTHER. This was the period of repair and absorption of Military Roads by County Authorities. The absorption was almost completed by 1814, but a small mileage was kept in repair by the Government until 1864.

Understanding the ballistic event : methodology and observations relevant to ceramic armour

Healey, Adam January 2017 (has links)
The only widely-accepted method of gauging the ballistic performance of a material is to carry out ballistic testing; due to the large volume of material required for a statistically robust test, this process is very expensive. Therefore a new test, or suite of tests, that employ widely-available and economically viable characterisation methods to screen candidate armour materials is highly desirable; in order to design such a test, more information on the armour/projectile interaction is required. This work presents the design process and results of using an adapted specimen configuration to increase the amount of information obtained from a ballistic test. By using a block of ballistic gel attached to the ceramic, the fragmentation generated during the ballistic event was captured and analysed. In parallel, quasi-static tests were carried out using ring-on-ring biaxial disc testing to investigate relationships between quasi-static and ballistic fragment fracture surfaces. Three contemporary ceramic armour materials were used to design the test and to act as a baseline; Sintox FA alumina, Hexoloy SA silicon carbide and 3M boron carbide. Attempts to analyse the post-test ballistic sample non-destructively using X-ray computed tomography (XCT) were unsuccessful due to the difference in the density of the materials and the compaction of fragments. However, the results of qualitative and quantitative fracture surface analysis using scanning electron microscopy showed similarities between the fracture surfaces of ballistic fragments at the edges of the tile and biaxial fragments; this suggests a relationship between quasi-static and ballistic fragments created away from the centre of impact, although additional research will be required to determine the reason for this. Ballistic event-induced porosity was observed and quantified on the fracture surfaces of silicon carbide samples, which decreased as distance from centre of impact increased; upon further analysis this porosity was linked to the loss of a boron-rich second phase. Investigating why these inclusions are lost and the extent of the effect of this on ballistic behaviour may have important implications for the use of multi-phase ceramic materials as armour.

Gunnery and the struggle for the new science (1537-1687)

France, Catherine Ann January 2014 (has links)
This thesis re-examines the contribution of ballistics and gunnery to the emergence of modern science. It seeks to answer the question that inevitably emerges from A. R. Hall’s seminal Ballistics in the Seventeenth Century (1952): Why did early modern scientists and writers on gunnery include theoretical treatments of the trajectory of a gun in their works, despite the fact that it could be of no use to the practice of gunnery? Hall’s response to this perplexing question was simply that ballistic theory provided a scientific ‘veneer’ in support of attempts to gain patronage from rulers and military leaders who were anxious to gain an advantage in the new cannon warfare that played a crucial role in the development of the emerging European nation states from the end of the fifteenth century. Recent historiography, which has emphasised the role of etiquette and rhetoric in patronage relationships, has only served to bolster the credibility of Hall’s explanation, leading to an attenuation of the programme of the early modern writers who attempted to solve the mystery of the trajectory (‘the gunners’ question’). My thesis contends that, pace Hall, the struggle for the solution to the gunners’ question is paradigmatic for the resolution of unsolved issues in the history of science, and would aid substantially in delineating the role of mathematics and quantification not only in ballistics but in the transformation of natural enquiry into a recognisably modern enterprise. Whilst retaining the long-term chronological approach of Hall, my thesis re- examines in detail a number of central figures in the history of ballistics as historical actors, rather than focusing narrowly on theoretical results. This brings to the forefront their struggle to unite theory with practice and to persuade their audience of the necessity for a new approach to natural enquiry. Through a re-examination of key texts, the thesis attempts to uncover their wider programmatic aims. They all had in common a self-perception that they were involved in building a new science of motion that would lay certain foundations for practice, they sought commonalities in all the diverse domains of the natural and artificial world, and they recognised that this was the only route to new and certain knowledge.

Late Roman fortifications in the western Empire : a study of the origins and development of a defensive system, 260-400

Johnson, J. S. January 1976 (has links)
No description available.

A risk-based methodology for minimising weld distortion in steel ship production

Sukovoy, Oleg January 2002 (has links)
No description available.

On the use of B-spline technique in geometry and hydrodynamics of marine propellers

Prasetyawan, Ika January 2003 (has links)
No description available.

STEADY : feasibly of a floating stable working platform for precise deep water subsea operations

Grimwade, Jamie January 2002 (has links)
No description available.

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