School of Engineering (SoE)

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Open Access
Acoustic emission pulse analysis: an integrated system for transducer calibration and signal processing
(1982-10) Oliveras, Juan M.; Bannister, R. H.
The present thesis covers the pioneering effort of establishing an infrastructure for conducting research into the analysis of Acoustic Emission signatures, with emphasis being placed upon the recovery of the true surface waveform for a given transient input. The topics covered in this work are: The p·rovi s ion of the necessary computer software for the handling and processing of the data. Here, a method is included for the correction of phase errors introduced by the sampling/multiplexing of ·the signals, which provides the basis for the implementation of data convolution.techniques in the frequency domain. J°he development of an experimental rig and source of excitation, later applied to the design of transducers. The development of a new transducer configuration, capable of producing a relatively flat frequency response (±7dB) over the frequency range 300 KHz - 2 MHz. The development of a procedure for the calibration of transducers, based upon a modified reciprocity method. The technique produces the calibration of transducers in relative terms, requiring a comple- . . mentary method to provide the reference level for the calibration. As a means of assessing the proposed techniques, the transducer calibration was applied to the de-convolution of pulses generated with a step forcing function, and the results compared with an equivalent theoretical model previously published.
Open Access
Aerodynamic surface pressure measurement in atmosphere and wind tunnel on a vertical axis wind turbine blade using pressure transducers
(1989-09) Oram, C. E.; Garside, A. J.; Hales, R. L.; Moss, J. B.
Blade aerodynamic loads during operation of a wind turbine are poorly understood. Better measurements of these forces are needed for the design of more cost effective turbines. Existing estimates have been inferred from strain gauges in the blade structure, but such measurements are confused by the complexity of the blade's structural response. This present work has pressure tapped the blade surface and recorded at high speed, giving a highly detailed picture of dynamic events and blade loads. A modular blade was constructed for the 6m diameter Rutherford Appleton Vertical Axis Wind Turbine and instrumented with 32 semiconductor pressure transducers. A flow probe using a further three transducers projected ahead of the blade during some of the tests. The instrumented module was also operated in the oscillating mounting of the University of Glasgow's 1.6m by 2.4m wind tunnel. 1760 revolutions of data were collected in atmosphere with blade speed ratios down to about 2.0 and with a variety of blade leanout angles. Some 118 runs of a variety of waveform types and Reynolds numbers from 0.3 to 1.1 million, were collected from the blade in tunnel. Analysis of transducer calibrations concluded that the novel temperature correction technique used allowed pressure readings to 40Pa or better with 95% confidence. Confidence in measured pressures has allowed use of leading edge stagnation point pressure and position as a measure of wind in the rotor flowfield and as a surrogate measure of blade angle of attack. Blade surface pressures and integrated forces show the progression of dynamic stall with increase in wind speed, the dominance of the upstream blade pass in usefulness at low and moderate windspeeds and the rough equality at high windspeeds. Comparisons of wind tunnel and on-rotor data show much lower force and moment coefficients in atmosphere. Rotor 'goodness1 ratios of average blade tangential force to maximum blade and rotor force coefficients peak at a blade speed ratio of about 2.8. Goodness ratios show a mixed pattern with blade leanout. Analysis of pressure coefficient traces through stall indicate a mixed stall type starting at mid chord, moving to leading edge and thence to trailing edge.
Open Access
Airblast atomization : the effect of linear scale on the mean drop size
(1978-12) El-Shanawany, M. S. M. R.; Lefebvre, A. H.
Stationary prefilming-cup airblast atomizers, in which the fuel is first spread into a thin cylindrical sheet and then exposed on both sides to high velocity air, have several important advantages over other common methods of fuel injection in their application to continuous combustion systems. This thesis reports the results of a detailed programme of research on airblast atomization directed primarily to the investigation of the effect of atomizer linear scale, or size, on the mean drop diameter of sprays and, to the provision of a comprehensive picture of the performance of thin-sheet airblast atomizers over a wide range of working conditions. Three geometrically similar atomizers giving cross-sectional areas in the ratio of 1 : 4 : 16 were used; covering the range of prefilming cup diameter, D, from 19.05mm. to 76.20 millimeters, and were capable of handling various liquids at flow rates from 0.003kg/s up to 0.225 kg/s, at fuel pressures below 33 x 10^ N/m^ (about 50 p.s.i.). . It was found that atomizer scale has an appreciable direct effect on atomization quality. The Sauter mean diameter of low liquid viscosity sprays increases with the 0.44 power of atomizer linear dimension (D), while for liquids of high viscosity this effect is slightly higher.
Open Access
Airline deregulation: an analysis under different regulatory and operating environments
(1989-07) Etemadi-Nejad Alamdari, F.; Cordey-Hayes, M.
Like other transportation modes the airline industry has a long history of government regulation. In recent years however the theoretical and empirical bases for air service regulatory schemes have been questioned by opponents of such policies. In Western Europe there have been pressures for relaxation of regulation of the air transport industry with respect to air fares, service frequency and market access. Because changes in such public policies are likely to have a major impact, there is a considerable interest in their possible implications. It is the objective of this study to explore the interactions between fare and service frequency in different competitive environments, and to examine the rivalrous behaviour of airlines and their possible equilibrium position under deregulation. The study also considers the effect of a competing mode (rail) on air carriers performance under various competitive conditions. The individual carrier's performance is quantified in terms of fare, service frequency, resulting generalised costs, market share and financial results. A competition model is developed by which the objectives set above are achieved. The study is divided into three parts. The first part provides a framework within which the competition model can be built. This part also generates the policy questions which must be addressed, should relaxation of regulation take place in Europe. The second part explains the structure of the competition model and its characteristics. The assumptions upon which the model is built and its limitations are also discussed. The model consists of three sub-models: the market share model, the costing model and the reaction model. In the third part, with the aid of the model the policy questions generated in the first part are addressed and the general implications for carriers operating under different competitive conditions are discussed. Finally the technical and the policy conclusions are discussed. It is generally concluded that: competition results in lower fares and a more efficient airline industry; the impacts of competition are not evenly distributed amongst markets, routes and carriers; and the competition on equal terms amongst carriers plays an important role in maintaining the effectiveness of deregulation.
Open Access
The application of computational techniques to the design of thermal ice protection systems
(1990-03) Leah, C. W.; Eshelby, M. E.
A bibliography citing 1350 references related to all aspects of aircraft icing is presented. An ice adhesion database has been compiled, and a survey of ice adhesion test rig designs is presented. An ice shear adhesion test rig is designed, manufactured and operated. The results are added to and compared with those in the database. The adhesion of ice accreted on metal and non-metallic composite aircraft propeller blades in flight is assessed. A one-dimensional thermodynamic study of ice accreted on a non-metallic composite propeller blade with ’built-in1 electrothermal de-icing system is effected and compared with a solid metal blade. A two-dimensional aerofoil icing prediction program is modified and executed in series with additionally created software to predict icing on aircraft engine air intake duct lips in flight. Hence a new de-icing system design method is developed to replace and improve upon an existing one. Validation of the new design method is initiated and a programme for its completion is presented. Icing predictions produced using the new method correlate well with expected values derived by several methods. The new design method is incorporated in the sponsoring companies business with an appropriate computer hardware/software system and employed, in parallel with the ’old’ approach (till validation completion), on commercial projects. Market response indicates a definite preference for the new design method. The ’non-technical’ and other related practical topics of implementing the new de-icing system design method, including specification and installation of computer hardware and software are discussed. Marketing, financial and other commercially oriented subjects are addressed in justifying the research and the implications of introducing the new design method into the commercial business of the sponsoring organisation are considered. This research programme forms a part of a large, long term icing research commitment. Continued research subjects and investigative routes including the integration of ice adhesion mechanical characteristics into the de-icing system design method are discussed together with their relationship to this and the overall icing research plan.
Open Access
The application of electrolytic photoetching and photopolishing to AISI 304 stainless steel and the electrolytic photoetching of amorphous cobalt alloy
(1986-01) Talib, Talib Naji; Allen, David
The results presented cover broad aspects of a quantitative investigation into the elecrolytic etching and polishing of metals and alloys through photographically produced dielectric stencils (Photoresists). A study of the potential field generated between a cathode and relatively smaller anode sites as those defined by a dielectric stencil was carried out. Numerical, analytical and graphical methods yielded answers to the factors determining lateral dissolution (undercut) at the anode/stencil interface. A quasi steady state numerical model simulating the transient behavior of the partially masked electrodes undergoing dissolution was obtained. AISI 304 stainless steel was electrolytically photoetched in 10% w/w HC1 electrolyte. The optimised process parameters were utilised for quantifying the effects of galvanostatic etching of the anode as that defined by a relatively narrow adherent resist stencil. Stainless steel was also utilised in investigating electrolytic photopolishing. A polishing electrolyte (orthophosphoric acid —glycerol) was modified by the addition of a surfactant which yielded surface texture values of 70nm (Ra) and high levels of specular reflectance. These results were used in the production of features upon the metal surface through photographically produced precision stencils. The process was applied to the production of edge filters requiring high quality surface textures in precision recesses. Some of the new amorphous material exhibited high resistance to dissolution in commercially used spray etching formulations. One of these materials is a cobalt based alloy produced by chill block spinning. This material was also investigated and electro etched in 10% w/w HC1 solution. Although passivity was not overcome, by selecting suitable operating parameters the successful electro photoetching of precision magnetic recording head laminations was achieved. Similarly, a polycrystalline nickel based alloy also exhibiting passivity in commercially used etchants was successfully etched in the above electrolyte.
Open Access
The application of relative navigation to civil air traffic management
(2000-08) Sangpetchsong, K; Allerton, David J.
This thesis addresses navigation and guidance which will be required for air traffic management in Future Air Navigation Systems (FANS) and Free Flight. In particular, the thesis covers the issues of data fusion and integrity monitoring, to provide an adequate level of aircraft separation assurance, based on relative navigation (RELNAV). The evolution of air navigation systems is described. The principles of Kalman filtering and Joint Tactical Information Distribution System (JTIDS) RELNAV are covered. Sensor models of strapdown Inertial Navigation System (INS), Global Positioning System (GPS), and Automatic Dependent Surveillance-Broadcast (ADS-B) are developed in Matlab and integrated to form a hybrid navigation system. RELNAV algorithms for centralised and decentralised Kalman filtering are formulated, and their respective performances are analysed using Monte Carlo simulations for an airspace containing several aircraft. It is shown that RELNAV, based on the integration of INS and ADS-B, can enable aircraft to maintain safe separation independent of GPS, where it is assumed that an ADS-B datalink provides accurate time synchronisation. An alternative approach that integrates INS, GPS, and ADS-B is developed and analysed. It is shown that this approach is more applicable to civil aviation because it eliminates the needs to establish and manage several navigation communities simultaneously, in effect, exploiting GPS as the navigation controller. The source selection functions used for RELNAV are also developed, and the stability and performance of this technique is evaluated from simulation studies. A failure detection algorithm that monitors the residuals of a Kalman filter is derived and evaluated using Monte Carlo simulations of GPS failures. It is shown that this algorithm combines the use of likelihood functions and chi-squared tests, allowing both a false alarm rate to be selected and a failed sensor to be identified. Finally, an algorithm is developed for separation assurance to determine the probability that aircraft are closer than a pre-determined distance, taking into account flight path prediction errors. It is shown that this algorithm simplifies aircraft conflict detection in three dimensions and allows the conflict probability at a particular time to be determined. This approach is validated using Monte Carlo simulations of aircraft trajectories which include near-misses.
Open Access
An approach to configuration design synthesis of subsonic transport aircraft using artificial intelligence techniques
(1991-12) Pasaribu, H. M.; Fielding, John
This thesis outlines a computer system developed to tackle the configuration design synthesis of subsonic transport aircraft. The system provides an interactive design environment which combines the reasoning process of the aircraft configuration definition and the numerical analyses that lie behind the reasoning. The system applies Artificial Intelligence (AI) techniques to the configuration analysis. This gives the system the capability to reason with the configuration choices. The system is built in modules, with each module is clearly separated to deal with a complete analysis in a specific aspect of design. The integration of the modules is done through an intelligent interface and a common database. The interface also incorporates AI techniques in deciding the sequence of execution of the modules and the processing of the input/output data for a particular module. The interface permits the sharing of information among the modules and supports modularity and flexibility of the system for future development. Since each module is independent, it can be easily modified or replaced without disturbing the balance of the system. An extensive library of application programs is included in the engineering analysis module which enable detailed analysis to be performed. The system is equipped with a simplified database management and a special purpose graphics module which is extensively used for the presentation of the output. The system has been validated and tested. It can handle both propeller driven and jet engined aircraft. An example of the case studies is presented. The improvement of the system for future development is also considered. These include the extension of the knowledge base for dealing with problems in other modules, the enhancement of the application programs in the engineering module, and a possible interface with an established Computer Aided Drafting (CAD) system.
Open Access
The behaviour of polyurethane foam beams reinforced with thin walled steel sections for use in bus structures
(1980-08) Gaafar, Labib A.; Tidbury, G. H.
The thesis is directed to the theoretical determination of the behaviour of rigid skin polyurethane foam beams reinforced with thin walled steel sections. The aim is to enable the designer to predict the behaviour of bus body structure during accident situations in order to build safe buses. A literature search has revealed that very little work has been done in this particular field of research. Thus a preliminary test programme was made to investigate the beam behaviour in bending particularly at high deflection. The test results shown in Chapter 1 gave promising results for continuing the research. Chapter 2 is directed to elastic analysis of composite beams. One of the advanced methods to predict the elastic stiffness of sandwich beams is the interfacial shear method. This assumes an interfacial shear between the core and the faces of sandwich beams. So, by considering a similar assumption, i.e. an interfacial shear between the matrix and the reinforcement, an analysis was made to predict the stiffness of composite beams. Although this method highly overestimated the stiffness, it represents a good basis for the inelastic bending analysis which is more important for the present study. Chapter • 3 shows the inelastic bending analysis of composite beams. This analysis is based on TIMOSHENKO and JAMES curvature area method. The experimental verification of the theory is shown in Chapter 4. The theory shows good agreement with the experimental results. The shape of the reinforcement was optimised for uniaxial bending. This optimum composite section showed a weight saving when it was compared with equivalent energy absorbing rectangular steel tube. Impact tests were made using a pendulum designed specially to test cantilever beams at different speed and impact energies. The test results are presented in Chapter 5. These results showed that the composite beams behaviour is similar for both static and dynamic loading. To compare the composite beam with the constituent beams, the large deflection behaviour of thin walled channel section beams made of thin sheet steel has been investigated. The experiments consisted of cantilever bending tests with the beam loaded through the shear centre and through the centroid. When loaded through the shear centre the beam buckling took place in the compression flange at the root of the cantilever. When loaded through the centroid however, it was noted that the compression flange buckled at a fixed distance from the fixed end. The general theory of thin walled beams developed by Vlasov was applied to the problem and indicated that the maximum compression stress at the free edge of the flange would be a maximum at some distance from the fixed end. The value of the maximum compression stress obtained by the general linear theory was small and its position did not coincide with the experimental position. The Vlasov analysis has been modified to include the increase in the twisting moment due to the lateral deformation- of the beam along its length. Good agreement between the modified theory and experiment both for the position of the maximum compressive stress and for the twist of the cantilever at three points along its length. Because of the very low torsional stiffness of thin walled channel sections, the small deflection theory is only applicable for small bending loads applied through the centroid and the modified theory should be used for practical loading cases.
Open Access
Biosensor and bioelectrocatalysis studies of enzymes immobilized on graphite electrode materials
(1987-05) Schneider, B. H.; Higgins, I. J.; Turner, Anthony P. F.
The immobilization of glucose oxidase and lipoamide dehydrogenase on graphite electrodes was studied for their application in mediated bioelectrochemical systems. These are techniques where the electrons involved in an enzymatic redox reaction are either supplied by, or given to an electrode from the enzyme. In the biosensor mode, where a current is measured due to product oxidation, the immobilized enzyme may be used to monitor its substrate, for example a biosensor for glucose based on the enzyme glucose oxidase. In the bioelectrosynthesis mode, when a cathodic potential is applied to the electrode, electrons may be transferred to the enzyme via a mediator thereby driving a thermodynamically difficult reaction, such as the reduction of the coenzyme NAD+ . A glucose sensor based on glucose oxidase immobilized onto graphite foil electrodes which had been doped with the mediator dimethylferrocene was found to produce both a linear and rapid response to changes in glucose concentration in solution. The kinetics of this particular system were studied in depth in order to explain its behaviour. Results showed that the porous nature of the electrode material resulted in immobilization of the enzyme throughout a number of layers• Consequently, diffusion of glucose into the electrode became the rate limiting process at low glucose concentrations, which resulted in linear calibration curves. This was characterized by a substrate modulus, which was found to be sufficiently large to predict diffusional limitations. From this the effective rate of glucose diffusion within the electrode was estimated, and found to be up to 5 times smaller than that in free solution. The rapid response of the sensor, on the other hand, was due to the absence of any mass transfer limitations external to the electrode surface. When lipoamide dehydrogenase was employed in the same system it was found that complications arose due to coupling of NADH oxidation with the adsorbed mediator. By employing a less anodic potential of +150 mV vs. Ag/AgCl at NADH concentrations below 1 mM the detection of enzymatic oxidation of the coenzyme was achieved. Enzymatic reduction of NAD+ was achieved using lipoamide dehydrogenase immobilized onto graphite felt electrodes. This reaction was mediated by methyl viologen, with the enzyme-modified electrode used to reduce the mediator at a potential of -0.7 V ( vs. SCE ). In this fashion the reduced form of methyl viologen was recycled, thereby driving the reduction of NAD . By coupling this system to lactate dehydrogenase it was possible to effect the reduction of pyruvate.
Open Access
Buckling of corrugated core sandwich panels
(1969-09-19) Patel, N. G.; Griffin, K. H.
A computer program is developed to determine the buckling stress and deflections of symmetric corrugated core sandwich panels. In the program freedom for lateral deflections at core to face-plate junction is allowed for. Provision is also made to study the effect of variation of core bend radius. A range of test specimens using four basic core configurations is designed to assess the effect of core bend radius on the buckling stress of the panel. The computer program indicates that above a certain value of core bend radius there is a marked drop in the value of critical buckling stress and a change in buckling Mode. The values of deflections at core to face-plate junctions at low buckling wave-lengths are not reliable* Due to the limited range of the experimental work, it is not possible to draw any conclusions on the effect of core bend radius on the buckling stress. The method used for determining the experimental buckling load is somewhat subjective in application, and its accuracy is difficult to assess. In general, the experimental values of buckling stresses are 15% higher than those predicted by the computer program. These discrepancies are not large when dimensional and material property variations are considered and indicate that the computer results are giving the correct trend and are conservative. Recommendations are made for : (i) Investigation of the buckling deflections at low values of buckling wave-lengths for specimens with high face-plateto-core thickness ratio. (ii) A test programme covering a wider range of specimens than that covered by the test programme in this study. and (iii) Trying out the other two methods of determining the buckling load.
Open Access
Characterisation of mixture preparation in lean premixed prevaporised combustor modules by planar laser fluorescence imaging and computational fluid dynamics modelling
(2001-04) Davoudi, Henrik; Greenhalgh, Douglas A.
In order to minimise the environmental impact of combustion emissions, radically new combustor concepts are under development. Lean premixed prevaporised (LPP) combustion has the greatest potential to achieve low emissions, particularly with respect to oxides of nitrogen. The role of fuel preparation is crucial in the success of the LPP combustor concept. Planar laser-induced fluorescence (PLIF) has been used to determine fuel placement and concentration, while computational fluid dynamics (CFD) has provided insight into the internal aerodynamics of two premixers. In order to determine the local equivalence ratios in a realistic device a calibration method, for the PLIF signal, has been derived. The vapour phase fluorescence of naphthalene, in the presence of oxygen, was calibrated against known conditions of temperatures and air-fuel ratios. This calibration was undertaken for an atmospheric and isothermal (non-combusting) flow. With regard to the small engine LPP module, PLIF measurements of the vapour fuel provided images of quantitative local equivalence ratios, at the exit of the premixer. In addition, based on the results of the liquid-phase measurements the evaporated fuel fraction was estimated. The computed droplet trajectories, within the premixing duct, highlighted the importance of the initial fuel dispersion from the injector. Two approaches were identified for improving the vaporisation and increasing the homogeneity of the air-fuel mixture. The large engine LPP module was investigated for several geometries and operating conditions. The evolution of the fuel dispersion, for those geometries, was characterised by PLIF images of the vapour fuel. In addition, the flame position inside the optical premixing duct was captured by video imaging for each geometry. 2D and 3D CFD simulations were performed to provide an insight into the aerodynamics of the premixer. These results were the basis of a schematic fuel jet breakup study, for two different injector configurations. Finally, the operational characteristics of this novel LPP module, featuring a conical centre-body, are discussed.
Open Access
A class of upwind methods for conservation laws
(1994-06) Billett, S. J.; Toro, E. F.
Various new methods for the solution of hyperbolic systems of conservation laws in one, two and three space dimensions are developed. All are explicit, conservative timemarching methods that are second order accurate in space and time in regions of smooth flow and make use of local Riemann problems at intercell boundaries. In one space dimension, the Weighted Average Flux (w af ) approach of Toro is extended to generate a scheme that is stable with timesteps twice as large as those allowed by the stability conditions of the original scheme. A Riemann problem based extension of the Warming-Beam scheme is considered. Total Variation Diminishing (t v d ) conditions are enforced for both schemes. Numerical results for the Euler Equations of Gas Dynamics are presented. In two and three space dimensions, finite volume versions of the waf scheme on Cartesian grids are derived for the linear advection equation. Two two dimensional schemes are found that are second order accurate in space and time. One of these is extended for the solution of nonlinear systems of hyperbolic conservation laws in two separate ways. The resulting schemes are tested on the Shallow Water equations. The equivalent three dimensional schemes are also discussed. The two dimensional schemes are then extended for use on structured, body-fitted grids of quadrilaterals and one of these extensions is used to demonstrate the phenomena of Mach reflection of shallow water bores.
Open Access
Condition monitoring of slow speed rotating machinery using stress waves
(1998-06) Mba, David Uzo; Bannister, R. H.
Condition monitoring through the use of vibration analysis is an established and effective technique for detecting loss of mechanical integrity of a wide range and classification of rotating machinery. Equipment rotating at low rotational speeds present an increased difficulty to the maintenance engineer, since conventional vibration measuring equipment is not capable of measuring the fundamental frequency of operation, also, component distress at low operational speeds does not necessarily show an obvious change in vibration signature. This thesis presents a study of high frequency stress wave analysis as a means of detecting early stages of loss of mechanical integrity in slow speed machinery, the first of its kind. Investigations were centred on the Rotating Biological Contactor (RBC) which is used for sewage treatment in small communities and rotates between 0 .6 to 1 revolutions per minute. The mechanism of stress wave generation was the relative movements between mating components that were experiencing loss of mechanical integrity, for instance, the loss of tightening torque between clamped components. Development of the stress wave monitoring technique was accomplished by firstly, simulating a variety of mechanical faults on the test-rig, and secondly, by numerous ‘on-site’ tests on operational RBCs and their bearings. In application of this technique to operational RBCs and bearings, as well as cataloguing evidence of mechanical deficiencies associated with RBCs operated within the Severn Trent Water region, the author inspected 261 RBCs and covered over 35,000 miles, contributing to the uniqueness of this research programme. This research has provided Severn Trent Water limited with a PC-based monitoring system comprising an AE transducer, pre/post amplifiers, ADC board and software on which all diagnosis was undertaken. Furthermore, during the process of investigating reasons for the mechanical failures of the RBC, technical information was uncovered thereby assisting Severn Trent Water in perusing a more robust design of RBC. Moreover this work has assisted Severn Trent Water to maintain that envious reputation that over a number of years not one of the RBC sewage treatment works has failed its consent level as set by the Environmental Agency.
Open Access
The design and analysis of a reconfigurable flight control system for advanced civil aircraft
(1994-04) Oliva, A. P.; Cook, M. V.
This work is concerned with the design of a pitch-rate-commandattitude-hold Command and Stability Augmentation System in order that the augmented aircraft meets the Gibson dropback criterion, the Gibson phase-rate criterion and MIL-F—8785C requirements. The work shows two methods of design, pole-placement and optimal control, and discusses the design procedures, the advantages and disadvantages of each method. The work is also concerned with the redundancy aspect of the control law design, and so not only a sensor based design but also an observer-based design are investigated. In order to design the observer-based control law, a Doyle-Stein observer was implemented. Two methods showing how to design the observer are discussed and presented, and the special characteristics of this kind of observer are also considered. The performance of the observer-based control law was compared with that of the sensor-based control law. The failure transients and characteristics of the control law are also studied and presented. Finally an evaluation of the control law was carried out with a non-linear model of the B-747 aircraft, and a simple altitude-hold autopilot was designed to work together with the stability augmentation control law.
Open Access
The design and analysis of pipe diffusers for centrifugal compressors
(1997-12) Bennett, Ian; Elder, R. L.
Diffusers are necessary to convert the high velocity head of centrifugal compressor discharge flow into useful static pressure. One diffuser type that has shown a great deal of promise, particularly at high pressure ratios, are pipe diffusers. These have been successfully incorporated into centrifugal compressor stages in North America since the early 1970’s. With their commercial sensitivity, however, little design or detailed flow information has been published, and most of this literature is old, dating back twenty years to the design’s conception. This thesis is a compilation of pipe diffuser information, formed from the limited literature works and an intensive experimental parametric study. Two themes run through this thesis and are brought about by different reader needs. The first need is for design information. This must show the strengths and weakness of pipe diffusers and be of sufficient accuracy to potentially produce designs at the first attempt. The second need is to understand the flows within the diffuser itself, in order that through this knowledge further improvements can be made. Both of these requirements are addressed in this thesis. The studies are centred on, what was originally, a Rolls-Royce research centrifugal compressor impeller of 6:1 pressure ratio operating at 35,000 rpm with a tip speed of 533ms'1 consuming up to a nominal 1MW of power. Significant modifications to the original compressor assembly were made to allow modular changes of diffuser and permit detailed measurement access. Initially, a vaneless diffuser investigation was carried out with the primary aim of determining the flow entering the diffusers. This was followed by a diffuser throat sizing exercise as it is well recognised that the diffuser throat has a governing control over the complete stage performance. An exercise in changing the number of diffuser pipes was then undertaken, followed by a hybrid diffuser investigation incorporating an oval, rather than circular, cross-section. In all of these cases, detailed flow measurements were carried out using both conventional pneumatic instrumentation and a purposely developed unsteady pressure measurement data acquisition system. This system enabled detailed traverses of the diffuser throats to be undertaken. These unique measurements shed new light on the flow ‘seen’ by the pipe diffuser channel. Computational investigations using computational fluid dynamics (CFD) codes are carried out to compliment the experimental investigations.
Open Access
The design and development of high speed externally pressurized air bearings for an internal grinder
(1969-09-20) Ghosh, K.; Leete, D. L.
Briefly, the basic theory of externally pressurized air bearings which provides shaft support, with very low friction in high speed devices, has been discussed in this paper. Some considerations have been given to the various factors such as axial flow, circumferential flow, dispersion effect, compressibility,. effect and hydrodynamic effect. The main objective was to produce an air bearing system capable of running between 45,000 to 80,000 rev/min., driven by a belt, with the radial and axial stiffnesses of 250,000 lb/in. and 150,000 lb/in. respectively. Moreover, the air consumption rate had to be as low as possible, at a maximum supply pressure of 80 lb/in2 • (gauge), while at the same time the manufacturing method had to be as simple as possible. With the aim of satisfying these requirements, an experimental internal grinding head was designed and manufactured. Throughout the manufacturing stages, the most conventional production techniques were used; even the radial clearance of 0.0005:ins. between the shaft and the journal bearing was achieved by grinding and lapping, and also the smallest journal orifice hole diameter of 0.004 ins. was successfully produced by using a small drill. ·The tests consisted mainly of the verification of the predicted values of stiffness, volumetric air flow and free running and the effect of the driving method. The complete tests were carried out in two test rigs one for direct drive and another for belt drive. The test results revealed a satisfactory correlation between predicted an measured values. At the supply pressure of 80 lb/in. (gauge), the stiffnesses of 235,000 lb/in. and 244,000 lb/in. at the centre position of the rear and_ the front journal bearings, and 190,500 lb/in. and 200 7 000 lb/in. for the front and the rear thrust bearings respectively, were obtained. Without any rotation, the total air consumption was 0.95 ft3/min., which was 1{-% higher than the predicted value but, at 60 7 000 rev/min. due to hydrodynamic effects, the reduction of air consumption of 7½f; of the no rotational condition was observed. An actual speed of 75,000 rev/min. was successfully achieved by the experimental head. Further increase of speed was limited by the pull and the vibration induced by the belt.
Open Access
Design of an interactive finite element computer package for the analysis of the ride of a generalised off-road vehicle
(1987-02) Kamar, Elsayed Abdrabboh; Cookson, R. A.; El-Zafrany, A.
A versatile computer package, to evaluate ground vehicle ride comfort has been designed. Wheeled, tracked, and semitracked vehicles have been modelled. The emphasis has been placed upon the tracked vehicle suspension systems with the neatly ”standard" torsion bar arrangement operating with either telescopic or rotary-vane dampers. Substantial investigation of the four-bar linkage, associated with the rotary-vane damper, has been carried out and is presented here.The package includes linear ,nonlinear ,[2-V) ,and I3-Vj vehicle models. A new technique employing the finite element method (FEM) fat suspension system modelling has been developed. Several methods of numerical integration are available in the package .A new evident scheme based on a hypetosculatory Hermitian weighted residual of the second order for the solution of the system of differential equations which simulate the vehicle has been derived. Whenever necessary the error developed during the integration process was limited. The graphic display facility of digital computers has been used extensively in the present code. As an example, the damped eigen-value problem has been solved graphically. The graphical solution is simple, direct, and tellable compared to the analytical solution. The terrain configuration might be of either harmonic or atbitrary shape function. Two tolerence critetia have been employed fat tide comfort evaluation ,namely, the absorbed power critetion and the international standard organization ISO 2631 critetion.The two critetia are fully integrated into the package and operate automatically. All individual subroutines have been tested successfully for the purpose intended. Complete sectors have been validated by running various case studies. The results obtained from the package agree reasonably well with the analytical or experimental results. The package allows updating in response to new vehicle and vehicle-terrain technology and can be run on both time-skating or batch processing computer machines. The main package structute is independent of computer type.
Open Access
The development and evaluation of an instrument to assess and develop the desirable attributes of RAF Airmen
(2005-03) Johansen, Dawn; Asch, Rachel
The research reported in this thesis related specifically to Royal Air Force (RAF) personnel. The primary aim of the work was to design an instrument to assess and develop the desirable attributes of airmen regardless of rank, trade-group or location. The work comprised three separate but integrated studies that culminated in the successful introduction of the tool to the Recruit Training Squadron (RTS). The first study consisted of a job analysis based on repertory grid technique with data elicited from 128 RAF personnel with experiences of line management of airmen. This stage of the research yielded 117 constructs from which twenty desirable attributes (each illustrated by observable behavioural examples) were generated. The second study was conducted to assess the content validity and generalisability of the list of twenty attributes identified from the first study. Thirty three officers and airmen, who represented all RAF ranks, considered the face validity of the list: ranked the twenty items in order of importance; and rated a ‘good5, ‘average’ and ‘poor’ airmen on each of the attribute items. The results of this study were used to develop the instrument for recruit assessment and development. The final study was designed to examine the reliability and validity of the tool for use at RTS. In this stage of the research, RTS instructors were trained in the use of the tool which they then trialled with four separate recruit groups. In trial recruits were assessed on the development tool on three occasions over seven weeks. At the end of the initial training period development scores were correlated with standard assessment measures. The correlations between development instrument scores and standard training measures were all statistically significant, with some associations being particularly strong.
Open Access
The development of a design methodology for large cargo aircraft
(2008-11) Mederer, A.; Fielding, John
Detailed specialist knowledge of pre-design, design, aerodynamics, engine performances and flying performances is necessary for the pre-design of transport aeroplanes. In this paper, studies are described which provide the main detailed information on the above-mentioned specialist topics. All studies consists of a problem with a suitable solution and the associated results. The studies are part of the overall task “Systematic design study on a number of configurations for large aircraft types, in particular for cargo aeroplanes”. As part of the overall task, a design method was developed which is very user-friendly and which is suitable for the design of any aeroplane configurations, in particular for configurations of large passenger or transport aeroplanes. This thesis version shows how 11 transport aeroplane configurations of very different types can be drawn up. The configuration results are shown on a scale of 1 : 500 and can be directly used for more detailed studies, as they are based on calculations. 4 of the first 5 transport aeroplane configurations are basic configurations and were scaled between 200 to 10001 . Important flying performance characteristics were calculated for the configurations by the use of 8 PC programs additionally developed for this purpose. Validity studies have shown that the described design method provides useful results. The main result of the method is that very different transport aeroplane versions can be developed and compared in terms of flying performances. Currently, only a few very complex design methods are offered elsewhere which have the disadvantage that they are only intended for one aeroplane version. So far, the design method described in this method is fully applied to the first five configurations. A next step could be to also investigate the additional six configurations listed here with the method.