CoA. PhD, EngD, MPhil & MSc by research theses

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Open Access
An experimental study of an air-blast atomiser
(1967-10) Bryan, R. H.; Lefebvre, A. H.; Norster, Brian
Visual observations and an optical method of measuring the mean droplet size in sprays have been used to assess the performance of a prototype airblast atomiser, particularly at the low fuel and air flow conditions corresponding to engine cranking. The results obtained from this and a shroud version of the same basic atomiser have enabled design modifications to be made which have resulted in a marked improvement in performance, both in terms of the spraying characteristics of the atomiser at low fuel and air flows, and in terms of the measured droplet size produced. The latter for the final design was very close to that predicted by Wiggs for airblast atomisers operating at the test conditions employed. An apparatus has also been designed to enable tests on the atomisation quality of airblast atomisers to be carried out at pressures up to 250 p.s.i.,, using the same optical technique to make mean droplet size measurements.
Open Access
Closed loop stepping motor application in prosthetics
(1969-09) Williams, K. F.; Thomason, R.
In recent years much work has been done in many countries on the development of powered artificial limbs for use by adults and children with congenital deficiencies i.e. present at birth, and by amputees. The established methods of actuating these powered limbs are either by pneumatic motors, operated from compressed carbon dioxide or by electric motors. Some designs have also used hydraulic and electro-hydraulic actuators. In the development of the complete powered limb the following problems have also to be considered: (a). The design of the mechanical components and the harness for attaching the appliance to the body. (b). Control input units by means of which signals from the wearer operate the powered limb. Control input signals maybe either mechanical (bone movement) or electrical. (c). The control system mechanies, involving the type of feedback which should be used. This can be either visual feedback or sensory feedback from the forces exerted by the appliance.
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
Flame radiation & smoke emissions in gas turbine combustors
(1969-09-19) Russell, D. T.; Lefebvre, A. H.
The objective of this thesis was to investigate flame radiation and smoke emission phenomena in a combustor typical of those in use in aircraft gas turbine engines. One of the primary aspects of the investigation was to compare the performance of airblast atomisers with that of conventional swirl atomisers under as near identical conditions as possible. A brief study of combustion chamber processes and carbon formation and thermal radiation mechanisms was made, with consideration of such experimental data as exists in the literature. An airblast atomiser and combustion chamber was developed to a state whereby testing at rich mixtures at moderate combustion pressures could be performed for short periods. This enabled a preliminary comparison to be made monitoring the following parameters:- (i) Flame total radiation. (ii) Exhaust smoke level. (iii) Weak extinction. Data was collected at three different combustion pressures for various air-fuel ratios and chamber velocities. The results showed that the airblast atomiser offers significant advantages over swirl atomisers with regard to total flame radiation and exhaust smoke emissions whilst suffering from a poor weak extinction. A more detailed analysis was performed for swirl atomisers using the Schmidt Method to establish flame temperatures and emissivities. The object of this work was to assess the effects of droplet size and combustion pressure on flame radiation. Owing to the poor atomisation quality and fuel distribution of the airblast atomiser used for the preliminary work, two new injectors were designed. It was hoped that a detailed analysis for these injectors could be performed via the Schmidt Method in order to provide a comparison with the swirl atomisers. Unfortunately, manufacturing was not completed with sufficient time left for this analysis to be completed.
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
The interaction of an oscillating airfoil and/or flap with a separating flow
(1975-01) Lang, James D.; Christopher, P. A. T.
At present little is known of the dynamics of a separating and reattaching flowfield. This unsteady flow topic relates to a wide range of aerodynamic problems such as dynamic stall and contfol-sürface-buzz. An experiment was performed with the purpose of investigating the dynamics of a separated region and the effect of the region on the motion of a flap-type control surface. A NACA 0012 airfoil section was fitted with a movable spoiler and flap. Measurements were made of the unsteady, non-linear hinge-moment due to spoiler oscillation. Aerodynamic hinge-moment was also investigated with the spoiler fixed and the flap oscillated harmonically. Flap response to spoiler-induced forcing was also observed in addition to observations of coupled spoiler and flap system behavior. The coupled system exhibited limit-eyele oscillations. Flap response to spoiler-induced loading can be predicted well by use of a linear equation for flap motion which is forced by the effect of spoiler motion. The equation of motion includes attached flow values of aerodynamic damping and stiffness. A theory is developed which models separation bubble dynamics. It includes a quasi-steady model for the external shear-layer, and flow of mass within the bubble at a mean reversed-flow velocity. Pressure perturbations along the bubble are modeled also. The theory is used with the method of Beecham and Titchener in order to predict limit-cycle behavior of the coupled system. Good agreement with experimental results is achieved. The instant of instability and of growth of a laminar separation bubble at the leading-edge of an oscillating airfoil is also investigated theoretically. The beginning of dynamic stall is seen to be related to the dynamics of a separation bubble and the inviscid flowfield. The theory is applied also to a study of the phenomena of control-surface-buzz, where separation is induced by shock waves.
Open Access
The aeroelastic behaviour and response to turbulence of a class of high performance tailless sailplanes.
(1978-09) Banerjee, J. R.; Griffin, K. H.
The symmetric flutter and response characteristics of a class of tailless .sailplanes-:are investigated combining rigid--body dynamics with elastic modes of deformation. The methods used are based on the normal mode approach through the use of finite element techniques and unsteady aerodynamic theories in two dimensional flow. The flutter speed and. aeroelastic modes are critically examined and the results are compared with those of a tailed sailplane. The flutter speed of the tailless sailplane is found to be low in comparison with those of orthodox layout and a parametric study is undertaken to locate-the reason for this; recommendations are made for improvements. A method is proposed for the analysis of the. short period oscillation characteristics of flexible aircraft allowing for the-effects of unsteady aerodynamics. - It is then applied to the type of tailless sailplane under investigation. The response to gusts and turbulence is evaluated using both statistical and discrete gust methods. Comments are made from the calculated results about the aeroelastic behaviour of tailless sailplanes in general. Computer programs developed for detailed aero-elastic calculations are presented.
Open Access
The employment of jet V-STOL aircraft at sea
(1981-01) Kinch, M. J.; Howe, D.
The means by which the Royal Navy will continue to operate fixed-wing aircraft at sea is by employing VTOL or· given an aid to-take-off, STOVL aircraft. The aid being ' brought into service is -the Skijump, which permits a large increase in payload over unassisted VTOL. The effectiveness of skijump increases with its exit angle up to about 40°, but other considerations of size and ungainliness set a practical lim~tation nearer to 20°. The endspeeds required for ballistic launch off a skijump could be achieved or-enhanced by the use of assistance by catapult or rocket motor. Both of these would call for the initiation of programmes of full research and development, while the skijump, capable of conferring. equivalent performance if it is long enough, already exists. The· smallest number of aircraft in an airgroup able to keep up a useable flying task is three. A vessel big enough to mount three aircraft together with the gear necessary to support and arm them would be big enough to mount a skijump as well. Its size is dictated too by the sea conditions in which it is expected to keep operational. The vessel in question should be a displacement ship, either conventional (e.g. large frigate) or unconventional (e.g. Small Waterplane Area Twin Hull). There is no role here for either hovercraft or hydrofoil. Commitment to the skijump.in the ship means commitment to vectored-thrust as a means of propulsion in the next aircraft~ When specified it must be compatible with existing skijump decks, and it should be single-engined. Its targets for Reliability and Maintainability mµst be wholly related to the Availability called for, and must be given equal prominence with performance.
Open Access
The stability and post-buckling behaviour of stiffened plates in compression
(1990-02) Jhita, P. S.; Loughlan, Joseph
The investigation reported in this thesis was carried out to examine the behaviour of stiffened plates subjected to uniform end compression using energy methods. The thesis begins with a short introduction, followed by a review of the relevant literature. The basic differential equations and energy expressions, using plate theory are then derived. The theoretical analysis of the mechanics of local, lateral and overall instability of asymmetrically and symmetrically edge stiffened plates is then presented. The analysis is then extended to investigate the behaviour of infinitely wide panels with stiffeners of deformable cross section. The results obtained from this analysis are used to highlight the shortcomings of using an infinitely wide panel model to predict the behaviour of a panel of a finite size through comparison with existing work. This is then followed by the analysis of a simply supported panel of finite size stiffened by stiffeners of rigid cross section. Plate theory was used to model the skin and beam theory to model the stiffeners. The results obtained from the analysis compared favourably with those already existing. The method is then extended to investigate the post buckling behaviour of simply supported plates and stiffened panels. The post-buckling behaviour of plates has received a considerable amount of attention since plates can carry loads beyond the critical load. The use of this additional strength.is of great importance to the design of aerospace, naval and civil engineering structures since considerable weight savings can be achieved. In comparison the post-buckling of light gauge integrally stiffened panels has received far less attention. Most of the published literature concentrates on the interaction between the local and overall buckling modes and the sensitivity of panels to geometrical imperfections when the local and overall buckling loads are nearly coincident. In all the above investigations, the overall buckling load for the panel is assumed to be equal to the Euler load for a pin-ended strut with the cross-section equal to the repeated panel cross- section. This implies that the transverse edges of the panels are assumed to be free. In general, stiffened panels are supported by a system of crossframes. A consequence of this layout is that lateral support is provided on all boundaries of the panel and therefore the wide strut model is invalid. In the present work the panels are assumed.to be simply supported along all four edges. It is shown that the post-buckling behaviour of these panels is substantially different to that of the wide strut model. The thesis finishes with a summary of the findings and a list of the main conclusions.
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
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
Passive Techniques for Controlling the Flow in Supersonic Wing - Body Junctions
(1994-03) Blank, S. C.; Stollery, J. L.
Junction flows are common to all flight speeds and they are associated with undesirable features such as increases in drag, limitations on performance and at supersonic speeds high heat transfer rates. Junction flows are associated with performance losses in turbomachinery (around 30% of the total pressure losses in an axial turbine) and they can lead to premature detection of military underwater vessels. Junction fairings are widely used at subsonic speeds and correct fairing of the C-141 wing alone, could have resulted in potential fuel savings of approximately US $ 40,000 per year per aircraft which can be roughly translated into a $ 600,000 saving during the lifetime of each airframe. Typically, for a modern transport type of aircraft the wing juncture accounts for between 1 and 2 % of cruise drag and therefore, careful design of the wing junction is necessary. At supersonic speeds, by far the most disadvantageous feature associated with juncture design is high heat transfer rates due to shock / shock interaction. These heat transfer rates are sufficient to cause severe structural damage leading to component burn-off. Typical leading edge temperatures during re-entry for an aerospaceplane, like HOTOL, are around 2000 K, exclusive of increases in temperature caused by the interaction. Although drag reduction may not be so relatively critical at these flight speeds, the potential loss of control components, like stabilising fins, needs to be carefully examined and some configuration re-design may be necessary as a consequence. This research project is aimed at developing a technique through which the disadvantageous features associated with supersonic junction designs can be alleviated. It was found that through re-design of the wing / body junction the maximum mean static pressure local to the fin leading edge could be halved, the strength of the junction vortices could be lowered and the amount of separated flow reduced. The applications of the technology span all vehicles operating within the supersonic flight regime and therefore, the markets to which the technology is applicable are military aircraft, defence systems, aerospaceplanes and commercial supersonic transports. As the technology is, in principle, applicable to the design of commercial supersonic transport aircraft (HSCT) and the market for these vehicles is forecast to be worth up to $ 200 billion (FY 1987) an examination of the issues behind marketing this type of vehicle is presented in the non¬technical section. The presently available data produced by the major manufacturers were found to be lacking in the following areas (a) evaluations of market elasticity, (b) distribution techniques, (c) the availability of acquisition finance and financing techniques, (d) political sensitivity analysis (d) product life cycle analysis and (f) the relationship marketing of the venture.
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 effects of junction modifications on sharp-fin-induced glancing shock wave/turbulent boundary layer interaction
(1994-06) Koide, S.; Stollery, J. L.
The effects of junction modifications on the glancing shock wave/turbulent boundary layer interaction generated by a sharp fin placed on the wall of a supersonic wind tunnel were examined experimentally at a Mach number of 2.46 and a Reynolds number of 2.59xl06/m. The interactions between a turbulent boundary layer on the wall and shock-wave systems caused by a fin with a fillet and several fins with different strakes were examined individually in order to find an effective modification technique. The flow features obtained by oil flow visualization, surface pressure measurements and liquid crystal thermography were compared with the data from an unmodified fin to evaluate the effects of each modification. The comparisons indicated that a "srake-type" modification had a weakening effect on the interaction-induced separation. To understand the flowfield structures, three-dimensional surveys using laser-light-sheet flow visualization were employed with schlieren photography and oil flow visualization. In addition to these experimental observations, an Euler CFD solver was used to help understand the inviscid flow structures which play important roles in the interaction behaviour. Based on the data experimentally and numerically obtained, a method was proposed for predicting the junction shapes needed to prevent separation.
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
The application of neural networks to spacecraft control
(1994-08) Cooper, A.; Lewis, D. J. G.
This thesis investigates how two neural network-based control techniques can be applied to a specific spacecraft control problem. The neural networks used are simple backpropagation networks, consisting of one or more tansigmoidal neurons (neurons with tanh transfer functions) in a hidden layer, and a linear neuron in the output layer. The neural network control techniques investigated here are Direct Model Inversion and Indirect Model Inversion. The spacecraft control problem is that of reducing the vibrations of a spacecraft payload. The source of the vibrations is a mass imbalance in one of the reaction wheels of the spacecraft. Four components are represented in the spacecraft model. These are rigid body inertia, solar array flexure, fuel slosh and payload vibration. A simple sinusoidal signal is used to model the disturbance torque produced by the reaction wheel mass imbalance. The complete model is broadly based on the Solar Heliospheric Observatory (SOHO) that is due for launch in 1995. Each of the neural network control techniques used is shown to be successful in reducing the effects of the disturbance torques on the spacecraft payload. However, in each case, a simple positional feedback gain term provides more effective and reliable control.
Open Access
Structural design for passenger safety
(1996-05) Roots, Mark R.; Brown, J. C.
This thesis covers the design and analysis of a roll cage structure for use on a sports racing car. The method used to design and verify the roll structure was novel as small automotive companies tend to use evolution as a design tool. Evolutionary design works well for certain problems, however, is not well suited to major structural modifications. The method used in this report integrates the existing structure with the roll cage to improve the torsion stiffness and hence the handling of the vehicle. Careful integration of the roll cage with the rest of the chassis enabled the torsion stiffness to be increased by over 400 %. In addition the weight efficiency of the final chassis was increased over that of the original chassis by over 200 % . The investigation of the torsion stiffness was carried out using linear finite element analysis using the NASTRAN suite of programs. The second stage of the investigation was to develop this design into a crashworthy roll cage. The resulting model and design are presented in this report. The design of the crashworthy roll cage was carried out using non linear finite element analysis with N AS TRAN. The N AS TRAN results were then verified with a full structural test on the chassis. The results of the tests are presented and compared to the NASTRAN analysis results. Good correlation was achieved and the method showed promise for applications in the small automotive industries. The use of finite element analysis for the design of an integrated structure represented a novel application of a well established technique to an industry where experience is the main design tool. The results of the investigation were encouraging and a close correlation was achieved between the analysis and test results. Finite element analysis represents a relatively cheap and quick method of investigating the effect of structural changes. This method could be used for the design and development of new structures and would give a good indication of the effect of these changes. Small automotive companies, such as TVR, should find the technique particularly useful for both the design of new structures and for the modification of those already in use.
Open Access
Systems design and control of a freeflying space robotic manipulator system (ATLAS) for in-orbit satellite servicing operations
(1996-08-02) Ellery, Alexander; Bowling, Tom; Lewis, John
This thesis is concerned with a freeflyer robotic spacecraft for in-orbit satellite servicing employing a dedicated attitude control system, ATLAS (Advanced TeLerobotic Actuation System). It adopts a unique control system design to alleviate the reaction coupling between the spacecraft mounting and the manipulator such that control of both the spacecraft attitude and manipulator kinematics may be effected in real-time using present-day space-rated electronics. It has been found that very few additional computations are required to compensate the coupling problem over standard terrestrial resolved motion robot control algorithms and standard spacecraft attitude control techniques. A mathematical proof of the concept is outlined. The technique is also extended for dual-arm operation. Two manipulator arms are necessary for EVA-equivalence to afford maximum flexibility. Mutual collision possibilities will be eliminated by incorporating a modified Zambesi bridge via interrupt software whereby each manipulator is restricted to operations within its own quadrant. This eases the computational burden of monitoring arm-to-arm collisions in the open chain mode with little loss of flexibility. Closed chain mode is shown to be similar to the open chain mode but with the addition of certain kinematic and force constraints. Each arm must be capable of operating independently or cooperatively, necessitating a hierarachical control architecture which is compatible with the NASREM control architecture. Given that the single arm freeflyer is the baseline of this thesis and that dual arm configurations are merely extensions of this, a simulation program of the techniques outlined has been constructed to output some of the parameters o f interest. Consideration is also given to the possible commercial impact of such a system.
Open Access
A flexible, subsonic high altitude long endurance UAV conceptual design methodology
(1997-05) Chang, J. M.; Jones, R. I.
High Altitude Long Endurance (HALE) Unmanned Aerial Vehicles (UAVs) have been considered for use in both civil and military applications for some years. Their advantages, such as low cost, high survivability, long endurance, easy maintenance etc. relative to alternatives, make them useful to scientist and military personnel. In this thesis, a flexible conceptual design methodology for HALE UAVs has been developed. This has been implemented as a FORTRAN computer code. However, it is unlike some commercially available general aircraft design software which appears to the user as a ‘black box’. In this case, the code is broken-down into several subprograms which deal with the different aspects such as parametric study, drag, performance etc. Each of these can be either used as it stands, tailored to the user needs in a particular case or by-passed if more accurate methods or known values are available in a particular area. During production of the methodology problems were encountered in a number of areas due to the unusual operating regime and configurations of HALE UAVs. Obtaining engine data for the high altitude of interest was a problem. This was addressed through use of an existing engine modeling code to generate data. The high altitude also leads to low Reynolds numbers and along with the high aspect ratios typical of HALE UAV configurations, these place such vehicles beyond the validity limits of data sheet methods for prediction of a number of important parameters. Improved methods for the prediction of Oswald efficiency and maximum lift coefficient, in particular, are recommended to be sought. Accepting the above difficulties, an analysis of the Tier-II Plus, Global Hawk, was carried out using published data to provide some validation of the methodology and program. The results obtained provide confidence in the usefulness of the program in the analysis and investigation of HALE UAVs.
Open Access
Error control in finite elements for fluid modelling.
(Cranfield University, 1997-10) Onomor, E.M.; Morris, Alan J.
The main objective of this thesis was to ascertain and to catalogue the possible sources of errors in the finite element method when used for fluid modelling. Some of these errors are inherent in the finite element method whilst others are introduced by the user when performing a fluid mechanical analysis. This thesis distinguishes from the two and provides where possible, ways of preventing or controlling them. The form is based on the SAFESA Technical manual, which is an equivalent for structural analyses. Focus is then made, as an example, on a real world problem; "The Backward Facing Step" where, based on experimental data an element sensitivity analysis is performed within ANSYS/FLOTRAN. This analysis attempts to determine the magnitude of errors associated with prescribed element distortions in relation to aspect ratio, skew angle and taper ratio. The results contained within are in the form of graphical velocity profile plots, contour plots and tables at the varying distortions. The results show a strong deviation from the control mesh as the distortion is increased.