CoA. PhD, EngD, MPhil & MSc by research theses
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Item 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.Item Open Access Experimental investigation of lubricant film thickness in an automotive final drive unit.(Cranfield University, 2013-11) Fusco, Lucia; Sherwood, GlennSociety has been aware of the environmental impact of vehicles for some time now, with governments trying to control and reduce this impact by introducing emissions standards to control pollutants as well as CO₂ emissions. One way in which total emissions can be reduced is by increasing the efficiency of vehicles as a whole, resulting in greater fuel economy. Related to increased transmission efficiency, lubricant flow within a final drive unit (FDU) was researched, enabling a better understanding of the system through visualisation and laser induced fluorescence (LIF) measurements. A LIF measurement technique has been developed, along with a quantitative wedge calibration method, to measure lubricant thicknesses within a Jaguar Land Rover X150 FDU. The measurements and data recorded in this thesis are taken from an original clear-cased replica FDU, which proved to be suitable for visualisation and LIF measurements. The results show lubricant thickness trends are dependent on the fill volume and rotational speed of the gear. The measured peak lubricant thickness on the carrier- and cover-side of the crown wheel increased with fill volume. As the fill volume increased, the amount of lubricant entrained by the crown wheel increased, resulting in the increased lubricant thickness. As the equivalent vehicle road speed increased to approximately 8mph, the measured lubricant thickness increased to its maximum value of 1.75mm for a fill volume of 900ml. From 8mph onwards, the lubricant thickness was found to decrease again to less than 0.1mm at around 10mph. Up to 8mph, gravity appeared to be the overriding influence, pulling the lubricant from the crown wheel. At 8mph, these forces seemed to be in balance, resulting in the greatest measured lubricant thickness. Above 8mph, the force from the gear rotation ejected lubricant from the crown wheel. Gathered data and relationships provide new quantitative metrics for measurement and enhanced understanding of lubricant movement within the FDU. The methodology and equipment developed here for studying the FDU are suitable for wider use in any geared or lubricated system.Item Open Access An investigation into heat dissipation from a stationary commercial vehicle disc brake in parked conditions.(Cranfield University, 2013-11) Stevens, Kevin; Tirovic, Marko; Skipworth, HeatherDetailed understanding of heat dissipation from a stationary disc brake is of considerable importance for vehicle safety. This is essential for both park braking on inclines and for preventing brake fluid boiling in hydraulic brakes. Despite the experience proving the significance of such conditions, there is very little published data dealing with this phenomenon, and even ECE Regulation 13 does not specify hot parking braking performance. The problem of heat dissipation from stationary brake may appear simplistic but it is actually more complex than from a rotating disc, due to the lack of symmetry through or a dominant mode of heat transfer as natural convection is the only driving force behind the airflow. All three heat transfer modes exist in a transient process, with complex heat transfer paths within and between brake components. This Thesis investigates the cooling performance of a Commercial Vehicle (CV) brake whilst in stationary conditions. The research is predominantly orientated towards the thermal aspects of Electric Parking Brake (EPB) application in CVs. Contraction of large brake components after hot parking may lead to vehicle rollaway on inclines, with tragic consequences. An extensive theoretical and experimental study was conducted. An analytical model of a disc brake in free air was developed, enabling good prediction of disc temperatures and average surface convective heat transfer coefficients (hcₒnv) over the entire cooling range. A comprehensive CFD modelling of the 3-dimensional flowfield around the disc brake was also conducted, as well as predicting the surface convection coefficient distribution. Shear Stress Turbulence model was found to be most suitable for such studies. FE models were created to predict temperatures in all components of the brake assembly. A special Thermal Rig was developed for experimental validations, which uses an induction heater for heating the disc brake, and numerous surface mounted and embedded thermocouples for measuring component temperatures, as well as ‘free standing’ for determining air temperatures in specific points. IR cameras provided further temperature field information. The results clearly show little influence of the conductive heat dissipation mode. The study also showed, for the experimental arrangement used, a constant value of surface emissivity (ɛ = 0.92). With well-defined conductive and radiative heat dissipation modes, the emphasis was placed on investigating convective heat dissipation from a stationary disc brake. It has been demonstrated that the anti-coning straight vane design of brake disc does not cool effectively in stationary conditions. Expected ‘chimney effects’ in disc vent channels do not materialise due to large scale recirculation regions preventing airflow from entering the channels, which drastically reduces the convective cooling. Complex thermal interactions between the large assembly components are explained, with typical cooling time being just over an hour for disc brake cooling from 400°C to 100°C. Extracted heat transfer coefficients were used for establishing a complex FE assembly model, which enables accurate prediction of temperatures of individual components over the entire cooling period. The developed approach is used for predicting temperature of the existing brake assembly but is equally suited for generating new designs with more favourable characteristics. In addition to being a powerful design tool for assisting in EPB design and validation process, the methodology developed offers wide applications, such as thermal optimisation of the caliper housing for the installation of continuous wear monitoring sensors, smart slack adjusters (for low friction drag brakes), etc. EPBs in passenger cars have been successfully used for over 10 years now. They use a relatively simple approach for ensuring safe parking from hot by over-clamping (applying approximately twice the required actuating force) and re-clamping (repeated application after the vehicle has been parked). Large CV actuating forces prevent the use of over-clamping as this could damage the disc, whilst re-clamping would need to be repeated several times over a much longer period of time, requiring the vehicle battery to power the electronic systems for a longer period of time without recharging. Neither approach is acceptable, requiring a more in- depth thermal study of the CV brake in stationary conditions, as investigated in this Thesis. In addition to technical, there are marketing and financial aspects which make EPB introduction and acceptance in commercial vehicles very different to passenger car applications. Such an investigation was conducted, exploring the market the CV EPB will be sold in and whether it would accept the new technology. Two questionnaire analyses were carried out, with the second giving the respondent detailed information about the EPB. It was found that using an informed, knowledge based approach yielded more positive feedback to the proposed product. The outcome may be even considered more contrary than expected, rather than instigating mistrust, the new CV EPB technology created interest. Furthermore, reports of pneumatic malfunction indicated that independence from the pneumatic system should be used as the key selling point for the EPB, for all beneficiary segments.Item Open Access Development of a Port-Hamiltonian Model for use in oscillating water column control scheme investigations.(Cranfield University, 2014-12) Farman, Judith; Amaral Teixeira, JoaoWith global energy demand estimated to rise considerably and global warming accepted by the majority of scientists, the pressure to reduce fossil fuel usage is increasing. To this end, the UK government has set a target of generating 50% of electricity from renewable energy sources by 2050. It can therefore be deduced that decreasing the cost of renewable energy by increasing the energy capture is critical. Oscillating Water Columns (OWCs) employing bidirectional turbines coupled with generators can be used to capture energy from oceanic waves and convert it to electrical energy. This thesis includes a study to quantify the potential power smoothing that can be achieved from a wave farm of ideal OWC devices and from auxiliary hardware such as flywheel energy storage systems. Also detailed are the upgrades to the OWC test facility at Cranfield University, including the world-first capability to simulate polychromatic waves. This test facility has been employed to validate turbine characteristics derived from Computational Fluid Dynamic (CFD) numerical results. This thesis contains a literature review of the existing control strategies for OWCs that concludes that the optimization of power capture from individual components in the energy chain forces system-level compromises. This conclusion drove the development of an unique energy-based model of the complete wave-to-wire system utilizing port-Hamiltonian mechanics which mandated two modifications to the port-Hamiltonian framework. The first modification to the port-Hamiltonian framework resulted in a new generalized means of modeling systems where the potential energy is dependent on the momentum variables. The second modification expands the port-Hamiltonian framework to allow the modeling of ow source systems in addition to effort source systems. The port-Hamiltonian wave-to-wire OWC model enables the future development of a control approach that optimizes power capture at a system level. As a first step to achieving this goal an Injection Damping Assignment (IDA) Passivity Based Control (PBC) strategy was successfully applied to an OWC system and an energy storage flywheel system. These strategies pave the way for future developments utilizing optimization techniques, such as the use of cost functions to identify the peak efficiency operating condition.Item Open Access A physics-based maintenance cost methodology for commercial aircraft engines(Cranfield University, 2014-08) Stitt, Alice C.; Laskaridis, Panagiotis; Singh, RitiA need has been established in industry and academic publications to link an engine’s maintenance costs throughout its operational life to its design as well as its operations and operating conditions. The established correlations between engine operation, design and maintenance costs highlight the value of establishing a satisfactory measure of the relative damage due to different operating conditions (operational severity). The methodology developed in this research enables the exploration of the causal, physics-based relationships underlying the statistical correlations in the public domain and identifies areas for further investigation. This thesis describes a physics-based approach to exploring the interactions, for commercial aircraft, of engine design, operation and through life maintenance costs. Applying the “virtual-workshop” workscoping concept to model engine maintenance throughout the operating life captures the maintenance requirements at each shop visit and the impact of a given shop visit on the timing and requirements for subsequent visits. Comparisons can thus be made between the cost implications of alternative operating regimes, flight profiles and maintenance strategies, taking into account engine design, age, operation and severity. The workscoping model developed operates within a physics-based methodology developed collaboratively within the research group which encompasses engine performance, lifing and operational severity modelling. The tool-set of coupled models used in this research additionally includes the workscoping maintenance cost model developed and implements a simplified 3D turbine blade geometry, new lifing models and an additional lifing mechanism (Thermo-mechanical fatigue (TMF)). Case studies presented model the effects of different outside air temperatures, reduced thrust operations (derate), flight durations and maintenance decisions. The use of operational severity and exhaust gas temperature margin deterioration as physics based cost drivers, while commonly accepted, limit the comparability of the results to other engine-aircraft pairs as the definition of operational severity, its derivation and application vary widely. The use of a single operation severity per mission based on high pressure turbine blade life does not permit the maintenance to vary with the prevalent lifing mechanism type (cyclic / steady state).Item Open Access Optimal time and handling methods for motorsport differentials.(Cranfield University, 2014-12) Tremlett, Anthony; Assadian, Francis; Vaughan, Nicholas D.In the motorsport environment, where traction at one wheel is often compromised due to high cornering accelerations, Limited Slip Differentials (LSD) offer significant improvements in traction and vehicle stability. LSDs achieve these performance benefits through the transfer of torque from the faster to slower rotating driving wheel. In the majority of racing formulae, modern devices have evolved to become highly adjustable, allowing this torque bias to alter both ultimate vehicle performance and handling balance through specific corner entry, apex and corner exit phases. This work investigates methods to optimise LSD setup parameters, both for minimum lap time and desirable handling characteristics. The first stage of addressing this objective involved the creation of a range of contemporary motorsport LSD models. These included a plate or Salisbury type, a Viscous Coupling (VC) and a Viscous Combined Plate (VCP). A differential test rig was developed to validate these models. The parameter optimisation is addressed in two main parts. Firstly, a Quasi Steady State (QSS) time optimal method is used to maximise the vehicle's GG acceleration envelope using a direct, nonlinear program (NLP). A limitation of this approach however, is that system transients are neglected. This is addressed through the development of an alternative indirect, nonlinear optimal control (NOC) method. Both methods were able to find LSD setup parameters which minimised lap time, providing significant improvements over traditional open and locked devices. The NOC method however, was able to give greater insight into how a locked device ultimately limits the vehicle yaw response during quick direction changes. The time optimal analysis was extended to investigate aspects of vehicle stability and agility. These factors are known to have a major influence on driveability and thus, how much of the theoretical performance limit the driver can extract. A more unified GG diagram framework was implemented, to characterise both the vehicle's acceleration limits, and how its stability and agility changes leading up to this limit. The work has generated a number of novel contributions in this research field. Firstly, the creation and validation of a range of state-of-the-art motorsport LSD models. Secondly, the methodologies used to optimise LSD setup parameters, the results from which, have themselves provided the basis of a novel, vehicle speed dependent LSD device. Finally, a more practical and intuitive way to evaluate vehicle stability and agility at different cornering phases. This has laid the foundations of a procedure which not only maximises the vehicle's acceleration limits, but also allows its response to be tailored to suit individual driver preferences.Item 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.Item Open Access Dynamics and control of flexible articulated space manipulators with large payloads(2002-03) Wiedemann, Simon M.; Kirk, Colin L.This thesis studies the dynamics and control of flexible articulated space manipulators with large payloads similar to the Space Shuttle Remote Manipulator System. For dynamic response analyses an exact analytical method to compute natural frequencies and mode shapes of space manipulator systems with varying degrees of complexity is developed. Dynamic response analyses are performed comparing the results obtained using the exact mode shapes with those obtained when using assumed mode shapes for a series of different manipulator slew manoeuvres and Shuttle thruster firings. Possible methods for active vibration damping control of the manipulator are discussed, including the methods presented by other researchers. In this thesis it is proposed to use reaction wheels in a closed-loop control scheme, and its advantages and disadvantages compared to other methods are discussed. The problem of payload capturing and post-capture dynamics are addressed, as well as the dynamics following an emergency braking of the robot. For these cases, a simple method to estimate upper limits of dynamic responses is developed, and results obtained with this method for various example cases are compared with results computed by professional software. Finally the dynamic responses of a space station to various robot manoeuvres are analysed. These responses can have detrimental effects on micro-gravity and similar experiments. The analyses are performed using a simplified model of the International Space Station and its Mobile Remote Manipulator System.Item Open Access Some effects of transpiration on the boundary layer at the leading edge of a swept wing(2000-03) Smith, A.; Poll, D. I. A.The effect of transpiration on the boundary layer near the leading edge of a swept wing has been investigated using a large swept cylinder model with a laser-drilled titanium leading edge to model the leading edge of a swept wing. In the region near the leading edge, boundary layer transition due to crossflow instability has been examined. Natural transition on a porous surface was compared with that on a non-porous surface, and it was found that transition occurred at lower R ’s on the porous surface (ie there was a performance penalty due to the porous surface). The effect of suction on transition due to crossflow instability was then studied. It was found that only moderate amounts of suction were required to delay the onset of crossflow-induced transition and a simple algebraic model has been derived, in terms of R , Rex, and Cq, to describe transition on the porous surface with or without suction. It was also found that two-dimensional trip wires had a negligible effect on crossflow transition, except where they caused attachment-line contamination. On the attachment-line, several subjects were addressed. The effect of attachment-line blowing was considered, and good agreement was obtained with previous work. The effect of spanwise blowing length was also addressed, and a simple algebraic model was derived, in terms of R , s/rj, and Cq, to describe attachment-line transition due to blowing. A comparison has also been made with linear stability theory. The effect of suction at the wing-fiiselage junction was examined as an alternative to suction on the attachment-line. However, it was found that applying suction on the attachment-line when the boundary layer had attained infinite swept conditions was much more efficient than applying suction in the junction region. Suction was successfully used to relaminarise a turbulent attachment-line at R values between 600 and 950, the magnitude predicted for the next generation of large transport aircraft. During the experiments, no sign of critical oversuction was found. Finally, the behaviour of a relaminarised attachment-line flowing onto a non-porous surface was studied. The conditions for natural transition on the non-porous surface were measured, and it was found that they were the same as those predicted by previous work on an entirely non-porous attachment-line.Item Open Access Analysis and prediction of the low speed flow over a highly swept wing(2000-11) Shires, Andrew; Garry, Kevin P.; Fulker, J. L.A combined experimental and theoretical study is described of the low speed flow over a highly swept and cambered wing that simulates the flow features of a transonic manoeuvre condition. The thesis is divided into two parts: Part I examines the research objectives from a customer perspective, with background information on the project history and funding sources. Since the research is aimed at improving the aerodynamic performance of low observable configurations, stealth technologies are discussed and their implications for combat aircraft wing flows. The management chapter of the thesis then discusses the influences affecting the decision making process for the acquisition of weapon systems in the UK. Part II describes the design of a highly swept and cambered wing that generates strong adverse pressure gradients near the trailing edge, leading to three-dimensional separations in this region. Using surface flow visualisation the nature of these flows is defined, indicating how the position of a separated streamline moves forward with increasing angle of incidence. These observations are confirmed by flow predictions using the SAUNA Computational Fluid Dynamics (CFD) method that solves the Reynolds Averaged Navier-Stokes equations, employing a two-equation turbulence model. The mechanism of the flow separation is also predicted using CFD, indicating that a separated stream surface reattaches at the wing trailing edge, forming a ‘tunnel’ of separated flow. To the authors knowledge this represents the first time that the main physical features of such a complex three-dimensional separated flow has been modelled using a CFD method. From an evaluation of the CFD methods employed, a design process has been proposed by which a wing designer can determine if wing flows over similar configurations remain attached. Additionally, the velocity magnitudes within parts of the separated shear layers and the wake are obtained using an optical non-intrusive measurement technique and give good agreement with the theory. -Item 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.Item 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.Item Open Access Multiple and moving bodies: CFD research in an adaptive environment(2000-11) Ren, Tingrong; Edwards, John A.During this study a new solution adaptive scheme was developed which applied the structured Adaptive Mesh Refinement (AMR) algorithm directly into a Chimera grid system. Two new Computational Fluid Dynamics (CFD) methodologies, the Chimera grid method and the AMR algorithm, have been successfully integrated. The originality of this study is outlined below. 1).This new scheme integrated the Chimera grid method with the AMR algorithm. By using the Chimera grid method to mesh complicated configurations and then applying the AMR algorithm in different Chimera sub-domains to resolve complicated flow features the advantages of these two methods are combined. 2). Both Graph data structure and orthogonal list storage are employed in this new scheme to describing the Chimera sub-domain relationship and improve the region and point searching efficiency. These methods make this new scheme more flexible and more efficient than existing Chimera grid schemes and AMR schemes. 3). This study extended the application of the AMR algorithm. The main limitation of the Quirk's AMR code, poor geometric packing ability, has been replaced by a versatile Chimera grid scheme. 4). This study improved the accuracy of the Chimera inter-grid communication when simulating supersonic or hypersonic flows with strong discontinuities due to applying the AMR algorithm. 5). The combination of the versatile geometric packing ability of the Chimera grid method and the efficient computation ability of the AMR algorithm makes the current scheme capable of simulating multiple and moving body flow problem with strong discontinuities using moderate computational resources. The material in this thesis documents this development of the Chimera grid scheme with an existing AMR code, and the validation and applications of this scheme. Firstly, a Chimera grid scheme has been developed. Most of the tasks associated with the Chimera grid scheme are performed in a fully automated mode. The graph data structure and orthogonal list storage are used to describe the domain relationships. This allows the sub-domains to be arranged in an arbitrary manner and increases efficiency. Secondly, in order to properly integrate the Chimera grid scheme with the AMR, some modification work on the original AMR code had to be done. This work allowed the Chimera grid scheme to be successfully incorporated into the AMR code. Thirdly, this scheme has been employed to solve time-dependent and steady state shock hydrodynamics problems at supersonic and hypersonic speed. Various validation and application cases, such as, shock reflection, shock diffraction, shock/boundary interaction and multiple moving body flows at supersonic speeds are presented, analysed and compared with experimental results or numerical solutions either from the literature or obtained by using another CFD code. The simulations demonstrate the flexibility of the grid generation and the high efficiency and capability to resolve complex flow features. Finally, future research work arising from the present study has also been discussed and highlighted.Item 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.Item Open Access An approach to configuration design synthesis of subsonic transport aircraft using artificial intelligence techniques(1991-12) Pasaribu, H. M.; Fielding, JohnThis 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.Item Open Access Performance and CFD analyses for a novel and existing thrust reverser designs.(2014-04) Mahmood, Tashfeen; Sethi, VishalThe landing phase of any flight is the most important one with respect to safety. For a high bypass ratio turbofan engine, aircraft deceleration can be achieved by the use of thrust reversers, lift spoilers and brakes. The use of thrust reversers naturally contributes to a reduction in engine life while the use of brakes has operational limitations with respect to aircraft “turn-around times”. With a drive towards improved engine efficiency and lower overall weight, research into novel thrust reverser concepts is imperative to identify designs which offer improved reverser effectiveness and lower weight as well as ease of installation and storage. The main contributions to knowledge of this PhD research are related to feasibility assessments of the following two thrust reverser concepts: A novel vane target type hybrid reverser (VTTHR) design concept has been conceived and evaluated (at a preliminary level) by the author. The design incorporates a target type thrust reverser with cascade vanes. This idea may be patentable. NASA has developed and tested a core mounted target type thrust reverser (CMTTTR) for which experimental data is available in the public domain. The second contribution to knowledge of this PhD research is extensive studies of this design. These studies comprise 2D and 3D CFD analyses to assess design feasibility and provide an understanding of performance and flow physics of this thrust reverser for both static and landing conditions (not available in public domain). In addition to these studies, comprehensive studies of the impact of thrust reverser deployment on overall engine and component performance (for both a mixed and a separate exhaust high bypass ratio turbofan engine) were performed. The preliminary feasibility studies of the VTTHR, which were performed using 2D CFD, suggest that this new design may offer benefits in terms of greater reverser efficiency, weight and ease of storage, relative to conventional designs. Additionally, it was deduced from a large number of CFD investigations that this may be the only feasible “core mounted” thrust reverser design concept for future high bypass ratio engines. There are of course several additional studies (aerodynamic and structural) that need to be performed to mature this technology but the preliminary studies performed provide a good foundation for these. The use of a VTTHR reverser concept relocates reverser hardware to the core cowl, offering potential reductions in reverser and nacelle weight while allowing the nacelle lines to be optimized. Also, installation of VTTHR would benefit aircraft cruise performance, as during cruise flight there will be no losses due to flow leakage and pressure drops that normally occur across the stowed reverser hardware for conventional cascade type thrust reversers, thus, an improvement in specific fuel consumption and therefore mission fuel burn is expected. The CMTTTR models developed were successfully validated using experimental data. However it was concluded that this design may not be feasible because of issues related to reverser effectiveness, mass flow compatibility and runway clearance.Item 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.Item 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.Item 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.Item 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.