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Item Open Access 6U CubeSat design for Earth observation with 6.5m GSD, five spectral bands and 14Mbps downlink(Royal Aeronautical Society, 2010-11-30T00:00:00Z) Tsitas, S. R.; Kingston, JenniferThe design of a 6U Cube Sat including spacecraft systems and imagine payload is described for an Earth observation mission. From a Sun synchronous orbit at an altitude of 600km the design enables imaging with a 6.5m GSD, an optical MTF (on axis) of >59% at half Nyquist and >35% at Nyquist, a 26km swath, 12 bit digitisation and SNR of 120-200:one in five spectral bands; blue, green, red, red edge and near infrared. Data can be downlinked at the rate of 14 Mbps to a 3.7m S band ground station. This design allows an 8kg Cube Sat to perform Earth observation missions equivalent to those of current 50-150kg microsatellites, with a corresponding reduction in cost.Item Open Access Absence behavior as traffic crash predictor in bus drivers(Elsevier Science B.V., Amsterdam., 2009-12-31T00:00:00Z) af Wåhlberg, Anders E.; Dorn, LisaProblem: Various indicators of health have been shown to be associated with traffic crash involvement. As general health is also related to absence from work, the latter variable may be more strongly related to crashes, especially for professional drivers. Method: Bus driver absence from work was analyzed in association with their crash records. Two British samples and one Swedish sample were used. Results: One of the British samples yielded fair correlation between crash record and absence, while for the other the effect was restricted to the first three months of driving. The Swedish data had effects in the expected direction but these were not significant. Discussion: The use of an indirect, overall measurement of health, may be a viable method for predicting the traffic crash involvement for professional drivers, although replications are needed in larger samples and other populations. Impact on industry: The use of absence records for the identification of at risk drivers would seem to be a simple and useful method for companies with major fleets, and it also shows the importance of promoting employee health and well being at work as a potential method of reducing the cost, not only of absenteeism, but also of crashes in company vehicles.Item Open Access Acoustic emission during run-up and run-down of a power generation turbine.(Elsevier Science B.V., Amsterdam., 2004-05-01T00:00:00Z) Zuluaga-Giraldo, C.; Mba, David; Smart, M.The measurement of acoustic emission (AE) activity at the bearings of power generation turbines is evolving into a viable complementary diagnostic technique especially adept at indicating the early stages of shaft-seal rubbing. This paper reports on an ongoing investigation on the application of acoustic emission for shaft-seal rub detection in power generation turbines. A pre- requisite in developing such a technique requires an understanding of the operational AE background noise. The detection of shaft-seal, and blade-case, rubbing with AE has been reported [Electrical Eng. Japan 110 (2) (1990); Joint ASME/IEEE Power Generation Conference, October 4–8, 1981, St. Louis, MI, USA; International Conference on Condition Monitoring. Oxford, UK, July 2–4, 2003]. In these instances, the observations of AE activity were associated with particular dynamic and process conditions known to cause such defects. However, the effect of variations of turbine loading on AE activity is unknown. This report presents observations of AE activity during the run-up and run-down of a 500 MW steam turbine and is the first known document detailing correlations between AE, vibration and turbine loadItem Open Access Acoustic Emission Signal Classification in Condition Monitoring Using the Kolmogorov-Smirnov Statistic.(2001-01-01T00:00:00Z) Hall, L. D.; Mba, David; Bannister, R. H.Acoustic emission (AE) measurement at the bearings of rotating machinery has become a useful tool for diagnosing incipient fault conditions. In particular, AE can be used to detect unwanted intermittent or partial rubbing between a rotating central shaft and surrounding stationary components. This is a particular problem encountered in gas turbines used for power generation. For successful fault diagnosis, it is important to adopt AE signal analysis techniques capable of distinguishing between various types of rub mechanisms. It is also useful to develop techniques for inferring information such as the severity of rubbing or the type of seal material making contact on the shaft. It is proposed that modelling the cumulative distribution function of rub-induced AE signals with respect to appropriate theoretical distributions, and quantifying the goodness of fit with the Kolmogorov-Smirnov (KS) statistic, offer a suitable signal feature for diagnosis. This paper demonstrates the successful use of the KS feature for discriminating different classes of shaft- seal rubbing. A hierarchical cluster algorithm was employed for grouping extracted KS values. AE rub signals were simulated with various metallic seals and measured at the journal bearings of a test rig rotating at approximately 1500 rev/min. Also, the KS classification results were directly compared withmore established AE feature vectors.Item Open Access Acoustic Emission Waveform Changes for Varying Seeded Defect Sizes.(2006-01-01T00:00:00Z) Al-Dossary, Saad; Raja, Hamzah R. I.; Mba, DavidThe investigation reported in this paper was centered on the application of the Acoustic Emissions (AE) technology for characterising the defect sizes on a radially loaded bearing. The aim of this investigation was to ascertain the relationship between the duration of AE transient bursts associated with seeded defects to the actual geometric size of the defect. It is concluded that the geometric defect size can be determined from the AE waveform.Item Open Access Acoustic Emissions and monitoring bearing health(Taylor & Francis, 2003-01-01T00:00:00Z) Mba, DavidAcoustic emission (AE) was originally developed for non-destructive testing of static structures. however, over the years its application has been extended to health monitoring of rotating machines and bearings. It offers the advantage of earlier defect detection in comparison to vibration analysis. Current methodologies of applying AE for bearing diagnosis are reviewed. The investigation reported in this paper was centered on the application of standard acoustic emissions IAE) characteristic parameters on a radially loaded bearing. An experimental test-rig was designed to allow seeded defects on the inner and outer race. It is concluded that irrespective of the radial load, rotational speed and high levels of background noise. simple AE parameters such as e.m.s. and AE counts provided an indication of bearing defect. In addition to validating already established AE techniques, this investigation focuses on establishing an appropriate threshold level for AE counts.Item Open Access Acoustic emissions diagnosis of rotor-stator rubs using the KS statistic.(Elsevier Science B.V., Amsterdam, 2004-07-01T00:00:00Z) Hall, L. D.; Mba, DavidAcoustic emission (AE) measurement at the bearings of rotating machinery has become a useful tool for diagnosing incipient fault conditions. In particular, AE can be used to detect unwanted intermittent or partial rubbing between a rotating central shaft and surrounding stationary components. This is a particular problem encountered in turbines used for power generation. For successful fault diagnosis, it is important to adopt AE signal analysis techniques capable of distinguishing between various types of rub mechanisms. It is also useful to develop techniques for inferring information such as the severity of rubbing or the type of seal material making contact on the shaft. It is proposed that modelling the cumulative distribution function of rub-induced AE signals with respect to appropriate theoretical distributions, and quantifying the goodness of fit with the Kolmogorov–Smirnov (KS) statistic, offers a suitable signal feature for diagnosis. This paper demonstrates the successful use of the KS feature for discriminating different classes of shaft-seal rubbing.Item Open Access Adaptive control of a nonlinear aeroelastic system(Elsevier Science B.V., Amsterdam., 2011-07-01T00:00:00Z) Li, Daochun; Xiang, Jinwu; Guo, Shijun J.Aeroelastic two-dimensional wing section with both trailing-edge (TE) and leading-edge (LE) was investigated in this paper through numerical simulation in time domain. Structural stiffness and damping in pitch degree of freedom were represented by nonlinear polynomials. Open-loop limit cycle oscillation (LCO) characters of two examples were studied, and flutter boundaries with initial conditions were obtained. Parametric uncertainties in both pitch stiffness and damping were considered in the design of adaptive control laws to depress LCOs. Firstly an adaptive controller based on partial feedback linearization was derived for the wing section with a single TE control surface. Secondly a structured model reference adaptive control law was designed for the aeroelastic system with both TE and LE control surfaces. The results show that the designed control laws are effective for flutter suppression, and that considering damping uncertainty has positive effect on flutter control. It may reduce convergent time or increase flutter speed.Item Open Access Adaptive diagnosis of the bilinear mechanical systems.(Elsevier Science B.V., Amsterdam, 2009-07-01T00:00:00Z) Gelman, Leonid; Gorpinich, S; Thompson, CA generic adaptive approach is proposed for diagnosis of the bilinear mechanical systems. The approach adapts the free oscillation method for bilinearity diagnosis of mechanical systems. The expediency of the adaptation is proved for a recognition feature, the decrement of the free oscillations. The developed adaptation consists of variation of the adaptive likelihood ratio of the decrement with variation of the resonance frequency of the bilinear system. It is shown that in the cases of the frequency-independent and the frequency- dependent internal damping, the adaptation is expedient. To investigate effectiveness of the adaptation in these cases, a numerical simulation was carried out. The simulation results show that use of the adaptation increases the total probability of the correct diagnosis of system bilinearity.Item Open Access Aerodynamic and performance characteristics of a passive leading edge Kruger flap at low Reynolds numbers(Royal Aeronautical Society, 2012-07-31T00:00:00Z) Moraris, Vassilis Michael; Lawson, Nicholas J.; Garry, Kevin P.An experimental and numerical study was performed on a Clark Y aerofoil with a 10% chord leading edge Kruger flap to examine its aerodynamic performance at Reynolds numbers of 0.6 × 106, 1 × 106, and 1.6 × 106, to help to identify the forces and moments acting on a basic configuration. A detailed comparison of the numerical and experimental data is presented in this paper. The leading edge flap was effective at high angles of attack with an increase in CL of up to 18% over a conventional no flap configuration and delayed separation by up to 3°. The moments around the Kruger flap rotation point were calculated from the numerical analysis as an initial stage in the design of a UAV passive flap system and they are also presented in the paItem Open Access Aerodynamic investigations of ventilated brake discs.(Professional Engineering Publishing, 2005-01-01T00:00:00Z) Parish, D.; MacManus, David G.The heat dissipation and performance of a ventilated brake disc strongly depends on the aerodynamic characteristics of the flow through the rotor passages. The aim of this investigation was to provide an improved understanding of ventilated brake rotor flow phenomena, with a view to improving heat dissipation, as well as providing a measurement data set for validation of computational fluid dynamics methods. The flow fields at the exit of four different brake rotor geometries, rotated in free air, were measured using a five-hole pressure probe and a hot-wire anemometry system. The principal measurements were taken using two-component hot-wire techniques and were used to determine mean and unsteady flow characteristics at the exit of the brake rotors. Using phase-locked data processing, it was possible to reveal the spatial and temporal flow variation within individual rotor passages. The effects of disc geometry and rotational speed on the mean flow, passage turbulence intensity, and mass flow were determined. The rotor exit jet and wake flow were clearly observed as characterized by the passage geometry as well as definite regions of high and low turbulence. The aerodynamic flow characteristics were found to be reasonably independent of rotational speed but highly dependent upon rotor geometry.Item Open Access Aeroelastic dynamic response and control of an airfoil section with control surface nonlinearities(Elsevier Science B.V., Amsterdam, 2010-10-31T00:00:00Z) Li, Daochun; Guo, Shijun J.; Xiang, JinwuNonlinearities in aircraft mechanisms are inevitable, especially in the control system. It is necessary to investigate the effects of them on the dynamic response and control performance of aeroelastic system. In this paper, based on the state-dependent Riccati equation method, a state feedback suboptimal control law is derived for aeroelastic response and flutter suppression of a three degree-of-freedom typical airfoil section. With the control law designed, nonlinear effects of freeplay in the control surface and time delay between the control input and actuator are investigated by numerical approach. A cubic nonlinearity in pitch degree is adopted to prevent the aeroelastic responses from divergence when the flow velocity exceeds the critical flutter speed. For the system with a freeplay, the responses of both open- and closed-loop systems are determined with Runge-Kutta algorithm in conjunction with Henon's method. This method is used to locate the switching points accurately and efficiently as the system moves from one subdomain into another. The simulation results show that the freeplay leads to a forward phase response and a slight increase of flutter speed of the closed-loop system. The effect of freeplay on the aeroelastic response decreases as the flow velocity increases. The time delay between the control input and actuator may impair control performance and cause high-frequency motion and quasi-periodic vibration.Item Open Access AFM observation of surface topography of fibre Bragg gratings fabricated in germanium-boron codoped fibres and hydrogen-loaded fibres.(Elsevier Science B.V., Amsterdam., 2002-11-01T00:00:00Z) Wei, C. Y.; Ye, Chen-Chun; James, Stephen W.; Irving, Phil E.; Tatam, Ralph P.This paper reports the measurement of the surface topology of optical fibres containing a fibre Bragg grating (FBG) using an atomic force microscope (AFM). The AFM observation was made on FBGs fabricated via the phase mask technique in germanium–boron codoped optical fibres, in hydrogen-loaded germanium–boron codoped fibres and in standard telecommunications optical fibres. The surface images reveal that a spatial corrugation pattern was induced by the UV- irradiation, with a period that is half of the period of the phase mask. This UV-induced surface structure was found only on the side of the fibre facing towards the incident UV-irradiation and did not appear on the rear surface. The AFM probe scanned a 10×10 μm2 surface area at seven sites along the 6.0 mm length of fibre that was exposed to the UV-irradiation. The amplitude of the spatial corrugation pattern observed on the AFM image was quantified for each site. It was found that the amplitude in a range of 0.7–3.2 nm was a function of UV-laser intensity distribution and the type of fibre. Hydrogen loaded optical fibres exhibited a corrugation with an amplitude twice as large as that observed in the Ge–B doped fibres that were not hydrogen-loaded. This correlates with the increase in photosensitivity produced by the hydrogen loading. A similar UV- induced spatial corrugation was also observed on standard telecom fibres, but without inducing the refractive index change in the fibre core. The observation of surface topology provides an insight into the structural changes induced during FBG fabrication. UV-induced densification and laser ablation could account for the formation of the surfacItem Open Access Air traffic management innovation: the risks of STASIS(UK international Press Media & Events, 2007) Brooker, PeterStasis is a word used by the ancient Greeks to mean many different things: civil war, arguments between factions, ‘a stoppage’. Today it generally means a cessation of progress or change. ATM in Europe is in danger of being in stasis, because current ATM safety regulation policies are tending to make it more and more difficult to innovate, to introduce new technologies and ways of operating. The following essentially highlights the key findings of a group of published research papers analysing a variety of problems with ATM safety regulation policies. These policies mainly derive from the Eurocontrol Safety Regulation Commission (SRC), but also from ICAO. The case studies discussed are: the role of ground-based safety nets (Short Term Conflict Alert – STCA); air-based safety nets – Airborne Collision Avoidance Systems (ACAS); and risk assessment and mitigation in ATM (SRC’s Safety Regulatory Requirement Number 4 – ‘ESARR4’). These policies were no doubt developed with good intentions but, in quality management jargon, they are not ‘fit for purpose’.Item Open Access Air traffic management safety challenges(2007-10) Brooker, PeterThe primary goal of the Air Traffic Management (ATM) system is to control accident risk. ATM safety has improved over the decades for many reasons, from better equipment to additional safety defences. But ATM safety targets, improving on current performance, are now extremely demanding. Safety analysts and aviation decision-makers have to make safety assessments based on statistically incomplete evidence. If future risks cannot be estimated with precision, then how is safety to be assured with traffic growth and operational/technical changes? What are the design implications for the USA’s ‘Next Generation Air Transportation System’ (NextGen) and Europe’s Single European Sky ATM Research Programme (SESAR)? ATM accident precursors arise from (eg) pilot/controller workload, miscommunication, and lack of upto- date information. Can these accident precursors confidently be ‘designed out’ by (eg) better system knowledge across ATM participants, automatic safety checks, and machine rather than voice communication? Future potentially hazardous situations could be as ‘messy’ in system terms as the Überlingen mid-air collision. Are ATM safety regulation policies fit for purpose: is it more and more difficult to innovate, to introduce new technologies and novel operational concepts? Must regulators be more active, eg more inspections and monitoring of real operational and organisational practices?Item Open Access Air Traffic Safety: continued evolution or a new Paradigm.(Royal Aeronautical Society, 2007-10-01T00:00:00Z) Brooker, PeterThe context here is Transport Risk Management. Is the philosophy of Air Traffic Safety different from other modes of transport? – yes, in many ways, it is. The focus is on Air Traffic Management (ATM), covering (eg) air traffic control and airspace structures, which is the part of the aviation system that is most likely to be developed through new paradigms. The primary goal of the ATM system is to control accident risk. ATM safety has improved over the decades for many reasons, from better equipment to additional safety defences. But ATM safety targets, improving on current performance, are now extremely demanding. What are the past and current methodologies for ATM risk assessment; and will they work effectively for the kinds of future systems that people are now imagining and planning? The title contrasts ‘Continued Evolution’ and a ‘New Paradigm’. How will system designers/operators assure safety with traffic growth and operational/technical changes that are more than continued evolution from the current system? What are the design implications for ‘new paradigms’, such as the USA’s ‘Next Generation Air Transportation System’ (NextGen) and Europe’s Single European Sky ATM Research Programme (SESAR)? Achieving and proving safety for NextGen and SESAR is an enormously tough challenge. For example, it will need to cover system resilience, human/automation issues, software/hardware performance/ground/air protection systems. There will be a need for confidence building programmes regarding system design/resilience, eg Human-in-the-Loop simulations with ‘seeded errors’.Item Open Access Airborne Separation Assurance Systems: towards a work programme to prove safety(Elsevier, 2004-10) Brooker, PeterWith Full Delegation Airborne Separation Assurance System (ASAS), separation control would be delegated to the (properly equipped) aircraft, i.e. aircraft pilots are responsible for aircraft separation. The aim is to try to identify a tangible work programme – rational and evidence based, and within the compass of known techniques – that would prove safety. The task here is to create a framework in which to integrate these existing building blocks with results from additional work developed from well-specified experiments. Reasons for retaining the existing separation minima in an ASAS system are put forward. For the current system, comparatively large proportions of the Air Traffic Services risk budget should be allocated to ‘Reasonable Intent’ risk (effectively ‘right place on wrong flight path’). The key argument here is that mid-air collision in an ASAS environment will predominantly arise from this type of risk. The use of Probabilistic Risk Assessment, which requires the probabilities of safety-critical events to be estimated for ‘human components’ (Human Reliability Analysis), is reviewed. The danger is the creation of ‘over-elaborate’ models – ones whose parameters cannot be reliably estimated from the data likely to be obtainable. A simple model that can be soundly based on available data is proposed.Item Open Access Aircraft Noise: Annoyance, House Prices and Valuation(Institute of Acoustics, 2006-05) Brooker, Peter“Nobody wants to buy your house. It’s the aircraft noise. You’ll have to reduce the price a lot.” Aircraft noise around airports causes annoyance, and tends to reduce the price of affected properties. Can annoyance be ‘costed’ by examining house price reductions? Are there other ways of valuing annoyance in monetary terms? This short paper summarises key research results and poses some questions.Item Open Access Airframe manufacturers: Which has the better view of the future?(Elsevier Science B.V., Amsterdam., 2007-01-31T00:00:00Z) Mason, Keith J.For the development of Airbus' A380 and Boeing's B787 it seems that these manufacturers have differing views of future airline networks. This paper assesses from published sources the likely preferences of leisure and business passengers for different airline network approaches and also assesses airline strategies through the economic cycle. The manufacturers seem to have substitutable aircraft types. Both leisure and business travellers are increasingly price elastic and growth in both markets means both aircraft type will be successful aircraft meeting differing needs. However, airline market- share strategies are likely to undermine the success of hub by-pass or hub-to- hub focus strategies throughout the cycle. (C) 2006 Elsevier Ltd. All rights reserved.Item Open Access Airship-assisted space launch.(2004-03-01T00:00:00Z) Guenov, Marin D.; Peyron, VincentIntroduction Being lighter-than-air, airships do not seem to be an obvious platform choice for dropping of heavy objects. We have challenged the idea and this paper presents the summary of a speculative concept which utilises airships as a reusable first stage of a space launch system. The inspiration behind the concept was that if not much cheaper, the airship-assisted space launch will be environmentally friendlier- an argument which is likely to become even more important with time. During the development of the concept we have used as a base for comparison the Orbital Sciences Corp. Pegasus XL concept, which is currently the single operational aircraft-based space launch system. Alongside the challenges of estimating weight and cost of the very large airship required (approximately 728,000 m 3 ), the work presented in this paper concentrates mainly on the process of releasing the space launch vehicle from the airship.