Staff publications (SoE)

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Open Access
A 3D extension to cortex like mechanisms for 3D object class recognition
(2012-06-21T00:00:00Z) Flitton, Greg T.; Breckon, Toby P.; Megherbi, Najla
We introduce a novel 3D extension to the hierarchical visual cortex model used for prior work in 2D object recognition. Prior work on the use of the visual cortex standard model for the explicit task of object class recognition has solely concentrated on 2D imagery. In this paper we discuss the explicit 3D extension of each layer in this visual cortex model hierarchy for use in object recognition in 3D volumetric imagery. We apply this extended methodology to the automatic detection of a class of threat items in Computed Tomography (CT) security baggage imagery. The CT imagery suffers from poor resolution and a large number of artefacts generated through the presence of metallic objects. In our examination of recognition performance we make a comparison to a codebook approach derived from a 3D SIFT descriptor and demonstrate that the visual cortex method out-performs in this imagery. Recognition rates in excess of 95% with minimal false positive rates are demonstrated in the detection of a range of threat items
Open Access
3D planar velocity measurements, using Mach-Zehnder interferometric-filter-based planar Doppler velocimetry (MZI-PDV) and imaging fibre bundles
(2008-12-31T00:00:00Z) Lu, Z. H.; Charrett, Thomas O. H.; Ford, Helen D.; Tatam, Ralph P.; David, Sampson; Stephen, Collins; Kyunghwan, Oh; Ryozo, Yamauchi
Three component planar flow-field measurements are made using imaging fibre bundles to port different views of the measurement plane, defined by a laser light sheet, to a single imaging head. The Doppler frequency shifts of light scattered by particles entrained in the flow are transduced to intensity variations using a Mach-Zehnder interferometric filter. The free spectral range of the filter can be selected by adjusting the optical path difference of the interferometer. This allows the velocity measurement range, sensitivity and resolution to be varied. Any laser wavelength may be used. A phase locking system has been designed to stabilise the interferometric filter.
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, Jennifer
The 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.
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, Lisa
Problem: 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.
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 load
Open Access
Acoustic Emission for the detection of shaft-to-seal rubbing in large power generation turbines
(2006-01-01T00:00:00Z) Leahy, M.; Mba, David; Cooper, P.; Montgomery, A.; Owen, D.
An empirical investigation is undertaken in order to assess the potential of the AE technique for the detection of seal-to-rotor rubbing in steam turbines. Rubbing was induced at various axial locations along a 4 ½ tonne test rotor, rotating at 3000 rpm and supported by 7” (178mm) journal bearings. This paper examines the capabilities of bearing mounted AE transducers for the detection of seal-torotor rubbi
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.
Open Access
Acoustic Emission Waveform Changes for Varying Seeded Defect Sizes.
(2006-01-01T00:00:00Z) Al-Dossary, Saad; Raja, Hamzah R. I.; Mba, David
The 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.
Open Access
Acoustic Emissions and monitoring bearing health
(Taylor & Francis, 2003-01-01T00:00:00Z) Mba, David
Acoustic 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.
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, David
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 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.
Open Access
The acoustics of racing engine intake systems
(Elsevier, 2004-04-06) Harrison, M. F.; Dunkley, A.
Naturally aspirated racing engines have tuned intake systems and can now achieve volumetric efficiencies in excess of 125% and peak engine speeds in excess of 18,000 rev/min. Engines designed for single seater racing commonly dispense with the intake manifold and its convoluted and restricting flow path preferring single lengths of pipe feeding each cylinder separately. An investigation into the intake process on a single cylinder racing engine has shown that inertial ram effects make a strong contribution to the intake process at high engine speeds whereas acoustic resonance effects are more important to the rather weak wave action that occurs at low engine speeds. An acoustic model of the resonant wave action has proved useful in distinguishing between these two effects. The attributes of the acoustic model have been compared to those of more traditional time-marching gas-dynamics calculation methods. A decoupled hybrid method has been shown to yield calculations of the wave dynamics in the intake system of a single cylinder racing engine that show fair agreement with measured results up to the 10th harmonic of the engine cycle frequency. In a case study, the intake characteristics of a single cylinder racing engine have been shown to differ only slightly from those expected from the V10 engine on which it is based, although this will only be the case when the dimensions of the intake system are chosen appropriately.
Open Access
Acousto-optic frequency switching for single-camera planar Doppler velocimetry
(International Society for Optical Engineering; 1999, 2001-12-31T00:00:00Z) Ford, Helen D.; Nobes, David S.; Tatam, Ralph P.; Mercer, Carolyn R.; Cha, Soyoung S.; Shen, Gongxin X.
A single-camera Planar Doppler velocimetry system has been demonstrated, in which illumination beams at two closely-spaced optical frequencies are derived from a single Argon-ion laser. The frequency of one beam lies on an absorption line of iodine vapour, and the other just off the absorption line. The beams sequentially illuminate a plane within a seeded flow and the Doppler-shifted scattered light passes through an iodine cell onto a single solid-state camera. Light scattered from the measurement plane from the beam with its wavelength set to be off the absorption line is not affected by its passage through the cell, and provides a reference image, while that from the beam on the absorption line encodes the velocity information as a variation in transmission dependent upon the Doppler shift. The complex imaging system required for conventional PDV is eliminated, since superposition of the reference and signal images is automatic. The two beams are generated by an optical arrangement incorporating an acoustio- optic modulator, and are transmitted to the region of interest by a single mode optical fibre, which ensures both a smooth Gaussian illumination profile and co- linearity of the beams. The system is demonstrated using a spinning disc and a velocity resolution of +/-1 ms-1 is achieved.
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.
Open Access
Adaptive diagnosis of the bilinear mechanical systems.
(Elsevier Science B.V., Amsterdam, 2009-07-01T00:00:00Z) Gelman, Leonid; Gorpinich, S; Thompson, C
A 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.
Open Access
Adaptive object placement for augmented reality use in driver assistance systems
(2011-11-17T00:00:00Z) Bordes, Lucie; Breckon, Toby P.; Katramados, Ioannis; Kheyrollahi, Alireza
We present an approach for adaptive object placement for Augmented Reality (AR) use in driver assistance systems. Combined vanishing point and road surface detection enable the real-time adaptive emplacement of AR objects within a drivers' natural field of view for on-road information display. This work combines both automotive vision and multimedia production aspects of real-time visual engineering.
Open Access
Adaptive vibration condition monitoring technology for local tooth damage in gearboxes.
(Learned and Professional Society Publishers, 2005-08-01T00:00:00Z) Gelman, Leonid; Zimroz, R; Birkel, J; Leigh-Firbank, H; Simms, Daniel M.; Waterland, B; Whitehurst, G
An adaptive approach was applied for local tooth damage diagnostics in gearboxes. The expediency of adaptation was proved experimentally for the new diagnostic feature, the sum of normalized sideband amplitudes. The positive correlation between mesh amplitudes and their sideband amplitudes was found experimentally for the first time. Novel adaptive vibration condition monitoring technology for local tooth damage in gearboxes was developed and experimentally validated. The experimental results showed an increase in effectiveness of the diagnostics when the adaptive technology was used.
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 pa
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.
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, Jinwu
Nonlinearities 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.
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 surfac