bluuebunny/crossref_metadata_2025 huggingface dataset:
The weightshift-controlled microlight aeroplane
Authors: Gratton G B
Published: October 2002

Microlight aircraft are increasingly becoming the most popular segment of private aviation. In the United Kingdom the majority (about 2500 of a total fleet of 3500) of these aircraft are of the weightshift class, also known as flexwings or trikes. This paper introduces the main issues involved in the design and operation of this class of aeroplane.
Remote lift-fan engines
Authors: Arnulfo L , Pilidis P , Yin J , Probert D
Published: October 2002

The requirements imposed on advanced short take-off and vertical landing (ASTOVL) aircraft give rise to challenging demands on their propulsion systems. One possible approach is to have a high-performance turbofan of traditional design and an additional, but separate, fan to provide a major part of the lift during the take-off and landing manoeuvres. For such a design, there are several quite different choices of layout for providing the power to drive the remote fan by means of the core engine. These include shaft- and bleed-driven options. The choice will depend on the anatomy and required thermodynamic performance of the whole system. In this paper, several pertinent alternative engine designs are discussed, four of which, based on a high-performance low bypass ratio core engine, are studied in detail and their behaviours compared. Prima facie, the preferred choice is the engine with the shaft-driven fan: a slightly less acceptable choice is the high-pressure turbine exit bleed driven remote fan.
An expert system for the determination of stress concentration factors
Authors: Robinson P A , Swift K G , Raines M , Graham R H , Peckover S , Gill L
Published: October 2002

Fatigue failures of stressed components are invariably initiated at sites where there is some feature causing the local stress to be significantly higher than the nominal design stress. Determination of stress concentration factors is therefore essential for the correct design of components subject to fatigue-inducing loads. This paper reports on the development of an expert system for advising aerospace designers about stress concentrations. The stress concentration evaluation system (SCONES) encapsulates and combines analytical, experimental and heuristic information for determination and optimization of stress concentration factors.
Experimental aerodynamic characteristics of NACA 0012 airfoils with simulated glaze and rime ice
Authors: Cuerno-Rejado C , López-Martínez G , Escudero-Arahuetes J L , López-Díez J
Published: October 2002

Ice formation constitutes one of the major challenges to aviation safety, since several accidents have had their origin in this kind of phenomenon. The comprehension of ice accretion on unprotected airfoils, engine intakes, etc. is fundamental from the point of view of both aircraft design and certification requirements since large changes in aerodynamic behaviour and performance take place. The present paper describes tests conducted in a conventional wind tunnel on NACA 0012 airfoils with simulated rime and glaze ice, using laser Doppler velocimetry to measure the flow around the modified airfoils and also the velocity profiles along the viscous wake in order to obtain the drag coefficient. Distortions of the flow field lead to changes in the airfoil aerodynamic characteristics.
An algebraic grid motion technique for large deformations
Authors: Allen C B
Published: October 2002

Numerical simulation of the aeroelastic behaviour of wings and rotor blades requires the coupling of an unsteady flow-solver with a structural model. The moving and deforming surfaces resulting from unsteady simulations require deforming meshes during the simulation, and it is common practice to use simple interpolation of surface displacements and velocities onto the initial undisturbed mesh. However, such techniques result in poor grid quality, and possible grid crossover, when applied to large surface displacements or deformations. A new interpolation technique, for structured grids, is presented which is still simple in that it is driven solely by surface motion, but maintains grid quality near the surface by representing rotational effects there. Furthermore, since the scheme is fully analytic, the grid speeds required in an unsteady flow-solver are also available analytically, and the scheme is very cheap computationally.
A two-dimensional linearized unsteady Euler scheme for pulse response calculations
Authors: Gaitonde A L , Jones D P
Published: October 2002

An unsteady linearized Euler scheme for use on moving meshes is presented. This is derived from a scheme for the full non-linear unsteady Euler equations. This scheme is based on the Jameson cell-centred scheme, but is time-accurate and includes the necessary terms to account for grid motion. It is assumed that the unsteadiness in the flow and mesh is small. Using this assumption the discrete unsteady Euler equations are linearized about the full, non-linear, steady mean flow. The resulting equations are solved in the work presented here using a dual-time scheme. In the basic scheme no assumptions are made about the form of the perturbations other than that they are small. This permits the direct calculation of non-periodic flows, e.g. pulse responses. Linear pulse responses are a useful tool as they can be used to calculate the flow due to general inputs. The equations that would result from the assumption of harmonic flow are also derived. Results are presented for heave, pitch and ramp test cases and compared to full non-linear Euler results calculated using a dual-time scheme.
Designing composite structures: Lay-up selection
Authors: Weaver P M
Published: October 2002

The use of high-performance composite materials of the sort used in the aerospace and Formula 1 industries is becoming more widespread. On one level they are exciting to work with because they give scope for designing the ‘material’ in addition to a ‘structure’ through judicious placement of the ply orientation. Layers are stiff and strong in the fibre direction while weak and compliant in the transverse direction. It is this ability to tailor material properties layer by layer that gives designers huge potential in design. One possible explanation for the prevalent use of quasi- isotropic (‘black aluminium’) carbon composites in structures is the lack of available design tools. Analysis packages exist that will predict performance, but only for a given choice of fibre orientation. Here a design tool is presented that aids selection of fibre orientations. Optimization of laminate fibre angles is difficult for multiple-load cases and objectives since there are many local minima to assess. The alternative approach that is presented here, for flat plates and cylindrical shells, circumvents the need (in the early stages of design) for conventional optimization strategies that often prove difficult and complicated to implement. The basic idea is to build a database that stores appropriate properties of all permutations of lay-up angles for a laminate. Rather than access these properties by a question and answer, black-box technique, a graphical method is proposed. The designer can select viable laminates by first plotting a succession of two-dimensional charts containing relevant properties. Then, using simple on-screen techniques, the number of potential laminates is visually reduced by selecting those with desirable properties. Two case studies are presented to illustrate the selection method. The first concerns the optimization of a spar web, typically found in an aircraft wing structure, while the second concerns the optimization of a cylindrical shell, subject to axial compression, that undergoes simultaneous Euler-type buckling and local buckling.
Stability of an elastically connected two-body space station by the perturbation method
Authors: Ge Z-M , Ku S-C
Published: October 2002

This investigation deals with the stability, in a circular orbit, of a flexible space station consisting of two inertially identical rigid end bodies connected together by an elastic structure. The earth-pointing motion and the rotation with arbitrary initial angular velocity perpendicular to the orbital plane are studied by using the multiple-scales technique. The first-order approximate analytical solution and the conditions of stability are obtained.
Higher-order spectral techniques for machine vibration condition monitoring
Authors: Howard I M
Published: October 2002

The vibration signals measured from rotating machinery can be very complex and a number of machine malfunctions can create complicated modulation patterns which are sometimes difficult to detect and to understand. Conventional linear spectral analysis will be of limited use in particular instances when frequency components interact together to form new spectral components due to some non-linear process. Under these circumstances, various signal processing tools are available for performing sophisticated analysis of the measured vibration to detect the non-linear interaction of frequency components and hence changes in machine performance and condition. This paper presents two higher-order spectral analysis techniques, the bispectrum and the trispectrum, and demonstrates how they can be used to detect phase coherence between various frequency components. The theoretical relationship of the higher-order spectral techniques to the power spectrum is given along with the derivation of the normalized bispectrum and trispectrum using the Fourier series of phase- related signals to show that the higher-order spectral analysis techniques can detect various forms of phase coupling between frequency components as well as the strength of the phase coupling. The particular case of modulation is investigated to show the applicability of the higher-order spectral techniques to detect amplitude and phase modulation.
Knowledge-based geometric modelling of aircraft structures
Authors: Bates J P , Morris A J , Payne P N
Published: October 2002

Aerospace engineering offers a challenging test environment for advanced design systems and methods. Focusing particularly on knowledge-based engineering (KBE) systems, this paper demonstrates their application in automating the solid modelling of aircraft structures. The principles are illustrated through a case study example in which a description is given of the knowledge-based geometric modelling of light alloy fuselage frame sectors. The business benefits of using KBE systems in an aerospace engineering programme are quantified. Recommendations for the extended application of the technology to achieve strategic market advantage are also given.
Near-similarity approximation for compressible, laminar boundary layers on adiabatic walls
Authors: Horton H P
Published: October 2002

Two-dimensional, compressible, laminar boundary layers with zero heat transfer and a constant pressure gradient parameter are considered. Although it is well known that exact similarity is, in general, only possible when the Prandtl number is equal to unity, it is shown here that, at least for Prandtl numbers in the range from 0.5 to 2.0, a careful choice of transformation gives partial differential equations in which the streamwise derivatives are practically negligible, irrespective of Mach number. The set of ordinary differential equations which results from setting the streamwise derivatives to zero is proposed as a useful approximation for generating families of velocity and temperature profiles, for use in database methods for analysing boundary layer stability, for example.
Adhesives in engineering
Authors: Kinloch A J
Published: October 2002

When considering methods for joining materials, there are many advantages that engineering adhesives can offer, compared to the more traditional methods of joining such as bolting, brazing, welding, mechanical fasteners, etc. The advantages and disadvantages of using engineering adhesives are discussed and it is shown that it is possible to identify three distinct stages in the formation of an adhesive joint. Firstly, the adhesive initially has to be in a ‘liquid’ form so that it can readily spread over and make intimate molecular contact with the substrates. Secondly, in order for the joint to bear the loads that will be applied to it during its service life, the ‘liquid’ adhesive must now harden. In the case of adhesives used in engineering applications, the adhesive is often initially in the form of a ‘liquid’ monomer which polymerizes to give a high molecular weight polymeric adhesive. Thirdly, it must be appreciated that the load-carrying ability of the joint, and how long it will actually last, are affected by: (a) the design of the joint, (b) the manner in which loads are applied to it and (c) the environment that the joint encounters during its service life. Thus, to understand the science involved and to succeed in further developing the technology, the skills and knowledge from many different disciplines are required. Indeed, the input from surface chemists, polymer chemists and physicists, materials engineers and mechanical engineers are needed. Hence, the science and technology of adhesion and adhesives is a truly multidisciplined subject. These different disciplines have been brought together by developing a fracture mechanics approach to the failure of adhesive joints. The advances that have been made in applying the concepts of fracture mechanics to adhesive joints have enabled a better understanding of the fundamental aspects of adhesion and the more rapid extension of adhesives technology into advanced engineering applications.
Hypervelocity impact on spacecraft carbon fibre reinforced plastic/aluminium honeycomb
Authors: Taylor E A , Herbert M K , Gardner D J , Kay L , Thomson R , Burchell M J
Published: October 2002

Samples of a spacecraft primary external wall structure, as used in a low earth orbit remote sensing platform, have been tested to determine the response to the hypervelocity impact and ballistic limit (for mm-sized impactors) of the 47 mm thick structure at 5 km/s. A strong dependence of the ballistic limit on projectile density was identified. This programme was carried out using the two-stage light gas gun at the University of Kent at Canterbury. The equivalent diameters of the front and rear holes for each impact were analysed as a function of the impactor parameters. Damage equations derived by other experimenters were compared to the experimental results. X-ray non-destructive testing was used to determine the level of internal honeycomb damage for a sample. The dependence of the witness plate damage (placed behind the target to capture any ejecta from the rear surface) on the impactor parameters was recorded.

It was found that the use of ‘equivalent thicknesses’ of aluminium may not be appropriate as a general conversion factor for carbon fibre reinforced plastic (CFRP) facesheets. A simple damage equation is presented, based on the total hole size as a function of the impact energy. The ballistic limit cannot be defined solely in terms of impact energy and shows an additional dependence with projectile density. The amount and type of ejecta produced is a strong function of density and a less strong function of projectile diameter, and its production cannot be linked with the rear hole diameter.
Determination of superplastic constitutive equations and strain rate sensitivities for aerospace alloys
Authors: Kim T W , Dunne F P E
Published: October 2002

Constitutive equations for the superplastic behaviour of titanium and aluminium aerospace alloys have been presented and computational procedures developed for the determination of the material parameters arising in the equations. The equations include a description of grain growth kinetics with deformation enabling the influence of microstructure on superplastic deformation behaviour to be modelled.

Three predictive methods have been developed for the determination of strain rate sensitivity. The models represent the dependence of the strain rate sensitivity on strain, strain rate, and grain growth, and therefore, provide useful information for process design and optimization. The models are validated by comparison of predictions with experimental data reported in the literature and obtained in this work. Finally, two conventional experimental testing methods for the determination of strain rate sensitivity, namely the constant strain rate and strain rate jump methods are appraised using the methods developed.
Development of real time data monitoring and analysis techniques in the flight test environment
Authors: Hanney P D
Published: October 2002

Since the mid 1980s, British Aerospace's Military Aircraft Division has been committed to the concept of real time data monitoring and analysis in the flight test environment as a prime means of improving effectiveness. This paper presents an overview of the aerodynamic aspects of flight testing, the area which was chosen for the proof of concept phase and was utilized extensively on the experimental aircraft programme. The techniques developed and methods employed are discussed in more detail and examples of the achievements are given. The lessons learnt from the proof of concept phase are reviewed and the implementations of the concept on current major projects are briefly outlined.
An isothermal experimental investigation of turbulence transport through an abrupt axisymmetric expansion
Authors: Ahmed S A
Published: October 2002

A non-intrusive, two-component laser Doppler velocimeter was employed to measure the flow properties of a confined, isothermal, swirling flowfield in an axisymmetric sudden expansion research combustor. A constant angle swirler was used to stir the flow at the inlet of the combustor. Measurements of mean velocities, Reynolds stresses and triple products were carried out at axial distances ranging from 0.38 H (step height) to 18 H downstream of the swirler. Detailed experimental data are provided to help in the understanding of the behaviour of swirling, recirculating, axisymmetric and turbulent flows. Also, these detailed experimental data will be available for upgrading advanced numerical codes. The turbulent kinetic energy terms, convection, diffusion and production, were computed directly from the experimental data using central differencing, while the dissipation term was obtained from an energy balance equation. The swirling flow data are compared with the simple dump flow in the same experimental arrangement and it is shown that swirl enhances the production and distribution of turbulence energy in the combustor which, in turn, indicates thorough flow mixing and earlier flow recovery.
Aerodynamic modelling of multistage compressor flow fields Part 2: Modelling deterministic stresses
Authors: Hall E J
Published: October 2002

The primary purpose of this study was to investigate improved numerical techniques for predicting flows through multistage compressors. The vehicle chosen for this study was the Pennsylvania State University Research Compressor (PSRC). The PSRC facility consists of a 3 1/2-stage axial flow compressor which shares design features which are consistent with embedded stages of modern gas turbine engine axial flow compressors. In Part 2 of this two-part paper, time-dependent predictions of rotor- stator-rotor aerodynamic interactions are employed to quantify the levels and distribution of deterministic stresses resulting from the average-passage flow field description. Details of the spanwise and blade-to- blade distributions of the velocity correlations are examined and compared with results based on physical deterministic flow structures such as blade wakes and clearance flows. The predicted ‘apparent’ wake profile decay resulting from the interaction of the wake through a downstream blade row is presented and compared with test data. This ‘apparent’ wake profile decay is employed to define a simplified model for deterministic stress correlations in a steady state flow field prediction scheme which retains the ‘mixing- plane’ methodology. Calculations based on this proposed model are described and predicted results are compared with both time-dependent predictions and test data. The resulting prediction strategy is computationally efficient and also contains sufficient physical realism to permit its use in design studies.
Mathematical networks for thermal transient and non-transient progressive fatigue of engine components
Authors: Azzam H
Published: October 2002

Engine components can experience varying centrifugal loads, gas loads, oxidation, micro- structure transformation at high temperatures and stresses induced by temperature gradients. The life consumption of hot engine components depends not only on these factors but also on the time spent at constant-amplitude loads. The damage mechanism of engine components is therefore complex and requires formidable models. These models are not suitable for fatigue management or on-board systems because of their high computational costs. There is a need for efficient simulations that can accurately portray this complex damage mechanism and, at the same time, can be embedded in fatigue management and on-board systems. Mathematical networks were developed to fulfil this need and successfully synthesized the fatigue damage of aircraft structural components from flight parameters. In this paper, the feasibility of training the mathematical networks to synthesize fatigue of engine components is demonstrated. The mathematical attributes of the networks were based on information supplied by Rolls-Royce. The networks’ training mechanism was targeted at the minimization of errors in synthesized accumulative damage values. The mathematical networks synthesized the accumulative fatigue damage of three engine components successfully. One component was subject to non-thermal transient stresses and two components were subject to thermal transient stresses.
Risk aspects of a mission to a comet
Authors: Turner R F
Published: October 2002

Space science missions are rarely a repeat of a predecessor and thus in the wider view they do not have the benefit of heritage-related statistics. This paper discusses the cost and risk factors in gaining access to space and describes the challenges of the forthcoming Rosetta mission, which has the objective of conducting studies of a comet and its increasing activity as it moves towards the sun. It will fly in formation with the nucleus and later send a lander to its surface to conduct in situ measurements. Reference will be made to the further challenges for the scientific instruments faced by an eight-year period of inactivity during the cruise phase after launch.

Statistics have a part to play at the component and unit test levels but are increasingly less relevant at instrument, spacecraft and mission levels. Ultimately the designer is faced with a string of single-point failure possibilities, commencing with the launch vehicle and culminating with the unknown surface conditions that will greet the lander.
Analysing crack growth
Authors: Newby M
Published: October 2002

Deterministic models of crack growth can be fitted to experimental data. This paper shows that stochastic growth models are easy to use and provides a simple framework for data analysis. A simple transformation allows the standard linear regression model to be used and opens the way for a fully Bayesian analysis. The Bayesian analysis allows the incorporation of prior information and coherent predictions of crack length to be made. The parameters of the Paris-Erdogan model are readily evaluated directly from crack length data without the need for intermediate estimates of the crack growth rate. The approach lends itself to the analysis of properly designed experiments to determine the effect of environmental factors on the parameters of the Paris-Erdogan equation through the medium of accelerated failure time models. The paper also emphasizes the need for adequate communication between experimenter and statistician to ensure efficient experimental designs.
Probability and statistics in engineering design
Authors: Taylor J
Published: October 2002

This paper examines two methods of designing and manufacturing a product. The paper will outline what will be referred to as the tolerancing method of design and compare this to an alternative approach, which uses manufacturing process data. An argument will then be put forward for the use of the alternative approach by outlining the benefits.
Non-stationary compressible flow in ducts with varying cross-section
Authors: Igra O , Wang L , Falcovitz J
Published: October 2002

A comparative study of the interaction of shock wave or rarefaction wave with a converging duct separating long constant cross-section segments is presented. Quasi-one-dimensional computations are compared with fully two-dimensional computations. It is observed that in some cases the two-dimensional results approach the respective one-dimensional approximations over long times, while in other cases the two-dimensional computed flow is genuinely two-dimensional and cannot be reduced to a one-dimensional equivalent. In the latter cases, significant errors are incurred by analysing the flow using the quasi-one- dimensional duct flow approximation.
Impact damage in composite aircraft structures-experimental testing and numerical simulation
Authors: Zhang X
Published: October 2002

This paper describes a strategy for predicting internal damage in a laminated composite structure, when subjected to low-velocity impact. The aim was to obtain a better understanding of and cure for the notorious reduction in strength of aircraft compression panels when they suffered barely visible impact damage (BVID). A finite element model is presented which incorporates the non-linear behaviour due to gross deformation, interlaminar delamination and in-plane fibre and matrix failure. The strategy is validated by impact tests for a wide range of carbon/epoxy composite structures ranging from small stiff plates to realistic aircraft compression panels. It is demonstrated that the finite element model is capable of predicting impact damage in laminated composite structures and thus could be used as a design tool.
Essentially non-oscillatory schemes for the Euler equations on unstructured meshes
Authors: Zamecnik M , Hernández J A
Published: October 2002

A numerical scheme to solve the two-dimensional Euler equations around aerodynamic profiles is presented. The space domain is discretized by an unstructured mesh where triangular elements are used. The scheme uses a first- and a second-order finite volume method where evolution equations for the mean values are obtained at each cell. The first-order approximation is obtained by a constant approximation at each cell while the second-order approximation is obtained by a linear ENO (essentially non-oscillatory) polynomial. Fluxes at cell interfaces are determined using an approximate solver for the Riemann problem. The solution of the Riemann problem introduces the upwind characteristic of the scheme.

In this paper, particular emphasis is placed on the determination of fluxes at every cell interface, obtaining a compact expression for the resolution on unstructured meshes. The Burgers equation is analysed as a typical scalar case, and it is shown how the vectorial Riemann problem in unstructured meshes can be reduced to four scalar problems along four directions of propagation. This paper also shows how the use of a preconditioned technique based on local time step improves the convergence to the steady state solution. An anomalous behaviour in the convergence of the residuals in a second-order scheme is observed and it is related to the shock structure and the spatial approximation. Transonic and subsonic test cases of aerodynamic profiles are simulated as an application to advanced aerodynamic design.
Optimal sensor location for robust fault detection filter
Authors: Kim D , Kim Y
Published: October 2002

A fault detection filter is a full-order observer that can detect and isolate faults by constraining the residual vector due to a particular fault in a certain detection space. It is known that different faults can be perfectly isolated by designing a fault detection filter when a mutual isolability condition is satisfied. This paper discusses such a property in detail, considering the transmission zero in conjunction with the location and combination of sensors. Guidelines to choose the sensor location which enables the stable mutual isolation of different faults are proposed. Numerical results show that the fault detection filter with this sensor location is robust in the sense that it has minimal sensitivity to measurement noise.
Effect of motor length and propellant formulation on nozzleless solid rocket performance
Authors: Krishnan S , Ramakrishnan Rajesh
Published: October 2002

Experimental results are presented for four nozzleless motors of different length-diameter ( L/D) ratios using two different composite propellants. The experimental observations discussed are: the premature unchoking in motors of insufficient L/D ratios and the tendency for the propellant to extinguish under highly negative pressure gradient environment, both peculiar to nozzleless operation. A simple one- dimensional numerical scheme is presented to predict the performance of a nozzleless solid motor. Erosive burning, elastic grain deformation and L/D ratio-dependent combustion efficiency are considered in the scheme. A relatively simple procedure is followed to account for the coupling effect between port gas dynamics and elastic grain deformation. The experimental results are compared with those predicted by the numerical scheme. The predictions are in reasonable agreement with the experimental values. For a composite propellant the burning rate index n can significantly vary with respect to pressure. The application of this fact plays a very important role in accurately predicting the thrust-time trace of nozzleless motors.
A non-linear adaptive guidance algorithm for last-stage launcher control
Authors: Teofilatto P , De Pasquale E
Published: October 2002

On-line adaptive guidance algorithms are currently difficult to implement since algorithms involving trial and error are needed to solve the two-point boundary value problems related to the optimization process. These routines may require an unpredictable number of iterations to converge to a solution; moreover convergence itself cannot be assured a priori. This problem can be circumvented by linearizing the control strategy about the nominal trajectory. However, since the system to be controlled is intrinsically non-linear, the linearization may have a limited accuracy.

In this paper an adaptive guidance method is presented which drives the launcher to the target in an optimal way even if the deviations from the nominal trajectory are so large that the variations of the guidance parameter become non-linear. The adaptive guidance proposed avoids iterative algorithms or convergence routines, shows good accuracy and a computational time suitable for current on-board computers.
Transient resonance of rolling finned projectiles
Authors: Ananthkrishnan N , Raisinghani S C , Pradeep S
Published: October 2002

Finned projectiles that are intentionally spun are known to become locked in at a resonance condition where the roll rate matches the pitch/yaw frequency. This phenomenon, called roll lock-in, results in an amplification of the trim angle, which can lead to yaw instability. A less severe phenomenon is that of transient resonance where the roll rate locks in at resonance briefly before continuing to build up to the design value. However, the trim amplification during the brief period of resonance may be sufficient to destabilize the projectile. In this paper, the problem of transient resonance for finned projectiles with a centre-of-mass asymmetry is studied. Numerical simulations are used to illustrate transient normal and reverse resonance. No yaw amplification is seen in both cases; rather the absolute value of the complex angle of attack shows a drop during passage through resonance. It is suggested that this is a general feature of the yaw response of finned projectiles undergoing transient resonance.
A universal dimensionless model for the MacCready sailplane theory
Authors: Gómez-Tierno M A , Martínez-García J J , García-Juliá E
Published: October 2002

An improvement of the MacCready speed-to-fly theory used in sailplanes cross-country flights is outlined. Two different parameters characterizing the thermal are introduced (the vertical speed of the air inside the thermal and the thermal radius) and a universal dimensionless model is proposed, which can be applied to any sailplane. The maximum average cross-country speed, the optimum airspeeds in descent and climb, the rate of climb in the helical trajectory and other flight variables are calculated versus two abbreviated parameters condensing thermal and sailplane data.
Computational fluid dynamics prediction of intake ingestion relevant to short take-off and vertical landing aircraft
Authors: Behrouzi P , McGuirk J J
Published: October 2002

Intake ingestion can cause several major problems (e.g. compressor surge and stall) for short take-off and vertical landing (STOVL) aircraft operating in ground effect. Numerical predictions of the flowfield associated with a generic twin-jet plus intake model operating under ingestion flow conditions are reported using computational fluid dynamics (CFD) techniques. The results have been compared with laser Doppler anemometry (LDA) validation measurements taken in a specially designed test case configuration. The k-ε turbulence model and both first-order and second-order (QUICK) convection discretization schemes were employed. Fine meshes and second-order accurate discretization were found essential to produce solutions close to grid independence. A reasonable prediction of the general flow pattern has been achieved. Several features of the mean velocity field were close to the experimental results; however, the k-ε model was shown to produce significant errors in the prediction of the forward penetration distance of the ground sheet flow and in the shape of velocity profiles and turbulence levels near to the intake.
The use of suction to suppress disturbances in laminar flow caused by insect and other surface debris
Authors: Eustace R , Barrett R V
Published: October 2002

Aircraft that employ extensive laminar flow for drag reduction need measures to counter the potential breakdown to turbulence caused by surface debris picked up near the ground. Decontamination methods are being developed but may not be suitable where suction through microperforated skins is used to control the flow, owing to the likelihood of hole blockage. This paper examines an alternative, where the existing suction system is used to draw away the developing turbulent wedges behind individual particles, thus providing a degree of tolerance to surface contamination. A wind tunnel investigation was conducted, using a flat plate model with a configurable suction region, to simulate the essential features of the boundary layer on a laminar flow engine nacelle. This enabled the influence of the various flow and geometric parameters to be assessed. The results, taken at Reynolds numbers/m in the range 1.5-4.5 × 106, showed that turbulent wedges could be stabilized and removed, but that this required high levels of suction. The attendant increases in drag and suction system power make the method unattractive economically, although this situation would change if the increased suction could be applied only where required. The condition of self-induced transition at high suction flows was also investigated and was shown to limit the speed at which particle-induced turbulence could be suppressed.
The dynamics of an airborne towed target system with active control
Authors: Henderson J F , Potjewyd J , Ireland B
Published: October 2002

A fully three-dimensional computer simulation has been made of the dynamic behaviour of an airborne target towed by a tug aircraft via a cable, which has experienced problems in flight. The basic dynamics of the system are described and compared with the improvements that may be achieved both by passive modifications and by using active control of the target. The passive measures have been shown to have little significant effect, but active control, using tug/target relative velocity components for the error signal, has shown great improvement in the predicted behaviour.
A study of churning losses in dip-lubricated spur gears
Authors: Luke P , Olver A V
Published: October 2002

Churning losses contribute significantly, both to overall inefficiency and to oil heating, in many dip-lubricated transmission systems, notably in automotive applications. For this reason, a reasonably accurate estimate of churning loss is often desirable at the design stage. However, the published literature contains several empirical calculation methods that give widely different results, even within the claimed range of accuracy. For example, a single 72-tooth, 3 mm module spur gear rotating at 4500 r/min immersed in 20W50 motor oil to a depth of 54 mm would be predicted to exert a churning torque of 75 N m by the method of Boness but less than 5 N m by the method of Terekhov. In order to resolve the discrepancy, churning torques have been measured on a range of meshed and single spur gears with different speeds, lubricants and temperatures. Results are compared with the predictions from various literature sources.
Automated visual inspection of dry carbon-fibre reinforced composite preforms
Authors: Mitchell T A , Bowden R , Sarhadi M
Published: October 2002

A vision system is described which performs real-time inspection of dry carbon-fibre preforms during lay-up, the first stage in resin transfer moulding (RTM). The position of ply edges on the preform is determined in a two-stage process. Firstly, an optimized texture analysis method is used to estimate the approximate ply edge position. Secondly, boundary refinement is carried out using the texture estimate as a guiding template. Each potential edge point is evaluated using a merit function of edge magnitude, orientation and distance from the texture boundary estimate. The parameters of the merit function must be obtained by training on sample images. Once trained, the system has been shown to be accurate to better than ±1 pixel when used in conjunction with boundary models. Processing time is less than 1 s per image using commercially available convolution hardware. The system has been demonstrated in a prototype automated lay-up cell and used in a large number of manufacturing trials.
Experiments with CHRELMS patient-driven stimulator controllers for the restoration of function to paralysed legs
Authors: Donaldson N , Yu C-h
Published: October 2002

This paper examines the control of electrical stimulators for restoring the standing function to paraplegics. Patient-driven controllers are based on the knowledge that standing, using support handles, is guided by the neurologically intact natural motor control system, acting through the arms. One category of patient-driven controller is CHRELMS (Control by Handle Reactions of Leg Muscle Stimulation). The first experiments with patient-driven controllers are reported. Experiments in the CHRELMS control of one volunteer are described. Proportional control did not allow the subject to stand up because of the strategy he used, but integral control was successful. With it, he could stand up and sit down slowly, entirely guided by himself, as well as making other manoeuvres. Without changing controller mode, and by leaning forwards and backwards, he could ‘posture switch’ his support muscles. These are significant achievements and justify a larger study of patient-driven controllers. The subject's control strategies are discussed.
Boundary lubrication in vivo
Authors: Hills B A
Published: October 2002

Evidence is reviewed for the concept that the body employs essentially the same lubrication system in many sites in the body where tissues slide over each other with such ease. This system consists of fluid adjacent to surfaces coated with an oligolamellar lining of surface-active phospholipid (SAPL) acting as a back-up boundary lubricant wherever the fluid film fails to support the load—a likely event at physiological velocities. Particular attention is paid to the load-bearing joints, where the issue of identifying the vital active ingredient in synovial fluid is reviewed, coming down—perhaps predictably—in favour of SAPL. It is also explained how Lubricin and hyaluronic acid (HA) could have ‘carrier’ functions for the highly insoluble SAPL, while HA has good wetting properties needed to promote hydrodynamic lubrication of a very hydrophobic articular surface by an aqueous fluid wherever the load permits.

In addition to friction and wear, release is included as another major role of boundary lubricants, especially relevant in environments where proteins are found, many having adhesive properties. The discussion is extended to a mention of the lubrication of prosthetic implants and to disease states where a deficiency of boundary lubricant is implicated, particular attention being paid to osteoarthritis.
Studies of cardiac function and myocardial tissue characterization
Authors: Bom N , van der Steen A F W , Nosir Y F M
Published: October 2002

The heart can be studied using ultrasound techniques. The shape of the heart, its chambers, wall thicknesses, wall tissue characteristics as well as motion of walls and valve leaflets are all diagnostic information. In addition, the blood velocity and its timing within the cardiac cycle is an important diagnostic tool. In the present paper focus will be limited to the analysis of the left ventricular function as observed with two-dimensional and three-dimensional echocardiography and the characteristics of backscattered ultrasound information from the left ventricular chamber wall. Function of the heart is often studied by observation of local wall motion or comparison of chamber volume in maximum and minimum shapes during the cardiac cycle (ejection fraction). Integrated backscatter from the wall is described in examples of cardiac transplantation and hypertrophy. Study of cyclic variation of frequency-dependent attenuation and integrated backscatter indicates that these are independent parameters.
A study on dental vacuum system losses
Authors: Moutsoglou A , Han Y
Published: October 2002

An experimental study was conducted to document system head losses for dental vacuum systems. Experiments were performed to estimate pressure losses and pressure loss coefficients for pertinent dental treatment room hoses and fittings in high-volume evacuation systems. Pressure losses for some polyvinyl chloride (PVC) elbows used in dental plumbing systems were also measured and presented. Friction head losses in straight PVC piping are calculated and documented in graphical form. Calculated values for friction losses are found to correlate exceptionally well with measured experimental data.
Performance tests of vacuum pumps in small and large dental facilities
Authors: Moutsoglou A , Weng Y , Han Y
Published: October 2002

A study was conducted to compare and assess the performance of various vacuum pumps in small and large dental clinic operations. A four-chair dental clinic operation was set up at the laboratory to simulate a small dental clinic environment. The performance of two dry and two wet pumps was assessed in the laboratory via extensive performance data acquisition tests. Data were also collected in two small dental clinics of practising dentists. Large dental system performance tests were conducted at the Ellsworth Air Force Base and Minot Air Force Base dental clinics. At each clinic, data were collected with both the existent turbine pump and a rotary vane RAMVAC pump.
Investigation into the tribological condition of acetabular tissue after bipolar joint replacement hip surgery
Authors: Pickard J , Fisher J , Ingham E , Egan J , Hallett J
Published: October 2002

The aim of this research was to investigate the tribological condition of acetabular tissue before and after bipolar hip surgery. Articular cartilage was taken from the femoral head of patients undergoing primary joint replacement as a control. Tissue was also taken from the acetabular cups of patients undergoing revision hip surgery after primary bipolar surgery and compared with the control cartilage.

The biomechanical characteristics of the two tissue types were tested using friction and compression tests. The friction tests were carried out on a sliding friction rig under nominal contact stresses of 0.5 and 4 MPa. The compression tests were carried out under a 0.8 MPa contact stress.

The majority of the bipolar patients produced friction coefficients that were significantly higher than those produced by the control group, and the compression tests highlighted that the tissue from the bipolar patients produced a much greater rate of increase in displacement compared with the control cartilage. Histology showed major differences between the control cartilage and the bipolar tissue. The control cartilage showed a healthy collagen structure with a good distribution of proteoglycan whereas the majority of the bipolar tissue had lost tissue architecture and had a sparse fibrous structure.

The high friction coefficients with the bipolar tissue imply that the frictional torque at the outer head of the bipolar prosthesis would be large compared with the inner bearing frictional torque. It was therefore predicted that the motion of the bipolar prosthesis should occur at the inner bearing.
Design of spinous process hooks for flexible fixation of the lumbar spine
Authors: Leahy J C , Mathias K J , Heaton A , Shepherd D E T , Hukins D W L , Deans W F , Brian M W , Wardlaw D
Published: October 2002

A prototype flexible fixation system for the lumbar spine was subjected to tensile testing to failure and cyclic tensile testing in order to determine any regions of weakness. The system consisted of a spinous process hook and two laminar hooks made of stainless steel (316L). Each laminar hook was attached to the spinous process hook by a loop of polyester braid secured by a crimped metal sleeve. In five tensile tests, the system failed by irreversible deformation of the spinous process hook at 2.5 ° 0.3 kN (mean ° standard deviation). In three cyclic tests, in which the applied tension varied sinusoidally between 0.04 and 0.4 kN at a frequency of 5 Hz, failure occurred after less than 400000 loading cycles. This occurred as a result of fatigue crack initiation and propagation in the spinous process hook. A finite element model showed a stress concentration in the region where the crack occurred, which raised the applied stress above the tensile fatigue strength of this stainless steel. The spinous process hook was redesigned for manufacture in a titanium alloy (Ti-6Al-4V ELI) to minimize artefacts in magnetic resonance imaging. Further finite element models showed no unacceptable stress concentrations.
Mechanical testing of a flexible fixation device for the lumbar spine
Authors: Leahy J C , Mathias K J , Hukins D W L , Shepherd D E T , Deans W F
Published: October 2002

The aim of this study was to test mechanically a new flexible fixation system for the lumbar spine. This device incorporates loops of polyester braid which are secured by a crimped titanium sleeve. In tensile tests, all loops failed, by slippage through the crimped sleeve, at 434 ± 15 N (mean ± standard deviation from five loops) for a single crimp and 415 ± 15 N (from five loops) for two crimps. The intact system was then tested according to the ASTM standard. In a static test, all five specimens failed by slippage of the braid through the sleeve. Initial slippage occurred between 600 and 700 N, but the mean maximum load sustained was 1090 ± 140 N. Dynamic tests were performed on ten constructs at a frequency of 5 Hz, under a range of loading conditions. The maximum load applied in any of the tests was 825 N. Two constructs did not complete the required 5 × 106 test cycles because of fracture of their spinous process hooks. However, other tests, under the same conditions, showed no signs of failure. Fracture occurred as a result of fretting damage from the recommended stainless steel roll pins.