bluuebunny/crossref_metadata_2025 huggingface dataset:
Impairment of synaptic development in the hippocampus of diabetic Goto‐Kakizaki rats
Authors: Matsunaga Yuki , Negishi Takayuki , Hatakeyama Akinori , Kawagoe Yuta , Sawano Erika , Tashiro Tomoko
Published: July 2016

Insulin receptor signaling has been shown to regulate essential aspects of CNS function such as synaptic plasticity and neuronal survival. To elucidate its roles during CNS development in vivo, we examined the synaptic and cognitive development of the spontaneously diabetic Goto‐Kakizaki (GK) rats in the present study. GK rats are non‐obese models of type 2 diabetes established by selective inbreeding of Wistar rats based on impaired glucose tolerance. Though they start exhibiting only moderate hyperglycemia without changes in plasma insulin levels from 3 weeks postnatally, behavioral alterations in the open‐field as well as significant impairments in memory retention compared with Wistar rats were observed at 10 weeks and were worsened at 20 weeks. Alterations in insulin receptor signaling and signs of insulin resistance were detected in the GK rat hippocampus at 3 weeks, as early as in other insulin‐responsive peripheral tissues. Significant reduction of an excitatory postsynaptic scaffold protein, PSD95, was found at 5 w and later in the hippocampus of GK rats due to the absence of a two‐fold developmental increase of this protein observed in Wistar control rats between 3 and 20 w. In the GK rat hippocampus, NR2A which is a NMDA receptor subunit selectively anchored to PSD95 was also reduced. In contrast, both NR2 B and its anchoring protein, SAP102, showed similar developmental profiles in Wistar and GK rats with expression peaks at 2 and 3 w. The results suggest that early alterations in insulin receptor signaling in the GK rat hippocampus may affect cognitive performance by suppressing synaptic maturation.
Sympathy for Whom? Smith's Reply to Hume
Authors: MULLER HANS D.
Published: July 2016

This essay presents a critical examination and development of an exchange between Adam Smith and David Hume on the nature of sympathy. I identify four objections to Smith's account in a letter from Hume and then argue that Smith's system has the resources to reply to all of them. As such, this essay shows that Smith's system provides a more robust foundation for a sentiment-based system of ethics than has been traditionally recognized.
How Valuable Could a Material Object Be?
Authors: BAILEY ANDREW M. , RASMUSSEN JOSHUA
Published: July 2016

Arguments for substance dualism—the theory that we are at least partly nonmaterial beings—abound. Many such arguments begin with our capacity to engage in conscious thought and end with dualism. Such are familiar. But there is another route to dualism. It begins with our moral value and ends with dualism. In this article, we develop and assess the prospects for this new style of argument. We show that, though one version of the argument does not succeed, there may yet be a deep problem for standard physical accounts of our nature.
Air entrainment and bubble statistics in breaking waves
Authors: Deike Luc , Melville W. Kendall , Popinet Stéphane
Published: July 2016

We investigate air entrainment and bubble statistics in three-dimensional breaking waves through novel direct numerical simulations of the two-phase air–water flow, resolving the length scales relevant for the bubble formation problem, the capillary length and the Hinze scale. The dissipation due to breaking is found to be in good agreement with previous experimental observations and inertial scaling arguments. The air entrainment properties and bubble size statistics are investigated for various initial characteristic wave slopes. For radii larger than the Hinze scale, the bubble size distribution, can be described by $N(r,t)=B(V_{0}/2{\rm\pi})({\it\varepsilon}(t-{\rm\Delta}{\it\tau})/Wg)r^{-10/3}r_{m}^{-2/3}$ during the active breaking stages, where ${\it\varepsilon}(t-{\rm\Delta}{\it\tau})$ is the time-dependent turbulent dissipation rate, with ${\rm\Delta}{\it\tau}$ the collapse time of the initial air pocket entrained by the breaking wave, $W$ a weighted vertical velocity of the bubble plume, $r_{m}$ the maximum bubble radius, $g$ gravity, $V_{0}$ the initial volume of air entrained, $r$ the bubble radius and $B$ a dimensionless constant. The active breaking time-averaged bubble size distribution is described by $\bar{N}(r)=B(1/2{\rm\pi})({\it\epsilon}_{l}L_{c}/Wg{\it\rho})r^{-10/3}r_{m}^{-2/3}$, where ${\it\epsilon}_{l}$ is the wave dissipation rate per unit length of breaking crest, ${\it\rho}$ the water density and $L_{c}$ the length of breaking crest. Finally, the averaged total volume of entrained air, $\bar{V}$, per breaking event can be simply related to ${\it\epsilon}_{l}$ by $\bar{V}=B({\it\epsilon}_{l}L_{c}/Wg{\it\rho})$, which leads to a relationship for a characteristic slope, $S$, of $\bar{V}\propto S^{5/2}$. We propose a phenomenological turbulent bubble break-up model based on earlier models and the balance between mechanical dissipation and work done against buoyancy forces. The model is consistent with the numerical results and existing experimental results.
On the peculiar structure of a helical wake vortex behind an inclined prolate spheroid
Authors: Jiang Fengjian , Andersson Helge I. , Gallardo José P. , Okulov Valery L.
Published: July 2016

The self-similarity law for axisymmetric wakes has for the first time been examined and verified in a complex helical vortex in the far part of an asymmetric wake by means of direct numerical simulation (DNS). The helical vortex is the main coherent flow structure in the transitional non-axisymmetric wake behind an inclined 6:1 prolate spheroid at Reynolds number 3000 based on the minor axis. The gradual development of the complex helical vortex structure has been described in detail all the way from its inception at the spheroid and into the far wake. We observed a complex vortex composition in the generation stage, a rare jet-like wake pattern in the near wake and an abrupt change of helical symmetry in the vortex core without an accompanying change in flow topology, i.e. with no recirculation bubble.
Air–to–ground weapon aiming — a synopsis and a look to the future
Authors: Edwards K. L. , Lloyd S. J. , Ralph J. F.
Published: July 2016

A review of air–to–ground weapon aiming is given, with emphasis placed on the use of the head–up display (HUD), the main cockpit instrument used for accurate weapon aiming over the last 35 years. Nevertheless, the HUD is only of use for the aiming of forward–firing weapons. More advanced weapons have an off–axis capability and their aiming is greatly facilitated by the use of a helmet-mounted sight (HMS) or helmet–mounted display (HMD). The surface–to–air threat and the rules of engagement, particularly in operations other than war, place high demands on the aircrew and the weapon aiming system, both to stand off from the target and to have a high degree of confidence that it is the target. The requirement to perform an accurate in–flight transfer alignment of the weapon places further demands upon the aircrew. Timely and accurate target data, digitally received, plus an on–board targeting system which can automatically search for and recognise a target, are of great utility in the final stages prior to weapon release. The Defence Evaluation and Research Agency is performing research in these areas.
Trajectory tracking for a helicopter model
Authors: Avanzini G.
Published: July 2016

In this paper an algorithm for the trajectory tracking of a three-dimensional trajectory, assigned as a function of time, is presented. The proposed control system is suitable for application on unmanned aerial vehicles (UAVs) or for aircraft that require accurate path tracking, as in the case of rotorcraft in nap-of-the-earth (NOE) flight conditions. The control system logic features (i) an external loop based on a simple guidance scheme and a two-time-scale inverse simulation algorithm, and (ii) an inner loop, based on a linear-quadratic (LQ) full-state-feedback controller. In this way the control action is split into two contributions, i.e. a feedforward command, in order to follow the trajectory generated by the guidance scheme, and a feedback increment, for compensating external disturbances and model uncertainties. A rotorcraft model is used to demonstrate the algorithm capability in a NOE–like flight task. System robustness is analysed and control system performance are discussed in terms of the error between vehicle state and desired trajectory at a given time. Simulation of a representative manoeuvre shows that the feedforward estimate of the control action is accurate and only minor compensation is required from the LQ tracker. The algorithm is suitable for a number of applications, as (i) no simplifying assumptions are postulated for the model, (ii) there are no restrictions on the flight condition, and (iii) the computational time should allow for real–time implementation.
Life extending controller design for reusable rocket engines
Authors: Ray A. , Holmes M. S. , Lorenzo C. F.
Published: July 2016

The goal of life extending control (LEC) is to enhance structural durability of complex mechanical systems, such as aircraft, spacecraft, and energy conversion devices, without incurring any significant loss of performance. This paper presents a concept of robust life-extending controller design for reusable rocket engines, similar to the Space Shuttle Main Engine (SSME), via damage mitigation in both fuel and oxidiser turbines while achieving the required performance for transient responses of the main combustion chamber pressure and the oxidant/fuel mixture ratio. The design procedure makes use of a combination of linear robust control synthesis and nonlinear optimisation techniques. Results of simulation experiments on the model of a reusable rocket engine are presented to this effect.
Simulating the evacuation of a commercial airliner
Authors: Robbins C. R. , McKee S.
Published: July 2016

The discrete element method is modified so as to simulate the movement of passengers evacuating an aircraft. The results display reasonable agreement with timed trials. However, by focusing on the 1985 Manchester air disaster where only some of the exits could be opened and only then a considerable time after landing, it is argued that the certification procedures are inadequate.
The application of Pareto methods to multidisciplinary design optimisation
Authors: Harris J. C. , Fenwick S. V.
Published: July 2016

Multidisciplinary design optimisation (MDO) provides a framework for the timely exchange of data necessary to support the highly integrated tasks typical of aerospace design. This will help reduce the duration of the design cycle and improve efficiency of the final product. Well implemented MDO capabilities will play an increasingly important role in DERA's activities to support the definition of future system requirements and the assessment of new equipment.

The framework in which an MDO approach is realised must be flexible and accommodate the diverse range of individual discipline-based tools that contribute to the overall process. This paper describes DERA's activity within the EC Framework IV ‘FRONTIER’ project to investigate the use of modern graphical user interface (GUI) methods and genetic algorithms (GAs) for the combined aerodynamic and structural design of a modern combat aircraft. The application of the techniques to identify a Pareto frontier in high level design objective space that represents the boundary beyond which improvements cannot be made without sacrificing one or other aspect of overall aircraft performance is described. The scope of the methods as an aid during the definition of system requirements and for the evaluation of trade-offs during the concept assessment stage of a project is discussed.
QUACC, a novel method for predicting unsteady flows — including propellers and store release
Authors: Hunt D. L. , Childs M. , Maina M.
Published: July 2016

Aerospace designers are increasingly interested in predicting unsteady flowfields such as those associated with store release, rotating propellers etc. However, the cost of performing fully unsteady calculations is usually prohibitively expensive. In order to address this problem for unsteady flows driven by a moving surface, a novel method is presented which calculates the time derivates as an analytic function of the instantaneous flowfield. This allows an accurate solution of the unsteady flow equations to be calculated using a quasi-unsteady approach. The validity of this approach is demonstrated for a store release and a propeller test case. Possible extensions to this method for more complex unsteady flows are presented.
A strategic European approach to aerodynamics research, technology and development
Authors: Dexter P.C.
Published: July 2016

In spite of the best intentions of many national and international funding agencies, much of the research and technology development (RTD) activity undertaken in Europe over the past few years has often been duplicating the work of others and has not resulted in an increase in capability in key areas. This is not to denigrate the work that has been undertaken — but have we done the right work? The EC-funded Thematic Network ‘Targeted Research Action in Aerospace Aerodynamics’, (TRA3), has been initiated with the broad aims of improving collaboration between existing EC- supported projects and, more importantly, attempting to put in place a long-term strategy for European aerospace aerodynamics RTD. TRA3 is, amongst other things, attempting to answer three key questions:

• What are the important aerodynamic technologies?

• What is the European aerospace industry’s current capability in these areas?

• In which areas should Europe be investing to maintain a competi tive aerodynamics capability?

The major benefit and output expected from TRA3 is the creation of a co-ordinated European aerodynamics RTD programme. The TRA3 Management Board consists of seven people who represent a cross-section of the European aerospace industry and research establishments, together with a Project Officer from the European Commission. This Management Board is tasked with formulating long-term plans for nine ‘Key Technology Areas’ that encompass all of the important aerodynamic technologies. This paper outlines the progress that has been made in meeting the very ambitious initial aims of the demanding work programme.
Experimental and numerical Investigation of wind tunnel wall interference near Mach one
Authors: Mokry M. , Khalid M. , Mébarki Y. , Rebaine A.
Published: July 2016

Surface pressure measurements on the CAST-10-2/DOA 2 aerofoil, conducted in the IAR l.5m wind tunnel and supported by CFD simulations, are used to validate some new theoretical analyses of transonic wall interference. Based on the transonic freeze principle, it is shown that the stream Mach number correction is indeterminate near Mach one.
On (civil) aviation future(s)
Authors: Bushnell D. M.
Published: July 2016

This is the latest in the series of invited survey articles and has been written in his own imimitable style by Dennis Bushnell, Chief Scientist at the NASA Langley Research Center. Dennis is well known for his far-sighted and often controversial views. He gave the 1998 Wilbur and Orville Wright lecture at the Royal Aeronautical Society and an edited abbreviation of that talk was published in the January 1999 issue of Aerospace International. In this paper Dr Bushnell amplifies and extends the vision of his earlier work. We arc delighted to publish his forecast for civil aviation and would welcome any comments on the projects described.

John Stollery, Editor
Aeroservoelastic simulation by time-marching
Authors: Djayapertapa L. , Allen C. B.
Published: July 2016

The coupling of independent structural dynamic and inviscid aerodynamic models, in the time domain, is considered. The accuracy and CPU requirements of the two common approaches, namely ‘weak’ and ‘strong’ coupling procedures, are investigated. It is found that the strong coupling scheme is more accurate than the weak coupling approach, and only for large real time-steps is the strong coupling scheme more expensive. The computational method developed is used to perform transonic aeroelastic and aeroservoelastic calculations in the time domain, and used to compute stability (flutter) boundaries of 2D wing sections. A control law is implemented within the aeroelastic solver to investigate active means of flutter suppression via control surface motion. Comparisons of open and closed loop calculations show that the control law can successfully suppress the flutter and results in a significant increase in the allowable speed index in the transonic regime. The effect of structural nonlinearity, in the form of hinge axis backlash is also investigated. The effect is found to be destabilising, but the control law is shown to still alleviate the destabilising effect.
A new moving-boundary algorithm with application to SRM internal ballistics
Authors: Karimian S. M. H. , Amoli A.
Published: July 2016

In this paper a new moving-boundary algorithm is presented for the solution of two-dimensional flows on unstructured grids. Application of this algorithm is investigated by simulating the internal ballistics of solid rocket motors (SRM). Solution domain is discretised to a number of triangular elements using control-volume based finite-element (CVFE) method. Euler equations are integrated over the control volumes, and Roe's flux-difference scheme is used to evaluate flux vectors at the control-volume surfaces. To eliminate numerical errors due to grid movement, geometric conservation laws (GCL) are carefully implemented. The present algorithm recognises locations along the moving boundaries where the stretched elements result in a distorted grid. To avoid this, new elements are inserted through a local re-triangulation of elements in these regions. Internal ballistics of three SRMs with cylindrical grains burning from inside, are numerically simulated. Using a heat transfer model, erosive burning is included in calculation of propellant burning rate. The aftend of third SRM is tapered to demonstrate capability of present algorithm in solving problems with moving boundaries approaching each other. Very good agreement is observed between the time variations of head-end chamber pressure, obtained from the present work and the other methods.
The design of fly-by-wire flight control systems
Authors: Fielding C.
Published: July 2016

The design of an advanced flight control system (FCS) is a technically challenging task for which a range of engineering disciplines have to align their skills and efforts in order to achieve a successful system design. This paper presents an overview of some of the factors which need to be considered and is intended to serve as an introduction to this stimulating subject. Specific aspects covered are: flight dynamics and handling qualities, mechanical and fly-by-wire systems, control laws and air data systems, stores carriage, actuation systems, flight control computer implementation, flexible airframe dynamics, and ground and flight testing. The flight control system challenges and expected future developments are reviewed and a comprehensive set of references is provided for further reading.
Fuzzy modelling for aircraft dynamics identification
Authors: Mengall G.
Published: July 2016

A new methodology is described to identify aircraft dynamics and extract the corresponding aerodynamic coefficients. The proposed approach makes use of fuzzy modelling for the identification process where input/output data are first classified by means of the concept of fuzzy clustering and then the linguistic rules are extracted from the fuzzy clusters. The fuzzy rule-based models are in the form of affine Takagi-Sugeno models, that are able to approximate a large class of nonlinear systems. A comparative study is performed with existing techniques based on the employment of neural networks, showing interesting advantages of the proposed methodology both for the physical insight of the identified model and the simplicity to obtain accurate results with fewer parameters to be properly tuned.
Integrated air data sensors
Authors: Menzies M. A.
Published: July 2016

Avionics Specialties in partnership with Honeywell has developed an integrated air data pressure sensor known as the integrated multi-function probe (IMFP). This continuously flow-aligned pressure-sensing device was developed using a multidisciplinary design approach encompassing computational fluid dynamic, (CFD), flow analysis, and experimentation. The computational investigation was performed using the finite element code, CFDesign, by Blue Ridge Numerics and consisted of pressure distribution studies for varying flows around conical sections. The application and integration of this technology to previously developed flow alignment and pressure transducing products lead to design similarity analysis saving considerable development time. Initial experimentation used to develop and refine the design and analysis consisted of laboratory bench testing, low and high-speed wind tunnel investigations, and subsonic flight-testing. Final performance verification was accomplished through data reduction and analysis of an extensive flight test program using a Lockheed Martin F-16 Fighting Falcon. The analysis, design and performance verification of this innovative pressure-sensing device was investigated for direct comparison to conventional Pitot-static performance with particular emphasis toward military fighter aircraft applications.
The world of regional aircraft — challenges and opportunities
Authors: Summerfield P. H.
Published: July 2016

The regional air transport industry is slowly emerging from the ravages of a prolonged structural recession. Long term survival in an industry which has traditionally traded in one of the world's most aggressive market places, will impose enormous demands upon everyone involved. Those regional aircraft manufacturers and operators who are brave enough to take advantage of emerging technologies, adjust to new processes and develop highlyskilled and motivated people will be best equipped to meet the global demands of the marketplace in an ever-changing world.

The actions and achievements of Avro International Aerospace, a division of British Aerospace, with its Regional Avroliner family of aircraft provides an example through which to identify the key components in this process. The challenges facing the regional aircraft industry are identified, together with the resulting business opportunities and the significance of Government support, in order to draw appropriate conclusions with respect to the likely future of the industry.
Turbulence structure manipulation in a channel flow by outer layer devices
Authors: Iuso G.
Published: July 2016

An experimental study has been performed manipulating a fully developed turbulent channel flow, by means of blade manipulators known as outer layer devices (Olds). A large amount of investigation has been performed for boundary layer flow, whereas little research is available for internal flow manipulation. The influence on drag reduction for different configurations (single and tandem) and for some geometric parameters (distance from the wall and blade gap), have been analysed. Reynolds number effect has also been investigated. Some of the mechanisms involved in the skin friction reduction process are examined, in terms of time-space integral scales, Reynolds stresses and spectral analysis. Results show better efficiency for tandem configurations. These give high local skin friction reductions, up to 20%, which are strongly dependent on the manipulator distance from the wall, but have very little dependence on the blade gap and Reynolds number. Turbulence analysis displays reduced fluctuations in all three directions — as with space-time integral scales. Evidence of suppression for the large structures is also shown by spectral analysis. From a global balance it has been verified that no net drag reduction is obtained due to the additional drag introduced by the manipulators.
Airspace design: a conflict avoidance model emphasising pilot communication and perceptual capabilities
Authors: Fulton N. L.
Published: July 2016

Airspace is identified through well defined volumes of the Earth's atmosphere. Airspace control is defined to consist of rules and procedures by which aircraft conduct their flight and by which aircraft approach and cross volume boundaries. Airspace control should optimise the flow of traffic under the constraint that no collision occurs. To date, the design of airspace control has been largely heuristic. Two fundamentally opposed philosophies and designs have evolved over the last fifty years. There has been little, if any, formal comparison of the relative performance of these designs.

A new conceptual conflict-avoidance model is presented showing the need to maintain situational awareness for all conflicts. It reveals the essential requirement for communication channels in the conflict avoidance function. Human perceptual performance is related the required system response to conflict. These human factors can be mathematically related to physical parameters embodied in airspace rules and procedures. The impact of changes in airspace performance due to variations in physical parameters derived from models of the communication channels can now be measured. Use of the conflict-avoidance model presented in this paper identifies serious deficiencies in present designs and postulates that fundamental architectural changes are required to reduce safety hazards and produce designs of sufficient reliability, particularly for uncontrolled airspace. Designs based on stable and adequate communications are shown to be required and are now technologically feasible.
An Euler correction method for computing two-dimensional unsteady transonic flows
Authors: Das D. , Santhakumar S.
Published: July 2016

An Euler correction method is developed for unsteady, transonic inviscid flows. The strategy of this method is to treat the flow-field behind the shock as rotational flow and elsewhere as irrotational flow. The solution for the irrotational flow is obtained by solving the unsteady full-potential equation using Jameson's rotated time-marching finite-difference scheme. Clebsch's representation of velocity is followed for rotational flow. In this representation the velocities are decomposed into a potential part and a rotational part written in terms of scalar functions. The potential part is computed from the unsteady full potential equation with appropriate modification based on Clebsch's representation of velocity. The rotational part is obtained analytically from the unsteady momentum equation written in terms of Clebsch variables. This method is applied to compute the unsteady flow-field characteristics for an oscillating NACA 64A010 aerofoil. The results of the present calculation are found to be in good agreement with both Euler solution and experimental results.
Turbulence modelling for supercritical flows including examples with passive shock control
Authors: Sedaghat A. , Ackroyd J. A. D. , Wood N. J.
Published: July 2016

The aerodynamic performance of supercritical aerofoils at transonic speeds is strongly influenced by the shock wave-boundary-layer interaction. Passive shock control is one of the techniques used for controlling the undesirable effects of strong shock wave-boundary-layer interaction leading to extensive separation. Using passive shock control, the stall margin is increased and the onset of buffeting is delayed. Passive shock control is modelled by introducing a closed plenum chamber underneath a perforated surface at the foot of the shock wave where a combination of blowing and suction is generated. As a result, a strong normal shock wave is changed into a series of weak shock waves with lambda shape. Since the Baldwin-Lomax turbulence model has been used extensively for passive shock control modelling, which exhibits poor predictability for separated flows, an attempt has been made to modify the Reynolds normal stresses for this model so as to improve the accuracy of numerical results for flows with separation. Further modification to the Baldwin-Lomax model has been employed so that the mass transpiration effects are taken into account for the passive shock control computations. In this paper, a brief description on an implicit finite-volume TVD scheme in general coordinates is given and the details of the Balwin-Lomax turbulence model and its modifications are presented. The validated numerical results for several RAE 2822 aerofoil problems plus corresponding results for the modelled methods are presented and compared with some experimental data and other numerical results.
Combustion instability in a small liquid rocket motor
Authors: Osherov A. , Natan B.
Published: July 2016

An experimental investigation of high frequency combustion instability in a liquid rocket engine of 3kN thrust was conducted. The diagnostic method of detecting combustion instability was based on the measurement of the dynamic pressure following an artificial disturbance in the combustion chamber. Test data spectral analysis was performed by using the stochastic vibration data processing method. Although the engine has demonstrated an absence of tendency to spontaneous instability, insufficient stability of the original engine design was evident during tests with artificial triggers. A Helmholtz type resonator in form of partitioned cavities tuned to a few different, close frequencies was designed and installed in the combustion chamber wall to avoid spontaneous or triggered combustion instability. The experimental results from hot tests with artificial triggers confirmed the high efficiency of the applied acoustic resonator.
Aerodynamic simulation of heat shield separation test on ground
Authors: Chakraborty D. , Vasantha S.
Published: July 2016

The ability of a CFD technique to evaluate the performance of a heat shield separation system has been demonstrated. The evolution of the differential pressure across the heat shield surface has been estimated. The results of the analysis have been compared with the data from the separation test of the heat shield of an Indian launch vehicle. The pressure on the heat shield surface was estimated by solving the Navier Stokes equations using the Eulerian Lagrangian formulation. The results, which show good agreement with the observed results of a heat shield separation test on the ground, were found to be adequate for design purposes.
Tuning the axial singularity method for
accurate calculation of potential flow around
axisymmetric bodies
Authors: M. F. Zedan
Published: July 2016

The performance of axial line singularity methods has
been investigated systematically for various
solution parameters using carefully chosen test
cases. The results indicate that increasing the
number of elements and using stretched node
distribution improves the solution accuracy until
the matrix becomes near-singular. The matrix
condition number increases with these parameters as
well as with the order of intensity variation and
profile thickness. For moderate fineness ratios, the
linear methods outperform zero-order methods. The
linear doublet method performs best with control
points at the x-locations of nodes while the source
methods perform best with control points mid-way
between nodes. The doublet method has a condition
number an order of magnitude lower than the source
method and generally provides more accurate results
and handles a wider range of bodies. With
appropriate solution parameters, the method provides
excellent accuracy for bodies without slope
discontinuity. The smoothing technique proposed
recently by Hemsch has been shown to reduce the
condition number of the matrix; however it should be
used with caution. It is recommended to use it only
when the solution is highly oscillatory with a
near-singular matrix. A criterion for the optimum
value of the smoothing parameter is proposed.
A demonstration of the effect of the testing environment on unsteady aerodynamics experiments
Authors: Green R. B. , Galbraith R. A. McD.
Published: July 2016

The effects of windtunnel constraint during low speed unsteady aerodynamic experiments are assessed by comparing the data from two Naca 0015 models, one with a chord length of half the other. Ramp-up and ramp-down tests are considered, to distinguish between the effects of constraint upon separation and attachment. The unsteady separation process measured in terms of the normal force, pitching moment and stall vortex convection speed, is virtually unaffected by the difference in constraint between the two models, whereas the attachment process, assessed in terms of the normal force response and attachment behaviour, is sensitive to the size of the model.
A new approach to adaptive-wall windtunnel testing
Authors: Fakas E. , Bernstein L.
Published: July 2016

A technique is described whereby experiments may be conducted on models which are geometrically similar to only part of the full scale configuration with the windtunnel walls being contoured to simulate the flow over that part. In this way, higher spatial resolutions can be achieved in a windtunnel of moderate size. The method is demonstrated by studying the effects of tip geometry on the flow over a wing of aspect ratio 15 using a half wing model of chord 500 mm projecting 1031 mm into a test section of width 1200 mm.
An investigation of dynamic stall through the application of leading edge roughness
Authors: Green R.B. , Galbraith R.A.McD.
Published: July 2016

The dynamic stall characteristics of a NACA 0015 performing ramp-up motions are considered. Pressure data show the development and convection of structures at the leading and trailing edges, which indicate differing degrees of what are described as leading edge and trailing edge stall mechanisms. When a transition strip is placed at the leading edge, the characteristics of leading edge stall predominate, and the growth of the structure at the trailing edge is suppressed. In addition the stall vortex convection speed is observed to alter significantly, which is interpreted as a change in the vortex origin, size, strength and trajectory.
Constrained on-board attitude control using gas jet thrusters
Authors: Radice G. , Mclnnes C. R.
Published: July 2016

This paper analyses a new approach utilising potential functions to autonomously control constrained attitude slew manoeuvres using gas jet thrusters. The method hinges on defining a potential function from the geometric configuration of the satellite's current attitude, the final target attitude and any pointing constraint which may be present. It will be demonstrated that complex path shaping and planning can be achieved using little computational effort. The method is mathematically validated using Lyapunov's theorem, and so can be considered for safety critical applications.
Experimental evaluation of multivariable rotor control schemes
Authors: Mullen G. J. , Brinson P. R.
Published: July 2016

The performance and robustness of a classical multivariable controller and one H∞ compensator are assessed on a model rotor rig. Both control schemes are subjected to sinusoidal and step input tests in the pitch and roll axes under a range of operating conditions and configurations. A brief description of the characteristics of the rotor mathematical model is provided, followed by a summary of the design assessment criteria. Following a description of the two control law design techniques, the performance of each controller is verified on the mathematical model prior to evaluation on the rotor rig. In absolute terms, there is a poor correlation between the simulated and experimental values of the design assessment criteria for both controllers. However, in relative terms, the H∞ control law achieves higher levels of damping and lower cross-couplings than the classical scheme although the measured improvements are not as substantial as predicted. In experimental frequency response tests at increasing advance ratios and various rotorspeeds, the H∞ scheme again consistently achieves the lowest levels of cross-coupling. In summary, the results show that although there are practical performance and robustness benefits to be gained by employing more complex control algorithms, model uncertainty will substantially reduce the predicted benefits.
The contribution of fatigue usage monitoring systems to life extension in safe life and damage tolerant designs
Authors: Irving P. E. , Strutt J. E. , Hudson R. A. , Allsop K. , Strathern M.
Published: July 2016

Fatigue usage monitoring systems (Fums) offer considerable potential for life extension of aircraft parts. In this work the life extension benefits of Fums is assessed by adopting a probabilistic approach. The roles of damage law type and of service usage variability is explored. It is shown by analysis that in the absence of cycle to cycle load interaction effects, load sequence has no effect on eventual life in either linear or non linear damage laws, provided that the function describing the rate of damage growth has separable variables of stress and damage. This condition includes fracture mechanics crack growth laws. Monte Carlo simulations have been conducted of fatigue life distributions in helicopter rotor components. Variability in manoeuvre damage, when summed over a large number of manoeuvres, has little effect on scatter in overall lives. A fixed manoeuvre usage spectrum will result in very small scatter in lives, whereas keeping the usage constant for each helicopter and allowing it to vary between helicopters, produces a significantly increased variability. The influence of load factors on life is also assessed. The extent of possible maintenance credits is discussed together with the use of Bayesian updating to make optimum use of both prior design data and current loads or damage information provided by Fums.
On flexure-torsion flutter criteria
Authors: Simpson A.
Published: July 2016

The classical criteria of the 1920s for the avoidance of flexure-torsion flutter were based on parameters such as stiffness ratio and the position across the typical chord of the aerodynamic, elastic and mass centres.

In more recent times, and in the context of aeroelastic tailoring of lifting surfaces constructed with composite materials, a new terminology has emerged — as evident from technical papers produced in the USA over the past decade. The prevention of flexure-torsion flutter, or the raising of the critical speed, is now achieved by providing morewash-inor lesswash-out, where these terms do not have their established aeronautical meanings — and for this reason (and other, non-semantic ones) are to be deprecated.

By recourse to a typical section model (with quasi-steady and unsteady compressible aerodynamics), the writer argues that, for conventionally constructed wings, the new criteria are ‘fuzzy’ and incomplete versions of the earlier criteria in respect of the positioning of the various ‘centres’ (i.e.,elastic, mass and aerodynamic)across the typical chord, and therefore that the new terminology is redundant in this context.

For laminated composite wing structures, even when the construction is uniform and the fiexural axis straight, it is established that the inclination of this axis with respect to the CG and aerodynamic axes may be so large that the fiexural and shear centres at the tip could be several chords forward or aft of the mid-chord axis; the criteria of the 1920s are then irrelevant. The wash-in/wash-out criteria may then be said to ‘come into their own’, albeit that it is shown herein that they remain fuzzy and incomplete — even for quasisteady binary problems. A crude modal binary model of a rudimentary laminated composite wing is included to illustrate this and other features. By recourse to a higher-order flutter formulation, the writer demonstrates that the wash-in/wash-out criteria are, in certain respects, unreliable.
Incorporation of manufacturing information into an MDO environment
Authors: Gantois K. , Morris A. J.
Published: July 2016

The Paper describes a metal and composite recurrent cost model of a large civil aircraft wing structure for a multidisciplinary design, analysis and optimisation (MDO) environment. The work was part of a recent European MDO project (BE95-2056) which investigated methods for the integration of structures, aerodynamics, dynamics and manufacturing cost at the preliminary design stage.

The paper discusses the cost modelling approach, which is based on parametric and process cost model methods, and the integration of the cost models into an MDO process. Results for the cost models are shown.

A framework has been successfully developed which allows the incorporation of manufacturing cost models into an MDO environment. It allows a designer to evaluate cost changes with respect to specific design changes such as rib pitch, stringer pitch, wing area and wing sweep.
Sequential use of conceptual MDO and panel sizing methods for aircraft wing design
Authors: Butler R. , Lillico M. , Banerjee J. R. , Patel M. H. , Done G. T. S.
Published: July 2016

The optimisation results for composite and metallic versions of a regional aircraft wing are compared using the multidisciplinary optimisation (MDO) program CALFUNOPT. The program has been developed for the conceptual design stage and models the wing using just 11 beam elements. The wing has been optimised for three combinations of the following constraint cases: static strength; aeroelastic roll efficiency (represented by limiting the twist of the wing for an aileron loading) and aeroelastic divergence. As expected, comparison shows that the composite wing designs are significantly lighter than the metallic ones, due to the well-known tailoring of the composite material. However, the simple model reveals some insight that may be useful to the designer, and which could be lost within a more detailed finite element approach.

The upper-skin compression panels produced by the conceptual MDO program, for both versions of the wing, have then been optimised using the more detailed and accurate panel sizing tool VICONOPT, which takes buckling into account. Such optimisation increases the panel mass by 5-10% and also provides a suitable ratio of stiffener to skin area for use in the conceptual MDO model.
Prediction of tunnel wall upwash for delta wings including vortex breakdown effects
Authors: Traub L. W.
Published: July 2016

An incompressible method is presented to predict the upwash corrections associated with vortical flow as a result of wind-tunnel side wall effects. An image system is used to simulate the tunnel side walls which are assumed to be solid. An integral expression is formulated, representing the average upwash induced over the wing by the image system. Wall effects may be determined for flows with and without vortex breakdown. Comparisons of the results with upwash predictions from a Navier-Stokes study show close accord. The upwash expression also displayed the ability to successfully predict corrections for flows involving vortex breakdown.
Two and three component velocity measurements in a wind tunnel using PIV
Authors: Bearman P. W. , Harvey J. K. , Stewart J. N.
Published: July 2016

This paper describes the development of particle image velocimetry (PIV) to measure instantaneous spatial distributions of velocity in flows generated around models in a low speed wind tunnel with a test section 3m wide by 1·5m high. The difficulties associated with using PIV in air at this scale, and how they can be overcome, are discussed. Stereoscopic PIV is used to correct errors due to parallax that are present in velocity components measured in the plane of a light sheet when there is an accompanying flow through the sheet. This technique is also used to measure all three components of velocity in planes across a flow. It is found that apparently good estimates of a mean flow field can be obtained by averaging as few as ten instantaneous measurements of the flow field. The flows studied are generated by a 1/8 scale model of an aircraft for which the wing sweep can be varied. Measurements of velocities associated with the main vortex structures generated over the wing are presented for a sweep angle of 70°. Measurements of velocities recorded in the wake of a large fuel tank mounted below the wing, for a wing sweep of 45°, are also shown.
An eddy-viscosity limited algebraic stress model for shock-boundary-layer interaction
Authors: Richardson G. , Qin N.
Published: July 2016

This paper presents a μt-limited explicit algebraic stress model for shock-wave-turbulent boundary-layer interactions based on an investigation of various two-equation turbulence models. The results of the κ-ω model, the shear stress transport (SST) model, and a quadratic explicit algebraic stress model are presented and analysed for the Delery channel bump, and the Bachalo and Johnson axisym-metric bump test cases. While the κ-ω model failed to give good predictions, the SST model proved reasonably successful in predicting strong interaction problems. The non-linear quadratic explicit algebraic stress model gave improved results (when compared with the original κ-ω model) for the channel bump test cases, but was not as good as the SST model. Inspired by this investigation, a model formulation is proposed in which Bradshaw's assumption for eddy-viscosity limiting (as used in the SST model) is applied to a quadratic explicit algebraic stress model. The QSST model further improves the SST model for strong shock-boundary-layer interactions.
Effect of Mach number on the acoustic field of 2:1 elliptic-slot jet
Authors: Verma S. B. , Rathakrishnan E.
Published: July 2016

The shock-structure and the related acoustic field of underexpanded jets undergoes significant changes as the Mach number Mj is increased. The present investigation is carried out to study the effect of Mach number on an underexpanded 2:1 elliptic-slot jet. Experimental data are presented for fully expanded Mach numbers ranging from 1.3 to 2.0. It is observed that the ‘cross-over’ point at the end of the first cell at low Mach numbers gets replaced by a normal shock at a highly underexpanded condition resulting in the formation of a ‘barrel’ shock along the minor-axis side with a ‘bulb’ shock formed along the major-axis side. The above change in shock structure is accompanied by a related change in the acoustic field. The amplitude of fundamental frequency along the minor-axis side grows with Mj but falls beyond Mj = 1.75. Along the major-axis side, however, the fundamental frequency does not exist at low Mach numbers. It appears at Mj = 1.75 but then falls at Mj = 2.0. The related azimuthal directivity of overall noise levels (OASPL) shows significant changes with Mj.
Extract from A Wrack Behind: Cardington
Authors: Norton Lord Kings
Published: July 2016

The performance of German airships during the war, and the double crossing of the Atlantic by the airship R34 in 1919, sufficiently impressed the Air Ministry that it embarked on a British airship programme which produced R38 and R80. The Ministry was undoubtedly deterred by the appalling R38 disaster in 1921 but, presumably as a result of Professor Bairstow’s demonstration of the inexcusable inadequacy of the R38 design, they did not abandon their plans. After all R80, to the design of B.N. Wallis, the great engineer who became famous as Sir Barnes Wallis after the 1939-45 war, had been a success.

So in 1924 the Air Ministry decided to order two airships, each of five million cubic feet capacity. One, to be called R100, was ordered from the Airship Guarantee Company, a Vickers subsidiary headed by Sir Denniston Burney. It was to be built at Howden. The other, to be called R101, was to be built by the Air Ministry itself, at the Royal Airship Works, Cardington. At the head of the Burney design team was B.N. Wallis. At the head of the Air Ministry design team was V.C. Richmond.