Showing papers by "Vaughn College of Aeronautics and Technology published in 2000"

On Planetary Companions to the MACHO 98-BLG-35 Microlens Star

Abstract: We present observations of the microlensing event MACHO 98-BLG-35, which reached a peak mag- ni—cation factor of almost 80. These observations by the Microlensing Planet Search (MPS) and MOA collaborations place strong constraints on the possible planetary system of the lens star and show intriguing evidence for a low-mass planet with a mass fraction 4 ) 10~5 " v " 2 ) 10~4. A giant planet with v \ 10~3 is excluded from 95% of the region between 0.4 and 2.5 from the lens star, where is R E R E the Einstein ring radius of the lens. This exclusion region is more extensive than the generic ii lensing zone,ˇˇ which is 0.6¨1.6 For smaller mass planets, we can exclude 57% of the ii lensing zone ˇˇ for R E. v \ 10~4 and 14% of the lensing zone for v \ 10~5. The mass fraction v \ 10~5 corresponds to an Earth-mass planet for a lensing star of mass D0.3 A number of similar events will provide sta- M _ . tistically signi—cant constraints on the prevalence of Earth-mass planets. In order to put our limits in more familiar terms, we have compared our results to those expected for a solar system clone, averaging over possible lens system distances and orientations. We —nd that such a system is ruled out at the 90% con—dence level. A copy of the solar system with Jupiter replaced by a second Saturn-mass planet can be ruled out at 70% con—dence. Our low-mass planetary signal (few Earth masses to Neptune mass) is sig- ni—cant at the 4.5 p con—dence level. If this planetary interpretation is correct, the MACHO 98-BLG-35 lens system constitutes the —rst detection of a low-mass planet orbiting an ordinary star without gas giant planets.20 Subject headings: gravitational lensingplanetary systemsstars: low-mass, brown dwarfs

Aircraft noise social cost and charge mechanisms – a case study of Amsterdam Airport Schiphol

Abstract: The increasing trend of charging for aircraft noise nuisance to encourage the sustainable development of the air transport industry has resulted in a need to evaluate the real social costs of such externalities for the formulation of effective charge mechanisms. After comparing the current charge mechanisms at world airports as well as reviewing existing externality measurements, mathematical models are developed to calculate the noise social cost in monetary terms, and noise charge mechanisms are subsequently established. The hedonic price method is applied to calculate the annual social cost of aircraft noise during the landing and take-off stages of the flight. This is done by estimating the implicit costs of aircraft noise imposed through a decline in property values in the vicinity of the airport. The empirical results, using Amsterdam Airport Schiphol as the case study, show that the current noise charge level imposed by the Dutch Government is lower than the actual noise social cost resulting from aircraft movements. Several noise charge mechanism scenarios are derived according to the modelling results, as well as the environmental objectives of the airport related authorities.

A methodology for knowledge management implementation

Abstract: This article describes research work which was directed towards providing the automotive industry with a practical methodology that translates the conceptual ideas of knowledge management (KM) into a working programme with defined objectives, using industry terminology. The research also developed a supporting analysis methodology that enables an effective analysis of the influences on employee activities when creating and sharing valuable corporate knowledge, that spans technical and cultural boundaries. This happens through identifying the factors that impact on defined KM metrics. The analysis identifies the key influencing factors within a working environment. The research benefits are felt when the ground‐level drivers of KM behaviour are improved through links to an appropriate KM strategy. KM strategy may emphasise organisational cultural changes or IT changes or both in an endeavour to improve innovation, reduce business costs and reduce time to market of new products. An industrial case study was undertaken to validate the research.

Discovery of the optical counterpart and early optical observations of GRB 990712

Abstract: We present the discovery observations of the optical counterpart of the gamma-ray burst GRB 990712 taken 4.16 hr after the outburst and discuss its light curve observed in the V, R, and I bands during the first ~35 days after the outburst. The observed light curves were fitted with a power-law decay for the optical transient (OT), plus an additional component that was treated in two different ways. First, the additional component was assumed to be an underlying galaxy of constant brightness. The resulting slope of the decay is 0.97, and the magnitudes of the underlying galaxy are V = 22.3 ± 0.05, R = 21.75 ± 0.05, and I = 21.35 ± 0.05. Second, the additional component was assumed to be a galaxy plus an underlying supernova with a time-variable brightness identical to that of GRB 980425, appropriately scaled to the redshift of GRB 990712. The resulting slope of the decay is similar, but the goodness of fit is worse, which would imply that either this GRB is not associated with an underlying supernova or the underlying supernova is much fainter than the supernova associated with GRB 980425. The galaxy in this case is fainter: V = 22.7 ± 0.05, R = 22.25 ± 0.05, and I = 22.15 ± 0.05, and the OT plus the underlying supernova at a given time is brighter. Measurements of the brightnesses of the OT and the galaxy by late-time Hubble Space Telescope observation and ground-based observations can thus assess the presence of an underlying supernova.

A matrix-free preconditioned Newton/GMRES method for unsteady Navier-Stokes solutions

Abstract: The unsteady compressible Reynolds-averaged Navier–Stokes equations are discretized using the Osher approximate Riemann solver with fully implicit time stepping. The resulting non-linear system at each time step is solved iteratively using a Newton/GMRES method. In the solution process, the Jacobian matrix–vector products are replaced by directional derivatives so that the evaluation and storage of the Jacobian matrix is removed from the procedure. An effective matrix-free preconditioner is proposed to fully avoid matrix storage. Convergence rates, computational costs and computer memory requirements of the present method are compared with those of a matrix Newton/GMRES method, a four stage Runge–Kutta explicit method, and an approximate factorization sub-iteration method. Effects of convergence tolerances for the GMRES linear solver on the convergence and the efficiency of the Newton iteration for the non-linear system at each time step are analysed for both matrix-free and matrix methods. Differences in the performance of the matrix-free method for laminar and turbulent flows are highlighted and analysed. Unsteady turbulent Navier–Stokes solutions of pitching and combined translation–pitching aerofoil oscillations are presented for unsteady shock-induced separation problems associated with the rotor blade flows of forward flying helicopters. Copyright © 2000 John Wiley & Sons, Ltd.

The control of the post-buckling response in thin composite plates using smart technology

Abstract: Restoration forces, associated with embedded activated pre-strained shape memory alloy wires, have successfully been employed to enhance the post-buckling behaviour of various laminated plate structures. An extensive experimental and numerical programme has been conducted, the results of which will be presented. The manufacturing methodology of the hybrid SMA/carbon/epoxy plates is outlined. Such specimens feature 0.4-mm diameter shape memory alloy wires located within tubing at desired locations. Numerical thermal analysis has been employed to predict the non-uniform temperature profile, attributed to shape memory alloy activation through resistive heating, within the laminates. Structural finite element analysis has been employed to determine the hybrid plates' adaptive response while under the influence of a uniaxial compressive load in excess of its critical buckling value. It is shown that, utilising the considerable control authority generated, even for a small actuator volume fraction, the out-of-plane displacement of the post-buckled laminates can be significantly reduced. Such displacement alleviation allows for load redistribution away from the specimens' unloaded edges. With the increase in use of composite materials within aerospace platforms, it is envisaged that the hybrid adaptive SMA/laminate configuration will extend the operational performance over conventional materials and structures, particularly when the structure is exposed to an elevated temperature.

Wide-Field Camera for Gravitational Microlensing Survey: MOA-cam2

Abstract: We have constructed a large, mosaic CCD camera called MOA-cam2 which has 4096 × 6144-pixelsto search for gravitational microlensing events. MOA-cam2 has three4096 × 2048-pixel SITe CCD chips, which have a very high quantum efficiency (nearly 80% in the wave region 500 to 800 nm),and three buttable sides. We have placed the threechips side by side with 100 μm dead space. MOA-cam2 has been installed on the 61 cm Boller and Chivens telescope of the MOA collaboration at the Mt. John University Observatory (MJUO) in NewZealand since July 1998. The field coverage is 0.92° × 1.38° per exposure. The technical details of MOA-cam2 and the first images obtained with the Boller and Chivens telescope are presented. MOA-cam2 introduces a second phase of research on gravitational microlensing by the MOA collaboration.

Life enhancement of fatigue-aged fastener holes using the cold expansion process

Abstract: This paper examines the benefits of cold expanding fastener holes at various stages of the fatigue life in a 2024-T351 low-load transfer joint. The specimens were pre-cycled to 25, 50 and 7...

Modelling of Spall in an Anisotropic Aluminium Alloy

Abstract: Spall caused by hypervelocity impacts at the lower range of velocities could result in significant damage to spacecraft. A number of polycrystalline alloys, used in spacecraft manufacturing, exhibit a pronounced anisotropy in their mechanical properties. The aluminium alloy AA 7010, whose orthotropy is a consequence of the meso-scale phase distribution or grain morphology, has been chosen for this investigation. The material failure observed in plate impact was simulated using a number of spall models. The Hugoniot elastic limit and spall strength have been studied as a function of orientation, and compared to experimental results.

Calculation of compressible indicial response

Abstract: The present paper addresses the problem of extracting indicial response functions from solutions of the Navier-Stokes equations. Two approaches are considered. In the first, the indicial response is computed directly by modifying the local grid velocity to reflect the step change in plunge velocity. The computed data are then fitted using an assumed form for the response function and numerical optimisation techniques. In the second (indirect) approach, the general form of the lift transfer operator is determined analytically from the functional form of the assumed response. Using the lift transfer operator explicit solutions of the in-phase and quadrature components of the normal force time history can be obtained. The unknown coefficients in the response function are then extracted from computed data for harmonic motion by fitting the time history using the explicit solution. Computed response functions are presented for a range of Mach numbers and are compared with analytical results and indicial models currently used within the rotorcraft community. For the cases considered there is no significant difference between the response functions determined using the direct or indirect approach. Comparison of the computed results with existing models suggests that generalisation of the response to step changes in incidence using a two-pole approximation of the circulatory response together with the Prandtl-Glauert factor is not possible. However, comparison with higher order semi-empirical models is much improved, providing some justification for the use of such models. In addition to these observations, the extracted response functions suggest improvements to piston theory to account for thickness effects. The proposed modification of piston theory is based upon properties of the static pressure distribution and so can be used in conjunction with both CFD and experimental data.

Social costs of aircraft noise and engine emissions: case study of amsterdam's schiphol airport

Abstract: With the increasing trend of charging for externalities and the aim of encouraging the sustainable development of the air transport industry, there is a need to evaluate the real social costs of the undesirable side effects of aircraft noise and engine emissions. The mathematical models, based on extensive literature reviews of existing externality measurements, are developed to derive the social costs of noise and engine emissions from aircraft movements in monetary terms by using Amsterdam's Schiphol Airport as a case study. Furthermore, the results of a survey on the current noise and engine emissions charges are briefly described and compared. The hedonic price method is applied to calculate the annual social cost of aircraft noise during the landing and takeoff stages of the flight. In contrast, the direct evaluation method is applied to estimate the social cost of each engine exhaust pollutant during different flight modes. The empirical results have shown that the average social cost of noise per a...

Finite Element Modelling of Failure of a Multi-Material Target due to High Velocity Space Debris Impacts

Abstract: Lagrangian finite element methods have been used extensively in the past to study the non-linear transient behaviour of materials, ranging from crash tests of cars to simulating bird strikes on planes. However, as this type of space discretisation does not allow for motion of the material through the mesh when modelling extremely large deformations, the mesh becomes highly distorted. This paper describes some limitations and applicability of this type of analysis for high velocity impacts. A method for dealing with this problem by the erosion of elements is proposed, where the main driver is the definition of element failure strains. Results were compared with empirical perforation results and were found to be in good agreement. The results were then used to simulate high velocity impacts upon a multi-layered aluminium target in order to predict a ballistic limit curve. LS-DYNA3D was used as the FE solver for all simulations. Meshes were generated using Truegrid.

On the velocity profile of inclined jets in a boundary layer for vorticity production

Abstract: The velocity profiles of air-jet vortex generators have been investigated, and the effect of varying velocity profiles on vortex production has been assessed. In the simplest case of a jet generated by fluid effusing through a cylindrical hole drilled into a solid surface, the internal flow in the nozzle is critical to the development of jets to be used for vortex production. A series of Pitot traverses through a range of jet diameters and pitch angles has been made in order to characterize the jet development. In order to produce an axisymmetric jet profile, modifications were made to the jet nozzles, thereby overcoming the critical flow features within the jet nozzle.In order to assess the jets for vortex production, a range of air-jet vortex generator configurations have been used to produce discrete vortices in a turbulent flat plate boundary layer. Velocity vectors were measured over a cross-stream plane through the vortices, from which the vorticity could be derived across the plane. The vor...

Aerospace and the environment what contribution can aerodynamics make

Abstract: For the past 50 years civil air transport has been dominated by the combination of the gas turbine and the B-47 airframe configuration. Both these machines owed their creation to WW2 and both represented revolutionary concepts at the time. Oyer the years, the engine and the airframe have undergone considerable detailed refinement. The changes have resulted in very impressive improvements in performance. However, it is now very clear that both are close to some well defined asymptotic limits that bound their performance. The result is that further potential improvements are smaller in percentage terms, become harder to achieve technically and, consequently, come at increasingly higher cost. A hugely successful global industry has developed around this standard configuration. Increasingly, more and more companies use aircraft and, as their businesses grow, the demand for aircraft and air transport increases. However, the ability of the environment to absorb this growth is beginning to be questioned and new ideas are required if aviation is to be regarded as an unbounded and a truly sustainable activity.

Measurement of Pilot Opinion When Assessing Aircraft Handling Qualities

Abstract: The assessment of aircraft handling qualities poses an interesting measurement problem. Such assessments ha~e always been an important part in an aircraft's design and development process. Since the end of World War n, the US Department of Defense has required military aircraft to exhibit 'acceptable' handling qualities. Initially these qualities were defined simply in terms of stability and control. However, the more recent version of these specifications9 also incorporates pilot opinion in addition to the classical engineering parameters. Civil airworthiness requirements also require aircraft to demonstrate satisfactory handling qualities as part of the certification process. With the advent of fly-by-wire (FBW) flight control systems, the control engineer is no longer restricted to producing an aircraft that handles 'conventionally'. The control col. umn may now command flight path angle directly, rather than using the first-order surrogate of aircraft pitch rate. Alternatively the column may now make an acceleration (or 'g') demand. These options for flight path control, which were not available thirty years ago, have made the assessment of aircraft handling qualities even more important than in the past. There are now many more options from which to choose, and considerably more precise ways to refine an aircraft's behaviour. Despite the importance of providing an aircraft with acceptable handling qualities, it still remains difficult to define precisely what is meant by this term and it is even more difficult to operationalise through measurement. Harper and Cooper5 defined handling qualities as 'those qualities or characteristics of an aircraft that govern the ease and precision with which a pilot is able to perform the tasks required in support of the aircraft's role'. Gibson3 suggested that this definition be expanded to include the ease with which the pilot can compensate for any disturbing effects of the environment. However, both definitions implicitly incorporate pilot opinion. This is essential as the simple physical measurement of an aircraft's open-loop response to a disturbance input can give an extremely misleading impression about how easy it is to control. An aircraft may exhibit excellent open-loop stability, but when the pilot is trying to fly a high-gain, closedloop task such as air-to-air refuelling, it may be almost uncontrollable. An engineer makes judgements about the aircraft's handling qualities from data derived from only a part of the total pilot/vehicle system. The pilot alone can observe the complete dynamic behaviour of the aircraft. As a result, handling qualities cannot be defined simply by engineering descriptions of an aircraft's response to a pilot's input. Any assessment of handling qualities must include the pilot's perceptions of the aircraft's behaviour.

The application of oct-tree terrain models to real-time aircraft flight path planning

Abstract: This paper outlines a technique to represent terrain using tree structures, based on Morton ordering to avoid the use of pointers. This approach enables terrain data to be organised in a hierarchical form affording a trade-off between the speed of access to the terrain database and resolution of the terrain data extracted from the tree. A set of database access algorithms is developed that form the basis of path extraction needed for real-time mission management. Several examples are presented to illustrate the performance of the routeing algorithms developed in the paper.

Computing the motion of spinning finned projectiles

Abstract: The inertia characteristics of symmetrically finned projectiles are shown to be invariant of roll angle. This special property is used to derive despun' equations of motion so avoiding the rapid rates of change associated with the use of body fixed axes. By exploiting the special inertia and aerodynamic characteristics of symmetrically finned spinning projectiles it is possible to reduce the computer solution time required for long down range calculations. By combining the system with the use of quaternions for attitude determination, firings at high elevation can also be accommodated. A speed up by an order of magnitude is observed for the example of a 40mm shell