Equivalent noise bandwidth analysis from transfer functions
Equivalent noise bandwidth analysis and methods of computation from system transfer functions
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Analysis of high aspect ratio jet flap wings of arbitrary geometry.
Paper presents a design technique for rapidly computing lift, induced drag, and spanwise loading of unswept jet flap wings of arbitrary thickness, chord, twist, blowing, and jet angle, including discontinuities. Linear theory is used, extending Spence's method for elliptically loaded jet flap wings. Curves for uniformly blown rectangular wings are presented for direct performance estimation. Arbitrary planforms require a simple computer program. Method of reducing wing to equivalent stretched, twisted, unblown planform for hand calculation is also given. Results correlate with limited existing data, and show lifting line theory is reasonable down to aspect ratios of 5.
Lissaman, P. B. S.↗
Calorimetric detection of neutral-atom content of ion beam
Energy deposition technique deduces neutral-beam flux or dose from measured values of incremental resistance increases in platinum wire passed through beam. Steady-state heat balance analysis led to equivalent neutral-beam current. Method was used to detect neutral-atom content of 60-keV argon ion beam.
Roberts, A. S., Jr.↗
A constructive model potential method for atomic interactions
A model potential method is presented that can be applied to many electron single centre and two centre systems. The development leads to a Hamiltonian with terms arising from core polarization that depend parametrically upon the positions of the valence electrons. Some of the terms have been introduced empirically in previous studies. Their significance is clarified by an analysis of a similar model in classical electrostatics. The explicit forms of the expectation values of operators at large separations of two atoms given by the model potential method are shown to be equivalent to the exact forms when the assumption is made that the energy level differences of one atom are negligible compared to those of the other.
Bottcher, C.↗
Analysis of multiloop, multirate sampled-data systems
Based upon new identities between z-transforms at a basis rate, z-transforms at faster rates, and modified z-transforms, the equivalence between the frequency decomposition method and the switch decomposition method is precisely presented so that results of one method are easily obtained from results of the other. Next, a method is developed for determining the closed loop transfer function of multiloop, multirate sampled-data systems with noninteger ratio sampling rates. Previously, this process involved solving a complex system of equations with rational polynomial coefficients. Herein, this is avoided by introducing a systematic decomposition of matrix operators which naturally arise from the switch decomposition method. The matrix operators are simplified by introducing the shifted transforms of signals sampled at one of the faster rates.
Boykin, W. H.↗
Improved strain-gage calibration
Accuracy of quarter-bridge strain gage is improved by accounting for nonlinearity of bridges output for equivalent compression and tension strains. Method provides relationships that connect measured strain and shunt calibration.
Troke, R. W.↗
Alternate approaches to vibration and shock analysis using NASTRAN
A method that derives an approximate equivalent static load to a base excitation shock analysis is described. The transient analysis in the current level of NASTRAN, level 16, does not directly provide for either input acceleration forcing functions or enforced boundary displacement. In the suggested alternate analysis format, equivalent force input functions are applied to the constrained locations by using the artifice of placing a large mass, with respect to the total system mass, at the desired acceleration input points. This shortcut static analysis approach is presented to approximate the expensive and time consuming dynamics analysis approach to the base excitation shock analysis.
Denver, R. E.↗
Symmetry considerations in the scattering of identical composite bodies
Previous studies of the interactions between composite particles were extended to the case in which the composites are identical. The form of the total interaction potential matrix elements was obtained, and guidelines for their explicit evaluation were given. For the case of elastic scattering of identical composites, the matrix element approach was shown to be equivalent to the scattering amplitude method.
Norbury, J. W.↗
The extinction law in the open cluster NGC 457 and the intrinsic energy distribution of Phi Cassiopeiae (F0 Ia)
Five early B-type stars near the main-sequence turnoff in NGC 457 have been observed at low dispersion with the short-wavelength prime and the long-wavelength redundant cameras of the IUE satellite. The equivalent widths of spectral features that are particularly strong and sensitive to temperature and luminosity were computed in the cluster stars and in 20 lightly reddened stars of types O9-B3 and luminosity classes III-V. The comparison of the equivalent widths provides a reliable method for finding matching pairs. Having identified the best comparison star for each program star, binned fluxes were used to determine the mean extinction curve. In order to cover the visible region, monochromatic fluxes of Phi Cas were derived from observations with the intensified Reticon scanner mounted on the No. 2 0.9 m telescope of KPNO, and they were dereddened with the mean extinction curve of Savage and Mathis. Thus, the intrinsic energy distribution of Phi Cas were determined from 1500 to 5800 A for use in a detailed model-atmosphere analysis.
Rosenzweig, P.↗
Practical constraints on network architecture and signalling in the MSAT system
Telesat Mobile Inc. plans to provide mobile satellite communications services in Canada in 1993/4, in close cooperation with the American Mobile Satellite Consortium Inc., which will be providing services in the U.S.A. L-band frequencies will be used in multiple beams for communication with mobile terminals. Ku-band frequencies will be used for the feeder-links to fixed stations. The system will support voice and data communications. The baseline Canadian system will support approximately 450 assignable voice channels, some fraction of which will be the equivalent in data channels. The method of multiple access will be Frequency Division Multiple Access/Single Channel Per Carrier. The availability of frequencies, the availability of technology and the time scale for implementation all constrain the network architecture for the system. Further, it is important to have an open specification to encourage multiple equipment vendors. The interplay of these constraints is discussed.
Davies, N. George↗
Estimation of distributed acoustic lasers
The purpose of this paper is to present the results of a preliminary investigation of an indirect method which can be used to generate a set of equivalent point loads approximating an applied distributed acoustic load. The method combines the source information with the structure's modal characteristics and forces which give the same response as the applied acoustic load. The technique is demonstrated by predicting a set of point forces acting on a thin aluminum panel which simulate a normally-incident random pressure. The technique is verified by comparing measured strain autospectrums with estimated strain autospectrums generated using the predicting forces. Strain errors within 5 dB were achieved. A limited amount of information about the acoustic load could be deduced using the predicted force autospectrums and phase differences between these forces.
Elliott, K. B.↗
Bonding Aramid Rope To Metal Fitting
Method for joining Kevlar (or equivalent) aramid rope to tubular corrosion-resistant steel end fitting increases strength of joint under tension to approximately three-fourths that of rope itself. End fitting contains internal thread, which provides good bonding surface. Small radial hole enables injection of adhesive into bore.
To, Dung T.↗
Application of a robust linear control design to a truss structure with nonlinear joints
An efficient nonlinear equivalent beam finite-element method for the application of a full state feedback design is described, which is robust to plant uncertainties to a beamlike truss structure with nonlinear elements. The method may be extended to model nonlinear structures with other types of control systems, such as model-based compensators.
Webster, Mark↗
Design tradeoffs on engine-integrated hypersonic vehicles
Two classes of airbreathing hypersonic vehicle concepts, one for primarily cruise missions and the other for accelerator type missions, are presented. Both are designed with waverider airframes and hydrogen-fueled scramjet engine modules. Cruise configurations are optimized for the product of I(sp) and L/D while matching lift to weight and thrust to drag at some equivalence ratio. Accelerator configurations are optimized for effective specific impulse while matching lift to weight at an equivalence ratio of one. The method and computer code developed to optimize the configurations are discussed. The features and design tradeoffs for each class of vehicles are described. Recently available weight estimates for all-body waveriders have had a significant impact on the integrated configurations. Mach 8 vehicles at 40 km altitude optimized with the cruise objective function have L/Ds of 2.55 to 2.92 and I(sp)s of 2850 to 2940 sec. A Mach 14 vehicle at 40-km altitude optimized with the accelerator objective function has an I(sp) sub eff of 189 sec, and a Mach 10 vehicle an I(sp) sub eff of 880 sec.
O'Neill, Mary Kae L.↗
Some considerations on the integration of engine nacelles into low-boom aircraft concepts
A study of wind-tunnel data has shown why unexpected strong shock waves appeared in wind tunnel pressure signatures of two low-boom models, and has indicated that changes to the current methods for analyzing and designing low-boom aircraft are needed. The discussion provided corrections for the interface lift code, and suggested methods of treatment for the equivalent areas of the aircraft, especially the nacelles and the interference lift, which were to be used in the aircraft design and the sonic boom analysis.
Mack, Robert J.↗
Strategies for Engaging NASA Earth Scientists in K-12 Education and Public Outreach
Engagement of the Earth Science research community in formal education at the kindergarten through high school level and in various aspects of informal education and in professional development of practitioners in related fields has been and continues to be a challenge. A range of approaches is being used and new ones are constantly being tried. Fundamental to our strategies is an understanding of the priorities, skills, academic experiences, motivation, rewards and work experiences of most scientists. It is within this context that efforts to engage a scientist in education efforts are attempted. A key strategy is to limit our requests to activities where the scientist's contribution of time and expertise can have the most impact. Don't waste the scientist's time! Time is one of their most prized resources, it is extremely valuable to you, and to them, we treat their time like a treasured resource. The clearer a scientist's role, their unique contribution and the finite nature of their effort, the more likely they are to participate. It is critical that commitments made to scientists are kept. If they want and can do more, great! Don't expect or assume more will be forthcoming. Another approach that we use is to create periodic venues that, among other things, serve to identify individuals who have an interest or inclination to con , tribute to education efforts. Once identified we strive to determine their interests so that we can make the best match between their interests and the needs of the education program or efforts. In this way, we try to make the best use of their time while engaging them in efforts which will be personally rewarding, and will further the overall education objectives. In addition, we try to make it easier for scientists to participate by providing focused training, such as development of their interviewing skills, and exposure to key concepts, knowledge and skills which are well known among educators but are not common knowledge among scientists. Another strategy with which we are still struggling is how to create and provide career meaningful rewards for individuals who demonstrate excellence in education equivalent to excellence in science. We do not yet have a yardstick to measure excellence in education nor is there a consensus among scientific peers that these two can be equivalent. None-the-less, methods to identify excellence in education, such as the peer review process, are being tried with some success. Use of solicitation and selection of educational efforts via a peer review process that is the same as for scientific research to identify unique, interesting and creative ideas has been somewhat effective. Furthermore, the application of the same peer review process to the output of an educational effort is used to validate and ensure the quality of this output. An example will be used to illustrate the application of some of these strategies to the development of a high school Earth and Space System Science curriculum created in partnership with a local county school system (Anne Arundel County, MD).
Meeson, Blanche W.↗
Extraction of Airport Features from High Resolution Satellite Imagery for Design and Risk Assessment
The LPA Group, consisting of 17 offices located throughout the eastern and central United States is an architectural, engineering and planning firm specializing in the development of Airports, Roads and Bridges. The primary focus of this ARC project is concerned with assisting their aviation specialists who work in the areas of Airport Planning, Airfield Design, Landside Design, Terminal Building Planning and design, and various other construction services. The LPA Group wanted to test the utility of high-resolution commercial satellite imagery for the purpose of extracting airport elevation features in the glide path areas surrounding the Columbia Metropolitan Airport. By incorporating remote sensing techniques into their airport planning process, LPA wanted to investigate whether or not it is possible to save time and money while achieving the equivalent accuracy as traditional planning methods. The Affiliate Research Center (ARC) at the University of South Carolina investigated the use of remotely sensed imagery for the extraction of feature elevations in the glide path zone. A stereo pair of IKONOS panchromatic satellite images, which has a spatial resolution of 1 x 1 m, was used to determine elevations of aviation obstructions such as buildings, trees, towers and fence-lines. A validation dataset was provided by the LPA Group to assess the accuracy of the measurements derived from the IKONOS imagery. The initial goal of this project was to test the utility of IKONOS imagery in feature extraction using ERDAS Stereo Analyst. This goal was never achieved due to problems with ERDAS software support of the IKONOS sensor model and the unavailability of imperative sensor model information from Space Imaging. The obstacles encountered in this project pertaining to ERDAS Stereo Analyst and IKONOS imagery will be reviewed in more detail later in this report. As a result of the technical difficulties with Stereo Analyst, ERDAS OrthoBASE was used to derive aviation obstruction measurements for this project. After collecting ancillary data such as GPS locations, South Carolina Geodetic Survey and Aero Dynamics ground survey points to set up the OrthoBASE Block File, measurements were taken of the various glide path obstructions and compared to the validation dataset. This process yielded the following conclusions: The IKONOS stereo model in conjunction with Imagine OrthoBASE can provide The LPA Group with a fast and cost efficient method for assessing aviation obstructions. Also, by creating our own stereo model we achieved any accuracy better currently available commercial products.
Robinson, Chris↗
Evaluation of Lightning Induced Effects in a Graphite Composite Fairing Structure
Defining the electromagnetic environment inside a graphite composite fairing due to lightning is of interest to spacecraft developers. This paper is the first in a two part series and studies the shielding effectiveness of a graphite composite model fairing using derived equivalent properties. A frequency domain Method of Moments (MoM) model is developed and comparisons are made with shielding test results obtained using a vehicle-like composite fairing. The comparison results show that the analytical models can adequately predict the test results. Both measured and model data indicate that graphite composite fairings provide significant attenuation to magnetic fields as frequency increases. Diffusion effects are also discussed. Part 2 examines the time domain based effects through the development of a loop based induced field testing and a Transmission-Line-Matrix (TLM) model is developed in the time domain to study how the composite fairing affects lightning induced magnetic fields. Comparisons are made with shielding test results obtained using a vehicle-like composite fairing in the time domain. The comparison results show that the analytical models can adequately predict the test and industry results.
Trout, Dawn H.↗