Design and performance of block-coded communication systems.
Block coded frequency multiplexed PM COMMUNICATION system design and performance, considering simplification, cost and weight
COMMUNICATIONS SATELLITE↗
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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Teddy - A two-dimensional Lagrangian code for determining the wave propagation in elastic-plastic media
Finite difference methods and two dimensional Lagrangian code for determining wave propagation in elastic-plastic media - TEDDY program
Jones, A. H.↗
Minimum distance properties of convolutional code words of arbitrary length
Convolutional code words minimum distance- arbitrary length relationship for path memory performance measurement
Huth, G. K.↗
Method and apparatus for a single channel digital communications system
A method and apparatus are described for synchronizing a received PCM communications signal without requiring a separate synchronizing channel. The technique provides digital correlation of the received signal with a reference signal, first with its unmodulated subcarrier and then with a bit sync code modulated subcarrier, where the code sequence length is equal in duration to each data bit.
Couvillon, L. A., Jr.↗
PLOTTER: An independent computer program for the generation of graphical displays
A computer program is described for generating graphical information from input data or auxiliary analysis programs on a variety of graphical devices. Options are presented for tabulating the data in columnar format and for plotting auxiliary text in the vicinity of the plotted information. Display device selection is accomplished by interfacing the basic computer code through routines which convert the internally generated plot vectors to hardware commands for the display device. The plotting techniques employed in the computer program are discussed. User's instructions are presented with examples which illustrate the use of the program in generating plotted information from various sources and presenting the information in alternate plot formats. Technical discussion of the computer code is presented giving the physical characteristics, computer loading instructions and descriptions of the subroutines.
Glatt, C. R.↗
Digital receiver simulation
Digital simulation of the data link for the Saturn-Uranus spacecraft design is summarized. The data link is a 40 watt, 400 MegaHertz, 44 bit-a-second link, a power starved link, and uses convolution coding. Aspects of the link of particular interest are atmospheric scintillation and the Doppler to data rate ratio. The major characteristics of the scintillation are modeled in terms of tapped delay lines. A candidate system design and receiver design is developed. A computer flow diagram depicting a routine for the error rate and one for acquisition is presented. Various coding algorithms are analyzed since the convolution code is sensitive to the distribution of error and the actual pattern of the error.
Hinrichs, C.↗
Supercritical wing design using numerical optimization and comparisons with experiment
A numerical minimization scheme is used in conjunction with two-dimensional and three-dimensional inviscid transonic flow analysis codes to provide procedures for wing leading edge aerodynamic design. The procedures are demonstrated in the design of a new leading edge to improve C-141 cruise performance. For the high aspect ratio moderately swept C-141 wing, the 2-D procedure is shown to yield results which are in close agreement with those obtained using the 3-D technique. Although the 2-D approach uses much less computation time than the 3-D technique, the latter requires fewer manhours than the former. Comparisons of predicted and wind tunnel measured performance improvements are presented which verify the design procedures.
Lores, M. E.↗
Gamma-ray imaging with a rotating hexagonal uniformly redundant array
Laboratory experiments have been performed to demonstrate the capabilities of a gamma-ray imaging system employing a NaI Anger camera and a rotating coded aperture mask. The mask incorporates in its design a new type of hexagonal uniformly redundant array (HURA) which is essentially antisymmetric under 60 deg rotation. The image formation techniques are described and results are presented that demonstrate the imaging capability of the system for individual and multiple point sources of gamma-ray emission. The results are compared to analytical predictions for the imaging and point source localization capabilities of coded aperture systems using continuous detectors.
Cook, W. R.↗
The prediction of transonic loading advancing helicopter rotors
Two different schemes are presented for including the effect of rotor wakes on the finite-difference prediction of rotor loads. The first formulation includes wake effects by means of a blade-surface inflow specification. This approach is sufficiently simple to permit coupling of a full-potential finite-difference rotor code to a comprehensive integral model for the rotor wake and blade motion. The coupling involves a transfer of appropriate loads and inflow data between the two computer codes. Results are compared with experimental data for two advancing rotor cases. The second rotor wake modeling scheme in this paper is a split potential formulation for computing unsteady blade-vortex interactions. Discrete vortex fields are introduced into a three-dimensional, conservative, full-potential rotor code. Computer predictions are compared with two experimental blade-vortex interaction cases.
Strawn, R.↗
High speed inlet calculations with real gas effects
A 2-D steady-state Navier-Stokes solver has been upgraded to include the effects of frozen and equilibrium air chemistry for applications to high speed flight vehicles. To provide a computationally economical first order approximation to the high temperature physics, variable thermodynamic data is used for the chemically frozen mode to allow for a variation with temperature of the air specific heats and enthalpy. For calculations involving air in chemical equilibrium, a specially modified version of the NASA Lewis Chemical Equilibrium Code, CEC, is used to compute the chemical composition and resultant thermochemical properties. The upgraded solver is demonstrated by comparing results from calorically perfect (C sub p=constant), thermally perfect (frozen) and equilibrium air calculations for a variety of geometries, and flight Mach numbers.
Coirier, William J.↗
Evaluation of the constant pressure panel method (CPM) for unsteady air loads prediction
This paper evaluates the capability of the constant pressure panel method (CPM) code to predict unsteady aerodynamic pressures, lift and moment distributions, and generalized forces for general wing-body configurations in supersonic flow. Stability derivatives are computed and correlated for the X-29 and an Oblique Wing Research Aircraft, and a flutter analysis is carried out for a wing wind tunnel test example. Most results are shown to correlate well with test or published data. Although the emphasis of this paper is on evaluation, an improvement in the CPM code's handling of intersecting lifting surfaces is briefly discussed. An attractive feature of the CPM code is that it shares the basic data requirements and computational arrangements of the doublet lattice method. A unified code to predict unsteady subsonic or supersonic airloads is therefore possible.
Appa, Kari↗
Higher order turbulence closure models
Theoretical models are developed and numerical studies conducted on various types of flows including both elliptic and parabolic. The purpose of this study is to find better higher order closure models for the computations of complex flows. This report summarizes three new achievements: (1) completion of the Reynolds-stress closure by developing a new pressure-strain correlation; (2) development of a parabolic code to compute jets and wakes; and, (3) application to a flow through a 180 deg turnaround duct by adopting a boundary fitted coordinate system. In the above mentioned models near-wall models are developed for pressure-strain correlation and third-moment, and incorporated into the transport equations. This addition improved the results considerably and is recommended for future computations. A new parabolic code to solve shear flows without coordinate tranformations is developed and incorporated in this study. This code uses the structure of the finite volume method to solve the governing equations implicitly. The code was validated with the experimental results available in the literature.
Amano, Ryoichi S.↗
High speed inlet calculations with real gas effects
A 2-D steady-state Navier-Stokes solver has been upgraded to include the effects of frozen and equilibrium air chemistry for applications to high speed flight vehicles. To provide a computationally economical first order approximation to the high temperature physics, variable thermodynamic data is used for the chemically frozen mode to allow for a variation with temperature of the air specific heats and enthalpy. For calculations involving air in chemical equilibrium, a specially modified version of the NASA Lewis Chemical Equilibrium Code, CEC, is used to compute the chemical composition and resultant thermochemical properties. The upgraded solver is demonstrated by comparing results from calorically perfect (C sub p=constant), thermally perfect (frozen) and equilibrium air calculations for a variety of geometries, and flight Mach numbers.
Coirier, William J.↗
Implementation issues in source coding
An edge preserving image coding scheme which can be operated in both a lossy and a lossless manner was developed. The technique is an extension of the lossless encoding algorithm developed for the Mars observer spectral data. It can also be viewed as a modification of the DPCM algorithm. A packet video simulator was also developed from an existing modified packet network simulator. The coding scheme for this system is a modification of the mixture block coding (MBC) scheme described in the last report. Coding algorithms for packet video were also investigated.
Sayood, Khalid↗
Numerical computation of viscous flow about unconventional airfoil shapes
A new two-dimensional computer code was developed to analyze the viscous flow around unconventional airfoils at various Mach numbers and angles of attack. The Navier-Stokes equations are solved using an implicit, upwind, finite-volume scheme. Both laminar and turbulent flows can be computed. A new nonequilibrium turbulence closure model was developed for computing turbulent flows. This two-layer eddy viscosity model was motivated by the success of the Johnson-King model in separated flow regions. The influence of history effects are described by an ordinary differential equation developed from the turbulent kinetic energy equation. The performance of the present code was evaluated by solving the flow around three airfoils using the Reynolds time-averaged Navier-Stokes equations. Excellent results were obtained for both attached and separated flows about the NACA 0012 airfoil, the RAE 2822 airfoil, and the Integrated Technology A 153W airfoil. Based on the comparison of the numerical solutions with the available experimental data, it is concluded that the present code in conjunction with the new nonequilibrium turbulence model gives excellent results.
Ahmed, S.↗
Unified aeroacoustics analysis for high speed turboprop aerodynamics and noise. Volume 4: Computer user's manual for UAAP turboprop aeroacoustic code
The Unified AeroAcoustic Program (UAAP) code calculates the airloads on a single rotation prop-fan, or propeller, and couples these airloads with an acoustic radiation theory, to provide estimates of near-field or far-field noise levels. The steady airloads can also be used to calculate the nonuniform velocity components in the propeller wake. The airloads are calculated using a three dimensional compressible panel method which considers the effects of thin, cambered, multiple blades which may be highly swept. These airloads may be either steady or unsteady. The acoustic model uses the blade thickness distribution and the steady or unsteady aerodynamic loads to calculate the acoustic radiation. The users manual for the UAAP code is divided into five sections: general code description; input description; output description; system description; and error codes. The user must have access to IMSL10 libraries (MATH and SFUN) for numerous calls made for Bessel functions and matrix inversion. For plotted output users must modify the dummy calls to plotting routines included in the code to system-specific calls appropriate to the user's installation.
Menthe, R. W.↗
Application of a new Navier-Stokes inverse method to the design of advanced airfoils
A new inverse airfoil design method has been developed. This method couples a two-dimensional Navier-Stokes code to a residual-correction design algorithm to produce an efficient design code. Since this method can be used to design airfoils near the limits of performance capabilities, a technique to investigate the limits of lift has been developed to guide the design of new airfoils. Examples of the use of the inverse Navier-Stokes code and the maximum lift technology in the design of new airfoils are presented.
Narramore, J. C.↗
Update on results of SPRE testing at NASA
The space power research engine (SPRE I), a free-piston Stirling engine with a linear alternator, was tested as a candidate for high-capacity space power. A portion of the test data from the SPRE I, essentially in its baseline configuration while operating with helium at heat exchanger metal temperature ratios ranging from 1.6 to 2.4 and mean cycle pressures of 7.5 and 15.0 Mpa, are presented. HFAST computer code predictions are presented for comparison. The measured results at 7.5 and 15 MPa, from the first day, from the first day of testing, at temperature ratios from 1.6 to 2.0 agreed fairly well with the HFAST code predictions; within -8.8 percent to +11.9 percent for PV power and -2.7 to +1.07 percentage points for PV efficiency. Measured compression-space pressure amplitude was 5.1 to 11.1 percent below predictions; although these results were within the error bands, there was poorer agreement than observed for previous tests, and the transducer calibration is suspect. All of the dynamic pressure transducer calibrations will be verified before testing is resumed. Measured pressure phase angles were within -1.95 percent to +5.37 percent of the predictions, which is much closer than previously observed. The poor agreement of the measured heat flow to the heater with the code appears to be due to thermocouple degradation.
Cairelli, James E.↗