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Showing papers by "Langley Research Center published in 1979"


Journal Article•DOI•
TL;DR: In this article, the authors presented the stress-intensity factors for shallow and deep semi-elliptical surface cracks in plates subjected to tension and verified the accuracy of the three-dimensional finite-element models employed.

591 citations


01 Dec 1979
TL;DR: In this paper, a real-time piloted simulation was conducted to evaluate the high-angle-of-attack characteristics of a fighter configuration based on wind-tunnel testing of the F-16 with particular emphasis on the effects of various levels of relaxed longitudinal static stability.
Abstract: A real-time piloted simulation was conducted to evaluate the high-angle-of-attack characteristics of a fighter configuration based on wind-tunnel testing of the F-16, with particular emphasis on the effects of various levels of relaxed longitudinal static stability. The aerodynamic data used in the simulation was conducted on the Langley differential maneuvering simulator, and the evaluation involved representative low-speed combat maneuvering. Results of the investigation show that the airplane with the basic control system was resistant to the classical yaw departure; however, it was susceptible to pitch departures induced by inertia coupling during rapid, large-amplitude rolls at low airspeed. The airplane also exhibited a deep-stall trim which could be flown into and from which it was difficult to recover. Control-system modifications were developed which greatly decreased the airplane susceptibility to the inertia-coupling departure and which provided a reliable means for recovering from the deep stall.

396 citations


Journal Article•DOI•
TL;DR: An unstiffened panel buckling constraint for balanced, symmetric laminated composites is included on the global design level in a mathematical programming structural optimization procedure for designing wing structures.
Abstract: An unstiffened panel buckling constraint for balanced, symmetric laminated composites is included on the global design level in a mathematical programming structural optimization procedure for designing wing structures. Constraints are introduced by penalty functions, and Newton's method based on approximate second derivatives of the penalty terms is used as the search algorithm to obtain minimum-mass designs. Constraint approximations used during the optimization process contribute to the computational efficiency of the procedure. A criterion is developed that identifies the appropriate conservative form of the constraint approximations that are used with the optimization procedure. Minimum-mass design results are obtained for a multispar high-aspect-ratio wing subjected to material strength, minimum-gage, displacement, panel buckling and twist constraints. The material systems considered for the examples are all graphite-epoxy, graphite-epoxy with boron-epoxy spar caps, and all aluminum. The composite material designs are shown to have an advantage over the aluminum designs since they can often satisfy additional constraints with only small mass increases.

294 citations


Journal Article•DOI•
TL;DR: In this paper, the authors report on two recently deployed NASA satellite systems (SAM II and SAGE) that are monitoring the stratospheric aerosol layer and obtain vertical aerosol and gaseous extinction profiles with 1 km vertical resolution.
Abstract: The potential climatological and environmental importance of the stratospheric aerosol layer has prompted great interest in measuring the properties of this aerosol. In this paper we report on two recently deployed NASA satellite systems (SAM II and SAGE) that are monitoring the stratospheric aerosol. The satellite orbits are such that nearly global coverage is obtained. The instruments mounted in the space-craft are sun photometers that measure solar intensity at specific wavelengths as it is moderated by atmospheric particulates and gases during each sunrise and sunset encountered by the satellites. The data obtained are “inverted” to yield vertical aerosol and gaseous (primarily ozone) extinction profiles with 1 km vertical resolution. Thus, latitudinal, longitudinal, and temporal variations in the aerosol layer can be evaluated. The satellite systems are being validated by a series of ground truth experiments using airborne and ground lidar, balloon-borne dustsondes, aircraft-mounted impactor...

276 citations


01 Dec 1979
TL;DR: In this article, a three-dimensional finite-element analysis for shallow and deep semielliptical surface cracks in finite elastic isotropic plates subjected to tension or bending loads is presented.
Abstract: Stress-intensity factors calculated with a three-dimensional, finite-element analysis for shallow and deep semielliptical surface cracks in finite elastic isotropic plates subjected to tension or bending loads are presented. A wide range of configuration parameters was investigated. The ratio of crack depth to plate thickness ranged from 0.2 to 0.8 and the ratio of crack depth to crack length ranged from 0.2 to 2.0. The effects of plate width on stress-intensity variations along the crack front was also investigated. A wide-range equation for stress-intensity factors along the crack front as a function of crack depth, crack length, plate thickness, and plate width was developed for tension and bending loads. The equation was used to predict patterns of surface-crack growth under tension or bending fatigue loads. A modified form of the equation was also used to correlate surface-crack fracture data for a brittle epoxy material within + or - 10 percent for a wide range of crack shapes and crack sizes.

260 citations


Journal Article•DOI•
TL;DR: In this article, a Chebyshev expansion technique was applied to Poisson's equation on a square with homogeneous Dirichlet boundary conditions, and the spectral equations were solved in two ways - by alternating direction and by matrix diagonalization methods.

257 citations


Journal Article•DOI•
TL;DR: It is shown that for stratospheric measurements below about 25 km, molecular density uncertainties are the dominant source of error for wavelengths shorter than about 1.1 microm during nonvolcanic conditions.
Abstract: A methodology is presented for objective and automated determination of the uncertainty in lidar aerosol measurements. This methodology is based on standard error-propagation procedures, a large data base on atmospheric behavior, and long experience in lidar data processing. Algebraic expressions for probable error are derived as a function of the relevant parameters. The validity of these expressions is then tested by making simulated measurements and analyses in which random errors of appropriate size are injected at proper steps of the measurement and analysis process. An illustrative example is given where the methodology is applied to a new lidar system now being used for airborne measurements of the stratospheric aerosol.

225 citations


Journal Article•DOI•
TL;DR: In this paper, a modified transonic mixed-type equation is proposed to compute transonic flows around cylinders and airfoils with special emphasis on the explicit methods that are suitable for vector processing on the STAR 100 computer.
Abstract: New methods for transonic flow computations based on the full potential equation in conservation form are presented. The idea is to modify slightly the density (due to the artificial viscosity in the supersonic region), and solve the resulting elliptic-like problem iteratively. It is shown that standard discretization techniques (central differencing) as well as some standard iterative procedures (SOR, ADI, and explicit methods) are applicable to the modified transonic mixed-type equation. Calculations of transonic flows around cylinders and airfoils are discussed with special emphasis on the explicit methods that are suitable for vector processing on the STAR 100 computer.

180 citations


Journal Article•DOI•
TL;DR: The results of one Martian year of radio occultation measurements of the atmosphere and topography of Mars obtained using the Viking Orbiters are briefly summarized in this article, where the vertical distribution of tropospheric gas refractivity and ionospheric electron density obtained from atmospheric Doppler frequency perturbations of the S and X band radio tracking frequencies indicate large meteorological variations, with near-surface temperatures ranging from 150 to 250 K, 5-km atmospheric pressure ranging from 3.5 to 4.8 mbar.
Abstract: The results of one Martian year of radio occultation measurements of the atmosphere and topography of Mars obtained using the Viking Orbiters are briefly summarized. Determinations of the vertical distribution of tropospheric gas refractivity and ionospheric electron density obtained from atmospheric Doppler frequency perturbations of the S and X band radio tracking frequencies indicate large meteorological variations, with near-surface temperatures ranging from 150 to 250 K, 5-km atmospheric pressure ranging from 3.5 to 4.8 mbar, inversion layers over the polar caps and dust storms, and seasonal pressure variations. Double- and single-layered upper atmospheric electron density profiles were observed on the sunlit and dark sides of the planet, respectively. A topographic map of the Martian surface, obtained from the limb diffraction effects observed at ingress and egress, is found to agree well with the elevation contours of US Geological survey map M 25M 3 RMC, with the exception of the south polar and Alba Patera regions.

174 citations


Journal Article•DOI•
TL;DR: The results from this analysis indicate that aerosol, ozone, and neutral density vertical profiles can be retrieved to an accuracy better than 10% with about 1-km vertical resolution over most of the stratosphere.
Abstract: The paper discusses a possible data retrieval technique for the spaceborne Stratospheric Aerosol and Gas Experiment (SAGE). The SAGE instrument has four radiometric channels located at selected intervals in the 0.38-1.0-micron wavelength range. A data reduction procedure is described for minimization of experimental errors on the basis of a detailed simulation of the measurement sequence. An efficient and accurate inversion method is then used for the retrieval of all the constituent vertical profiles. Also, the effects of horizontally inhomogeneous distributions of the constituent vertical profiles are studied based on available data of their global distributions. A simple horizontally inhomogeneous model of stratospheric aerosol and ozone is employed to estimate the perturbation on the retrieval accuracies.

158 citations


01 Aug 1979
TL;DR: In this paper, the similitude requirements for the most general test conditions are presented in relation to the scaling relationships, test technique, test conditions (including supersonic flow), and test objectives.
Abstract: The similitude requirements for the most general test conditions are presented. These similitude requirements are considered in relation to the scaling relationships, test technique, test conditions (including supersonic flow), and test objectives. Particular emphasis is placed on satisfying the various similitude requirements for incompressible and compressible flow conditions. For free flying models tests, the test velocities for incompressible flow are scaled from Froude number similitude requirements and those for compressible flow are scaled from Mach number similitude requirements. The limitations of various test techniques are indicated, with emphasis on the free flying model.

Journal Article•DOI•
TL;DR: It is shown that network flow algorithms may be used to find a dynamic assignment that minimizes the sum of module execution costs, module residence costs, intermodule communication costs, and module reassignment costs.
Abstract: The problem of finding an optimal dynamic assignment of a modular program for a two-processor system is analyzed. Stone's formulation of the static assignment problem is extended to include the cost of dynamically reassigning a module from one processor to the other and the cost of module residence without execution. By relocating modules during the course of program execution, changes in the locality of the program can be taken into account. It is shown that network flow algorithms may be used to find a dynamic assignment that minimizes the sum of module execution costs, module residence costs, intermodule communication costs, and module reassignment costs. Techniques for reducing the size of the problem are described for the case where the costs of residence are negligible.

Proceedings Article•DOI•
J. E. Carter1•
01 Jan 1979
TL;DR: In this paper, a viscous-inviscid iteration procedure is presented which is applicable to separated flows and converges rapidly, and does not require numerical smoothing, at least in the cases computed thus far.
Abstract: A new viscous-inviscid iteration procedure is presented which is applicable to separated flows. The new procedure is simple, converges rapidly, and does not require numerical smoothing, at least in the cases computed thus far. Calculations are presented for both incompressible and compressible separated flow in the juncture region between an axisymmetric body and sting. The viscous computation is obtained with a recently developed inverse boundary-layer procedure which is no more complicated than a standard direct finite-difference boundary-layer technique. The inviscid computation is made with an axisymmetric transonic code called RAXBOD, in which surface injection is used to represent the viscous effects.

Journal Article•DOI•
TL;DR: In this paper, meteorological data from the landers has been analyzed for the period just before first storm arrival to just after second storm arrival, with the objectives of defining the meteorological phenomena during the storm period, determining those associated with storm and dust arrival, and evaluating the effects on synoptic conditions and the general circulation.
Abstract: Meteorological instrumentation aboard the Viking Mars Landers measures wind, temperature, and pressure. Two global dust storms occurred during northern autumn and winter, observed both by the orbiters and by the landers. The meteorological data from the landers has been analyzed for the period just before first storm arrival to just after second storm arrival, with the objectives of defining the meteorological phenomena during the storm period, determining those associated with storm and dust arrival, and evaluating the effects on synoptic conditions and the general circulation. Times of dust arrival over the sites could be defined fairly closely from optical and pressure (solar tide) data, and dust arrival was also accompanied by changes in diurnal temperature range, temperature maxima, and temperature minima. The arrivals of the storms at Viking Lander 1 were accompanied by significant increases in wind speed and pressure. No such changes were observed at Viking Lander 2. It is possible that surface material could have been raised locally at Viking Lander 1. Throughout the period except for the time following the second dust storm the synoptic picture at Viking Lander 2 was one of eastward moving cyclonic and anticyclonic systems. These disappeared following the second storm, a phenomenon which may be related to the storm.

01 Jan 1979
TL;DR: In this paper, a procedure which provides sonic-boom-minimizing equivalent area distributions for supersonic cruise conditions is described and extended previous analyses to permit relaxation of the extreme bluntness required by conventional lowboom shapes and includes propagation in a real atmosphere.
Abstract: A procedure which provides sonic-boom-minimizing equivalent area distributions for supersonic cruise conditions is described. This work extends previous analyses to permit relaxation of the extreme bluntness required by conventional low-boom shapes and includes propagation in a real atmosphere. The procedure provides area distributions which minimize either shock strength or overpressure.

Journal Article•DOI•
TL;DR: The steady response to orography as described by shallow-water equations on the sphere is examined in an attempt to provide insight into the dynamical effects of large-scale orographic features on atmospheric motion as discussed by the authors.
Abstract: The steady response to orography as described by shallow-water equations on the sphere is examined in an attempt to provide insight into the dynamical effects of large-scale orographic features on atmospheric motion. The model equations and the zonal flows and orography used in the study are described. The results for simple mountains and for the earth orography are given. The two-dimensional nature of the horizontal propagation on the sphere is emphasized. The results give interesting indications of the regions of influence of mountains and suggest that quantitative theories of the stationary waves must involve a full representation of the spherical domain.

Journal Article•DOI•
TL;DR: Comparisons are made between the water vapor DIAL measurements and data obtained from locally launched rawinsondes, and agreement was found to be within the uncertainty of the rawinsonde data to an altitude of 3 km.
Abstract: A ground-based differential absorption lidar (DIAL) system is described which has been developed for vertical range-resolved measurements of water vapor. The laser transmitter consists of a ruby-pumped dye laser, which is operated on a water vapor absorption line at 724.372 nm. Part of the ruby laser output is transmitted simultaneously with the dye laser output to determine atmospheric scattering and attenuation characteristics. The dye and ruby laser backscattered light is collected by a 0.5-m diam telescope, optically separated in the receiver package, and independently detected using photomultiplier tubes. Measurements of vertical water vapor concentration profiles using the DIAL system at night are discussed, and comparisons are made between the water vapor DIAL measurements and data obtained from locally launched rawinsondes. Agreement between these measurements was found to be within the uncertainty of the rawinsonde data to an altitude of 3 km. Theoretical simulations of this measurement were found to give reasonably accurate predictions of the random error of the DIAL measurements. Confidence in these calculations will permit the design of aircraft and Shuttle DIAL systems and experiments using simulation results as the basis for defining lidar system performance requirements.

Journal Article•DOI•
C. Swift1, L. Wilson1•
TL;DR: In this article, a theory for the radar imaging of ocean waves is presented under the assumptions that a swell propagates through an ensemble of Bragg scatterers and that the integration time of the synthetic aperture radar (SAR) is small compared to the angular velocity of the swell.
Abstract: A theory for the radar imaging of ocean waves is presented under the assumptions that a swell propagates through an ensemble of Bragg scatterers and that the integration time of the synthetic aperture radar (SAR) is small compared to the angular velocity of the swell. Results are prsented which show image development and distortions caused by the radial velocities and accelerations of the swell. Neglecting small wave bunching and tilts due to the longer underlying waves, and considering only one-dimensional geometries, the mechanism of wave motions are considered and their efforts on the production of the usual intensity Pattern representing the wave image are studied. The analysis shows that in certain situations a processed image can appear which has twice the spatial period of the actual long wave on the ocean, which can confuse the interpretation of ocean wave analysis.

Journal Article•DOI•
25 May 1979-Science
TL;DR: Surface condensates formed at the Viking 2 lander site during the winter and additional observations suggest that surface erosion rates due to dust redistribution may be substantially less than those predicted on the basis of pre-Viking observations.
Abstract: The imaging systems on board the two Viking landers have documented eolian processes and condensate formation on the Martian surface during the first Mars year of operation. During the winter, the formation of what appeared to be solid H2O and CO2 at the Viking 2 lander site was noted. The condensate formation suggested that solar radiative heating dominates atmospheric conductive heating on Mars. In addition, the Viking observations indicated that Martian surface erosion due to dust distribution may be lower than previously thought.

Journal Article•DOI•
TL;DR: The daily mean pressures at two locations on Mars, observed over 57% of a Martian year, reveal a semiannual oscillation with a peak-to-peak difference that is 26% of the mean pressure as discussed by the authors.
Abstract: The daily mean pressures at two locations on Mars, observed over 57% of a Martian year, reveal a semiannual oscillation with a peak-to-peak difference that is 26% of the mean pressure. This intrinsically Martian phenomenon is caused by exchange of CO2 between the atmosphere and the winter polar caps. Evidence is presented that the difference in pressure at the two landers varies with season and that the seasonal variation is not completely removed by hydrostatic correction for the difference in elevation. The mass CO2 sublimed from the south polar cap is estimated to be greater than or equal to 7.9 x 10 to the 12th metric tons, corresponding to a mean thickness of solid CO2 over the maximum extent of that cap of greater than or equal to 23 cm. Estimates are formed of the meridonal wind speed conveying gas out of the dissipating cap and the associated zonal geostrophic wind, both averaged over longitude. The results are approximately 2.3 m/sec and 14 m/sec, respectively.

Proceedings Article•DOI•
01 Jul 1979
TL;DR: In this paper, the authors examined the aero-acoustics associated with model nozzles operating supersonically and compared the shock structure and radiated shock noise of Mach 1.5 and 2.0 noizles with those of a convergent nozzle over a wide nozzle pressure ratio range corresponding to a fully expanded Mach number between unity and 237.
Abstract: The paper examines the aeroacoustics associated with model nozzles operating supersonically. In particular, the shock structure and radiated shock noise of Mach 1.5 and 2.0 nozzles are compared with those of a convergent nozzle over a wide nozzle pressure ratio range corresponding to a fully expanded Mach number between unity and 2.37. The nozzles were operated unheated both with and without a tab for screech tone suppression. The measurements show differences between the shock cell spacing of convergent and convergent-divergent nozzles, and the scaling relation appears to be a function of the exit-to-throat velocity ratio of each nozzle type. The acoustic measurements indicate the extent of the pressure ratio range where a C-D nozzle achieves a noise reduction benefit. At the design point of the Mach 1.5 nozzle, the total integrated sound power from this nozzle is 6 dB less than a convergent nozzle operating at the same pressure ratio and thrust

01 Aug 1979
TL;DR: In this article, a correlation of available self ignition data for supersonic hydrogen-air mixtures in configurations representative of scramjet combustors was made, and the correlation was examined in light of simplified ignition-limit models.
Abstract: A correlation of available self ignition data for supersonic hydrogen-air mixtures in configurations representative of scramjet combustors was made. The correlation was examined in light of simplified ignition-limit models. The data and model included cases of injection from transverse fuel jets on walls, transverse jets behind swept and unswept steps, and transverse injection ahead of swept and unswept steps and strut bases. The results provide useful guidance for predicting self ignition in a variety of applications. The likely regions for self ignition in a combustor are given in order of merit.

Journal Article•
TL;DR: In this article, the relativistic effective core potential (ECP) for uranium and a nonrelativistic ECP for fluorine was used to calculate the electron affinity of UF6 (7.1 eV).
Abstract: The paper presents ab initio calculations performed on the electronic states of UF6, UF6(+), and UF6(-) using a relativistic effective core potential (ECP) for uranium and a nonrelativistic ECP for fluorine. In most of the calculations 56 valence electrons are treated explicitly using a contracted (3s 3p 2d 2f/2s2p) Gaussian basis. It is noted that various ECP's were explored, but all yield an overall charge density of U(+2.4)/F(-0.4)/6. In addition, the bonding in the ground state of UF6 is discussed. SCF and CI calculations on UF6(+) are compared with the experimental photoelectron spectrum and with previous scattered wave calculations. Further, the role of spin-orbit coupling in the states of UF6(+) and UF6(-) is covered. Finally, it is concluded that the calculated electron affinity of UF6 (7.1 eV) is considerably larger than in current experimental estimates, but the relative energies of the states of UF6(-) are in agreement (0.1-0.2 eV) with those of the experiment.

Journal Article•DOI•
TL;DR: Comparisons with previously published experimental data show that accounting for imperfections improves correlation between theory and experiment and is applicable to general cross sections under general loading conditions causing buckling.
Abstract: A computer code for obtaining the dimensions of optimum (least mass) stiffened composite structural panels is described. The procedure, which is based on nonlinear mathematical programming and a rigorous buckling analysis, is applicable to general cross sections under general loading conditions causing buckling. A simplified method of accounting for bow-type imperfections is also included. Design studies in the form of structural efficiency charts for axial compression loading are made with the code for blade and hat stiffened panels. The effects on panel mass of imperfections, material strength limitations, and panel stiffness requirements are also examined. Comparisons with previously published experimental data show that accounting for imperfections improves correlation between theory and experiment.

Book Chapter•DOI•
TL;DR: In this paper, an experimental investigation has been conducted to determine the effect of low-velocity impact damage and unloaded circular holes on the compressive strength of a 48-ply orthotropic graphite/epoxy flat laminate.
Abstract: An experimental investigation has been conducted to determine the effect of low-velocity impact damage and unloaded circular holes on the compressive strength of a 48-ply orthotropic graphite/epoxy flat laminate. Specimens were impacted by a 1.27-cm-diameter aluminum sphere with speeds from 52 to 101 m/x to simulate momenta typical of low-velocity impact hazards that can occur in commercial aircraft service. It is shown that low-velocity impact damage can significantly degrade the static compressive strength of the laminate. Specimens that fail at axial strains above 0.008 in the undamaged condition can fail at strains as low as 0.0031 when impacted at 100 m/s. Circular holes also reduce the static compressive strength of the laminate. The failure strain decreases as the hole diameter increases.

Journal Article•DOI•
TL;DR: In this paper, a number of problem areas which limit the realization of the full potential of computerized symbolic manipulation in structural mechanics are examined and some of the means of alleviating them are discussed.

I. Abel1•
01 Feb 1979
TL;DR: In this paper, an analytical technique for predicting the performance of an active flutter-suppression system is presented based on the use of an interpolating function to approximate the unsteady aerodynamics.
Abstract: An analytical technique for predicting the performance of an active flutter-suppression system is presented. This technique is based on the use of an interpolating function to approximate the unsteady aerodynamics. The resulting equations are formulated in terms of linear, ordinary differential equations with constant coefficients. This technique is then applied to an aeroelastic model wing equipped with an active flutter-suppression system. Comparisons between wind-tunnel data and analysis are presented for the wing both with and without active flutter suppression. Results indicate that the wing flutter characteristics without flutter suppression can be predicted very well but that a more adequate model of wind-tunnel turbulence is required when the active flutter-suppression system is used.


Book Chapter•DOI•
01 Jan 1979
TL;DR: In this article, the authors presented stress-intensity factors, calculated by a 3D finite-element analysis, for shallow or deep quarter-elliptical corner cracks at the edge of a hole in a finite-thickness plate.
Abstract: This paper presents stress-intensity factors, calculated by a three-dimensional finite-element analysis, for shallow or deep quarter-elliptical corner cracks at the edge of a hole in a finite-thickness plate. The plate was subjected to remote uniform tension, remote bending, or simulated pin loading in the hole; a wide range of configuration parameters was investigated. To verify the accuracy of the three-dimensional finite-element models employed, convergence was studied by varying the numbers of degrees of freedom. The stress-intensity factor variations along the crack front are compared with solutions from the literature.

Book Chapter•DOI•
01 Jan 1979
TL;DR: In this paper, the authors compared 14 different solutions for the stress-intensity factors at failure of a surface crack in a finite plate subjected to uniform tension and evaluated the accuracy of the various solutions by correlating fracture data on surface-cracked tension specimens made of a brittle epoxy material.
Abstract: The stress-intensity factor solutions proposed for a surface crack in a finite plate subjected to uniform tension are reviewed. Fourteen different solutions for the stress-intensity factors are compared. These solutions were obtained over the past 16 years using approximate analytical methods, experimental methods, and engineering estimates. The accuracy is assessed of the various solutions by correlating fracture data on surface-cracked tension specimens made of a brittle epoxy material. Fracture of the epoxy material was characterized by a constant value of stress-intensity factor at failure. Thus, the correctness of the various solutions is judged by the variations in the stress-intensity factors at failure. The solutions were ranked in order of minimum standard deviation. The highest ranking solutions correlated 95 percent of data analyzed within + or - 10 percent, whereas the lowest ranking solutions correlated 95 percent of data analyzed within + or - 20 percent. However, some solutions could be applied to all data considered, whereas others are limited with respect to crack shapes and crack sizes that could be analyzed.