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Showing papers by "Langley Research Center published in 1980"


Journal ArticleDOI
TL;DR: In this paper, a two-stream approximation to radiative transfer theory for particulate media is shown to be represented by identical forms of coupled differential equations if the intensity is replaced by integrals of the intensity over hemispheres.
Abstract: Existing two-stream approximations to radiative transfer theory for particulate media are shown to be represented by identical forms of coupled differential equations if the intensity is replaced by integrals of the intensity over hemispheres. One set of solutions thus suffices for all methods and provides convenient analytical comparisons. The equations also suggest modifications of the standard techniques so as to duplicate exact solutions for thin atmospheres and thus permit accurate determinations of the effects of typical aerosol layers. Numerical results for the plane albedos of plane-parallel atmospheres are given for conventional and modified Eddington approximations, conventional and modified two-point quadrature schemes, the hemispheric-constant method and the delta-function method, all for comparison with accurate discrete-ordinate solutions. A new two-stream approximation is introduced that reduces to the modified Eddington approximation in the limit of isotropic phase functions and to the exact solution in the limit of extreme anisotropic scattering. Comparisons of plane albedos and transmittances show the new method to be generally superior over a wide range of atmospheric conditions (including cloud and aerosol layers), especially in the case of nonconservative scattering.

528 citations


Journal ArticleDOI
TL;DR: In this paper, a reduced basis technique and a computational algorithm are presented for predicting the nonlinear static response of structures, where a total Lagrangian formulation is used and the structure is discretized by using displacement finite element models.
Abstract: A reduced basis technique and a computational' algorithm are presented for predicting the nonlinear static response of structures. A total Lagrangian formulation is used and the structure is discretized by using displacement finite element models. The nodal displacement vector is expressed as a linear combination of a small number of basis vectors and a Rayleigh-Ritz technique is used to approximate the finite element equations by a reduced system of nonlinear equations. The Rayleigh-Ritz approximation functions (basis vectors) are chosen to be those commonly used in the static perturbation technique namely, a nonlinear solution and a number of its path derivatives. A procedure is outlined for automatically selecting the load (or displacement) step size and monitoring the solution accuracy. The high accuracy and effectiveness of the proposed approach is demonstrated by means of numerical examples.

414 citations


Journal ArticleDOI
01 Oct 1980
TL;DR: Microwave remote sensing is rapidly reaching the stage of maturity enjoyed by optical and infra-red systems as mentioned in this paper, and microwave radiometers have proven their capability to measure wind speed and direction over the ocean, ocean wave height, the topography of the earth, and the conditions of crops.
Abstract: Microwave remote sensing is rapidly reaching the stage af maturity enjoyed by optical and infra-red systems. The value of microwaves is that the atmosphere is almost transparent within this band. Microwaves therefore offer a view of the earth surface that is completely unobstructed by clouds. Both passive and active microwave systems have been utilized for measuring several geophysical phenomena. Microwave radiometers have, for example, measured ocean temperature and salinity, winds over the ocean, soil moisture through vegetation, and the age of arctic ice. Active microwave systems (scatterometers, short pulse altimeters, and imaging radars) have proven their capability to measure wind speed and direction over the ocean, ocean wave height, the topography of the earth, and the conditions of crops. Numerous other applications can be found in the recent technical literature. As detailed examples of the value of microwave remote sensing, this article describes two systems which are approaching an operational stage.

404 citations


Journal ArticleDOI
TL;DR: In this article, a nonreflecting boundary condition is presented for numerical solution of the time-dependent compressible Navier-Stokes equations when these equations are used to obtain a steady state.

371 citations


Journal ArticleDOI
TL;DR: The thermal structure of the Venus atmosphere and differences in structure with latitude (up to 60 deg) and clock hour (from midnight to 8 AM) have been measured in situ from a height of 126 km to the surface by instruments on the four Pioneer Venus entry probes as discussed by the authors.
Abstract: The thermal structure of the Venus atmosphere and differences in structure with latitude (up to 60 deg) and clock hour (from midnight to 8 AM) have been measured in situ from a height of 126 km to the surface by instruments on the four Pioneer Venus entry probes. It is found that thermal contrasts below 45 km are a few K, with the midlatitudes warmer than both equatorial and high latitudes. Considerable temperature and pressure differences with latitude develop in the clouds (25 K and 20 mbar level). In addition, upward of 110 km, there is evidence of large-amplitude temperature oscillations with altitude, believed to signify the presence of large-amplitude waves, perhaps thermal tides. Agreement of structure data from other Pioneer Venus experiments is generally excellent.

327 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of unmixedness on reaction in turbulent flow were investigated using a parabolic marching simulation of a super-sonic air stream with a finite-rate chemistry system.
Abstract: Good agreement has been obtained between published profiles of composition and pitot pressure with the calculated results from a computer program in which finite rate chemistry was used. Significant differences are noted between results calculated using 7 species and 8 reactions and those calculated using 12 species and 25 reactions. Differences are also found between results in which the effect of unmixedness on reaction in turbulent flow is applied or is not applied. ULTI-REACTION finite-rate chemistry has been used for many years in computer simulation of complex flowfields, and results have been good in laminar flows. Mixing of fuel and air is faster in turbulent flows than in laminar flows, but in turbulent flows the folding together of large volumes of fluid alternately rich in either fuel or oxygen produces the phenomenon of "unmixedness" in which the time-averaged temperature and composition at a point do not represent correctly the degree to which fuel and air are mixed on a molecular scale. Thus, the use of time-averaged values of temperatures and concentrations in the finite-rate chemistry equations is incorrect and can lead to serious errors in calculated results. This by no means rules out the use of time- averaged values, since the effects of unmixedness may be small for many turbulent, reacting flows. One purpose of this paper is to demonstrate that this is so by calculating some results with and without the effects of unmixedness. Another purpose of the paper is to report improvement in the ability of a computer program to simulate burning of H 2 in a super- sonic air stream when an eddy breakup chemistry model is replaced with one in which finite reaction rates, corrected for unmixedness, are used. In a prior investigation,1 the usefulness of a parabolic marching computer program was evaluated by comparing computed results with data from five experimental test cases. Mixing of fuel and oxidant was computed for parallel in- jection of H2 using a two-equation turbulence model, and the extent of chemical reaction was deduced by comparing the data with results obtained from three different assumptions: 1) no reaction, corresponding to zero combustion efficiency; 2) complete burning of all fuel mixed with oxygen, corresponding to combustion efficiency = 1; and 3) finite-rate burning based on the rate of decay of large turbulent eddies into small ones. The last of these assumptions, the eddy- breakup (EBU) model,2 provided a means for obtaining combustion efficiency values intermediate between 0 and 1 and is believed to be useful as a tool to account for the effects of unmixedness on chemical reaction in turbulent flows if chemical reaction rates are large enough so that the production of combustion products is limited by the mixing rate. In this paper three of the experimental test cases used in the previous computer program evaluation are reanalyzed using the same program but with a finite-rate chemistry system reported by Spiegler. 3 In this chemistry system the effect of unmixedness on individual reactions is modeled by decreasing any rate for which one or more of the species involved goes negative during fluctuation of its concentration about the average value. (Temperature fluctuations are not considered.) In addition to calculations using Spiegler's system of 7 species and 8 reactions, calculations were also made using 12 species and 25 reactions. The latter system required the solution of twice as many differential equations for chemical species, but this was judged to be necessary in order to examine the effect of the added equations on the generation rates of radicals such as H, O, and OH. The elemental reactions by means of which H2 and O2 are transformed into H2O provide multiple paths between the reactants and the product, most of which depend on the presence of high concentrations of radicals. The relative importance of the paths changes as conditions in the flow change, and it is important not to neglect any path which might be a large source or sink for one or more of the radicals, since such a path might be critical for prediction of ignition.

301 citations


01 Aug 1980
TL;DR: Three new options were incorporated into an existing computer program for the design and analysis of low speed airfoils that permit the analysis of airfoil having variable chord (variable geometry), a boundary layer displacement iteration, and theAnalysis of the effect of single roughness elements.
Abstract: A conformal mapping method for the design of airfoils with prescribed velocity distribution characteristics, a panel method for the analysis of the potential flow about given airfoils, and a boundary layer method have been combined With this combined method, airfoils with prescribed boundary layer characteristics can be designed and airfoils with prescribed shapes can be analyzed All three methods are described briefly The program and its input options are described A complete listing is given as an appendix

240 citations


Journal ArticleDOI
TL;DR: In this article, it was found that the meteoroids between 4 and 5 AU are not in direct circular or near-circular orbits near the ecliptic plane and the spatial density of 10 to -9 g meteoroids is essentially constant between 1 and 18 AU.
Abstract: The meteoroid penetration detectors on Pioneer 10 (channel 0) recorded 95 penetrations through the 25-micron stainless steel test material while the spacecraft was between 1 and 18 AU. The spatial density of 10 to the -9 g meteoroids is found to be essentially constant between 1 and 18 AU. The meteoroid penetration detectors on Pioneer 11 recorded 87 penetrations (55 on channel 0 and 32 on channel 1) through the 50-micron stainless steel test material while the spacecraft was between 1 and 9 AU. It is found that the meteoroids between 4 and 5 AU are not in direct circular or near-circular orbits near the ecliptic plane. The Pioneer 11 data obtained between 4 and 5 AU are best explained by the meteoroids being in randomly inclined orbits of high eccentricity. If meteoroids are in these cometlike orbits, the great increase in penetration flux previously measured near Jupiter with the Pioneer 10 experiment cannot be attributed to gravitational focusing unless the size distribution of meteoroids changes substantially between 1 and 5 AU. At Saturn encounter, the penetration flux increased by about three orders of magnitude, probably as the result of impacts from ring particles. Saturn's ring E is estimated to be 1800 km thick with an optical thickness greater than 10 to the -8.

177 citations


Journal ArticleDOI
TL;DR: In this article, the authors presented stress-intensity factors for a wide range of semi-elliptical surface cracks on the inside of pressurized cylinders, which were calculated by a three-dimensional finite-element method using singularity elements along the crack front and linear strain elements elsewhere.
Abstract: The paper presents stress-intensity factors for a wide range of semi-elliptical surface cracks on the inside of pressurized cylinders. The ratio of crack depth to crack length ranged from 0.2 to 1; the ratio of crack depth to wall thickness ranged from 0.2 to 0.8; and the ratio of wall thickness to vessel radius was 0.1 to to 0.25. The stress-intensity factors were calculated by a three-dimensional finite-element method using singularity elements along the crack front and linear-strain elements elsewhere. An equation for the stress-intensity factors was obtained which applies over a wide range of configuration parameters and was within about 5 percent of the present results. A comparison was also made between the results and other analyses of internal surface cracks in cylinders. The results from a boundary-integral equation method were in agreement and those from another finite-element method were in fair agreement (+ or - 8 percent) with the results.

152 citations


Proceedings ArticleDOI
01 Jun 1980
TL;DR: In this article, an aerodynamic and acoustic measurements of shock-free and shock-containing plumes were acquired for several supersonic free-jet model nozzles for the purpose of investigating important features of the broadband shock noise generation process.
Abstract: Aerodynamic and acoustic measurements of shock-free and shock-containing plumes were acquired for several supersonic free-jet model nozzles. The purpose was to investigate important features of the broadband shock noise generation process. The aerodynamic measurements include the variation of shock cell spacing and strength as a function of nozzle pressure ratio, and longitudinal turbulent-mass-flux axial development as determined by a hot-film probe. In addition, correlations of the hot-film probe with a near-field microphone were obtained. These measurements provide useful information concerning the relation of peak shock noise frequency and level with variations in shock cell spacing and strength. In general, it is shown that a distinction must be made between plumes containing weak and strong imbedded shocks. Strong shocks diminish the level of emitted shock noise and influence the behavior of the jet mixing noise process. The probable location and spectral content for the shock-shear layer interaction mechanism is indicated by the correlations. Numerical inviscid plume comparisons with experimental data are also included.

126 citations


01 Jan 1980
TL;DR: In this paper, the authors examined the drag characteristics of longitudinally ribbed surfaces where the rib dimensions are the order of the initial turbulent wall burst region near the wall, and showed that the drag reduction was confirmed by reductions in the momentum thickness, turbulent velocity fluctuations, and Reynolds stress profiles.
Abstract: The paper examines the drag characteristics of longitudinally ribbed surfaces where the rib dimensions are the order of the initial turbulent wall burst region near the wall. Direct drag measurements are presented for symmetric and unsymmetric V-groove, and (larger wavelength) transverse curvature riblets. The direct drag data indicate net drag reductions as large as 7% for certain V-groove riblets with heights in terms of law of the wall coordinates h+ less than 30. For one of the riblet models, the drag reduction is confirmed by reductions in the momentum thickness, turbulent velocity fluctuations, and Reynolds stress profiles. Although the direct drag data for the transverse curvature riblets showed drag increases, certain models did show that the drag increase diminished with increasing velocity. This trend is opposite to the normal one found for rough surfaces and should be investigated further.

Journal ArticleDOI
TL;DR: In this article, the authors measured the modulation transfer functions (the ratio of the cross spectrum of the line-of-sight orbital speed and backscattered microwave power to the autospectrum of the LOS orbital speed) at 9.375 and 1.5 GHz (Bragg wavelengths of 2.3 and 13 cm) for winds up to 10 m/s and ocean wave periods from 2-18 s.
Abstract: Short gravity-capillary waves, the equilibrium, or the steady state excitations of the ocean surface are modulated by longer ocean waves. These short waves are the predominant microwave scatterers on the ocean surface under many viewing conditions so that the modulation is readily measured with CW Doppler radar used as a two-scale wave probe. Modulation transfer functions (the ratio of the cross spectrum of the line-of-sight orbital speed and backscattered microwave power to the autospectrum of the line-of-sight orbital speed) were measured at 9.375 and 1.5 GHz (Bragg wavelengths of 2.3 and 13 cm) for winds up to 10 m/s and ocean wave periods from 2-18 s. The measurements were compared with the relaxation-time model; the principal result is that a source of modulation other than straining by the horizontal component of orbital speed, possibly the wave-induced airflow, is responsible for most of the modulation by waves of typical ocean wave period (10 s). The modulations are large; for unit coherence, spectra of radar images of deep-water waves should be proportional to the quotient of the slope spectra of the ocean waves by the ocean wave frequency.

Journal ArticleDOI
TL;DR: In this article, an atmospheric composition, temperature, and density model based on the orbiter atmospheric drag vertical structure is presented, which shows that atomic oxygen is the major component in the Venus atmosphere above 145 km at night and above 160 km during the day with mixing ratios over 0.1 near 140 km.
Abstract: Atmospheric densities of Venus were measured from the orbital decay of the Pioneer Venus from Dec. 9, 1978 to Aug. 7, 1979 near the 16 deg latitude between 140 and 190 km during the entire day. Comparative atmospheric densities on earth at 150 km are higher by a factor of 3.5 with only a 1% diurnal variation; an atmospheric composition, temperature, and density model based on the orbiter atmospheric drag (OAD) vertical structure is presented. The model shows that atomic oxygen is the major component in the Venus atmosphere above 145 km at night and above 160 km during the day with mixing ratios over 0.1 near 140 km; drag measurements indicate O concentrations from 1 x 10 to the 9th/cu cm in daytime to 3 x 10 to the 7th/cu cm at night. It is concluded that the neutral upper atmosphere of Venus is surprisingly insensitive to solar extreme UV variations and changes in the solar wind.

Patent
14 Aug 1980
TL;DR: In this article, an acoustic oral hygiene unit that uses acoustic energy to oscillate mild abrasive particles 17a in a water suspension 17 which is then directed in a low pressure stream onto the teeth.
Abstract: This invention is an acoustic oral hygiene unit that uses acoustic energy to oscillate mild abrasive particles 17a in a water suspension 17 which is then directed in a low pressure stream onto the teeth. The oscillating abrasives scrub the teeth clean removing food particles, plaque, calculous, and other foreign material from tooth surfaces, interproximal areas, and tooth-gingiva interface more effectively than any previous technique. The relatively low power output and the basic design makes the invention safe and convenient for everyday use in the home without special training. This invention replaces all former means of home dental prophylaxis, and requires no augmentation to fulfill all requirements for daily oral hygienic care.

DissertationDOI
01 Jan 1980
TL;DR: The Split Coefficient Matrix (SCM) finite difference method for solving hyperbolic systems of equations is presented in this paper, which is a new method based on the mathematical theory of characteristics.
Abstract: The Split Coefficient Matrix (SCM) finite difference method for solving hyperbolic systems of equations is presented. This new method is based on the mathematical theory of characteristics. The development of the method from characteristic theory is presented. Boundary point calculation procedures consistent with the SCM method used at interior points are explained. The split coefficient matrices that define the method for steady supersonic and unsteady inviscid flows are given for several examples. The SCM method is used to compute several flow fields to demonstrate its accuracy and versatility. The similarities and differences between the SCM method and the lambda-scheme are discussed.

01 Aug 1980
TL;DR: In this paper, an experiment was conducted at static conditions to determine the internal performance effects of nozzle throat contouring, the result of increasing the circular-arc throat radius, and a two-dimensional inviscid theory was applied to the five configurations.
Abstract: An experiment was conducted at static conditions to determine the internal performance effects of nozzle throat contouring, the result of increasing the circular-arc throat radius. Five nonaxisymmetric converging-diverging nozzles were tested at nozzle pressure ratios up to 9.0. Data are presented as internal thrust ratios, discharge coefficients, and static-pressure distributions. Comparisons of internal performance data for the five nozzles show that throat contouring increases the value of discharge coefficient but has no significant effect on internal thrust ratio except in cases of internal flow separation. To illustrate the use of the two dimensional converging-diverging (2-D C-D) nozzle data base, a two dimensional inviscid theory was applied to the five configurations. The generally good agreement of data with theoretical results indicates that two-dimensional inviscid theory can be successfully applied to the prediction of 2-D C-D nozzle internal flow.

Journal ArticleDOI
TL;DR: In this article, a simple rational approach is presented for developing micropolar beam models for large repetitive beam-like planar lattices with rigid joints, which have independent microrotation, and displacement fields and are characterized by their strain and kinetic energies.

Journal ArticleDOI
TL;DR: The Seasat-A satellite scatterometer (SASS) was designed to measure ocean surface wind speed and direction in twenty-four (24) independent cells over a 1000-km swath.
Abstract: The Seasat-A satellite scatterometer (SASS) was designed to measure ocean surface wind speed and direction in twenty-four (24) independent cells over a 1000-km swath. It operated in the interrupted CW mode at a frequency of 14.6 GHz with four (4) fan beam antennas and used Doppler filtering in the receiver for resolving the cells on the surface. The instrument began operating in space on July 6, 1978, and gathered normalized radar cross section ( \sigma^{0} ) data for approximately 2290 h. The purpose of this paper is to describe the in-orbit evaluation of the SASS hardware and its compatibility with the spacecraft. It has been determined that the scatterometer operated flawlessly throughout the mission, met all design requirements, and established a good data base for geophysical processing.

01 Nov 1980
TL;DR: In this article, a computer code for analyzing and sizing uniaxially-stiffened composite panels is described, and the capability of the PASCO computer code and the approach used in the structural analysis and sizing are described.
Abstract: A computer code denoted PASCO which can be used for analyzing and sizing uniaxially-stiffened composite panels is described. Buckling and vibration analyses are carried out with a linked-plate analysis computer code denoted VIPASA, which is incorporated in PASCO. Sizing is based on nonlinear mathematical programming techniques and employs a computer code denoted CONMIN, also incorporated in PASCO. Design requirements considered are initial buckling, material strength, stiffness, and vibration frequency. The capability of the PASCO computer code and the approach used in the structural analysis and sizing are described.

Journal ArticleDOI
TL;DR: In this paper, the current status of passive microwave remote sensing of the ocean is reviewed and the physics of emission and instrumentation are highlighted in order to establish a relationship between the thermal emission and retrieved geophysical parameters.
Abstract: This paper reviews the current status of passive microwave remote sensing of the ocean. The physics of emission and instrumentation are highlighted in order to establish a relationship between the thermal emission and retrieved geophysical parameters. A discussion then follows on measurements of temperature, salinity, windspeed, etc. using passive microwave systems. These measurements are related to the accuracy and spatial resolution required by the users. The status of passive microwave remote sensing is summarized and recommendations for future research are presented.

Journal ArticleDOI
TL;DR: In this paper, a series of experimental studies utilizing approximately 2200 test subjects has led to the development of a general empirical model for the prediction of passenger ride discomfort in the presence of complex noise and vibration inputs.
Abstract: A series of experimental studies utilizing approximately 2200 test subjects has led to the development of a general empirical model for the prediction of passenger ride discomfort in the presence of complex noise and vibration inputs The ranges of vibration and noise stimuli used to derive the model included the amplitudes and frequencies that are known to most influence passenger comfort The ride quality model accounts for the effects of combined axis vibrations (up to three axes simultaneously) and includes corrections for the effect of vibration duration and interior noise Output of the model consists of an estimate of the passenger discomfort produced by a given noise and/or vibration environment The discomfort estimate is measured along a continuous scale that spans the range from below discomfort threshold to values of discomfort that are far above discomfort threshold

Journal ArticleDOI
01 Jan 1980
TL;DR: A significant effort has been devoted during the last 10 years to develop a route to thermally stable polymers without the evolution of volatile by-products as discussed by the authors, and some success has been attained by reducing the volatile level through B-staging, which is generally accompanied by reduced resin flow and also by using an intricate bleeder system and a long cure cycle.
Abstract: A significant effort has been devoted during the last 10 years to develop a route to thermally stable polymers without the evolution of volatile by-products. Most high-temperature polymers are prepared by condensation polymerization which involves the elimination of volatiles. These volatiles are responsible for severe problems encountered in the fabrication of parts, particularly thick and large components. Some success has been attained by reducing the volatile level through B-staging, which is generally accompanied by reduced resin flow and also by using an intricate bleeder system and a long cure cycle. These modifications are generally unacceptable for production-line use due to cost and reliability. A few high-temperature polymers can be processed as thermoplastics. However, the resin form is unacceptable for complex components (e.g., prepreg too boardy) and high temperature and pressure are generally required. In an attempt to circumvent these problems, work has concentrated on the develop...

Journal ArticleDOI
TL;DR: In this article, a nulling, parallel-linkage sensing element was developed for a skin-friction balance in order to minimize the introduction of extraneous forces, including misalignment and off-center normal forces.
Abstract: A nulling, parallel-linkage sensing element has been developed for a skin-friction balance in order to minimize the introduction of extraneous forces. Advantages of the present element over the conventional single-pivot sensing element include its insensitivity to element misalignment and off-center normal forces. Wind tunnel tests of the effects of gap size and element misalignment on parallel-linkage balance measurements indicate the greater sensitivity of the device to misalignment at small gap sizes and large lip sizes, as well as its relative insensitivity to off-center normal forces. It is concluded that a parallel-linkage device with a small lip is virtually insensitive to gap size and element misalignment, representing an improvement in skin-friction-measuring characteristics.

Book ChapterDOI
01 Jan 1980
TL;DR: In this paper, a computer code is described for proportioning or sizing laminate layers and cross-sectional dimensions, and the code is used to develop structural efficiency data for a variety of configurations, loading conditions, and constraint conditions.
Abstract: Structural technology of laminated filamentary-composite stiffened-panel structures under combined in-plane and lateral loadings is discussed. Attention is focused on (1) methods for analyzing the behavior of these structures under load and for determining appropriate structural proportions for weight efficient configurations, and (2) effects of impact damage and geometric imperfections on structural performance. Recent improvements in buckling analysis involving combined in-plane compression and shear loadings and transverse shear deformations are presented. A computer code is described for proportioning or sizing laminate layers and cross-sectional dimensions, and the code is used to develop structural efficiency data for a variety of configurations, loading conditions, and constraint conditions. Experimental data on buckling of panels under in-plane compression is presented to validate the analysis and sizing methods and to illustrate structural performance and efficiency obtained from representative structures. Experimental results show that strength of panels under in-plane compression can be degraded by low-velocity impact damage. Mechanisms of impact-damage initiation and propagation are described. Finally, data are presented that indicates the matrix is a significant factor influencing tolerance to impact damage.

01 Nov 1980
TL;DR: In this article, an analytical technique for approximating unsteady aerodynamic forces in the time domain was presented for an aeroelastic, cantilevered, semispan wing which indicate a good fit to the aerodynamic force for oscillatory motion can be achieved with a matrix Pade approximation having fourth order numerator and second order denominator polynomials.
Abstract: An analytical technique is presented for approximating unsteady aerodynamic forces in the time domain. The order of elements of a matrix Pade approximation was postulated, and the resulting polynomial coefficients were determined through a combination of least squares estimates for the numerator coefficients and a constrained gradient search for the denominator coefficients which insures stable approximating functions. The number of differential equations required to represent the aerodynamic forces to a given accuracy tends to be smaller than that employed in certain existing techniques where the denominator coefficients are chosen a priori. Results are shown for an aeroelastic, cantilevered, semispan wing which indicate a good fit to the aerodynamic forces for oscillatory motion can be achieved with a matrix Pade approximation having fourth order numerator and second order denominator polynomials.

Journal ArticleDOI
TL;DR: In this article, a model based on a physical picture of boundary layer vorticity being swept around the edge by spanwise flow on the flap was developed and solved and the resulting noise radiation calculated.
Abstract: The recently observed phenomenon of high noise radiation from the side edges of flaps in flow is investigated by way of a simple two-dimensional model problem. The model is based upon a physical picture of boundary layer vorticity being swept around the edge by spanwise flow on the flap. The model problem is developed and solved and the resulting noise radiation calculated. Further, a mathematical condition for the vortex to be captured by the potential flow and swept around the edge is derived. The results show that the sound generation depends strongly upon the strength of the vorticity and distance from the edge and that it can be more intense than the more common trailing edge noise source in agreement with the experimental observations.

Proceedings ArticleDOI
01 Jul 1980
TL;DR: In this article, an approximate method for predicting the viscosity of partially ionized gas mixtures is proposed, which is suitable for use with complex flowfields and heat transfer calculations.
Abstract: An approximate method is proposed for predicting the viscosity of partially ionized gas mixtures. This technique expresses the viscosity of a mixture in terms of the viscosities of the individual pure components, is simple in form, and does not require large computer run times or storage. Thus, the technique is suitable for use with complex flowfields and heat-transfer calculations. Results for gas mixtures which are representative of the atmospheres of Jupiter, Earth, and Venus, are presented and it is shown that the results compare favorably with detailed kinetic-theory analyses.

Journal ArticleDOI
TL;DR: In this paper, the authors describe the algorithms used to convert engineering unit data obtained from the Seasat-A satellite scatterometer (SASS) to radar scattering coefficients and associated supporting parameters.
Abstract: This paper describes the algorithms used to convert engineering unit data obtained from the Seasat-A satellite scatterometer (SASS) to radar scattering coefficients ( \sigma\deg ) and associated supporting parameters. A description is given of the instrument receiver and related processing used by the scatterometer to measure signal power backscattered from the earth's surface. The applicable radar equation used for determining \sigma\deg is derived. Sample results of SASS data processed through current algorithm development facility (ADF) \sigma\deg algorithms are presented which include \sigma\deg values for both water and land surfaces, \sigma\deg signatures for these two surface types are seen to have distinctly different characteristics. As expected, \sigma\deg values for water show strong dependence on both incidence angle and wind speed. For land, \sigma\deg values are relatively independent of incidence angle above 20\deg and have values in the range -14 dB. \sigma\deg measurements of the Amazon rain forest indicate the usefulness of this type of data as a stable calibration reference target. Using this Amazon data, relative biases between all four antennas and both polarizations are shown to be less than 0.4 dB.

Journal ArticleDOI
TL;DR: In this paper, the authors developed a model for the static, free vibration and buckling analysis of repetitive spatial beam-like lattices with rigid joints, which is characterized by their strain energy, potential energy due to initial stresses and kinetic energy from which the governing differential equations and boundary conditions can be derived.

Patent
07 Feb 1980
TL;DR: In this article, a thin layer of a perforated foil film is interposed between adjacent laminae of a composite formed from prepreg tapes to enable lamina adherence through the perforations.
Abstract: This invention relates to an interlaminar separation system for composites wherein a thin layer of a perforated foil film is interposed between adjacent laminae of a composite formed from prepreg tapes to thereby permit laminae adherence through the perforations and produce a composite structure having improved physical property characteristics