Showing papers by "Langley Research Center published in 1978"
TL;DR: In this paper, a mathematical model of the cavity tones and pressure oscillation phenomenon based on the coupling between shear layer instabilities and acoustic feedback is developed to help in understanding the tone generation mechanism.
Abstract: Experimental measurements of the frequencies of discrete tones induced by flow over rectangular cavities were carried out over a range of low subsonic Mach numbers to provide a reliable data base for (aircraft wheel well) cavity noise consideration. A mathematical model of the cavity tones and pressure oscillation phenomenon based on the coupling between shear layer instabilities and acoustic feedback is developed to help in understanding the tone generation mechanism. Good agreement is found between discrete tone frequencies predicted by the model and experimental measurements over a wide range of Mach numbers. Evidence of tones generated by the cavity normal mode resonance mechanism at very low subsonic Mach numbers is also presented.
437 citations
TL;DR: In this article, the problem of pole-assignment in a linear time-invariant multivariable system using output feedback is considered, and sufficient conditions are derived to assign an almost arbitrary set of min (n,m+r- 1) distinct eigenvalues, where n, m, and r are the number of states, inputs, and outputs, respectively.
Abstract: The problem of pole-assignment in a linear time-invariant multivariable system using output feedback is considered. New sufficient conditions are derived to assign an almost arbitrary set of min (n,m+r- 1) distinct eigenvalues, where n, m , and r are the number of states, inputs, and outputs, respectively. The analysis also highlights the freedom in selection of closed-loop eigenvectors which can be used for response shaping.
191 citations
TL;DR: In this paper, a simple, rational approach is presented for developing continuum models for large repetitive beam and plate-like lattices with arbitrary configurations subjected to static, thermal, and dynamic loadings.
Abstract: A simple, rational approach is presented for developing continuum models for large repetitive beam- and platelike lattices with arbitrary configurations subjected to static, thermal, and dynamic loadings. The continuum models for these structures are shear flexible beams and plates. They account for local effects in the repeating element of the actual structure and are characterized by their thermoelastic strain and kinetic energies, from which the equations of motion and constitutive relations can be derived. The procedure for developing the expressions for thermoelastic strain and kinetic energies of the continuum involves introducing basic assumptions regarding the variation of the temperature, displacement, and strain components in one or two directions (for plate- and beamlike lattices) and obtaining effective thermoelastic and dynamic coefficients of the continuum in terms of material properties and geometry of the original lattice structure. The high accuracy of the continuum models developed is demonstrated by means of numerical examples. AltA2,Ab,Ad
177 citations
TL;DR: In this paper, it was shown that the normalized radar cross-section (NRCS) of the ocean is a function of only the friction velocity at the ocean's surface, and the dependence of the NRCS on radar variables such as frequency, incidence angle, polarization, etc.
Abstract: From the mid 1960s to the present, the normalized radar cross-section (NRCS) of the ocean has been measured using airborne radars operating over a frequency range of 0.4 to 14 GHz. Analyses of these data have shown that the NRCS was proportional to the ocean surface wind speed raised to some power, but the values of the exponent remained in dispute. This paper extends previous work and uses these NRCS measurements to demonstrate that to the first order, the NRCS is a function of only the friction velocity at the ocean's surface. Further analyses characterize the dependence of the NRCS on radar variables such as frequency, incidence angle, polarization, etc. Finally, recommendations are made for using Ku-band radars at large incidence angles for remote sensing of the wind friction velocity vector.
109 citations
01 Jul 1978
TL;DR: In this article, the authors investigated the drag characteristics of longitudinally ribbed surfaces using various configurations which attempt to confine the turbulent wall bursts to regions of small transverse extent in the initial birth region.
Abstract: An investigation is conducted regarding the drag characteristics of longitudinally ribbed surfaces using various configurations which attempt to confine the turbulent wall bursts to regions of small transverse extent in the initial birth region. The ratio of heat transfer increase to drag increase for the high area ratio rib configurations is determined and the heat transfer efficiency of the present surfaces is compared with data found in the literature. The drag data obtained indicate local 'wetted area skin friction' reductions but due to the increased surface area the planform drag is increased in most instances. There is no indication of drag reduction with the rectangular ribbed models that had sharp leading and fin tip edges. Heat transfer data indicate that several of the triangular grooved models have efficiencies approximately 10 percent higher than that of a smooth flat plate.
103 citations
TL;DR: In this paper, the authors used a third-generation system using null balancing and feed-back noise injection to estimate sea surface temperature and salinity with an accuracy of 1.5 km.
Abstract: Sea-surface temperature with an accuracy of 1 °C and salinity with an accuracy of 1‰ were measured with a 1.43 and 2.65 GHz radiometer system after correcting for the influence of cosmic radiation, intervening atmosphere, sea-surface roughness, and antenna beamwidth. The radiometers are a third-generation system using null-balancing and feed-back noise injection. Flight measurements from aircraft over bay regions and coastal areas of the Atlantic resulted in contour maps with spatial resolution of 0.5 km.
99 citations
TL;DR: In this paper, the authors summarize some meteorological results from Viking for northern summer, autumn and winter and calculate the number of Rossby waves present at a given instant for these seasons.
Abstract: We summarize some meteorological results from Viking for northern summer, autumn and winter. Little Sol-to-Sol meteorological change was observed during summer, except for secular pressure change. However, a regular sequence of weather disturbances, interpreted as baroclinic waves, appeared primarily at VL-2 during autumn and winter. The number of Rossby waves present at a given instant is calculated to be 4 and 6 for these seasons. The extreme regularity and low wave number make these systems closely resemble the baroclinic waves of rotating annulus experiments.
94 citations
TL;DR: The Riccati transfer matrix method as discussed by the authors is a new technique for analyzing structural members, which makes use of an existing large catalog of transfer matrices for various structural members such as rotating shafts.
Abstract: The Riccati transfer matrix method is a new technique for analyzing structural members. This new technique makes use of an existing large catalog of transfer matrices for various structural members such as rotating shafts. The numerical instability encountered when calculating high resonant frequencies, static response of a flexible member on a stiff foundation, or the response of a long member by the transfer matrix method is eliminated by the Riccati transfer matrix method. The computational time and storage requirements of the Riccati transfer matrix method are about half the values for the transfer matrix method. A rotating shaft analysis demonstrates the numerical accuracy of the method.
87 citations
TL;DR: Status and recent developments of substructuring techniques and their application to structural analysis and design are summarized and the potential benefits of using such techniques with new computing hardware such as CDC STAR-100 and minicomputer systems are discussed.
86 citations
TL;DR: The interaction between atomic hydrogen and the (0001) surface of Be has been studied by using clusters of Be atoms to simulate the substrate in this paper, where an H atom is added to the Be clusters at four high symmetry adsorption sites.
Abstract: The interaction between atomic hydrogen and the (0001) surface of Be has been studied by using clusters of Be atoms to simulate the substrate. The largest cluster used contains 22 Be atoms, 14 in the first layer and 8 in a second layer. An H atom is added to the Be clusters at four high symmetry adsorption sites. Ab initio molecular orbital Hartree-Fock wave functions have been obtained and the interaction energy of H with the Be cluster is studied as a function of vertical distance from the surface. Thorough studies of various aspects of the computations and of the appropriate interpretation of the cluster results are reported. Our results show that three of the sites considered have similar binding energies, De ≅ 50 kca/mol (≅2.1 × 105 J/mol), and (vertical) equilibrium distances from the surface, re ≅ 0.1 nm. For the fourth site, H directly over a Be atom, De is ≅30 kca/mol(1.3 × 105 J/mol), and re is ≅ 0.14 nm. We expect that the dissociative adsorption of H2 on Be(0001) will be exothermic. A model calculation for diffusion of H into the bulk indicates that this process is energetically unfavorable for an ideal (0001) surface. The vibrational energies for the motion of H normal to the surface are found to be substantially different for sites with different surface coordinations. The nature of the covalent bond formed between H and Be(0001) is analyzed.
85 citations
01 Mar 1978
TL;DR: In this paper, the capabilities of a computer program are explored, and computed results are compared with data The comparisons are restricted to two-dimensional flows Subsonic and supersonic flows, ducted and nonducted, reacting and nonreacting, are considered.
Abstract: The capabilities of a computer program are explored, and computed results are compared with data The comparisons are restricted to two-dimensional flows Subsonic and supersonic flows, ducted and nonducted, reacting and nonreacting, are considered An evaluation of models used for turbulence and chemical reaction was included Constants in the dissipation rate of turbulent kinetic energy, turbulence model, which produces mixing in good agreement with data, are the same for all calculations Experimental data are reported for coaxial injection at matched pressure (1 atm or 1013 kPa) of a cold, Mach 2, hydrogen jet into a hot, Mach 2, vitiated airstream Profiles of pitot pressure and gas composition obtained from water cooled probes are reported and compared with theoretical results
TL;DR: In this article, a steady-state 1-D radiative-convective-photochemical model was used to determine the response of stratospheric temperatures and O3, O(1D), O(3P), and N2O constituent distributions to UV variability.
Abstract: Observational evidence suggests the presence of solar UV variability in the spectral range 0.175-0.310 micron during the 11-year solar cycle. The present paper reports the results of a study using a steady-state 1-D radiative-convective-photochemical model conducted to determine the response of stratospheric temperatures and O3, O(1D), O(3P), and N2O constituent distributions to UV variability. Results show that concentrations of constituents and the thermal structure may be altered significantly for the altitude interval between 20 and 55 km.
TL;DR: In this paper, the results of lidar observations, at Hampton (Virginia), of the stratospheric aerosol vertical distribution for a period of 22 months (October 1974 to July 1976) after the volcanic eruption of the Volcan de Fuego in Guatemala were discussed.
Abstract: The paper summarizes and discusses results of lidar observations, at Hampton (Virginia), of the stratospheric aerosol vertical distribution for a period of 22 months (October 1974 to July 1976) after the volcanic eruption of the Volcan de Fuego in Guatemala. Data are presented in terms of lidar scattering ratio, vertically integrated aerosol backscattering, layer structure and location, and rawinsonde temperature profiles as a function of time. The results reveal a sudden increase in the stratospheric aerosol content after the volcanic eruption as well as its subsequent decline. There exists a high degree of correlation between the integrated aerosol backscattering and the tropopause height such that as one decreases the other increases and vice versa. Rapid decay of the stratospheric aerosol is found to occur over the late winter to early spring period.
TL;DR: In this paper, a program for providing research data on aerodynamic loads and active control systems on wings with supercritical airfoils in the transonic speed range is described, and a Firebee II target drone vehicle has been modified for use as a flight test facility.
Abstract: A program for providing research data on aerodynamic loads and active control systems on wings with supercritical airfoils in the transonic speed range is described. Analytical development, wind tunnel tests, and flight tests are included. A Firebee II target drone vehicle has been modified for use as a flight test facility. The program currently includes flight experiments on two aeroelastic research wings. The primary purpose of the first flight experiment is to demonstrate an active control system for flutter suppression on a transport-type wing. Design and fabrication of the wing are complete and after installing research instrumentation and the flutter suppression system, flight testing is expected to begin in early 1979. The experiment on the second research wing - a fuel-conservative transport type - is to demonstrate multiple active control systems including flutter suppression, maneuver load alleviation, gust load alleviation, and reduce static stability. Of special importance for this second experiment is the development and validation of integrated design methods which include the benefits of active controls in the structural design.
TL;DR: A parametric analysis of the Shuttle-borne differential absorption lidar concept for the measurement of atmospheric trace constituent profiles in the nadir viewing mode is presented and the criterion of an optimum constituent optical depth is developed and applied to generate estimates of range resolved measurement errors.
Abstract: A parametric analysis of the Shuttle-borne differential absorption lidar concept for the measurement of atmospheric trace constituent profiles in the nadir viewing mode is presented. The criterion of an optimum constituent optical depth is developed and applied to generate estimates of range resolved measurement errors. These errors emphasize the fundamental limitations for establishing the feasibility of range-resolved differential absorption lidar measurements from Shuttle. With current lidar system technology, atmospheric backscatter density profiles may be adequately determined up to about 60-km altitude at the doubled-ruby wavelength, 3472 A, for a 1-J/pulse laser and a 1-sq m receiver. Potential range-resolved measurements of stratospheric and mesospheric trace constituents by differential absorption from Shuttle altitudes are limited to H2O, CH4, N2O, O3, and CO, species which can be more easily measured by passive limb viewing techniques. Range-resolved water vapor data for the lower troposphere may be obtained with accuracies which would be competitive with those from passive sensors.
01 Jul 1978
TL;DR: In this article, the general mass characteristics of long lightly loaded columns for space applications are investigated by studying four column concepts: a simple tubular column, a three longer-on truss column constructed of tubular members, the third is a three-longer-on-truss column composed of solid rod members, and the fourth is an open grid work isogrid wall tubeular column.
Abstract: The general mass characteristics of long lightly loaded columns for space applications are investigated by studying four column concepts. The first is a simple tubular column, the second is a three longeron truss column constructed of tubular members, the third is a three longeron truss column constructed of solid rod members, and the fourth is an open grid work isogrid wall tubular column. Design procedures, which include an initial imperfection in the straightness of the column, are developed for the different concepts and demonstrated numerically. A new set of structural efficiency parameters are developed for lightly loaded columns and are used to show a comparison of the masses of the four column concepts investigated.
TL;DR: In this article, high-energy electron trajectories in a plasma focus are measured as functions of position, time, energy, and angle of emission, and the spatial resolution of the X-ray emission shows that low-energy X-rays are emitted from the anode surface.
Abstract: Measurements are made of high-energy electron trajectories in a plasma focus as functions of position, time, energy, and angle of emission. The spatial resolution of the X-ray emission shows that low-energy X-rays are emitted from the anode surface. It is also suggested that the highest energy X-rays originate from a small region on the axis. The so-called shadow technique shows that the electron beam is perpendicular to the anode surface. Polar diagrams of medium and high-energy X-rays agree with the bremsstrahlung emission from a relativistic electron beam, the current of which is several 100 A.
01 Jan 1978
TL;DR: In this article, a simple rational approach is presented for developing continuum models for large repetitive beam-like and plate-like lattices with arbitrary configurations subjected to static, thermal and dynamic loadings.
Abstract: A simple, rational approach is presented for developing continuum models for large repetitive beam-like and plate-like lattices with arbitrary configurations subjected to static, thermal and dynamic loadings. The continuum models for these structures are shear flexible beams and plates. They account for local effects in the repeating element of the actual structure and are characterized by their thermoelastic strain and kinetic energies from which the equations of motion and constitutive relations can be derived. The procedure for developing the expressions for thermoelastic strain and kinetic energies of the continuum involves introducing basic assumptions regarding the variation of the temperature, displacement and strain components in one or two directions (for plate-like and beam-like lattices) and obtaining effective thermoelastic and dynamic coefficients of the continuum in terms of material properties and geometry of the original lattice structure. The high accuracy of the continuum models developed is demonstrated by means of numerical examples.
TL;DR: In this paper, a two-scale radar-scattering model is used to convert the normalized radar cross-section measurements to sea-surface wind stress and neutral stability wind vector.
Abstract: On the SeaSat-A satellite, a microwave scatterometer will be used to infer the wind vector over the world's oceans. This paper describes an algorithm to convert the scatterometer's normalized radar cross-section measurements to sea-surface wind stress and neutral stability wind vector. The algorithm is based on experimental NRCS data from aircraft measurements and a two-scale radar-scattering model. The technique uses Bayes' probabilistic equation to infer the friction velocity vector, from which the wind stress and neutral stability wind vectors are determined. Two examples of inverted radar data are presented: 1) a comparison of aircraftradar-inferred friction velocity vector to that derived from surface wind measurements in the New York Bight and 2) a simulated SeaSat-A measurement inversion in which comparisons are made of the recovered and sample wind fields.
TL;DR: In this article, the single configuration (sc) wavefunctions for 15 states of CaO arising (nominally) from six electron occupancies are calculated at the SCF level and analyzed qualitatively in terms of Mulliken populations and an approximate overlap criterion.
Abstract: Electronic wavefunctions for 15 states of CaO arising (nominally) from six electron occupancies are calculated at the single configuration (sc) SCF level and analyzed qualitatively in terms of Mulliken populations and an approximate overlap criterion. The accuracy of the sc approximation is assessed and shown to be highly inadequate in several cases. Approximate Te's are extracted from these results when warranted by the quality of the sc wavefunctions. An improved two configuration wavefunction for the lowest 1 Sigma + state is also determined and discussed in detail.
TL;DR: In this paper, the effect of radiant heating and cooling of droplets by using the Eddington approximation for the solution of the radiative transfer equation was investigated, assuming that the cloud is isothermal and has a constant size spectrum with altitude.
Abstract: In standard treatments of the mass and energy budget of cloud droplets, radiant energy transfer is neglected on the grounds that the temperature difference between the droplet and its surroundings is small. This paper includes the effect of radiant heating and cooling of droplets by using the Eddington approximation for the solution of the radiative transfer equation. Although the calculation assumes that the cloud is isothermal and has a constant size spectrum with altitude, the heating or cooling of droplets by radiation changes the growth rate of the droplets very significantly. At the top of a cloud with a base at 2500 m and a top at 3000 m, a droplet will grow from 9.5 to 10.5 microns in about 4 min, assuming a supersaturation ratio of 1.0013. Such a growth rate is more than 20 times the growth rate for condensation alone, and may be expected to have a significant impact on estimates of precipitation formation as well as on droplet spectrum calculations.
TL;DR: A series of wind-tunnel and laboratory tests were conducted at the NASA Langley V/STOL tunnel facility to determine both the detailed structure and the induced effects of aspect-ratio-4.0 rectangular jets both in a subsonic crosswind and in quiescent conditions as mentioned in this paper.
Abstract: A series of wind-tunnel and laboratory tests were conducted at the NASA Langley V/STOL tunnel facility to determine both the detailed structure and the induced effects of aspect-ratio-4.0 rectangular jets both in a subsonic crosswind and in quiescent conditions. Wind-tunnel tests were conducted on both blunt (nozzle major axis normal to free stream) and streamwise (nozzle major axis parallel to free stream) nozzle orientations for jet injection angles ranging from 15 to 90 degrees at jet-to-crossflow velocity ratios of 4, 8, and 10. Results indicate that the blunt nozzle induced effects are more significant than those produced by comparable streamwise-oriented jets and that both the flow-field structure and induced effects of streamwise-oriented rectangular jets are quite similar to those created by round jets. Additionally, it is shown that significant differences exist in the vortex flow fields generated by the same rectangular nozzle mounted in two different test hardware configurations.
01 Jan 1978
TL;DR: In this paper, 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.
TL;DR: The Mars viking gas chromatograph-mass spectrometer is described, designed to determine the composition of the Martian atmosphere and detect and identify chemical compounds vaporized or pyrolyzed from the Martian soil.
Abstract: The Mars viking gas chromatograph–mass spectrometer is described. The system is designed to determine the composition of the Martian atmosphere and detect and identify chemical compounds vaporized or pyrolyzed from the Martian soil. Construction details, performance data, data processing methods, and references to manufacturing and test procedures are also provided.
01 Feb 1978
TL;DR: In this paper, an optimization procedure is developed based on the responses of a system to continuous gust inputs, which yields a flutter suppression system which minimizes control surface activity in a gust environment.
Abstract: An optimization procedure is developed based on the responses of a system to continuous gust inputs. The procedure uses control law transfer functions which have been partially determined by using the relaxed aerodynamic energy approach. The optimization procedure yields a flutter suppression system which minimizes control surface activity in a gust environment. The procedure is applied to wing flutter of a drone aircraft to demonstrate a 44 percent increase in the basic wing flutter dynamic pressure. It is shown that a trailing edge control system suppresses the flutter instability over a wide range of subsonic mach numbers and flight altitudes. Results of this study confirm the effectiveness of the relaxed energy approach.
TL;DR: High resolution spectra in the region of the v(2) band of nitric acid have been obtained for selected portions of the HNO(3) spectrum using tunable diode laser techniques and absolute line intensities and line positions are presented.
Abstract: High resolution spectra in the region of the v(2) band of nitric acid have been obtained for selected portions of the HNO(3) spectrum using tunable diode laser techniques. Continuous spectra are presented from 1718.97 cm(-1) to 1729.57 cm(-1), with a spectral resolution
TL;DR: In this article, an experimental investigation has been conducted to understand the physical mechanism of noise generation from a turbulent wall jet discharging over a flat plate and interacting with its sharp trailing edge.
Abstract: An experimental investigation has been conducted to understand the physical mechanism of noise generation from a turbulent wall jet discharging over a flat plate and interacting with its sharp trailing edge. An aspect ratio 10 rectangular nozzle was used to provide the wall jet. Measurements made consist of farfield noise, surface pressure fluctuations, turbulent velocity fluctuations, and two-point space-time cross-correlations among these quantities. Results are presented which suggest strongly that the generation mechanism is the interaction of the convecting large scale quasi-orderly disturbance in the upper free shear layer of the wall jet with the trailing edge. The interaction also excites large scale strong vortical motion in the trailing edge wake. The dominant part of the sound field is highly coherent and in phase opposition across the trailing edge.
TL;DR: The data on Phobos obtained during this first encounter period are comparable in quantity to all of the data on Mars returned by Mariner flights 4, 6, and 7.
Abstract: Viking Orbiter-1 (VO-1) made a series of close flybys of the Martian satellite Phobos in February and May 1977. A description is presented of the results obtained during the flybys in February. The flyby geometries for the encounter period in February are shown in a graph. The trajectory design gave flybys on the illuminated side of Phobos within 80 to 300 km during the entire encounter period. The primary encounter observations of Phobos included visual and infrared imaging as well as radio tracking of VO-1 while it was under the gravitational influence of Phobos. Visual imaging was obtained from two narrow-angle television cameras. Infrared observations were obtained from an infrared thermal mapper. Radio data included S- and X-band Doppler and ranging data to VO-1 with a 10-second Doppler count. Assuming for Phobos a volume of 500 + or - 900 cu km, a mean density of 1.9 + or - 0.6 g/cu cm is obtained for it on the basis of the processed data.
TL;DR: Tunable diode laser spectroscopy is used to measure the infrared vibration-rotation spectra of the ClO radical, a radical generated in a flow system where a Cl2-He mixture passes through a microwave discharge to dissociate the Cl2.
Abstract: Tunable diode laser spectroscopy is used to measure the infrared vibration-rotation spectra of the ClO radical. The radical is generated in a flow system where a Cl2-He mixture passes through a microwave discharge to dissociate the Cl2. An O3-O2 mixture from an ozone generator is injected into the system downstream of the microwave discharge where O3 combines with Cl to form ClO. By adjusting the gas flow rates to yield an excess of Cl atoms, all the ozone is combined. ClO concentration is measured with UV absorption at 2577 and 2772 A and a deuterium lamp as a continuous source. Total cell pressure is 5.5 torr. The diode laser spectrometer is calibrated with ammonia lines as a reference where possible. The frequency of vibration-rotation lines is expressed as a function of rotational quantum number, fundamental vibrational frequency, and the rotational constants of the upper and lower vibrational states.
01 Jan 1978
TL;DR: In this paper, an approximate computational technique has been developed for predicting inviscid, radiating flows about blunt probes entering atmospheres consisting of hydrogen and helium, which is well suited for performing parametric trade studies for outer planet entries.
Abstract: An approximate computational technique has been developed for predicting inviscid, radiating flows about blunt probes entering atmospheres consisting of hydrogen and helium. The technique is rapid and versatile and is well suited for performing parametric trade studies for outer planet entries. Details of the computational technique, the thermodynamic correlations, the 58-step absorption coefficient model and the analytic shock shape equations are discussed. Good comparisons of the radiative heating computed by the approximate method and by detailed calculations are obtained.