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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Dissolution of bulk specimens of silicon nitride

An accurate chemical characterization of silicon nitride has become important in connection with current efforts to incorporate components of this material into advanced heat engines. However, there are problems concerning a chemical analysis of bulk silicon nitride. Current analytical methods require the pulverization of bulk specimens. A pulverization procedure making use of grinding media, on the other hand, will introduce contaminants. A description is given of a dissolution procedure which overcomes these difficulties. It has been found that up to at least 0.6 g solid pieces of various samples of hot pressed and reaction bonded silicon nitride can be decomposed in a mixture of 3 mL hydrofluoric acid and 1 mL nitric acid overnight at 150 C in a Parr bomb. High-purity silicon nitride is completely soluble in nitric acid after treatment in the bomb. Following decomposition, silicon and hydrofluoric acid are volatilized and insoluble fluorides are converted to a soluble form.

Davis, W. F.↗
NASA NTRS1981

Inlet design technology development - Supersonic cruise research

An inlet technology development program for future supersonic cruise aircraft is in progress. Areas being emphasized are inlet aerodynamic and control system design requirements for efficient and reliable operation. Off-design conditions, such as angle of incidence, starting, and noise abatement are major considerations. Flow analysis procedures are being developed to predict the internal inviscid and viscous flows in axisymmtric supersonic inlets for these operating conditions. Also under development are control systems that will have significant interfaces with the engine control system, the flight control system, and the airframe avionics system. The analytical methods are being supported and validated with representative experiments.

Syberg, J.↗
NASA NTRS1981

Summary of high-lift and control surface research on NASA general aviation airfoils

Summary findings and bibliographical information are presented for airfoil and airfoil-related research conducted at Wichita State University during the past decade. Topics include flap, aileron, and spoiler design data for new airfoils, extensive flow measurements, modifications to older airfoils, new symmetrical sections and contributions to analytical methods for cases with partial separation.

Wentz, W. H., Jr.↗
NASA NTRS1981

Numerical and classical analysis of V/STOL aircraft using selected propulsion systems

The development needed for the evolution of selected V/STOL research vehicles into optimized antisubmarine warfare (ASW) aircraft configurations, using numerical procedures and traditional analytical methods, has been examined. Three propulsion systems, which represent state-of-the-art development aimed at solving the thrust-vectoring and attitude-control problems of V/STOL aircraft, are analyzed. The use of NASA computer programs for aircraft synthesis (ACSYNT), and for optimizing configurations (COMMIN), coupled with contractor-supplied propulsion system data provides for accurate performance prediction of the selected ASW configurations. Particular emphasis on the transition phase between the research vehicle and the optimized configuration demonstrates the strengths and weaknesses of using generic research aircraft instead of building prototypes to demonstrate new technology

Wilson, S. B., III↗
NASA NTRS1981

Scattering of waves from periodic surfaces

In order to study the scattering of waves from periodic surfaces, the basic grating equations are reviewed, and a general approach for scattering from impenetrable and penetrable media is formulated. Three analytical methods for scattering on a conducting sinusoidal surface for both TE and TM polarized waves are compared. In The Masel, Merrill, and Miller (MMM) method for quantum scattering of atoms (1975, 1976), the surface field expansions are expressed in terms of Fourier series. The Modified Physical Optics (MPO) method (DeSanto, 1975; Whitman and Schwering, 1977) uses surface field expansions consisting of a leading term proportional to the physical optics approximation multiplied by a Fourier series expansion. The Waterman's Plane Harmonics (WPH) approach (1975) makes use of basis functions which are downward plane harmonics evaluated on the surface. The MMM method proved to be the most efficient one in terms of rate and range of convergence. For dielectric media with periodic rough surfaces, an improved method is developed for calculating the reflected and transmitted powers, and the results are compared with experimental data obtained at optical frequencies.

Chuang, S.-L.↗
NASA NTRS1983

Designing Glass Panels for Economy and Reliability

Analytical method determines probability of failure of rectangular glass plates subjected to uniformly distributed loads such as those from wind, earthquake, snow, and deadweight. Developed as aid in design of protective glass covers for solar-cell arrays and solar collectors, method is also useful in estimating the reliability of large windows in buildings exposed to high winds and is adapted to nonlinear stress analysis of simply supported plates of any elastic material.

Moore, D. M.↗
NASA NTRS1981

Analytical and experimental study of flow phenomena in noncavitating rocket pump inducers

The flow processes in rocket pump inducers are summarized. The experimental investigations were carried out with air as the test medium. The major characteristics features of the rocket pump inducers are low flow coefficient (0.05 to 0.2) large stagger angle (70 deg to 85 deg) and high solidity blades of little or no camber. The investigations are concerned with the effect of viscosity not the effects of cavitation. Flow visualization, conventional and hot wire probe measurement inside and at the exit of the blade passage, were the analytical methods used. The experiment was carried out using four three and two bladed inducers with cambered blades. Both the passage and the exit flow were measured. The basic research and boundary layer investigation was carried out using a helical flat plate (of some dimensions as the inducer blades tested), and flat plate helical inducer (four bladed). Detailed mean and turbulence flow field inside the passage as well as the exit of the rotor were derived from these measurement. The boundary layer, endwall, and other passage data reveal extremely complex nature of the flow, with major effects of viscosity present across the entire passage. Several analyses were carried out to predict the flow field in inducers. These included an approximate analysis, the shear pumping analysis, and a numerical solution of exact viscous equations with approximate modeling for the viscous terms.

Lakshminarayana, B.↗
NASA NTRS1981

Airframe-propulsion system aerodynamic interference predictions at high transonic Mach numbers including off-design engine airflow effects

The transonic speed regime for airplanes at conditions where inlet spillage takes place is discussed. A wind tunnel test program to evaluate aerodynamic performance penalties associated with propulsion system installation and operation at subsonic through low supersonic speeds was conducted. The accuracy of analytic methods for predicting transonic engine airframe interference effects was assessed. Study variables included Mach number, angle of attack, relative nacelle location, and nacelle mass flow ratio. Results include test theory comparisons of forces as well as induced pressure fields. Prediction capability of induced shock wave strength and locations is assessed. It was found that large interference forces due to engine location and flow spillage occur at transonic speeds, that theory explains these effects; and that theory can predict quantitatively these effects.

Kulfan, R. M.↗
NASA NTRS1982

Study on application of aerospace technology to improve surgical implants

The areas where aerospace technology could be used to improve the reliability and performance of metallic, orthopedic implants was assessed. Specifically, comparisons were made of material controls, design approaches, analytical methods and inspection approaches being used in the implant industry with hardware for the aerospace industries. Several areas for possible improvement were noted such as increased use of finite element stress analysis and fracture control programs on devices where the needs exist for maximum reliability and high structural performance.

Johnson, R. E.↗
NASA NTRS1982

Harmonic well matter densities and Pauli correlation effects in heavy-ion collisions

A generalized optical model heavy ion reaction theory is extended to include correlation effects between projectile and target constituents according to the Pauli exclusion principle. These correlation effects are significant for accurately predicting cross sections for projectile nucleus abrasions, but are relatively unimportant for determining total and absorption cross sections for heavy ion collisions. For lighter nuclei, predictive capabilities were also improved by developing an analytic method for extracting their nuclear single particle density distributions from experimentally measured harmonic well charge density distributions. This improved theory is compared with previous theoretical predictions and recent experimental results.

Townsend, L. W.↗
NASA NTRS1982

A study of resonant-cavity and fiberglass-filled parallel baffles as duct silencers

Acoustical performance and pressure drop were measured for two types of splitters designed to attenuate sound propagating in ducts - resonant-cavity baffles and fiberglass-filled baffles. Arrays of four baffles were evaluated in the 7- by 10-foot wind tunnel number 1 at Ames Research Center at flow speeds from 0 to 41 m/sec. The baffles were 2.1 m high, 305 to 406 mm thick, and 3.1 to 4.4 m long. Emphasis was on measurements of silencer insertion loss as affected by variations of such parameters as baffle length, baffle thickness, perforated skin geometry, cavity size and shape, cavity damping, wind speed, and acoustic field directivity. An analytical method for predicting silencer performance is described and compared with measurements. With the addition of cavity damping in the form of 25-mm foam linings, the insertion loss above 250 Hz of the resonant-cavity baffles was improved 2 to 7 db compared with the undamped baffles; the loss became equal to or greater than the insertion loss of comparable size fiberglass baffles at frequencies above 250 Hz. Variations of cavity size and shape showed that a series of cavities with triangular cross-sections (i.e., variable depth) were superior to cavities with rectangular cross sections (i.e., constant depth). In wind, the undamped, resonant-cavity baffles generated loud cavity-resonance tones; the tones could be eliminated by cavity damping.

Soderman, P. T.↗
NASA NTRS1981

Analysis of cracks emanating from a circular hole in unidirectional fiber reinforced composites, part 2

An analytical method is developed for cracks emanating from a circular hole in an off-axis unidirectional fiber-reinforced composite. The method which is formulated by using conservation laws of elasticity and fundamental relationships in anisotropic fracture mechanics, provides a convenient and accurate means to examine the complicated crack behavior, when used in conjunction with a suitable numerical scheme such as the finite element method. The formulation is eventually reduced to a system of linear algebraic equations of mixed-mode stress intensity factors. Fracture parameters, describing crack-tip deformation and fracture in the composite, are obtained explicitly. Effects of material anisotropy and crack/hole geometry are examined also. Of particular interest are the energy release rates associated with crack extension; their values are evaluated for various cases. Results show that mixed-mode stress intensity factors and energy release rates associated with the cracks emanating from a hole change very appreciably with fiber orientation in the composite. K sub 1 and G increase monotonically with increasing theta; but K sub 2 reaches its maximum at theta = 45 deg, and then decreases gradually as theta increases further.

Wang, S. S.↗
NASA NTRS1982

Aircraft icing research at NASA

Research activity is described for: ice protection systems, icing instrumentation, experimental methods, analytical modeling for the above, and in flight research. The renewed interest in aircraft icing has come about because of the new need for All-Weather Helicopters and General Aviation aircraft. Because of increased fuel costs, tomorrow's Commercial Transport aircraft will also require new types of ice protection systems and better estimates of the aeropenalties caused by ice on unprotected surfaces. The physics of aircraft icing is very similar to the icing that occurs on ground structures and structures at sea; all involve droplets that freeze on the surfaces because of the cold air. Therefore all icing research groups will benefit greatly by sharing their research information.

Reinmann, J. J.↗
NASA NTRS1982

Measured pressure distributions, aerodynamic coefficients and shock shapes on blunt bodies at incidence in hypersonic air and CF4

Pressure distributions, aerodynamic coefficients, and shock shapes were measured on blunt bodies of revolution in Mach 6 CF4 and in Mach 6 and Mach 10 air. The angle of attack was varied from 0 deg to 20 deg in 4 deg increments. Configurations tested were a hyperboloid with an asymptotic angle of 45 deg, a sonic-corner paraboloid, a paraboloid with an angle of 27.6 deg at the base, a Viking aeroshell generated in a generalized orthogonal coordinate system, and a family of cones having a 45 deg half-angle with spherical, flattened, concave, and cusp nose shapes. Real-gas effects were simulated for the hperboloid and paraboloid models at Mach 6 by testing at a normal-shock density ratio of 5.3 in air and 12 CF4. Predictions from simple theories and numerical flow field programs are compared with measurement. It is anticipated that the data presented in this report will be useful for verification of analytical methods for predicting hypersonic flow fields about blunt bodies at incidence.

Miller, C. G., III↗
NASA NTRS1981

Calculation of sensitivity derivatives in thermal problems by finite differences

The optimum design of a structure subject to temperature constraints is considered. When mathematical optimization techniques are used, derivatives of the temperature constraints with respect to the design variables are usually required. In the case of large aerospace structures, such as the Space Shuttle, the computation of these derivatives can become prohibitively expensive. Analytical methods and a finite difference approach have been considered in studies conducted to improve the efficiency of the calculation of the derivatives. The present investigation explores two possibilities for enhancing the effectiveness of the finite difference approach. One procedure involves the simultaneous solution of temperatures and derivatives. The second procedure makes use of the optimum selection of the magnitude of the perturbations of the design variables to achieve maximum accuracy.

Haftka, R. T.↗
NASA NTRS1982

Aerodynamic characteristics of airfoils with ice accretions

Results of a wind tunnel test to evaluate the performance of an airfoil with simulated rime ice are presented with theoretical comparisons. A NACA 65A413 airfoil was tested in the OSU 6 x 22 inch Transonic Airfoil Wind Tunnel at a Reynolds number near three million and Mach numbers from 0.20 to 0.80. The model was tested in four configurations to determine the aero-dynamic effects of the roughness and shape of a rime ice accretion. The simulated rime ice shape was obtained analytically using a time-stepping dry ice accretion computer code. Lift, drag, moment coefficients, and pressure distributions for the clean and simulated rime ice cases are reported. The measured degradation in airfoil performance is compared to an analytical method which uses existing airfoil analysis computer codes with empirical corrections for the surface roughness. A discussion of the empirical surface roughness correction and uses of other airfoil computer methods is included.

Bragg, M. B.↗
NASA NTRS1980

On the barrier to crystal nucleation in lunar glasses

The paper describes an analytical method for calculating in detail the size distributions of small crystallites and nuclei in supercooled liquids as they are being quenched to form a glass and subsequently reheated above the glass transition to produce crystallization. This method is applied to experiments performed using differential thermal analysis (DTA) to estimate the barriers to crystal nucleation and the cooling rates required to form glasses or bodies with various degrees of crystallinity. DTA data and derived nucleation barriers are reported for anorthite and for the following lunar compositions: 15498, 15418, matrix and intrusion compositions of breccia 15286, Apollo 15 green glass, Luna 24 highland basalt, and 65016.

Yinnon, H.↗
NASA NTRS1982

Effect of interferogram smearing on atmospheric limb sounding by Fourier transform spectroscopy

An analytical method for the analysis of absorption spectra obtained from the interferograms of an interferometer operated in the solar occultation mode, in which an interferogram is smeared with individual interferogram components generated by the passage of rays at different tangent altitudes, is described. The creation of strong sidelobes on absorption lines by the interferogram smearing leads to the recommendation of a strong apodization on the interferogram for the solar occultation experiment. The application of these concepts to the simultaneous retrieval of temperature and pressure from CO2 4.3-micron band stratospheric absorption spectra includes the analysis of the continuum absorptions by the pressure-induced N2 fundamental bands and by far wings of the CO2 v3 band. Agreement is reported between observed and simulated spectra.

Park, J. H.↗