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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Severe winds in the DFW microburst measured from two aircraft

Advanced analytical methods are applied to the digital flight data and Air Traffic Control radar records from two airliners, Delta flight 191 and American flight 539, that penetrated a microburst at the Dallas/Ft. Worth airport on August 2, 1985. The results for Delta 191 (which crashed) show that the aircraft encountered a strong downburst followed by a strong outflow accompanied by large and rapid changes in the vertical wind. The rapid changes in the vertical wind detected near the ground are attributed to vortex-induced turbulence. The next following aircraft, American 539, made a go-around 110 sec after Delta 191 and traversed the microburst at an altitude of about 2500 ft above the ground. The measured winds during this go-around indicate a broad pattern of downflow in the microburst, with regions of upflow at the extreme edges. The combined results indicate a microburst that was increasing in size with vortex-induced turbulence embedded in a strong outflow near the ground. These wind measurements provide a realistic description of the microburst wind environment that can be used in simulator studies and pilot training, and provide a standard of comparison for ongoing experiments and modeling of microbursts involving vortex rings.

Wingrove, R. C.↗
NASA NTRS1988

Gear Handbook

Reference publication integrates results of 15 years of NASA-related gear research compiled to form complete design synthesis using latest analytical methods, materials, and lubrication analysis and techniques.

Coy, John J.↗
NASA NTRS1985

Film cooling heat transfer on a turbine airfoil

The objectives of the current program are to develop an analytical approach, based on boundary layer theory, for predicting the effects of airfoil cooling on downstream heat transfer rates and to verify the resulting analytical method by comparison of predictions with hot cascade data obtained under this program.

Hylton, Larry D.↗
NASA NTRS1987

Aerodynamic sensitivities from subsonic, sonic and supersonic unsteady, nonplanar lifting-surface theory

The technique of implicit differentiation has been used in combination with linearized lifting-surface theory to derive analytical expressions for aerodynamic sensitivities (i.e., rates of change of lifting pressures with respect to general changes in aircraft geometry, including planform variations) for steady or oscillating planar or nonplanar lifting surfaces in subsonic, sonic, or supersonic flow. The geometric perturbation is defined in terms of a single variable, and the user need only provide simple expressions or similar means for defining the continuous or discontinuous global or local perturbation of interest. Example expressions are given for perturbations of the sweep, taper, and aspect ratio of a wing with trapezoidal semispan planform. In addition to direct computational use, the analytical method presented here should provide benchmark criteria for assessing the accuracy of aerodynamic sensitivities obtained by approximate methods such as finite geometry perturbation and differencing. The present process appears to be readily adaptable to more general surface-panel methods.

Yates, E. Carson, Jr.↗
NASA NTRS1985

An analysis of sound absorbing linings for the interior of the NASA Ames 80 x 120-foot wind tunnel

It is desirable to achieve low frequency sound absorption in the tests section of the NASA Ames 80X120-ft wind tunnel. However, it is difficult to obtain information regarding sound absorption characteristics of potential treatments because of the restrictions placed on the dimensions of the test chambers. In the present case measurements were made in a large enclosure for aircraft ground run-up tests. The normal impedance of the acoustic treatment was measured using two microphones located close to the surface of the treatment. The data showed reasonably good agreement with analytical methods which were then used to design treatments for the wind tunnel test section. A sound-absorbing lining is proposed for the 80X120-ft wind tunnel.

Wilby, J. F.↗
NASA NTRS1987

The 58th Shock and Vibration Symposium, volume 1

The proceedings of the 58th Shock and Vibration Symposium, held in Huntsville, Alabama, October 13 to 15, 1987 are given. Mechanical shock, dynamic analysis, space shuttle main engine vibration, isolation and damping, and analytical methods are discussed.

Pilkey, Walter D.↗
NASA NTRS1984

Large-Scale Advanced Prop-Fan (LAP) blade design

This report covers the design analysis of a very thin, highly swept, propeller blade to be used in the Large-Scale Advanced Prop-Fan (LAP) test program. The report includes: design requirements and goals, a description of the blade configuration which meets requirements, a description of the analytical methods utilized/developed to demonstrate compliance with the requirements, and the results of these analyses. The methods described include: finite element modeling, predicted aerodynamic loads and their application to the blade, steady state and vibratory response analyses, blade resonant frequencies and mode shapes, bird impact analysis, and predictions of stalled and unstalled flutter phenomena. Summarized results include deflections, retention loads, stress/strength comparisons, foreign object damage resistance, resonant frequencies and critical speed margins, resonant vibratory mode shapes, calculated boundaries of stalled and unstalled flutter, and aerodynamic and acoustic performance calculations.

Violette, John A.↗
NASA NTRS1987

Evaluation of closed cubic failure criterion for graphite/epoxy laminates

An analytical method has been developed to ensure closure of the cubic form of the tensor polynomial strength criterion. The intrinsic complexity of the cubic function is such that special conditions must be met to close the failure surface in three-dimensional stress space. These requirements are derived in terms of non-intersecting conditions for asymptotes and an asymptotic plane. To demonstrate the validity of this approach, closed failure surfaces were derived for two graphite/epoxy material systems (3M SP288-T300 and IM7 8551-7). The agreement of test data with this model clearly shows that it is possible to use a higher order cubic failure theory with confidence.

Tennyson, R. C.↗
NASA NTRS1987

On meteor stream spatial structure theory

The classical spatial representation of meteor streams is an elliptical torus with variable cross section. The position of this torus in space is determined by the mean orbit elements that may be obtained directly from observations of individual meteor stream particles when crossed by the Earth. Since the orbits of individual particles of a stream differ from each other, the distance between them on a plane normal to the mean orbit of elliptical torus forms some area, i.e., a cross section. The size and form of these cross sections change with the change of the direction among the mean orbit and are completely defined by the dispersion values of the orbit elements in a stream. An attempt was made to create an analytical method that would permit description of the spatial and time parameters of meteor streams, i.e., the form and size of their cross section, density of incident flux and their variations along the mean orbit and in time. In this case, the stream is considered as a continuous flux rather than a set of individual particles.

Andreev, G. V.↗
NASA NTRS1987

Propulsion estimation techniques

A brief overview of statistical tools needed to perform post flight/test reconstruction of state variables is given. Linear regression, recursive linear regression, and the exact connection between the Kalman filter and linear regression are discussed. The regression connection is expected to serve as an aid in the application of a recently developed analytical method of flight reconstruction to single engine test firing data.

Temple, Enoch C.↗
NASA NTRS1987

The integration of a mesh reflector to a 15-foot box truss structure. Task 3: Box truss analysis and technology development

To demonstrate the design and integration of a reflective mesh surface to a deployable truss structure, a mesh reflector was installed on a 15 foot box truss cube. The specific features demonstrated include: (1) sewing seams in reflective mesh; (2) mesh stretching to desired preload; (3) installation of surface tie cords; (4) installation of reflective surface on truss; (5) setting of reflective surface; (6) verification of surface shape/accuracy; (7) storage and deployment; (8) repeatability of reflector surface; and (9) comparison of surface with predicted shape using analytical methods developed under a previous task.

Bachtell, E. E.↗
NASA NTRS1988

The 58th Shock and Vibration Symposium

Dynamic analysis, dynamic testing, space shuttle main engine vibration, isolation and damping and analytical methods are among the topics discussed.

Pilkey, Walter D.↗
NASA NTRS1988

Impact damage in composite laminates

Damage tolerance requirements have become an important consideration in the design and fabrication of composite structural components for modern aircraft. The ability of a component to contain a flaw of a given size without serious loss of its structural integrity is of prime concern. Composite laminates are particularly susceptible to damage caused by transverse impact loading. The ongoing program described is aimed at developing experimental and analytical methods that can be used to assess damage tolerance capabilities in composite structures subjected to impulsive loading. Some significant results of this work and the methodology used to obtain them are outlined.

Grady, Joseph E.↗
NASA NTRS1986

SR-7A aeroelastic model design report

A scale model was designed to simulate the aeroelastic characteristics and performance of the 2.74 meter (9 ft.) diameter SR-7L blade. The procedures used in this model blade design are discussed. Included in this synopsis is background information concerning scaling parameters and an explanation of manufacturing limitations. A description of the final composite model blade, made of titanium, fiberglass, and graphite, is provided. Analytical methods for determining the blade stresses, natural frequencies and mode shapes, and stability are discussed at length.

Nagle, D.↗
NASA NTRS1987

Analysis, prediction, and prevention of edge delamination in rotor system structures

Analytical methods such as simple sublaminate analysis, as well as quasi three-dimensional finite element analysis, provide insight into delamination characteristics and reliable trend data with which to make rapid evaluations of competitive concepts in the design environment. It is concluded that free edge delamination can be managed by analysis and prevented by design. However, in order to ensure durable composite structures, more work is needed to characterize delamination that occurs from other sources, such as matrix cracking and ply drops.

Chan, Wen S.↗
NASA NTRS1987

Mixing, transport and combustion in sprays

The state-of-the-art in analytical methods for sprays and drop/turbulence interactions in combustion processes is presented with reference to dilute sprays, and dilute dispersed flows, that contain well-defined dispersed-phase elements in volume fractions lower than 1 percent. Attention is given to the near-injector dense spray region. The methods tested are those of locally homogeneous flow, deterministic separated flow, and stochastic separated flow; the first of these was ineffective due to its ignoring finite interphase transport rates, and the second failed by ignoring turbulent dispersion. Stochastic separated flow methodology yielded encouraging results through its treatment of both finite interphase transport rates and dispersed-phase/turbulence interactions.

Faeth, G. M.↗
NASA NTRS1988

Theory and simulation of electromagnetic beam modes and whistlers

Using particle-in-cell simulations and analytical methods, a study of the nonlinear evolution of electromagnetic instabilities driven by an anisotropic electron beam in an external magnetic field is performed. The unstable waves are either whistlerlike or beam-mode-like depending on the external field strength and beam velocity. The evolution of the particle distribution differs significantly in the two regimes. Even in the presence of a faster electrostatic instability, the electromagnetic waves grow to a significant amplitude. In certain cases, an energetic tail is formed, resulting in enhanced Cerenkov emission of electrostatic waves. The initial evolution of the particle distribution is explained in terms of the interaction of a given linearly unstable wave with the self-consistent perturbed distribution.

Newman, David L.↗