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At least 1,675 records · Page 93
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Strain Rate Dependent Modeling of Polymer Matrix Composites

A research program is in progress to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. Strain rate dependent inelastic constitutive equations have been developed to model the polymer matrix, and have been incorporated into a micromechanics approach to analyze polymer matrix composites. The Hashin failure criterion has been implemented within the micromechanics results to predict ply failure strengths. The deformation model has been implemented within LS-DYNA, a commercially available transient dynamic finite element code. The deformation response and ply failure stresses for the representative polymer matrix composite AS4/PEEK have been predicted for a variety of fiber orientations and strain rates. The predicted results compare favorably to experimentally obtained values.

Goldberg, Robert K.↗
NASA NTRS1983

The SIFT Code Specification

The specification of Software Implemented Fault Tolerance (SIFT) consists of two parts, the specifications of the SIFT models and the specifications of the SIFT PASCAL program which actually implements the SIFT system. The code specifications are the last of a hierarchy of models describing the operation of the SIFT system and are related to the SIFT models as well as the PASCAL program. These Specifications serve to link the SIFT models to the running program. The specifications are very large and detailed and closely follow the form and organization of the PASCAL code. In addition to describing each of the components of the SIFT code, the code specifications describe the assumptions of the upper SIFT models which are required to actually prove that the code will work as specified. These constraints are imposed primarily on the schedule tables.

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NASA NTRS1976

Atmospheric analysis and prediction model development, volume 1

A set of hemispheric atmospheric analysis and prediction models was designed and tested. All programs were executed on either a 63 x 63 or 187 x 187 polar stereographic grid of the Northern Hemisphere. Parameters for objective analysis included sea surface temperature, sea level pressure, and twelve levels (from 1,000 to 100 millibars) of temperatures, heights, and winds. Stratospheric extensions (up to 10 millibars) were also provided. Four versions of a complex atmospheric prediction model, based on primitive equations, were programmed and tested. These models were executed on either the 63 x 63 or 187 x 187 grid, using either five or ten computational layers. The coarse-mesh (63 x 63) models were tested using real data for the period 21-23 April 1976. The fine-mesh (187 x 187) models were debugged, but insufficient computer resources precluded production tests. Preliminary test results for the 63 x 63 models are provided. Problem areas and proposed solutions are discussed.

Kesel, P. G.↗
NASA NTRS1992

Status of the variable diameter centerbody inlet program

The Variable Diameter Centerbody (VDC) inlet is an ongoing research program at LeRC. The VDC inlet is a mixed compression, axisymmetric inlet that has potential application on the next generation supersonic transport. This inlet was identified as one of the most promising axisymmetric concepts for supersonic cruise aircraft during the SCAR program in the late 1970's. Some of its features include high recovery, low bleed, good angle-of-attack tolerance, and excellent engine airflow matching. These features were demonstrated at LeRC in the past by the design and testing of fixed hardware models. A current test program in the LeRC 10' x 10' Supersonic Wind Tunnel (SWT) will attempt to duplicate these features on model hardware that actually incorporates a flight-like variable diameter centerbody mechanism.

Saunders, John D.↗
NASA NTRS1987

Validation of a real-time engineering simulation of the UH-60A helicopter

A real-time simulation of the UH-60A Black Hawk Helicopter based on the Sikorsky Gen Hel mathematical model is compared with flight test data and Sikorsky's nonreal-time computer program. An overview of the mathematical model is given, including a description of updates and expansion of the model by NASA. Also, real-time programming requirements and techniques are explained. The simulation displays very good agreement with flight test data and excellent with the nonreal-time program on which it is based. The large dedication of effort required to develop the real-time program suggests a need for development of generalized techniques for real-time simulation of high-fidelity physical models of rotorcraft.

Ballin, Mark G.↗
NASA NTRS1974

NASA Flight Research Center scale F-15 remotely piloted research vehicle program

The NASA Flight Research Center undertook a remotely piloted research vehicle (RPRV) program with a 3/8-scale model of an F-15 aircraft to determine the usefulness of the RPRV testing technique in high-risk flight testing such as spin testing. The results of the first flights of the program are presented. The program has shown that the RPRV technique, including the use of a digital control system, is a viable method for obtaining flight research data. Also presented are some negative aspects that have been learned about the RPRV technique in terms of model size, command frequency, and launch technique.

Layton, G. P.↗
NASA NTRS1972

Transonic wind tunnel tests of a .015 scale space shuttle booster model

Details of the test program, an outline of the test procedure, and results of the investigation in tabular form are presented. The base drag reduction potential was determined at cruise conditions (M = .40) of a modified base region, with and without base bleed flow. Transonic effects and cruise control effectiveness of the new base region were also obtained. The tests were performed at Mach numbers from 0.40 to 1.10, at angles of attack from -4 to +20 degrees and at angles of sideslip from -6 to +6 degrees, all at a Reynolds number of 6.56 million per meter (2.0 million per foot).

Dennis, R. J.↗
NASA NTRS1974

Model optimization using statistical estimation

Program revises initial or prior estimate of stiffness and mass parameters to parameters yielding frequency and mode characteristics in agreement with test data. Variances are also calculated and consequently define uncertainties of final estimates.

Collins, J. D.↗
NASA NTRS1975

Four-dimensional worldwide atmospheric models: ANYPT and ANYRG

Computer programs read magnetic-tape data bases and computer meteorological profiles for any position, time, and height (from zero to 25 km). System assists in analyses of distortion of information obtained from aircraft-mounted or spacecraft-mounted electromagnetic sensors.

Johnson, D.↗
NASA NTRS1976

Study leading to the refinement of the SRB structural analysis program

The constructed SRB math model was used for the analysis of the 85/32/5(VV/VH/theta) cavity collapse load condition for the aft end of the SRB structure. Linear, nonlinear collapse and bifurcation buckling analyses were performed. The linear and bifurcation buckling analyses showed that structural integrity and positive margins of safety are maintained for the applied maximum load case using a design factor of 1.25. The nonlinear collapse analysis predicts stresses in the skirt above the yield for a load factor of 1.0. Applying the 1.25 design factor gives a negative margin of safety against the material ultimate. The predicted collapse occurs at a load factor higher than 1.25.

Jones, W. E.↗
NASA NTRS1982

Circumferential pressure distributions in a model labyrinth seal

A research program to isolate and study leakage flow through labyrinth glands was initiated. Circumferential pressure distributions were measured in the labyrinth glands with geometry appropriate to the high pressure labyrinths in large steam turbines. Knowledge of this pressure distribution is essential as it is this unequal pressure field that results in the destabilizing force. Parameters that are likely to affect the pressure distributions are incorporated into the test rig. Some preliminary pressure profiles are presented.

Leong, Y. M. M. S.↗
NASA NTRS1982

Planetary atmospheres program

Non-solar compositional models of the troposphere of Jupiter, halide cloud condensation and volatile element inventories on Venus, and shock-wave processing of interstellar cloud materials are discussed.

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NASA NTRS1984

Performance degradation of a model helicopter rotor with a generic ice shape

An experimental program using a commercially available remotely controlled model helicopter in the Texas A&M University (TAMU) subsonic wind tunnel has been conducted to investigate the performance degradation resulting from the simulated formation of ice on the leading edge of the main rotor blades in both hover and forward flight. The rotor blades utilized a NACA 0012 airfoil with a 2.5-in. constant chord. A generic ice shape derived from a predetermined natural ice condition was applied to the 53.375-in.-diameter main rotor, and thrust and torque coefficients were measured for the main rotor as functions of velocity, main rotor rpm, fuselage angle of incidence, collective pitch angle, and spanwise extent of icing. The model helicopter test exhibited significant performance degradation of the main rotor when generic ice was added. An increase of approximately 150 percent in torque coefficient to maintain a constant thrust coefficient was noted when generic ice had been applied to the 85 percent rotor radial location. Also, considerable additional degradation occurred when generic ice was applied to the 100 percent rotor radial location, as compared with the 85 percent simulated ice performance values, indicating the sensitivity of the rotor tip region.

Korkan, K. D.↗