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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Improvement of program to calculate electronic properties of narrow band gap materials

The program was improved by reprogramming it so it will run on both a SUN and a VAX. Also it is easily transportable as it is on a disk for use on a SUN. A computer literature search resulted in some improved parameters for Hg(1-x)Cd(x)Te and a table of parameters for Hg(1-x)Zn(x)Te. The effects of neutral defects were added to the program, and it was found, as expected, that they contribute very little to the mobility at temperatures of interest. The effect were added of varying the following parameters: dielectric constants, screening parameters, disorder energies, donor and acceptor concentrations, momentum matrix element, different expressions for energy gap, and transverse effective charge.

Patterson, James D.↗
NASA NTRS1991

An improved compression molding technology for continuous fiber reinforced composite laminate. Part 1: AS-4/LaRC-TPI 1500 (HFG) Prepreg system

Poor processability of fiber reinforced high performance polyimide thermoplastic resin composites is a well recognized issue which, in many cases, prohibits the fabrication of composite parts with satisfactorily consolidated quality. Without modifying the resin matrix chemistry, improved compression modeling procedures were proposed and investigated with the AS-4/LaRC-TPI 1500 High Flow Grade (HFG) prepreg system. Composite panels with excellent C-scans can be consistently molded by this method under 700 F and a consolidation pressure as low as 100 psi. A mechanism for the consolidation of the composite under this improved molding technique is discussed. This mechanism reveals that a certain degree of matrix shear and tow filament slippage and nesting between plies occur during consolidation, which leads to a reduction of the consolidating pressure necessary to offset the otherwise intimate inter fiber-fiber contact and consequently achieves a better consolidation quality. Outstanding short beam shear strength and flexural strength were obtained from the molded panels. A prolonged consolidation step under low pressure, i.e., 100 psi at 700 F for 75 minutes, was found to significantly enhance the composite mechanical properties.

Hou, Tan-Hung↗
NASA NTRS1989

Improved reference models for middle atmosphere ozone

Improvements are provided for the ozone reference model which is to be incorporated in the COSPAR International Reference Atmosphere (CIRA). The ozone reference model will provide considerable information on the global ozone distribution, including ozone vertical structure as a function of month and latitude from approximately 25 to 90 km, combining data from five recent satellite experiments (Nimbus 7 LIMS, Nimbus 7 SBUV, AE-2 SAGE, Solar Mesosphere Explorer (SME) UVS, and SME IR). The improved models are described and use reprocessed AE-2 SAGE data (sunset) and extend the use of SAGE data from 1981 to the period 1981-1983. Comparisons are shown between the ozone reference model and various nonsatellite measurements at different levels in the middle atmosphere.

Keating, G. M.↗
NASA NTRS1991

The NASA aircraft noise prediction program improved propeller analysis system

The improvements and the modifications of the NASA Aircraft Noise Prediction Program (ANOPP) and the Propeller Analysis System (PAS) are described. Comparisons of the predictions and the test data are included in the case studies for the flat plate model in the Boundary Layer Module, for the effects of applying compressibility corrections to the lift and pressure coefficients, for the use of different weight factors in the Propeller Performance Module, for the use of the improved retarded time equation solution, and for the effect of the number grids in the Transonic Propeller Noise Module. The DNW tunnel test data of a propeller at different angles of attack and the Dowty Rotol data are compared with ANOPP predictions. The effect of the number of grids on the Transonic Propeller Noise Module predictions and the comparison of ANOPP TPN and DFP-ATP codes are studied. In addition to the above impact studies, the transonic propeller noise predictions for the SR-7, the UDF front rotor, and the support of the enroute noise test program are included.

Nguyen, L. Cathy↗
NASA NTRS1990

Improved evaluation of optical depth components from Langley plot data

A simple, iterative procedure to determine the optical depth components of the extinction optical depth measured by a solar radiometer is presented. Simulated data show that the iterative procedure improves the determination of the exponent of a Junge law particle size distribution. The determination of the optical depth due to aerosol scattering is improved as compared to a method which uses only two points from the extinction data. The iterative method was used to determine spectral optical depth components for June 11-13, 1988 during the MAC III experiment.

Biggar, S. F.↗
NASA NTRS1991

An improved three-dimensional aerodynamics model for helicopter airloads prediction

The importance of unsteady aerodynamic effects due to rotor blade motion is demonstrated for a helicopter in high-speed forward flight. These unsteady effects are modeled as surface boundary conditions to a three-dimensional, unsteady Computational Fluid Dynamics (CFD) code called the Full-Potential Rotor Code (FPR). These boundary conditions cause significant changes in the computed lift and pitching moment at the front and rear of the rotor disk. Airloads from the modified FPR code are then iteratively coupled with the helicopter comprehensive code, CAMRAD/JA. Computed airloads show good agreement with flight-test data when lift values from the FPR code are used in the coupled calculation. However, the computed airloads from CAMRAD/JA along also show good agreement with the experimental data. Thus for this case one cannot demonstrate a significant improvement in computed airloads with the hybrid coupled scheme. The addition of the pitching moment values from the FPR code into the CAMRAD/JA calculation slows down the overall iterative convergence and does not yield any improvement in the final results.

Strawn, Roger C.↗
NASA NTRS1991

Improved algorithms for mapping pipelined and parallel computations

Recent work on the problem of mapping pipelined or parallel computations onto linear array, shared memory, and host-satellite systems is extended. It is shown how these problems can be solved even more efficiently when computation module execution times are bounded from below, intermodule communication times are bounded from above, and the processors satisfy certain homogeneity constraints. The improved algorithms have significantly lower time and space complexities than the more general algorithms: in one case, an O(nm3) time algorithm for mapping m modules onto n processors is replaced with an O(nm log m) time algorithm, and the space requirements are reduced from O(nm2) to O(m). Run-time complexity is reduced further with parallel mapping algorithms based on these improvements, which run on the architectures for which they create mappings.

Nicol, David M.↗
NASA NTRS1991

Development of improved ablative materials for ASRM

A program to improve ablative materials for the Advanced Solid Rocket Motor (ASRM) is briefly discussed. The main concerns with the baseline material are summarized along with the measures being undertaken to obtain improvements. The materials involved in the program, all of which have been manufactured and are now being evaluated, are mentioned.

Canfield, A.↗
NASA NTRS1991

The use of curvilinear fiber format to improve buckling resistance of composite plates with central circular holes

The gains in buckling performance are explored that can be achieved by deviating from the conventional straightline fiber format and considering the situation whereby the fiber orientation in a layer, or a group of layers, can vary from point to point. The particular situation studied is a simply supported square plate with a centrally located hole loaded in compression. By using both a sensitivity analysis and a gradient-search technique, fiber orientation in a number of regions of the plate are selected so as to increase the buckling load relative to baseline straightline designs. The sensitivity analysis is used to determine which regions of the plate have the most influence on buckling load, and the gradient search is used to find the design that is believed to represent the absolute maximum buckling load for the conditions prescribed. Convergence studies and sensitivity of the final design are discussed. By examining the stress resultant contours, it is shown how the curvilinear fibers move the load away from the unsupported hole region of the plate to the supported edges, thus increasing the buckling capacity. The tensile capacity of the improved buckling design is investigated, and it is shown that both tensile capacity and buckling capacity can be improved with the curvilinear fiber concept.

Hyer, M. W.↗
NASA NTRS1990

Strategy for contamination control to improve Wide-Field/Planetary Camera far-ultraviolet performance

A multifaceted contamination control strategy has been developed for the second generated Wide-Field and Planetary Camera (WFPC-2) to improve the FUV stability by several orders of magnitude, compared to the first camera (WFPC-1). The strategy involves: improved on-orbit boil-off capability of the detector optics, added internal shielding and instrument venting, in-process subassembly vacuum bakeout at elevated temperatures, material substitution, sample testing in ultraclean vacuum facility, and internal instrument contamination-transport modeling. A science performance goal of 1 percent photometric accuracy at 1470 A over an extended time (of at least 30 days) has been established as a contamination control target for WFPC-2. The WFPC-2 is currently planned to be launched by the Shuttle in mid-1993 and replace the WFPC-1 which was recently launched with the HST.

Leschly, Kim↗
NASA NTRS1992

Improvements In Processing And Aiming For Squint-Mode SAR

Improved technique for aiming antenna of synthetic-aperture radar (SAR) operating in squint imaging mode (SIM) complements improved algorithm for processing raw SIM SAR data. Developed to reduce deleterious effects of two unique characteristics of SIM SAR: large range walk and large variation of Doppler centroid as function of range.

Chang, Chi Y.↗
NASA NTRS1992

Improved PLL For FM Demodulator

Phase-locked loop (PLL) for frequency demodulator contains improved frequency-to-voltage converter producing less ripple than conventional phase detector. In improved PLL, phase detector replaced by state estimator, implemented by ramp/sample-and-hold circuit. Intended to reduce noise in receiver of frequency-modulated (FM) telemetry link without sacrificing bandwidth. Also applicable to processing received FM signals.

Kirkham, Harold↗
NASA NTRS1992

Improvement Of The Helmholtz Absorber

Helmholtz-resonator system improved to enable it to absorb sound at more than one frequency without appreciable loss of effectiveness at primary frequency. Addition of annular cavities enables absorption of sound at harmonic frequencies in addition to primary frequency. Improved absorber designed for use on structures of high transmission loss. Applied to such machines as fixed-speed engines and fans.

Morrow, Duane L.↗
NASA NTRS1991

Improved compression molding technology for continuous fiber reinforced composite laminates. Part 2: AS-4/Polyimidesulfone prepreg system

AS-4/polyimidesulfone (PISO2) composite prepreg was utilized for the improved compression molding technology investigation. This improved technique employed molding stops which advantageously facilitate the escape of volatile by-products during the B-stage curing step, and effectively minimize the neutralization of the consolidating pressure by intimate interply fiber-fiber contact within the laminate in the subsequent molding cycle. Without the modifying the resin matrix properties, composite panels with both unidirectional and angled plies with outstanding C-scans and mechanical properties were successfully molded using moderate molding conditions, i.e., 660 F and 500 psi, using this technique. The size of the panels molded were up to 6.00 x 6.00 x 0.07 in. A consolidation theory was proposed for the understanding and advancement of the processing science. Processing parameters such as vacuum, pressure cycle design, prepreg quality, etc. were explored.

Baucom, Robert M.↗
NASA NTRS1991

The implementation and validation of improved landsurface hydrology in an atmospheric general circulation model

Landsurface hydrological parameterizations are implemented in the NASA Goddard Institute for Space Studies (GISS) General Circulation Model (GCM). These parameterizations are: (1) runoff and evapotranspiration functions that include the effects of subgrid scale spatial variability and use physically based equations of hydrologic flux at the soil surface, and (2) a realistic soil moisture diffusion scheme for the movement of water in the soil column. A one dimensional climate model with a complete hydrologic cycle is used to screen the basic sensitivities of the hydrological parameterizations before implementation into the full three dimensional GCM. Results of the final simulation with the GISS GCM and the new landsurface hydrology indicate that the runoff rate, especially in the tropics is significantly improved. As a result, the remaining components of the heat and moisture balance show comparable improvements when compared to observations. The validation of model results is carried from the large global (ocean and landsurface) scale, to the zonal, continental, and finally the finer river basin scales.

Johnson, Kevin D.↗
NASA NTRS1990

Partnership for Continuous Improvement

The proceedings are presented of the sixth annual conference on quality control between NASA and its contractors. The emphasis is placed on a commitment to quality and excellence that guarantees mission success. A forum is provided for representatives from government, industry, and academia to exchange ideas and experiences, encouraging total quality performance that results in high quality products and services. Key points are highlighted from the presentations and activities are described that have resulted in a broad range of improvements in products and services from government, industry, and academia. Long term commitment to quality is an essential requirement that ensures future success. That commitment reinterates the dedication to excellence in space exploration and to national quality and productivity improvement.

Source record↗
NASA NTRS1992

Wind profiler signal detection improvements

Research is described on potential improvements to the software used with the NASA 49.25 MHz wind profiler located at Kennedy Space Center. In particular, the analysis and results are provided of a study to (1) identify preferred mathematical techniques for the detection of atmospheric signals that provide wind velocities which are obscured by natural and man-made sources, and (2) to analyze one or more preferred techniques to demonstrate proof of the capability to improve the detection of wind velocities.

Hart, G. F.↗
NASA NTRS1992

Use of microgravity to improve the efficiency and power output of Nd-doped laser glasses

The objectives of this research are to: (1) obtain further evidence and understand the science for the reported improvement in chemical homogeneity in glasses prepared in microgravity; and (2) study the feasibility of improving the optical and fluorescence properties, particularly, the limit for Nd(+3) concentration quenching and threshold energy for laser action for laser glasses prepared in microgravity. Attention was directed to ground based investigation whose primary purpose was to determine the suitability and conditions for processing these laser glasses in space. This report describes that the scientific and technical information required for planning flight experiments for these glasses have been obtained, and the preparation for handling and analyzing post flight samples have also been taken. Instruments required for measuring the fluorescence properties of interest have been constructed. The optical and fluorescence properties for the glasses have been measured and made available for comparative property analysis.

Ray, Chandra S.↗