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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3

Thermal Management Tools for Propulsion System Trade Studies and Analysis

Energy-related subsystems in modern aircraft are more tightly coupled with less design margin. These subsystems include thermal management subsystems, vehicle electric power generation and distribution, aircraft engines, and flight control. Tighter coupling, lower design margins, and higher system complexity all make preliminary trade studies difficult. A suite of thermal management analysis tools has been developed to facilitate trade studies during preliminary design of air-vehicle propulsion systems. Simulink blocksets (from MathWorks) for developing quasi-steady-state and transient system models of aircraft thermal management systems and related energy systems have been developed. These blocksets extend the Simulink modeling environment in the thermal sciences and aircraft systems disciplines. The blocksets include blocks for modeling aircraft system heat loads, heat exchangers, pumps, reservoirs, fuel tanks, and other components at varying levels of model fidelity. The blocksets have been applied in a first-principles, physics-based modeling and simulation architecture for rapid prototyping of aircraft thermal management and related systems. They have been applied in representative modern aircraft thermal management system studies. The modeling and simulation architecture has also been used to conduct trade studies in a vehicle level model that incorporates coupling effects among the aircraft mission, engine cycle, fuel, and multi-phase heat-transfer materials.

McCarthy, Kevin↗

Multiyear slant-path rain fade statistics at 28.56 GHz for Wallops Island, Va.

The multiyear rain fade statistics collected in the Wallops Island, Va., area at 28.56 GHz during 1977 through 1979 showed that the overall fade distributions for the individual years showed small differences. Exceedance time variations were observed in the monthly and time of day fade data from year to year, but the second year fades relative to the first year had less than 20% rms deviation. These results are useful to designers of earth-satellite communications systems which require reliable fade statistics for establishing link-margin requirements. The Wallops Island fade distribution had an rms decibel deviation of less than 14% when compared with the International Radio Consultative Committee prediction model.

Goldhirsh, J.↗

Use of ILTV Control Laws for LaNCETS Flight Research

A report discusses the Lift and Nozzle Change Effects on Tail Shock (LaNCETS) test to investigate the effects of lift distribution and nozzle-area ratio changes on tail shock strength of an F-15 aircraft. Specific research objectives are to obtain inflight shock strength for multiple combinations of nozzle-area ratio and lift distribution; compare results with preflight prediction tools; and update predictive tools with flight results. The objectives from a stability and control perspective are to ensure adequate aircraft stability for the changes in lift distribution and plume shape, and ensure manageable transient from engaging and disengaging the ILTV research control laws. In order to change the lift distribution and plume shape of the F-15 aircraft, a decade-old Inner Loop Thrust Vectoring (ILTV) research control law was used. Flight envelope expansion was performed for the test configuration and flight conditions prior to the probing test points. The approach for achieving the research objectives was to utilize the unique capabilities of NASA's NF-15B-837 aircraft to allow the adjustment of the nozzle-area ratio and/or canard positions by engaging the ILTV research control laws. The ILTV control laws provide the ability to add trim command biases to canard positions, nozzle area ratios, and thrust vectoring through the use of datasets. Datasets consist of programmed test inputs (PTIs) that define trims to change the nozzle-area ratio and/or canard positions. The trims are applied as increments to the normally commanded positions. A LaNCETS non-linear, six-degrees-of-freedom simulation capable of realtime pilot-in-the-loop, hardware-in-the-loop, and non-real-time batch support was developed and validated. Prior to first flight, extensive simulation analyses were performed to show adequate stability margins with the changes in lift distribution and plume shape. Additionally, engagement/disengagement transient analysis was also performed to show manageable transients.

Moua, Cheng↗

Throat-bypass bleed systems for increasing the stable airflow range of a Mach 2.50 axisymmetric inlet with 40-percent internal contraction

The results of an experimental investigation to increase the stable airflow range of a super sonic mixed-compression inlet are presented. Various throat-bypass bleeds were located on the inlet cowl. The bleed types were distributed porous normal holes, a forward slanted slot, or distributed educated slots. Large inlet stability margins were obtained with the inlet throat bleed systems if a constant pressure was maintained in the throat-bypass bleed plenum. Stability limits were determined for steady-state and limited transient internal air flow changes. Limited unstart angle-of-attack data are presented.

Sanders, B. W.↗

Low Average Sidelobe Slot Array Antennas for Radiometer Applications

In radiometer applications, it is required to design antennas that meet low average sidelobe levels and low average return loss over a specified frequency bandwidth. It is a challenge to meet such specifications over a frequency range when one uses resonant elements such as waveguide feed slots. In addition to their inherent narrow frequency band performance, the problem is exacerbated due to modeling errors and manufacturing tolerances. There was a need to develop a design methodology to solve the problem. An iterative design procedure was developed by starting with an array architecture, lattice spacing, aperture distribution, waveguide dimensions, etc. The array was designed using Elliott s technique with appropriate values of the total slot conductance in each radiating waveguide, and the total resistance in each feed waveguide. Subsequently, the array performance was analyzed by the full wave method of moments solution to the pertinent integral equations. Monte Carlo simulations were also carried out to account for amplitude and phase errors introduced for the aperture distribution due to modeling errors as well as manufacturing tolerances. If the design margins for the average sidelobe level and the average return loss were not adequate, array architecture, lattice spacing, aperture distribution, and waveguide dimensions were varied in subsequent iterations. Once the design margins were found to be adequate, the iteration was stopped and a good design was achieved. A symmetric array architecture was found to meet the design specification with adequate margin. The specifications were near 40 dB for angular regions beyond 30 degrees from broadside. Separable Taylor distribution with nbar=4 and 35 dB sidelobe specification was chosen for each principal plane. A non-separable distribution obtained by the genetic algorithm was found to have similar characteristics. The element spacing was obtained to provide the required beamwidth and close to a null in the E-plane end-fire direction. Because of the alternating slot offsets, grating lobes called butterfly lobes are produced in non-principal planes close to the H-plane. An attempt to reduce the influence of such grating lobes resulted in a symmetric design.

Rengarajan, Sembiam↗

Bivariate normal, conditional and rectangular probabilities: A computer program with applications

Some results for the bivariate normal distribution analysis are presented. Computer programs for conditional normal probabilities, marginal probabilities, as well as joint probabilities for rectangular regions are given: routines for computing fractile points and distribution functions are also presented. Some examples from a closed circuit television experiment are included.

Swaroop, R.↗

Aeolian Sediment Transport Pathways and Aerodynamics at Troughs on Mars

Interaction between wind regimes and topography can give rise to complex suites of aeolian landforms. This paper considers aeolian sediment associated wit11 troughs on Mars and identifies a wider range of deposit types than has previously been documented. These include wind streaks, falling dunes, "lateral" dunes, barchan dunes, linear dunes, transverse ridges, sand ramps, climbing dunes, sand streamers, and sand patches. The sediment incorporated into these deposits is supplied by wind streaks and ambient Planitia sources as well as originating within the trough itself, notably from the trough walls and floor. There is also transmission of sediment between d~~neTsh. e flow dynamics which account for the distribution of aeolian sediment have been modeled using two-dimensional computational fluid dynamics. The model predicts flow separation on the upwind side of the trough followed by reattachment and acceleration at the downwind margin. The inferred patterns of sediment transport compare well with the distribution of aeolian forms. Model data indicate an increase of wind velocity by approx. 30 % at the downwind trough margin. This suggests that the threshold wind speed necessary for sand mobilization on Mars will be more freq~~entmlye t in these inclined locations.

Bourke, Mary C.↗

Stimulated emission of AKR in regions of a weakly unstable electron velocity distribution

While, according to the cyclotron maser theory, auroral kilometric radiation generates auroral zone instability whose consequent radiation is in many respects consistent with observations, in situ velocity distribution measurements by satellites show only moderate positive gradients which would be only marginally unstable, implying a low radiation level. Numerical simulations are conducted alternatively using an observed electron-velocity distribution and an idealized loss-cone distribution. The expected amplification of X-mode radiation, as well as effects which go beyond the behavior of a simple amplifying medium, emerge in the results.

Kainer, S.↗

Structural tailoring using the SSME/STAEBL code

Space Shuttle Main Engine/Structural Tailoring of Engine Blades (SSME/STAEBL) was developed by systematically modifying and enhancing the STAEBL code developed by Pratt and Whitney under contract to NASA Lewis Research Center. STAEBL was designed for application to gas turbine blade design. Typical design variables include blade thickness distribution and root chord. Typical constraints include resonance margins, root stress, and root to chord ratios. In this program, the blade is loaded by centrifugal forces only. Additions and modifications of STAEBL included in SSME/STAEBL include (1) thermal stress analysis; (2) gas dynamic (pressure) loads; (3) temperature dependent material and thermal properties; (4) forced vibrations; (5) tip displacement constraints; (6) single crystal material analysis; (7) blade cross section stacking offsets; and (8) direct time integration algorithm for transient dynamic response. Capabilities are also included which permit data transfer from finite element models and stand-alone analysis.

Rubinstein, Robert↗

Investigate the height dependency of the micro-/defect-structure and mechanical properties of additively manufactured AlF357 aluminum alloy

When the laser powder bed fusion (L-PBF) additive manufacturing method is employed to build parts with increased heights, there is a possibility that defects are increased in part. This study investigates the effect of build height on the micro-/defect-structure and, consequently, the mechanical properties of L-PBF AlF357, an Al-Si-Mg alloy family. Tall vertical cylinders of 316 mm with 15 mm diameter were fabricated and cut into specimens at different heights. Although not much difference is observed in the microstructure (grain size and morphology), the defects' size and population slightly vary with height. Nonetheless, the tensile properties of the L-PBF AlF357 are found to be independent of height. This is ascribed to the approximately identical microstructure and marginal difference in the defect's size and distribution along the heights.

Laser powder bed fusion (L-PBF)↗

Global organization of tectonic deformation on Venus

The geographic organization of surface deformation on Venus as on Earth is a key to understanding the global tectonic system. To date we have mapped the distribution of three unambiguous tectonic land forms on Venus: (1) linear foldbelts analogous to those at plate margins of the Earth; (2) linear rift zones, analogous to continental rifts on the Earth; and (3) distributed plains deformation in the form of wrinkle ridges and extensional faults and fractures. The linear foldbelts are the dominant structural style in the Northern Hemisphere; ninety percent of the planet's foldbelts lie above the equator. In contrast, compressive deformation in the Southern Hemisphere is dominated by two large, sweeping patterns of wrinkle ridges. The two hemispheres are divided by an equatorial region that is largely covered by rift zones and several large tessera blocks. A tectonic model of generally poleward convergence of the Northern Hemisphere explains the distribution of foldbelts and rift zones. In our model, a northern hemispherical plate (or system of plates) moves poleward and deforms along discrete, predominately longitudinal bands. We recognize four types of foldbelts based on their relationships to other large-scale tectonic features on Venus. There are foldbelts that lie within the low plains, foldbelts associated with coronae, novae and chasmata, foldbelts that lie at the margins of poly-deformed tessera plateaus, and the folded mountain belts around Lakshmi Planum. We see a geometric increase in the area of fold belts when normalized to percent area at a given latitude. This increase is consistent with our model of poleward convergence. Also, the orientations of most foldbelts are either approximately north-south or parallel to lines of latitude in the northern hemisphere. This observation is also consistent with the model in that the longitudinal bands are the result of the decreasing area of the sphere as the plate moves poleward and the latitudinal belts are the direct result of poleward compression. The trends of wrinkle ridges have been mapped over the planet and several large, sweeping patterns evidently reflect long-wavelength topography. Using wrinkle ridges as paleostress indicators, we have developed local and regional stress trajectory maps.

Bilotti, Frank↗

ATM CMG bearing failure analysis

The cause or causes for the failure of ATM CMG S/N 5 (Skylab 1) and the anomalies associated with ATM CMG S/N 6 (Skylab 2) were investigated. Skylab telemetry data were reviewed and presented in the form of parameter distributions. The theory that the problems were caused by marginal bearing lubrication was studied along with the effects of orbital conditions on lubricants. Bearing tests were performed to investigate the effect of lubricant or lack of lubricant in the ATM CMG bearings and the dispersion and migration of the lubricant. The vacuum and weightless conditions of space were simulated in the bearing tests. Analysis of the results of the tests conducted points to inadequate lubrication as the predominant factor causing the failure of ATM CMG S/N 5 (Skylab 1) and the anomalies associated with ATM CMG S/N 6 (Skylab 2).

Source record↗

Melt Pond Conditions on Declining Arctic Sea Ice Over 1979-2016: Model Development, Validation, and Results

A melt pond (MP) distribution equation has been developed and incorporated into the Marginal Ice-Zone Modeling and Assimilation System to simulate Arctic MPs and sea ice over 1979-2016. The equation differs from previous MP models and yet benefits from previous studies for MP parameterizations as well as a range of observations for model calibration. Model results show higher magnitude of MP volume per unit ice area and area fraction in most of the Canada Basin and the East Siberian Sea and lower magnitude in the central Arctic. This is consistent with Moderate Resolution Imaging Spectroradiometer observations, evaluated with Measurements of Earth Data for Environmental Analysis (MEDEA) data, and closely related to top ice melt per unit ice area. The model simulates a decrease in the total Arctic sea ice volume and area, owing to a strong increase in bottom and lateral ice melt. The sea ice decline leads to a strong decrease in the total MP volume and area. However, the Arctic-averaged MP volume per unit ice area and area fraction show weak, statistically insignificant downward trends, which is linked to the fact that MP water drainage per unit ice area is increasing. It is also linked to the fact that MP volume and area decrease relatively faster than ice area. This suggests that overall the actual MP conditions on ice have changed little in the past decades as the ice cover is retreating in response to Arctic warming, thus consistent with the Moderate Resolution Imaging Spectroradiometer observations that show no clear trend in MP area fraction over 2000-2011.

sea ice↗

Antipodal hotspot pairs on the earth

The results of statistical analyses performed on three published hotspot distributions suggest that significantly more hotspots occur as nearly antipodal pairs than is anticipated from a random distribution, or from their association with geoid highs and divergent plate margins. The observed number of antipodal hotspot pairs depends on the maximum allowable deviation from exact antipodality. At a maximum deviation of not greater than 700 km, 26 to 37 percent of hotspots form antipodal pairs in the published lists examined here, significantly more than would be expected from the general hotspot distribution. Two possible mechanisms that might create such a distribution include: (1) symmetry in the generation of mantle plumes, and (2) melting related to antipodal focusing of seismic energy from large-body impacts.

Rampino, Michael R.↗

Rain rate statistics and fade distributions at 20 and 30 GHz derived from a network of rain gauges in the Mid-Atlantic coast over a five year period

A network of ten tipping bucket rain gauges located within a grid 70 km north-south and 47 km east-west in the Mid-Atlantic coast of the United States was used to analyze rain rate and modeled slant path attenuation distributions at 20 and 30 GHz. It was shown that, for realistic fade margins at 20 GHz and above, the variable integration times results are adequate to estimate slant path attenuations using models which require 1 min averages. Crane's Global Model was used to derive fade distributions at 20 and 30 GHz.

Goldhirsh, Julius↗

Fade margin calculation for channels impaired by Rician fading

Excess path loss due to multipath severely restricts the performance of power limited mobile networks such as those using satellite-aided links. To reduce multipath related losses, the higher elevation angle of the spacecraft can be exploited by utilizing mobile antennas which reduce the strength of the multipath reflections in favor of the line-of-sight signal. The presence of a strong and stable path in a fading link will change the envelope statistics of the received waveform from Rayleigh to a more favorable Rician distribution. It is determined that the excess path loss, or fade margin, of a Rician channel when coherent detection of binary phase shift keying (BPSK) or quaternary phase shift keying (QPSK) signals is considered. The results are presented parametrically such that they can be applied to a wide range of propagation characteristics from heavy fading to nonfading situations. Furthermore, similar results are also given for the case where only limited coverage is provided.

Davarian, F.↗

Are We Shaking Too Much? An Inquiry into Environmental Random Vibration Testing Margins

Problem Statement: The conventional, MIL-STD-810 approach to vibration environment derivation is perhaps too conservative, leading to unnecessary failures during acceptance & qualification vibration testing of Armstrong’s one-off flight equipment. Objective: This presentation explores some alternative understandings of the distributions of vibration severity in nonstationary environments. Proposed methods of sorting and adding appropriate margin are explored.

Scott L. Stebbins↗