Low variable thrust interplanetary trajectory data
Algorithm for generating low variable thrust interplanetary trajectory data for mission analysis of electrical propulsion systems
Mac Kay, J. S.↗
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Results for “variable generation”
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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Experimental investigation of a variable speed constant frequency electric generating system from a utility perspective
As efforts are accelerated to improve the overall capability and performance of wind electric systems, increased attention to variable speed configurations has developed. A number of potentially viable configurations have emerged. Various attributes of variable speed systems need to be carefully tested to evaluate their performance from the utility points of view. With this purpose, the NASA experimental variable speed constant frequency (VSCF) system has been tested. In order to determine the usefulness of these systems in utility applications, tests are required to resolve issues fundamental to electric utility systems. Legitimate questions exist regarding how variable speed generators will influence the performance of electric utility systems; therefore, tests from a utility perspective, have been performed on the VSCF system and an induction generator at an operating power level of 30 kW on a system rated at 200 kVA and 0.8 power factor.
Herrera, J. I.↗
Numerical experiments with a stochastic zonal climate model
A zonally averaged energy balance climate model is developed to generate zonal temperature variability through fluctuating meridional energy transports. Stochastic transport fluctuations are included in the model by multiplying the eddy diffusion coefficients by Gaussian random deviates. For a variability of eddy coefficients of 50 percent, the model is found to generate an interannual temperature variability of 0.03 K for the global temperature, and 0.04 and 0.05 K for the Northern and Southern Hemispheres, respectively. It is shown that the temperature variability level generated is linearly related to the transport variability level introduced. An increase in the level of model-generated temperature variability and a change in the shape of variance spectra of temperature anomaly time series are obtained by switching from the multiplicative noise model to an additive noise model. The results of these model studies are compared with a time series of central England temperatures as well as GCM generated climate variability.
Schneider, S. H.↗
Design criteria for selection of aircraft electric power generation and distribution systems
STOL aircraft electric power variable frequency generation and high voltage DC distribution with secondary square wave AC distribution
Lee, C. H.↗
Spline approximation of quantile functions
The study reported here explored the development and utility of a spline representation of the sample quantile function of a continuous probability distribution in providing a functional description of a random sample and a method of generating random variables. With a spline representation, the random samples are generated by transforming a sample of uniform random variables to the interval of interest. This is useful, for example, in simulation studies in which a random sample represents the only known information about the distribution. The spline formulation considered here consists of a linear combination of cubic basis splines (B-splines) fit in a least squares sense to the sample quantile function using equally spaced knots. The following discussion is presented in five parts. The first section highlights major results realized from the study. The second section further details the results obtained. The methodology used is described in the third section, followed by a brief discussion of previous research on quantile functions. Finally, the results of the study are evaluated.
Schiess, J. R.↗
Role of Oceanic Internal Instability in the Generation of Low‐Frequency Variability in the Indian Ocean
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S. Anjana↗
Crossing shock wave turbulent boundary layer interactions - Variable angle and shock generator length geometry effects at Mach 3
By comparing the detailed wall static pressure distributions for 9 inch and 11 inch long fins generating a crossing shock configuration at M = 2.93, the high resolution results of the 9 inch fins are shown to be free of exit effects. Analysis of the static pressure profiles have delineated the limited regions where the single fin results are valid. The characteristics of the complex interaction, with varying shock wave strength, have been described. The data provide a critical test for computational fluid dynamics which, in its initial phase, has performed poorly in predicting the measured wall static pressure distributions.
Bogdonoff, S. M.↗
Effects of Some Primary Variables of Rectangular Vortex Generators on the Static-pressure Rise Through a Short Diffuser
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Valentine, E Floyd↗
Application of variable optics to solar simulation systems for generation of high intensity light beams.
Variable optical system with remote and continuous adjustment of beam for solar simulation, permitting maximum test facility utilization
Harris, T. I.↗
Colorado Front Range Disasters: Understanding the Impact of Forest Management on the Cameron Peak and CalWood Fire
Along the Colorado Front Range, forest management has gained significant attention due to uncharacteristically large fires that burned late in 2020. The Cameron Peak Fire (largest in Colorado recorded history) and the CalWood Fire collectively burned an estimated 219,019 acres from August through December of 2020. Project partners at the Coalition for the Poudre River Watershed, Colorado State Forest Service, Ben Delatour Scout Ranch, The Nature Conservancy, Colorado Forest Restoration Institute, and Colorado State University were interested in understanding the effectiveness of previous forest treatments in reducing burn severity within the Cameron Peak Fire and the CalWood Fire. We first collated a forest treatment dataset from pre-existing datasets by reclassifying over 29,000 treatments, which occurred across the Northern Colorado Front Range between 1970-2020. Secondly, we mapped three burn severity indices using Landsat 8 OLI and Sentinel-2 MSI Earth observations and compared them to soil burn severity field data. Thirdly, a total of 35 topographic, disturbance, forest structure, and treatment predictor variables were generated across the fires. Finally, we assessed relationships between these predictor variables and burn severity using the random forest algorithm. Model results indicate that the primary drivers of burn severity were elevation and distance to treatment edge for the Cameron Peak Fire and fire area and forest canopy cover for the CalWood Fire. Further analysis of these variables paired with field data is necessary to understand the relationship between burn severity and treatments to guide future restoration efforts, improve forest resiliency, and mitigate fire risks.
Neal Swayze↗
Effect of water injection and off scheduling of variable inlet guide vanes, gas generator speed and power turbine nozzle angle on the performance of an automotive gas turbine engine
The Chrysler/ERDA baseline automotive gas turbine engine was used to experimentally determine the power augmentation and emissions reductions achieved by the effect of variable compressor and power engine geometry, water injection downstream of the compressor, and increases in gas generator speed. Results were dependent on the mode of variable geometry utilization. Over 20 percent increase in power was accompanied by over 5 percent reduction in SFC. A fuel economy improvement of at least 6 percent was estimated for a vehicle with a 75 kW (100 hp) engine which could be augmented to 89 kW (120 hp) relative to an 89 Kw (120 hp) unaugmented engine.
Warren, E. L.↗
A hybrid electrical power system for aircraft application.
Possible improvements to present aircraft electrical power systems for use in future advanced types of aircraft have been investigated. The conventional power system is examined, the characteristics of electric loads are reviewed, and various methods of power generation and distribution are appraised. It is shown that a hybrid system, with variable-frequency generation and high-voltage dc distribution, could overcome some of the limitations of the conventional system.
Lee, C. H.↗
Variable Mixing Nozzle Design with Slotted Vortex Generators for Jet Noise Reduction
A new variable geometry turbofan nozzle concept is presented with the dual goals of airport noise reduction and high propulsive efficiency at cruise, while employing only a single moving part. The nozzle utilizes a number of curved vanes to function as vortex generators (VGs) during takeoff and initial climb. Streamwise vortices provide an increase in mixing between the jet and external stream, with a resulting decrease in high frequency noise generation and a noise source distribution which is more amenable to airframe-based shielding. Unlike conventional VGs, the vanes are positioned without transverse incidence, and a pressure difference across the surface of each vane is created via an adjacent slot. During high altitude flight, when nozzle efficiency concerns outweigh any preference for jet noise reduction, all slots may be closed through rotation of a slotted ring inside the nozzle. RANS-based numerical analysis is performed to calculate propulsive metrics, determine noise source characteristics and understand various design parameter sensitivities. A new formulation is developed to approximately correct computed noise intensities for any throttle adjustments required to maintain takeoff thrust, and a rough estimate of shielding effectiveness is proposed by means of integration over a spatially distributed noise source. A total of 19 different nozzle geometries are considered in the present study. Results indicate significant noise benefits at takeoff, including a 2 kHz fly-over noise reduction of roughly 2-3 dB, while allowing for less than 15% of the net thrust reduction at supersonic cruise calculated for a fixed-penetration chevron nozzle.
Jet Noise↗
Grid sensitivity capability for large scale structures
The considerations and the resultant approach used to implement design sensitivity capability for grids into a large scale, general purpose finite element system (MSC/NASTRAN) are presented. The design variables are grid perturbations with a rather general linking capability. Moreover, shape and sizing variables may be linked together. The design is general enough to facilitate geometric modeling techniques for generating design variable linking schemes in an easy and straightforward manner. Test cases have been run and validated by comparison with the overall finite difference method. The linking of a design sensitivity capability for shape variables in MSC/NASTRAN with an optimizer would give designers a powerful, automated tool to carry out practical optimization design of real life, complicated structures.
Nagendra, Gopal K.↗
Large-Scale Circulation and Climate Variability
The causes of regional climate trends cannot be understood without considering the impact of variations in large-scale atmospheric circulation and an assessment of the role of internally generated climate variability. There are contributions to regional climate trends from changes in large-scale latitudinal circulation, which is generally organized into three cells in each hemisphere-Hadley cell, Ferrell cell and Polar cell-and which determines the location of subtropical dry zones and midlatitude jet streams. These circulation cells are expected to shift poleward during warmer periods, which could result in poleward shifts in precipitation patterns, affecting natural ecosystems, agriculture, and water resources. In addition, regional climate can be strongly affected by non-local responses to recurring patterns (or modes) of variability of the atmospheric circulation or the coupled atmosphere-ocean system. These modes of variability represent preferred spatial patterns and their temporal variation. They account for gross features in variance and for teleconnections which describe climate links between geographically separated regions. Modes of variability are often described as a product of a spatial climate pattern and an associated climate index time series that are identified based on statistical methods like Principal Component Analysis (PC analysis), which is also called Empirical Orthogonal Function Analysis (EOF analysis), and cluster analysis.
Perlwitz, J.↗
Observational aspects of the low-frequency intraseasonal variability of the atmosphere in middle latitudes
An integrated description of the planetary-scale structures that emerge as organized entities on intraseasonal temporal scales in the middle latitudes is developed. Spatial scales of atmospheric motions involved in the generation of variability in the LF range are specified. An overview of the 3D structure of the seasonally averaged eddies in which the intraseasonal fluctuations are superposed is presented. The generation and maintenance mechanisms possibly responsible for the existence of the seasonal, quasi-stationary disturbances are discussed. It is shown that in the LF, low-zonal wavenumber part of the spectrum, the power displayed by standing variance exceeds that of propagating variance and vice versa for HFs and wavenumbers.
Pandolfo, Lionel↗
Rolls-Royce Low Noise Highly Variable Cycle Nozzle for Next Generation Supersonic Aircraft
An overview of the work performed by Rolls-Royce under contract NNL08AA29C is presented. The work includes computational fluid dynamic (CFD) analysis for, and design of, a highly variable cycle exhaust model for the Supersonic project (NRA NN06ZEA001N). The CFD analysis shows that the latest design improvements to the clam shell doors have increased flow through the ejector over that achieved with previous designs.
Sokhey, Jack S.↗
Dynamic compensatory pattern matching in a fuzzy rule-based control system
A dynamic compensatory matching procedure is suggested as a method to generate an aggregated measure for evaluating the appropriateness of rules for control systems. It is a dynamic weighted matching technique which takes into account incomplete information under real-time requirements. The initial weights of importance of variables are generated with a generalized neural network architecture and a gradient descent algorithm. An intuitive compensatory scheme based on correlations among input variables of training data is adopted so that the system is coherent to a noisy environment.
Sun, Chuen-Tsai↗