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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS2020

Designing Shading Schemes for Microphone Phased Arrays

A technique is proposed for designing sensor weightings, or array shading functions, for microphone phased arrays. The presented method attempts to maintain mathematical simplicity while maximizing array gain for a desired mainlobe beamwidth. It does so using the two-parameter optimization of a family of functions. The shading design process is described and applied to an array used recently in the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel. Several variants of the method are compared to an existing shading scheme for the array, along with a more general optimization formulation. Results are presented for both an idealized point source and experimental data from the wind tunnel test. The shading schemes are shown to improve the behavior of array operations, but have a stronger impact on visual interpretation of maps than on source level calculations. The study results show that the two-parameter optimization scheme provides favorable characteristics while maintaining implementation simplicity.

Christopher J Bahr↗
DOE OSTI2022

Membrane‐electrode assembly design parameters for optimal CO 2 reduction

Commercial-scale generation of carbon-containing chemicals and fuels by means of electrochemical CO 2 reduction (CO 2 R) requires electrolyzers operating at high current densities and product selectivities. Membrane-electrode assemblies (MEAs) have been shown to be suitable for this purpose. In such devices, the cathode catalyst layer controls both the rate of CO 2 R and the distribution of products. In this study, we investigate how the ionomer-to-catalyst ratio (I:Cat), catalyst loading, and catalyst-layer thickness influence the performance of a cathode catalyst layer containing Ag nanoparticles supported on carbon. In this paper, we explore how these parameters affect the cell performance and establish the role of the exchange solution (water vs. CsHCO 3 ) behind the anode catalyst layer in cell performance. We show that a high total current density is best achieved using an I:Cat ratio of 3 at a Ag loading of 0.01–0.1 mg Ag /cm 2 and with a 1.0 M solution of CsHCO 3 circulated behind the anode catalyst layer. For these conditions, the optimal CO partial current density depends on the voltage applied to the MEA. The work also reveals that the performance of the cathode catalyst layer is limited by a combination of the electrochemically active surface area and the degree to which mass transfer of CO 2 to the surface of the Ag nanoparticles and the transport of OH – anions away from it limit the overall catalyst activity. Hydration of the ionomer in the cathode catalyst layer is found not to be an issue when using an exchange solution. The insights gained allowed for a Ag CO 2 R MEA that operates between 200 mA/cm 2 and 1 A/cm 2 with CO faradaic efficiencies of 78–91%, and the findings and understanding gained herein should be applicable to a broad range of CO 2 R MEA-based devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1975

System design of a rudder coordination system

The application of the parameter optimization computer program to the design of a rudder coordination system for the F-8 airplane is summarized. The flight condition was Mach 0.56 at 20,000 feet altitude. The system configuration selected consisted of signal paths that fed yaw rate and aileron signals to the rudder. The two signal paths were summed and then modified by a high pass filter to eliminate any steady state bias signal. The input axis of the yaw gyro was perpendicular to the aircraft zero lift line and the trim angle of attack was 7.75 degrees. The parameter optimization was used to design the complete system first, and then a root locus analysis of the individual component effects was made. The results are presented.

Whitaker, H. P.↗
DOE OSTI2025

Directed energy deposition of functionally graded V-4Cr-4Ti to Fe-9Cr transition for fusion power systems

This study proposes a graded structure via additive manufacturing for divertor and first wall blanket applications in fusion reactors. Materials were selected based on thermodynamic calculations to operate from 1100 °C at the plasma-facing level to 550 °C at the structural steel level. Conventional joining methods often lead to failures due to discrete reaction layers with significant mechanical property differences. Using laser beam-directed energy deposition (LB-DED), this study demonstrates the fabrication of a VCrTi-Gr91 steel functionally graded component through a novel process parameter optimization framework. A systematic approach included powder characterization, single-track depositions, and construction of printability maps. Near full-density specimens of each interlayer were additively manufactured, and a transition from V-based alloys to reduced activation ferritic martensitic steels was achieved. Computational material selection of interlayer alloys and thermodynamic/diffusion kinetics simulations prevented most interface incompatibilities. A brittle intermetallic formed at one interface, causing cracking, which was not predicted by current thermodynamic models. Transition alloy design approach was updated with a more recent database and a mitigation strategy has been proposed to eliminate the formation of deleterious intermetallic phases. Ultimately, LB-DED has proven effective for producing multi-material graded systems for fusion applications, with the demonstrated process parameter optimization framework applicable to various materials.

Additive manufacturing↗
NASA NTRS1993

A time optimal Space Station reboost guidance strategy

A closed-loop guidance strategy for time and fuel optimal reboost of Space Station Freedom is discussed in this paper. The reboost maneuver is formulated as an optimal control problem rather than a parameter optimization problem, the parameters being the thrust switching times. In the present approach the thrust switching structure need not be prescribed a priori to solve the resulting two point boundary value problem. Non-optimality of singular control or intermediate thrust is proved by utilizing the second order Kelley condition or the Generalized Legendre-Clebsch condition. Only a few sets of initial co-states and time-to-go guess values need to be stored on-board for a wide range of reboost scenarios.

Kumar, Renjith R.↗
NASA NTRS1993

A time-optimal Space Station reboost guidance strategy

A closed-loop guidance strategy for time and fuel optimal reboost of Space Station Freedom is discussed in this paper. The reboost maneuver is formulated as an optimal control problem rather than a parameter optimization problem, the parameters being the thrust switching times. In the present approach the thrust switching structure need not be prescribed a priori to solve the resulting two point boundary value problem. Non-optimality of singular control or intermediate thrust is proved by utilizing the second order Kelley condition or the Generalized Legendre-Clebsch condition. Only a few sets of initial co-states and time-to-go guess values need to be stored on-board for a wide range of reboost scenarios.

Kumar, Renjith R.↗
DOE OSTI2022

Dissipation and Bathymetric Sensitivities in an Unstructured Mesh Global Tidal Model

Abstract The mechanisms and geographic distribution of global tidal dissipation in barotropic tidal models are examined using a high resolution unstructured mesh finite element model. Mesh resolution varies between 2 and 25 km and is especially focused on inner shelves and steep bathymetric gradients. Tidal response sensitivities to bathymetric changes are examined to put into context response sensitivities to frictional processes. We confirm that the Ronne Ice Shelf dramatically affects Atlantic tides but also find that bathymetry in the Hudson Bay system is a critical control. We follow a sequential frictional parameter optimization process and use TPXO9 data‐assimilated tidal elevations as a reference solution. From simulated velocities and depths, dissipation within the global model is estimated and allows us to pinpoint dissipation at high resolution. Boundary layer dissipation is extremely focused with 1.4% of the ocean accounting for 90% of the total. Internal tide friction is much more distributed with 16.7% of the ocean accounting for 90% of the total. Often highly regional dissipation can impact basin‐scale and even ocean wide tides. Optimized boundary layer friction parameters correlate very well with the physical characteristics of the locality with high friction factors associated with energetic tidal regions, deep ocean island chains, and ice covered areas. Global complex M 2 tide errors are 1.94 cm in deep waters. Total global boundary layer and internal tide dissipation are estimated, respectively, at 1.83 and 1.49 TW. This continues the trend in the literature toward attributing more dissipation to internal tides.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Cyclotron Production of PET Radiometals in Liquid Targets: Aspects and Prospects

: The present review describes the methodological aspects and prospects of the productionof Positron Emission Tomography (PET) radiometals in a liquid target using low-medium energymedical cyclotrons. The main objective of this review is to delineate and discuss the critical factorsinvolved in the liquid target production of radiometals, including type of salt solution, solutioncomposition, beam energy, beam current, the effect of irradiation duration (length of irradiation)and challenges posed by in-target chemistry in relation with irradiation parameters. We also summarizethe optimal parameters for the production of various radiometals in liquid targets. : Additionally, we discuss the future prospects of PET radiometals production in the liquid targetsfor academic research and clinical applications. Significant emphasis has been given to the productionof 68 Ga using liquid targets due to the growing demand for 68 Ga labeled PSMA vectors, [ 68 Ga]-Ga-DOTATATE, [ 68 Ga]Ga-DOTANOC and some upcoming 68 Ga labeled radiopharmaceuticals.Other PET radiometals included in the discussion are 86 Y, 63 Zn and 89 Zr.

Pharmacology & Pharmacy↗
DOE OSTI2025

Characterizing Seasonal Variation of the Atmospheric Mixing Layer Height Using Machine Learning Approaches

As machine learning becomes more integrated into atmospheric science, XGBoost has gained popularity for its ability to assess the relative contributions of influencing factors in the atmospheric boundary layer height. To examine how these factors vary across seasons, a seasonal analysis is necessary. However, dividing data by season reduces the sample size, which can affect result reliability and complicate factor comparisons. To address these challenges, this study replaces default parameters with grid search optimization and incorporates cross-validation to mitigate dataset limitations. Using XGBoost with four years of data from the atmospheric radiation measurement (ARM) (Southern Great Plains (SGP) C1 site, cross-validation stabilizes correlation coefficient fluctuations from 0.3 to within 0.1. With optimized parameters, the R value can reach 0.81. Analysis of the C1 site reveals that the relative importance of different factors changes across seasons. Lower tropospheric stability (LTS, ~0.53) is the dominant factor at C1 throughout the year. However, during DJF, latent heat flux (LHF, 0.44) surpasses LTS (0.22). In SON, LTS (0.58) becomes more influential than LHF (0.18). Further comparisons among the four long-term SGP sites (C1, E32, E37, and E39) show seasonal variations in relative importance. Notably, during JJA, the differences in the relative importance of the three factors across all sites are lower than in other seasons. This suggests that boundary layer development in the summer is not dominated by a single factor, reflecting a more intricate process likely influenced by seasonal conditions such as enhanced convective activity, higher temperatures, and humidity, which collectively contribute to a balanced distribution of parameter impacts. Furthermore, the relative importance of LTS gradually increases from morning to noon, indicating that LTS becomes more significant as the boundary layer approaches its maximum height. Consequently, the LTS in the early morning in autumn exhibits greater relative importance compared to other seasons. This reflects a faster development of the mixing layer height (MLH) in autumn, suggesting that it is easier to retrieve the MLH from the previous day during this period. The findings enhance understanding of boundary layer evolution and contribute to improved boundary layer parameterization.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1974

A dual extremum principle for a population equation

A dual extremum principle for the Verhulst-Pearl population equation is constructed using a complementary variational technique. The dual formulation utilizes a minimum principle recently developed by Leitmann to convert the functional optimization problem into a parameter optimization problem.

Chan, W. L.↗
NASA NTRS1996

Optimizing Process Parameters to Produce Single Phase YBa2Cu3O7 Powder

Process parameters such as temperature and time are varied to obtain single phase (pure) YBa2Cu307 powders. X-ray diffraction patterns of superconducting and nonsuperconducting powders are observed in situ in normal and elevated temperature environments to confirm known strong peaks that are unique to YBa2Cu307. Peaks vary in magnitude as a result of superconducting - nonsuperconducting phase transitions. Known strong peaks serve as our basis in monitoring transitional changes. Peak isotherms obtained experimentally are correlated with theoretical models to identify the weighting factor that characterizes the optimum isotherm. By isolating the parameters under which 100% peak growth occurs most rapidly, we obtain the optimum isotherm. The choices made for firing temperature and atmosphere were determined to be the primary factors necessary to ensure sample purity.

Hurley, J. S.↗
NASA NTRS2011

Method for Predicting and Optimizing System Parameters for Electrospinning System

An electrospinning system using a spinneret and a counter electrode is first operated for a fixed amount of time at known system and operational parameters to generate a fiber mat having a measured fiber mat width associated therewith. Next, acceleration of the fiberizable material at the spinneret is modeled to determine values of mass, drag, and surface tension associated with the fiberizable material at the spinneret output. The model is then applied in an inversion process to generate predicted values of an electric charge at the spinneret output and an electric field between the spinneret and electrode required to fabricate a selected fiber mat design. The electric charge and electric field are indicative of design values for system and operational parameters needed to fabricate the selected fiber mat design.

Wincheski, Russell A.↗
DOE OSTI2024

Autocalibration of the E3SM Version 2 Atmosphere Model Using a PCA-Based Surrogate for Spatial Fields

Global Climate Model tuning (calibration) is a tedious and time-consuming process, with high-dimensional input and output fields. Experts typically tune by iteratively running climate simulations with hand-picked values of tuning parameters. Many, in both the statistical and climate literature, have proposed alternative calibration methods, but most are impractical or difficult to implement. We present a practical, robust, and rigorous calibration approach on the atmosphere-only model of the Department of Energy's Energy Exascale Earth System Model (E3SM) version 2. Our approach can be summarized into two main parts: (a) the training of a surrogate that predicts E3SM output in a fraction of the time compared to running E3SM, and (b) gradient-based parameter optimization. To train the surrogate, we generate a set of designed ensemble runs that span our input parameter space and use polynomial chaos expansions on a reduced output space to fit the E3SM output. We use this surrogate in an optimization scheme to identify values of the input parameters for which our model best matches gridded spatial fields of climate observations. To validate our choice of parameters, we run E3SMv2 with the optimal parameter values and compare prediction results to expertly-tuned simulations across 45 different output fields. This flexible, robust, and automated approach is straightforward to implement, and we demonstrate that the resulting model output matches present day climate observations as well or better than the corresponding output from expert tuned parameter values, while considering high-dimensional output and operating in a fraction of the time.

54 ENVIRONMENTAL SCIENCES↗