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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Streamlined Convergence Acceleration for CFD Codes

Enigma, a simplified interface to the PETSc library, is shown to enable the rapid solution of discrete partial differential equations. Two CFD codes, LAURA and HyperSolve, use Enigma to compute steady solutions of the Navier-Stokes equations. Using PETSc, Enigma is shown to provide a Jacobian-Free Newton-Krylov method (JFNK), globalized with pseudotransient continuation, that improves efficiency over the point-implicit relaxation method traditionally used by LAURA. It is shown that iterative error has a large impact on surface heat transfer predicted by LAURA on an axisymmetric sphere-cone geometry. Also, the convergence rate of HyperSolve simulating subsonic flow over a delta wing geometry with the JFNK method is shown to be more efficient than employing a defect correction method as the nonlinear solver.

Thompson, Kyle B.↗
NASA NTRS1989

Accurate simulation of vortical flows

Even with recent supercomputers having a large memory, Navier-Stokes simulations for vortical flows do not provide satisfactory results because of the lack of grid resolution to accurately simulate the strength of separation vortices. To overcome this problem, a zonal method is proposed to increase the number of grid points locally. Interface scheme which is critical for an efficient and stable zonal method is based on the Fortified Navier-Stokes concept. Application to both two-dimensional conical and three-dimensional delta wing problems indicates this simple zonal method can improve the accuracy of vortical flow simulations.

Fujii, Kozo↗
NASA NTRS2009

Long Term Measurement of the Vapor Pressure of Gold in the Au-C System

Incorporating the {Au(s,l) + graphite} reference in component activity measurements made with the multiple effusion-cell vapor source mass spectrometry (multicell KEMS) technique provides a fixed temperature defining ITS-90 (T(sub mp)(Au) = 1337.33K) and a systematic method to check accuracy. Over a 2 year period delta H sub(298)Au was determined by the 2nd and 3rd law methods in 25 separate experiments and were in the ranges 362.2 plus or minus 3.3 kJmol(sup -1) and 367.8 plus or minus 1.1 kJmol(sup -1), respectively. This 5 kJmol-1 discrepancy is transferred directly to the measured activities. This is unacceptable and the source of this discrepancy needs to be understood and corrected. Accepting the 2nd law value increases p(Au) by about 50 percent, brings the 2nd and 3rd law values into agreement and removes the T dependence in the 3rd law values. While compelling, there is no way to independently determine instrument sensitivities, S(sub Au), with T in a single experiment with KEMS. This lack of capability is stopping a deeper understanding of this problem. In addition, the Au-C phase diagram suggests a eutectic invariant reaction: L-Au(4.7at%C) = FCC-Au(0.08at%C) + C(graphite) at T(sub e) approximately 1323K. This high C concentration in Au(l) must reduce p(Au) in equilibrium with {Au(s,l) + graphite} and raises some critical questions about the Gibbs free energy functions of Au(s,l) and the Au fixed point (T(sub mp)(Au) = 1337.33K) which is always measured in graphite.

Copland, Evan H.↗
DOE OSTI2021

Linear convergence of accelerated conditional gradient algorithms in spaces of measures

A class of generalized conditional gradient algorithms for the solution of optimization problem in spaces of Radon measures is presented. The method iteratively inserts additional Dirac-delta functions and optimizes the corresponding coefficients. Under general assumptions, a sub-linear [see formula in PDF] rate in the objective functional is obtained, which is sharp in most cases. To improve efficiency, one can fully resolve the finite-dimensional subproblems occurring in each iteration of the method. We provide an analysis for the resulting procedure: under a structural assumption on the optimal solution, a linear [see formula in PDF] convergence rate is obtained locally.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1989

Using the radiative temperature difference at 3.7 and 11 microns to track dust outbreaks

The radiative temperature difference between 3.7 and 11 microns (Delta T) is investigated as a possible method for tracking dust outbreaks. Theoretical calculations indicate that the technique would be most sensitive to dust loading during the day when the Delta Ts are enhanced by reflection of 3.7-micron solar radiation. The feasibility of tracking dust outbreaks is demonstrated by comparing satellite observations with surface estimates of visibility. Theoretical calculations also demonstrate the potential of inferring the dust layer optical depth from these spectral measurements.

Ackerman, Steven A.↗
NASA NTRS2007

Lightning Charge Retrievals: Dimensional Reduction, LDAR Constraints, and a First Comparison with LIS Satellite Data

A "dimensional reduction" (DR) method is introduced for analyzing lightning field changes (DELTAEs) whereby the number of unknowns in a discrete two-charge model is reduced from the standard eight (x, y, z, Q, x', y', z', Q') to just four (x, y, z, Q). The four unknowns (x, y, z, Q) are found by performing a numerical minimization of a chi-square function. At each step of the minimization, an Overdetermined Fixed Matrix (OFM) method is used to immediately retrieve the best "residual source" (x', y', z', Q'), given the values of (x, y, z, Q). In this way, all 8 parameters (x, y, z, Q, x', y', z', Q') are found, yet a numerical search of only 4 parameters (x, y, z, Q) is required. The DR method has been used to analyze lightning-caused DeltaEs derived from multiple ground-based electric field measurements at the NASA Kennedy Space Center (KSC) and USAF Eastern Range (ER). The accuracy of the DR method has been assessed by comparing retrievals with data provided by the Lightning Detection And Ranging (LDAR) system at the KSC-ER, and from least squares error estimation theory, and the method is shown to be a useful "stand-alone" charge retrieval tool. Since more than one charge distribution describes a finite set of DELTAEs (i.e., solutions are non-unique), and since there can exist appreciable differences in the physical characteristics of these solutions, not all DR solutions are physically acceptable. Hence, an alternative and more accurate method of analysis is introduced that uses LDAR data to constrain the geometry of the charge solutions, thereby removing physically unacceptable retrievals. The charge solutions derived from this method are shown to compare well with independent satellite- and ground-based observations of lightning in several Florida storms.

Koshak, W. J.↗
NASA NTRS1984

Numerical and experimental determination of secondary separation on delta wings in subsonic flow

A quasi-three-dimensional boundary layer method for conical inviscid flows is presented. The model was developed to characterize the flow fields over slender delta wings, particularly the shed vortex sheet. A steady, incompressible, laminar boundary layer is assumed and a solution is obtained with the Smith (1966) finite difference code. Predictions are compared with oil flow patterns and surface pressure measurements for 74 and 80 deg delta wings at 0-20 deg angles of attack. The model is capable of accurately predicting the secondary separation lines. Inviscid velocities derived from panel methods lead, however, to inaccurate pressure distributions.

Dejarnette, F. R.↗
NASA NTRS1952

An Approximate Method of Calculating the Deformations of Wings Having Swept, M or W, A, and Swept-Tip Plan Forms

An approximate method of calculating the deformations of wings of uniform thickness having swept, M or W, Delta, and swept-tip plan forms is presented. The method employs an adjustment to the elementary beam theory to account for the effect of the triangular root portion of a swept wing on the deformation of the outboard section of the wing. To demonstrate the general applicability of the method, the modified elementary theory is applied to the more complex M or W, Delta, and swept-tip plan forms as well as to swept plan forms. For the purpose of calculating angles of attack, it is shown that the unmodified elementary beam theory applied to that part of the wing outboard of the root triangle produces satisfactory results. However, for calculating deflections it is necessary to include the effects of the root-triangle deformation.

Zender, George W.↗
NASA NTRS2007

Lightning Charge Retrievals: Dimensional Reduction, LDAR Constraints, and a First Comparison with LIS Satellite Data

A "dimensional reduction" ("DR") method is introduced for analyzing lightning field changes ((Delta)Es) whereby the number of unknowns in a discrete two-charge model is reduced from the standard eight (x, y, z, Q, x', y', z', Q') to just four (x, y, z, Q). The four unknowns (x, y, z, Q) are found by performing a numerical minimization of a chi-square function. At each step of the minimization, an overdetermined fixed matrix (OFM) method is used to immediately retrieve the best "residual source" (x', y', z', Q'), given the values of (x, y, z, Q). In this way, all eight parameters Ix. y, z, Q, x', y', z', Q') are found, yet a numerical search of only four parameters (x, y, z, Q) is required. The DR method has been used to analyze lightning-caused (Delta)Es derived from multiple ground-based electric field measurements at the NASA Kennedy Space Center (KSC) and U.S. Air Force Eastern Range (ER). The accuracy of the DR method has been assessed by comparing retrievals with data provided by the lightning detection and ranging (LDAR) system at the KSC-ER. and from least squares error estimation theory, and the method is shown to be a useful "stand alone" charge retrieval tool. Since more than one charge distribution describes a finite set of (Delta)Es (i.e., solutions are nonunique), and since there can be appreciable differences in the physical characteristics of these solutions, not all DR solutions are physically acceptable. Hence. an alternative and more accurate method of analysis is introduced that uses LDAR data to constrain the geometry of the charge solutions. thereby removing physically unacceptable retrievals. The charge solutions derived from this method are shown to compare well with independent satellite- and ground-based observations of lightning m several Florida storms.

Koshak, W. J.↗
NASA NTRS1978

Three dimensional steady and unsteady asymmetric flow past wings of arbitrary planforms

The nonlinear discrete vortex method is extended to treat the problem of asymmetric flows past a wing with leading edge separation, including steady and unsteady flows. The problem is formulated in terms of a body fixed frame of reference and the nonlinear-discrete vortex method is modified accordingly. Although the method is general, only examples of flows past delta wings are presented due to the availability of experimental data as well as approximate theories. Comparison of results with experimental results for a delta wing undergoing a steady rolling motion at zero angle of attack demonstrate the superiority of the present method over existing approximate theories in obtaining highly accurate loads. Numerical results for yawed wings at large angles of attack are also presented. In all cases, total load coefficients, pressure distributions, and shapes of the free vortex sheets are shown.

Kandil, O. A.↗
NASA NTRS1982

Lateral aerodynamics of delta wings with leading edge separation

An unsteady vortex lattice method is presented for the calculation of the aerodynamic forces acting on lifting surfaces undergoing complex three dimensional motion. For the present case the nonsymmetric motion of a slender delta wing was considered and the resulting lateral characteristics were calculated. The flow separation line was specified along the wing leading edge and the emanating vortex sheet shape and rollup was then calculated. Numerical results are presented for the combined high angle of attack and side slip condition and for the wing constant roll and coning motions.

Katz, J.↗
NASA NTRS1991

A method for computing instantaneous downtrack error from TDRS Doppler residuals

A simple method has been developed which calculates the instantaneous downtrack error in an orbiting vehicle's state vector from TDRS (Tracking and Data Relay Satellite) Doppler observation residuals. The downtrack error is expressed as a delta-time correction to the timetag of the vehicle's state vector. The method requires only a few easily obtained parameters and is easy to implement. This paper details the derivation of computing a delta-time correction from TDRS Doppler observation residuals and evaluates the method's assumptions and limitations. The results presented show that typically the method computes delta-time corrections that are less than five percent off from the true timetag error for Doppler observation residuals within twenty minutes of closest approach to the TDRS.

Haas, Franklin M., Jr.↗
NASA NTRS1980

Strake/delta wing interactions at high angles of attack

The method of vortex discretization is used to analyze the interaction of the vorticity generated by a strake, with the flow over a delta wing. The validity of the approach is first established by making comparisons with established methods for dealing with delta wings, after which compound delta planforms are discussed. An understanding of the favorable interference effects normally associated with this type of configuration is obtained and results are presented to quantify the expected lift increments resulting from the strake interaction.

Bloor, M. I. G.↗
NASA NTRS1989

Calculating climate attractor dimension from delta O-18 records by the Grassberger-Procaccia algorithm

The Grassberger-Procaccia method of calculating dimension from a time series is applied to 14 late Pleistocene delta O-18 records. A step-by-step sequence leading from data to the Grassberger-Procaccia dimension is outlined, and the problems encountered when dealing with observed (as opposed to theoretical) data are discussed; for the climatic proxy data these problems include situations where the time series is not very long, is noisy and/or smoothed, and is not sampled at a constant time interval. The delta O-18 records to be used are described, and the results are presented and compared with previously published dimension calculations. New dimension interpretations are assessed, and an example using a synthetic time series that illustrates the possible error due to inconsistencies in the time scale is analyzed.

Maasch, Kirk A.↗
NASA NTRS1973

The solution of transcendental equations

Some of the existing methods to globally approximate the roots of transcendental equations namely, Graeffe's method, are studied. Summation of the reciprocated roots, Whittaker-Bernoulli method, and the extension of Bernoulli's method via Koenig's theorem are presented. The Aitken's delta squared process is used to accelerate the convergence. Finally, the suitability of these methods is discussed in various cases.

Agrawal, K. M.↗
DOE OSTI2022

Analysis of leading edge protection application on wind turbine performance through energy and power decomposition approaches

Abstract Wind power production is driven by, and varies with, the stochastic yet uncontrollable wind and environmental inputs. To compare a wind turbine's performance, a direct comparison on power outputs is always confounded by the stochastic effect of weather inputs. It is therefore crucial to control for the weather and environmental influence. Toward that objective, our study proposes an energy decomposition approach. We start with comparing the change in the total energy production and refer to the change in total energy as delta energy. On this delta energy, we apply our decomposition method, which is to separate the portion of energy change due to weather effects from that due to the turbine itself. We derive a set of mathematical relationships allowing us to perform this decomposition and examine the credibility and robustness of the proposed decomposition approach through extensive cross‐validation and case studies. We then apply the decomposition approach to Supervisory Control and Data Acquisition data associated with several wind turbines to which leading‐edge protection was carried out. Our study shows that the leading‐edge protection applied on blades may cause a small decline to the power production efficiency in the short term, although we expect the leading‐edge protection to benefit the blade's reliability in the long term.

17 WIND ENERGY↗
DOE OSTI2025

Two-dimensional ring polymer molecular dynamics determination of the MnO + + H 2 /D 2 reaction rates on a Δ-machine learned potential energy surface

In this work, we investigate the impact of nuclear quantum effects in the kinetics of the MnO + + H 2 reaction, a prototypical system for gas-phase H 2 activation by transition metal oxide ions. The DFT based potential energy surfaces (PESs) for the lowest-lying quintet and septet spin states reported in our previous work are improved by 2953 newly calculated CCSD(T)/AVDZ points using a delta-machine learning (Δ-ML) method. To examine nuclear quantum effects, the rate coefficients are computed using ring-polymer molecular dynamics (RPMD). Due to the mechanistic complexity of the reaction, two reaction coordinates are necessary to map out the free-energy surface and an extended RPMD rate theory is developed. The calculated RPMD rate coefficients on the new PES are in better agreement with experimental data. The calculated kinetic isotope effects (KIEs) range from 1.6 to 1.8, also in good agreement with the experimental values. Additionally, the converged RPMD rate coefficients are 2.3 to 3.1 times higher than their classical counterparts across the studied temperature range, suggesting the presence of moderate nuclear quantum effects in this reaction.

Liu, Yang [University of New Mexico, Albuquerque, ↗
NASA NTRS1977

Three dimensional steady and unsteady asymmetric flow past wings of arbitrary planforms

The nonlinear discrete vortex method was extended to treat the problem of asymmetric flows past a wing with leading-edge separation, including steady and unsteady flows. The problem was formulated in terms of a body-fixed frame of reference, and the nonlinear discrete vortex method was modified accordingly. Only examples of flows past delta wings are presented. Comparison of these results with experimental results for a delta wing undergoing a steady rolling motion at zero angle of attack demonstrates the superiority of the present method in obtaining highly accurate loads. Numerical results for yawed wings at large angles of attack are also presented. In all cases, total load coefficients, pressure distributions and shapes of the free-vortex sheets are shown.

Kandil, O. A.↗