Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Convergence analysis”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
NASA NTRS2022

Diurnal Waves Forced By Horizontal Convergence of Near-Surface Winds on Mars

Boundary-layer winds near steeply sloped topography excite a distinct type of atmospheric wave. Basic properties of the waves were determined through analysis of 7 Mars years of temperature profiles from the Mars Climate Sounder on Mars Reconnaissance Orbiter. A more complete understanding of the waves was derived from a simulation with the NASA Ames Mars General Circulation Model. This type of wave appears in the tropics in the vicinity of conspicuous surface features, such as large volcanoes and the rim of Isidis Planitia. The amplitude is typically 5–10 K, the vertical wavelength is about 40 km, the zonal wavelength is about 1400 km, and the zonal phase speed relative to the surface is about 25 m s−1. The wave forcing comes from horizontal convergence of the near-surface winds, which generates a daily surge in the vertical winds. These convergence zones were not previously recognized as an important source of atmospheric waves on Mars. Strong forcing occurs only within a limited range of local time, producing wave packets (diurnal pulses) rather than steady oscillations. Waves are present throughout the year and their properties vary with season. Near the solstices, the wave amplitude is largest in the tropics of the summer hemisphere, where the convergence zones are stronger than in the winter hemisphere. The diurnal-mean zonal winds, which vary with latitude and season, control the direction of propagation of the predominant waves through filtering by critical levels.

Mars↗
DOE OSTI2020

Spectral Mesh-Free Quadrature for Planar Regions Bounded by Rational Parametric Curves

This article presents spectral, mesh-free, Green’s theorem-based numerical quadrature schemes for integrating functions over planar regions bounded by rational parametric curves. Our algorithm proceeds in two steps: (1) We first find intermediate quadrature rules for line integrals along the region’s boundary curves corresponding to Green’s theorem. (2) We then use a high-order quadrature rule to compute the numerical antiderivative of the integrand along a coordinate axis, which is used to evaluate the Green’s theorem line integral. We present two methods to compute the intermediate quadrature rule. The first is spectrally accurate (it converges faster than any algebraic order with respect to number of quadrature points) and is relatively easy to implement, but has no guarantee of polynomial exactness. The second guarantees exactness for polynomial integrands up to a pre-specified degree with an a priori-known number of quadrature points and retains the convergence properties of the first, but is slightly more complicated. The quadrature schemes have applications to computation of geometric moments, immersogeometric analysis, conservative field transfer between high-order meshes, and initialization of multi-material simulations with rational geometry. We compare the quadrature schemes produced using our method to other methods in the literature and show that they are much more efficient both in terms of number of quadrature points and computational time. We provide an open-source implementation of the algorithm in MATLAB.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

Parametric Optimization of Erosive Wear Response of TiAlN-Coated Aluminium Alloy Using Taguchi Method

In this research work, high-velocity oxy-fuel thermal spraying is used to develop TiAlN coatings on AA1050 and AA5083 aluminium alloy substrates. Slurry wear behavior of coatings is evaluated using jet-type test rig. Surface studies were carried out to investigate the potential erosion mechanism. The influence of key parameters identified using the Taguchi analysis is also corroborated with a wear model. The potential mechanism identified by wear model is in excellent convergence with that observed experimentally. Mixed ploughing and cutting, formation of platelets, abrasion grooves and cracks are witnessed as primary mechanisms causing loss of coating. Results indicate that impact velocity is recognized as a highly contributing parameter with contribution ratio of 79.24 and 83.75% followed by impingement angle with contribution ratio of 15.81 and 11.58% for AA1050 and AA5083, respectively. The important sequences of the control parameters are recognized to be impact velocity > impingement angle > erodent feed rate > erodent size for AA1050 and impact velocity > impingement angle > erodent size > erodent feed rate for AA5083. The best possible combination of control parameters for AA1050 and AA5083 to achieve minimal wear rate with respect to impact velocity, erodent size, impingement angle and erodent feed rate is 30 m/s, 225 µm, 30°, 160 g/min and 25 m/s, 150 µm, 30°, 160 g/min, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Urban heat islands can influence the wind energy resource during heatwaves

Urban wind energy is critical for sustainable electricity generation in cities. However, little research has explored how the urban heat island (UHI) effect influences wind energy, particularly in heatwaves when energy demand surges. In this study, we examine wind energy distribution in the Boston–Providence metropolitan area during heatwaves, using Weather Research and Forecasting (WRF) model integrated with Building Energy Parameterization/Building Energy Model (BEP/BEM). Two scenarios, a realistic case and a hypothetical case without urban warmth, were compared to isolate UHI impacts. Results reveal that UHI induces a "wind energy loss zone" in this urban area, reducing wind power density (WPD) by 20–30 W/m 2 at 50–100 m, while suburban/rural areas exhibit a "wind energy gain zone," with WPD increases up to 40 W/m 2 at 150–200 m. These losses diminish with distance from urban centers and become negligible beyond main urban and suburban sprawl. Heatwave expands the urban "loss zone", while amplifying wind energy gains in suburban/rural areas, driven by stronger thermal gradients and weakened background winds that intensify air convergence in urban and urban-rural circulations, thereby exacerbating urban wind energy losses by 15–20 %. An analysis of 235 wind farms using turbine power curves reveals that built areas dependent on stand-alone or off-grid turbines face significant energy deficits during a heatwave. Wind energy drops by up to 25 %, while cooling-related building energy demand rises 30–40 % during a heatwave. These findings underscore the need for strategic urban wind energy planning to ensure reliable power during extreme heat.

Energy - Wind↗
DOE OSTI2018

Progress on Complex Langevin simulations of a finite density matrix model for QCD

We study the Stephanov model, which is an RMT model for QCD at finite density, using the Complex Langevin algorithm. Naive implementation of the algorithm shows convergence towards the phase quenched or quenched theory rather than to intended theory with dynamical quarks. A detailed analysis of this issue and a potential resolution of the failure of this algorithm are discussed. We study the effect of gauge cooling on the Dirac eigenvalue distribution and time evolution of the norm for various cooling norms, which were specifically designed to remove the pathologies of the complex Langevin evolution. The cooling is further supplemented with a shifted representation for the random matrices. Unfortunately, none of these modifications generate a substantial improvement on the complex Langevin evolution and the final results still do not agree with the analytical predictions.

Bloch, Jacques↗
DOE OSTI2016

Benchmark study of the two-dimensional Hubbard model with auxiliary-field quantum Monte Carlo method

Ground-state properties of the Hubbard model on a two-dimensional square lattice are studied by the auxiliary-field quantum Monte Carlo method. Accurate results for energy, double occupancy, effective hopping, magnetization, and momentum distribution are calculated for interaction strengths of U/t from 2 to 8, for a range of densities including half-filling and n = 0.3,0.5,0.6, 0.75, and 0.875. At half-filling, the results are numerically exact. Away from half-filling, the constrained path Monte Carlo method is employed to control the sign problem. Our results are obtained with several advances in the computational algorithm, which are described in this paper in detail. We discuss the advantages of generalized Hartree-Fock trial wave functions and its connection to pairing wave functions, as well as the interplay with different forms of Hubbard-Stratonovich decompositions. We study the use of different twist angle sets when applying the twist averaged boundary conditions. We propose the use of quasirandom sequences, which improves the convergence to the thermodynamic limit over pseudorandom and other sequences. With it and a careful finite size scaling analysis, we are able to obtain accurate values of ground-state properties in the thermodynamic limit. Detailed results for finite-sized systems up to 16 × 16 are also provided for benchmark purposes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Efficient Probabilistic Visualization of Local Divergence of 2D Vector Fields with Independent Gaussian Uncertainty

This work focuses on visualizing uncertainty of local divergence of two-dimensional vector fields. Divergence is one of the fundamental attributes of fluid flows, as it can help domain scientists analyze potential positions of sources (positive divergence) and sinks (negative divergence) in the flow. However, uncertainty inherent in vector field data can lead to erroneous divergence computations, adversely impacting downstream analysis. While Monte Carlo (MC) sampling is a classical approach for estimating divergence uncertainty, it suffers from slow convergence and poor scalability with increasing data size and sample counts. Thus, we present a two-fold contribution that tackles the challenges of slow convergence and limited scalability of the MC approach. (1) We derive a closed-form approach for highly efficient and accurate uncertainty visualization of local divergence, assuming independently Gaussian-distributed vector uncertainties. (2) We further integrate our approach into Viskores, a platform-portable parallel library, to accelerate uncertainty visualization. In our results, we demonstrate significantly enhanced efficiency and accuracy of our serial analytical (speed-up up to 1946×) and parallel Viskores (speed-up up to 19698×) algorithms over the classical serial MC approach. We also demonstrate qualitative improvements of our probabilistic divergence visualizations over traditional mean-field visualization, which disregards uncertainty. We validate the accuracy and efficiency of our methods on wind forecast and ocean simulation datasets.

Ouermi, Timbwaoga [University of Utah]↗
DOE OSTI2013

Focused Evolution of HIV-1 Neutralizing Antibodies Revealed by Structures and Deep Sequencing

Antibody VRC01 is a human immunoglobulin that neutralizes about 90% of HIV-1 isolates. To understand how such broadly neutralizing antibodies develop, we used x-ray crystallography and 454 pyrosequencing to characterize additional VRC01-like antibodies from HIV-1-infected individuals. Crystal structures revealed a convergent mode of binding for diverse antibodies to the same CD4-binding-site epitope. A functional genomics analysis of expressed heavy and light chains revealed common pathways of antibody-heavy chain maturation, confined to the IGHV1-2*02 lineage, involving dozens of somatic changes, and capable of pairing with different light chains. Broadly neutralizing HIV-1 immunity associated with VRC01-like antibodies thus involves the evolution of antibodies to a highly affinity-matured state required to recognize an invariant viral structure, with lineages defined from thousands of sequences providing a genetic roadmap of their development.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Method for Calculating Delayed Gamma-Ray Response in the ACRR Central Cavity and FREC-II Cavity Using MCNP

This document presents the process for a new method developed for the characterization of the delayed gamma-ray radiation fields in pulse reactors like the Annular Core Research Reactor (ACRR) and the Fueled Ring External Cavity (FREC-II). The environments used to test this method in the ACRR were FF, LB44, PLG and CdPoly, and the environments used in the FREC-II were FF with rods-down, FF with rods-up, CdPoly with rods-down and CdPoly with rods-up. All environment configurations used the same fission product gamma-ray source energy spectrum. This method required the fission sites located in the MCNP KCODE source tapes. A FORTRAN script was written to translate and extract the coordinates for the fission sites. The 10K fission sites were then input it into an MCNP SOURCE mode script. Using a MATLAB script, a parametric analysis was done, and it helped determine that 10K fission sites are an appropriate number of coordinates to converge to the correct answer. The method gave excellent results and was tested in the ACRR, FREC-II and White Sands Missile Range (WSMR). This method can be applied to other pulse research reactors as well.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
NASA NTRS1972

Stability analysis of Riccati covariance equations of Kalman filter.

The present paper takes the basic mathematical approach to analyze the stability of Riccati equations. First, a simple stability criterion like that of the linear constant coefficient system is sought for the nonlinear constant Riccati Equation. Then, a complete analysis on the limiting covariance P follows. The analysis is focussed on the main theorem. Finally, the computational aspects of the Riccati equations are analyzed with examples. The application of this analysis is to provide a simple stability criterion for the Kalman filter computation to test and predict filter convergence and thus modify filter parameters accordingly.

Teng, L.↗
NASA NTRS1977

Absorption spectrum of Pb I between 1350 and 2041 A

The high resolution absorption spectrum of Pb I is reported between 1350 and 2041 A. Transitions are observed from the 6p2 (1/2,1/2)0, (3/2,1/2)1, and (3/2,1/2)2 levels to levels with J less than or equal to 2 associated with 6pns and 6pnd configurations. Energy levels have been determined with n(asterisk) values as high as 74. More than 500 spectral features and 370 odd parity energy levels are reported, a major part of which are new. These observations include five electric quadrupole transitions and 31 nuclear-spin-induced transitions from the Pb-207 isotope. Ionization limits of 59819.57 per cm and 73900.64 per cm have been determined for levels converging on the 6p 2P(1/2)O and 6p 2P(3/2)O levels of Pb II, respectively. An analysis of these data in terms of Lu-Fano graphical methods and multichannel quantum defect parametrization also is presented.

Brown, C. M.↗
NASA NTRS1986

Transonic airfoil analysis and design in nonuniform flow

A nonuniform transonic airfoil code is developed for applications in analysis, inverse design and direct optimization involving an airfoil immersed in propfan slipstream. Problems concerning the numerical stability, convergence, divergence and solution oscillations are discussed. The code is validated by comparing with some known results in incompressible flow. A parametric investigation indicates that the airfoil lift-drag ratio can be increased by decreasing the thickness ratio. A better performance can be achieved if the airfoil is located below the slipstream center. Airfoil characteristics designed by the inverse method and a direct optimization are compared. The airfoil designed with the method of direct optimization exhibits better characteristics and achieves a gain of 22 percent in lift-drag ratio with a reduction of 4 percent in thickness.

Chang, J. F.↗
NASA NTRS1988

Exact image theory for the slab problem

Exact image theory, recently introduced for the exact solution of problems involving homogeneous half spaces and microstrip-like geometries, is developed here for the problem of homogeneous slab of isotropic dielectric and/or magnetic material in free space. Expressions for image sources, creating the exact reflected and transmitted fields, are given and their numerical evaluation is demonstrated. Nonradiating modes, guided by the slab and responsible for the loss of convergence of the image functions, are considered and extracted. The theory can be applied, for example, in an analysis of finite ground planes in microstrip antenna structures.

Lindell, I. V.↗
NASA NTRS1989

Numerical algorithms for computations of feedback laws arising in control of flexible systems

Several continuous models will be examined, which describe flexible structures with boundary or point control/observation. Issues related to the computation of feedback laws are examined (particularly stabilizing feedbacks) with sensors and actuators located either on the boundary or at specific point locations of the structure. One of the main difficulties is due to the great sensitivity of the system (hyperbolic systems with unbounded control actions), with respect to perturbations caused either by uncertainty of the model or by the errors introduced in implementing numerical algorithms. Thus, special care must be taken in the choice of the appropriate numerical schemes which eventually lead to implementable finite dimensional solutions. Finite dimensional algorithms are constructed on a basis of a priority analysis of the properties of the original, continuous (infinite diversional) systems with the following criteria in mind: (1) convergence and stability of the algorithms and (2) robustness (reasonable insensitivity with respect to the unknown parameters of the systems). Examples with mixed finite element methods and spectral methods are provided.

Lasiecka, Irena↗
NASA NTRS1995

Pseudo-time method for optimal shape design using the Euler equations

We exploit a novel idea for the optimization of flows governed by the Euler equations. The algorithm consists of marching on the design hypersurface while improving the distance to the state and costate hypersurfaces. We consider the problem of matching the pressure distribution to a desired one, subject to the euler equations, both for subsonic and supersonic flows. The rate of convergence to the minimum for the cases considered is 3 to 4 times slower than that of the analysis problem. Results are given for Ringleb flow and a shockless recompression case.

Iollo, Angelo↗
NASA NTRS2000

Parallel performance investigations of an unstructured mesh Navier-Stokes solver

A Reynolds-averaged Navier-Stokes solver based on unstructured mesh techniques for analysis of high-lift configurations is described. The method makes use of an agglomeration multigrid solver for convergence acceleration. Implicit line-smoothing is employed to relieve the stiffness associated with highly stretched meshes. A GMRES technique is also implemented to speed convergence at the expense of additional memory usage. The solver is cache efficient and fully vectorizable, and is parallelized using a two-level hybrid MPI-OpenMP implementation suitable for shared and/or distributed memory architectures, as well as clusters of shared memory machines. Convergence and scalability results are illustrated for various high-lift cases.

Mavriplis, Dimitri J.↗
NASA NTRS1997

Distributed-Memory Computing With the Langley Aerothermodynamic Upwind Relaxation Algorithm (LAURA)

The Langley Aerothermodynamic Upwind Relaxation Algorithm (LAURA), a Navier-Stokes solver, has been modified for use in a parallel, distributed-memory environment using the Message-Passing Interface (MPI) standard. A standard domain decomposition strategy is used in which the computational domain is divided into subdomains with each subdomain assigned to a processor. Performance is examined on dedicated parallel machines and a network of desktop workstations. The effect of domain decomposition and frequency of boundary updates on performance and convergence is also examined for several realistic configurations and conditions typical of large-scale computational fluid dynamic analysis.

Riley, Christopher J.↗
NASA NTRS2014

Using Ensemble Short-Term Initialized Coupled NASA GEOS5 Climate Model Integrations to Study Convective Bias Growth

The representation of convective processes, particularly deep convection in the tropics, remains a persistent problem in climate models. In fact structural biases in the distribution of tropical rainfall in the CMIP5 models is hardly different than that of the CMIP3 versions. Given that regional climate change at higher latitudes is sensitive to the configuration of tropical forcing, this persistent bias is a major issue for the credibility of climate change projections. In this study we use model output from integrations of the NASA Global Earth Observing System Five (GEOS5) climate modeling system to study the evolution of biases in the location and intensity of convective processes. We take advantage of a series of hindcast experiments done in support of the US North American Multi-Model Ensemble (NMME) initiative. For these experiments a nine-month forecast using a coupled model configuration is made approximately every five days over the past 30 years. Each forecast is started with an updated analysis of the ocean, atmosphere and land states. For a given calendar month we have approximately 180 forecasts with daily means of various quantities. These forecasts can be averaged to essentially remove "weather scales" and highlight systematic errors as they evolve. Our primary question is to ask how the spatial structure of daily mean precipitation over the tropics evolves from the initial state and what physical processes are involved. Errors in parameterized convection, various water and energy fluxes and the divergent circulation are found to set up on fast time scales (order five days) compared to errors in the ocean, although SST changes can be non-negligible over that time. For the month of June the difference between forecast day five versus day zero precipitation looks quite similar to the difference between the June precipitation climatology and that from the Global Precipitation Climatology Project (GPCP). We focus much of our analysis on the influence of SST gradients, associated PBL baroclinicity enabled by turbulent mixing, the ensuing PBL moisture convergence, and how changes in these processes relate to convective precipitation bias growth over this short period.

Cohen, Charlie↗