Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “model diagnostics”

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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Ultrafast Laser Diagnostics for Energetic-Material Ignition Mechanisms: Tools for Physics-Based Model Development.

We present the results of an LDRD project to develop diagnostics to perform fundamental measurements of material properties during shock compression of condensed phase materials at micron spatial scales and picosecond time scales. The report is structured into three main chapters, which each focus on a different diagnostic devel opment effort. Direct picosecond laser drive is used to introduce shock waves into thin films of energetic and inert materials. The resulting laser - driven shock properties are probed via Ultrafast Time Domain Interferometry (UTDI), which can additionally be used to generate shock Hugoniot data in tabletop experiments. Stimulated Raman scattering (SRS) is developed as a temperature diagnostic. A transient absorption spectroscopy setup has been developed to probe shock - induced changes during shock compressio n. UTDI results are presented under dynamic, direct - laser - drive conditions and shock Hugoniots are estimated for inert polystyrene samples and for the explosive hexanitroazobenzene, with results from both Sandia and Lawrence Livermore presented here. SRS a nd transient absorption diagnostics are demonstrated on static thin - film samples, and paths forward to dynamic experiments are presented.

Kearney, Sean Patrick↗
DOE OSTI2025

flat10MIP: an emissions-driven experiment to diagnose the climate response to positive, zero and negative CO2 emissions

Abstract. The proportionality between global mean temperature and cumulative emissions of CO2 predicted in Earth system models (ESMs) is the foundation of carbon budgeting frameworks. Deviations from this behavior could impact estimates of required net-zero timings and negative emissions requirements to meet the Paris Agreement climate targets. However, existing ESM diagnostic experiments do not allow for direct estimation of these deviations as a function of defined emissions pathways. Here, we perform a set of climate model diagnostic experiments for the assessment of transient climate response to cumulative CO2 emissions (TCRE), the Zero Emissions Commitment (ZEC), and climate reversibility metrics in an emissions-driven framework. The emissions-driven experiments provide consistent independent variables simplifying simulation, analysis and interpretation, with emissions rates more comparable to recent levels than existing protocols using model-specific compatible emissions from the CMIP DECK 1pctCO2 experiment, where emissions rates tend to increase during the experiment, such that at the time of CO2 doubling in year 70, emissions are much greater than present-day values. A base experiment, “esm-flat10”, has constant emissions of CO2 of 10 GtC per year (near-present-day values), and initial results show that the TCRE estimated in this experiment is about 0.1 K less than that obtained using 1pctCO2. A subset of ESMs exhibit land carbon sinks that saturate during this experiment. A branch experiment, esm-flat10-zec, illustrates that both positive and negative ZEC effects are less pronounced under esm-flat10 than under 1pctCO2 – the magnitude of ZEC50 in ESMs is, on average, reduced by 30 % compared with 1pctCO2 branch experiments. A final experiment, esm-flat10-cdr, assesses climate reversibility under negative emissions, where we find that peak warming may occur before or after net zero and that the asymmetry in temperature at a given level of cumulative emissions between the positive and negative emissions phases is well described by ZEC in most models. Further, we find that existing probabilistic simple climate model (SCM) ensembles tend to overestimate temperature reversibility compared with ESMs, highlighting the need for additional constraints. We propose a set of climate diagnostic indicators to quantify various aspects of climate reversibility. These experiments were suggested as potential candidates in CMIP7 and have since been adopted as “fast track” simulations.

Sanderson, Benjamin M↗
DOE OSTI2017

Multiscale Methods for Accurate, Efficient, and Scale-Aware Models of the Earth System

The major goal of this project was to contribute improvements to the infrastructure of an Earth System Model in order to support research in the Multiscale Methods for Accurate, Efficient, and Scale-Aware models of the Earth System project. In support of this, the NCAR team accomplished two main tasks: improving input/output performance of the model and improving atmospheric model simulation quality. Improvement of the performance and scalability of data input and diagnostic output within the model required a new infrastructure which can efficiently handle the unstructured grids common in multiscale simulations. This allows for a more computationally efficient model, enabling more years of Earth System simulation. The quality of the model simulations was improved by reducing grid-point noise in the spectral element version of the Community Atmosphere Model (CAM-SE). This was achieved by running the physics of the model using grid-cell data on a finite-volume grid.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1990

A wave dynamical interpretation of Saturn's polar hexagon

The hexagonal, pole-centered cloud feature in Saturn's northern atmosphere, as revealed in Voyager close-encounter imaging mosaics, may be interpreted as a stationary Rossby wave. The wave is embedded within a sharply peaked eastward jet (of 100 meters per second) and appears to be perturbed by at least one anticyclonic oval vortex immediately to the south. The effectively exact observational determination of the horizontal wave number and phase speed, applied to a simple model dispersion relation, suggests that the wave is vertically trapped and provides a diagnostic template for further modeling of the deep atmospheric stratification.

Allison, M.↗
DOE OSTI2017

Application of quantitative methods for reliability testing of a nuclear power plant digital rod position indication diagnostic system - 391

Obsolescence, aging, reliability, and performance issues are driving nuclear facilities to replace conventional analog Instrumentation and Control (I and C) systems with digital technologies. In addition, the designs of the next generation of nuclear reactors, including Small Modular Reactors (SMRs), will incorporate digital I and C for most, if not all, of their safety and non-safety related functions. As part of an on-going research and development (R and D) effort under the auspices of the U.S. Department of Energy (DOE), Analysis and Measurement Services Corporation (AMS) is developing a platform to provide automated testing of digital I and C systems and create a standard method of evaluation for reliability assessments. This hands-on R and D effort has produced a Software Reliability Tester (SRT), which is a set of software and hardware tools designed to automate the testing of digital I and C systems to measure and quantify how well the systems perform under normal operating conditions and in the presence of faults. Furthermore, the SRT provides the foundation for a practical tool to automate verification and validation (V and V) activities and reduce the amount of testing time of digital I and C systems. When combined with its capabilities of integrating both reliability and fault tolerance quantification, the SRT can be used to ensure that digital I and C implementations are both safe and cost-effective for the nuclear industry. This paper describes the application of the SRT to perform V and V of a new Digital Rod Position Indication (DRPI) diagnostic system. The DRPI diagnostic system is a digital system that monitors the rod address and rod position data bus voltages of typical DRPI systems in nuclear power plants to detect and diagnose faults. For this application, the SRT was configured to exercise the inputs of the DRPI diagnostic system, and test cases were generated for common system faults such as address and data bit errors, bus voltage, and timing problems. These test cases were applied by the SRT hardware as voltage inputs to the DRPI diagnostic system and the outputs were compared to expected values generated by a model of the DRPI diagnostic system. Included in the paper is a description of the overall design of the SRT including the hardware and software architectures. Methodologies for automating test cases are also described. V and V using the SRT demonstrates the benefits of automated testing and qualification to provide a quantitative assessment of reliability and cost effective implementation of digital I and C in existing and next generation nuclear power plants. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2018

Modeling of a Laser-Induced Rydberg Spectroscopy diagnostic for Direct Measurement of the Local Electric Field in the Edge Region of NSTX/NSTX-U

We discuss a novel diagnostic allowing direct measurements of the local electric field in the edge region in NSTX/NSTX-U. This laser based diagnostic's principle consists of depleting the naturally populated $n=3$ level to a Rydberg state --sensitive to electric fields-- that will result in a suppression of part of the $D_{\alpha}$ emission. We refer to this approach as Laser-Induced Rydberg Spectroscopy (LIRyS). It is shown that the local electric field can be measured through the Stark induced resonances observed as dips in the $D_\alpha$ emission. Using forward-modeling of simulated absorption spectra, we show precisions reaching \SI{\pm 2}{\kilo\volt\per\meter} in regions with a local electric field of \SI{15}{\kilo\volt\per\meter}.

Electric field↗
NASA NTRS1997

The attenuation of gamma-ray emission in strongly-magnetized pulsars

Gamma rays from pulsars can be efficiently attenuated in their magnetospheres via the mechanism of single photon pair production and the exotic quantum electrodynamics (QED) process of photon splitting. The modeling of strongly magnetized gamma ray pulsars focusing on the escape or attenuation of photons emitted near the pole at the neutron star surface in dipole fields in a Schwarzschild metric is considered. It was found that pair production and splitting totally inhibit emission above a value of between 10 and 30 MeV in PSR 1509-58 whose surface field is inferred as being high. The principle predictions of the attenuation analysis are reviewed and the observational diagnostic capabilities of the model are considered. The diagnostics include the energy of the gamma ray turnover and the spectral polarization, which constrain the estimated polar cap size and field strength and can determine the relative strength of splitting and pair creation.

Baring, Matthew G.↗
DOE OSTI2019

Cosmological aspects of a hyperbolic solution in f(R,T) gravity

This article deals with a cosmological scenario in f(R,T) gravity for a flat FLRW model of the universe. We consider the f(R,T) function as f(R)+f(T) which starts with a quadratic correction of the geometric term f(R) having structure f(R)=R+αR{sup 2}, and a linear matter term f(T)=2λT. To achieve the solution of the gravitational field equations in the f(R,T) formalism, we take the form of a geometrical parameter, i.e. scale factor a(t)=sinh{sup (1/n)}(βt) (Chawla et al., 2013), where β and n are model parameters. An eternal acceleration can be predicted by the model for 0<n<1, while the cosmic transition from the early decelerated phase to the present accelerated epoch can be anticipated for n≥1. The obtained model facilitates the formation of structure in the Universe according to the Jeans instability condition as our model transits from radiation dominated era to matter dominated era. We study the varying role of the equation of state parameter ω. We analyze our model by studying the behavior of the scalar field and discuss the energy conditions on our achieved solution. We examine the validity of our model via Jerk parameter, Om diagnostic, Velocity of sound and Statefinder diagnostic tools. We investigate the constraints on the model parameter n and H{sub 0} (Hubble constant) using some observational datasets: SNeIa dataset, H(z) (Hubble parameter) dataset, BAO (Baryon Acoustic Oscillation data) and their combinations as joint observational datasets H(z) + SNeIa and H(z) + SNeIa + BAO. It is testified that the present study is well consistent with these observations. We also perform some cosmological tests and a detailed discussion of the model.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2017

Review of the Global Models Used Within Phase 1 of the Chemistry-Climate Model Initiative (CCMI)

We present an overview of state-of-the-art chemistry-climate and chemistry transport models that are used within phase 1 of the Chemistry-Climate Model Initiative (CCMI-1). The CCMI aims to conduct a detailed evaluation of participating models using process-oriented diagnostics derived from observations in order to gain confidence in the models' projections of the stratospheric ozone layer, tropospheric composition, air quality, where applicable global climate change, and the interactions between them. Interpretation of these diagnostics requires detailed knowledge of the radiative, chemical, dynamical, and physical processes incorporated in the models. Also an understanding of the degree to which CCMI-1 recommendations for simulations have been followed is necessary to understand model responses to anthropogenic and natural forcing and also to explain inter-model differences. This becomes even more important given the ongoing development and the ever-growing complexity of these models. This paper also provides an overview of the available CCMI-1 simulations with the aim of informing CCMI data users.

CCMI↗
NASA NTRS1993

A multiple-mode three-dimensional model of VLF propagation in the earth-ionosphere waveguide in the presence of localized D region disturbances

Transient localized D region disturbances, such as those associated with lightning discharges, affect the characteristics of VLF waves propagating in the Earth-ionosphere waveguide. In particular, both phase and amplitude changes in the subionospheric signal can be observed at receiving sites as a result of the wave scattering that takes place in the disturbed region. In the present paper we present a multiple-mode three-dimensional model of VLF propagation in the Earth-ionosphere waveguide in the presence of localized D region disturbances. The model takes into account great circle (GC) propagation paths with realistic ground and ionospheric conductivity changes that result in mode conversion along the path. It is assumed that conductivity changes transverse to the GC paths are negligible except in the vicinity of the D region disturbance and that mode coupling is negligible within the disturbed region. This new model is applied to experimental observations and is found to be in general agreement. The diagnostics potential of the model for characterizing energetic particle precipitation events is discussed.

Poulsen, William L.↗
DOE OSTI2018

Evapotranspiration simulations in ISIMIP2a—Evaluation of spatio-temporal characteristics with a comprehensive ensemble of independent datasets

Actual land evapotranspiration (ET) is a key component of the global hydrological cycle and an essential variable determining the evolution of hydrological extreme events under different climate change scenarios. However, recently available ET products show persistent uncertainties that are impeding a precise attribution of human-induced climate change. Here, we aim at comparing a range of independent global monthly land ET estimates with historical model simulations from the global water, agriculture, and biomes sectors participating in the second phase of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP2a). Among the independent estimates, we use the EartH2Observe Tier-1 dataset (E2O), two commonly used reanalyses, a pre-compiled ensemble product (LandFlux-EVAL), and an updated collection of recently published datasets that algorithmically derive ET from observations or observations-based estimates (diagnostic datasets). A cluster analysis is applied in order to identify spatiotemporal differences among all datasets and to thus identify factors that dominate overall uncertainties. The clustering is controlled by several factors including the model choice, the meteorological forcing used to drive the assessed models, the data category (models participating in the different sectors of ISIMIP2a, E2O models, diagnostic estimates, reanalysis-based estimates or composite products), the ET scheme, and the number of soil layers in the models. By using these factors to explain spatial and spatio-temporal variabilities in ET, we and that the model choice mostly dominates (24%{40% of variance explained), except for spatio-temporal patterns of total ET, where the forcing explains the largest fraction of the variance (29%). The most dominant clusters of datasets are further compared with individual diagnostic and reanalysis-based estimates to assess their representation of selected heat waves and droughts in the Great Plains, Central Europe and Western Russia. Although most of the ET estimates capture these extreme events, the generally large spread among the entire ensemble indicates substantial uncertainties.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Doppler Backscattering Data Analysis and Integrated Modeling with OMFIT

One Modeling Framework for Integrated Tasks (OMFIT) is a widely used software tool in the magnetic fusion research community. OMFIT provides magnetic fusion energy researchers with a framework for the development of special-purpose physics modules. This paper describes an OMFIT physics module pertaining to the Doppler Backscattering (DBS) fusion plasma diagnostic. DBS measures density fluctuations and flow velocity through plasma scattering of electromagnetic waves. The OMFIT DBS module was developed to analyze experimental DBS data and facilitate modeling of DBS systems installed on multiple tokamak devices. The OMFIT DBS module is designed to support several analysis workflows: detailed analysis of experimental data, experimental planning, and theory-based synthetic diagnostic modeling. The DBS module uses integrated modeling by leveraging other OMFIT physics modules to perform tasks related to DBS, e.g. ray/beam–tracing simulations, edge-localized mode–synchronized data analysis, magnetic equilibrium reconstruction, and fitting kinetic profile data. Furthermore, this paper describes several supported workflows and serves a reference for the OMFIT DBS module.

Doppler backscattering↗
DOE OSTI2014

High resolution transmission spectroscopy as a diagnostic for Jovian exoplanet atmospheres: constraints from theoretical models

We present high resolution transmission spectra of giant planet atmospheres from a coupled three-dimensional (3D) atmospheric dynamics and transmission spectrum model that includes Doppler shifts which arise from winds and planetary motion. We model Jovian planets covering more than two orders of magnitude in incident flux, corresponding to planets with 0.9-55 day orbital periods around solar-type stars. The results of our 3D dynamical models reveal certain aspects of high resolution transmission spectra that are not present in simple one-dimensional (1D) models. We find that the hottest planets experience strong substellar to anti-stellar (SSAS) winds, resulting in transmission spectra with net blueshifts of up to 3 km s{sup –1}, whereas less irradiated planets show almost no net Doppler shifts. We find only minor differences between transmission spectra for atmospheres with temperature inversions and those without. Compared to 1D models, peak line strengths are significantly reduced for the hottest atmospheres owing to Doppler broadening from a combination of rotation (which is faster for close-in planets under the assumption of tidal locking) and atmospheric winds. Finally, high resolution transmission spectra may be useful in studying the atmospheres of exoplanets with optically thick clouds since line cores for very strong transitions should remain optically thick to very high altitude. High resolution transmission spectra are an excellent observational test for the validity of 3D atmospheric dynamics models, because they provide a direct probe of wind structures and heat circulation. Ground-based exoplanet spectroscopy is currently on the verge of being able to verify some of our modeling predictions, most notably the dependence of SSAS winds on insolation. We caution that interpretation of high resolution transmission spectra based on 1D atmospheric models may be inadequate, as 3D atmospheric motions can produce a noticeable effect on the absorption signatures.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1987

Impulsive H-alpha diagnostics of electron-beam-heated solar flare model chromospheres

Time-dependent H-alpha profiles were computed for the dynamic model atmospheres of Fisher, Canfield, and McClymont (1985) simulating the effects of an intense impulsively initiated power-law beam of electrons incident on the chromosphere. The temporal response of H-alpha arises from three separate physical mechanisms, whose relative importance varies over the line profile. The fastest variations (typically less than 0.1 s for the explosive heating discussed here) arise from energy imbalance; these are apparent on chromospheric heating and cooling time scales and have their greatest amplitude at line center. Slower variations arise from ionization imbalance and are most apparent in the blue wing. The slowest variations arise from hydrodynamic effects and are related to the formation of a chromospheric condensation; these are most apparent in the red wing. These results provide a basis for the design and analysis of observations of H-alpha, in coordination with hard X-rays or microwaves, to test mechanisms of energy transport in solar flares.

Canfield, Richard C.↗
NASA NTRS1994

The formation of Hurricane Frederic of 1979

A high-resolution global model forecast of the formation of Hurricane Frederic of 1979 is analyzed by means of several diagnostic computations on the model's output history. The formation is addressed from an analysis of limited-area energetics where the growth of eddy kinetic energy is examined. The question on internal versus external forcing during the formative stage of the hurricane is explored by means of the Kuo-Eliassen framework for the radial-vertical circulation of the hurricane. The intensity of the predicted hurricane is diagnosed from a detailed angular momentum budget following the three-dimensional motion of parcels arriving at the maximum wind belt. Overall, the successful simulation of the hurricane has enabled us to make such a detailed diagnosis of the predicted hurricane at a high resolution. The principal findings of this study are that a north-south-oriented heating function maintained a zonal easterly flow that supplied energy barotropically during the growth of an African wave. The growth of eddy kinetic energy is somewhat monotonic and slow throughout the history of the computations. The initial development of the easterly wave appears to be related to the widespread weak convective heating that contributes to a covariance of heating and temperature and of temperature and vertical velocity. The hurricane development period is seen as one where both the barotropic and convective processes contribute to the growth of eddy kinetic energy.

Krishnamurti, T. N.↗
NASA NTRS2017

Modeling for Battery Prognostics

For any battery-powered vehicles (be it unmanned aerial vehicles, small passenger aircraft, or assets in exoplanetary operations) to operate at maximum efficiency and reliability, it is critical to monitor battery health as well performance and to predict end of discharge (EOD) and end of useful life (EOL). To fulfil these needs, it is important to capture the battery's inherent characteristics as well as operational knowledge in the form of models that can be used by monitoring, diagnostic, and prognostic algorithms. Several battery modeling methodologies have been developed in last few years as the understanding of underlying electrochemical mechanics has been advancing. The models can generally be classified as empirical models, electrochemical engineering models, multi-physics models, and molecular/atomist. Empirical models are based on fitting certain functions to past experimental data, without making use of any physicochemical principles. Electrical circuit equivalent models are an example of such empirical models. Electrochemical engineering models are typically continuum models that include electrochemical kinetics and transport phenomena. Each model has its advantages and disadvantages. The former type of model has the advantage of being computationally efficient, but has limited accuracy and robustness, due to the approximations used in developed model, and as a result of such approximations, cannot represent aging well. The latter type of model has the advantage of being very accurate, but is often computationally inefficient, having to solve complex sets of partial differential equations, and thus not suited well for online prognostic applications. In addition both multi-physics and atomist models are computationally expensive hence are even less suited to online application An electrochemistry-based model of Li-ion batteries has been developed, that captures crucial electrochemical processes, captures effects of aging, is computationally efficient, and is of suitable accuracy for reliable EOD prediction in a variety of operational profiles. The model can be considered an electrochemical engineering model, but unlike most such models found in the literature, certain approximations are done that allow to retain computational efficiency for online implementation of the model. Although the focus here is on Li-ion batteries, the model is quite general and can be applied to different chemistries through a change of model parameter values. Progress on model development, providing model validation results and EOD prediction results is being presented.

Prognostics↗
DOE OSTI2022

Evaluating Tropical Precipitation Relations in CMIP6 Models with ARM Data

Abstract A set of diagnostics based on simple, statistical relationships between precipitation and the thermodynamic environment in observations is implemented to assess phase 6 of the Coupled Model Intercomparison Project (CMIP6) model behavior with respect to precipitation. Observational data from the Atmospheric Radiation Measurement (ARM) permanent field observational sites are augmented with satellite observations of precipitation and temperature as an observational baseline. A robust relationship across observational datasets between column water vapor (CWV) and precipitation, in which conditionally averaged precipitation exhibits a sharp pickup at some critical CWV value, provides a useful convective onset diagnostic for climate model comparison. While a few models reproduce an appropriate precipitation pickup, most models begin their pickup at too low CWV and the increase in precipitation with increasing CWV is too weak. Convective transition statistics compiled in column relative humidity (CRH) partially compensate for model temperature biases—although imperfectly since the temperature dependence is more complex than that of column saturation. Significant errors remain in individual models and weak pickups are generally not improved. The conditional-average precipitation as a function of CRH can be decomposed into the product of the probability of raining and mean precipitation during raining times (conditional intensity). The pickup behavior is primarily dependent on the probability of raining near the transition and on the conditional intensity at higher CRH. Most models roughly capture the CRH dependence of these two factors. However, compensating biases often occur: model conditional intensity that is too low at a given CRH is compensated in part by excessive probability of precipitation.

54 ENVIRONMENTAL SCIENCES↗