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Results for “SIMULATED EMISSION”

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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

The Atmospheric Effects of HSCT Emissions Simulated by a 3-Wave Interactive Model

An interactive model which couples a semi-spectral dynamical model, a radiative transfer code and a two-dimensional chemistry transport model (2-D CTM), is used to assess the atmospheric effects of the High-Speed Civil Transport (HSCT) engine emissions. The residual mean meridional circulation, the zonal-mean temperature and the eddy diffusion coefficients are calculated using zonal means and three longest zonal waves of dynamical variables integrated in the semi-spectral dynamical model. They are used in the 2-D CTM to simulate the distribution of trace gases in the atmosphere. The simulated ozone is sent to the radiative transfer code to calculate the heating rates, which drive the dynamics. This radiative coupling connects the dynamical and photochemical processes and creates feedback when the atmosphere is perturbed. It is found that in most areas the ozone depletion caused by HSCT emissions calculated using the 3-wave model has the features similar to, but with significantly larger magnitude than that calculated by the AER 2-D CTM with prescribed transport parameters and temperature. The difference is mostly due to the differences in the circulation in the two models. The radiative feedback effects are investigated by comparing the ozone depletion calculated with the baseline dynamics and with the dynamics perturbed by the HSCT emissions. The feedback through changes in the residual mean meridional circulation and the eddy diffusion coefficients has moderate effects on the simulated ozone depletion. It reduced the ozone depletion by 20-30% in northern mid and high-latitudes. However, the feedback through changes in the zonal- mean temperature is negligible.

Shia, R.-L.↗
NASA NTRS1994

Loop heating by D.C. electric current and electromagnetic wave emissions simulated by 3-D EM particle zone

We have shown that a current-carrying plasma loop can be heated by magnetic pinch driven by the pressure imbalance between inside and outside the loop, using a 3-dimensional electromagnetic (EM) particle code. Both electrons and ions in the loop can be heated in the direction perpendicular to the ambient magnetic field, therefore the perpendicular temperature can be increased about 10 times compared with the parallel temperature. This temperature anisotropy produced by the magnetic pinch heating can induce a plasma instability, by which high-frequency electromagnetic waves can be excited. The plasma current which is enhanced by the magnetic pinch can also excite a kinetic kink instability, which can heat ions perpendicular to the magnetic field. The heating mechanism of ions as well as the electromagnetic emission could be important for an understanding of the coronal loop heating and the electromagnetic wave emissions from active coronal regions.

Sakai, J. I.↗
NASA NTRS2001

Divine-garrett model and Jovian synchrotron emission

Simulations of synchrotron emission from relativistic electrons trapped in Jupiter's magnetic field are used to evaluate the energetic electron distribution of the Divine-Garrett Jupiter radiation belt model at radial distances less than 4 Jovian radii.

Radial diffusion-models electrons jupiter↗
NASA NTRS1992

Instrumental and observational requirements for space-based imaging of magnetospheric emissions

Simulated images of extreme ultraviolet (EUV) emissions from energetic outflowing ions have been constructed to study techniques for remotely sensing the dynamic behavior of hot plasmas in the near-Earth environment. These calculations include realistic assumptions about the energetic ion outflow from high latitudes and take into account the effects of cold plasmaspheric and ionospheric ions. The energetic ion outflow is determined from a statistical study based on five years of measurements from the Energetic Ion Composition Spectrometer on Dynamics Explorer 1. The simulated images change significantly with viewing geometry and certain spacecraft locations are clearly favorable for observing emissions from energetic ions. For example, for a near equatorial orbit, viewing locations greater than 9 Earth radii are required to observe outflowing ions above the cold plasmaspheric background. We will discuss other important considerations for magnetospheric imaging including the sensitivity requirements of the detector. In particular, we consider the performance of multi-layer optics for EUV wavelengths.

Robinson, R. M.↗
NASA NTRS1998

Simulated infrared emission spectra of highly excited polyatomic molecules: a detailed model of the PAH-UIR hypothesis

A detailed description of the polycyclic aromatic hydrocarbon (PAH)/unidentified infrared band (UIR) mechanism is presented in which experimental spectral bandshape functions are used to simulate IR emission spectra for individual molecules. These spectra are additively superimposed to produce a conglomerate spectrum representative of a family of PAH molecules. Ab initio vibrational frequencies and intensities for nine PAHs (neutral and cationic) as large as ovalene are used in conjunction with measured bandshape and temperature-dependent redshift data to simulate the UIR bands. The calculated spectra of cations provide a closer match to the UIRs than do those of the neutrals. However, the PAH cations used in the simulations fail to reproduce the details of the UIR emission spectra. The discrepancies are potentially alleviated if both larger PAHs and a greater number of PAHs were included in the simulation.

Non-NASA Center↗
NASA NTRSDate not supplied

Sensitivity of Simulated Radiative Emission from Nitrogen Flows to Chemical Parameters

Numerical models of hypersonic flows rely on chemistry data inferred from experiments and quantum calculations. Experiments from NASA's Electric Arc Shock Tube (EAST) measure the spectral emission of strong shocks in pure nitrogen flows. These spectral profiles are only approximately captured by numerical simulations. To address these discrepancies, one wishes to calibrate some of the chemical parameters to better match experiment. Because there are hundreds of parameters in the numerical model, a sensitivity analysis was carried out on the entire chemistry database to determine which parameters are most important to analyze in the future. In order to perform this work it was necessary to generate a consistent chemical database that interfaced with both the CFD and line-by-line radiation solver. Using Monte Carlo methods, the total Sobol index was calculated for important parameters. Twenty parameters were identified as important across the nitrogen system. However, it was noted that in some spectral regions, the parametric uncertainty was unable to bound EAST measurements. Further improvements could be made by increasing the parameter uncertainties or addressing other sources of modeling error.

Kaelan B Hansson↗
NASA NTRSDate not supplied

Sensitivity of Simulated Radiative Emission from Nitrogen Flows to Chemical Parameters

Numerical models of hypersonic flows rely on chemistry data inferred from experiments and quantum calculations. Experiments from NASA's Electric Arc Shock Tube (EAST) measure the spectral emission of strong shocks in pure nitrogen flows. These spectral profiles are only approximately captured by numerical simulations. To address these discrepancies, one wishes to calibrate some of the chemical parameters to better match experiment. Because there are hundreds of parameters in the numerical model, a sensitivity analysis was carried out on the entire chemistry database to determine which parameters are most important to analyze in the future. In order to perform this work it was necessary to generate a consistent chemical database that interfaced with both the CFD and line-by-line radiation solver. Using Monte Carlo methods, the total Sobol index was calculated for important parameters. Twenty parameters were identified as important across the nitrogen system. However, it was noted that in some spectral regions, the parametric uncertainty was unable to bound EAST measurements. Further improvements could be made by increasing the parameter uncertainties or addressing other sources of modeling error.

Kaelan Hansson↗
NASA NTRS1996

Experimental Characterization of Gas Turbine Emissions at Simulated Flight Altitude Conditions

NASA's Atmospheric Effects of Aviation Project (AEAP) is developing a scientific basis for assessment of the atmospheric impact of subsonic and supersonic aviation. A primary goal is to assist assessments of United Nations scientific organizations and hence, consideration of emissions standards by the International Civil Aviation Organization (ICAO). Engine tests have been conducted at AEDC to fulfill the need of AEAP. The purpose of these tests is to obtain a comprehensive database to be used for supplying critical information to the atmospheric research community. It includes: (1) simulated sea-level-static test data as well as simulated altitude data; and (2) intrusive (extractive probe) data as well as non-intrusive (optical techniques) data. A commercial-type bypass engine with aviation fuel was used in this test series. The test matrix was set by parametrically selecting the temperature, pressure, and flow rate at sea-level-static and different altitudes to obtain a parametric set of data.

GAS TURBINES↗
NASA NTRS1993

A Probabilistic Model for Simulating Magnetoacoustic Emission Responses in Ferromagnets

Magnetoacoustic emission (MAE) is a phenomenon where acoustic noise is generated due to the motion of non-180 magnetic domain walls in a ferromagnet with non-zero magnetostrictive constants. MAE has been studied extensively for many years and has even been applied as an NDE tool for characterizing the heat treatment of high-yield low carbon steels. A complete theory which fully accounts for the magnetoacoustic response, however, has not yet emerged. The motion of the domain walls appears to be a totally random process, however, it does exhibit features of regularity which have been identified by studying phenomena such as 1/f flicker noise and self-organized criticality (SOC). In this paper, a probabilistic model incorporating the effects of SOC has been developed to help explain the MAE response. The model uses many simplifying assumptions yet yields good qualitative agreement with observed experimental results and also provides some insight into the possible underlying mechanisms responsible for MAE. We begin by providing a brief overview of magnetoacoustic emission and the experimental set-up used to obtain the MAE signal. We then describe a pseudo-probabilistic model used to predict the MAE response and give an example of the predicted result. Finally, the model is modified to account for SOC and the new predictions are shown and compared with experiment.

Namkung, M.↗
NASA NTRS2002

The Effect of Transport and Circulation Differences on Stratospheric Ozone Recovery in Two 35-year Three-dimensional Simulations

The NASA Global Modeling Initiative (GMI) has completed two 35-year simulations with WMO future baseline boundary conditions that simulate increasing N2O and CH4 emissions and decreasing organic chlorine and bromine emissions. Simulations were done with the GMI offline chemistry and transport model using 1) 1 year of winds from the Finite-Volume General Circulation Model (FV-GCM), repeated for the 35 years, and 2) 1 year of winds from the Finite-Volume Data Assimilation System (FV-DAS), repeated for 35-years. The simulations have full stratospheric chemistry. To understand differences in simulated ozone recoveries, basic transport and circulation differences between these models are evaluated. The distribution of mean age of stratospheric air in the FV-GCM run agrees well with observations in the lower stratosphere but the FV-DAS ages are generally too low. This implies circulation and mixing differences that will affect the distributions of other trace species such as CH4, NO, and the organic halogens, all of which are responding to changing boundary conditions and are involved in ozone loss. Realism of model transport is evaluated, with particular attention given to regions and seasons where ozone recovery is expected. Preliminary results indicate increasing ozone trends in the lowermost stratosphere in summer and in the Antarctic and Arctic lower stratosphere in winter and spring.

Bhartia, P. K.↗
NASA NTRS1989

Three-dimensional simulation of whistler mode excited by the Spacelab 2 electron beam

During the Spacelab 2 mission, while an electron beam was being ejected from the Shuttle, the Plasma Diagnostics Package (PDP) detected a clear funnel-shaped emission that is believed to be caused by whistler-mode emission from the electron beam. In order to understand the mechanism of this emission, simulations with a three-dimensional partially magnetostatic code have been performed. The simulation results show that whistler-mode and lower hybrid waves are excited by the electron beam, which is initially localized in the column in the three-dimensional simulation system, and that they propagate away from the beam. The wave spectra of the electric and magnetic fields diagnosed at some points show several peaks due to the waves excited by the electron beam. The frequency range of these spectra is in qualitative agreement with the PDP data. The intense narrowband electrostatic emission near the electron plasma frequency is observed by the simulations. The simulation results show that the beam instability is responsible for the generation mechanism of these emissions.

Nishikawa, K.-I.↗
NASA NTRS2021

Radio Simulations of Upgoing Extensive Air Showers Observed from Low-Earth Orbit

Tau neutrinos interacting in the Earth can result in upgoing extensive air showers. These showers produce optical and radio emission that can be detected by orbital and suborbital platforms. We present results of radio emission simulations using ZHAireS for observation from low-Earth orbit as part of NASA's nuSpaceSim program to develop a comprehensive end-to-end simulation package to model these signals. Peculiar properties of the radio emission arise from the fact that these showers develop in extremely rarified portions of the Earth's atmosphere and, being observed from hundreds of kilometers distance, have distinct coherent emission features compared to ground observations.

Romero-Wolf, Andrew↗
NASA NTRS2016

The Effects of Consistent Chemical Kinetics Calculations on the Pressure-Temperature Profiles and Emission Spectra of Hot Jupiters

In this work we investigate the impact of calculating non-equilibrium chemical abundances consistently with the temperature structure for the atmospheres of highly-irradiated, close-in gas giant exoplanets. Chemical kinetics models have been widely used in the literature to investigate the chemical compositions of hot Jupiter atmospheres which are expected to be driven away from chemical equilibrium via processes such as vertical mixing and photochemistry. All of these models have so far used pressure-temperature (P-T) profiles as fixed model input. This results in a decoupling of the chemistry from the radiative and thermal properties of the atmosphere, despite the fact that in nature they are intricately linked. We use a one-dimensional radiative-convective equilibrium model, ATMO, which includes a sophisticated chemistry scheme to calculate P-T profiles which are fully consistent with non-equilibrium chemical abundances, including vertical mixing and photochemistry. Our primary conclusion is that, in cases of strong chemical disequilibrium, consistent calculations can lead to differences in the P-T profile of up to 100 K compared to the P-T profile derived assuming chemical equilibrium. This temperature change can, in turn, have important consequences for the chemical abundances themselves as well as for the simulated emission spectra. In particular, we find that performing the chemical kinetics calculation consistently can reduce the overall impact of non-equilibrium chemistry on the observable emission spectrum of hot Jupiters. Simulated observations derived from non-consistent models could thus yield the wrong interpretation. We show that this behaviour is due to the non-consistent models violating the energy budget balance of the atmosphere.

planets and satellites↗
NASA NTRS1993

First results from a laboratory facility for measurement of emission spectra under simulated planetary conditions

We have developed a laboratory spectroscopic facility for the measurement of emission spectra under simulated planetary conditions. Spectral measurements are made from 6 to 13 microns with a scanning grating monochromator equipped with a HgCdTl detector. An environment chamber in service in Hawaii for several years in which we can control the temperature from 77 K to 500 K, the pressure from 10(exp -5) torr to two atmospheres, has been equipped with a 77 K or 273 K cold shield. The shield serves to minimize light reflected off the sample and to aid in development of thermal gradients for obtaining spectra under conditions simulating the thermal environment of airless bodies. Samples are placed in small cups on a temperature controlled substrate allowing measurements of emission due to heating from below by the substrate, or from illumination from a solar simulation source.

Lucey, Paul G.↗
NASA NTRS1992

Imaging solar flares in hard X-rays using Fourier telescopes

The sun emits hard X-rays (above 10 keV) during solar flares. Imaging hard X-ray sources on the sun with spatial resolutions on the order of 1-5 arcsec and integration times of 1 sec will provide greater insight into the energy release processes during a solar flare. In these events, tremendous amounts of energy stored in the solar magnetic field are rapidly released leading to emission across the electromagnetic spectrum. Two Fourier telescope designs, a spatial modulation collimator and a rotating modulation collimator, were developed to image the full sun in hard X-rays (10-100 keV) in an end-to-end simulation. Emission profiles were derived for two hard X-ray solar flare models taken from the current solar theoretical literature and used as brightness distributions for the telescope simulations. Both our telescope models, tailored to image solar sources, were found to perform equally well, thus offering the designer significant flexibility in developing systems for space-based platforms. Given sufficient sensitive areas, Fourier telescopes are promising concepts for imaging solar hard X-rays.

Campbell, Jonathan W.↗