Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Corridor”

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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Understanding the rotation of coronal holes

In an earlier study we found that the rotation of coronal holes could be understood on the basis of a nearly current-free coronal field, with the holes representing open magnetic regions. In this paper we illustrate the model by focusing on the case of CH1, the rigidly rotating boot-shaped hole observed by Skylab. We show that the interaction between the polar fields and the flux associated with active regions produces distortions in the coronal field configuration and thus in the polar-hole boundaries; these distortions corotate with the perturbing nonaxisymmetric flux. In the case of CH1, positive-polarity field lines in the northern hemisphere 'collided' with like-polarity field lines fanning out from a decaying active region complex located just below the equator, producing a midlatitude corridor of open field lines rotating at the rate of the active region complex. Sheared coronal holes result when nonaxisymmetric flux is present at high latitudes, or equivalently, when the photospheric neutral line extends to high latitudes. We demonstrate how a small active region, rotating at the local photospheric rate, can drift through a rigidly rotating hole like CH1. Finally, we discuss the role of field-line reconnection in maintaining a quasi-potential coronal configuration.

Wang, Y.-M.↗
NASA NTRS1993

Stratospheric aircraft exhaust plume and wake chemistry

Progress to date in an ongoing study to analyze and model emissions leaving a proposed High Speed Civil Transport (HSCT) from when the exhaust gases leave the engine until they are deposited at atmospheric scales in the stratosphere is documented. A kinetic condensation model was implemented to predict heterogeneous condensation in the plume regime behind an HSCT flying in the lower stratosphere. Simulations were performed to illustrate the parametric dependence of contrail droplet growth on the exhaust condensation nuclei number density and size distribution. Model results indicate that the condensation of water vapor is strongly dependent on the number density of activated CN. Incorporation of estimates for dilution factors into a Lagrangian box model of the far-wake regime with scale-dependent diffusion indicates negligible decrease in ozone and enhancement of water concentrations of 6-13 times background, which decrease rapidly over 1-3 days. Radiative calculations indicate a net differential cooling rate of the plume about 3K/day at the beginning of the wake regime, with a total subsidence ranging between 0.4 and 1 km. Results from the Lagrangian plume model were used to estimate the effect of repeated superposition of aircraft plumes on the concentrations of water and NO(y) along a flight corridor. Results of laboratory studies of heterogeneous chemistry are also described. Kinetics of HCl, N2O5 and ClONO2 uptake on liquid sulfuric acid were measured as a function of composition and temperature. Refined measurements of the thermodynamics of nitric acid hydrates indicate that metastable dihydrate may play a role in the nucleation of more stable trihydrates PSC's.

Miake-Lye, R. C.↗
NASA NTRS1993

Sand transport on Mars: Preliminary results from models

Most studies of active aeolian processes on Mars have focused on dust, i.e., particles approximately 1 micron in diameter that are transported in suspension by wind. The presence of sand dunes on Mars indicates that larger grains (approximately greater than 60 microns, transported primarily in saltation) are also present. Although indirect evidence suggests that some dunes may be active, definitive evidence is lacking. Nonetheless, numerous studies demonstrate that sand is substantially easier to transport by wind than dust, and it is reasonable to infer that sand transportation in saltation occurs under present Martian conditions. In order to assess potential source regions, transportation pathways, and sites of deposition for sand on Mars, an iterative sand transport algorithm was developed that is based on the Mars General Circulation Model of Pollack et al. The results of the dust transport model are then compared with observed surface features, such as dune field locations observed on images, and surficial deposits as inferred from Viking IRTM observations. Preliminary results suggest that the north polar dune fields in the vicinity of 270 degrees W, 70 degrees N originated from weathered polar layered plains centered at 280 degrees W, 85 degrees N, and that Thaumasia Fossae, southern Hellas Planitia, and the area west of Hellespontus Montes are sand depositional sites. Examples of transportation 'corridors' include a westward pathway in the latitudinal band 35 degrees N to 45 degrees N, and a pathway southward from Solis Planum to Thaumasia Fossae, among others.

Greeley, R.↗
NASA NTRS1994

Situational reaction and planning

One problem faced in designing an autonomous mobile robot system is that there are many parameters of the system to define and optimize. While these parameters can be obtained for any given situation determining what the parameters should be in all situations is difficult. The usual solution is to give the system general parameters that work in all situations, but this does not help the robot to perform its best in a dynamic environment. Our approach is to develop a higher level situation analysis module that adjusts the parameters by analyzing the goals and history of sensor readings. By allowing the robot to change the system parameters based on its judgement of the situation, the robot will be able to better adapt to a wider set of possible situations. We use fuzzy logic in our implementation to reduce the number of basic situations the controller has to recognize. For example, a situation may be 60 percent open and 40 percent corridor, causing the optimal parameters to be somewhere between the optimal settings for the two extreme situations.

Yen, John↗
NASA NTRS1994

Endangered and potentially endangered wildlife on John F. Kennedy Space Center and faunal integrity as a goal for maintaining biological diversity

Buffer zones for space operations provide for a wildlife diversity unsurpassed among most federal facilities in the continental U.S. demonstrating the coexistence possible with one of man's greatest technological achievements. This document ranks 119 resident or migratory wildlife species that are endangered or declining. The ranking system herein was based on species' vulnerability to extinction and the relevance of Kennedy Space Center (KSC) for maintaining populations in the U.S. and Florida. One amphibian, 19 reptiles, 80 birds, and 19 mammals were considered endangered or declining. KSC is an integral area for regional species diversity being the focus of the Merritt Island/Cape Canaveral/Turnbull Ecosystem which is part of the Indian River Lagoon watershed, an estuary of national significance. Many species that use this system also use the nearby St. Johns River Basin ecosystem. These two ecosystems are biological corridors between temperate Carolinian and tropical/subtropical Caribbean biotic provinces. Threats to biological diversity on KSC were also reviewed. Traditional environmental assessments, resulting from environmental regulation guidelines, focus on environmental contaminants and habitat lost due to construction. However, this review suggested that small population sizes, isolation of populations, ecosystem and habitat fragmentation, road mortality, and other edge effects may represent more critical threats to biological diversity than the traditional topics.

Breininger, David R.↗
NASA NTRS1994

Case study of a low-reflectivity pulsating microburst: Numerical simulation of the Denver, 8 July 1989, storm

On 8 July 1989, a very strong microburst was detected by the Low-Level Windshear Alert system (LLWAS), within the approach corridor just north of Denver Stapleton Airport. The microburst was encountered by a Boeing 737-200 in a 'go-around' configuration which was reported to have lost considerable air speed and altitude during penetration. Data from LLWAS revealed a pulsating microburst with an estimated peak velocity change of 48 m/s. Wilson et al. reported that the microburst was accompanied by no apparent visible clues such as rain or virga, although blowing dust was present. Weather service hourly reports indicated virga in all quadrants near the time of the event. A National Center for Atmospheric Research (NCAR) research Doppler radar was operating; but according to Wilson et al., meaningful velocity could not be measured within the microburst due to low radar-reflectivity factor and poor siting for windshear detection at Stapleton. This paper presents results from the three-dimensional numerical simulation of this event, using the Terminal Area Simulation System (TASS) model. The TASS model is a three-dimensional nonhydrostatic cloud model that includes parameterizations for both liquid and ice phase microphysics, and has been used in investigations of both wet and dry microburst case studies. The focus of this paper is the pulsating characteristic and the very-low radar reflectivity of this event. Most of the surface outflow contained no precipitation. Such an event may be difficult to detect by radar.

Proctor, Fred H.↗
NASA NTRS1994

Three dimensional model calculations of the global dispersion of high speed aircraft exhaust and implications for stratospheric ozone loss

Two-dimensional (zonally averaged) photochemical models are commonly used for calculations of ozone changes due to various perturbations. These include calculating the ozone change expected as a result of change in the lower stratospheric composition due to the exhaust of a fleet of supersonic aircraft flying in the lower stratosphere. However, zonal asymmetries are anticipated to be important to this sort of calculation. The aircraft are expected to be restricted from flying over land at supersonic speed due to sonic booms, thus the pollutant source will not be zonally symmetric. There is loss of pollutant through stratosphere/troposphere exchange, but these processes are spatially and temporally inhomogeneous. Asymmetry in the pollutant distribution contributes to the uncertainty in the ozone changes calculated with two dimensional models. Pollutant distributions for integrations of at least 1 year of continuous pollutant emissions along flight corridors are calculated using a three dimensional chemistry and transport model. These distributions indicate the importance of asymmetry in the pollutant distributions to evaluation of the impact of stratospheric aircraft on ozone. The implications of such pollutant asymmetries to assessment calculations are discussed, considering both homogeneous and heterogeneous reactions.

Douglass, Anne R.↗
NASA NTRS1994

Impact of stratospheric aircraft on calculations of nitric acid trihydrate cloud surface area densities using NMC temperatures and 2D model constituent distributions

A parameterization of NAT (nitric acid trihydrate) clouds is developed for use in 2D models of the stratosphere. The parameterization uses model distributions of HNO3 and H2O to determine critical temperatures for NAT formation as a function of latitude and pressure. National Meteorological Center temperature fields are then used to determine monthly temperature frequency distributions, also as a function of latitude and pressure. The fractions of these distributions which fall below the critical temperatures for NAT formation are then used to determine the NAT cloud surface area density for each location in the model grid. By specifying heterogeneous reaction rates as functions of the surface area density, it is then possible to assess the effects of the NAT clouds on model constituent distributions. We also consider the increase in the NAT cloud formation in the presence of a fleet of stratospheric aircraft. The stratospheric aircraft NO(x) and H2O perturbations result in increased HNO3 as well as H2O. This increases the probability of NAT formation substantially, especially if it is assumed that the aircraft perturbations are confined to a corridor region.

Considine, David B.↗
NASA NTRS1994

Atmospheric propagation at larger lateral distances from the flight track

Sonic booms received on the ground tend to be restricted to a region of finite lateral extent below the flight track. This occurs because of refraction and because the effective speed of sound, even with winds taken into account, decreases with altitude in the lower atmosphere. Not all rays proceeding initially downwards from the flight track within an allowable range of initial directions will reach the ground. The restricted region which can be reached by rays impacting the ground is known as the primary carpet. However, weak rumbles are heard in the nominal shadow zone beyond the edge of this carpet. A full wave theory is necessary for explaining waveforms in that region, and the present paper gives a matched asymptotic expansion technique for a suitable approximate full wave theory that involves a relatively small number of parameters. The outer solution is derived from the structure of the system of rays that impact near the corridor edge; the inner solution involves a solution of the parabolic equation and results in the special functions encountered in the diffraction of sound over the tops of hills.

Pierce, Allan D.↗
NASA NTRS1994

Extraordinary line-emitting knots in the Crab Nebula

Extraordinary, semistellar, line-emitting knots are apparent in images of the Crab Nebula which were obtained with the Goddard Fabry-Perot imager at the Michigan-Dartmouth-MIT Observatory. The knots are most prominent for (O III) lambda 5007 emission through a 5.3 A (Full Width at Half Maximum (FWHM)) bandpass centered at 5015.3 A, with representative fluxes of roughly 10(exp -14) ergs/sq cm. They are aligned in arcs, seven to the north and four to the south, from the pulsar. The northern group appears to be in a bounded corridor through the filamentary structure. Measurements over a 2 year baseline yield proper motions of order 0.1 sec/yr, corresponding to transverse velocities of order 900 km/s for a distance of 1830 pc. The knots are characterized by remarkably strong (Ar III) emission, possibly indicating high argon abundances, high gas temperatures, or anomalous physical processes.

Macalpine, Gordon M.↗
NASA NTRS1997

Total Solar Eclipse of 1999 August 11

On 1999 August 11, a total eclipse of the Sun will be visible from within a narrow corridor which traverses the Eastern Hemisphere. The path of the Moon's umbral shadow begins in the Atlantic and crosses central Europe, the Middle East, and India, where it ends at sunset in the Bay of Bengal. A partial eclipse will be seen within the much broader path of the Moon's penumbral shadow, which includes northeastern North America, all of Europe, northern Africa, and the western half of Asia. Detailed predictions for this event are presented and include besselian elements, geographic coordinates of the path of totality, physical ephemeris of the umbra, topocentric limb profile corrections, local circumstances for approximately 1400 cities, maps of the eclipse path, weather prospects, the lunar limb profile, and the sky during totality. Tips and suggestions are also given on how to safely view and photograph the eclipse.

Espenak, Fred↗
NASA NTRS1997

A Candidate Wake Vortex Strength Definition for Application to the NASA Aircraft Vortex Spacing System (AVOSS)

A significant effort is underway at NASA Langley to develop a system to provide dynamical aircraft wake vortex spacing criteria to Air Traffic Control (ATC). The system under development, the Aircraft Vortex Spacing System (AVOSS), combines the inputs of multiple subsystems to provide separation matrices with sufficient stability for use by ATC and sufficient monitoring to ensure safety. The subsystems include a meteorological subsystem, a wake behavior prediction subsystem, a wake sensor subsystem, and system integration and ATC interfaces. The proposed AVOSS is capable of using two factors, singly or in combination, for reducing in-trail spacing. These factors are wake vortex motion out of a predefined approach corridor and wake decay below a strength that is acceptable for encounter. Although basic research into the wake phenomena has historically used wake total circulation as a strength parameter, there is a requirement for a more specific strength definition that may be applied across multiple disciplines and teams to produce a real-time, automated system. This paper presents some of the limitations of previous applications of circulation to aircraft wake observations and describes the results of a preliminary effort to bound a spacing system strength definition.

Hinton, David A.↗
NASA NTRS1997

HO(x) Measurements in SONEX with the Airborne Tropospheric Hydrogen Oxides Sensor (ATHOS)

SONEX, which was delayed by aircraft inspection problems, began the second week of October and concluded in mid-November with 16 flights. These flights covered the Pacific Ocean off the western United States, transits across the United States, the western coast of Europe, and the North and Central Atlantic Ocean. Particular attention was paid to the North Atlantic Flight Corridor. ATHOS collected high-quality HO(x) data on 15 flights. Observations taken at 5 Hz were typically averaged into 20-second measurements. Each 20-second measurement has precision 1(sigma) of less than 0.01 pptv. OH measurements were generally made from the surface to flight altitudes. HO2 measurements, which require reagent NO flow, were made from flight altitudes to near the top of the planetary boundary layer. Measured OH and HO2 during SONEX was generally lower than the measured OH and HO2 during SUCCESS (April-May, 1996, central United States). Whereas during SUCCESS midday OH was 0.1-0.5 pptv and HO2 was 3-15 pptv, during SONEX midday OH was 0.02-0.2 pptv and HO2 was 0.5-8 pptv. Part of this difference results from the midday solar zenith angles, which were larger during SONEX than during SUCCESS due to both the season and the generally higher latitudes sampled during SONEX. However, some of the difference may be due to differences in HOx sources, since less air influenced by convection was sampled during SONEX. These possibilities await post-flight calibrations of ATHOS and analysis of observations of HO(x) and simultaneously measured meteorology and trace species.

Brune, William M.↗
NASA NTRS1997

Surface-Based Observations of Contrail Occurrence Over the US, Apr. 1993 to Apr. 1994

Surface observers stationed at 19 U.S. Air Force Bases and Army Air Stations recorded the daytime occurrence of contrails and cloud fraction on an hourly basis for the period April 1993 through April 1994. Each observation uses one of four main categories to report contrails as unobserved, non-persistent, persistent, and indeterminate. Additional classification includes the co-occurrence of cirrus with each report. The data cover much of the continental U.S. including locations near major commercial air routes. The mean annual frequency of occurrence in unobstructed viewing conditions is 13 percent for these sites. Contrail occurrence varied substantially with location and season. Most contrails occurred during the winter months and least during the summer with a pronounced minimum during July. Although nocturnal observations are not available, it appears that the contrails have a diurnal variation that peaks during mid morning over most areas. Contrails were most often observed in areas near major commercial air corridors and least often over areas far removed from the heaviest air traffic. A significant correlation exists between mean contrail frequency and aircraft fuel usage above 7 km suggesting predictive potential for assessing future contrail effects on climate.

Minnis, Patrick↗
NASA NTRS1997

Aircraft Vortex Spacing System (AVOSS) Concept and Development

The AVOSS goal is to: (1) Support TAP goal of improving instrument operations capacity 12-15% while maintaining safety; (2) Provide dynamical aircraft wake vortex spacing criteria to ATC systems at capacity limited facilities with required lead time and stability for use in establishing aircraft arrival scheduling; and (3) System development and concept demonstration. The AVOSS system concept is to separate aircraft from encounters with wake vortices of an operationally unacceptable strength. In doing so, define protected corridor from outer marker to runway and predict time for vortex to clear ("Transport Time"), define operationally unacceptable wake strength and predict time to decay ("Decay Time"), combine and provide to ATC automation ("Residence Time"), and monitor safety and provide predictor feedback with wake vortex detection subsystem.

Hinton, David A.↗
NASA NTRS1960

An Approximate Analytical Method for Studying Atmosphere Entry of Vehicles with Modulated Aerodynamic Forces

The dimensionless, transformed, nonlinear differential equation developed in NASA TR R-11 for describing the approximate motion and heating during entry into planetary atmospheres for constant aerodynamic coefficients and vehicle shape has been modified to include entries during which the aerodynamic coefficients and the vehicle shape are varied. The generality of the application of the original equation to vehicles of arbitrary weight, size, and shape and to arbitrary atmospheres is retained. A closed-form solution for the motion, heating, and the variation of drag loading parameter m/C(D)A has been obtained for the case of constant maximum resultant deceleration during nonlifting entries. This solution requires certain simplifying assumptions which do not compromise the accuracy of the results. The closed-form solution has been used to determine the variation of m/C(D)A required to reduce peak decelerations and to broaden the corridor for nonlifting entry into the earth's atmosphere at escape velocity. The attendant heating penalty is also studied.

Levy, Lionel L., Jr.↗
NASA NTRS1961

The Use of Drag Modulation to Limit the Rate at Which Deceleration Increases During Nonlifting Entry

The method developed in NASA TN D-319 for studying the atmosphere entry of vehicles with varying aerodynamic forces has been applied to obtain a closed-form solution for the motion, heating, range, and variation of the vehicle parameter m/C(D)A for nonlifting entries during which the rate of increase of deceleration is limited. The solution is applicable to vehicles of arbitrary weight, size, and shape, and to arbitrary atmospheres. Results have been obtained for entries into the earth's atmosphere at escape velocity during which the maximum deceleration and the rate at which deceleration increases were limited. A comparison of these results with those of NASA TN D-319, in which only the maximum deceleration was limited, indicates that for a given corridor depth, limiting the rate of increase of deceleration and the maximum deceleration requires an increase in the magnitude of the change in M/C(D)A and results in increases in maximum heating rate, total heat absorbed at the stagnation point, and range.

Levy, Lionel L., Jr.↗
NASA NTRS1961

A Study of the Effect of Errors in Measurement of Velocity and Flight-Path Angle on the Guidance of a Space Vehicle Approaching the Earth

An analysis was made of the guidance of a space vehicle approaching the earth at supercircular velocity through an entrance corridor containing a desired perigee altitude. Random errors were assumed in the measurement of velocity and flight-path angle and in obtaining the desired thrust impulse. The method described in NASA Technical Note D-191 of scheduling corrections at different values of the angle between perigee and the vehicle's position vector and a slight modification of this method were investigated as a means of correcting perigee altitude when the vehicle's predicted position was at programmed correction points not within a specified deadband about the desired perigee altitude. The study showed that modifying the angular method of NASA Technical Note D-191 by adding another correction near the initial point did not improve the efficiency and accuracy of the angular method. It was found that in some cases the use of a correction procedure which included a deadband could be more costly in total corrective velocity than a procedure which neglected the deadband. This was especially true if a large degree of confidence was required in the total corrective velocity. It was apparent from the results that a correction with a deadband limit in the guidance scheme was more sensitive to the initial conditions, the corrective procedure, the deadband, and the degree of confidence required than a correction without a deadband limit.

White, Jack A.↗