SEARCH · Engineering Papers

Results for “Zonal problem”

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.

SourceResearch connectionFrom yearThrough year

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

125 records · Page 7

All sources NASA NTRS DOE OSTI

NASA NTRS1987

Down-to-earth supercomputing at NASA Ames

The requirements for computers for aerospace vehicle design problems, in particular fluid dynamics, are examined. The levels of approximation to Navier-Stokes equations are: (1) linearized inviscid form, (2) nonlinear inviscid equation, (3) Reynolds-averaged Navier-Stokes equation, (4) large eddy simulation with models for subgrid scale turbulence, and (5) full Navier-Stokes equations to calculate laminar/turbulent transition and turbulence dissipation. The Cray 2 with 256 megaword memory and 4.1 nsec clock and the Cray X-MP/48 with a 128 megaword memory and a 9.5 nsec clock of the Ames facility are described, and an example revealing their applicability is presented. The use of zonal methods to simulate aerodynamic flow fields numerically is discussed. Consideration is given to the development of a program for simulation of aerodynamic flow fields, the compilers, symbolic debuggers, the scheduling of multiple CPUs, and the analysis and storage of the data.

Stevens, Kenneth G., Jr.↗

NASA NTRS2004

A 3D Convective Model for the Jovian Wind Bands

In an earlier paper, we proposed that Jupiter's alternating wind bands are a manifestation of the global interaction between rotation and convection in a shallow layer. The model, however, was obtained from linearization of the 2D equations of motions. At HKUST/Hong Kong, we are now trying to study this problem by rigorous numerical simulation. Using a three-dimensional spectral numerical code, we compute models for the outermost layer of Jupiter's convective envelope. Two cases have been studied. In one the atmospheric pressure varies from 1 to 23 bar, and in the other from 1 to 115 bar. The physical parameters (internal energy flux, rotation rate) are chosen to be close to those expected, but solar heating, chemistry, as well as dynamical influences from deeper layers are ignored. The models generate wind field patterns that contain alternating jet streams with resemblance to the Jovian bands. Instantaneous values of the mean zonal flow at the equator reach 80 m/sec. Yet the mean meridional flows are less than 1% of such value. The meridional temperature profile at the cloud top level also shows a double hump structure of a few degrees (as observed) in the subtropics. Though there is not complete quantitative agreement (caused perhaps by neglected effects like solar radiation), these models demonstrate, in principle, the feasibility of generating a Jovian type wind pattern through the interaction of fast rotation and convection in a thin shell.

Mayr, H. G.↗

NASA NTRS2000

The Impact of Withholding Observations from TOMS or SBUV Instruments on the GEOS Ozone Data Assimilation System

In a data assimilation system (DAS), model forecast atmospheric fields, observations and their respective statistics are combined in an attempt to produce the best estimate of these fields. Ozone observations from two instruments are assimilated in the Goddard Earth Observing System (GEOS) ozone DAS: the Total Ozone Mapping Spectrometer (TOMS) and the Solar Backscatter Ultraviolet (SBUV) instrument. The assimilated observations are complementary; TOMS provides a global daily coverage of total column ozone, without profile information, while SBUV measures ozone profiles and total column ozone at nadir only. The purpose of this paper is to examine the performance of the ozone assimilation system in the absence of observations from one of the instruments as it can happen in the event of a failure of an instrument or when there are problems with an instrument for a limited time. Our primary concern is for the performance of the GEOS ozone DAS when it is used in the operational mode to provide near real time analyzed ozone fields in support of instruments on the Terra satellite. In addition, we are planning to produce a longer term ozone record by assimilating historical data. We want to quantify the differences in the assimilated ozone fields that are caused by the changes in the TOMS or SBUV observing network. Our primary interest is in long term and large scale features visible in global statistics of analysis fields, such as differences in the zonal mean of assimilated ozone fields or comparisons with independent observations, While some drifts in assimilated fields occur immediately, after assimilating just one day of different observations, the others develop slowly over several months. Thus, we are also interested in the length of time, which is determined from time series, that is needed for significant changes to take place.

Stajner, Ovanka↗

NASA NTRS1995

Blocked Grid Technologies as Applied to Aerodynamic Configurations

The advantages and disadvantages of the blocked grid methodology are discussed using results from ENSAERO, CNS, and CNS-FV. The first two codes are based on finite differences and the last on cell-centered finite volume formulation. Techniques that enhance the utility of the blocked (or patched) grid methodology are described. These techniques include mesh discontinuous zonal interfaces, sliding zonal interfaces, fast search procedures, and virtual zones. All of these methods are designed with two goals; namely extend the use of patched grids to unsteady aerodynamics, e.g. oscillating control flaps, and provide the user more flexibility in the grid topologies available for gridding complex aerodynamic configurations. For example, the use of virtual zones allows the user the choice of using one grid topology for surface grids, and another for the volume grids. This additional flexibility has a large impact in the amount of calendar time required to block and grid a complex aerodynamic configuration. Several examples are shown demonstrating the new features. Other issues involving grid generation are also discussed. In particular the existing problems of defining grid quality measures which are relevant are also described.

Klopfer, Goetz↗

NASA NTRS1992

Eccentricity and argument of perigee control for orbits with repeat ground tracks

In order to gain an understanding into the problem of eccentricity (e) and argument of perigee (omega) control for TOPEX/Poseidon, the two cases where the highest latitude crossing time and one of the equator crossings are held constant are investigated. Variations in e and omega cause a significant effect on the satellite's ground-track repeatability. Maintaining e and omega near their frozen values will minimize this variation. Analytical expressions are found to express this relationship while keeping an arbitrary point of the ground track fixed. The initial offset of the ground track from its nominal path determines the subsequent evolution of e and omega about their frozen values. This long-term behavior is numerically determined using an earth gravitational field including the first 17 zonal harmonics. The numerical results are plotted together with the analytical constraints to see if the later values of e and omega cause unacceptable deviation in the ground track.

Vincent, Mark A.↗

NASA NTRS1991

Grid generation about complex three-dimensional aircraft configurations

The problem of obtaining three dimensional grids with sufficient resolution to resolve all the flow or other physical features of interest is addressed. The generation of a computational grid involves a series of compromises to resolve several conflicting requirements. On one hand, one would like the grid to be fine enough and not too skewed to reduce the numerical errors and to adequately resolve the pertinent physical features of the flow field about the aircraft. On the other hand, the capabilities of present or even future supercomputers are finite and the number of mesh points must be limited to a reasonable number: one which is usually much less than desired for numerical accuracy. One technique to overcome this limitation is the 'zonal' grid approach. In this method, the overall field is subdivided into smaller zones or blocks in each of which an independent grid is generated with enough grid density to resolve the flow features in that zone. The zonal boundaries or interfaces require special boundary conditions such that the conservation properties of the governing equations are observed. Much work was done in 3-D zonal approaches with nonconservative zonal interfaces. A 3-D zonal conservative interfacing method that is efficient and easy to implement was developed during the past year. During the course of the work, it became apparent that it would be much more feasible to do the conservative interfacing with cell-centered finite volume codes instead of the originally planned finite difference codes. Accordingly, the CNS code was converted to finite volume form. This new version of the code is named CNSFV. The original multi-zonal interfacing capability of the CNS code was enhanced by generalizing the procedure to allow for completely arbitrarily shaped zones with no mesh continuity between the zones. While this zoning capability works well for most flow situations, it is, however, still nonconservative. The conservative interface algorithm was also implemented but was not completely validated.

Klopfer, Goetz H.↗

NASA NTRS1989

A knowledge-based approach to automated flow-field zoning for computational fluid dynamics

An automated three-dimensional zonal grid generation capability for computational fluid dynamics is shown through the development of a demonstration computer program capable of automatically zoning the flow field of representative two-dimensional (2-D) aerodynamic configurations. The applicability of a knowledge-based programming approach to the domain of flow-field zoning is examined. Several aspects of flow-field zoning make the application of knowledge-based techniques challenging: the need for perceptual information, the role of individual bias in the design and evaluation of zonings, and the fact that the zoning process is modeled as a constructive, design-type task (for which there are relatively few examples of successful knowledge-based systems in any domain). Engineering solutions to the problems arising from these aspects are developed, and a demonstration system is implemented which can design, generate, and output flow-field zonings for representative 2-D aerodynamic configurations.

Vogel, Alison Andrews↗

NASA NTRS1999

Jupiter's Deep Flowing Thermocline

The observed banded wind structure of Jupiter and Saturn remains an outstanding problem in planetary fluid dynamics. Both planets exhibit super-rotational equatorial jets (exceeding the underlying rotation of the magnetic fields tied to their deep fluid interiors), with speeds of some 100 and 400m/s, respectively, and counter-flowing lots at higher latitudes;. Recent analyses of the 1995 Galileo probe measurements, Hubble Telescope observations of the 1994 Shoemaker-Levy9 comet crash, and Earth-based infrared mapping provide evidence for a variably stratified, deeply seated flow layer. A now conceptual model for the jovian current system is proposed, in some ways resembling the oceanic thermocline, assuming a mixed distribution of potential vorticity atop a tropospheric wind layer of latitudinally variable stratification. A simple analytic version of the model links the strength, shape, and direction of the alternating zonal currents on Jupiter and Saturn to a single parameter equivalent to the internal deformation scale for an inferred deep stable region.

Allison, Michael↗

NASA NTRS2012

Estimating Climatological Bias Errors for the Global Precipitation Climatology Project (GPCP)

A procedure is described to estimate bias errors for mean precipitation by using multiple estimates from different algorithms, satellite sources, and merged products. The Global Precipitation Climatology Project (GPCP) monthly product is used as a base precipitation estimate, with other input products included when they are within +/- 50% of the GPCP estimates on a zonal-mean basis (ocean and land separately). The standard deviation s of the included products is then taken to be the estimated systematic, or bias, error. The results allow one to examine monthly climatologies and the annual climatology, producing maps of estimated bias errors, zonal-mean errors, and estimated errors over large areas such as ocean and land for both the tropics and the globe. For ocean areas, where there is the largest question as to absolute magnitude of precipitation, the analysis shows spatial variations in the estimated bias errors, indicating areas where one should have more or less confidence in the mean precipitation estimates. In the tropics, relative bias error estimates (s/m, where m is the mean precipitation) over the eastern Pacific Ocean are as large as 20%, as compared with 10%-15% in the western Pacific part of the ITCZ. An examination of latitudinal differences over ocean clearly shows an increase in estimated bias error at higher latitudes, reaching up to 50%. Over land, the error estimates also locate regions of potential problems in the tropics and larger cold-season errors at high latitudes that are due to snow. An empirical technique to area average the gridded errors (s) is described that allows one to make error estimates for arbitrary areas and for the tropics and the globe (land and ocean separately, and combined). Over the tropics this calculation leads to a relative error estimate for tropical land and ocean combined of 7%, which is considered to be an upper bound because of the lack of sign-of-the-error canceling when integrating over different areas with a different number of input products. For the globe the calculated relative error estimate from this study is about 9%, which is also probably a slight overestimate. These tropical and global estimated bias errors provide one estimate of the current state of knowledge of the planet's mean precipitation.

Global Precipitation Climatology Project (GPCP)↗

NASA NTRS1988

How many upper Eocene microspherule layers: More than we thought

The scientific controversy over the origin of upper Eocene tektites, microtektites and other microspherules cannot be logically resolved until it is determined just how many events are involved. The microspherule-bearing beds in marine sediments have been dated using standard biozonal techniques. Although a powerful stratigraphic tool, zonal biostratigraph has its limitations. One is that if an event, such as a microspherule occurrence, is observed to occur in a zone at one locality and then a similar event observed in the same zone at another locality, it still may be unwarranted to conclude that these events exactly correlate. To be in a zone a sample only need be between the fossil events that define the zone boundaries. It is often very difficult to accurately determine where within a zone one might be. Further, the zone defining events do not everywhere occur at the same points in time. That is, the ranges of the defining taxa are not always filled. Thus, the length of time represented by a zone (but not, of course, its chronozone) can vary from place to place. These problems can be offset by use of chronostratigraphic modelling techniques such as Graphic Correlation. This technique was used to build a Cretaceous and Cenozoic model containing fossil, magnetopolarity, and other events. The scale of the model can be demonstrated to be linear with time. This model was used to determine the chronostratigraphic position of upper Eocene microspherule layers.

Hazel, Joseph E.↗

NASA NTRS1993

Implementation of the Baldwin-Barth turbulence model into the ZETA code and its diagnosis

The Baldwin-Barth turbulence model was implemented into Zeta, a time-accurate, zonal, integro-differential code for incompressible laminar and turbulent flows. The implementation procedure is patterned after the model subroutine in ARC2D. The results of ZETA with the Baldwin-Barth turbulence model were compared with experimental data, with ZETA using Baldwin-Lomax model, and with ARC2D using the Baldwin-Barth model. The Baldwin-Barth model subroutine was tested by inputting an ARC2D velocity solution of an NACA-0012 airfoil at R(sub e) = 3.9 x 10(exp 6) and alpha = 5 deg. The resultant turbulent viscosity and Reynolds stresses compared favorably with the original data. For the same grid having grid points inside the laminar sublayer, which is necessary due to the one-equation nature of the model, ZETA however predicts early separation. It was found that the current ZETA has problem with such a fine grid. Further work is in progress to solve this problem.

Low, Scott L.↗

NASA NTRS1993

Analyzing Martian winds and tracer concentrations using Mars Observer data

During the courses of a day, the Mars Observer spacecraft will acquire globally distributed profiles of the martian atmosphere. It is highly desirable that this data be assembled into synoptic weather maps (complete specifications of the atmospheric pressure, temperature, and winds at a given time), which can in turn be used as starting points in the study of many meteorological phenomena. Unfortunately, the special nature of the Mars Observer data presents several challenges above and beyond the usual difficult problem of data initialization. Mars Observer atmospheric data will consist almost exclusively of asynoptic vertical profiles of temperatures (or radiances) and pressures, whereas winds are generally in balance with horizontal gradients of these quantities (which will not be observed). It will therefore be necessary to resort to dynamical models to analyze the wind fields. As a rule, data assimilation into atmospheric models can result in the generation of spurious gravity waves, so special steps must be taken to suppress these. In addition, the asynoptic nature of the data will require a four-dimensional (space and time) data assimilation scheme. The problem is to find a full set of meteorological fields (winds and temperatures) such that, when marched forward in time in the model, they achieve a best fit (in the weighted least-squares sense) to the data. The proposed solution is to develop a model especially for the Mars Observer data assimilation problem. Gravity waves are filtered from the model by eliminating all divergence terms from the prognostic divergence equation. This leaves a diagnostic gradient wind relation between the rotational wind and the temperature field. The divergent wind is diagnosed as the wind required to maintain the gradient wind balance in the presence of the diabatic heating. The primitive equations of atmospheric dynamics (with three principal dependent variables) are thus reduced to a simpler system with a single prognostic equation for temperature - the variable that will be best observed. (This balance system was apparently first derived by Charney as a first-order Rossby number expansion of the equations of motion). Experience with a full primitive equation model of the martian atmosphere indicates that a further simplification is possible: at least for short-term integrations, the model can be linearized about the zonally symmetric basic state.

Houben, Howard C.↗

NASA NTRS1994

Global QBO in circulation and ozone. Part 2: A simple mechanistic model

Although the phenomenon of equatorial quasi-biennial oscillation is relatively well understood, the problem of how the equatorially confined quasi-biennial oscillation (QBO) wave forcing can induce a signal in the extratropics of comparable or larger magnitude remains unsolved. A simple mechanistic model is constructed to provide a quantitative test of the hypothesis that the phenomenon of extratropical QBO is mainly caused by an anomalous seasonal circulation induced by an anomalous Eliassen-Palm (E-P) flux divergence. The anomaly in E-P flux divergence may be caused in turn by the relative poleward and downward shift of the region of irreversible mixing (breaking) of the extratropical planetary waves during the easterly phase of the equatorial QBO as compared to its westerly phase. The hemispheric nature of the anomaly wave forcing in solstice seasons (viz., no wave breaking in the summer hemisphere) induces a global circulation anomaly that projects predominantly into the first few zonal Hough modes of Plumb. Such a global QBO circulation pattern, although difficult to measure directly, is reflected in the distribution of stratospheric tracers transported by it. Our model produces a global pattern of QBO anomaly in column ozone that appears to account for much of the unfiltered interannual variability in the column ozone observed by the total ozone mapping spectrometer (TOMS) instrument aboard the Nimbus satellite. Furthermore, the model produces the characteristic spectrum of the observation with peaks at periods of 20 and 30 months.

Tung, K. K.↗

NASA NTRS2019

Efficient computation of optimal low thrust gravity perturbed orbit transfers

We have developed a new method for solving low-thrust fuel-optimal orbit transfer problems in the vicinity of a large body (planet or asteroid), considering a high-fidelity spherical harmonic gravity model. The algorithm is formulated via the indirect optimization method, leading to a two-point boundary value problem (TPBVP). We make use of a hyperbolic tangent smoothing law for performing continuation on the thrust magnitude to reduce the sharpness of the control switches in early iterations and thus promote convergence. The TPBVP is solved using the method of particular solutions (MPS) shooting method and Picard-Chebyshev numerical integration. Application of Picard-Chebyshev integration affords an avenue for increased efficiency that is not available with step-by-step integrators. We demonstrate that computing the particular solutions with only a low-fidelity force model greatly increases the efficiency of the algorithm while ultimately achieving near machine precision accuracy. A salient feature of the MPS is that it is parallelizable, and thus further speedups are available. It is also shown that, for near Earth orbits and over a small number of en-route revolutions around the Earth, only the zonal perturbation terms are required in the costate equations to obtain a solution that is accurate to machine precision and optimal to engineering precision. The proposed framework can be used for trajectory design around small asteroids and also for orbit debris rendezvous and removal tasks.

Junkins, John L.↗

NASA NTRS2001

Venus Multiprobe Mission

A summary of the proposal for the Discovery Program Venus Multiprobe Mission (VMPM) which was submitted in 1994 will be presented. The major goal of the mission was to provide sufficient observations of winds and thermal structure in the Venus atmosphere that the mechanism producing the atmospheric superrotation could be identified. The superrotation has been a major unsolved problem of planetary science for over 30 years. In spite of many theoretical efforts and many spacecraft missions to Venus, the principal driving mechanism(s) remain undetermined. Sixteen small probes, modeled after the Pioneer Venus small probes, would enter the Venus atmosphere, and measure winds, temperatures, and pressures from 60 km to the surface. Towards the bottom of the atmosphere, measurements would be made at 10 meter intervals. Temperature and pressure measurements are similar to those used on Pioneer Venus, but are four times more sensitive. Winds would be obtained by dual-frequency, differential. long-baseline interferometry, using S- and X-band transmitters on the probes, and four receiving telescopes round the Pacific rim. The precision of wind measurements is 0.05 ms- 1 or better, at least twenty times more precise than for Pioneer Venus. Ground based observations occurring in conjunction with the multiprobe entries would provide a temporal context for the upper boundary to the probe observations. UV and near IR features would be tracked for periods of hours to weeks to obtain cloud level zonal mean and transient eddy circulations with accuracies of 10 /ms or better. The data would be processed into wind and opacity maps. A hierarchy of atmospheric numerical models would be used to distinguish different dynamical elements existing in the data. Primary among the models was the development of a Venus general circulation model containing all known physical processes.

Young, Richard E.↗

NASA NTRS2002

Individual thermal profiles as a basis for comfort improvement in space and other environments

BACKGROUND: The development of individualized countermeasures to address problems in thermoregulation is of considerable importance for humans in space and other extreme environments. A methodology is presented for evaluating minimal/maximal heat flux from the total human body and specific body zones, and for assessing individual differences in the efficiency of heat exchange from these body areas. The goal is to apply this information to the design of individualized protective equipment. METHODS: A multi-compartment conductive plastic tubing liquid cooling/warming garment (LCWG) was developed. Inlet water temperatures of 8-45 degrees C were imposed sequentially to specific body areas while the remainder of the garment was maintained at 33 degrees C. RESULTS: There were significant differences in heat exchange level among body zones in both the 8 degrees and 45 degrees C temperature conditions (p < 0.001). The greatest amount of heat was absorbed/released by the following areas: thighs (8 degrees C: -2.12 +/- 0.14 kcal min(-1); 45 degrees C: +1.58 +/- 0.23); torso (8 degrees C: -2.12 +/- 0.13 kcal min(-1); 45 degrees C: +1.31 +/- 0.27); calves (8 degrees C: -1.59 +/- 0.26 kcal min(-1); 45 degrees C: +1.53 +/- 0.24); and forearms (8 degrees C: -1.67 +/- 0.29 kcal x min(-1); 45 degrees C: +1.45 +/- 0.20). These are primarily zones with relatively large muscle mass and adipose tissue. Calculation of absorption/release heat rates standardized per unit tube length and flow rate instead of zonal surface area covered showed that there was significantly greater heat transfer in the head, hands, and feet (p < 0.001). The areas in which there was considerable between-subject variability in rates of heat transfer and thus most informative for individual profile design were the torso, thighs, shoulders, and calves or forearms. CONCLUSIONS: The methodology developed is sensitive to individual differences in the process of heat exchange and variations in different body areas, depending on their size and tissue mass content. The design of individual thermal profiles is feasible for better comfort of astronauts on long-duration missions and personnel in other extreme environments.

NASA Discipline Life Sciences Technologies↗

NASA NTRS2012

Highlights of TOMS Version 9 Total Ozone Algorithm

The fundamental basis of TOMS total ozone algorithm was developed some 45 years ago by Dave and Mateer. It was designed to estimate total ozone from satellite measurements of the backscattered UV radiances at few discrete wavelengths in the Huggins ozone absorption band (310-340 nm). Over the years, as the need for higher accuracy in measuring total ozone from space has increased, several improvements to the basic algorithms have been made. They include: better correction for the effects of aerosols and clouds, an improved method to account for the variation in shape of ozone profiles with season, latitude, and total ozone, and a multi-wavelength correction for remaining profile shape errors. These improvements have made it possible to retrieve total ozone with just 3 spectral channels of moderate spectral resolution (approx. 1 nm) with accuracy comparable to state-of-the-art spectral fitting algorithms like DOAS that require high spectral resolution measurements at large number of wavelengths. One of the deficiencies of the TOMS algorithm has been that it doesn't provide an error estimate. This is a particular problem in high latitudes when the profile shape errors become significant and vary with latitude, season, total ozone, and instrument viewing geometry. The primary objective of the TOMS V9 algorithm is to account for these effects in estimating the error bars. This is done by a straightforward implementation of the Rodgers optimum estimation method using a priori ozone profiles and their error covariances matrices constructed using Aura MLS and ozonesonde data. The algorithm produces a vertical ozone profile that contains 1-2.5 pieces of information (degrees of freedom of signal) depending upon solar zenith angle (SZA). The profile is integrated to obtain the total column. We provide information that shows the altitude range in which the profile is best determined by the measurements. One can use this information in data assimilation and analysis. A side benefit of this algorithm is that it is considerably simpler than the present algorithm that uses a database of 1512 profiles to retrieve total ozone. These profiles are tedious to construct and modify. Though conceptually similar to the SBUV V8 algorithm that was developed about a decade ago, the SBUV and TOMS V9 algorithms differ in detail. The TOMS algorithm uses 3 wavelengths to retrieve the profile while the SBUV algorithm uses 6-9 wavelengths, so TOMS provides less profile information. However both algorithms have comparable total ozone information and TOMS V9 can be easily adapted to use additional wavelengths from instruments like GOME, OMI and OMPS to provide better profile information at smaller SZAs. The other significant difference between the two algorithms is that while the SBUV algorithm has been optimized for deriving monthly zonal means by making an appropriate choice of the a priori error covariance matrix, the TOMS algorithm has been optimized for tracking short-term variability using month and latitude dependent covariance matrices.

Bhartia, Pawan↗