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At least 415 records · Page 23

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NASA NTRS1989

Methodology for analysis and simulation of large multidisciplinary problems

The Integrated Structural Modeling (ISM) program is being developed for the Air Force Weapons Laboratory and will be available for Air Force work. Its goal is to provide a design, analysis, and simulation tool intended primarily for directed energy weapons (DEW), kinetic energy weapons (KEW), and surveillance applications. The code is designed to run on DEC (VMS and UNIX), IRIS, Alliant, and Cray hosts. Several technical disciplines are included in ISM, namely structures, controls, optics, thermal, and dynamics. Four topics from the broad ISM goal are discussed. The first is project configuration management and includes two major areas: the software and database arrangement and the system model control. The second is interdisciplinary data transfer and refers to exchange of data between various disciplines such as structures and thermal. Third is a discussion of the integration of component models into one system model, i.e., multiple discipline model synthesis. Last is a presentation of work on a distributed processing computing environment.

Russell, William C.↗

NASA NTRS1993

Experimental aerodynamic characteristics of a generic hypersonic accelerator configuration at Mach numbers 1.5 and 2.0

An experimental investigation of the static longitudinal and lateral-directional aerodynamic characteristics of a generic hypersonic research vehicle was conducted in the Langley Unitary Plan Wind Tunnel (UPWT). A parametric study was performed to determine the interference effects of various model components. Configuration variables included delta and trapezoidal canards; large and small centerline-mounted vertical tails, along with a set of wing-mounted vertical tails; and a set of model noses with different degrees of bluntness. Wing position was varied by changing the longitudinal location and the incidence angle. The test Mach numbers were 1.5 and 2.0 at Reynolds numbers of 1 x 10(exp 6) per foot, 2 x 10(exp 6) per foot, and 4 x 10(exp 6) per foot. Angle of attack was varied from -4 degrees to 27 degrees, and sideslip angle was varied from -8 degrees to 8 degrees. Generally, the effect of Reynolds number did not deviate from conventional trends. The longitudinal stability and lift-curve slope decreased with increasing Mach number. As the wing was shifted rearward, the lift-curve slope decreased and the longitudinal stability increased. Also, the wing-mounted vertical tails resulted in a more longitudinally stable configuration. In general, the lift-drag ratio was not significantly affected by vertical-tail arrangement. The best lateral-directional stability was achieved with the large centerline-mounted tail, although the wing-mounted vertical tails exhibited the most favorable characteristics at the higher angles of attack.

Walker, Ira J.↗

NASA NTRS2011

Deep UV Luminosity Functions at the Infall Region of the Coma Cluster

We have used deep GALEX observations at the infall region of the Coma cluster to measure the faintest UV luminosity functions (LFs) presented for a rich galaxy cluster thus far. The Coma UV LFs are measured to M(sub uv) = -10.5 in the GALEX FUV and NUV bands, or 3.5 mag fainter than previous studies, and reach the dwarf early-type galaxy population in Coma for the first time. The Schechter faint-end slopes (alpha approximately equal to -1.39 in both GALEX bands) are shallower than reported in previous Coma UV LF studies owing to a flatter LF at faint magnitudes. A Gaussian-plus-Schechter model provides a slightly better parametrization of the UV LFs resulting in a faint-end slope of alpha approximately equal to -1.15 in both GALEX bands. The two-component model gives faint-end slopes shallower than alpha = -1 (a turnover) for the LFs constructed separately for passive and star forming galaxies. The UV LFs for star forming galaxies show a turnover at M(sub UV) approximately equal to -14 owing to a deficit of dwarf star forming galaxies in Coma with stellar masses below M(sub *) = 10(sup 8) solar mass. A similar turnover is identified in recent UV LFs measured for the Virgo cluster suggesting this may be a common feature of local galaxy clusters, whereas the field UV LFs continue to rise at faint magnitudes. We did not identify an excess of passive galaxies as would be expected if the missing dwarf star forming galaxies were quenched inside the cluster. In fact, the LFs for both dwarf passive and star forming galaxies show the same turnover at faint magnitudes. We discuss the possible origin of the missing dwarf star forming galaxies in Coma and their expected properties based on comparisons to local field galaxies.

Hammer, D. M.↗

NASA NTRS1994

Two-temperature X-ray emission from the planetary nebula NGC 7293

ROSAT Position Sensitive Proportional Counter (PSPC) observations of the planetary nebula NGC are reported here. This planetary nebula is here the first discovered to show clearly two components in its X-ray spectrum. A two-component model consisting of a blackbody and a Raymond-Smith thermal plasma is fitted to the observed ROSAT PSPC spectrum. This results in a temperature of T(sub 1) = 1.4 x 10(exp 5) K for the blackbody component and a temperature T(sub 2) = 8.7 x 10(exp 6) K for the hot plasma component, at a hydrogen column density N(sub H) = 1.4 x 10(exp 20)/sq cm. The temperature of the blackbody component is consistent with the helium Zanstra temperature of the central star, indicating that it may be attributed to the photosphere of the central star. The high-temperature component is possibly from a corona around the central star, which may be related to a strong convection in the star. An alternative explanation is that the hot plasma resides in a hot bubble predicted by the interacting wind model. A lower limit of the electron density in the hot plasma is found to be approximately 10/cu cm.

Leahy, D. A.↗

NASA NTRS1980

Equivalent source modeling of the main field using MAGSAT data

The software was considerably enhanced to accommodate a more comprehensive examination of data available for field modeling using the equivalent sources method by (1) implementing a dynamic core allocation capability into the software system for the automatic dimensioning of the normal matrix; (2) implementing a time dependent model for the dipoles; (3) incorporating the capability to input specialized data formats in a fashion similar to models in spherical harmonics; and (4) implementing the optional ability to simultaneously estimate observatory anomaly biases where annual means data is utilized. The time dependence capability was demonstrated by estimating a component model of 21 deg resolution using the 14 day MAGSAT data set of Goddard's MGST (12/80). The equivalent source model reproduced both the constant and the secular variation found in MGST (12/80).

Source record↗

NASA NTRS1993

Implementation of the block-Krylov boundary flexibility method of component synthesis

A method of dynamic substructuring is presented which utilizes a set of static Ritz vectors as a replacement for normal eigenvectors in component mode synthesis. This set of Ritz vectors is generated in a recurrence relationship, which has the form of a block-Krylov subspace. The initial seed to the recurrence algorithm is based on the boundary flexibility vectors of the component. This algorithm is not load-dependent, is applicable to both fixed and free-interface boundary components, and results in a general component model appropriate for any type of dynamic analysis. This methodology was implemented in the MSC/NASTRAN normal modes solution sequence using DMAP. The accuracy is found to be comparable to that of component synthesis based upon normal modes. The block-Krylov recurrence algorithm is a series of static solutions and so requires significantly less computation than solving the normal eigenspace problem.

Carney, Kelly S.↗

NASA NTRS1995

The Unusual X-Ray Collision Morphology of NGC 4782/4783 (3C 278)

Deep ROSAT HRI (High-Resolution Imager) imaging of the X-ray-emitting gas associated with the colliding elliptical galaxy pair NGC 4782/4783 reveals for the first time the complexity of the hot gas distribution in a pair of close interacting galaxies. The HRI image of NGC 4782/4783 shows hot gas around each galaxy, a high surface brightness X-ray bridge connecting the galaxy pair, tidal-like tails emerging from the two galaxies, and a sheet of gas at the interaction interface between the two galaxies. The hot gas distributions do not peak at the optical centers of the galaxies but are displaced in the same sense as the tidal distensions seen in the optical luminosity distributions. All of these remarkable features show the complexity of structure that develops in the hot gas distribution when both hydrodynamical and tidal forces come into play during collisions between ellipticals with hot gas components. Models by Borne and Colina of the bent two-sided radio jet 3C 278 (associated with NGC 4782) indicated that there must be a strong interaction between the hot gas components of NGC 4782,/4783 and that the deflection of the radio jets is likely caused by the ram pressure exerted on the jet plasma by the hot gas associated with the passing companion NGC 4783. These conclusions are qualitatively confirmed by the HRI image and substantiate the major role played by the hot interstellar medium, and its asymmetries, in the propagation and entrainment of radio jets in colliding radio host ellipticals.

Colina, Luis↗

NASA NTRS2009

Assessing the Uncertainty of Land Surface Fluxes Derived from Operational Analyses

Operational numerical weather prediction systems assimilate tremendous amounts of observations to produce global analyses of the atmospheric states. Since the systems include significant contributions from the model components, physical fields, such as the turbulent heat fluxes, can also be derived. However, the physical fields are indirectly constrained by the data assimilation, and so subject to uncertainty in the model parameterizations. Recently, 10 international operational analyses have been collected and reprocessed through the Coordinated Enhanced. Observing Period (CEOP). Comparisons against independent observations (global precipitation and outgoing longwave radiation) show that while there is significant range of the individual analyses, the ensemble of analyses provide data closest the observations. Here, we evaluate the collection of land surface turbulent heat fluxes. The data are available for Oct 2002 - Dec 2004, at 6 hourly, daily and monthly intervals. An ensemble mean and its variance have been computed. we will analyze the range of analysis results at daily and seasonal time scales, and where possible compare with existing observations.

Bosilovich, Michael G.↗

NASA NTRS2020

MPAS - Ocean Simulation Quality for Variable-Resolution North American Coastal Meshes

Climate model components utilizing unstructured meshes enable variableresolution, regionally enhanced simulations within global domains. Here we investigate the relationship between mesh quality and simulation statistics using the JIGSAW unstructured meshing library and the Model for Prediction Across ScalesOcean (MPASOcean) with a focus on Gulf Stream dynamics. In the base configuration, the refined region employs 8 km cells that extend 400 km from the coast of North America. This coastal refined region is embedded within a lowresolution global domain, with cell size varying latitudinally between 30 and 60 km. The resolution transition region between the refined region and background mesh is 600 km wide. Three sensitivity tests are conducted: 1) the quality of meshes is intentionally degraded so that horizontal cells are progressively more distorted; 2) the transition region from high to low resolution is steepened; and 3) resolution of the coastal refinement region is varied from 30 km to 8 km. Overall, the ocean simulations are shown to be robust to mesh resolution and quality alterations. Meshes that are substantially degraded still produce realistic currents, with Southern Ocean transports within 0.4% and Gulf Stream transports within 12% of highquality mesh results. The narrowest transition case of 100 km did not produce any spurious effects. Refined regions with high resolution produce eddy kinetic energy and sea surface height variability that are similar to the highresolution reference simulation. These results provide heuristics for the design criteria of variableresolution climate model domains.

Hoch, Kristin E.↗

NASA NTRSDate not supplied

TPSAS-NF1676L-33512-DND

INTRODUCTION: In an effort to quantify the predictive capability of the Livermore Software Technology Corporation (LSTC)-provided Hybrid III (small female, mid-size male, and large male) anthropomorphic test device (ATD) finite element models (FEMs) within aerospace loading environments, the National Aeronautics and Space Administration (NASA) performed a series of sled tests with the isolated head-neck complex of each ATD. These tests and subsequent modeling efforts revealed significant deficiencies in the large male head neck FEM. Differences in both the shape and material properties between the FEM and the physical ATD were identified. In order to improve the predictive response of the FEM, a model development effort was undertaken to update the head-neck complex to better represent the geometric and material properties of the physical ATD.METHODS: To better match the physical geometry, a new neck component model was meshed and implemented into the Hybrid III large male head-neck complex. The updated geometry and weight were verified against measurements of the physical ATD to insure accuracy. The primary source of material discrepancy between the physical ATD and FEM was found to be in the material definition of the rubber neck pucks. Using LS-Opt the material properties of this part were calibrated to match physical response of the head-neck complex in the isolated head-neck testing performed. RESULTS AND DISCUSSION: The updated geometry and calibrated material properties were shown to significantly improve the FEM predictive accuracy under lateral, rear, and frontal impacts with combined horizontal and vertical loading. The results of this study demonstrate an effective means for improving ATD FEM response through isolated component level testing and material parameter optimization. The improved and quantified accuracy of the Hybrid III large male FEM head-neck complex stemming from with work lends to confidence in its future use for occupant protection evaluation of large male occupants

J Putnam↗

DOE OSTI2021

Using Machine Learning to Develop a Predictive Understanding of the Impacts of Extreme Water Cycle Perturbations on River Water Quality

This whitepaper addresses to two focal areas – (3) Insight gleaned from complex data using Artificial Intelligence (AI), and other advanced techniques (primary), and (2) Predictive modeling through the use of AI techniques and AI-derived model components (secondary). This topic is directly relevant to four DOE Earth and Environmental Systems Science Division Grand Challenges: integrated water cycle, biogeochemistry, drivers and responses in the Earth system, and data-model integration.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2021

The radio loudness of SDSS quasars from the LOFAR Two-metre Sky Survey: ubiquitous jet activity and constraints on star formation

ABSTRACT We examine the distribution of radio emission from ∼42 000 quasars from the Sloan Digital Sky Survey, as measured in the LOFAR Two-metre Sky Survey (LoTSS). We present a model of the radio luminosity distribution of the quasars that assumes that every quasar displays a superposition of two sources of radio emission: active galactic nuclei (jets) and star formation. Our two-component model provides an excellent match to the observed radio flux density distributions across a wide range of redshifts and quasar optical luminosities; this suggests that the jet-launching mechanism operates in all quasars but with different powering efficiency. The wide distribution of jet powers allows for a smooth transition between the ‘radio-quiet’ and ‘radio-loud’ quasar regimes, without need for any explicit bimodality. The best-fitting model parameters indicate that the star formation rate of quasar host galaxies correlates strongly with quasar luminosity and also increases with redshift at least out to z ∼ 2. For a model where star formation rate scales as $L_{\rm bol}^{\alpha } (1+z)^{\beta }$, we find α = 0.47 ± 0.01 and β = 1.61 ± 0.05, in agreement with far-infrared studies. Quasars contribute ≈0.15 per cent of the cosmic star formation rate density at z = 0.5, rising to 0.4 per cent by z ∼ 2. The typical radio jet power is seen to increase with both increasing optical luminosity and black hole mass independently, but does not vary with redshift, suggesting intrinsic properties govern the production of the radio jets. We discuss the implications of these results for the triggering of quasar activity and the launching of jets.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2010

J-2X Turbopump Cavitation Diagnostics

The J-2X is the upper stage engine currently being designed by Pratt & Whitney Rocketdyne (PWR) for the Ares I Crew Launch Vehicle (CLV). Propellant supply requirements for the J-2X are defined by the Ares Upper Stage to J-2X Interface Control Document (ICD). Supply conditions outside ICD defined start or run boxes can induce turbopump cavitation leading to interruption of J-2X propellant flow during hot fire operation. In severe cases, cavitation can lead to uncontained engine failure with the potential to cause a vehicle catastrophic event. Turbopump and engine system performance models supported by system design information and test data are required to predict existence, severity, and consequences of a cavitation event. A cavitation model for each of the J-2X fuel and oxidizer turbopumps was developed using data from pump water flow test facilities at Pratt & Whitney Rocketdyne (PWR) and Marshall Space Flight Center (MSFC) together with data from Powerpack 1A testing at Stennis Space Center (SSC) and from heritage systems. These component models were implemented within the PWR J-2X Real Time Model (RTM) to provide a foundation for predicting system level effects following turbopump cavitation. The RTM serves as a general failure simulation platform supporting estimation of J-2X redline system effectiveness. A study to compare cavitation induced conditions with component level structural limit thresholds throughout the engine was performed using the RTM. Results provided insight into system level turbopump cavitation effects and redline system effectiveness in preventing structural limit violations. A need to better understand structural limits and redline system failure mitigation potential in the event of fuel side cavitation was indicated. This paper examines study results, efforts to mature J-2X turbopump cavitation models and structural limits, and issues with engine redline detection of cavitation and the use of vehicle-side abort triggers to augment the engine redline system.

Santi, I. Michael↗

NASA NTRS1998

Global Qualitative Flow-Path Modeling for Local State Determination in Simulation and Analysis

For qualitative modeling and analysis, a general qualitative abstraction of power transmission variables (flow and effort) for elements of flow paths includes information on resistance, net flow, permissible directions of flow, and qualitative potential is discussed. Each type of component model has flow-related variables and an associated internal flow map, connected into an overall flow network of the system. For storage devices, the implicit power transfer to the environment is represented by "virtual" circuits that include an environmental junction. A heterogeneous aggregation method simplifies the path structure. A method determines global flow-path changes during dynamic simulation and analysis, and identifies corresponding local flow state changes that are effects of global configuration changes. Flow-path determination is triggered by any change in a flow-related device variable in a simulation or analysis. Components (path elements) that may be affected are identified, and flow-related attributes favoring flow in the two possible directions are collected for each of them. Next, flow-related attributes are determined for each affected path element, based on possibly conflicting indications of flow direction. Spurious qualitative ambiguities are minimized by using relative magnitudes and permissible directions of flow, and by favoring flow sources over effort sources when comparing flow tendencies. The results are output to local flow states of affected components.

Malin, Jane T.↗

DOE OSTI2024

A Prefire Approach for Probabilistic Assessments of Postfire Debris‐Flow Inundation

Increases in wildfire activity and rainfall intensification are driving more postfire debris flows (PFDF) in many regions around the world. PFDFs are most common in the first postfire year and may even occur before a fire is fully controlled. This underscores the importance of assessing postfire hazards before a fire starts. Evaluation of PFDF hazards prior to fire can help strategize interventions lessening the negative effects of future fires. However, debris-flow runout and inundation analyses are not routine in PFDF hazard assessments, partially due to time constraints and substantial uncertainties in boundary conditions. Here, we propose a prefire PFDF inundation assessment framework using a debris-flow runout model based on the Herschel-Bulkley (HB) rheology (HEC-RAS v6.1). We constrain model inputs and parameters using Bayesian posterior analysis, rainfall-runoff simulations, and a debris-flow volume model. We use observations from recent PFDF incidents in northern Arizona, USA, to calibrate model components and then apply our prefire inundation assessment framework in a nearby unburned area. Specifically, we (a) identify yield stress as the most influential factor on inundation extent and arrival time in a HB model, (b) establish posterior distributions for model parameters suitable for forward modeling by leveraging uncertainties in field observations, and (c) implement a predictive forward analysis in an area that has not burned recently to evaluate PFDF inundation under several future fire scenarios. This study improves our ability to assess postfire debris-flow hazards before a fire begins and provides guidance for future applications of single-phase rheological models when assessing PFDF hazards.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2024

A Prefire Approach for Probabilistic Assessments of Postfire Debris-Flow Inundation

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1980

A Mathematical Model for Vertical Attitude Takeoff and Landing (VATOL) Aircraft Simulation: Model Description Application - Volume 1

A mathematical model of a high performance airplane capable of vertical attitude takeoff and landing (VATOL) was developed. An off line digital simulation program incorporating this model was developed to provide trim conditions and dynamic check runs for the piloted simulation studies and support dynamic analyses of proposed VATOL configuration and flight control concepts. Development details for the various simulation component models and the application of the off line simulation program, Vertical Attitude Take-Off and Landing Simulation (VATLAS), to develop a baseline control system for the Vought SF-121 VATOL airplane concept are described.

Fortenbaugh, R. L.↗

DOE OSTI2021

NRAP-Open-IAM Analytical Reservoir Model: Development and Testing

Geological carbon sequestration (GCS) is a key technology for reducing global carbon dioxide (CO 2 ) emissions. Over the last decade, the U.S. Department of Energy has invested in understanding the science base, developing practical implementation methods, and demonstrating secure GCS technologies to mitigate the environmental impacts associated with the atmospheric release of CO 2 . As part of the National Risk Assessment Partnership, a systems-level risk assessment tool, called the NRAP-Open-IAM, has been developed to conduct risk assessment and enable safe operations at a GCS site. The current NRAP-Open-IAM contains a simple reservoir model component that calculates the evolution of CO 2 saturation and fluid pressure in a storage reservoir during CO 2 injection operations. This report presents the development and testing of a new analytical reservoir reduced-order model (ROM), which is extended from an existing semi-analytical model for estimation of CO 2 and brine leakage along legacy wells, and enhances the capability of the NRAP-Open-IAM to simulate more types of reservoir conditions. The developed model is validated against three reference studies, and the results indicate that the new ROM predicts the behavior of the two-phase fluids (brine and injected CO 2 ) well and is applicable to different reservoir simulation boundary conditions (i.e., constant pressure boundary and infinite-acting boundary) without a priori user specification of the boundary type. Sensitivity analysis for a set of model parameters is performed using 4,000 synthetic cases prepared via a fully automated process and using machine-learning-based feature selection. The stochastic analysis identifies gravitational number (i.e., ratio of gravitational forces to viscous force) and distance between the injection well and observation location as the most impactful parameters for matching the pressure and CO 2 saturation, respectively, between the numerical simulations and the ROM. This report details the possible ROM uncertainties and serves as a guide for users to understand the use and limitations of this ROM. The code implementation of the model will be released as a module within the NRAP-Open-IAM.

54 ENVIRONMENTAL SCIENCES↗