Search NASA⌕ Search

SEARCH · Search NASA

Results for “Model initialization”

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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

A Technique for Assimilating GOES-Derived Land Surface Products into Regional Models to Improve the Representation of Land Surface Forcing

As the parameterizations of surface energy budgets in regional models have become more complete physically, models have the potential to be much more realistic in simulations of coupling between surface radiation, hydrology, and surface energy transfer. Realizing the importance of properly specifying the surface energy budget, many institutions are using land-surface models to represent the lower boundary forcing associated with biophysical processes and soil hydrology. However, the added degrees of freedom due to inclusion of such land-surface schemes require the specification of additional parameters within the model system such as vegetative resistances, green vegetation fraction, leaf area index, soil physical and hydraulic characteristics, stream flow, runoff, and the vertical distribution of soil moisture. A technique has been developed for assimilating GOES-IR skin temperature tendencies into the surface energy budget equation of a mesoscale model so that the simulated rate of temperature change closely agrees with the satellite observations. A critical assumption of the technique is that the availability of moisture (either from the soil or vegetation) is the least known term in the model's surface energy budget. Therefore, the simulated latent heat flux, which is a function of surface moisture availability, is adjusted based upon differences between the modeled and satellite-observed skin temperature tendencies. An advantage of this technique is that satellite temperature tendencies are assimilated in an energetically consistent manner that avoids energy imbalances and surface stability problems that arise from direct assimilation of surface shelter temperatures. The fact that the rate of change of the satellite skin temperature is used rather than the absolute temperature means that sensor calibration is not as critical. An advantage of this technique for short-range forecasts is that it does not require a complex land-surface formulation within the atmospheric model. As a result, the need to specify poorly known soil and vegetative characteristics is eliminated. The GOES assimilation technique has been incorporated into the PSU/NCAR MM5. Results will be presented to demonstrate the ability of the assimilation scheme to improve short-term simulations of near-surface air temperature and mixing ratio during the warm season for several selected cases during June of 1995 and June 1997 which exhibit a variety of atmospheric and land-surface conditions. In addition, the simulations produced by the assimilation technique will be compared with those produced by the MM5/BATS coupled model initialized with soil water content derived from a soil hydrology model.

Lapenta, William M.↗
NASA NTRSDate not supplied

Challenges in Understanding Radiation Belt Dynamics: Insights from Two Storm Periods

The periods of May 27 - June 5, 2017 and Oct 24 — 29, 2016 are 'unusual' in terms of radiation belt dynamics and their solar wind driving conditions. The first period was under the influence of a slow CME-led major geomagnetic storm with Dstmin = -125 nT and the second period was under high speed solar wind streams. Observations from Van Allen Probes show great variabilities in different electron energy channels for both periods. During the second period of Oct 24 - 29, 2016, electron fluxes are found to be near the highest upper limit among various storms during 2013–2018 (Hua, Bortnik and Ma, 2022). In this paper, we provide solar wind sources and geomagnetic conditions for these two storm periods and point out challenges in understanding, modeling, and forecasting radiation belt dynamics. In-depth analysis of modeling results utilizing radiation belt models available at the Community Coordinated Modeling Center such as VERB and CIMI will be performed. Initial modeling results indicate rather large discrepancies with the observations. Model validation using different metrics introduced in Zheng et al. (2019) will be carried out to gain a deeper understanding of the physical processes involved and to identity potential causes of modeling inadequacies.

Yihua Zheng↗
NASA NTRS1990

An AI-based approach to structural damage identification by modal analysis

Flexible-structure damage is presently addressed by a combined model- and parameter-identification approach which employs the AI methodologies of classification, heuristic search, and object-oriented model knowledge representation. The conditions for model-space search convergence to the best model are discussed in terms of search-tree organization and initial model parameter error. In the illustrative example of a truss structure presented, the use of both model and parameter identification is shown to lead to smaller parameter corrections than would be required by parameter identification alone.

Glass, B. J.↗
NASA NTRS2015

Face Sheet/Core Disbond Growth in Honeycomb Sandwich Panels Subjected to Ground-Air-Ground Pressurization and In-Plane Loading

Typical damage modes in light honeycomb sandwich structures include face sheet/core disbonding and core fracture, both of which can pose a threat to the structural integrity of a component. These damage modes are of particular interest to aviation certification authorities since several in-service occurrences, such as rudder structural failure and other control surface malfunctions, have been attributed to face sheet/core disbonding. Extensive studies have shown that face sheet/core disbonding and core fracture can lead to damage propagation caused by internal pressure changes in the core. The increasing use of composite sandwich construction in aircraft applications makes it vitally important to understand the effect of ground-air-ground (GAG) cycles and conditions such as maneuver and gust loads on face sheet/core disbonding. The objective of the present study was to use a fracture mechanics based approach developed earlier to evaluate the loading at the disbond front caused by ground-air-ground pressurization and in-plane loading. A honeycomb sandwich panel containing a circular disbond at one face sheet/core interface was modeled with three-dimensional (3D) solid finite elements. The disbond was modeled as a discrete discontinuity and the strain energy release rate along the disbond front was computed using the Virtual Crack Closure Technique (VCCT). Special attention was paid to the pressure-deformation coupling which can decrease the pressure load within the disbonded sandwich section significantly when the structure is highly deformed. The commercial finite element analysis software, Abaqus/Standard, was used for the analyses. The recursive pressure-deformation coupling problem was solved by representing the entrapped air in the honeycomb cells as filled cavities in Abaqus/Standard. The results show that disbond size, face sheet thickness and core thickness are important parameters that determine crack tip loading at the disbond front. Further, the pressure-deformation coupling was found to have an important load decreasing effect [6]. In this paper, a detailed problem description is provided first. Second, the analysis methodology is presented. The fracture mechanics approach used is described and the specifics of the finite element model, including the fluid-filled cavities, are introduced. Third, the initial model verification and validation are discussed. Fourth, the findings from a closely related earlier study [6] are summarized. These findings provided the basis for the current investigation. Fifth, an aircraft ascent scenario from 0 to 12192 m (0 to 40000 ft) is considered and the resulting crack tip loading at the disbond front is determined. In-plane loading to simulate maneuvers and gust conditions are also considered. Sixth, the results are shown for a curved panel, which was used to simulate potential fuselage applications. Finally, a brief summary of observations is presented and recommendations for improvement are provided.

Chen, Zhi M.↗
NASA NTRS2016

Magnetic Shield Design Modeling and Validation for SWOT Spacecraft Ka-Band Extended Interaction Klystron

Two Extended Interaction Klystrons (EIKs) containing strong permanent magnets were modeled magnetically in a representative spacecraft geometry using commercial finite element modeling techniques and were validated against measurements made at varying distances. Initial modeling results for the 63 A-m2 (amperes per square meter) dipole moment magnets showed that magnetic shields would be necessary in order to meet magnetic field requirements for the Surface Water and Ocean Topography (SWOT) spacecraft, which contains components that are susceptible to external DC (Direct Current) magnetic fields. JPL (Jet Propulsion Laboratory) and the EIK vendor proposed cold rolled steel and mu-metal as potential shield materials along with proposed thicknesses of 0.5 millimeters and 1.5 millimeters. Magnetic shields made from each of these materials were designed and modeled in software, taking high-field saturation into account. Prototype magnetic shields with these parameters were then built, measured with an existing EIK, and compared against modeling results. For single-axis field measurements along the dipole axis, modeling results were within 7 gauss of the measured values at 10 centimeters from the magnet, and converged to less than 1.5 gauss at distances greater than 14 centimeters from the magnet. Three-axis field measurements at locations of interest showed that model correlation improved to within 4 gauss at 11 centimeters and 2 gauss for distances ranging between 15 centimeters and 36 centimeters.

Gonzales, Edward↗
NASA NTRS2016

Magnetic Shield Design Modeling and Validation for SWOT Spacecraft Ka-Band Extended Interaction Klystron

Two Extended Interaction Klystrons (EIKs) containing strong permanent magnets were modeled magnetically in a representative spacecraft geometry using commercial finite element modeling techniques and were validated against measurements made at varying distances. Initial modeling results for the 63 A-m2 dipole moment magnets showed that magnetic shields would be necessary in order to meet magnetic field requirements for the Surface Water and Ocean Topography (SWOT) spacecraft, which contains components that are susceptible to external DC magnetic fields. JPL and the EIK vendor proposed cold rolled steel and mu-metal as potential shield materials along with proposed thicknesses of 0.5 mm and 1.5 mm. Magnetic shields made from each of these materials were designed and modeled in software, taking highfield saturation into account. Prototype magnetic shields with these parameters were then built, measured with an existing EIK, and compared against modeling results. For single-axis field measurements along the dipole axis, modeling results were within 7 gauss of the measured values at 10 cm from the magnet, and converged to less than 1.5 gauss at distances greater than 14 cm from the magnet. Three-axis field measurements at locations of interest showed that model correlation improved to within 4 gauss at 11 cm and 2 gauss for distances ranging between 15 cm and 36 cm.

Gonzales, Edward↗
NASA NTRS1987

High-resolution heat-transfer-coefficient maps applicable to compound-curve surfaces using liquid crystals in a transient wind tunnel

Tests were performed in a transient heat transfer tunnel in which the model under test was preheated prior to allowing room temperature air to be suddenly drawn over the model. The resulting movement of isothermal contours on the model is revealed using a surface coating of thermochromic liquid crystals that display distinctive colors at particular temperatures. A video record is obtained of a temperature and time data pair for all points on the model during a single test. Experiments on a duct model are reported in which the model was preheated using a hot air stream. A manner in which initial model temperature nonuniformities could be taken into account was investigated. The duct model was also tested with a steady-state measurement technique and results were compared with the transient measurements, but recognizing that differences existed between the upstream thermal boundary conditions. The steady-state and transient measurements were shown to be consistent with predicted values. The main advantage of this transient heat transfer technique using liquid crystals is that since the test model need not be actively heated, high-resolution measurements on surfaces with complex shapes may be obtained.

Jones, T. V.↗
NASA NTRS1988

High-resolution heat-transfer-coefficient maps applicable to compound-curve surfaces using liquid crystals in a transient wind tunnel

Tests were performed in a transient heat transfer tunnel in which the model under test was preheated prior to allowing room temperature air to be suddenly drawn over the model. The resulting movement of isothermal contours on the model is revealed using a surface coating of thermochromic liquid crystals that display distinctive colors at particular temperatures. A video record is obtained of a temperature and time data pair for all points on the model during a single test. Experiments on a duct model are reported in which the model was preheated using a hot air stream. A manner in which initial model temperature nonuniformities could be taken into account was investigated. The duct model was also tested with a steady-state measurement technique and results were compared with the transient measurements, but recognizing that differences existed between the upstream thermal boundary conditions. The steady-state and transient measurements were shown to be consistent with predicted values. The main advantage of this transient heat transfer technique using liquid crystals is that since the test model need not be actively heated, high-resolution measurements on surfaces with complex shapes may be obtained.

Jones, Terry V.↗
NASA NTRS2018

Ozone Sensitivity to Varying Greenhouse Gases and Ozone-Depleting Substances in CCMI-1 Simulations

Ozone fields simulated for the first phase of the Chemistry-Climate Model Initiative (CCMI-1) will be used as forcing data in the 6th Coupled Model Intercomparison Project. Here we assess, using reference and sensitivity simulations produced for CCMI-1, the suitability of CCMI-1 model results for this process, investigating the degree of consistency amongst models regarding their responses to variations in individual forcings. We consider the influences of methane, nitrous oxide, a combination of chlorinated or brominated ozone-depleting substances, and a combination of carbon dioxide and other greenhouse gases. We find varying degrees of consistency in the models' responses in ozone to these individual forcings, including some considerable disagreement. In particular, the response of total-column ozone to these forcings is less consistent across the multi-model ensemble than profile comparisons. We analyse how stratospheric age of air, a commonly used diagnostic of stratospheric transport, responds to the forcings. For this diagnostic we find some salient differences in model behaviour, which may explain some of the findings for ozone. The findings imply that the ozone fields derived from CCMI-1 are subject to considerable uncertainties regarding the impacts of these anthropogenic forcings. We offer some thoughts on how to best approach the problem of generating a consensus ozone database from a multi-model ensemble such as CCMI-1.

CCMI↗
NASA NTRS2018

GMI-IPS: Processing & Visualization Software Used in ATom DC-8 Aircraft Studies

NASA's Atmospheric Tomography Mission (ATom) deployed in each of the four seasons during 2016-2018, the DC-8 aircraft in order to establish global-scale datasets intended to improve the representation of chemically reactive gases in global atmospheric chemistry models (ACMs). The Global Modeling Initiative (GMI) executed simulations for each ATom flight using the GMI Chemistry Transport Model (GMI-CTM) to provide species concentrations of chemical gases along the DC-8 flight transects. To solve the problem of translating the GMI-CTM simulation data to the unique spatial resolutions of each ATom flight, the GMI ICARTT Processing Software (GMI-IPS) was developed.The GMI-IPS is written in Python and provides data processing, flight extraction, and visualization support for aircraft research projects using ICARTT format, which is a standard format for airborne instrument data. Additionally, the GMI-IPS interpolates global gridded model data from Hierarchical Data Format (HDF) to ICARTT compatible flight transects. Software classes for instruments and collections provided by the ATom DC-8 aircraft such as MER10, MMS, etc. are derived from a common base class. Other functionality provided by the GMI-IPS are: deriving missing flight entries along a transect, reading ICARTT entries from file, and providing Python data structures for storing flight and model information, and more.The GMI-IPS is GIT source controlled, has approximately 30,000 lines of code, and supports parallelization across data collections. It delivered GMI-CTM data for more than forty distinct DC-8 aircraft flights that took place under ATom. The output ICARTT files adhere to format standard V1.1, and pass the scan utility provided by NASA LaRC Airborne Science Data for Atmospheric Composition. This presentation will include a software and methods overview, and results from ATom, including assessments using the GMI-CTM showing how well observations from ATom flight transects represent a broader region.

Damon, M. R.↗
NASA NTRS2015

Comparative Analysis of Static and Dynamic Probabilistic Risk Assessment

This study examines three different methodologies for producing loss-of-mission (LOM) and loss-of-crew (LOC) risks estimates for probabilistic risk assessments (PRA) of crewed spacecraft. The three bottom-up, component-based PRA approaches examined are a traditional static fault tree, a dynamic Monte Carlo simulation, and a fault tree hybrid that incorporates some dynamic elements. These approaches were used to model the reaction control system thruster pod of a generic crewed spacecraft and mission, and a comparative analysis of the methods is presented. The methodologies are assessed in terms of the process of modeling a system, the actionable information produced for the design team, and the overall fidelity of the quantitative risk evaluation generated. The system modeling process is compared in terms of the effort required to generate the initial model, update the model in response to design changes, and support mass-versus-risk trade studies. The results are compared by examining the top-level LOM/LOC estimates and the relative risk driver rankings at the failure mode level. The fidelity of each modeling methodology is discussed in terms of its capability to handle real-world system dynamics such as cold-sparing, changes in mission operations due to loss of redundancy, and common cause failure modes. The paper also discusses the applicability of each methodology to different phases of system development and shows that a single methodology may not be suitable for all of the many purposes of a spacecraft PRA. The fault tree hybrid approach is shown to be best suited to the needs of early assessments during conceptual design phases. As the design begins to mature, the level of detail represented in the risk model must go beyond redundancy and nominal mission operations to include dynamic, time- and state-dependent system responses as well as diverse system capabilities. This is best accomplished using the dynamic simulation approach, since these phenomena are not easily captured by static methods. Ultimately, once the design has been finalized and the goal of the PRA is to provide design validation and requirement verification, more traditional, static fault tree approaches may become as appropriate as the simulation method.

Mattenberger, Christopher J.↗
NASA NTRS2008

Improving Air Quality Forecasts with AURA Observations

Past studies have identified model initial and boundary conditions as sources of reducible errors in air-quality simulations. In particular, improving the initial condition improves the accuracy of short-term forecasts as it allows for the impact of local emissions to be realized by the model and improving boundary conditions improves long range transport through the model domain, especially in recirculating anticyclones. During the August 2006 period, we use AURA/OMI ozone measurements along with MODIS and CALIPSO aerosol observations to improve the initial and boundary conditions of ozone and Particulate Matter. Assessment of the model by comparison of the control run and satellite assimilation run to the IONS06 network of ozonesonde observations, which comprise the densest ozone sounding campaign ever conducted in North America, to AURA/TES ozone profile measurements, and to the EPA ground network of ozone and PM measurements will show significant improvement in the CMAQ calculations that use AURA initial and boundary conditions. Further analyses of lightning occurrences from ground and satellite observations and AURA/OMI NO2 column abundances will identify the lightning NOx signal evident in OMI measurements and suggest pathways for incorporating the lightning and NO2 data into the CMAQ simulations.

Newchurch, M. J.↗
NASA NTRS1988

An alternative to Guyan reduction of finite-element models

Structural modeling is a key part of structural system identification for large space structures. Finite-element structural models are commonly used in practice because of their general applicability and availability. The initial models generated by using a standard computer program such as NASTRAN, ANSYS, SUPERB, STARDYNE, STRUDL, etc., generally contain tens of thousands of degrees of freedom. The models must be reduced for purposes of identification. Not only does the magnitude of the identification effort grow exponentially as a function of the number of degrees of freedom, but numerical procedures may also break down because of accumulated round-off errors. Guyan reduction is usually applied after a static condensation. Misapplication of Guyan reduction can lead to serious modeling errors. It is quite unfortunate and disappointing, since the accuracy of the original detailed finite-element model one tries very hard to achieve is lost by the reduction. First, why and how Guyan reduction always causes loss of accuracy is examined. An alternative approach is then introduced. The alternative can be thought of as an improvement of Guyan reduction, the Rayleigh-Ritz method, and in particular the recent algorithm of Wilson, Yuan, and Dickens. Unlike Guyan reduction, the use of the alternative does not need any special insight, experience, or skill for partitioning the structural degrees of freedom. In addition to model condensation, this alternative approach can also be used for predicting analytically, quickly, and economically, what are those structural modes that are excitable by a force actuator at a given trial location. That is, in the excitation of the structural modes for identification, it can be used for guiding the placement of the force actuators.

Lin, Jiguan Gene↗
NASA NTRS2004

Comparisons of Observations with Results from 3D Simulations and Implications for Predictions of Ozone Recovery

Although chemistry and transport models (CTMs) include the same basic elements (photo- chemical mechanism and solver, photolysis scheme, meteorological fields, numerical transport scheme), they produce different results for the future recovery of stratospheric ozone as chlorofluorcarbons decrease. Three simulations will be contrasted: the Global Modeling Initiative (GMI) CTM driven by a single year\'s winds from a general circulation model; the GMI CTM driven by a single year\'s winds from a data assimilation system; the NASA GSFC CTM driven by a winds from a multi-year GCM simulation. CTM results for ozone and other constituents will be compared with each other and with observations from ground-based and satellite platforms to address the following: Does the simulated ozone tendency and its latitude, altitude and seasonal dependence match that derived from observations? Does the balance from analysis of observations? Does the balance among photochemical processes match that expected from observations? Can the differences in prediction for ozone recovery be anticipated from these comparisons?

Douglass, Anne R.↗
NASA NTRS2015

Modeling of Local BEAM Structure for Evaluation of MMOD Impacts to Support Development of a Health Monitoring System

This report summarizes initial modeling of the local response of the Bigelow Expandable Activity Module (BEAM) to micrometeorite and orbital debris (MMOD) impacts using a structural, non-linear, transient dynamic finite element code. Complementary test results for a local BEAM structure are presented for both hammer and projectile impacts. Review of these data provided guidance for the transient dynamic model development. The local model is intended to support predictions using the global BEAM model, described in a companion report. Two types of local models were developed. One mimics the simplified Soft-Goods (fabric envelop) part of the BEAM NASTRAN model delivered by the project. The second investigates through-the-thickness modeling challenges for MMOD-type impacts. Both the testing and the analysis summaries contain lessons learned and areas for future efforts.

Lyle, Karen H.↗
NASA NTRS2010

An Algorithm for the Fitting of Planet Models to Kepler Light Curves

We describe an algorithm which fits model planetary system parameters to light curves from Kepler Mission target stars. The algorithm begins by producing an initial model of the system which is used to seed the fit,with particular emphasis on obtaining good transit timing parameters. An attempt is then made to determine whether the observed transits are more likely due to a planet or an eclipsing binary. In the event that the transits are consistent with a transiting planet, an iterative fitting process is initiated: a wavelet-based whitening filter is used to eliminate stellar variations on timescales long compared to a transit; a robust nonlinear fitter operating on the whitened light curve produces a new model of the system; and the procedure iterates until convergence upon a self-consistent whitening filter and planet model. The fitted transits are removed from the light curve anda search for additional planet candidates is performed upon the residual light curve. The fitted models are used in additional tests which identify false positive planet detections: multiple planet candidates with near-identical fitted periods are far more likely to be an eclipsing binary, for example, while target stars in which the model lightcurve is correlated with the star centroid position may indicate a background eclipsing binary, and subtraction of all model planet candidates yields a light curve of pure noise and stellar variability, which can be used to study the probability that the planet candidates result from statistical fluctuations in the data.

Exoplanet↗
NASA NTRS2019

Optimizing Umkehr Ozone Profile Retrievals

NOAA Dobson Umkehr ozone profile records have been collected since the 1970s. Umkehr ozone profiles are used to monitor stratospheric ozone recovery predicted to occur by the 2050s. Current operational Dobson Umkehr profile algorithms produce data that have uncertainty on the order of ~ 5 % in the stratosphere. However, when large volcanic eruptions inject aerosols into the stratosphere, the errors can be as large as 70 %. In order to evaluate Umkehr records for aerosol-related and instrumental artifacts, we compare observations with a Hindcast simulation of the NASA Merra-2 Global Modeling Initiative (GMI) Replay (M2GMI, Orbe et al, 2017; Wargan et al, 2018) and Chemistry Transport Model (GMI CTM, Strahan et al, 2013, Strahan et al, 2016). The biases found between the models and observations are summarized for each Dobson calibration and volcanic eruption period, thus providing a reference tool for homogenization of the Umkehr time series and removal of volcanic aerosol errors.

Petropavlovskikh, I.↗
NASA NTRS2015

Modeling of Global BEAM Structure for Evaluation of MMOD Impacts to Support Development of a Health Monitoring System

This report summarizes the initial modeling of the global response of the Bigelow Expandable Activity Module (BEAM) to micrometeorite and orbital debris(MMOD) impacts using a structural, nonlinear, transient dynamic, finite element code. These models complement the on-orbit deployment of the Distributed Impact Detection System (DIDS) to support structural health monitoring studies. Two global models were developed. The first focused exclusively on impacts on the soft-goods (fabric-envelop) portion of BEAM. The second incorporates the bulkhead to support understanding of bulkhead impacts. These models were exercised for random impact locations and responses monitored at the on-orbit sensor locations. The report concludes with areas for future study.

Lyle, Karen H.↗