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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Software reliability growth models dominated by randomness

The Jelinski-Moranda and Geometric models for software reliability failed the consistency test which was proposed. These models were challenged to take data which comes from a process which they have correctly modeled and to make predictions about the reliability of that process. It was found that either model, given data precisely from a process it correctly models, will usually fail to make good predictions. These problems are attributed to randomness in the data used as input to the models and a remedy is indicated for this lack of robustness, namely replication of data.

Shen, Wenhui↗
NASA NTRS2017

Verification Testing: Meet User Needs Figure of Merit

Verification is the process through which Modeling and Simulation(M&S) software goes to ensure that it has been rigorously tested and debugged for its intended use. Validation confirms that said software accurately models and represents the real world system. Credibility gives an assessment of the development and testing effort that the software has gone through as well as how accurate and reliable test results are. Together, these three components form Verification, Validation, and Credibility(VV&C), the process by which all NASA modeling software is to be tested to ensure that it is ready for implementation. NASA created this process following the CAIB (Columbia Accident Investigation Board) report seeking to understand the reasons the Columbia space shuttle failed during reentry. The reports conclusion was that the accident was fully avoidable, however, among other issues, the necessary data to make an informed decision was not there and the result was complete loss of the shuttle and crew. In an effort to mitigate this problem, NASA put out their Standard for Models and Simulations, currently in version NASA-STD-7009A, in which they detailed their recommendations, requirements and rationale for the different components of VV&C. They did this with the intention that it would allow for people receiving MS software to clearly understand and have data from the past development effort. This in turn would allow the people who had not worked with the MS software before to move forward with greater confidence and efficiency in their work. This particular project looks to perform Verification on several MATLAB (Registered Trademark)(The MathWorks, Inc.) scripts that will be later implemented in a website interface. It seeks to take note and define the limits of operation, the units and significance, and the expected datatype and format of the inputs and outputs of each of the scripts. This is intended to prevent the code from attempting to make incorrect or impossible calculations. Additionally, this project will look at the coding generally and note inconsistencies, redundancies, and other aspects that may become problematic or slow down the codes run time. Certain scripts lacking in documentation also will be commented and cataloged.

validation↗
NASA NTRSDate not supplied

Evaluation of Preliminary Buffet Forcing Function Development based on Wind-Tunnel Tests of Geometrically-similar Models

The current state-of-the-art for launch vehicle buffet load estimation involves wind tunnel testing of highly instrumented rigid models and data processing of experimental unsteady pressure measurements to estimate the fluctuating aerodynamic loads. The model and instrumentation requirements to accomplish this type of testing are significant. The rigid model, in particular, must be built with relatively high geometric fidelity to approximate similar aerodynamic phenomena that will occur during the full-scale vehicle flight. Due to this requirement, several iterative wind tunnel tests are often required during the design maturation of the vehicle. For preliminary buffet load estimation, however, data from previous launch vehicle wind tunnel tests of geometrically similar models can be used to provide initial buffet environment estimates before a high geometric fidelity wind tunnel test has been conducted. In this paper, two components of this preliminary buffet estimation process are described: (1) assembly of buffet forcing functions from multiple data sources and (2) scaling of these buffet forcing functions to geometrically-similar components of a target vehicle configuration. The impacts of these estimation methods on the full-vehicle buffet forcing functions, including their longitudinal distribution along the vehicle, frequency-content at individual stations, and station-to-station coherence, are investigated. Considerations for using these methods to extrapolate wind tunnel data to geometrically similar models are also discussed.

Patrick S Heaney↗
NASA NTRS2013

Model-Based Verification and Validation of the SMAP Uplink Processes

This case study stands as an example of how a project can validate a system-level design earlier in the project life cycle than traditional V&V processes by using simulation on a system model. Specifically, this paper describes how simulation was added to a system model of the Soil Moisture Active-Passive (SMAP) mission's uplink process.Also discussed are the advantages and disadvantages of the methods employed and the lessons learned; which are intended to benefit future model-based and simulation-based V&V development efforts.

verification and validation (V&V)↗
NASA NTRS2018

Hybrid Reduced Order Model for N2-N2 Interactions for Application to Dissociation and Energy Transfer Processes

This work presents a general framework for model reduction of non-equilibrium energy transfer and dissociation processes. The multi-group maximum-entropy method is coupled with the quasi-classical trajectory method to directly construct a reduced order model for chemical non-equilibrium. Kinetic data is calculated by applying detailed balance at a microscopic level, overcoming the limitation of calculating recombination kinetic data. This approach enables the construction of a reduced order model for kinetics which bypasses the need to compute state-to-state kinetic data. This physics based reduced order model ensures that an equilibrium distribution is reached given infinite time, while allowing for non-equilibrium distributions during the relaxation and dissociation processes. A proof-of-concept test case demonstrates the applicability of this model by comparison with state-to-state kinetic data for the N2(Chi (sup 1) Sigma ((sub g), (sup plus sign)) minus N ((exp 4) S (sub u)) system with excellent agreement.

Maximum Entropy↗
NASA NTRS1992

Comparing the results of an analytical model of the no-vent fill process with no-vent fill test results for a 4.96 cu m (175 cu ft) tank

NASA-Lewis has been investigating a no-vent fill method for refilling cryogenic storage tanks in low gravity. Analytical modeling based on analyzing the heat transfer of a droplet has successfully represented the process in 0.034 and 0.142 sq m commercial dewars using liquid nitrogen and hydrogen. Recently a large tank (4.96 sq m) was tested with hydrogen. This lightweight tank is representative of spacecraft construction. This paper presents efforts to model the large tank test data. The droplet heat transfer model is found to overpredict the tank pressure level when compared to the large tank data. A new model based on equilibrium thermodynamics has been formulated. This new model is compared to the published large scale tank's test results as well as some additional test runs with the same equipment. The results are shown to match the test results within the measurement uncertainty of the test data except for the initial transient wall cooldown where it is conservative (i.e., overpredicts the initial pressure spike found in this time frame).

Taylor, William J.↗
NASA NTRS1994

Effects of stratospheric aerosol surface processes on the LLNL two-dimensional zonally averaged model

We have investigated the effects of incorporating representations of heterogeneous chemical processes associated with stratospheric sulfuric acid aerosol into the LLNL two-dimensional, zonally averaged, model of the troposphere and stratosphere. Using distributions of aerosol surface area and volume density derived from SAGE II satellite observations, we were primarily interested in changes in partitioning within the Cl- and N- families in the lower stratosphere, compared to a model including only gas phase photochemical reactions. We have considered the heterogeneous hydrolysis reactions N2O5 + H2O(aerosol) yields 2 HNO3 and ClONO2 + H2O(aerosol) yields HOCl + HNO3 alone and in combination with the proposed formation of nitrosyl sulfuric acid (NSA) in the aerosol and its reaction with HCl. Inclusion of these processes produces significant changes in partitioning in the NO(y) and ClO(y) families in the middle stratosphere.

Connell, Peter S.↗
NASA NTRS2019

Continuously Improving Parametric Modeling with Historical Data on the ICESat-2 Mission

This paper delves into the details of the Joint Confidence Level (JCL) process performed for the Ice, Cloud, and Land Elevation Satellite (ICESat)-2 mission and how past performance was incorporated into subsequent JCL models to enable the project to continuously analyze potential slips to their launch readiness date (LRD). One year prior to the mission Preliminary Review (mPDR), the JCL model development process began. The first model was well received at the mPDR, held on October 10, 2012, and the input received by the Standing Review Board was incorporated into the model for the official data drop for key decision point (KDP)-C. The 70% JCL results of the October 2012 mPDR model forecast an LRD of February 2017 and associated cost of $830M. This result in 2012 immediately highlighted potential challenges with the project-planned LRD of July 2016. The year following the mPDR, the project had sustained a oneyear slip in the LRD due to problematic systems engineering requirement issues which impacted all project subsystems. This slip moved the project planned LRD from July 2016 to July 2017, an additional 5 months beyond the 2012 model’s 70% JCL result for the LRD of February 2017. As the project was quickly approaching the mission Critical Design Review (mCDR), the need for reliable JCL results increased significantly. The project held discussions on the JCL modeling process and focused on the input uncertainty distributions. Specifically, to identify the uncertainty distributions that the 2012 mPDR model would have needed to produce a 70% LRD result of July 2017. This led the project to compare multiple uncertainty distributions, and ultimately spurred the project to utilize uncertainty distributions that incorporated project past performance and historical data to forecast potential LRD slips. The revised results, created in 2014 and utilizing the new uncertainty distributions, showed that with 70% confidence, the ICESat-2 mission would launch in August 2018 with a cost of $1,044M. Today, ICESat-2 is scheduled to launch on September 15, 2018 with a project management (PM) agreement value of $1,056M. This illustrates how a JCL model can be continuously improved to produce valuable results for a project, even in cases of LRD delays. The primary reason for the ICESat-2 LRD delay is due to a laser failure on the primary instrument. Laser failure was one of the highest risk and uncertainty drivers within the JCL model. The project placed the most risk in this area of the model, and the model further identified the laser as the top risk driver and contributor to the LRD result. This further illustrates how a JCL can be used to predict and quantify possible issues on new technology missions.

Krygiel, Joseph↗
NASA NTRS1995

Task Analytic Models to Guide Analysis and Design: Use of the Operator Function Model to Represent Pilot-Autoflight System Mode Problems

Task-analytic models structure essential information about operator interaction with complex systems, in this case pilot interaction with the autoflight system. Such models serve two purposes: (1) they allow researchers and practitioners to understand pilots' actions; and (2) they provide a compact, computational representation needed to design 'intelligent' aids, e.g., displays, assistants, and training systems. This paper demonstrates the use of the operator function model to trace the process of mode engagements while a pilot is controlling an aircraft via the, autoflight system. The operator function model is a normative and nondeterministic model of how a well-trained, well-motivated operator manages multiple concurrent activities for effective real-time control. For each function, the model links the pilot's actions with the required information. Using the operator function model, this paper describes several mode engagement scenarios. These scenarios were observed and documented during a field study that focused on mode engagements and mode transitions during normal line operations. Data including time, ATC clearances, altitude, system states, and active modes and sub-modes, engagement of modes, were recorded during sixty-six flights. Using these data, seven prototypical mode engagement scenarios were extracted. One scenario details the decision of the crew to disengage a fully automatic mode in favor of a semi-automatic mode, and the consequences of this action. Another describes a mode error involving updating aircraft speed following the engagement of a speed submode. Other scenarios detail mode confusion at various phases of the flight. This analysis uses the operator function model to identify three aspects of mode engagement: (1) the progress of pilot-aircraft-autoflight system interaction; (2) control/display information required to perform mode management activities; and (3) the potential cause(s) of mode confusion. The goal of this paper is twofold: (1) to demonstrate the use of the operator functio model methodology to describe pilot-system interaction while engaging modes And monitoring the system, and (2) to initiate a discussion of how task-analytic models might inform design processes. While the operator function model is only one type of task-analytic representation, the hypothesis of this paper is that some type of task analytic structure is a prerequisite for the design of effective human-automation interaction.

Degani, Asaf↗
NASA NTRS1980

Multispectral data acquisition and classification - Computer modeling for smart sensor design

In this paper a model of the processes involved in multispectral remote sensing and data classification is developed as a tool for designing and evaluating smart sensors. The model has both stochastic and deterministic elements and accounts for solar radiation, atmospheric radiative transfer, surface reflectance, sensor spectral reponses, and classification algorithms. Preliminary results are presented which indicate the validity and usefulness of this approach. Future capabilities of smart sensors will ultimately be limited by the accuracy with which multispectral remote sensing processes and their error sources can be computationally modeled.

Park, S. K.↗
NASA NTRS1972

Culling of redundant data

The inversion of a large data set, with it errors, is demonstrated and the tradeoff curve, or resolving power calculations, are discussed. Consideration is given to inverse problems of the earth, represented in the idealized form of a single scaler function of a single coordinate. The difference between the functional for the real earth and the functional for some model is formulated. A procedure is given for using the linear relationships between the differences in the data and the differences in the model as side conditions. Through a process of diagonalization a model is created that fits the data. The data are culled by accepting only those relative standard errors that are less than 100 percent.

Gilbert, F.↗
NASA NTRS1974

Thermal preparation of foods in space-vehicle environments

Convection is the primary heat transfer mechanism for most foods heated in an earth-based environment. In contrast, in the low-gravity environment of space flight, the primary heat transfer mechanism is conduction (or radiation in the absence of a conducting medium). Conduction heating is significantly slower and less efficient than convection heating. This fact poses a problem for food heating during space flight. A numerical model has been developed to evaluate this problem. This model simulates the food-heating process for Skylab. The model includes the effect of a thermally controlled on/off heat flux. Parametric studies using this model establish how the required heating time is affected by: the thermal diffusivity of the nutrient materials, the power level of the heater, the initial food temperatures, and the food container dimensions.

Bannerot, R. B.↗
NASA NTRS1977

Computational design of the basic dynamical processes of the UCLA general circulation model

The 12-layer UCLA general circulation model encompassing troposphere and stratosphere (and superjacent 'sponge layer') is described. Prognostic variables are: surface pressure, horizontal velocity, temperature, water vapor and ozone in each layer, planetary boundary layer (PBL) depth, temperature, moisture and momentum discontinuities at PBL top, ground temperature and water storage, and mass of snow on ground. Selection of space finite-difference schemes for homogeneous incompressible flow, with/without a free surface, nonlinear two-dimensional nondivergent flow, enstrophy conserving schemes, momentum advection schemes, vertical and horizontal difference schemes, and time differencing schemes are discussed.

Arakawa, A.↗
NASA NTRS1979

A comparison of limited-area energetic processes between observations and primitive equation model predictions

Energetic analyses of the NMC initial conditions and NMC six-layer primitive equation operational prediction model 12-hr forecast for a developing cyclone are presented. Consideration is given to the total kinetic energy, the energetics of the divergent and nondivergent flows and the baroclinic (vertical shear flow) and barotropic (vertical mean flow) components of the kinetic energy. It is found that the model initial conditions lose 10-15% of the kinetic energy at various levels compared to a limited-area multivariate statistical analysis of the observational data, leading to a decrease in the horizontal kinetic energy flux, a misrepresentation of the synoptic scale wave system in the 12-hr forecast. Similar results are obtained for the nondivergent flow, while the divergent flow energetics are not reproduced accurately by the model. The horizontal flux terms of the vertical mean and vertical shear energetics are also not found to be reproduced in the upper levels, although horizontal flux contributions to the baroclinic component are improved at middle and lower levels. Finally, vertical shear kinetic energy generation is found to be well represented in the model prediction, however kinetic energy conversion between vertical shear and mean flow is not reproduced in the lower layer.

Alpert, J. C.↗
NASA NTRS1982

Numerical modeling and optimization of polymer melt processing operations

The application of finite element computer analyses to polymer flows of the type encountered in melt processing operations is described. A code capable of predicting values of fluid veleocity, pressure, shear stress, and temperature at any point within the flow field was developed. As such, is is of value in diagnosing such processing problems as regions of fluid stagnation at which thermal degradation may occur, or regions of excessive shear deformation which lead to thermomechanical damage. It is further able to generate predictions of the forces which must be applied to the melt to achieve the desired flow, and this information is of value in designing processing equipment of optimal efficiency and minimum energy consumption.

Roylance, D.↗
NASA NTRS1983

Quasi-axisymmetric circulation and superrotation in planetary atmospheres

Atmospheric superrotation is ubiquitous in the solar system, and numerous theoretical models have been proposed to describe the effect. However, no model is fully accepted. Problems are primarily related to an understanding of the angular momentum and the energy budgets. In connection with the present investigation, attention is given to hybrid models, where three-dimensional models may describe eddy processes and two-dimensional symmetric models may describe the global scale circulation in the framework of a viscous medium. It is believed that the concept of an axisymmetric circulation is still useful. It is the main purpose of the current investigation to explore some of the properties of the circulation in planetary atmospheres. It is assumed that the eddy transports are downgradient or diffusive in nature. Energy and momentum are perceived to cascade from the global scale circulation driven by the sun to the smaller scale eddies which in turn determine the diffusive properties. A numerical model of the Venusian circulation is presented, and results are discussed for different conditions of static stability.

Mayr, H. G.↗