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At least 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Results of an A109 simulation validation and handling qualities study

The results for the validation of a mathematical model of the Agusta A109 helicopter, and subsequent use of the model as the baseline for a handling qualities study of cockpit centerstick requirements, are described. The technical approach included flight test, non-realtime analysis, and realtime piloted simulation. Results of the validation illustrate a time- and frequency-domain approach to the model and simulator issues. The final A109 model correlates well with the actual aircraft with the Stability Augmentation System (SAS) engaged, but is unacceptable without the SAS because of instability and response coupling at low speeds. Results of the centerstick study support the current U.S. Army handling qualities requirements for centerstick characteristics.

Eshow, Michelle M.↗
NASA NTRS1990

Design for validation, based on formal methods

Validation of ultra-reliable systems decomposes into two subproblems: (1) quantification of probability of system failure due to physical failure; (2) establishing that Design Errors are not present. Methods of design, testing, and analysis of ultra-reliable software are discussed. It is concluded that a design-for-validation based on formal methods is needed for the digital flight control systems problem, and also that formal methods will play a major role in the development of future high reliability digital systems.

Butler, Ricky W.↗
NASA NTRS1991

CFD validation for forebody inlet interactions

Topics covered include the computational fluid dynamics (CFD) task force philosophy, a road map for CFD code validation, computer code validation requirements for forebodies and inlets, the criteria for choosing recommended experiments, an all-body hypersonic experiment, and centerline heat transfer. Information is given in viewgraph form.

Marvin, J. G.↗
NASA NTRS1991

Validation of lidar and satellite remote sensing

Validation of observations is an important part of any remote sensing program. With respect to aerosols this is exceedingly difficult because each technique typically measures a different aerosol parameter. Correlative sensors, therefore, must be capable of measuring the same parameter over the same size range or include enough measurements to properly characterize the aerosol, possibly with the assistance of models. In any correlative measurement program, simultaneity in space and time is required. This can be less restrictive during periods of atmospheric stability. The discussion is presented which is focused on the validation programs developed for NASA's Stratospheric Aerosol Measurement (SAM II), and the Stratospheric Aerosol and Gas Experiments I and II (SAGE I and II). To date these were limited to the stratosphere. Since satellite sensors are capable of providing near-global and long-term observations, periodic correlative observations over various global locations and seasons are required for assuring that data quality is unchanged, or for understanding any changes observed.

Mccormick, M. P.↗
NASA NTRS1990

Validation of a flight simulation model of the AH-64 Apache attack helicopter against flight test data

The FLYRT simulation model of the U.S. Army/McDonnell Douglas AH-64 Apache attack helicopter is validated against flight test data. The approach used for validation involves matching static trim attitudes and control positions and driving the model with measured control time histories to compare dynamic responses such as angular rates and normal acceleration. Flight test data is processed to determine kinematic consistency in the angular degrees of freedom. Modeling problems associated with aerodynamic interaction of the main rotor wake on the horizontal stabilator and engine response timing are identified. Appropriate model updates are made which result in good overall model correlation throughout the flight regime investigated.

Harding, J. W.↗
NASA NTRS1991

Infrared imaging - A validation technique for computational fluid dynamics codes used in STOVL applications

The need for a validation technique for computational fluid dynamics (CFD) codes in STOVL applications has led to research efforts to apply infrared thermal imaging techniques to visualize gaseous flow fields. Specifically, a heated, free-jet test facility was constructed. The gaseous flow field of the jet exhaust was characterized using an infrared imaging technique in the 2 to 5.6 micron wavelength band as well as conventional pitot tube and thermocouple methods. These infrared images are compared to computer-generated images using the equations of radiative exchange based on the temperature distribution in the jet exhaust measured with the thermocouple traverses. Temperature and velocity measurement techniques, infrared imaging, and the computer model of the infrared imaging technique are presented and discussed. From the study, it is concluded that infrared imaging techniques coupled with the radiative exchange equations applied to CFD models are a valid method to qualitatively verify CFD codes used in STOVL applications.

Hardman, R. R.↗
NASA NTRS1991

A validation tool for the Earth Radiation Budget Experiment nonscanning radiometers

Two data sets for one geographical scene are used as a comparative validation tool to verify the quality of radiometer measurements taken for NASA's Earth Radiation Budget Experiment (ERBE). The measurements are taken from four independent nonscanning radiometers installed on the Earth Radiation Budget Satellite and two NOAA spacecraft. Two radiometers measure radiation in the 0.2-50-micron range, and two measure solar reflected energy in spectral band ranging from 0.2 to 5 microns. Calculated top-of-atmosphere flux-value measurements for day and night demonstrate significant correlation as well as consistency and stability over a three-year period. It is concluded that intercomparisons of intersections between the satellites are necessary over varied geographical scenes to utilize the subject method in validating the measurements of the ERBE nonscanning radiometer.

Bolden, William C.↗
NASA NTRS1991

Validation of chemistry models employed in a particle simulation method

The chemistry models employed in a statistical particle simulation method, as implemented in the Intel iPSC/860 multiprocessor computer, are validated and applied. Chemical relaxation of five-species air in these reservoirs involves 34 simultaneous dissociation, recombination, and atomic-exchange reactions. The reaction rates employed in the analytic solutions are obtained from Arrhenius experimental correlations as functions of temperature for adiabatic gas reservoirs in thermal equilibrium. Favorable agreement with the analytic solutions validates the simulation when applied to relaxation of O2 toward equilibrium in reservoirs dominated by dissociation and recombination, respectively, and when applied to relaxation of air in the temperature range 5000 to 30,000 K. A flow of O2 over a circular cylinder at high Mach number is simulated to demonstrate application of the method to multidimensional reactive flows.

Haas, Brian L.↗
NASA NTRS1990

Human performance measurement: Validation procedures applicable to advanced manned telescience systems

As telescience systems become more and more complex, autonomous, and opaque to their operators it becomes increasingly difficult to determine whether the total system is performing as it should. Some of the complex and interrelated human performance measurement issues are addressed as they relate to total system validation. The assumption is made that human interaction with the automated system will be required well into the Space Station Freedom era. Candidate human performance measurement-validation techniques are discussed for selected ground-to-space-to-ground and space-to-space situations. Most of these measures may be used in conjunction with an information throughput model presented elsewhere (Haines, 1990). Teleoperations, teleanalysis, teleplanning, teledesign, and teledocumentation are considered, as are selected illustrative examples of space related telescience activities.

Haines, Richard F.↗
NASA NTRS1992

A turbulence model for iced airfoils and its validation

A turbulence model based on the extension of the algebraic eddy viscosity formulation of Cebeci and Smith developed for two dimensional flows over smooth and rough surfaces is described for iced airfoils and validated for computed ice shapes obtained for a range of total temperatures varying from 28 to -15 F. The validation is made with an interactive boundary layer method which uses a panel method to compute the inviscid flow and an inverse finite difference boundary layer method to compute the viscous flow. The interaction between inviscid and viscous flows is established by the use of the Hilbert integral. The calculated drag coefficients compare well with recent experimental data taken at the NASA-Lewis Icing Research Tunnel (IRT) and show that, in general, the drag increase due to ice accretion can be predicted well and efficiently.

Shin, Jaiwon↗
NASA NTRS1991

Expert system verification and validation study. Delivery 3A and 3B: Trip summaries

Key results are documented from attending the 4th workshop on verification, validation, and testing. The most interesting part of the workshop was when representatives from the U.S., Japan, and Europe presented surveys of VV&T within their respective regions. Another interesting part focused on current efforts to define industry standards for artificial intelligence and how that might affect approaches to VV&T of expert systems. The next part of the workshop focused on VV&T methods of applying mathematical techniques to verification of rule bases and techniques for capturing information relating to the process of developing software. The final part focused on software tools. A summary is also presented of the EPRI conference on 'Methodologies, Tools, and Standards for Cost Effective Reliable Software Verification and Validation. The conference was divided into discussion sessions on the following issues: development process, automated tools, software reliability, methods, standards, and cost/benefit considerations.

French, Scott↗
NASA NTRS1992

SeaWiFS technical report series. Volume 5: Ocean optics protocols for SeaWiFS validation

Protocols are presented for measuring optical properties, and other environmental variables, to validate the radiometric performance of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), and to develop and validate bio-optical algorithms for use with SeaWiFS data. The protocols are intended to establish foundations for a measurement strategy to verify the challenging SeaWiFS accuracy goals of 5 percent in water-leaving radiances and 35 percent in chlorophyll alpha concentration. The protocols first specify the variables which must be measured, and briefly review rationale. Subsequent chapters cover detailed protocols for instrument performance specifications, characterizing and calibration instruments, methods of making measurements in the field, and methods of data analysis. These protocols were developed at a workshop sponsored by the SeaWiFS Project Office (SPO) and held at the Naval Postgraduate School in Monterey, California (9-12 April, 1991). This report is the proceedings of that workshop, as interpreted and expanded by the authors and reviewed by workshop participants and other members of the bio-optical research community. The protocols are a first prescription to approach unprecedented measurement accuracies implied by the SeaWiFS goals, and research and development are needed to improve the state-of-the-art in specific areas. The protocols should be periodically revised to reflect technical advances during the SeaWiFS Project cycle.

Mueller, James L.↗
NASA NTRS1992

A turbulence model for iced airfoils and its validation

A turbulence model based on the extension of the algebraic eddy viscosity formulation of Cebeci and Smith developed for two-dimensional flows over smooth and rough surfaces is described for iced airfoils and validated for computed ice shapes obtained for a range of total temperatures varying from 28 to -15 F. The validation is made with an interactive boundary layer method which uses a panel method to compute the inviscid flow and an inverse finite difference boundary layer method to compute the viscous flow. The interaction between inviscid and viscous flows is established by the use of the Hilbert integral. The calculated drag coefficients compare well with recent experimental data taken at the NASA-Lewis Icing Research Tunnel (IRT) and show that, in general, the drag increase due to ice accretion can be predicted well and efficiently.

Shin, Jaiwon↗
NASA NTRS1992

A technique for global monitoring of net solar irradiance at the ocean surface. II - Validation

The generation and validation of the first satellite-based long-term record of surface solar irradiance over the global oceans are addressed. The record is generated using Nimbus-7 earth radiation budget (ERB) wide-field-of-view plentary-albedo data as input to a numerical algorithm designed and implemented based on radiative transfer theory. The mean monthly values of net surface solar irradiance are computed on a 9-deg latitude-longitude spatial grid for November 1978-October 1985. The new data set is validated in comparisons with short-term, regional, high-resolution, satellite-based records. The ERB-based values of net surface solar irradiance are compared with corresponding values based on radiance measurements taken by the Visible-Infrared Spin Scan Radiometer aboard GOES series satellites. Errors in the new data set are estimated to lie between 10 and 20 W/sq m on monthly time scales.

Chertock, Beth↗
NASA NTRS1987

Needs and status of CFD code validation

The two types of Computational Fluid Dynamics code validations, solution-to-solution comparison and solution-to-experiment comparison, are discussed. It is suggested that to develop more detailed experiments the following things are necessary: (1) further development of turbulence models; (2) better methods for numerical validation of CFD codes; (3) evaluation of disagreements; and (4) continued determination of experimental scatter. All data and results are presented in viewgraph form.

Holst, Terry L.↗
NASA NTRS1987

High-speed code validation

The topics are presented in viewgraph form and include the following: NFL body experiment; high-speed validation problems; 3-D Euler/Navier-Stokes inlet code; two-strut inlet configuration; pressure contours in two longitudinal planes; sidewall pressure distribution; pressure distribution on strut inner surface; inlet/forebody tests in 60 inch helium tunnel; pressure distributions on elliptical missile; code validations; small scale test apparatus; CARS nonintrusive measurements; optimized cone-derived waverider study; etc.

Barnwell, Richard W.↗
NASA NTRS1987

CFD validation experiments at the Lockheed-Georgia Company

Information is given in viewgraph form on computational fluid dynamics (CFD) validation experiments at the Lockheed-Georgia Company. Topics covered include validation experiments on a generic fighter configuration, a transport configuration, and a generic hypersonic vehicle configuration; computational procedures; surface and pressure measurements on wings; laser velocimeter measurements of a multi-element airfoil system; the flowfield around a stiffened airfoil; laser velocimeter surveys of a circulation control wing; circulation control for high lift; and high angle of attack aerodynamic evaluations.

Malone, John B.↗