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  • STRUCTURAL MECHANICS  (9)
  • Earth Resources and Remote Sensing  (6)
  • 1
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    Pre-Launch Radiometric Characterization of JPSS-1 VIIRS Thermal Emissive Bands (2016)
    In:  CASI
    Details
    Publication Date: 2019-05-21
    Description: Pre-launch characterization and calibration of the thermal emissive spectral bands on the Joint Polar Satellite System (JPSS-1) Visible Infrared Imaging Radiometer Suite (VIIRS) is critical to ensure high quality data products for environmental and climate data records post-launch. A comprehensive test program was conducted at the Raytheon El Segundo facility in 2013-2014, including extensive environmental testing. This work is focused on the thermal band radiometric performance and stability, including evaluation of a number of sensor performance metrics and estimation of uncertainties. Analysis has shown that JPSS-1 VIIRS thermal bands perform very well in relation to their design specifications, and comparisons to the Suomi National Polar-orbiting Partnership (SNPP) VIIRS instrument have shown their performance to be comparable.
    Keywords: Earth Resources and Remote Sensing
    Type: GSFC-E-DAA-TN29811 , Remote Sensing (ISSN 2072-4292); 8; 1; 47
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  • 2
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    On the solution of problems involving impact type loading (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The response of beam and plate members to pulse and impact loading is investigated, and numerical methods are analyzed and compared. The equations of motion, the finite difference and finite element methods, the time integration/Runge-Kutta techniques, and material modeling are discussed in detail. It is found that both the finite difference and the finite element methods could be accurately employed to discretize the spatial variation in the displacements. Central differences or a fourth order Runge-Kutta algorithm could be used for the time integration. The total energy of the system would give the stability and accuracy of the solution. Results showed that the finite element method provided better efficiency in obtaining accurate solution than the finite difference method when a scalar processor is used. However, the finite difference method was more efficient on the vector processor. Therefore, the most efficient method of solution depends on the type of computer present for the analysis.
    Keywords: STRUCTURAL MECHANICS
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  • 3
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    Response of composite plates subjected to acoustic loading (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The objectives of the project were to investigate numerical methodology for the determination of narrowband response in the geometrically nonlinear regime, to determine response characteristics for geometrically nonlinear plates subjected to random loading and to compare the predictions with experiments to be performed at NASA-Langley. The first two objectives were met. The response of composite plates subjected to both narrowband and broadband excitation were studied and the results are presented and discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-184618 , NAS 1.26:184618
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  • 4
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    Biaxial load effects in the mechanics of fracture (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Experimental findings on the effects of biaxial loading on fracture toughness, non-self-similar growth problems, fatigue crack propagation, and subcritical growth properties are reviewed, together with the fundamental analytical solutions for problems of crack in an elastic solid under biaxial loading. Basic asymptotic field representations, and some stress-intensity factor solutions are presented. The effects of biaxial loading on problems involving plastic deformation are illustrated with recent numerical results. Early asymptotic solutions for a nonlinear elastic solid are discussed with emphasis on the solution of problems with significant plastic deformation, and on stable crack growth. A brief survey of the applications literature, and recommendations for future studies are included.
    Keywords: STRUCTURAL MECHANICS
    Type: Aeronautical Society of India, Journal (ISSN 0001-9267); 36; 221-236
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  • 5
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    Vibration response of geometrically nonlinear elastic beams subjected to pulse and impact loading (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: An understanding of the response of composite laminates to foreign object impact is of fundamental importance to the design and the accurate evaluation of aircraft and aerospace structures. A characterization of the basic deformation response of the system is needed for the accurate and consistent modeling of the damage caused by the impact. The response to low velocity impact of foreign objects (less than 10 m/sec at 10 J of impact energy or less) is of particular interest because it corresponds to tool drop problems. An investigation of the vibration response of a simple square beam was conducted, taking into account both sharp initial velocity pulse conditions and simulated impact conditions. Attention is given to nonlinear beam theory, boundary conditions and materials modeling, initial conditions and impact modeling, and a solution of the obtained system of partial differential equations by the finite difference approach.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures (ISSN 0045-7949); 20; 4 19
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  • 6
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    Vibration characteristics of the HPOTP (High Pressure Oxygen Turbopump) of the SSME (Space Shuttle Main Engine) (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A review is presented of various rotordynamic problems which have been encountered and eliminated in developing the current flight engines, and continuing subsynchronous problems which are being encountered in developing a 109% power level engine. The basic model for the High Pressure Oxygen Turbopump (HPOTP) of the SSME including the structural dynamic model for the rotor and housing and component models for the liquid and gas seals, turbine-clearance excitation forces, and impeller-diffuser forces are discussed. Results from a linear model are used to examine the synchronous response and stability characteristics of the HPOTP, examining bearing load and stability problems associated with the second critical speed. Various seal modifications are examined and shown to have favorable consequences with respect to bearing reactions and stability.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Marshall Space Flight Center Advan. High Pressure O2(H2 Technol; p 452-481
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  • 7
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    Energy conservation in the transient response of nonlinear beam vibration problems subjected to pulse loading - A numerical approach (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The nonlinear vibration response of a double cantilevered beam subjected to pulse loading over a central sector is studied. The initial response is generated in detail to ascertain the energetics of the response. The total energy is used as a gauge of the stability and accuracy of the solution. It is shown that to obtain accurate and stable initial solutions an extremely high spatial and time resolution is required. This requirement was only evident through an examination of the energy of the system. It is proposed, therefore, to use the total energy of the system as a necessary stability and accuracy criterion for the nonlinear response of conservative systems. The results also demonstrate that even for moderate nonlinearities, the effects of membrane forces have a significant influence on the system. It is also shown that while the fundamental response is contained in a first mode envelope, the fluctuations caused by the higher order modes must be resolved.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures (ISSN 0045-7949); 19; 3 19
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  • 8
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    A numerical solution of Duffing's equations including the prediction of jump phenomena (1987)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Numerical methodology for the solution of Duffing's differential equation is presented. Algorithms for the prediction of multiple equilibrium solutions and jump phenomena are developed. In addition, a filtering algorithm for producing steady state solutions is presented. The problem of a rigidly clamped circular plate subjected to cosinusoidal pressure loading is solved using the developed algorithms (the plate is assumed to be in the geometrically nonlinear range). The results accurately predict regions of solution multiplicity and jump phenomena.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA PAPER 87-0917
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  • 9
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    MODIS Solar Calibration Simulation Assisted Refinement (2004)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: A detailed optical radiometric model has been created of the MODIS instruments solar calibration process. This model takes into account the orientation and distance of the spacecraft with respect to the sun, the correlated motions of the scan mirror and the sun, all of the optical elements, the detector locations on the visible and near IR focal planes, the solar diffuser and the attenuation screen with all of its hundreds of pinholes. An efficient computational scheme, takes into account all of these factors and has produced results which reproduce the observed time dependent intensity variations on the two focal planes with considerable fidelity. This agreement between predictions and observations, has given insight to the causes of some small time dependent variations and how to incorporate them into the overall calibration scheme. The radiometric model is described and modeled and actual measurements are presented and compared.
    Keywords: Earth Resources and Remote Sensing
    Type: SPIE Conference; Nov 08, 2004 - Nov 12, 2004; Honolulu, HI; United States
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  • 10
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    Polarization Ray Trace Model of the MODIS Instrument (2004)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: Sunlight reflected from the earth is, to a certain extent, polarized. Radiometers, such as the MODIS instrument on board the TERRA and AQUA spacecraft, are to a certain extent polarizers. Accurate radiometric measurements must take into account both the polarization state of the scene and the polarization sensitivity of the measuring instrument. The measured polarization characteristics of the MODIS instruments are contained in various radiometric models. Continued use of these radiometric math models, over a number of years, have shown where these models can be improved. Currently a MODIS polarization ray trace model has been created which models the thin film structure on the optical elements. This approach is described and modeled and measured instrument polarization sensitivity results presented.
    Keywords: Earth Resources and Remote Sensing
    Type: 2004 Conference on Characterization and Radiometry Calibration for Remote Sensing; Aug 01, 2004; UT; United States
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