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At least 1,765 records · Page 98

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NASA NTRS1999

Physics Based Modeling and Rendering of Vegetation in the Thermal Infrared

We outline a procedure for rendering physically-based thermal infrared images of simple vegetation scenes. Our approach incorporates the biophysical processes that affect the temperature distribution of the elements within a scene. Computer graphics plays a key role in two respects. First, in computing the distribution of scene shaded and sunlit facets and, second, in the final image rendering once the temperatures of all the elements in the scene have been computed. We illustrate our approach for a simple corn scene where the three-dimensional geometry is constructed based on measured morphological attributes of the row crop. Statistical methods are used to construct a representation of the scene in agreement with the measured characteristics. Our results are quite good. The rendered images exhibit realistic behavior in directional properties as a function of view and sun angle. The root-mean-square error in measured versus predicted brightness temperatures for the scene was 2.1 deg C.

Smith, J. A.↗

NASA NTRS1999

On the Fast Evaluation Method of Temperature and Gas Mixing Ratio Weighting Functions for Remote Sensing of Planetary Atmospheres in Thermal IR and Microwave

Evaluation of weighting functions in the atmospheric remote sensing is usually the most computer-intensive part of the inversion algorithms. We present an analytic approach to computations of temperature and mixing ratio weighting functions that is based on our previous results but the resulting expressions use the intermediate variables that are generated in computations of observable radiances themselves. Upwelling radiances at the given level in the atmosphere and atmospheric transmittances from space to the given level are combined with local values of the total absorption coefficient and its components due to absorption of atmospheric constituents under study. This makes it possible to evaluate the temperature and mixing ratio weighting functions in parallel with evaluation of radiances. This substantially decreases the computer time required for evaluation of weighting functions. Implications for the nadir and limb viewing geometries are discussed.

Ustinov, E. A.↗

NASA NTRS2004

Implementation of Finite Rate Chemistry Capability in OVERFLOW

An implementation of both finite rate and equilibrium chemistry have been completed for the OVERFLOW code, a chimera capable, complex geometry flow code widely used to predict transonic flow fields. The implementation builds on the computational efficiency and geometric generality of the solver.

Olsen, M. E.↗

NASA NTRS2004

Category 3: Sound Generation by Interacting With a Gust

Solve the time-dependent inviscid flow equations for this geometry subject to the specified inflow/outflow mean conditions and the fluctuating inflow velocity distortion. (1) Compute the unsteady solution until periodicity in pressure is achieved by showing that at least two successive periods are identical. Periodicity must be achieved on both the airfoil surface and the inflow/outflow boundaries. (2) Once periodicity is achieved, compute the pressure frequency spectra on the reference airfoil on both the upper and lower surfaces at x=(-0.25c,0.00, +0.25c), on the inflow boundary at (x,y)={1.5c,-0.3c), (-1.5c,0.0),(-1.5c,0.3c)} and on the outflow boundary at (x,y)= {(1.5c,-0.3c),(1.5c,0.0), (1.5c,0.3c)}. Express the spectral results in dB using the standard definition 20 log(P(sub(r.m.s)/P(sub ref), where p(sub ref) == 20 microPa. (3) Extract the harmonic pressure distributions on the inflow and outflow boundaries (i.e., on x= -/+ 1.5c lines) at the fundamental frequency omega and apply a Fourier transform in y direction to identify the spatial (i.e., mode order) structure of the pressure perturbations. Express the result in dB for each mode order. Repeat the process for the frequencies 2omega and 3omega.

Envia, Edmane↗

NASA NTRS2008

Overview of NASA's Integrated Design and Engineering Analysis (IDEA)Environment

Historically, the design of subsonic and supersonic aircraft has been divided into separate technical disciplines (such as propulsion, aerodynamics and structures) each of which performs their design and analysis in relative isolation from others. This is possible in most cases either because the amount of interdisciplinary coupling is minimal or because the interactions can be treated as linear. The design of hypersonic airbreathing vehicles, like NASA s X-43, is quite the opposite. Such systems are dominated by strong non-linear interactions between disciplines. The design of these systems demands that a multi-disciplinary approach be taken. Furthermore, increased analytical fidelity at the conceptual design phase is highly desirable as many of the non-linearities are not captured by lower fidelity tools. Only when these systems are designed from a true multi-disciplinary perspective can the real performance benefits be achieved and complete vehicle systems be fielded. Toward this end, the Vehicle Analysis Branch at NASA Langley Research Center has been developing the Integrated Design & Engineering Analysis (IDEA) Environment. IDEA is a collaborative environment for parametrically modeling conceptual and preliminary launch vehicle configurations using the Adaptive Modeling Language (AML) as the underlying framework. The environment integrates geometry, configuration, propulsion, aerodynamics, aerothermodynamics, trajectory, closure and structural analysis into a generative, parametric, unified computational model where data is shared seamlessly between the different disciplines. Plans are also in place to incorporate life cycle analysis tools into the environment which will estimate vehicle operability, reliability and cost. IDEA is currently being funded by NASA s Hypersonics Project, a part of the Fundamental Aeronautics Program within the Aeronautics Research Mission Directorate. The environment is currently focused around a two-stage-to-orbit configuration with a turbine based combined cycle (TBCC) first stage and reusable rocket second stage. This paper provides an overview of the development of the IDEA environment, a description of the current status and detail of future plans.

Robinson, Jeffrey S.↗

NASA NTRS2009

LOX/Methane Main Engine Glow Plug Igniter Tests and Modeling

Ignition data for tests with a LOX/methane igniter that utilized a glow plug as the ignition source are presented. The tests were conducted in a vacuum can with thermally conditioned (cold) hardware. Data showing the effects of glow plug geometry, type, and igniter operating conditions are discussed. Comparisons between experimental results and multidimensional, transient computer models are also made.

Breisacher, Kevin↗

NASA NTRS2009

Discrete Adjoint-Based Design Optimization of Unsteady Turbulent Flows on Dynamic Unstructured Grids

An adjoint-based methodology for design optimization of unsteady turbulent flows on dynamic unstructured grids is described. The implementation relies on an existing unsteady three-dimensional unstructured grid solver capable of dynamic mesh simulations and discrete adjoint capabilities previously developed for steady flows. The discrete equations for the primal and adjoint systems are presented for the backward-difference family of time-integration schemes on both static and dynamic grids. The consistency of sensitivity derivatives is established via comparisons with complex-variable computations. The current work is believed to be the first verified implementation of an adjoint-based optimization methodology for the true time-dependent formulation of the Navier-Stokes equations in a practical computational code. Large-scale shape optimizations are demonstrated for turbulent flows over a tiltrotor geometry and a simulated aeroelastic motion of a fighter jet.

Nielsen, Eric J.↗

NASA NTRS2013

Reefing Line Tension in CPAS Main Parachute Clusters

Reefing lines are an essential feature to manage inflation loads. During each Engineering Development Unit (EDU) test of the Capsule Parachute Assembly System (CPAS), a chase aircraft is staged to be level with the cluster of Main ringsail parachutes during the initial inflation and reefed stages. This allows for capturing high-quality still photographs of the reefed skirt, suspension line, and canopy geometry. The over-inflation angles are synchronized with measured loads data in order to compute the tension force in the reefing line. The traditional reefing tension equation assumes radial symmetry, but cluster effects cause the reefed skirt of each parachute to elongate to a more elliptical shape. This effect was considered in evaluating multiple parachutes to estimate the semi-major and semi-minor axes. Three flight tests are assessed, including one with a skipped first stage, which had peak reefing line tension over three times higher than the nominal parachute disreef sequence.

Ray, Eric S.↗

NASA NTRS2016

WebGeocalc: Web Interface to SPICE

The WebGeocalc tool (WGC) provides a web-based graphical user interface to many of the observation geometry calculations available from the “SPICE” system. WGC is based on client-server architecture. A user selects calculation parameters using GUI widgets in a Web browser. The request is sent to a WGC geometry server that performs the calculation and sends results back to the client. WGC can compute various geometric parameters such as positions, orientations, and surface intercept coordinates for a series of times; perform geometric event searches for time intervals when a geometric condition is met; and perform time conversions. WGC offers many features such as plotting and downloading results. Currently only the NAIF group at JPL operates a WGC server that has access to all data on the NAIF web site but WGC can be deployed on any computer that has Java, Apache Tomcat server, MySQL Community Server, and SPICE data.

Semenov, Boris↗

NASA NTRS2016

WebGeocalc: Web Interface to SPICE

Semenov, Boris↗

NASA NTRSDate not supplied

Numerical Investigation of Flow Over Periodic Hill

Hybrid turbulence modeling strategies that blend between large-eddy simulation and Reynolds-averaged Navier-Stokes promise to make optimal use of the available grid resolution. A delayed detached eddy simulation hybrid turbulence modeling strategy, based on the shear-stress transport turbulence model, was implemented into a finite-volume compressible Navier-Stokes code. Then the flow through a two-dimensional periodic hill channel was simulated. This geometry is a widely accepted benchmark test case for validating hybrid turbulence modeling strategies. The computational grid for the simulation was downloaded from a hybrid turbulence model validation website. The present hybrid turbulence model simulation predicts the size of the separated flow region as well as velocity and Reynolds stress profiles in good agreement with large-eddy simulation reference data.

Computational Fluid Dynamics↗

NASA NTRSDate not supplied

High-Fidelity CFD Verification Workshop 2024: Spalart-Allmaras QCR2000-R Turbulence Model

This is an invited paper for the SciTech 2023 special session, High-Fidelity CFD Verification Pre-Workshop. The paper presents three benchmark cases for verification of Reynolds-averaged Navier-Stokes solvers. The verification studies focus on a one-equation Spalart-Allmaras model, SA-neg-QCR2000-R. The benchmark cases are a two-dimensional subsonic flow around a Joukowski airfoil, a subsonic three-dimensional flow around an extruded NACA0012 wing in a tunnel, and a subsonic flow around a wing-body configuration developed by Boeing for verification of solvers participating in the High-Lift Prediction Workshop. The turbulence-model formulation, geometry, flow conditions, grids, and the desired submission data are described in detail. Reference solutions computed by established codes are shown.

CFD↗

NASA NTRSDate not supplied

CFD Validation Study of a Hypersonic Cone-Slice-Flap Variable Geometry Configuration

Model validation is the process of determining the degree of accuracy between physical reality and the model. The result of model validation can either be used to improve the model through calibration or quantify the model-form uncertainty. This work focuses on providing the model-form uncertainty through an area metric for a hypersonic cone-slice-flap variable geometry configuration given uncertainty in both the simulation and experimental data. The research here compares two different turbulence models for the simulations. For a variable geometry, performing uncertainty quantification to capture the model-form uncertainty on every configuration is computationally challenging. This work lays out a procedure that can give an accurate representation of the model-form uncertainty using a small number of high-fidelity runs and many low-fidelity runs on multiple configurations. Running this comparison provides a quantifiable measurement for the accuracy of each turbulence model for this type of design. The high-fidelity CFD solver used was VULCAN-CFD and the low-fidelity results came from Cart3D. The experimental data came from the 20-Inch Mach 6 Tunnel located at NASA Langley Research Center. The present work showed that the using both the Spalart and Allamaras and Menter Shear-Stress Transport turbulence models overpredicted the drag and lift coefficient, while underpredicting the pitching moment coefficient. The model-form uncertainty estimate resulted in up to a 13.6% change in the total uncertainty for the drag coefficient, up to a 57.4% change in total uncertainty for the lift coefficient, and up to a 100% change in total uncertainty for the pitching moment coefficient.

Laura M. White↗

NASA NTRSDate not supplied

CFD Validation Study of a Hypersonic Cone-Slice-Flap Variable Geometry Configuration

Model validation is the process of determining the degree of accuracy between physical reality and the model. The result of model validation can either be used to improve the model through calibration or quantify the model-form uncertainty. This work focuses on providing the model-form uncertainty through an area metric for a hypersonic cone-slice-flap variable geometry configuration given uncertainty in both the simulation and experimental data. For a variable geometry, performing uncertainty quantification to capture the model-form uncertainty on every configuration is computationally challenging. This work lays out a procedure that can give an accurate representation of the model-form uncertainty using a small number of high-fidelity runs and many low-fidelity runs on multiple configurations. Running this comparison provides a quantifiable measurement for the accuracy of each turbulence model for this type of design. The high-fidelity CFD solver used was VULCAN-CFD and the low-fidelity results came from Cart3D. The experimental data came from the 20-Inch Mach 6 Tunnel located at NASA Langley Research Center. The present work showed that the turbulence simulation overpredicted the drag and lift coefficient, while underpredicting the pitching moment coefficient. The model-form uncertainty estimate resulted up to a 13.6% change in the total uncertainty for the drag coefficient, up to a 57.4% change in total uncertainty for the lift coefficient, and up to a 100% change in total uncertainty for the pitching moment coefficient.

Laura White↗

NASA NTRS1982

Thermal radiation view factor: Methods, accuracy and computer-aided procedures

The computer aided thermal analysis programs which predicts the result of predetermined acceptable temperature range prior to stationing of these orbiting equipment in various attitudes with respect to the Sun and the Earth was examined. Complexity of the surface geometries suggests the use of numerical schemes for the determination of these viewfactors. Basic definitions and standard methods which form the basis for various digital computer methods and various numerical methods are presented. The physical model and the mathematical methods on which a number of available programs are built are summarized. The strength and the weaknesses of the methods employed, the accuracy of the calculations and the time required for computations are evaluated. The situations where accuracies are important for energy calculations are identified and methods to save computational times are proposed. Guide to best use of the available programs at several centers and the future choices for efficient use of digital computers are included in the recommendations.

Kadaba, P. V.↗

NASA NTRS1996

Program Helps Specify Paths For Numerically Controlled Tools

ESDAPT computer program provides graphical programming environment for developing APT (Automatically Programmed Tool) programs for controlling numerically controlled machine tools. Establishes graphical user interface providing user with APT syntax-sensitive text-editing subprogram and windows for displaying geometry and tool paths. APT geometry statements also created by use of menus and screen picks. Written in C language, yacc, lex, and XView for use on Sun4-series computers running SunOS.

Premack, Timothy↗

NASA NTRS1992

Forward-scatter radiant mapping

Forward-scatter systems have been much neglected for the study of meteors and meteor streams. A great deal of this neglect stems from the complicated geometry which has made the interpretation of results difficult in the past. This no longer presents a problem because of the computer power now available. There are practical advantages in using forward-scatter in that low-power transmitters are much easier to handle than the high-power ones used in pulsed back-scatter radars. The data reduction of the CW signals is also significantly simpler. Because the forward-scatter reflection geometry increases the duration of the echoes relative to the back-scatter case, the problem of the underdense ceiling is partially alleviated. We have built a 'short hop' forward-scatter system between Ottawa and London (Ont) for which the transmitter and receiver are separated by about 500 km. With it, we are able to measure unambiguously the directions of arrival of the echoes using a 5-antenna interferometer. Morton and Jones (1982, MN, 198, 737) have shown how the echo direction distribution can be deconvolved to yield the meteor radiant distribution for back-scatter data. We have extended the technique to the forward-scatter case and present some preliminary meteor radiant distribution maps.

Jones, James↗

NASA NTRS1993

Computation of crossing shock/turbulent boundary layer interaction at Mach 8.3

A three-dimensional (3D) hypersonic crossing shock wave/turbulent boundary-layer interaction is examined numerically at Mach 8.3. The test geometry consists of a pair of opposing sharp fins of angle alpha = 15 deg, mounted on a flat plate. Two theoretical models are evaluated. The full (3D) Reynolds-averaged Navier-Stokes equations are solved using the Baldwin-Lomax and the Rodi (modified k-epsilon) turbulence models. Computed results for both cases show good agreement with experiment for flat plate surface pressure and for flowfield profiles of pitot pressure and yaw angle, indicating that the flowfield is primarily rotational and inviscid. Fair to poor agreement is obtained for surface heat transfer, indicating a need for more accurate turbulence models. The overall flowfield structure is similar to that observed in previous crossing shock interaction studies.

Narayanswami, N.↗