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At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Improvement in the quality of flow visualization in the Langley 0.3-meter transonic cryogenic tunnel

Optical diagnostic techniques have not been as successful in the 0.3-Meter Transonic Cryogenic Tunnel as in conventional wind tunnels. This paper describes a simple shadowgraph experiment which allowed evacuation of the optical paths outside the test section. The results show that refractive index variations induced by temperature gradients outside the test section account for most of the image degradation. Earlier reports had erroneously attributed this degradation to inhomogeneities in the test section. Evacuation of the paths leading to and from the test section significantly improves the quality of flow visualization.

Snow, W. L.↗
NASA NTRS2008

LOCAD-PTS: Operation of a New System for Microbial Monitoring Aboard the International Space Station (ISS)

Microorganisms within the space stations Salyut, Mir and the International Space Station (ISS), have traditionally been monitored with culture-based techniques. These techniques involve growing environmental samples (cabin water, air or surfaces) on agar-type media for several days, followed by visualization of resulting colonies; and return of samples to Earth for ground-based analysis. This approach has provided a wealth of useful data and enhanced our understanding of the microbial ecology within space stations. However, the approach is also limited by the following: i) More than 95% microorganisms in the environment cannot grow on conventional growth media; ii) Significant time lags occur between onboard sampling and colony visualization (3-5 days) and ground-based analysis (as long as several months); iii) Colonies are often difficult to visualize due to condensation within contact slide media plates; and iv) Techniques involve growth of potentially harmful microorganisms, which must then be disposed of safely. This report describes the operation of a new culture-independent technique onboard the ISS for rapid analysis (within minutes) of endotoxin and -1, 3-glucan, found in the cell walls of gram-negative bacteria and fungi, respectively. This technique involves analysis of environmental samples with the Limulus Amebocyte Lysate (LAL) assay in a handheld device. This handheld device and sampling system is known as the Lab-On-a-Chip Application Development Portable Test System (LOCAD-PTS). A poster will be presented that describes a comparative study between LOCAD-PTS analysis and existing culture-based methods onboard the ISS; together with an exploratory survey of surface endotoxin throughout the ISS. It is concluded that while a general correlation between LOCAD-PTS and traditional culture-based methods should not necessarily be expected, a combinatorial approach can be adopted where both sets of data are used together to generate a more complete story of the microbial ecology on the ISS.

Maule, J.↗
NASA NTRS1982

Flow visualization in a cryogenic wind tunnel using holography

Results of holographic flow visualization from tests made in the Langley 0.3 meter transonic cryogenic tunnel are presented. The tunnel was operated over a temperature range from 100 to 300 K and a pressure range from 1.1 to 4 atm. Interferometry at the facility may be of limited use at the low temperature high pressure conditions because of the jumbled nature of the reference fringes. The shadowgraph technique appears to be the best means of visualizing shocks at these high density conditions. The spot size at the focus of the reconstructed beams was measured and used as an indicator of density fluctuations in the flow field. These density fluctuations appear to be caused by temperature fluctuations of the test gas which are relatively independent of tunnel conditions.

Burner, A. W.↗
NASA NTRS1985

Flow visualization in a cryogenic wind tunnel using holography

Results of holographic flow visualization from tests made in the Langley 0.3 meter transonic cryogenic tunnel are presented. The tunnel was operated over a temperature range from 100 to 300 K and a pressure range from 1.1 to 4 atm. Interferometry at the facility may be of limited use at the low temperature high pressure conditions because of the jumbled nature of the reference fringes. The shadowgraph technique appears to be the best means of visualizing shocks at these high density conditions. The spot size at the focus of the reconstructed beams was measured and used as an indicator of density fluctuations in the flow field. These density fluctuations appear to be caused by temperature fluctuations of the test gas which are relatively independent of tunnel conditions.

Burner, A. W.↗
NASA NTRS1997

Application-Controlled Demand Paging for Out-of-Core Visualization

In the area of scientific visualization, input data sets are often very large. In visualization of Computational Fluid Dynamics (CFD) in particular, input data sets today can surpass 100 Gbytes, and are expected to scale with the ability of supercomputers to generate them. Some visualization tools already partition large data sets into segments, and load appropriate segments as they are needed. However, this does not remove the problem for two reasons: 1) there are data sets for which even the individual segments are too large for the largest graphics workstations, 2) many practitioners do not have access to workstations with the memory capacity required to load even a segment, especially since the state-of-the-art visualization tools tend to be developed by researchers with much more powerful machines. When the size of the data that must be accessed is larger than the size of memory, some form of virtual memory is simply required. This may be by segmentation, paging, or by paged segments. In this paper we demonstrate that complete reliance on operating system virtual memory for out-of-core visualization leads to poor performance. We then describe a paged segment system that we have implemented, and explore the principles of memory management that can be employed by the application for out-of-core visualization. We show that application control over some of these can significantly improve performance. We show that sparse traversal can be exploited by loading only those data actually required. We show also that application control over data loading can be exploited by 1) loading data from alternative storage format (in particular 3-dimensional data stored in sub-cubes), 2) controlling the page size. Both of these techniques effectively reduce the total memory required by visualization at run-time. We also describe experiments we have done on remote out-of-core visualization (when pages are read by demand from remote disk) whose results are promising.

Cox, Michael↗
NASA NTRS1994

A new technique for the measurement of surface shear stress vectors using liquid crystal coatings

Research has recently shown that liquid crystal coating (LCC) color-change response to shear depends on both shear stress magnitude and direction. Additional research was thus conducted to extend the LCC method from a flow-visualization tool to a surface shear stress vector measurement technique. A shear-sensitive LCC was applied to a planar test surface and illuminated by white light from the normal direction. A fiber optic probe was used to capture light scattered by the LCC from a point on the centerline of a turbulent, tangential-jet flow. Both the relative shear stress magnitude and the relative in-plane view angle between the sensor and the centerline shear vector were systematically varied. A spectrophotometer was used to obtain scattered-light spectra which were used to quantify the LCC color (dominant wavelength) as a function of shear stress magnitude and direction. At any fixed shear stress magnitude, the minimum dominant wavelength was measured when the shear vector was aligned with and directed away from the observer; changes in the relative in-plane view angle to either side of this vector/observer aligned position resulted in symmetric Gaussian increases in measured dominant wavelength. Based on these results, a vector measurement methodology, involving multiple oblique-view observations of the test surface, was formulated. Under present test conditions, the measurement resolution of this technique was found to be +/- 1 deg for vector orientations and +/- 5% for vector magnitudes. An approach t o extend the present methodology to full-surface applications is proposed.

Reda, Daniel C.↗
NASA NTRS2016

Preliminary Investigation of Surface Treatments to Enhance the Wear Resistance of 60-Nitinol

The use of protective surface treatments on 60-Nitinol (60wt%Ni-40wt%Ti) was studied. Various nitriding techniques as well as a (Ti, Al)N coating were evaluated visually, microscopically, and by hardness and scratch testing. The chemical composition of the surface treatments was investigated by x-ray techniques. The results indicate that very hard (greater than 1,000 HK) and adherent surface layers can be produced on 60-Nitinol. Further work is needed to determine the tribological properties of these surface treatments in relevant operating environments.

Nitinol↗
NASA NTRS2015

Global Skin-Friction Measurements Using Particle Image Surface FLow Visualization and a Luminescent Oil-Film

A quantitative global skin-friction measurement technique is proposed. An oil-film is doped with a luminescent molecule and thereby made to fluoresce in order to resolve oil-film thickness, and Particle Image Surface Flow Visualization is used to resolve the velocity field of the surface of the oil-film. Skin-friction is then calculated at location x as (x )xh, where x is the displacement of the surface of the oil-film and is the dynamic viscosity of the oil. The data collection procedure and data analysis procedures are explained, and preliminary experimental skin-friction results for flow over the wing of the CRM are presented.

FISF↗
NASA NTRS2002

Visualizing Spatially Varying Distribution Data

Box plot is a compact representation that encodes the minimum, maximum, mean, median, and quarters information of a distribution. In practice, a single box plot is drawn for each variable of interest. With the advent of more accessible computing power, we are now facing the problem of visual icing data where there is a distribution at each 2D spatial location. Simply extending the box plot technique to distributions over 2D domain is not straightforward. One challenge is reducing the visual clutter if a box plot is drawn over each grid location in the 2D domain. This paper presents and discusses two general approaches, using parametric statistics and shape descriptors, to present 2D distribution data sets. Both approaches provide additional insights compared to the traditional box plot technique

Kao, David↗
NASA NTRS2003

Utilization of the Space Vision System as an Augmented Reality System For Mission Operations

Augmented reality is a technique whereby computer generated images are superimposed on live images for visual enhancement. Augmented reality can also be characterized as dynamic overlays when computer generated images are registered with moving objects in a live image. This technique has been successfully implemented, with low to medium levels of registration precision, in an NRA funded project entitled, "Improving Human Task Performance with Luminance Images and Dynamic Overlays". Future research is already being planned to also utilize a laboratory-based system where more extensive subject testing can be performed. However successful this might be, the problem will still be whether such a technology can be used with flight hardware. To answer this question, the Canadian Space Vision System (SVS) will be tested as an augmented reality system capable of improving human performance where the operation requires indirect viewing. This system has already been certified for flight and is currently flown on each shuttle mission for station assembly. Successful development and utilization of this system in a ground-based experiment will expand its utilization for on-orbit mission operations. Current research and development regarding the use of augmented reality technology is being simulated using ground-based equipment. This is an appropriate approach for development of symbology (graphics and annotation) optimal for human performance and for development of optimal image registration techniques. It is anticipated that this technology will become more pervasive as it matures. Because we know what and where almost everything is on ISS, this reduces the registration problem and improves the computer model of that reality, making augmented reality an attractive tool, provided we know how to use it. This is the basis for current research in this area. However, there is a missing element to this process. It is the link from this research to the current ISS video system and to flight hardware capable of utilizing this technology. This is the basis for this proposed Space Human Factors Engineering project, the determination of the display symbology within the performance limits of the Space Vision System that will objectively improve human performance. This utilization of existing flight hardware will greatly reduce the costs of implementation for flight. Besides being used onboard shuttle and space station and as a ground-based system for mission operational support, it also has great potential for science and medical training and diagnostics, remote learning, team learning, video/media conferencing, and educational outreach.

Maida, James C.↗
NASA NTRS1992

RGB-NDVI colour composites for visualizing forest change dynamics

The study presents a simple and logical technique to display and quantify forest change using three dates of satellite imagery. The normalized difference vegetation index (NDVI) was computed for each date of imagery to define high and low vegetation biomass. Color composites were generated by combining each date of NDVI with either the red, green, or blue (RGB) image planes in an image display monitor. Harvest and regeneration areas were quantified by applying a modified parallelepiped classification creating an RGB-NDVI image with 27 classes that were grouped into nine major forest change categories. Aerial photographs and stand history maps are compared with the forest changes indicated by the RGB-NDVI image. The utility of the RGB-NDVI technique for supporting forest inventories and updating forest resource information systems are presented and discussed.

Sader, S. A.↗
NASA NTRS1983

Cloud cover typing from environmental satellite imagery. Discriminating cloud structure with Fast Fourier Transforms (FFT)

The use of two dimensional Fast Fourier Transforms (FFTs) subjected to pattern recognition technology for the identification and classification of low altitude stratus cloud structure from Geostationary Operational Environmental Satellite (GOES) imagery was examined. The development of a scene independent pattern recognition methodology, unconstrained by conventional cloud morphological classifications was emphasized. A technique for extracting cloud shape, direction, and size attributes from GOES visual imagery was developed. These attributes were combined with two statistical attributes (cloud mean brightness, cloud standard deviation), and interrogated using unsupervised clustering amd maximum likelihood classification techniques. Results indicate that: (1) the key cloud discrimination attributes are mean brightness, direction, shape, and minimum size; (2) cloud structure can be differentiated at given pixel scales; (3) cloud type may be identifiable at coarser scales; (4) there are positive indications of scene independence which would permit development of a cloud signature bank; (5) edge enhancement of GOES imagery does not appreciably improve cloud classification over the use of raw data; and (6) the GOES imagery must be apodized before generation of FFTs.

Logan, T. L.↗
NASA NTRS1992

Processing infrared images of aircraft lapjoints

Techniques for processing IR images of aging aircraft lapjoint data are discussed. Attention is given to a technique for detecting disbonds in aircraft lapjoints which clearly delineates the disbonded region from the bonded regions. The technique is weak on unpainted aircraft skin surfaces, but can be overridden by using a self-adhering contact sheet. Neural network analysis on raw temperature data has been shown to be an effective tool for visualization of images. Numerical simulation results show the above processing technique to be an effective tool in delineating the disbonds.

Syed, Hazari↗
NASA NTRS1992

WELDSMART: A vision-based expert system for quality control

This work was aimed at exploring means for utilizing computer technology in quality inspection and evaluation. Inspection of metallic welds was selected as the main application for this development and primary emphasis was placed on visual inspection, as opposed to other inspection methods, such as radiographic techniques. Emphasis was placed on methodologies with the potential for use in real-time quality control systems. Because quality evaluation is somewhat subjective, despite various efforts to classify discontinuities and standardize inspection methods, the task of using a computer for both inspection and evaluation was not trivial. The work started out with a review of the various inspection techniques that are used for quality control in welding. Among other observations from this review was the finding that most weld defects result in abnormalities that may be seen by visual inspection. This supports the approach of emphasizing visual inspection for this work. Quality control consists of two phases: (1) identification of weld discontinuities (some of which may be severe enough to be classified as defects), and (2) assessment or evaluation of the weld based on the observed discontinuities. Usually the latter phase results in a pass/fail judgement for the inspected piece. It is the conclusion of this work that the first of the above tasks, identification of discontinuities, is the most challenging one. It calls for sophisticated image processing and image analysis techniques, and frequently ad hoc methods have to be developed to identify specific features in the weld image. The difficulty of this task is generally not due to limited computing power. In most cases it was found that a modest personal computer or workstation could carry out most computations in a reasonably short time period. Rather, the algorithms and methods necessary for identifying weld discontinuities were in some cases limited. The fact that specific techniques were finally developed and successfully demosntrated to work illustrates that the general approach taken here appears to be promising for commercial development of computerized quality inspection systems. Inspection based on these techniques may be used to supplement or substitute more elaborate inspection methods, such as x-ray inspections.

Andersen, Kristinn↗
NASA NTRSDate not supplied

Particle Seeding Method for Small-Scale, High-Pressure Nozzles

NASA tests new launch and reentry vehicle configurations in wind tunnels, where flow visualizations and quantitative flowfield measurements are often desired. Some of these vehicles have rocket motors for propulsion, retro-propulsion, or reaction control. High-pressure air is used to supply these rocket motor plumes. However, it is difficult to make off-body measurements in these regions, for several reasons. First, the plumes themselves lack seeding particles for flow diagnostics, and at the low pressures after expansion, Rayleigh scattering or other molecular techniques yield insufficient signal for flow velocity measurements. Second, the plumes displace particle-seeded tunnel air, preventing measurements in the vicinity of the plume. Third, the plumes force shock waves ahead of the vehicle, which melts the ice crystal fog commonly used for visualization and measurement techniques in certain facilities. In the current work, a novel method for seeding the flow in these small-scale, high-pressure nozzles has been devised and initially demonstrated, potentially enabling quantitative and qualitative measurements with particle-based instruments such as Doppler global velocimetry or particle image velocimetry. The method involves a Venturi contraction to draw the seed liquid out of a reservoir and into the nozzle channel, wherein shearing forces atomize the seed into particles. The concept was tested with a laser sheet visualization, which demonstrated that the flow rate of liquid spray was controllable; a valve could be adjusted to drop the flow rate by up to 65%. This relatively inexpensive and simple technique may prove useful in wind tunnel experiments involving particle-based laser diagnostics and small, high-pressure nozzles.

Aditya S. Acharya↗
NASA NTRSDate not supplied

Particle Seeding Method for Small-Scale, High-Pressure Nozzles

NASA tests new launch and reentry vehicle configurations in wind tunnels, where flow visualizations and quantitative flowfield measurements are often desired. Some of these vehicles have rocket motors for propulsion, retro-propulsion, or reaction control. High-pressure air is used to supply these rocket motor plumes. However, it is difficult to make off-body measurements in these regions, for several reasons. First, the plumes themselves lack seeding particles for flow diagnostics, and at the low pressures after expansion, Rayleigh scattering or other molecular techniques yield insufficient signal for flow velocity measurements. Second, the plumes displace particle-seeded tunnel air, preventing measurements in the vicinity of the plume. Third, the plumes force shock waves ahead of the vehicle, which melts the ice crystal fog commonly used for visualization and measurement techniques in certain facilities. In the current work, a novel method for seeding the flow in these small-scale, high-pressure nozzles has been devised and initially demonstrated, potentially enabling quantitative and qualitative measurements with particle-based instruments such as Doppler global velocimetry or particle image velocimetry. The method involves a Venturi contraction to draw the seed liquid out of a reservoir and into the nozzle channel, wherein shearing forces atomize the seed into particles. The concept was tested with a laser sheet visualization, which demonstrated that the flow rate of liquid spray was controllable; a valve could be adjusted to drop the flow rate by up to 65%. This relatively inexpensive and simple technique may prove useful in wind tunnel experiments involving particle-based laser diagnostics and small, high-pressure nozzles.

lasers↗
NASA NTRS1976

Particle and flow field measurements by laser holography

Holograms make transmission recordings of aerodynamic events which are real-illuminated with ground-glass light diffusers and with no requirements for precision. The three-dimensional interferograms can be recorded by stored-beam, double-exposure, and double-plate techniques. Weak traveling shock waves, generated by rotating blade rows of an aircraft fan compressor, can be visualized by rapid double-exposure holograms recorded with a ruby laser. The same laser technique can also determine flow velocities from holograms of small flow-entrained particles. Particles larger than one-quarter millimeter are recorded under rear diffuse illumination conditions. Smaller particles can be recorded by their own forward scattering of laser light through the sensitivity of the holographic process for weak signals. Since the holographic apparatus can be path-matched, both particle and flow interferograms can be recorded with lasers of short coherence length.

Wuerker, R. F.↗