Spatial cross-correlating velocimeter

Image analysis – Histogram processing – For setting a threshold

Patent

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

382 42, 7386106, G06K 900

Patent

active

052492389

DESCRIPTION:

BRIEF SUMMARY
e domain of greatest practical interest.


BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, related figures have the same number but different alphabetic suffixes.
FIGS. 1(a)-1(b): Two digitized images of the random motion of air in a room, illuminated by a copper vapor laser sheet. The image in FIG. 1b was taken 0.5 second after that in FIG. 1a.
FIGS. 2(a)-2(b): a) Subimages of a pair of digitized image arrays b) Spatial cross-correlation function for a sub-image pair, showing shift of the peak from (0,0). This function was computed from two arrays of random numbers, the second generated by shifting the first. After shifting, uncorrelated random numbers were added to each array to simulate noise.
FIG. 3: Flow Chart of the Spatial Cross-Correlation Velocimeter method.
FIGS. 4(a)-4(b): Creation of light sheet from (a) a laser source and (b) from a non-laser source.
FIG. 5: The effect of noise on the determination of the correlation peak between two shifted arrays of a random number set. The ordinate is the amplitude of the second-highest peak in the correlation, as a percentage of the highest. The abcissa is the amplitude of uncorrelated noise as a percentage of the amplitude of the shifted random set.
FIG. 6: Arrangement used in implementation of the SCV method to measure the displacement of a solid surface with sandpaper attached to it.
FIG. 7: 7.times.5 vector plot showing the displacement of the solid surface.
FIG. 8: Measured versus actual values of displacement of the solid surface.
FIG. 9: Arrangement used to implement the SCV method to measure the surface velocity of water around an airfoil placed at high angle of attack.
FIG. 10: Vector plot of separated flow over the airfoil.
FIG. 11: Vector plot of instantaneous water surface velocity behind a circular cylinder.
FIG. 12: Arrangement for SCV around a wing in a 2.14 m.times.2.74 m wind tunnel.
FIGS. 13(a)-13(c): Sequence of instantaneous velocity plots around the wing in plunging motion.
FIG. 14: Spatial cross-correlation between sub-images with quasi-periodic intensity distributions.


DESCRIPTION OF THE PREFERRED EMBODIMENT

Transfer of momentum in fluids occurs primarily through large, coherent flow structures. These structures have finite lifetimes, so that there must be some degree of correlation between the features of two images taken within a time interval which is shorter than the integral time scale of the local motion. The desired end result is an accurate, quantitative representation of the velocity vector at as many points as possible in the area of interest. The differences between the two images would be caused by the following:
a) convection of features by the mean fluid motion,
b) exchange of fluid across the illuminated region,
c) distortion of the flow structures by shear and dilatation,
d) noise in the image acquisition and processing.
The problem is to determine the direction and magnitude of (a), and the detailed velocity distribution from (c), despite the errors and noise caused by (b) and (d). If (a) overwhelms the other effects, the displacements of given features of the image can be easily measured at a few points, averaged, and converted to velocity using the known time difference between the two images. When effects (b), (c), and (d) are present, this must be performed statistically, using information from every element of the two images. This is achieved by spatial cross-correlation.
To obtain an image, the flow is "seeded" with particles which scatter light. Alternatively, in some flows, the motion of density gradients or concentration gradients can be detected. As seen from FIG. 1, one needs to distinguish only the patterns formed by large numbers of particles, not the individual particles themselves, to discern fluid motion. Also, the patterns can be statistically random. In fact, the more random they are, the easier it is to obtain and interpret the results.
Consider a cross-section A of a flowfield, shown in FIG. 1(a), illuminated with intensity I.sub.1 (x,y) of light or other electromagnetic radiation. We assum

REFERENCES:
patent: 4019038 (1977-04-01), Critten et al.
patent: 4248085 (1981-02-01), Coulthard
patent: 4257275 (1981-03-01), Kurita et al.
patent: 4598593 (1986-07-01), Sheen et al.
patent: 4604904 (1986-08-01), Massen
patent: 4707130 (1987-11-01), Hofmann et al.
patent: 4729109 (1988-03-01), Adrian et al.
patent: 4733962 (1988-03-01), Brendemuehl
patent: 4752727 (1988-06-01), Schneider
patent: 4859055 (1989-08-01), Gal et al.
patent: 4866639 (1989-09-01), Adrian
patent: 4912519 (1990-03-01), Yoshida et al.
patent: 4976154 (1990-12-01), Schneider et al.
patent: 4980922 (1990-12-01), Leib
patent: 5011273 (1991-04-01), Farrell
patent: 5029481 (1991-07-01), Keech
Lakshmurarasimha, A. Tabakoff, W. Metwally, A., "LDV Measurements in the Vortex Region of a Radial Inflow Turbine", AIAA Paper 89-1823, Jun. 12-14, 1989.
Komerath, N. M. et al, "The Velocity Field of a Lifting Model Rotor Blade in Hover", Mar. 1988, pp. 250-257, Journal of Aircraft.
Bachalo, W. D. et al, "Phase/Doppler Spray Analyzer for Simultaneous Measurements of Drop Size & Velocity Distributions", Optical Engineering, vol. 23, No. 5, Sep./Oct. 1984, pp. 583-590.
Hiller, B. et al, "Laser-Induced Fluorescence Technnique for Velocity Field Measurements in Subsonic Gas Flows", Optics Letters, 8(9) 474-476, 1983.
Hiller, B. et al, "Simultaneous Measurements of Velocity & Pressure Fields in Subsonic and Supersonic Flows Through Image-Intensified Detection of Laser-Induced Fluorescence", AIAA Paper 86-0161, AIAA 24th Aerospace Science Meeting, Reno, Nev., Jan. 1986.
Miles, J., Rayleigh Scattering.
Meynart, R., "Digital Image Processing for Speckle Flow Velocimetry", Review of Scientific Instruments, 53(1), Jan. 1982, pp. 110-111.
Smith, C. A., Lourenco, L. M. M. et al., "The Development of Laser Speckle Velocimetry for the Measurement of Vortical Flow Fields", AIAA 86-0768, Mar. 1986.
Shepherd, W. C. F., Third Symposium on Combustion, Flame & Explosion Phenomena, Williams & Wilkins, 1949, pp. 301-316.
Reuss, D. L. et al, "Two Dimensinal Velocity Measurements in a Laminar Flame Using Particle Image Velocimetry", Combustion Science & Technology, Oct. 1989, pp. 73-83.
Post, M. et al, "Comparison of Two-Color Particle Imaging Velocimetry Data & Calculated Velocity Field in a Turbine Cascade", AIAA Paper 91-0274, 29th Aerospace Sciences Meeting, Reno, Nev., Jan. 1991.
Shakarriz,, A. et al "Quantitative Visualization of Junction Vortices Using Particle Displacement Velocimetry", AIAA Paper 91-0269, 29th Aerospace Sciences Meeting, Reno, Nev., Jan. 1991.
Yao, C. S. & Adrian, R. J., "Orthogonal Compression & 1-D Analysis Technique for Measurement of 2-D Particle Displacements in Pulsed Laser Velocimetry", Applied Optics, vol. 23, 1984, pp. 1687-1689.
James, M. R., et al "A High Accuracy Automated Strain-Field Mapper", Experimental Mechanics, Mar. 1990, pp. 60-67.
Gonzales, R. C., "Digital Image Processing", Addison-Wesley Publishing Co., Applied Mathematics & Computation Series, No. 13, 1982, pp. 58-65.
Pierce, A. D., "Acoustics An Introduction to Its Physical Principles & Applications", McGraw-Hill, 1981, pp. 86-88.
Komerath, N. M., Fawcett, P. A., & Ballarini, D., "Planar Velocimetry Using Digital Cross-Corrrelations". Developments in Theoretical & Applied Mechanics, vol. XV, Georgia Institute of Technology, Mar. 23, 1990.
Planar Velocimetry by Spatial Cross Correlation: Theoretical Basis and Validation, N. M. Komerath, P. A. Fawcett; 21st Plasma Dynamics, Fluid Dynamic

LandOfFree

Say what you really think

Search LandOfFree.com for the USA inventors and patents. Rate them and share your experience with other people.

Rating

Spatial cross-correlating velocimeter does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Spatial cross-correlating velocimeter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spatial cross-correlating velocimeter will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFUS-PAI-O-2196358

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.