Spatial cross-correlating velocimeter
First Claim
1. A method of measuring velocities at a plurality of locations in a moving medium exhibiting imagable inhomogeneities that move with the medium, said method comprising the steps of:
- (a) obtaining a first image of the inhomogeneities within a predetermined area of the medium;
(b) obtaining a second image of the inhomogeneities within the predetermined area of the medium with the second image being obtained within a time period sufficiently short to insure that substantially all of the inhomogeneities captured within the first image are present in the second image;
(c) digitizing the information contained in the first and second images obtained in steps (a) and (b);
(d) constructing a first numerical array representative of the digitized information produced in step (c) for the first image;
(e) constructing a second numerical array representative of the digitized information produced in step (c) for the second image;
(f) partitioning each of the first and second numerical arrays into a plurality of sub-arrays with each sub-array corresponding to one of the plurality of locations in the moving medium for which the velocity is to be measured;
(g) determining the cross-correlation matrix between each sub-array of the first numerical array and the corresponding sub-array of the second numerical array;
(h) identifying the extreme value within each of the cross-correlation matrices determined in step (g);
(i) for each cross-correlation matrix from step (g), determining the vector corresponding to the displacement within the matrix of the extreme value from the position corresponding to no displacement;
(j) converting each vector determined in step (i) to a vector having units of spacial displacement; and
(k) applying the known time between the first image and the second image to convert each displacement vector to a corresponding velocity vector.
0 Assignments
0 Petitions
Accused Products
Abstract
This invention enables the simultaneous measurement of two components of instantaneous velocity at several points over an area in a specified cross-section of a flowing fluid or on a vibrating solid surface. It is applicable to large areas, and to situations where the measurement must be conducted from large distances. It uses digital cross-correlation, between two images taken within a short time interval, of the scattering patterns from the plane of interest. The patterns can be random, periodic, or quasi-periodic, and the individual light-scattering features of the patterns need not be resolved. The information density in the images can vary from being sparse to dense. Since high values of correlation coefficients are not required, the method survives substantial amounts of noise in the images. The method is suitable for implementation with very short facility run-times. The post-processing is fully automated and is performed using moderate computational resources. The invention consists of the concept, the method, and the present implementations of the method.
-
Citations
19 Claims
-
1. A method of measuring velocities at a plurality of locations in a moving medium exhibiting imagable inhomogeneities that move with the medium, said method comprising the steps of:
-
(a) obtaining a first image of the inhomogeneities within a predetermined area of the medium; (b) obtaining a second image of the inhomogeneities within the predetermined area of the medium with the second image being obtained within a time period sufficiently short to insure that substantially all of the inhomogeneities captured within the first image are present in the second image; (c) digitizing the information contained in the first and second images obtained in steps (a) and (b); (d) constructing a first numerical array representative of the digitized information produced in step (c) for the first image; (e) constructing a second numerical array representative of the digitized information produced in step (c) for the second image; (f) partitioning each of the first and second numerical arrays into a plurality of sub-arrays with each sub-array corresponding to one of the plurality of locations in the moving medium for which the velocity is to be measured; (g) determining the cross-correlation matrix between each sub-array of the first numerical array and the corresponding sub-array of the second numerical array; (h) identifying the extreme value within each of the cross-correlation matrices determined in step (g); (i) for each cross-correlation matrix from step (g), determining the vector corresponding to the displacement within the matrix of the extreme value from the position corresponding to no displacement; (j) converting each vector determined in step (i) to a vector having units of spacial displacement; and (k) applying the known time between the first image and the second image to convert each displacement vector to a corresponding velocity vector. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
-
-
10. A method of determining selected dynamics within a preselected substantially planar region of a fluid flow comprising the steps of:
-
(a) inducing within the flow patterns that emulate the movement of fluid within the flow; (b) obtaining a first image of the patterns within the preselected substantially planar region of the flow; (c) delaying for a time sufficient to allow the patterns within the preselected substantially planar region to shift with the moving fluid by a predetermined amount; (d) obtaining a second image of the patterns within the preselected substantially planar region of the flow; (e) digitizing the first image to generate a first numerical matrix with the elements of the first matrix being indicative of a predetermined characteristic of the imaged patterns; (f) digitizing the second image to generate a second numerical matrix with the elements of the second matrix being indicative of the predetermined characteristic of the imaged patterns; (g) calculating the cross-correlation between the second numerical matrix and the first numerical matrix; (h) identifying the location of the extreme value of the cross-correlation; and (i) mathematically converting the identified location of the extreme value to units of the selected dynamics to be determined. - View Dependent Claims (11, 12, 13, 14, 15, 16, 18, 19)
-
-
17. An apparatus for determining selected dynamics within a preselected substantially planar region of a fluid flow comprising the steps of:
-
means for inducing within the flow patterns that emulate the movement of fluid within the flow; means for obtaining a first image of the patterns within the preselected substantially planar region of the flow; means for inducing a delay for a time sufficient to allow the patterns within the preselected substantially region to shift with the moving fluid by a predetermined amount; means for obtaining a second image of the patterns within the preselected substantially planar region of the flow; means for digitizing the first image to generate a first numerical matrix with the elements of the first matrix being indicative of a predetermined characteristic of the imaged patterns; means for digitizing the second image to generate a second numerical matrix with the elements of the second matrix being indicative of the predetermined characteristic of the imaged patterns; means for calculating the cross-correlation between the second numerical matrix and the first numerical matrix; means for identifying the location of the extreme value of the cross-correlation; and means for mathematically converting the identified location of the extreme value to units of the selected dynamics to be determined.
-
Specification