Photogrammetric recession measurements of an ablating surface
First Claim
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1. A system for measuring recession of an ablative surface during testing in an arcjet facility, the system comprising:
- (1) at least first and second cameras, positioned in or adjacent to an arcjet facility so that each camera views an ablating surface of a test article, having an arbitrary shape, from a different direction, and so that each of the at least first and second cameras acquires time-synchronized images of the ablating surface at a sequence of spaced apart imaging times during which the ablating surface is exposed to flow of a heated fluid in the arcjet facility and thereby undergoes ablation;
(2) a calibration mechanism for providing camera calibration coefficients for each of the at least first and second cameras by imaging a three dimensional calibration object and determining approximate transformations between two dimensional image-plane coordinates and three-dimensional physical object-space coordinates;
(3) a three dimensional surface grid of nodes that conforms to an initial shape of the ablating surface, to define measurement points on the ablating surface; and
(4) a computer that is programmed;
(a) to define image-plane coordinates for corresponding measurement points for each of the at least first and second cameras by mapping the nodes of the surface grid from the physical object-space coordinates to the image-plane coordinates for each of the at least first and second cameras;
(b) to track measurement points from each of the at least first and second cameras for the sequence of imaging times; and
(c) to compute the physical object-space coordinates of each measurement point from the image-plane coordinates and the camera calibration coefficients for the at least first and second cameras, to thereby estimate recession of the ablating surface.
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Abstract
An instrument and method for measuring the time history of recession of an ablating surface of a test article during testing in a high enthalpy thermal test facility, such as an arcjet. The method advances prior art by providing time-history data over the full ablating surface without targets and without any modifications to the test article. The method is non-intrusive, simple to implement, requires no external light source, and does not interfere with normal operations of the arcjet facility.
19 Citations
9 Claims
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1. A system for measuring recession of an ablative surface during testing in an arcjet facility, the system comprising:
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(1) at least first and second cameras, positioned in or adjacent to an arcjet facility so that each camera views an ablating surface of a test article, having an arbitrary shape, from a different direction, and so that each of the at least first and second cameras acquires time-synchronized images of the ablating surface at a sequence of spaced apart imaging times during which the ablating surface is exposed to flow of a heated fluid in the arcjet facility and thereby undergoes ablation; (2) a calibration mechanism for providing camera calibration coefficients for each of the at least first and second cameras by imaging a three dimensional calibration object and determining approximate transformations between two dimensional image-plane coordinates and three-dimensional physical object-space coordinates; (3) a three dimensional surface grid of nodes that conforms to an initial shape of the ablating surface, to define measurement points on the ablating surface; and (4) a computer that is programmed; (a) to define image-plane coordinates for corresponding measurement points for each of the at least first and second cameras by mapping the nodes of the surface grid from the physical object-space coordinates to the image-plane coordinates for each of the at least first and second cameras; (b) to track measurement points from each of the at least first and second cameras for the sequence of imaging times; and (c) to compute the physical object-space coordinates of each measurement point from the image-plane coordinates and the camera calibration coefficients for the at least first and second cameras, to thereby estimate recession of the ablating surface. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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Specification