1 / 17

High precision image-based tracking of a rigid body moving within a fluid

High precision image-based tracking of a rigid body moving within a fluid. Stuart Laurence, Jan Martinez Schramm German Aerospace Center (DLR), G öttingen, Germany APS/DFD, 23 November 2010. Motivation.

stormy
Télécharger la présentation

High precision image-based tracking of a rigid body moving within a fluid

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. High precision image-based tracking of a rigid body moving within a fluid Stuart Laurence, Jan Martinez Schramm German Aerospace Center (DLR), Göttingen, Germany APS/DFD, 23 November 2010

  2. Motivation • Visualization-based techniques an attractive option for measuring displacements (and derived quantities) of rigid bodies in fluids, as they are completely non-intrusive • Particularly attractive for force-measurement in short-duration hypersonic facilities, as few other options available • However, measurement precision critical – in past (film-based analog techniques) displacement measurements limited to ~50 μm • Focus here on edge-detection-based techniques combined with least-squares fitting (suitable for silhouette images from schlieren, etc.) • Assumptions: no changes to body profile; motion two dimensional + one axis of rotation

  3. Analytic-fitting technique Edge detection Model edge tracing and sub-pixel detection Least-squares fitting

  4. Free-flight measurements with analytic-fitting technique • Image-based measurements show reasonable agreement with accelerometer measurements • Response time for 14 kfps estimated to be ~0.5 ms

  5. Problems with analytic-fitting technique • Model cross-sectional profile must be expressible analytically (can be avoided by using, e.g., splines) • For all but simplest geometries, fitting procedure is iterative (slow!) • Reasonably complete profile required for convergence

  6. Edge-tracking technique • Based on matching closest edge-points in reference and displaced images • Edge angle assumed to be the same for each edge-point pair

  7. Edge-tracking technique • Based on matching closest edge-points in reference and displaced images • Edge angle assumed to be the same for each edge-point pair linear least-squares problem for Δx and Δy b) with errors a) no errors

  8. Application of edge-tracking technique

  9. Error estimation through artificial image analysis • Errors introduced by pixellation/edge-detection (can be reduced through more precise algorithms) and CCD noise (unavoidable at given light conditions) • Such errors can be estimated through analysis of artificially constructed images

  10. Error determination from calibrated sphere measurements • Precision-machined 40-mm diameter sphere controlled by linear displacement stepper • Magnification ~300 μm/pixel • Position determination from tracking techniques compared with inputted displacements • Standard error ~1.3 μm (A) Shimadzu HPV-1; (B) Telephoto lens; (C) Precision-machined sphere; (D) Linear displacement stage; (E) Light source; (F) Light-diffusing material

  11. Errors in constant acceleration measurements • Error in measured constant acceleration, a, can be determined from assumed displacement error (δ): (n = number of measurement points) • For micron-level precision in displacement, accurate (~1%) acceleration measurements possible even for millisecond test times

  12. Errors in constant acceleration measurements • Error in measured constant acceleration, a, can be determined from assumed displacement error (δ): (n = number of measurement points) • For micron-level precision in displacement, accurate (~1%) acceleration measurements possible even for millisecond test times

  13. Conclusions • Technique originally developed for bodies with analytically expressible cross-sections • Generalized to arbitrary body geometries • Displacement measurements to micron level for wind-tunnel scale models – allows acceleration measurements to <1% under typical conditions • Generalization to three-dimensional motions?

  14. Application of edge-tracking technique

  15. Shock-wave surfing Error in edge-point locations Optical distortions can become problematic for large fields-of-view Can be corrected for using reference images

  16. Shock-wave surfing Displacements Optical distortions can become problematic for large fields-of-view Can be corrected for using reference images

  17. Shock-wave surfing Force coefficients Optical distortions can become problematic for large fields-of-view Can be corrected for using reference images

More Related