1 Imaging Techniques for Flow and Motion Measurement Lecture 18 Lichuan Gui University of Mississippi 2011 Large-scale PIV and Stereo High-Speed Imaging

2 Large-Scale PIV River surface flow measurement City map river Tower Video set at 40m height Camera view Floating tracer

3 Large-Scale PIV River surface flow measurement Original image Calibrated image Physical & image coordinates Flow filed

4 Large-Scale PIV Distorted image calibration Physical & image coordinates - Physical coordinates (X,Y) - Image coordinates (x,y) - Calibration marking points (X k,Y k )  (x k,y k ) for k=1,2, ,N - Image calibration function Minimal N=4 for determining constants b i (i=1,2, ,8) - inverse calibration function Straight-line-conserved transformation

5 Large-Scale PIV Distorted image calibration 4 marking points >4 marking points – least square approach

6 Large-Scale PIV Evaluation of LSPIV recordings - Low-Image-Density PIV mode Particle image tracking or individual particle image pattern tracking - Low Re-number in many cases Average correlation method for steady flows Consecutive LSPIV recordingsEvaluation results Example of LSPIV tests for steady water surface flow

7 Large-Scale PIV –References Muto Y, Baba Y, Aya S (2002) Velocity measurements in open channel flow with rectangular embayments formed by spur dykes. Annuals of Disas. Prev. Res. Inst., Kyoto Univ., No.45B-2 Fujita I, Aya S, Deguchi T (1997) Surface velocity measurement of river flow using video images of an oblique angle. Proc. 27 th IAHR Cong., San Francisco, Vol.B, No.1, pp –Practice with EDPIV Work with sample: IMAGE GROUP: DISTORTED PIV IMAGES

8 Stereo High-Speed Imaging Gray value resolution 10-bit CMOS sensor 17.5µm pixels Frame rate & digital resolution 1024  2000 fps 1024  8000 fps - High-speed camera

Stereo High-Speed Imaging - Optical configuration outside the camera Mirror Lens Mirror Alate Mirror image Mirror image Front view Side view

10 Stereo High-Speed Imaging Lens adaptor Mirrors Image sensor (1024  256) Block Slit apertures Lens Mirror images - Optical configuration inside the camera

11 Stereo High-Speed Imaging High-speed camera MirrorsBack lighting Tethered fire ant alate Microphones - Experimental setup with sound recording

12 Stereo High-Speed Imaging - Experimental setup with sound recording Sound recorded from bottom & rear with MCDL

13 Stereo High-Speed Imaging - Sample image & postprocessing Raw image BackgroundProcessed

14 Stereo High-Speed Imaging 70 frames in the period of 8.8 ms (114Hz), bar chart represents sound pressure Synchronize motion w. sound in one period - Synchronize motion w. sound in one period

15 Stereo High-Speed Imaging - New optic table and magnetic holders for higher precision - New template for adjusting mirror angles to ensure 90 o difference between front and side- views - Tested ant body carefully oriented - Improved system for wing motion reconstruction

16 Stereo High-Speed Imaging O: root of the wing T: tip of the wing3: the 3 rd point at the wing surface Position & orientation of the wing - Position & orientation of the wing the wing assumed to be a planar surface without thickness

17 Stereo High-Speed Imaging Wing root position - Wing root position More frames may be necessary for higher accuracy & reliability

18 Stereo High-Speed Imaging D view of the wing surface - 3D view of the wing surface  : angle between wing surface & plane through OT & OZ  xy : wing angle in xy-plane  zy : wing angle in yz-plane Angles Pink: wing surface Yellow: OT & OZ Planes Axis of the wing: OT Axis of ant body: OZ Axis's

19 Stereo High-Speed Imaging Wing surface function: OT&OZ surface function: Wing rotation angle: - Data reduction equations

20 Stereo High-Speed Imaging - Example I: BIFA male test on July 8, 2006 Image size: 590  190 pixels, digital resolution: pixel/mm Body weight: 5.5 mg Body length: 6 mm

21 Stereo High-Speed Imaging - Wing tip position of the BIFA male

22 Stereo High-Speed Imaging - Wing angles of the BIFA male

23 Stereo High-Speed Imaging - High resolution picture of the forewing OT Image size: 850×300 pixels Digital resolution: 128 pixel/mm

24 Stereo High-Speed Imaging - High resolution picture of the hindwing OT L H Gray value distribution: G(L,H) Image size: 850×300 pixels Digital resolution: 128 pixel/mm

25 Stereo High-Speed Imaging - Simulating images form three view angles (x,y,z) H L g f (x,y)=G(L,H) Front view image: g s (z,y)=G(L,H) Side view image: g t (x,z)=G(L,H) Top view image:

26 Stereo High-Speed Imaging - Original (top) and simulated (bottom) images

27 Stereo High-Speed Imaging - Reconstructed 3D view of the male

28 Stereo High-Speed Imaging - Overlapped image of 74 frames

29 Stereo High-Speed Imaging –Reference Gui L, Fink T, Cao Z, Sun D, Seiner JM and Streett DA (2010) Fire ant alate wingmotion data and numerical reconstruction. Journal of Insect Science 10:9,available online: