1 Imaging Techniques for Flow and Motion Measurement Lecture 18 Lichuan Gui University of...

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Imaging Techniques for Flow and Motion Measurement

Lecture 18

Lichuan Gui

University of Mississippi

2011

Large-scale PIV and Large-scale PIV and

Stereo High-Speed ImagingStereo High-Speed Imaging

2

Large-Scale PIVLarge-Scale PIVRiver surface flow measurement

City map

river

Tower

Video set at 40m height

Camera view

Floating tracer

3

Large-Scale PIVLarge-Scale PIVRiver surface flow measurement

Original image

Calibrated image

Physical & image coordinates

Flow filed

4

Large-Scale PIVLarge-Scale PIVDistorted image calibration

Physical & image coordinates- Physical coordinates (X,Y)

- Image coordinates (x,y)

- Calibration marking points (Xk,Yk) (xk,yk) for k=1,2,,N

- Image calibration function

1,

1 54

876

54

321

ybxb

bybxbY

ybxb

bybxbX

Minimal N=4 for determining constants bi (i=1,2,,8)

- inverse calibration function

716242516574

6381143846

716242516574

8275532785

bbbbYbbbbXbbbb

bbbbYbbbXbbby

bbbbYbbbbXbbbb

bbbbYbbbXbbbx

Straight-line-conservedtransformation

5

Large-Scale PIVLarge-Scale PIVDistorted image calibration

4

3

2

1

4

3

2

1

8

7

6

5

4

3

2

1

444444

333333

222222

111111

444444

333333

222222

111111

1000

1000

1000

1000

0001

0001

0001

0001

Y

Y

Y

Y

X

X

X

X

b

b

b

b

b

b

b

b

yxYyYx

yxYyYx

yxYyYx

yxYyYx

XyXxyx

XyXxyx

XyXxyx

XyXxyx4 marking points

>4 marking points – least square approach

N

kkkkkkkkkkkkk YXbbybxbYXybYXxbbybx

1

287654321

8,,2,10

iforbi

6

Large-Scale PIVLarge-Scale PIVEvaluation 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 recordings Evaluation results

Example of LSPIV tests for steady water surface flow

7

Large-Scale PIVLarge-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. 27th IAHR Cong., San Francisco, Vol.B, No.1, pp.227-232

– Practice with EDPIV

• Work with sample: IMAGE GROUP: DISTORTED PIV IMAGES

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Gray value resolution

10-bit CMOS sensor

17.5µm pixels

Frame rate & digital resolution

10241024 @ 2000 fps

1024256 @ 8000 fps

- High-speed camera

Stereo High-Speed ImagingStereo High-Speed Imaging- Optical configuration outside the

camera Mirror

Lens

Mirror

Alate

Mirrorimage

Mirror image

Front view

Side view

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Lens adaptor

Mirrors

Image sensor (1024256)

Block

Slit apertures

Lens

Mirror images

- Optical configuration inside the camera

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High-speed camera Mirrors Back lighting

Tethered fire ant alate Microphones

- Experimental setup with sound recording

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Stereo High-Speed ImagingStereo High-Speed Imaging- Experimental setup with sound recording

Sound recorded from bottom & rear with MCDL

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Stereo High-Speed ImagingStereo High-Speed Imaging- Sample image & postprocessing

Raw image

Background

Processed

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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

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- New optic table and magnetic holders for higher precision

- New template for adjusting mirror angles to ensure 90o difference between front and side- views

- Tested ant body carefully oriented

- Improved system for wing motion reconstruction

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O: root of the wing T: tip of the wing 3: the 3rd 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

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Stereo High-Speed ImagingStereo High-Speed Imaging- Wing root positionWing root position

More frames may be necessary for higher accuracy & reliability

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Stereo High-Speed ImagingStereo High-Speed Imaging- 3D view of the wing surface D 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

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Wing surface function:

BzAxy

333 BzAxy

BzAxy ttt

B

A

zy

xy

1

1

tan

tan

OT&OZ surface function:

Cxy tt xyC /

Wing rotation angle:

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1cos

2221

CBA

CA

- Data reduction equations

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Stereo High-Speed ImagingStereo High-Speed Imaging- Example I: BIFA male test on July 8, 2006

Image size: 590190 pixels, digital resolution: 22.35 pixel/mm

Body weight: 5.5 mg Body length: 6 mm

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t/T [T=9.25 ms]

Win

gtip

posi

tion

[mm

]

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

xt

yt

zt

Forwing

t/T [T=9.25 ms]

Win

gtip

posi

tion

[mm

]

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

xt

yt

zt

Hindwing

- Wing tip position of the BIFA male

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t/T [T=9.25 ms]

Win

gsu

rfac

ean

gles

[]

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-120.0

-90.0

-60.0

-30.0

0.0

30.0

60.0

90.0

120.0

xy

zy

Hindwing

t/T [T=9.25 ms]

Win

gsu

rfac

ean

gles

[]

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-120.0

-90.0

-60.0

-30.0

0.0

30.0

60.0

90.0

120.0

xy

zy

Forewing

- Wing angles of the BIFA male

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Stereo High-Speed ImagingStereo High-Speed Imaging- High resolution picture of the forewing

O T

Image size: 850×300 pixels Digital resolution: 128 pixel/mm

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Stereo High-Speed ImagingStereo High-Speed Imaging- High resolution picture of the hindwing

O T

LH

Gray value distribution: G(L,H)

Image size: 850×300 pixels Digital resolution: 128 pixel/mm

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Stereo High-Speed ImagingStereo High-Speed Imaging- Simulating images form three view angles

(x,y,z)H

L

gf(x,y)=G(L,H)

Front view image:

gs(z,y)=G(L,H)

Side view image:

gt(x,z)=G(L,H)

Top view image:

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

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

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

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– 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: http://insectscience.org/10.19

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