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04/21/23 © 2012 UNIVERSITY OF ROSTOCK | FACULTY OF COMPUTER SCIENCE AND ELECTRICAL ENGINEERING
On Optical Quantification of Cavitation Properties
Stefan BorchertWillfried KrögerStephan HöhneNils DamaschkeZhiliang Zhou
Institute of General Electrical Engineering University of Rostock
CAV 2012, Singapore, 13.08.-16.08.2012
Institut für Allgemeine Elektrotechnik
KonKav I project (funded by BMWI)
Goals – Quantitative water quality
measurements– Quantitative cavitation property measurements
Imaging techniques– Shadow imaging – Laser calibration
Project partners– Hamburg Ship Model Basin (HSVA)– Potsdam Model Basin (SVA)– Technical University of Hamburg Harburg (TU-HH)– University of Rostock (URO)
04/21/23 © 2012 UNIVERSITY OF ROSTOCK | FACULTY OF COMPUTER SCIENCE AND ELECTRICAL ENGINEERING 2
Institut für Allgemeine Elektrotechnik
1. Lighting and cameras
Requirements
Diffuse lighting– Transmitted light (with diffusor)– Diffuse reflection– Glaring reflection– Direct lighting
Object lens– Small depth of focus -> large apterture – Large depth of focus -> small aperture
04/21/23 © 2012 UNIVERSITY OF ROSTOCK | FACULTY OF COMPUTER SCIENCE AND ELECTRICAL ENGINEERING 3
Best Quality
Worst Quality
Institut für Allgemeine Elektrotechnik
1. Lighting and cameras
Diffuse Reflector
Shadow imaging camera
Stroboscope
04/21/23 © 2012 UNIVERSITY OF ROSTOCK | FACULTY OF COMPUTER SCIENCE AND ELECTRICAL ENGINEERING 4
Institut für Allgemeine Elektrotechnik
2. Shadow imaging – cavitation thickness
Large aperture
2D foil
Sharp plane
Perspective view
Optical axis
Tunnel Window
WATER AIR
Sheet caviatation
04/21/23 © 2012 UNIVERSITY OF ROSTOCK | FACULTY OF COMPUTER SCIENCE AND ELECTRICAL ENGINEERING 5
Institut für Allgemeine Elektrotechnik
2. Shadow imaging – cavitation thickness
2D foil – no cavitation 2D foil – with cavitation
04/21/23 © 2012 UNIVERSITY OF ROSTOCK | FACULTY OF COMPUTER SCIENCE AND ELECTRICAL ENGINEERING 6
1 pixel = 40µm 1392x1040 pixel
Institut für Allgemeine Elektrotechnik
2. Shadow imaging – cavitation thickness
Occurrence of detected edges Extracted cavitation edges
Max
Mean
Min
Foil
04/21/23 © 2012 UNIVERSITY OF ROSTOCK | FACULTY OF COMPUTER SCIENCE AND ELECTRICAL ENGINEERING 7
1 pixel = 40µm 1392x1040 pixel
Institut für Allgemeine Elektrotechnik
3. Laser calibration
Average laser position Laser position regression
Required to convert image coordinates to physical coordinates- Physical step size is known (traversed by defined distance)- Laser also used to set depth of focus position
04/21/23 © 2012 UNIVERSITY OF ROSTOCK | FACULTY OF COMPUTER SCIENCE AND ELECTRICAL ENGINEERING 8
Institut für Allgemeine Elektrotechnik
2 stereometric cameras – identical object lens
4. Shadow imaging – tip vortex
04/21/23 © 2012 UNIVERSITY OF ROSTOCK | FACULTY OF COMPUTER SCIENCE AND ELECTRICAL ENGINEERING 9
Institut für Allgemeine Elektrotechnik
4. Shadow imaging – tip vortex
Propeller blade tip Binary representation
04/21/23 © 2012 UNIVERSITY OF ROSTOCK | FACULTY OF COMPUTER SCIENCE AND ELECTRICAL ENGINEERING 10
1 pixel = 70µm 1392x1040 pixel
Institut für Allgemeine Elektrotechnik
4. Shadow Imaging – tip vortex
Example frames Color coded occurence
04/21/23 © 2012 UNIVERSITY OF ROSTOCK | FACULTY OF COMPUTER SCIENCE AND ELECTRICAL ENGINEERING 11
1 pixel = 70µm 1392x1040 pixel
Institut für Allgemeine Elektrotechnik
5. Experimental results – 2D foil
Occurrence of detected edges
Extracted cavitation edges
inception σ=3 σ=2
04/21/23 © 2012 UNIVERSITY OF ROSTOCK | FACULTY OF COMPUTER SCIENCE AND ELECTRICAL ENGINEERING 12
Institut für Allgemeine Elektrotechnik
5. Experimental results – tip vortex
Occurrence of tip vortex – Stereo 1 (straight)
inception σ=3 σ=2
Occurrence of tip vortex – Stereo 2 (tilted)
04/21/23 © 2012 UNIVERSITY OF ROSTOCK | FACULTY OF COMPUTER SCIENCE AND ELECTRICAL ENGINEERING 13
Institut für Allgemeine Elektrotechnik
Conclusions
Limited optical access poses challenges– Non-tilted viewing angle if possible– Transmitted light if possible
Intermittent cavitation behavior poses challenges– Analyze temporal occurrence– Capture a large number of frames
Cavitation can be quantified– Laser calibration enables coordinate conversion
04/21/23 © 2012 UNIVERSITY OF ROSTOCK | FACULTY OF COMPUTER SCIENCE AND ELECTRICAL ENGINEERING 14
Institut für Allgemeine Elektrotechnik
Thanks for your attention
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04/21/23 © 2012 UNIVERSITY OF ROSTOCK | FACULTY OF COMPUTER SCIENCE AND ELECTRICAL ENGINEERING 15