AutoCAD,
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95
EE, 1990
ammetry -
ochschule
THE DYNAMIC DIGITAL PHOTOGRAMMETRIC MEASUREMENT AND VISUALISATION OF A 21M WIND TURBINE
ROTOR BLADE UNDERGOING STRUCTURAL ANALYSIS.
S. Robson and H. B. Setan.
Engineering Surveying Research Centre
Department of Civil Engineering
City University London, EC1V OHB
UNITED KINGDOM
Tel: +44 171 477 8000 xtn 3682
Facsimile: +44 171 8570
Email: S.Robson @city.ac.uk
Faculty of Surveying and Real Estate
Universiti Teknologi Malaysia
Locked Bag 791, 80990 Johor Bahru
MALAYSIA
Tel: +60 7-557 6160 xtn 2813
Facsimile: - +60 7 55 66 163
ISPRS Commission V, Working Group 3
KEY WORDS: Engineering, Metrology, Monitoring, Deformation Analysis, Digital Photogrammetry.
ABSTRACT
The testing and monitoring of structural components is standard practice in the construction industry, its aims being the
establishment of specifications, conformance to design and subsequent monitoring during and after construction.
Conventional structural monitoring methods include the use of a variety of instrumentation, for example, strain gauges,
electro-levels and deflection gauges. These are only capable of measuring deformation in, at most, two dimensions.
Digital photogrammetry combined with conventional survey can provide a complimentary non-contact measurement
technique able to quickly provide three dimensional spatial information of verifiable quality.
1. INTRODUCTION
Recent advances in camera sensor technology and
computer hardware mean that non-contact, on-line
inspection methods based on automated digital image
measurement offer much potential. Through international
research and development digital imaging technologies
allied with photogrammetric techniques are becoming
capable of achieving object space precision of the order
of 1:200,000 and better (Beyer 1995). Collaborative
research at City University has produced a suite of semi-
automated calibration, image capture and measurement
techniques which allow the accurate and reliable
computation of 3D co-ordinates within small object
volumes (Robson et al 1995).
The work described in this paper is based on the
photogrammetric co-ordination of retro-reflective targets
using a research orientated spatial acquisition system
which can employ between three and six multiplexed
analog CCD cameras. Target images are rapidly
measured and correlated to sub-pixel accuracies (Clarke
et al 1995) from which 3D co-ordinates may be
automatically computed using photogrammetric bundle
adjustment techniques. The algorithms for calibration of
the cameras used in this process have been modified to
include the variation of lens distortion with object space
distance where appropriate data are available (Fraser
and Shortis 1992). Physical and statistical checking
procedures are used throughout to ensure that the
resultant data are accurate, precise and reliable (Cooper
and Robson 1994).
The potential of these low cost videometric components is
now being explored within the structural monitoring
programme at City University. Some initial trial
experiments have been conducted to asses the ability of
493
the system to measure simple structures such as an |-
Beam under static loading (Robson and Cooper 1995),
and fine art wood panel paintings under changes in
environmental condition (Robson et al 1995). This paper
describes the system's application to the more
complicated case of the loading of a large composite wind
turbine rotor blade.
Figure 1 A wind turbine blade under test.
2. STRUCTURAL TESTING
City University is a key centre for the testing of large
composite wind turbine rotor.blades. Full scale structural
testing of rotor blades may be required for design
verification or for assessing the structural integrity of the
rotor blade. Various types of testing process are used
including fatigue tests, static tests and modal tests. The
example application described in this paper is a
distributed static loading test of a 21m long wind turbine
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996
