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OPTIMIZATION PROBLEMS OF PHOTOGRAMMETRIC METHOD OF HYPERBOLIC COOLING TOWER MEASUREMENTS
Jézef WoZniak
Technical University of Wroclaw,
Institute of Geotechnics and Hydrotechnics Wroclaw, Plac Grunwaldzki 9, Poland
ABSTRACT :
In dependence on possibilities of signalling and on univocal identification of observed and control points
on external surface of reinforced concrete cooling tower, there are shown advantages and disadvantages of
monophotogrammetric method in comparison with stereophotogrammetric method.
There are shown some examples of graphic results presentation by means of own and commonly accessible packages
of computer programs.
KEY WORDS: Cooling towers, Deformation measurement, Photogrammetry.
1. INTRODUCTION
Reinforced concrete cooling towers which belong to
the biggest engineering thin-walled structures,
because of their geometric shape (mainly because of
relation between shell thickness to its diameter)
need constant macroscopic ‘inspection and shell
deformation investigation, because of industrial
aggressive atmosphere influence and also constant
surface wetting (Chauvel at all 1990, Golczyk 1989,
Owczarzy 1989, Owczarzy 1991).
Detailed investigations about reasons of almost ten
collapses of reinforced concrete hyperboloid cooling
towers, which took place since 1965 in Great Britain,
France and Poland, did not several one immediate
cause of disaster.
In reasons! analyses of not only collapses of cooling
towers but also minor impairments, there are
emphasized, apart from external factors, mainly very
strong wind pressure with variable velocity, the
realization imperfections and exploitation mistakes
(Golczyk 1989, Owczarzy 1989). Effects of these
incorrectnesses are phenomena:
- concrete degradation because of lack of maintenance
and preservation repairs;
- residual and dynamic deformations of the shell.
Evaluation of shell's stability and strength is
carried out to determine the cooling towers' state of
safety and exploitation reliability, taking into
consideration the investigations' results of above
mentioned phenomena. Mostly applied is the method of
finite element with taking into account the
geometrical and physical shell's imperfection. A net
of finite elements is generated on shell's surface
which theoretical shape is one sheet axially
symmetric hyperboloid. Values of geometrical and
physical imperfections are assigned to node lines,
but inside the net, these values are linearly
approximated. The geometrical imperfection values in
the finite element net taken from geodetic or
photogrammetric measurements results.
After cooling tower collapses, mainly in Great
Britain and France, there was determined the range of
cyclic geodetic and photogrammetric measurements of
all remaining cooling towers. At the first stage,
there are carried out the measurements of real shape
of shell outer surface with simultaneous record of
all injuries and defects in shell using photographic,
photogrammetric and thermovisional technics. During
subsequent inspection measurements carried out in the
aim to record the injuries’ and defects’ alterations,
there are used the same measurement method, with
particular consideration of photogrammetric method.
Besides photogrammetric methods, there are also used
for cooling tower shape investigations some special
geodetic system e.g.: measuring system Wild Leitz
ATMS - automatic theodolite measuring system, which
329
permits to determine, with a great accuracy, an
unlimited quantity of unsignalled points on cooling
tower surface without application of reflectors
(Katowski, 1990).
2. PHOTOGRAMMETRIC METHODS TO DETERMINE
GEOMETRIC IMPERFECTIONS
Collapse of a cooling tower at power station in
Turoszów, Poland, 1987, caused greater interest in
technic state of all remaining towers in Poland.
Determination necessity of real shape of cooling
towers external surface contributed to elaboration of
new methods or taking advantage of existing ones,
which permit to get the data for evaluation of
investigated objects stability. These methods can be
divided in two groups: monophotogrammetry and
sterephotogrammetry. Each of these methods has its
advantages and disadvantages, which may be essential
according to the measurement purpose, art of
geometric imperfections or possibilities of check-up
points’ signalling on cooling tower surface.
2.1 Monophotogrammetry method
Monophotogrammetry method used to investigation of
rotation surface shapes, is based on conic sections
method which, in classical solutions, is used to
determine the approximation parameters of a
hyperboloid and inclination of geometric axis.
when applicating monophotogrammetry, the conic
sections method (surrounding tangents’ method) is
used to the shape investigation on planes which
contains the tangency points of radii connecting
projection center which cooling tower surface
(Wozniak, 1988).
At the first stage of investigations, there is to be
determined the real and theoretical shape of cooling
tower external surface on ground of photogrammetric
pictures, taken from camera stands surrounding the
tower. Theoretic shape of rotational hyperboloid
surface at the plane containing tangency points of
observation radii from a given stand differs
according to coordinates of projection center
S(Xy5 ¥ys 2) and to hyperboloid semi-axes a and b.
General equations of the tangent lines, determining
the geometrical intersection point of vectors
perpendicular to the tangent direction and vectors
tangent to the direction from a given camera stand
has the following form:
2 2
2 2 pi Deyn (1)
z
2 2
a^ Zg a^ Ze £o
Assuming for each camera stand a local coordinate
system SCO, V > 2) » equation (1) in projection on
plane YZ shows a straight line with an inclination
angle e of the vertical (Fig. 1.).
