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(
Dx
150 mm) for each “flight” along the flume length.
The narrow-flume flying-probe bed-sensing transducers were arranged in four
rows (seven-eight probes along each row) across the flume (Fig.
9
), giving eight
continuous transects parallel to the flume centreline, with
Dx
20.6-24.8 mm,
Dy
¼
¼
12.5 mm and
¼
Dy
25 mm. For each flume, the probe positions along the flume were staggered
so that regular measurement grids wouldbeobtainedwhenthecarriagewas
moving and the Seatek probes were firing in sequence (Fig.
9
). For each recorded
bed surface, the collected data were filtered and cleaned to give a final digital
elevation map (DEM) from which the bed morphology could be quantified and
analysed.
Analyses of the collected flying-probe data confirm earlier indications (e.g.
Nordin
1971
; Goring et al.
1999
; Butler et al.
2001
) that the geometry of the 2D
autocorrelation function (or the closely related second-order structure function)
when applied to sand-bed elevation fields can provide an effective means of
assessing the three-dimensionality of sand waves (e.g. Coleman et al.
2008a
;
Coleman and Nikora
2011
). Application of 2D autocorrelation or structure function
analyses to measured bed morphologies can potentially aid quantitative assessment
of (a) the bed configuration per se, (b) the role of mobile-bed sand-wave form on
flow resistance, (c) the effects on sand-wave form of channel side-walls and the
channel aspect-ratio, and (d) the role of bedform shape on overhead turbulence and
sediment-transport characteristics (e.g. Best
2005
; Schindler and Robert
2005
;
Fernandez et al.
2006
).
¼
3.3 Bedform Four-Dimensionality and an IPT Carriage
While undertaking the flying-probe tests of the above SWAT.nz research
programme, it was realised that an improved carriage system could be utilised for
tests of moving instrumentation. A separate project was initiated to provide a
moving platform on which transducers and sensors may be mounted, with power
for the platform and the sensors supplied via an IPT (Induction Power Transfer)
system. With The University of Auckland being the world leader in IPT technology,
the system was also designed to enable both commands for carriage motor control
and also wide-bandwidth data from measuring instruments to be dynamically
transmitted across the IPT link between the carriage and a remote computer away
from the flume.
The IPT carriage facility (Fig.
4d
) was installed in 2005, with power supplied and
data transferred across an air gap by the IPT system (Saxena
2005
;Mu
2005
). The
carriage was successfully operated at controlled speeds of up to 2 m/s in initial tests,
although the use of larger support wheels for the carriage will enable greater carriage
speeds. The IPT system means that any potential hazard of accidental electric shock
is essentially completely removed, and there are no trailing wires and no sliding
contacts (Fig.
4d
). The needs met by the IPT carriage include: safely powering a
carriage moving above a water-filled flume over distances of up to 50 m; control of
