Low cost on-line non-invasive sewer flow monitoring
Andy Nichols, Kirill Horoshenkov, Simon Tait, Simon Shepherd and Yanmin Zhang
Collaborators:• Open University• Cardiff University• Stanford University• Yorkshire Water Services
Funding:• Yorkshire Water Services• EPSRC grant EP/G015341/1
Andy Nichols | [email protected]
‘Traditional’ flow monitor (submerged acoustic Doppler)
Operates from within the flow.Estimates flow depth and velocity
Main disadvantages:• Permanent obstruction to the flow• Accumulation of debris – maintenance requirements• Backscatter approach – power requirements
Andy Nichols | [email protected]
Airborne Doppler flow monitor
Operates from above the flowEstimates flow depth and velocity
Main advantages:• Minimal obstruction to the flow
– only when surcharged• Minimal accumulation of debris
– minimal maintenance
Main disadvantages:• Backscatter approach
– power requirements• Assumption of surface pattern
behaviour
• The free surface pattern does not simply travel along like a car on a motorway.
• Features may appear, fluctuate, oscillate, merge, separate, dissipate.
• The vertical motion can cause a Doppler shift comparable to that of the horizontal motion.
• Above all, the behaviour is not understood, so precisely what the device measures cannot be defined.
BUT: Perhaps the surface fluctuation behaviour can be used….
Wave probe1. An ultrasonic beam is fired toward the dynamic surface.2. The signal is reflected to a receiver.3. The phase of the received signal fluctuates according to the surface. 1
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3
Andy Nichols | [email protected]
Measuring temporal surface fluctuations at a point – forward scatter
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Time series from two wave probes seperated by 30mm
Andy Nichols | [email protected]
Tracking surface fluctuations
2 wave series separated by a small distance
• Multiple receivers allow a fluctuation time series to be recorded from multiple known locations on the free surface.
• Time series from nearby points can be quite different (hence the issues with the Doppler approach),
• BUT similar enough to estimate the temporal lag (by cross-correlation), and hence the surface velocity.
So we can measure advection velocity between pairs of reflection points, and can use a time-of-flight technique to
measure flow depth, and hence estimate flow rate.
BUT
We can also cross correlate between pairs of reflection points to obtain a
spatial correlation function
Andy Nichols | [email protected]
But can we do more?- Measuring the spatial evolution of the surface pattern
)2cos()( 10
2/ 22
LeW w
This describes the nature of the free surface pattern and relates to the
underlying turbulence, which is governed by the flow conditions, allowing a number
of empirical relationships to be drawn.
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Andy Nichols | [email protected]
Conclusions• Forward scatter airborne acoustics allow unambiguous measurement of flow surface
behaviour.
• Tracking the free surface pattern in this manner allows velocity estimation.
• Time-of-flight measurements can provide depth data, in order to estimate flow rate.
• Further information regarding the flow conditions is encoded in the free surface pattern.
Thank You
Low cost on-line non-invasive sewer flow monitoring
Andy Nichols, Kirill Horoshenkov, Simon Tait, Simon Shepherd and Yanmin Zhang