Focussing acoustic waves with intent to control biofouling in water pipes

Abstract

The colonisation of water pipes by macro-fouling organisms,
such as barnacles and mussels, has presented a significant problem to
industries drawing water from infested sources. Some of these creatures
have been shown to be sensitive to low frequency sound and vibration,
which have the potential to disrupt settlement and control population
growth without the need for chemical interventions. The applicability of
acoustic techniques to this problem is critically dependent on the achievable
range of guided waves in the fluid or pipe wall which attenuate with
distance from the actuation position due to mechanical losses.
In this paper, fluid waves are considered owing to their typically lower
attenuation rates. A fluid-filled pipe is modelled analytically as a 2D rigid
walled duct. Higher order acoustic waves, which are dispersive immediately
above cut-on, are focussed at a target position using a transient excitation.
The input waveform is obtained by filtering and time-reversing
the impulse response so as to compensate for dispersion thereby compressing
the signal in time and space. Simulations show that peak pressures
can be obtained that are more than an order of magnitude higher
than those achievable by harmonic excitation. Future work will model
focussing of waves in a 3D pipe with fluid-structure coupling for which
experimental validation will be sought.

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