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Scale Modelling of Sound Propagation From Offshore Piling Operations

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Phillip Moxley

on 10 February 2010

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Transcript of Scale Modelling of Sound Propagation From Offshore Piling Operations

Scale Modelling of Sound Propagation
From Offshore Piling Operations Initial Brief Issues related to a scale model method Project Development Methodology Results Current Goals Construction of an accurate scale model is actually very complex Attempting scale-model experiments in a water tank presents many practical problems; Sound speed does not scale with the model, it remains constant.
This will lead to reflections from the sides of the tank affecting data.
To minimise reflections in results we would require a very large water
tank and significant absorption material. Predictions for sound propagatiopn through the sediment (and sediment-pipe interface modelling) requires complex modelling on a micro scale. Use of hydrophones produces signals with a higher signal to noise ratio in a reflective tank
Can we reduce the problem at the source? First Preliminary Experiment: Second Preliminary Experiment: Response of one pipe to impact from metal weight
Microphone used to sample frequency response in air at 1.5m
Accelerometers used to sample vibration at quarter-pipe-length intervals
No way of standardising the impact velocity
Microphone and accelerometer used were unsuited for the measurements.
Problems: Suggestions: More appropriate to conduct experiment in Anechoic Chamber to reduce effect of room reflections
Use of larger pipes will lower the frequency range of interest to within the frequency range of our accelerometers Response of pipes to impact from metal weight
Pipes used were much larger and varied in terms of shell-thickness, diameter and a ratio of the two.
New impact rig designed to standardise impact velocity
Microphone used to sample frequency response in air at 1.5m
Accelerometers used to sample vibration at quarter-pipe-length intervals
Experiment conducted in ISVR small anechoic chamber to miminise reflections
Results from the first preliminary experiment were discarded due to clipping issues
Helped us to acknowledge problems and design a better set up Determine pipe behavioural characteristics in air
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Infer information about behaviour in water from air data
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Gather necessary equipment for water based experiment
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Begin second round of testing Issues:
Scaling of parameters and characteristics
i.e. frequency scaling, energy scaling, impact velocity modelling
Build time excessive for timescale of project
Minimum available pipe thickness the limiting factor on scaling
Modelling of rise-time of impact Difficulties obtaining clean results from messy data, requires extensive processing. 2 part investigation on pipe behaviour: in air and in water
Use results to inform decisions on how best to conduct water-based experiments. Refocus on the behavious of thin-walled cylinders to impacts in order to investigate the sound generation process. use results from water-based experiments to understand the sound generations process. To improve understanding of sound radiation process in marine pile driving operations
To do this via construction of a scale model
To construct an appropriate system of signal capture and analysis for the model Project Outline Thank You Ellen Harrison - Liisa Kilpi - Phill Moxley - Dan Rowe Preliminary experiments in air on various pipes to determine pipe characteristics and evaluate trends Results of second experiment in air are being used to :
formulate ideas of pipe behaviour to impacts
analyse trends
make predictions on water based behaviour
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