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Performance of an auger dredging cutter for subsea dredging and mining

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Sarkar, M (2013) Performance of an auger dredging cutter for subsea dredging and mining. PhD thesis, University of Tasmania.

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Abstract

Increasing use of deep-water dredger and miner vehicles has been anticipated for
resource collection, engineering construction and environmental protection. Among
existing deep-dredging equipment designs submersible dredgers have advantages over
others such as surface designs.
Considering the limitations of commercially available and conceptualised submersible
dredgers, a different type - the ‘Swimming Remotely Operated Submersible Dredger’
(SROSD) is conceptualised in this research. In its working mode, it imitates a walking
motion by using spuds that are also used for station keeping during dredging. When
required, the vehicle can swim by means of vector thrusters. The vector thrusters also
help in position-keeping and motion-control during swimming. To offset high forces
generated during excavation of hard materials, spuds, variable buoyancy tanks and control
planes are included as secondary station-keeping devices. The general arrangement and
the sub-systems of the conceptualised vehicle are described.
For swimming and control in a submerged condition, the vehicle is ballasted to a neutrally
buoyant condition. Balancing of the excavation forces is necessary for efficient production
and this is a design problem with submersible dredgers. A transverse axis auger cutter
capable of surgical cutting with low force fluctuations is used in the design. A theoretical
model of the cutting forces in vertical and horizontal directions generated by this type of
cutter is proposed.
An experiment was designed to measure the cutting forces generated by this cutter.
Comparisons between the power requirements derived from the experiment and the
theoretical model were done to validate the model. The measured experimental power
requirements were found to be within the calculated power ranges for dredging loose to
slightly compacted sand in similar operating conditions.
In a further experiment to assess the spillage from the cutter in operation, near and far
field turbidity generation by the auger was measured by using turbidity sensors.
Measurements of turbidity were taken to indicate the environmental impact of the auger.
It was observed that the turbidity increase was dependent on the relative position
between the probes and the auger and its shroud. It is hoped that, through this work, a new design of vehicle, along with the reaction force
analysis of the excavation and the turbidity measurements will significantly contribute to
the evolution of existing deep-dredging and mining equipment leading to improved
efficiency, increased mobility and position control while minimising environmental
disturbance.

Item Type: Thesis (PhD)
Keywords: Dredging, dredger, excavation, dredging cutter, auger
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Date Deposited: 01 Oct 2013 06:11
Last Modified: 15 Sep 2017 01:06
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