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Abstract

The strategic requirement for naval submarines to operate in near surface and littoral
environments continues to increase as they are more frequently employed to support
joint force missions. The operational workload for helmsmen and the risk to mission
safety and success are significantly increased due to the interaction between the
submarine and the free-surface. This thesis reports on an experimental investigation
into the effects of submergence depth, speed of advance and length-to-diameter ratio
on the interaction between a streamlined axisymmetric body and the free-surface when
travelling in a near-surface condition.
A broad review of the existing literature indicates that little work has been published
to date on the effects of length-to-diameter on the near-surface performance of
streamlined axisymmetric bodies. Furthermore, there is little or no experimental data
available describing the vertical force and moment that act on a shallowly submerged
body moving beneath the free-surface. Nonetheless, there is evidence to confirm that
the requirement for submarine near-surface operation is significant and that a wellfounded
understanding of submarine near-surface performance is needed.
A model scale experimental program was conducted to measure and observe the
resistance, lift force, trimming moment and wave field generated by a series of
submerged bodies of revolution moving at constant forward speed. The Joubert
conventional submarine geometry was tested in its bare hull configuration in three
length-to-diameter ratio formats: 7.30, 8.50 and 9.50. The three geometries possess
the same maximum diameter. The models were tested at velocities that correspond to
a Froude number range of 0.10 to 0.50 inclusive and at centreline submergence depths
of between 1 and 3.5 hull diameters.
The results of the experiment indicate that the wave resistance, lift force and trimming
moment all vary periodically with speed and are directly influenced by the wavelength
of the free-surface wave field generated by the submerged body. The steady-state
wave field itself is a direct function of the submerged body’s length-to-diameter ratio
and speed of advance (Froude number). The magnitude of the forces and trimming
moment were found to diminish exponentially with an increase in submergence depth.
Considering the submergence depths and speeds experienced by naval submarines
when conducting near-surface operations, it is concluded that the effect of wave
resistance is a secondary issue and that the vertical lift force is of the greatest
operational significance. Based on the test results of the three Joubert hull geometries,
it was observed that for near-surface operation a larger length-to-diameter ratio is
preferable for achieving minimum resistance and vertical plane motion (lower relative
lift force and trimming moment).
An evaluation of the SHIPFLOW 4.7 potential flow software program was completed
using the experimentally measured data in conjunction with additional published
experimental and numerical wave resistance data. Good correlation was observed for
the predictions of lift force and trimming moment. Mixed results were achieved when
comparing the numerically predicted and experimentally measured wave resistance.
Nonetheless, it is concluded that the potential flow method offers an inexpensive and
suitable approach to evaluating the near-surface performance of submarine type
geometries.

Item Type:	Thesis - PhD
Authors/Creators:	Dawson, E
Keywords:	Submarine, hydrodynamics, Length-to-Diameter, potential flow, wave-making, controllability
Copyright Holders:	Copyright the Author
Copyright Information:	Copyright 2014 the Author
Item Statistics:	View statistics for this item

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