The broaching of ships in following seas

Renilson, M.R. (1981) The broaching of ships in following seas. PhD thesis, University of Glasgow.

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The two aims of this work were: (1) to develop a theoretical
technique for determining the conditions where a broach would occur,
and (2) to identify the principal factors affecting the liability of
a ship to broach.
The first step was to develop a mathematical model based on the
conventional manoeuvring equations with coefficients which were
functions of the ship's longitudinal position in the wave, but independent
of encounter frequency. Next, a theoretical method for calculating
the values of some of the coefficients as functions of wave
position was developed using a strip theory approach and the results
compared with those obtained experimentally. The experimental technique
involved using a planar motion mechanism to oscillate a constrained
model balanced on a wave created by a wave dozer in a circulating
water channel. Although the agreement was poor and experimental
scatter high for some of the coefficients, the more important ones
were predicted quite well using the theory. Constrained model experiments were also --carried out in calm
water in order to determine the approximate value of the roll coupling
terms and it was found that, since they were small, the roll equation
could be ignored as a first approximation.
It was then possible to study the stability of the lateral and
longitudinal motions separately for various wavelengths and to determine
that the principal factor causing a broach was the large wave induced
yaw moment combined with the small restoring moment available
from the rudder operating with reduced effectiveness. The lateral and
longitudinal equations were then combined using a digital/analogue
hybrid simulation permitting the conditions which caused a broach to
be determined. When the results from the simulation-were compared
with results which had already been carried out by the
Admiralty Marine Technology Establishment at Haslar there was fairly
good agreement, implying that this method could be used to determine
whether a proposed design would meet an acceptable standard. Finally, possible improvements to the simulation were suggested
and guidelines for reducing the liability to broach were given both
for the operator and the designer.

Item Type: Thesis (PhD)
Subjects: T Technology > TC Hydraulic engineering. Ocean engineering
Colleges/Schools: College of Science and Engineering > School of Engineering
Supervisor's Name: Supervisor, not known
Date of Award: 1981
Depositing User: Miss Louise Annan
Unique ID: glathesis:1981-6615
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Aug 2015 10:32
Last Modified: 14 Aug 2015 10:32

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