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Document Description
Title
Statics
and
dynamics
of a
tension
leg
platform
in
intact
and
tether
damage
conditions
Author
Deb
,
Manas
Kumar
Description
Thesis
(M.Eng.)--Memorial
University
of
Newfoundland
,
1987.
Engineering
and
Applied
Science
Date
1986
Pagination
xiv, 261 leaves : ill.
Subject
Drilling
platforms--Anchorage;
Offshore
structures--Dynamics;
Offshore
structures--Hydrodynamics
Degree
M.Eng.
Degree Grantor
Memorial University of Newfoundland. Faculty of Engineering and Applied Science
Discipline
Engineering and Applied Science
Language
Eng
Notes
Bibliography:
leaves
105-112.
Abstract
The
aim
of the
present
investigation
is
to
study
the
static
and
dynamic
behaviour
of a
tension
leg
platform
in the
intact
condition
and
after
partial
or
total
loss
of
tether
at any
corner.
The
exercise
involves
formulating
the
statics
and
dynamics
of
column
stabilised
structures
with
taut
moorings
and
implementing
the
same
in
appropriate
computer
softwares.
Formulations
are also
made
to
calculate
the
equilibrium
tensions
after
a
loss
of
tether.
--
The
computer
program
for
hydrostatics
is
capable
of
generating
the
standard
hydrostatic
information
as
well
as
locating
the
equilibrium
configuration
of the
floating
body
under
a
given
set
of
external
static
loads.
This
is
used
to
assess
the
statical
stability
of the
tension
leg
platform
in
damaged
cases
and
compare
the
same
with its
various
other
configurations.
--
Under
the
category
of
hydrodynamic
analysis
,
two
major
types
of
approaches
,
namely
'frequency
domain'
and
'time
domain'
are
employed.
In the
frequency
domain
approach
,
wave
amplitudes
and
all
displacements
are
assumed
to be
small.
Also
,
integration
of the
hydrodynamic
forces
is
carried
out
over
the
mean
wetted
surface
of the
body.
The
wave
excitation
forces
are
calculated
via
a
'Morison
type'
formula
and an
iterative
scheme
is
adopted
to
handle
the
nonlinear
drag
term.
This
analysis
is
used
to
compute
the
'response
amplitude
operators'
(RAOs)
in
intact
and
damaged
conditions.
Significant
responses
are also
computed
using
these
RAOs
and
Pierson-Moskowitz
wave
spectra
for
chosen
wind
speeds.
In the
time
domain
analysis
,
though
assumptions
similar
to
frequency
domain
analysis
are
made
regarding
the
incident
wave.
However
,
no
restriction
is
put
on the
motion
of the
body.
The
excitation
and the
reactive
forces
are
calculated
over
the
instantaneous
wetted
surface
and at the
displaced
position.
Nonlinear
equations
of
motion
are
integrated
using
Adam's
method.
This
analysis
is
used
to
obtain
time-series
data
of
motion
and
tension
responses
in
order
to
study
the
variation
of
steady
state
amplitudes
in
intact
and
damaged
conditions
as
well
as
transients
following
a
loss
of
tether.
--
A
special
study
of the
occurrence
of
Mathieu
type
dynamic
instability
in
tension
leg
platforms
is
also
undertaken.
A
formulation
to
calculate
unstable
combinations
of
wave
height
and
frequency
is
developed
based
on
Floquet
theory
for
periodic
systems.
The
effect
of
various
pertinent
parameters
including
loss
of
tether
on
instability
is
also
investigated.
--
Furthermore
, a
1:100
scale
model
of a
representative
tension
leg
platform
is
designed
and
fabricated.
Experiments
are
conducted
in
regular
and
irregular
waves
in
both
intact
and
damaged
configurations
and the
experimental
observations
are
compared
with those
predicted
by the
theoretical
models.
--
It
is
seen
that a
complete
loss
of
tether
at any
corner
can
reduce
the
statical
stability
of a
tension
leg
platform
drastically.
A
loss
of
tether
, in
general
,
is
found
to
increase
the
platform
motions
in
vertical
planes
as
well
as the
static
and
dynamic
tensions
in the
remaining
intact
tethers.
Total
loss
of
tether
at
one
corner
induces
snap
loads
in
one
or
more
corners.
Depending
on the
wave
height
and
frequency
, these
snap
loads
could
be
high
enough
to
trigger
further
tether
failures.
With
regard
to
Mathieu
type
dynamic
instability
,
even
a
25%
loss
of
total
axial
stiffness
of the
tethers
is
seen
to have
insignificant
effect
on the
occurrence
of
such
instability.
Type
Text
Resource Type
Electronic
thesis
or
dissertation
Format
Image/jpeg;
Application/pdf
Source
Paper copy kept in the Centre for Newfoundland Studies, Memorial University Libraries
Local Identifier
75402329
Rights
The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission.
Collection
Electronic
Theses
and
Dissertations
Scanning Status
Completed
PDF File
(29.54
MB)
--
http://collections.mun.ca/PDFs/theses/Deb_ManasKumar.pdf
CONTENTdm file name
53194.cpd
