## Jan's advert## My own bibliography on ocean engineering, structural reliability, ship rolling etc.:biblio.txt (size 456 KB), last updated:2013.01.01 This is a simple databse in ASCII format (plus Norwegian characters: æ, ø, å). Blank lines separate the items. A 2-character key identifies each attibute, as follows: %A=Author, %T=Title, %J=Journal, %V=Volume, %N=Number,%P=Pages, %I=Issuer, %D=Date, %C=City, ... |

OMAE2014-23446_v7.pdf
(size 1.2 MB), from 33rd International Conference on Ocean, Offshore and Arctic Engineering, San Francisco.

ABSTRACT - A probabilistic metocean model for hurricane conditions is
briefly described. The model is based on site-specific, hindcast
data and defines the time variation of the metocean conditions
during the realisation of a hurricane at the site. The annual
extreme value distribution of mooring line tension for a large,
semi-submersible, mobile drilling unit is computed. Time
domain analysis is applied to obtain the short-term, extreme
value distribution of line tension, conditional on stationary
metocean conditions. A large number of different conditions are
considered. A response surface is used to interpolate on the
short-term distribution parameters in order to describe the
tension response during the varying conditions associated with
the passage of a hurricane. The hurricane duration is split into a
sequence of 15-minute intervals such that the conditions can be
assumed stationary during each such short interval. The tension
distribution, conditional on the realisation of a hurricane, is
accumulated across the sequence of short intervals. The
distribution of hurricanes is taken into account to obtain the
tension distribution in a random hurricane. Finally, the
frequency of hurricanes is taken into account to give the annual
extreme distribution of line tension. The characteristic tension
computed using 10-year return conditions and the ISO 19901-7
design standard is found to correspond to a return period of 29
years in the test case. The effects of various assumptions in the
design analysis are investigated. Sensitivities to simplifications
of the metocean model are considered. The effects of
uncertainties in the response calculation and in the distribution
of peak significant wave height during hurricanes are quantified
and included in the response analysis.

omae2013-10735.pdf
(size 1254 KB), from 32nd International Conference on Ocean, Offshore and Arctic Engineering, Nantes.

ABSTRACT - Hindcast data for a specific location is utilised to develop a
joint probability function for the metocean variables that are
expected to have a significant effect on mooring line tensions
for a floating platform moored at that location. The main
random variables comprise: peak significant wave height, peak
wind speed, peak surface current speed, peak wave direction,
peak wind direction and peak current direction, where "peak"
indicates the maximum intensity of the metocean effect during
a random hurricane. The time lead of peak wind relative to peak
waves and the time lag of peak current after peak wind are
included as random variables. It is also necessary to describe
the time variation around the peak events. Simple models are
assumed based on inspection of the time variations during
severe hurricanes. Only the part of the hurricane during which
the significant wave height exceeds 80% of the peak value is
taken into account. The duration of this interval is included.
Linear variation is assumed for the directions, hence the rates of
change of the 3 directions are included. A linear (triangular)
plus parabolic model is assumed for the time variation of the
intensities of the 3 metocean effects around their respective
peaks. A single parameter is required to define the proportion
of linear and parabolic models for each effect and the values of
this parameter for each of the 3 metocean effects are also
included as random variables.
A random hurricane can be drawn from this metocean
model, such that the time variation of the metocean actions is
deterministic once the values of the random variables have been
selected. The overall duration of the hurricane is split into short
intervals, each of 15 minutes duration, such that stationary
response may be assumed during each short interval. The
extreme value distribution of line tension during each short
interval is obtained. These distributions are combined to obtain
the extreme distribution of line tension during the hurricane.
Second order reliability methods are applied to integrate over
the distribution of the metocean variables and obtain the
distribution of extreme tension during a random hurricane. The
annual frequency of hurricanes is used to derive the annual
extreme value distribution of line tension.
The model is intended for the reliability analysis of the
ultimate limit state of mooring lines, but may also be applicable
to other response variables. The present paper is primarily
concerned with the metocean model, but it is intended to
include sample results for the extreme line tension.

Hull_vibration_effects_under_harsh_conditions_v8.pdf
(size 425 KB), from RINA/SSNAME Int. Symp. on Ship Design & Construction,
Shanghai, 2007.

ABSTRACT - Wave-induced, hull girder vibration is known to have a significant
effect on fatigue in some types of ships. Extensive measurements on ore and
bulk carriers in service have been used to investigate and quantify these
effects. A pilot study has been carried out in an attempt to use some of the
same data to determine if there is also a significant effect on extreme wave
loads. A few time series of hull bending stresses from two bulk carriers,
operating in the North Atlantic iron ore trade, have been analysed. Harsh
conditions due to a combination of waves, heading, speed and draught have
been sought in order to approach extreme conditions. Somewhat milder
conditions have also been included to investigate trends. Long, continuous
records, which imply greater confidence in response statistics than is
available from shorter records, have been obtained from harsh, stationary
conditions. Low pass filtering has been applied to separate the ordinary,
non-vibratory, wave-induced stresses from the total wave-induced stresses.
Stress maxima and minima have been extracted from the time series and
distribution functions have been fitted to these data. The results show a
significant contribution to the total stress from the vibratory component,
even under the harshest conditions that were available. This indicates that
hull girder vibrations may need to be taken into account in the prediction of
the extreme stresses in certain ship types.

moorfls_v8.pdf (size 234 KB), from
Int. Conf. on Computational Methods in Marine Engineering MARINE 2005.

ABSTRACT - A structural reliability method is applied to calibrate the safety
factor of a fatigue design method for the mooring lines of floating offshore
platforms. Both methods are based on the Miner Palmgren hypothesis for the
accumulation of fatigue damage. The reliability analysis takes explicit
account of the various uncertainties in the fatigue capacity, the damage
accumulation and the calculation of mooring line tensions. These
uncertainties are all intended to be covered by the safety factor in the
design analysis. The uncertainty in the fatigue capacity is developed for
chain and steel wire rope. A test set of six floating platforms in various
water depths is considered. The effect of varying numbers of mooring line
components is taken into account. A target probability of failure is
established. The safety factor of the design method is calibrated to yield
designs close to the target probability. This calibration is effected by
minimising an objective function based on the difference between target
probability and calculated probability of failure for the mooring lines in
the test set. Under-design is penalised more heavily than over-design.

OMAE2004-51227.pdf (size 315 KB),
from Offshore Mechanics and Arctic Engineering Conf., 2004.

ABSTRACT - Experience from recent reliability analyses of jacket platforms is
used to discuss selected aspects of probabilistic modelling in more detail.
These modelling details can have a significant effect on the computed
reliabilities. An overview of basic considerations and failure modes in
jacket reliability analysis is included to set the various details into
context. Ultimate limit states for jackets in relatively shallow water are
emphasised; i.e. quasi-static structural response is applicable. The
following topics are considered: (a) Failure modes and some requirements to
load and resistance analysis. (b) Directionality in loading and resistance.
(c) Random periods of individual extreme waves. (d) Foundations – axial and
lateral capacity modelling for multiple piles and model uncertainty for pile
capacity.

OMAE2003-37472.pdf (size
695 KB), from Offshore Mechanics and Arctic Engineering Conf., 2003.

ABSTRACT - A structural reliability analysis is carried out on a jacket
platform in 75 m water depth, in the South China Sea. A platform collapse
failure mode is considered, with emphasis on uncertain soil conditions around
the pile foundations, due to gas seepage while the platform has been in
service. Random environmental conditions due to wind, waves and current are
taken into account, based on observed data. Allowance for the short duration
of environmental measurements is included and has a marked effect on the
results. Two response surfaces are applied in the reliability calculation, to
model the loads and the system capacity.

OMAE2002-28409.pdf (size 123 KB),
from Offshore Mechanics and Arctic Engineering Conf., 2002.

ABSTRACT - The use of risk-based inspection planning for offshore structural
components is becoming quite familiar. This paper describes an application of
this technique to mooring chain. In many cases, the technique is based on
probabilistic modelling of fatigue crack growth in the structural components,
and updating of the failure probability on the basis of inspections. The
extension of this basis from a single component to very many components is
necessary to tackle series systems, such as mooring chain, where a fatigue
fracture can arise in any chain link. The theoretical basis for the analysis
is described, including details of the model for stochastic dependency
between the chain links. Results are shown that compare failure probabilities
for a single chain link and a chain segment. The effects of various levels of
inspection coverage are illustrated. An example of a cost optimal inspection
plan is developed for mooring chain on an FPSO in the northern North Sea.

NIF_RBI_Moor.pdf (size 86 KB), from
conf. on Dynamic Positioning and Mooring of Floating Offshore Structures,
organised by the Norwegian Society of Chartered Engineers, 2001.

ABSTRACT - The present work describes a first attempt to apply risk-based
inspection planning to mooring chain. The main challenges in the analysis are
to provide a realistic model for probabilistic crack-growth in a single chain
link, and to take a large number of chain links into account, with a
realistic correlation between links. The result of the analysis is a plan
stating when it is cost-optimal to inspect the chain. Some results are shown
for chain from a turret-moored ship in Norwegian waters. The uppermost chain
segment in the most heavily loaded mooring line is considered. This chain has
been conservatively designed, with a fatigue safety factor of 10. The present
example is intended to illustrate the method without providing full details
of the case study.

omae99_6010.pdf (size 139 KB), from
Offshore Mechanics and Arctic Engineering Conf., 1999.

ABSTRACT - A reliability analysis is developed for the welded joints of the
tendons on the Jolliet TLP. Two potential failure modes are considered: (a)
fatigue failure in terms of growth of a fatigue crack through the tendon wall
thickness, and (b) rupture due to brittle fracture or plastic collapse in the
presence of a fatigue crack. Linear fracture mechanics are used to model the
growth of a fatigue crack. Final rupture is modelled using a failure
assessment diagram approach defined in PD6493 (from BSI, 1997). Material data
from the production testing of the tendons are applied. Initial crack sizes
are based on measurements made during the initial in-service inspection
carried out in 1989/90. Extreme load distributions are based on the original
design analyses of the TLP, while fatigue loads are based on in-service
measurements. Axial tension and transverse bending moments at the tendon
joint are included in both cases. The annual probability of failure is
computed as a function of the time elapsed since the inspection. Both failure
modes and the combination of the two failure modes are considered. Comparison
of these results with a suitable target reliability level is used to evaluate
when the next inspection of the tendon joint welds should be performed.

OMAE98-1457_Mooring_ULS.pdf (size 1.4 MB), from
17th Int. Conf. Offshore Mechanics and Arctic Engineering, 1998, Lisbon.

ABSTRACT - Structural reliability analysis has been used to calibrate a
design equation for mooring lines in their ultimate limit state. The
calibration is based on six test cases, for mooring systems in water
depths ranging from 70m to 2000m. Three of the cases apply to a
turret-positioned
ship and three to a semisubmersible.
Conventional catenary mooring systems with chain and/or wire
components have been studied, whereas taut moorings with tibre
rope are not yet included. Environmental conditions from the
Norwegian continental shelf and from the Gulf of Mexico have
been considered. A design equation format involving two partial
safety factors, applied to two tension components is
recommended. The two components are: (i) the static tension due
to pretension and due to tension induced at the offset position
corresponding to the mean environmental forces in an
environmental state, and (ii) the dynamic tension component due
to time-varying loads; i.e. in this paper defined as the sum of time-
varying low-frequency and wave-frequency tensions in the
environmental state. The recipes for characteristic values of the
tension components and the line capacity are specified, and partial
safety factors are given.

OMAE98-1458_Mooring_PLS.pdf (size 998 KB), from
17th Int. Conf. Offshore Mechanics and Arctic Engineering, 1998, Lisbon.

ABSTRACT - A structural reliability analysis is formulated for a progressive
collapse limit state of offshore mooring systems. The failure of
two adjacent mooring lines is considered in some detail, while
incorporating the empirical frequency of line failures in the
modelling of the initial line failure. Reliability results are
presented for the mooring system of a semisubmersible platform,
and a turret-positioned ship. A simplified design rule for the
progressive collapse limit state is discussed and the reliability
results are utilised in a preliminary calibration of the design rule.
Additional test cases are required to finalise the calibration.

OMAE98-1460_Mooring_Code.pdf (size 704 KB), from
17th Int. Conf. Offshore Mechanics and Arctic Engineering, 1998, Lisbon.

ABSTRACT - DNV's mooring code, given in the Rules for Classification of
Mobile Offshore Units and known as POSMOOR, will be modified
in accordance with the findings of the joint industry project
"Reliability-Based, Cost-Effective, Design Methods for Deep
Water Mooring Systems - DEEPMOOR". Other international
mooring codes and DNV's code are currently based on formats
with a single safety factor or utilization factor. This format will be
replaced by a limit state format, which is already widely used in the
oil offshore industry.
The code will be reformulated in terms of three limit state
functions: ULS (Ultimate Limit State), PLS (Progressive collapse
Limit State) and FLS (fatigue limit state).
The partial safety factors involved in the limit state functions
will be based on calibration against structural reliability analyses.
An alternative formulation of the characteristic strength of mooring
line components will be introduced, based on component test data.
If such data is not available, then the characteristic strength can
still be derived from the conventional minimum breaking strength.