|
|
|
Publication Abstracts Structural Integrity and Health Monitoring COTech501:
Integrity
management of offshore structures and its implication on computation
of structural action effects and resistance
T Moan
Abstract.
An overview of integrity management of offshore structures, with
emphasis on the oil and gas energy sector, is given. Based on
relevant accident experiences and means to control the associated
risks, accidents are categorized from a technical-physical as well as
human and organizational point of view. Structural risk relates to
extreme actions as well as structural degradation. Risk mitigation
measures, including adequate design criteria, inspection, repair and
maintenance as well as quality assurance and control of engineering
processes, are briefly outlined. The current status of risk and
reliability methodology to aid decisions in the integrity management
is briefly reviewed. Finally, the need to balance the uncertainties
in data, methods and computational efforts and the cautious use and
quality assurance and control in
applying high fidelity methods to avoid human errors, is
emphasized, and with a plea to develop
both high fidelity as well as efficient, simplified methods
for design. Keywords.
Deterioration, In-service experiences, Offshore structures, Quality
management, Structural integrity. COTech502:
Analytical
and numerical investigation of bolted steel ring flange connection
for offshore wind monopile foundations C
A Madsen1*,
J-C
Kragh-Poulsen2, K
J Thage3 and M
J Andreassen4 3COWI
A/S, Department of Major Bridges International, Parallelvej 2,
DK-2800 Kgs. Lyngby, Denmark Abstract.
The
monopile foundation is the dominant solution for support of wind
turbines in offshore wind farms. It is normally grouted to the
transition piece which connects the foundation to the turbine.
Currently, the bolted steel ring flange connection is investigated as
an alternative. The monopile--transition piece connection has
specific problems, such as out-of-verticality and installation damage
from driving the MP into the seabed and it is not fully known how to
design for these. This paper presents the status of the ongoing
development work and an estimate of what still needs to be covered in
order to use the connection in practice. This involves presentation
of an analytical and non-linear FE analysis procedure for the
monopile-transition piece connection composed of two L flanges
connected with preloaded bolts. The connection is verified for
ultimate and fatigue limit states based on an integrated load
simulation carried out by the turbine manufacturer. Keywords.
Bolted
steel ring flange connection, L flange, offshore monopile foundation,
ultimate limit state, fatigue limit state, Markov matrices COTech504:
Natural
frequency and vibration analysis of jacket type foundation for
offshore wind power Y-C
Hung,
Y-Y Chang and S-Y Chen Abstract.
There
are various types of foundation structure for offshore wind power,
engineers may assess the condition of ocean
at wind farm, and arrange the
transportation,
installation
of each structure members, furthermore, considering the ability of
manufacture steel structure as well, then make an optimum design. To
design jacket offshore structure, unlike onshore cases, offshore
structure also need to estimate the wave excitation effect. The aim
of this paper is to study the difference of natural frequency between
different kinds of structural
stiffness and discuss the effect of different
setting of boundary condition
during analysis, besides, compare this value with the natural
frequency of sea wave, in order to avoid the resonance effect. In
this paper, the finite element analysis software ABAQUS is used to
model and analyze the natural vibration behavior of the jacket
structure. Keywords.
Finite
element, jacket structure, natural frequency.
COTech505:
Fracture
mechanics analysis for a mooring system subjected to tension and
out-of-plane bending X
Xue and N-Z Chen School
of Engineering, Newcastle University, Newcastle upon Tyne, United
Kingdom Abstract.
A fracture mechanics analysis for the
mooring system of a semi-submersible accounting for out-of-plane
bending (OPB) is presented in this paper. Stress ranges acting on the
mooring chain links are calculated based on tension and OPB of
mooring chain links induced by motions of wave frequency (WF) and low
frequency (LF). The narrow-banded method is used for predicting the
combined mooring loading process. Initial cracks are assumed to
propagate from surfaces of chain links and stress intensity factors
are then calculated in terms of stress ranges determined by a finite
element analysis. The influence of the OPB on the remaining service
life of mooring chain links is investigated and the results show that
the remaining service life of mooring chain links connecting to
fairleads is significantly reduced due to the OPB effects. Keywords.
Mooring
chain, Out-of-plane bending (OPB), Fracture mechanics, Fatigue COTech506: Effect of Corrosion on the Buckling Capacity of Tubular Members Fridtjof
H. Øyasæter, Ashish Aeran, Sudath C. Siriwardane and Ove Mikkelsen Abstract.
Offshore
installations are subjected to harsh marine environment and often
have damages from corrosion. Several experimental and numerical
studies were performed in the past to estimate buckling capacity of
corroded tubular members. However, these studies were either based on
limited experimental tests or numerical analyses of few cases
resulting in semi-empirical relations. Also, there are no guidelines
and recommendations in the currently available design standards. To
fulfil this research gap, a new formula is proposed to estimate the
residual strength of tubular members considering corrosion and
initial geometrical imperfections.
The proposed formula is verified with results from finite
element analyses performed on several members and for varying
corrosion patch parameters. The members are selected to represent the
most relevant Eurocode buckling curve for tubular members. It is
concluded that corrosion reduces the buckling capacity significantly
and the proposed formula can be easily applied by practising
engineers without performing detailed numerical analyses. Keywords.
Buckling,
Corrosion, Finite element
analysis, Jacket structure, Tubular members COTech507:
An
Accurate Fatigue Damage Model for Welded Joints Subjected to Variable
Amplitude Loading Ashish Aeran, Sudath
C. Siriwardane, Ove Mikkelsen, and Ivar Langen Abstract. Researchers in the past have proposed several fatigue damage models to
overcome the shortcomings of
the commonly used Miner’s rule. However, requirements of material
parameters or S-N curve modifications restricts their practical
applications. Also, application of most of these models under
variable amplitude loading conditions have not been found. To
overcome these restrictions, a new fatigue damage model is proposed
in this paper. The proposed model can be applied by practicing
engineers using only the S-N curve given in the standard codes of
practice. The model is verified with experimentally derived damage
evolution curves for C 45 and 16 Mn and gives better agreement
compared to previous models. The model predicted fatigue lives are
also in better correlation with experimental results compared to
previous models as shown in earlier published work by the authors.
The proposed model is applied to welded joints subjected to variable
amplitude loadings in this paper. The model given around 8% shorter
fatigue lives compared to Eurocode given Miner’s rule. This shows
the importance of applying accurate fatigue damage models for welded
joints. Keywords.
Fatigue
damage
model, variable amplitude loading, welded joints, fatigue life Nirosha
D. Adasooriya, Tor Hemmingsen and Dimitrios Pavlou Abstract.
Structures
exposed to aggressive environmental conditions are often subjected to
time-dependent loss of coating and loss of material due to corrosion;
this causes reduction in the cross-sectional properties of the
members, increased surface roughness, surface irregularities and
corrosion pits, and degradation of material strengths. These effects
have been identified and simulated in different research studies.
However, time and corrosive media dependent fatigue strength curves
for materials have not been discussed in the design or assessment
guidelines for structures. This paper attempts to review the
corrosion degradation process and available approaches/models used to
determine the fatigue strength of corroded materials and to
interpolate corrosion deterioration data. High cycle fatigue and full
range fatigue life formulae for fatigue strength of corroded
materials are proposed. The above formulae depend on the endurance
limit of corroded material, in addition to the stress-life fatigue
curve parameters of the uncorroded material. The endurance limit of
corroded material can
either be determined by a limited number of tests in the very
high-cycle fatigue region or predicted by an analytical approach.
Comparison with experimentally measured corrosion fatigue behavior of
several materials is provided and discussed. Keywords:
Corrosion,
Fatigue
strength, Metals
|
 |
