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Faculté des Sciences appliquées
Faculté des Sciences appliquées
MASTER THESIS
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Master thesis : Fatigue Analysis of Temporary Offshore Structures using Monte Carlo Simulations

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Jens, Katharina ULiège
Promotor(s) : Baert, Benjamin
Date of defense : 23-Sep-2022 • Permalink : http://hdl.handle.net/2268.2/16567
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Title : Master thesis : Fatigue Analysis of Temporary Offshore Structures using Monte Carlo Simulations
Author : Jens, Katharina ULiège
Date of defense  : 23-Sep-2022
Advisor(s) : Baert, Benjamin 
Committee's member(s) : Morato Dominguez, Pablo Gabriel ULiège
Medina Mánuel, Antonio 
Herreros, Miguel Ángel 
de Vicente Peño, Mario 
Saettone, Simone 
Language : English
Number of pages : 117
Discipline(s) : Engineering, computing & technology > Mechanical engineering
Institution(s) : Université de Liège, Liège, Belgique
Degree: Master : ingénieur civil mécanicien, à finalité spécialisée en "Advanced Ship Design"
Faculty: Master thesis of the Faculté des Sciences appliquées

Abstract

[fr] The Orion, an offshore heavy lift DP3 installation vessel owned by DEME Group, is deployed
worldwide to install monopiles of up to 2,500 tons with its 5,000-ton crane. A seafastening
structure holding the monopiles on board of the vessel is exposed to cyclic loading due to waves
encountered at sea. The fatigue life of this monopile seafastening, therefore, needs to be
analyzed to ensure its integrity during installation and transport operations. For this, the
applicability of different fatigue estimation methods is investigated throughout the thesis.
Firstly, simplified fatigue analysis methods are tested to obtain an order of magnitude of the
expected fatigue damage and to determine its criticality. The lambda factor method is adapted
to offshore structures providing an approach to represent a variable load history by estimating
equivalent stress cycles at a constant stress range. In another simplified method, the fatigue
damage is approximated using a weighted sum approach. By calculating the fatigue damage for
one hour spent in specified nautical areas, the total damage of different operational profiles can
easily be assessed. This approach is further developed by applying the Monte Carlo technique
to determine the damage expected for one hour of operation.
Secondly, Monte Carlo simulations are implemented in Python to study the fatigue life of the
seafastening in detail. In the simulation, the considered sea states are defined based on scatter
diagrams and the vessel’s motion response is determined for every hour of operation. The stress
ranges resulting from the accelerations of the monopile, as well as the number of stress cycles
that the seafastening structure on the vessel experiences are calculated. Based on the stress
occurrences, the partial fatigue damage of every hour and, ultimately, the total fatigue damage
are estimated. By varying the input parameters of the analysis and evaluating the effect on the
fatigue damage, recommendations on the optimal operational profile with respect to the fatigue
life of the seafastening are made.
With a predicted fatigue life of 660 years, the seafastening is not expected to fail due to fatigue
damage during the specified operational period of 10 years. This result is obtained with the
Monte Carlo approach which considers the most accurate representation of the sea state and the
seafastening’s reactions to loads out of the tested methods. Nevertheless, the weighted sum
method is found to be a valuable tool for fast fatigue estimations providing accurate results but
missing the effects of quadratic roll damping.


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Author

  • Jens, Katharina ULiège Université de Liège > Master ing. civ. méc. (EMSHIP+)

Promotor(s)

Committee's member(s)

  • Morato Dominguez, Pablo Gabriel ULiège Université de Liège - ULiège > Département ArGEnCo > ANAST (Systèmes de transport et constructions navales)
    ORBi View his publications on ORBi
  • Medina Mánuel , Antonio
  • Herreros , Miguel Ángel
  • de Vicente Peño, Mario
  • Saettone, Simone
  • Total number of views 109
  • Total number of downloads 437










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