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Fatigue Analysis of Offshore Drilling Unit
Md Rezaul Karim
Master Thesis
presented in partial fulfillment of the requirements for the double degree:
“Advanced Master in Naval Architecture” conferred by University of Liege "Master of Sciences in Applied Mechanics, specialization in Hydrodynamics,
Energetics and Propulsion” conferred by Ecole Centrale de Nantes
developed at West Pomeranian University of Technology, Szczecin in the framework of the
“EMSHIP” Erasmus Mundus Master Course
in “Integrated Advanced Ship Design”
Ref. 159652-1-2009-1-BE-ERA MUNDUS-EMMC
Supervisor:
Prof. Maciej Taczala, West Pomeranian University of Technology, Szczecin
Reviewer: Prof. Hervé Le Sourne, ICAM
Szczecin, February 2015
P 2 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
Contents DECLARATION OF AUTHORSHIP ....................................................................................... 6
ABBREVIATIONS .................................................................................................................... 7
ABSTRACT ............................................................................................................................... 8
SHORT DESCRIPTION ............................................................................................................ 9
1. INTRODUCTION ................................................................................................................ 10
1.1 Background ................................................................................................................ 10
1.2 Objective .................................................................................................................... 10
1.3 Methodology .............................................................................................................. 10
1.4 Schedule..................................................................................................................... 12
1.5 Types of Fatigue Failure: ........................................................................................... 12
1.6 Sources of Fatigue: .................................................................................................... 13
2. OFFSHORE DRILLING PLATFORMS: ........................................................................ 14
2.1 Introduction: .............................................................................................................. 14
2.2 Components of Offshore Rigs: .................................................................................. 14
2.3 Category: ................................................................................................................... 15
3. STUCTURE ANALYZED: SEMISUMMERSIBLE UNIT ............................................ 22
3.1 Introduction: .............................................................................................................. 22
3.2 Classification: ............................................................................................................ 22
3.3 Example of similar model: ........................................................................................ 23
4. SOFTWARE PROCEDURE: .......................................................................................... 25
4.1 Introduction: .............................................................................................................. 25
4.2 Sesam Genie: ............................................................................................................. 25
4.3 HydroD-Wadam: ....................................................................................................... 26
4.4 Sestra: ........................................................................................................................ 27
4.5 Xtact: ......................................................................................................................... 28
4.6 Postresp:..................................................................................................................... 29
4.7 Stofat:......................................................................................................................... 29
5. STRUCTURAL MODELLING ....................................................................................... 30
5.1 Modelling Set-Up ...................................................................................................... 30
5.2 Pontoon: ..................................................................................................................... 32
5.3 Column: ..................................................................................................................... 32
5.5 Deck: .......................................................................................................................... 33
5.5 Derrick: ...................................................................................................................... 34
5.6 Boundary Conditions: ................................................................................................ 35
5.7 Panel Model: .............................................................................................................. 36
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5.8 Morison Model: ......................................................................................................... 38
5.9 Structural Model: ....................................................................................................... 39
6. HYDRODYNAMIC ANALYSIS: ................................................................................... 41
6.1 Analysis Setup ........................................................................................................... 41
6.2 Global Motion Response Analysis: ........................................................................... 47
7. GLOBAL STRUCTURAL STRENGTH ANALYSIS .................................................... 54
8. GLOBAL FATIGUE ANALYSIS AND RESULT: ........................................................ 56
9. CONCLUSIONS AND RECOMMENDATIONS: ......................................................... 61
REFERENCES ......................................................................................................................... 63
APPENDIX .............................................................................................................................. 64
Appendix A: Summary of Model Properties ........................................................................ 64
Appendix B: Element Fatigue Check Result ........................................................................ 68
ACKNOWLEDGEMENTS ..................................................................................................... 84
P 4 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
List Of Figures
Figure 1 Flowchart of Methodology ........................................................................................ 11 Figure 2 Detail Schedule with Gantt chart ............................................................................... 12 Figure 3 Component of offshore rigs (19) ............................................................................... 15
Figure 4 Common Types of Drilling Rigs (BOEMRE, 2010c) ............................................... 16 Figure 5 Fixed Platform Rig (Left) and Gravity-Based Structure (Right) (Source: Prof:
Tadeusz Graczyk Lectures at ZUT) ......................................................................................... 17 Figure 6 Varieties of mobile offshore drilling units (MODUs). Drill Barge (TODCO via
NETL, 2011), Jack-Up Rig (Transocean, 2011), Semi-submersible Rig (Eni, 2008), Drill Ship
(BP p.l.c., 2011). ...................................................................................................................... 19 Figure 7 Tension Leg Platform (Magnolia TLP, Source: Prof: Tadeusz Graczyk Lectures at
ZUT) ......................................................................................................................................... 21 Figure 8 Column Stabilized Semisubmersibles (Left: Ring Pontoon Design, Right: Twin
Pontoon Design, Source: Petrowiki) ........................................................................................ 23
Figure 9 Similar Drilling Platform model (Maersk Drilling deep-water semi-submersible rig
Source: Prof: Tadeusz Graczyk Lectures at ZUT) ................................................................... 23
Figure 10 Semi-submersible platform - Maersk Drilling deep-water semi-submersible rig
(Source: Prof: Tadeusz Graczyk Lectures at ZUT) .................................................................. 24 Figure 11 Flowchart of Software Procedure ............................................................................ 25 Figure 12 Schematic illustration of the capabilities of Sestra (12) .......................................... 28
Figure 13 Color coding of structural members ........................................................................ 31 Figure 14 Color coding of thickness ........................................................................................ 31
Figure 15 Pontoon .................................................................................................................... 32 Figure 16 Column ..................................................................................................................... 33 Figure 17 Deck ......................................................................................................................... 33
Figure 18 Deck Framing System .............................................................................................. 34 Figure 19 Derrick ..................................................................................................................... 34
Figure 20 Boundary conditions (Source: DNV-RP-C103_2012-04) ....................................... 35
Figure 21 Boundary conditions applied on pontoons ............................................................... 36
Figure 22 Panel Model ............................................................................................................. 37 Figure 23 Wet Surface for Hydrodynamic Analysis ................................................................ 37 Figure 24 Meshed Panel Model ............................................................................................... 38
Figure 25 Morison Meshed Model ........................................................................................... 38 Figure 26 Structural Mesh Model ............................................................................................ 39
Figure 27 Problematic mesh elements. .................................................................................... 39 Figure 28 Final Structural Mesh Model ................................................................................... 40 Figure 29 Hydro Model of Semisubmersible Drilling Platform .............................................. 41
Figure 30 Four compartments inside two pontoons ................................................................. 43 Figure 31 Off body points to define sea state grid .................................................................. 43 Figure 32 Mass model of the Drilling Unit .............................................................................. 44 Figure 33 RAO for different wave directions at relative points (0, 0, and 35) ........................ 47 Figure 34 RAO of Heave ......................................................................................................... 48
Figure 35 RAO of Roll ............................................................................................................. 48 Figure 36 RAO of Pitch ........................................................................................................... 49
Figure 37 Damping Matrix ....................................................................................................... 49 Figure 38 RAO at relative point (0, 0, and 35) after addition of damping ............................... 50
Figure 39 Surface wave loads at 180 degree heading and 0.053 Hz frequency (Pitch RAO) . 51 Figure 40 Surface wave loads at 270 degree heading and 0.045 Hz frequency (Heave RAO) 51 Figure 41Surface wave loads at 270 degree heading and 0.042 Hz frequency (Roll RAO) .... 52 Figure 42 Surface wave loads at 180 degree heading and 0.033 Hz frequency (Surge RAO) 52 Figure 43 Surface wave loads at 270 degree heading and 0.033 Hz frequency (Sway RAO) . 53
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Figure 44 Surface wave loads at 315 degree heading and 0.166 Hz frequency (YAW RAO) 53 Figure 45 Global structural model ........................................................................................... 54
Figure 46 Von-Misses Stress at 45 degree wave heading and 0.1111 Hz excitation frequency
.................................................................................................................................................. 55
Figure 47 Von-Misses Stress on Column ................................................................................. 55 Figure 48 Scatter Diagram for the North Atlantic (Source: DNV-RP-C205) .......................... 56 Figure 49 DNV-SN Curves (Stofat_UM) ................................................................................ 57 Figure 50 DNVC-I SN curve plotted from STOFAT .............................................................. 57 Figure 51 Wave Spreading function for short crested Sea ....................................................... 58
Figure 52 Definition of the wave direction (heading angle) in this investigation. ................... 59 Figure 53 Maximum Usage Factor of the Structure ................................................................. 59 Figure 54 Fatigue Life of Global Structure .............................................................................. 60
List of Tables Table 1 Main Dimensional Parameter for Semisubmersible Analyzed ................................... 24
Table 2 Material Properties of the Structural Model (St52) ..................................................... 30 Table 3 Sea State Direction Set ............................................................................................... 42 Table 4 Mass Model Properties of the Structure ...................................................................... 44
Table 5 Load cases for Heading and Wave periods ................................................................. 45 Table 6 Long term response from Postresp .............................................................................. 50 Table 7 Fatigue life in Critical connections ............................................................................. 60
P 6 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
DECLARATION OF AUTHORSHIP
I declare that this thesis and the work presented in it are my own and have been generated by
me as the result of my own original research.
Where I have consulted the published work of others, this is always clearly attributed.
Where I have quoted from the work of others, the source is always given. With the exception
of such quotations, this thesis is entirely my own work.
I have acknowledged all main sources of help.
Where the thesis is based on work done by myself jointly with others, I have made clear exactly
what was done by others and what I have contributed myself.
This thesis contains no material that has been submitted previously, in whole or in part, for the
award of any other academic degree or diploma.
I cede copyright of the thesis in favour of the West Pomeranian University of Technology
Szczecin, Poland.
Date: Signature
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ABBREVIATIONS
CN
COG
CT
DNV
GL
Hs
FE
FP
FEA
JP
L-File
MODU
NA
OS
RAO
RP
Tp
TLP
UM
Classification Notes
Centre of Gravity
Compliant Tower Platforms
Det Norske Veritas
Germanischer Lloyd
Significant Height
Finite Element
Fixed Platform
Finite Element Analysis
Jack-up Platform
Load Interface File
Mobile offshore drilling units
North Atlantic
Offshore Standard
Response Amplitude Operator
Recommended Practice
Peak Period
Tension Leg Platform
User Manual
P 8 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
ABSTRACT
Drilling operation in deep water, harsh environment and remote locations becomes a key trend
for the offshore industry to fulfil increasing demand for energy. For operational conditions wave
induced loads are more significant for the offshore installations. Therefore, to ensure integrity
and structural safety, the wave induced loads have to be taken into account. One of the
approaches to accomplish this task is to perform a fatigue analysis with the extreme
environmental loading on the offshore platform using rules and practices recommended by
classification societies.
The main objective of the thesis has been to present a case study of a semisubmersible drilling
unit regarding the fatigue analysis. The applied approach consisted in finite element modelling
of the global structure, applying hydrodynamic loads using recommended offshore design
codes, transferring wave loads from hydrodynamic model to structural model and perform the
fatigue analysis with most unfavorable combination of environmental conditions. Among
different methods of fatigue analysis, the spectral method is considered as most suitable in
which long term distribution of stresses is calculated using wave scatter data.
For finite element modelling SESAM Genie was used while HydroD Wadam was used to
analyze hydrodynamic loads and also transfer the loads to the finite element model for
subsequent structural analysis. These hydrodynamic loads were applied for a number of wave
directions and for a range of wave frequencies covering the necessary sea states and the results
in form of stresses were obtained. These results were then used to calculate fatigue damages at
given points in the structural model using another software – Stofat.
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SHORT DESCRIPTION
A short description of this whole paper is given below:
This paper contains nine chapters in total. First chapter described the introduction of the project
including what is to be achieved, why this project needs to be done, methodology of the project
and detail time allocation with chart.
Second chapter contains a brief overview of the offshore drilling structures, different types of
offshore structures, their basis of applications and operation
In third chapter, the description of Semisubmersible platform which is used as a case study for
the current master thesis has been given with brief overview, types and example.
Fourth chapter includes a brief description of software tool used for this thesis and flowchart of
methodology.
Fifth chapter presents the global structural modeling of the drilling unit studied in detail. It
describes the 3d modelling for FE analysis with material properties, meshing and boundary
conditions to perform subsequent analysis
Sixth chapter contains Hydrodynamic Analysis of the structure including detailed overview of
analysis setup, mass model properties and subsequent global motion response for the given set
of extreme environmental loading conditions.
Global structural strength is presented on Seventh chapter with detailed load case and von-
misses stress
Finally global fatigue analysis result is listed in eighth chapter with SN-curve and scatter data
of the desired location.
Ninth is a conclusion chapter, which deals with the initial aim and objectives, achievement and
some suggestions for the future development of the work.
References and some important appendices are attached at the end.
P 10 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
1. INTRODUCTION
1.1 Background
As drilling extended further offshore into deeper water to access additional energy resources,
the structures are also largely exposed to stresses which induced by time variation. These type
of stress pattern are the forces generated principally by the sea waves. These loads are repeated
for thousands of cycles through the lifetime of the structure. After many cycles the accumulated
damage reduces the ability of the structural member to withstand loading. Global Fatigue
analysis is one of the approach to quantify wave induced load effects to ensure integrity and
structural safety of the offshore platform. A methodology has been developed for global fatigue
analysis of an offshore drilling unit with extreme environmental loading condition.
1.2 Objective
The main objective is to determine screening fatigue lives based upon DNV S-N curve and
wave scatter data. The calculated fatigue life indicate the distribution of fatigue sensitive area.
In order to meet the objective, the following sub-targets are to be fulfilled for the Global Model
analysis:
Make a 3D-model of the structure for FE analysis
Calculate the hydrodynamic loads in the frequency domain.
Identify critical locations with respect to von Mises stress for different wave direction.
Identify fatigue critical locations using linear FE-analysis. Perform the analysis for
different wave directions (heading angles).
1.3 Methodology
The objective with this study is to simulate numerically and analyze the structure response
followed by the fatigue life of an offshore drilling unit considering wave direction, magnitude
of wave loads and the location of interest. Following numerical analysis have been performed:
Hydrodynamic Analysis
Structural Response Analysis
Fatigue Analysis
Figure 1 depicts the methodology of the thesis and all the steps has been described briefly on
later sections.
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“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
Figure 1 Flowchart of Methodology
For the FE modeling and analysis of the drilling unit, DNV software Sesam GeniE has been
used. The hydrodynamic simulation is carried out in the DNV software HydroD Wadam. The
hydrodynamic simulations are performed in the frequency domain for the structure operating
in north Atlantic. For the frequency domain, a Bretschneider spectrum with 26 frequencies and
8 wave directions are chosen. The global motion response of the structure was analyzed using
a post-processing software named POSTRESP. The FE-simulations are carried out in the DNV
software SESTRA for linear structural FE-analysis. The fatigue analysis was done in STOFAT
and results are graphically presented with XTRACT. A brief description of software used for
analysis is given in Chapter four.
3D-Modelling
(Sesam-GeniE)
Hydrodynamic Analysis
(HydroD-Wadam)
Structural Analysis
(Sestra)
Global Response
(Xtract)
Fatigue Analysis
(Stofat)
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Master Thesis developed at West Pomeranian University of Technology, Szczecin
1.4 Schedule
Detail schedule of the thesis is presented below with Microsoft Project Gantt chart.
Figure 2 Detail Schedule with Gantt chart
1.5 Types of Fatigue Failure:
Two categories of fatigue damage are generally recognized and they are termed high frequency
and low frequency fatigue. In high frequency fatigue, failure is initiated in the form of small
cracks, which grow slowly and which may often be detected and repaired before the structure
is endangered. High frequency fatigue involves several millions of cycles of relatively low
stress (less than yield) and is typically encountered in machine parts rotating at high speed or
in structural components exposed to severe and prolonged vibration. Low frequency fatigue
involves higher stress levels, up to and beyond yield, which may result in cracks being initiated
after several thousand cycles.
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1.6 Sources of Fatigue:
Cyclic Load
Whipping
Springing
Engines and propeller
1.6.1 Cyclic Loads:
Offshore structures of all types are generally subjected to cyclic loading from wind, current and
waves. Dynamic wave produce stress fluctuations in the structural members and joints and are
the primary cause of fatigue damages. In deep water environments wind loads represent a
contribution of about 5 % to the environmental loading. Current loads are mostly considered to
be unimportant in the dynamic analysis of offshore structures, because their frequencies are not
sufficient to excite the structures. Wave loads are considered as the main source of excitation
for current piece of work.
1.6.2 Whipping:
Shocks between wave and ship bow is known as slamming, this shocks generates vibration
which is known as Whipping. So it is induced by wave impacts under the ship’s flared bow, the
overhanging stern, or the bottom, leads to transient, decaying hull girder vibrations which
typically occur in moderate or harsh seaways. For the current thesis work whipping is not taken
into account because of deep-water consideration and non-flared bow.
1.6.3 Springing:
Springing is caused by regular, periodic wave trains that excite resonant hull girder vibrations
occurring in low to moderate seaways. If excitation of waves equal to 1st beam or 2nd beam
natural frequency of structure then resonant occur and passenger moves/ jumps with structure.
As springing is negligible in deep-water, it is not considered for current work.
1.6.4 Engine Excitation Frequency:
High frequency response coming from engine or propeller creates severe vibration and initiate
fatigue cracks on nearby parts.
P 14 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
2. OFFSHORE DRILLING PLATFORMS:
2.1 Introduction:
One of the remarkable accomplishments of the petroleum industry has been the development
of technology that allows for drilling wells offshore to access additional energy resources. The
basic offshore wellbore construction process is not significantly different than the rotary drilling
process used for land based drilling. The main differences are the type drilling rig and modified
methods used to carry out the operations in a more complex situation. Depending on the
circumstances, the platform may be fixed to the ocean floor, may consist of an artificial island,
or may float.
For offshore drilling a mechanically stable offshore platform or floating vessel from which to
drill must be provided. These range from permanent offshore fixed or floating platforms to
temporary bottom-supported or floating drilling vessels.
Despite an increase in complexity, improvements in drilling technology have allowed more
complex well patterns to be drilled to a greater depth such that additional hydrocarbon resources
can be developed at a greater distance from the drilling or production structure, allowing more
energy to be produced with less environmental impact.
2.2 Components of Offshore Rigs:
Following are the major components of the offshore rigs as presented on figure 3 as well.
Hull – initially rigs were built out of tanker hulls, so the terminology remains same
Power Module – converts available fuel into power for the station
Process Module – onboarding and offloading of supplies and products
Drilling Module – the traditional drilling rig apparatus
Quarters Module – where the crew sleeps and eats
Wellbay Module – access to the well and other equipment
Derrick – the oil derrick
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Figure 3 Component of offshore rigs (19)
2.3 Category:
There are two basic categories of offshore drilling rigs those that can be moved from place to
place, allowing for drilling in multiple locations, and those rigs that are temporarily or
permanently placed on a fixed-location platform (platform rigs). Jack-ups, semisubmersibles
and drill-ships make up the majority of the offshore rig fleet and all are used worldwide. Other
rig types such as platform rigs, inland barges and tender-assisted rigs are used as well, but they
are fewer in number and are generally used in specific geographic areas. Common types of
offshore platforms are listed below:
Jack-up drilling rig
Fixed platform
Gravity-based structure
Compliant Tower
Tension-leg platform
Spar platform
Semi-submersible platform
Drillship
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Master Thesis developed at West Pomeranian University of Technology, Szczecin
Figure 4 Common Types of Drilling Rigs (BOEMRE, 2010c)
Common types of drilling rigs are presented with figure 4 with a brief description below:
Fixed platforms are built on concrete or steel legs, or both, anchored directly onto the
seabed, supporting a deck with space for drilling rigs, production facilities and crew
quarters. Such platforms are, by virtue of their immobility, designed for very long term
use (for instance the Hibernia platform). Various types of structure are used, steel jacket,
concrete caisson, floating steel and even floating concrete. Steel jackets are vertical
sections made of tubular steel members, and are usually piled into the seabed. Concrete
caisson structures, pioneered by the Condeep concept, often have in-built oil storage in
tanks below the sea surface and these tanks were often used as a flotation capability,
allowing them to be built close to shore and then floated to their final position where
they are sunk to the seabed. Fixed platforms are economically feasible for installation
in water depths up to about 1,700 ft (520 m)
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Figure 5 Fixed Platform Rig (Left) and Gravity-Based Structure (Right) (Source: Prof: Tadeusz Graczyk
Lectures at ZUT)
A Gravity Based Structure can either be steel or concrete and is usually anchored
directly onto the seabed. Steel GBS are predominantly used when there is no or limited
availability of crane barges to install a conventional fixed offshore platform, for
example in the Caspian Sea. There are several steel GBS in the world today (e.g.
offshore Turkmenistan Waters (Caspian Sea) and offshore New Zealand). Steel GBS do
not usually provide hydrocarbon storage capability. These structures are generally
feasible in shallow water depth till 100 m although the deepest GBS being used at Troll
field in Norway at water depth of 303 m.
A compliant tower (CT) is a fixed rig structure normally used for the offshore
production of oil or gas. The rig consists of narrow, flexible (compliant) towers and a
piled foundation supporting a conventional deck for drilling and production operations.
Compliant towers are designed to sustain significant lateral deflections and forces, and
are typically used in water depths ranging from 1,500 and 3,000 feet (450 and 900 m).
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At present the deepest is Petronius in 535 m of water (the tallest freestanding structure
in the world.), in operation since 1998. With the use of flex elements such as flex legs
or axial tubes, resonance is reduced and wave forces are de-amplified. This type of rig
structure can be configured to adapt to existing fabrication and installation equipment.
Compared with floating systems, such as Tension-leg platforms and SPARs, the
production risers are conventional and are subjected to less structural demands and
flexing. This flexibility allows it to operate in much deeper water, as it can 'absorb' much
of the pressure exerted on it by the wind and sea. It can deflect (sway) in excess of 2%
of height. Despite its flexibility, the compliant tower system is strong enough to
withstand hurricane conditions.
Mobile Offshore Drilling Unit (MODU) are drilling rigs that are used exclusively to
drill offshore and that float either while drilling or when being moved from location to
another. They fall into two general types: bottom-supported and floating drilling rigs.
Bottom-supported drilling rigs are barges or jack-ups. Floating drill rigs include
submersible and semi-submersible units and drill ships. Various MODUs are presented
on Figure 6.
A drilling barge consists of a barge with a complete drilling rig and ancillary equipment
constructed on it. Drilling barges are suitable for calm shallow waters (mostly inland
applications) and are not able to withstand the water movement experienced in deeper,
open water situations. When a drilling barge is moved from one location to another, the
barge floats on the water and is pulled by tugs. When a drilling barge is stationed on the
drill site, the barge can be anchored in the floating mode or in some way supported on
the bottom. The bottom-support barges may be submerged to rest on the bottom or they
may be raised on posts or jacked-up on legs above the water. The most common drilling
barges are inland water barge drilling rigs that are used to drill wells in lakes, rivers,
canals, swamps, marshes, shallow inland bays, and areas where the water covering the
drill site in not too deep.
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Figure 6 Varieties of mobile offshore drilling units (MODUs). Drill Barge (TODCO via NETL, 2011),
Jack-Up Rig (Transocean, 2011), Semi-submersible Rig (Eni, 2008), Drill Ship (BP p.l.c., 2011).
Submersible drilling rigs are similar to barge rigs but suitable for open ocean waters of
relative shallow depth. The drilling structure is supported by large submerged pontoons
that are flooded and rest on the seafloor when drilling. After the well is completed, the
water is pumped out of the tanks to restore buoyancy and the vessel is towed to the next
location.
Jack-up drilling rigs are similar to a drilling barge because the complete drilling rig is
built on a floating hull that must be moved between locations with tug boats. Jack-ups
are the most common offshore bottom-supported type of drilling rig. There are two jack-
up types; independent-leg jack-ups make up the majority of the existing fleet. They have
legs that penetrate into the seafloor and the hull jacks up and down the legs. Mat-
supported jack-ups are as the name implies, the mat rests on the seafloor during drilling
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operations. Cantilever jack-ups are able to skid out over the platform or well location,
while slot units have a slot that fits around a platform when drilling development wells.
Once on location, a jack-up rig is raised above the water on legs that extend to the
seafloor for support. Jack-ups can operate in open water or can be designed to move
over and drill though conductor pipes in a production platform. These MODU's-Mobile
Offshore Drilling Units are typically used in water depths up to 400 feet (120 m),
although some designs can go to 550 ft (170 m) depth. They are designed to move from
place to place, and then anchor themselves by deploying the legs to the ocean bottom
using a rack and pinion gear system on each leg.
Semisubmersibles are a common type of floating structure used in the exploration and
production of offshore hydrocarbons. These platforms have hulls of sufficient buoyancy
to cause the structure to float, but the structural/equipment weight of the platform and
the mooring system keeps the structure upright. Typically, four to eight vertical, surface
piercing columns are connected to these pontoons. The columns themselves may have
cross and horizontal bracing to provide structural strength and triangulated rigidity for
the platform. The minimal water plane area contributed by the vertical columns results
in long heave, pitch and roll natural periods and the hydrodynamic loading can be
minimized at the dominant wave period by careful selection of pontoon volume and
water plane area. A more detailed description of this type of offshore platforms has been
discussed in the Chapter 3 of this thesis.
A drillship is a maritime vessel that has been fitted with drilling apparatus. It is most
often used for exploratory offshore drilling of new oil or gas wells in deep water or for
scientific drilling. The drillship can also be used as a platform to carry out well
maintenance or completion work such as casing and tubing installation or subsea tree
installations. It is often built to the design specification of the oil Production Company
and/or investors, but can also be a modified tanker hull outfitted with a dynamic
positioning system to maintain its position over the well. The greatest advantages these
modern drill ships have is their ability to drill in water depths of more than 2500 meters
and the time saved sailing between oilfields worldwide. Drill ships are completely
independent, in contrast to semi-submersibles and jack up barges. In order to drill, a
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marine riser is lowered from the drillship to the seabed with a blowout preventer (BOP)
at the bottom that connects to the wellhead.
TLPs are floating platforms tethered to the seabed in a manner that eliminates most
vertical movement of the structure. TLPs are used in water depths up to about 6,000 feet
(2,000 m). The "conventional" TLP is a 4-column design which looks similar to a
semisubmersible. Proprietary versions include the Seastar and MOSES mini TLPs; they
are relatively low cost, used in water depths between 600 and 4,300 feet (180 and 1,300
m). Mini TLPs can also be used as utility, satellite or early production platforms for
larger deep-water discoveries. An example of TLP is given below.
Figure 7 Tension Leg Platform (Magnolia TLP, Source: Prof: Tadeusz Graczyk Lectures at ZUT)
Spars are moored to the seabed like TLPs, but whereas a TLP has vertical tension
tethers, a spar has more conventional mooring lines. The spar has more inherent stability
than a TLP since it has a large counterweight at the bottom and does not depend on the
mooring to hold it upright. It also has the ability, by adjusting the mooring line tensions
(using chain-jacks attached to the mooring lines), to move horizontally and to position
itself over wells at some distance from the main platform location. The first production
spar was Kerr-McGee's Neptune, anchored in 1,930 ft (590 m) in the Gulf of Mexico;
however, spars (such as Brent Spar) were previously used as FSOs.
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Master Thesis developed at West Pomeranian University of Technology, Szczecin
3. STUCTURE ANALYZED: SEMISUMMERSIBLE UNIT
3.1 Introduction:
For current work Semi-submersible drilling unit is used which are the most common type of
offshore floating drilling rigs and can operate in deep water and usually move from location to
location under their own power. These platforms have hulls (columns and pontoons) of
sufficient buoyancy to cause the structure to float, but of weight sufficient to keep the structure
upright; can be ballasted up or down by altering the amount of flooding in buoyancy tanks.
“Semis” as they are called as the have columns that are ballasted to remain on location either
by mooring lines attached to seafloor anchors or may be held in place by adjustable thrusters
which are rotated to hold the vessel over the desired location known as dynamically positioned.
Semi-submersibles can be used in water depths from 200 to 10,000 feet (60 to 3,000 m).
3.2 Classification:
Most common design of semisubmersible rigs are the column-stabilized semisubmersible unit
where two horizontal pontoons are connected via cylindrical or rectangular columns to the
drilling deck above the water. Column stabilized semisubmersible units design can be classified
as follows (figure 8)
Ring Pontoon Semisubmersibles: Ring pontoon designs normally have one continuous
lower hull (pontoons and nodes) supporting 4-8 vertical columns. The vertical columns are
supporting the upper deck.
Twin Pontoon Semisubmersibles: Twin pontoon designs normally have two lower
pontoons, each supporting 2-4 vertical columns. The 4-8 vertical columns are supporting
the upper deck. In addition it may be strengthened with diagonal braces supporting the
deck and horizontal braces connecting the pontoons or columns.
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“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
Figure 8 Column Stabilized Semisubmersibles (Left: Ring Pontoon Design, Right: Twin Pontoon Design,
Source: Petrowiki)
3.3 Example of similar model:
For the current thesis, simplified model of a twin pontoon column stabilized semisubmersible
unit is considered which consist of 4 sets of columns legs, 2 horizontal pontoons, 2 bracings
and a drilling derrick that has been chosen to perform fatigue analysis. In Figure below a similar
existing model of the semisubmersible drilling unit has been shown
Figure 9 Similar Drilling Platform model (Maersk Drilling deep-water semi-submersible rig Source: Prof:
Tadeusz Graczyk Lectures at ZUT)
P 24 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
Figure 9 and 10 represent Column stabilized dynamically positioned semisubmersible drilling
rigs with capability to attach to an 8-point pre-installed mooring system; provisions to attach to
a 12- point pre-installed mooring system.
Figure 10 Semi-submersible platform - Maersk Drilling deep-water semi-submersible rig (Source: Prof:
Tadeusz Graczyk Lectures at ZUT)
Main technical dimensions of analyzed structure of current thesis are listed below in Table 1
Table 1 Main Dimensional Parameter for Semisubmersible Analyzed
Parameters Technical Data
Characteristic Length= Length of Pontoon 80.6 m
Height of Pontoon 7.5 m
Width of Pontoon 16 m
Height of Column 33.5 m
Diameter of Column 12.9 m
Height of Deck 8 m
Spacing of Columns, center to center 54.72 m
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“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
4. SOFTWARE PROCEDURE:
4.1 Introduction:
SESAM software package developed by DNV is used for modelling and analysis of the
structure. The DNV software package SESAM consists of different modules which depend on
the simulation that is supposed to be carried out. The following SESAM-software is used;
GeniE, HydroD-WADAM, SESTRA, POSTRESP, STOFAT and XTRACT. Flowchart and
brief description of software procedure is given below:
Figure 11 Flowchart of Software Procedure
4.2 Sesam Genie:
The Sesam GeniE software is a software tool for designing and analyzing offshore and maritime
structures made of beams and plates. Modelling, analysis and results processing are performed
in the same graphic user interface. The use of concept technology makes the Sesam
GeniE software highly efficient for integrating stability, loading, strength assessment and CAD
exchange. All data are persistent enabling the engineers to do efficient iterative re-design of a
structure.
Global MOdel-GeniE
(T1.FEM)
Wadam
(G1.SIF, L1.FEM)
Sestra
(R1.SIN)
Stofat
.Vtf
Postresp
Xtract
Xtract
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For floating structures, the Sesam GeniE software can perform static and dynamic linear
analysis for structures subjected to wave, wind, current, and ballast and equipment layout. The
loads and accelerations from the waves and compartment content are defined by the Sesam
HydroD software and they are automatically applied to the structure model independent of the
hydrodynamic panel model.
The wave loads create input to fatigue assessments of both beams and plates using a stochastic
approach. By using the sub-modelling techniques it is very easy to perform a global fatigue
analysis to scan for critical areas
GeniE may be used as a stand-alone tool using a direct analysis approach which also include:
Finite element mesh generation
Finite element analysis
Finite element results visualization
Environmental loads calculation
Code checking and rule based design
Openness towards leading CAD vendors
4.3 HydroD-Wadam:
The Sesam HydroD software is a tool for hydrostatic and hydrodynamic analysis. For the
hydrodynamic part of analysis a sub module included in the HydroD package named as Wadam
has been used. Wadam is a general analysis program for calculation of wave-structure
interaction for fixed and floating structures of arbitrary shape, structures and ship hulls.
The Wadam software is based on widely accepted linear methods for marine hydrodynamics,
the 3-D radiation-diffraction theory employing a panel model and Morison equation in
linearized form employing a beam model. These analyses are normally performed in the
frequency domain, but it is also possible to do it in time domain (Linear as well as non-
linear).The loads are automatically used by the structural analysis. The response and loads may
be graphically assessed in animations. The analysis capabilities in Wadam comprise:
Calculation of hydrostatic data and inertia properties
Calculation of global responses
Calculation of selected global responses of a multi-body system
Automatic load transfer to a finite element model for subsequent structural analysis
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“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
First and second order 3D potential theory for large volume structures
Morison’s equation and potential theory when the structure comprises of both slender
and large volume parts. The forces at the slender part may optionally be calculated using
the diffracted wave kinematics calculated from the presence of the large volume part of
the structure.
The Wadam results may be presented directly as complex transfer functions or converted to
time domain results for a specified sequence of phase angles of the incident wave. For fixed
structures Morison’s equation may also be used with a time domain output option to calculate
drag forces due to time independent current.
The same analysis model may be applied to both the calculation of global responses in Wadam
and the subsequent structural analysis. For shell and solid element models Wadam also provides
automatic mapping of pressure loads from a panel model to a differently meshed structural
finite element model.
4.4 Sestra:
Sestra is the program for linear static and dynamic structural analysis within the SESAM
program system. It uses a displacement based finite element method. Sestra is computing the
local element matrices and load vectors, assembling them into global matrices and load vectors.
The global matrices are used by algebraic numerical algorithms to do the requested static,
dynamic or linearized buckling analysis. It is interfaced with other program modules of SESAM
for:
Finite element model generation — performed by the preprocessors
Load calculation — performed by the hydrodynamic analysis programs
Results evaluation and presentation — performed by the postprocessors
The analysis capabilities of Sestra are schematically illustrated in Figure 12
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Master Thesis developed at West Pomeranian University of Technology, Szczecin
Figure 12 Schematic illustration of the capabilities of Sestra (12)
Structural response due to dynamic loading can be analyzed by a quasi-static method, i.e. a
static analysis in Sestra with ‘quasi-static’ loads. The method involves neglecting dynamic
effects of the structure. A quasi-static analysis is often used when the frequency or time-
variation of the load is much lower than the lowest Eigen frequency of the structure. This is
also called stiffness controlled dynamics because the mass and damping forces in the structure
are small compared to the forces resulting from elastic and possible inelastic strains.
4.5 Xtact:
Xtract software is a FE results presentation postprocessor – a high-performance general purpose
model and results visualization program. Xtract presents structural analysis results in alternative
ways: deformed model, contour (iso-) curves, and numeric data on model display, X-Y graphs
and tabulated data. Based on stresses computed by the analysis program Xtract computes and
presents derived stresses: stresses decomposed into membrane and bending parts, principal
stresses and von Mises stress. In addition to its general presentation features the animation
feature of Xtract is especially useful for presenting results from hydrodynamic analyses. The
motion of a vessel in waves may be animated with the resulting stresses in the hull. Interactive
zooming, rotating, panning and cutting allows to achieve the best view of your model.
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“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
4.6 Postresp:
The Postresp software have been used to do statistical post-processing of general responses
given as transfer functions in the frequency domain analysis performed for global response of
the platform. The transfer functions have been generated by the hydrodynamic program HydroD
Wadam.
4.7 Stofat:
The Stofat software is a postprocessor for fatigue design. The fatigue calculations are based on
responses given as stress transfer functions. The stresses are generated by hydrodynamic
pressure loads acting on the model. These loads are applied for a number of wave directions
and for a range of wave frequencies covering the necessary sea states. The loads are applied to
a finite element model of the structure whereupon the finite element calculation produces results
as stresses in the elements. Stofat uses these results to calculate fatigue damages at given points
in the structural model. The program also calculates usage factors representing the amount of
fatigue damage that the structure has suffered during a specific design life
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5. STRUCTURAL MODELLING
5.1 Modelling Set-Up
The objective of the global structural modeling is to create Panel model, Morison and global
structural finite element model of the drilling platform for use in hydrodynamic and subsequent
structural analysis.
The SI-units has been used to for modelling:
Mass = [kg]
Length = [m]
Time = [s]
Applying these units in the analysis the output will then have the following units:
Force = [N] = [kgm/s2]
Stress = [N/m2] = [Pa]
St52 is used as a material which has following properties:
Table 2 Material Properties of the Structural Model (St52)
Material Property Value Unit
Yield Stress 2.35x 108 Pa
Density 7850 Kg/m3
Young’s Modulus 2.1x1011 Pa
Poison’s Ratio 0.3
Thermal co-efficient 1.2x10-5 delC-1
Damping co-efficient 0.03 N.s/m
Modelling has been done with Sesam GeniE as shown below with color-coding:
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“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
Figure 13 Color coding of structural members
Connections between deck and column, column and pontoon are modelled with thicker plate
which is also presented with color coding below:
Figure 14 Color coding of thickness
P 32 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
Global model includes following:
the longitudinal stiffness of the pontoons,
the axial and bending stiffness of the braces,
the axial and bending stiffness of the columns,
the in plane and vertical bending stiffness of the deck
5.2 Pontoon:
The pontoon has been created with shell elements where upper parts are as flat plates and lower
parts are as cylindrical and spherical as shown in Figure 15. Both top and bottom of the pontoon
are flat and rectangular. Longitudinal bulkhead is used which runs along the longitudinal central
axis of each of the pontoon. Longitudinal bulkhead and pontoon shell are key components of
the pontoon. To get geometric stiffness between pontoon shell and longitudinal bulkhead
couple of transvers watertight bulkheads are modelled. Combined framing is used. Local
reinforcements and minor reinforcement has been omitted in the global analysis model.
Figure 15 Pontoon
5.3 Column:
Four Vertical circular columns are modelled to withstand global stiffness as shown below on
Figure 16. Both longitudinal and transverse bulkheads are included with vertical shell plates.
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“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
Pontoon and deck connections are possibly the critical region of stress concentration and are
also modelled.
Figure 16 Column
5.5 Deck:
The transversal and longitudinal bulkheads are modeled along with the outer deck shell member
(Figure 17). The girders and the framing system to the upper deck shell were modelled using
T-section and stiffeners are modelled with L-Section bar. Local details i.e. brackets, buckling
stiffeners, etc. has been neglected as they don’t contribute significantly to the global strength.
Figure 17 Deck
P 34 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
Figure 18 Deck Framing System
5.5 Derrick:
Derrick that holds the drilling apparatus has been created with two different pipes (diameter)
as shown on Fig. 19 that contains four vertical legs continued by the sloping legs to the top.
Outer frames are created with the pipe diameter 1m and thickness 0.05m. Outer pipes are
connected with crossbar pipes of 0.8 m diameter and 0.04 m thickness.
Figure 19 Derrick
El. 38.5
El. 46 m
El. 55 m
El. 65 m
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“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
5.6 Boundary Conditions:
To avoid rigid body motion of a global structural model at least 6 degrees of freedom have to
be fixed. Three vertical supports should be defined by springs representing the total water
plan stiffness of the structure:
𝑘 = 𝜌𝑤.𝑔. 𝐴𝑤.
Where
Aw = is the total water plan area of the unit (m2).
ρ = density of water = 1025 Kg/m3
g= gravity of 9.81m/s2
k = 1025 kg/m3 x 9.81 m/sec2 x Aw = 10 055x Aw [N/m]
A set of boundary conditions is illustrated in Figure, with the following restraints:
3 vertical restraints (Z)
2 transversal horizontal restraints (Y)
1 longitudinal horizontal restraint (X).
In the figure the two points with fixation in Y have the same Y-coordinate and all three points
have the same Z-coordinate.
Figure 20 Boundary conditions (Source: DNV-RP-C103_2012-04)
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Master Thesis developed at West Pomeranian University of Technology, Szczecin
Figure 21 Boundary conditions applied on pontoons
The spring stiffness below each corner column is then kspring = k/3 = kz 1, 2, 3. In addition,
horizontal supporting, in transverse and longitudinal direction, is represented by springs equal
0.1 (10% of vertical stiffness is applied in the horizontal direction) of the total vertical spring
stiffness. The transverse horizontal stiffness is applied in two (2) support points, y-direction,
and one (1) spring element is applied in the longitudinal, x direction. kx1 = ky1, 2.
5.7 Panel Model:
A panel model is used to calculate hydrodynamic forces from potential theory. It is the part of
structural model that subjected to the water. Panel model modelling a dummy hydrodynamic
pressure load is applied to the wet surface. Only outer surface of pontoons and columns are
taken into account as a panel model and no internal structural components and bulkheads were
considered as they are not exposed to the hydrodynamic pressure. Wet surface of the structure
that has defined as a panel model is shown below in Figure 22 and Figure 23
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“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
Figure 22 Panel Model
Simple meshing techniques have been used to create the panel model. Since the model is double
symmetric only one quarter of the panel model is modelled as shown in Figure 24. The
remaining parts of the model are generated in Software Wadam by the yz-xz symmetry option.
Figure 23 Wet Surface for Hydrodynamic Analysis
P 38 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
Figure 24 Meshed Panel Model
5.8 Morison Model:
The Morison model consists of beam elements representing the transverse bracing. It is used to
viscous damping and drag forces (Morrison forces) of the unit using Morison theory. The
buoyancy and mass forces will be calculated by the panel (radiation and diffraction) model. The
slender pipe sections of Morison model connects the pontoon-column assembly of the structure.
The drag coefficients were assumed as a uniform numerical value of 0.7(Cd) in the horizontal
and vertical axes of the semisubmersible platform for the hydrodynamic analysis. The added
mass coefficient, Ca is set to 0.0 (The added mass is defined as Cm = 1+ Ca in HydroD).A default
value of meshing element length was used to create the mesh model of the Morison elements
as shown below in Figure 25.
Figure 25 Morison Meshed Model
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“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
5.9 Structural Model:
It consists of all the structural components including the bulkheads, the girders, bracings and
other key structural connections of the drilling platform. This structural model included the
panel and the Morison model along with the finite element assembly of the deck structure as
illustrated in Figure 26.
Figure 26 Structural Mesh Model
During analysis, problems are detected on some local area elements because of inappropriate
meshing (Figure 27).After checking the Sestra.lis file, bad elements shapes are identified and
fine mesh is used only on the particular elements to get the appropriate result (Figure 28)
Figure 27 Problematic mesh elements.
P 40 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
Figure 28 Final Structural Mesh Model
In the modelling of structural model a combination of dummy hydro pressure load, equipment’s
load and self-weight load is applied. However during the hydrodynamic analysis elements
below still water lines is separated from dry elements with defined hydrodynamic pressure.
Fine mesh
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“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
6. HYDRODYNAMIC ANALYSIS:
Wave loads are computed by HydroD Wadam using Morison’s equation and potential theory.
Wadam is an integrated part of the SESAM suite of programs which is tailored to calculate
wave loads on models created by the SESAM Genie. The results from the Wadam global
response analysis stored on a Hydrodynamic Results Interface File (G-file) for statistical post
processing in Postresp. The loads mapped to structural finite elements stored on the Loads
Interface File (L-file) for a subsequent structural analysis in Sestra.
A Hydro model was created using HydroD software to perform hydrodynamic analysis on the
global structure of the drilling unit. Hydro model is shown in Figure 29 below which is
consisted of finite element model of the structure.
Figure 29 Hydro Model of Semisubmersible Drilling Platform
6.1 Analysis Setup
Analysis was set up to get motion response and transferring the wave loads to structural model.
All models including Panel, Morison and Structural model was translated by -13.5m in z
directions which is considered as operating draft of the unit to ensure that mean sea level is
around z= 0 as per recommendation of the software manuals. This operating draft of 13.5 m
P 42 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
allows an acceptable balance of net buoyancy and static forces acting on the semisubmersible
model analyzed with minimal trim and heel condition.
For analysis setup following steps has been defined in HydroD Wadam package:
Analysis was done with frequency domain and the drag effects of the incident waves
were defined as linearization by stochastic method.
First direction defined with 0 degree and last direction 315 degree with respect to the
platform longitudinal axis to the sea state with the step value 45 degree
Table 3 Sea State Direction Set
No. of Direction Direction(deg)
1 0
2 45
3 90
4 135
5 180
6 225
7 270
8 315
Period is set between 0.5 to 25 sec with the step value 1 sec
Spectrum is setup to Bretshneider spectrum which is also known as a 2 parameter
Pierson-Moskowitz spectrum where only Hs (significant wave height) and Tp (Peak
period) need to be defined. Design wave was selected based on most extreme
environmental conditions of North Sea with 100 year return period. Significant Wave
height Hs=13.6m and Peak Period (Tp) =16s was found for the current operation of
mobile offshore units.
Spreading function of exponent 2 is selected to define short crested sea where main
heading is assumed to be 45 degree with respect to longitudinal axis. In short crested
sea other wave directions are taken into account than the current main wave direction
Hydro model is defined as floating
The water depth of the location was assumed to be uniform 300 m in the central North
Sea region and typical water depth for operation of drilling unit in that region. Water
density, Kinematic viscosity and Gravity is also defined with the value 1025Kg/m3,
1.19e-006m2/s and 9.80665 m/s2 respectively.
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“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
Sea state duration is selected as 3 hours which has been introduced as a standard time
between registrations of sea states when measuring waves. In connection with stochastic
response analysis, linear (Airy) theory is used
Four compartments are created inside two pontoons are shown in Figure 30, which
contains fluid with 900 Kg/m3 density. Same permeability is assigned for all
compartments
Figure 30 Four compartments inside two pontoons
To calculate wave pressure on defined point and to define grid to represent sea surface
off body points are used which was then post processed in Postresp is show in Figure
31 below. The range for the off-body points was taken as a grid system between (300m,
200m) to (-300m, -200m) with an interval of 25m in x axis and 20m in y axis.
Figure 31 Off body points to define sea state grid
Drift forces are calculated with far field integration (horizontal) method
P 44 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
Higher frequency limit in HydroD is around 2, too fine mesh create too much nodes
which may make size problem in Stofat so rather coarse mesh is used for global
analysis
Mass Model properties for the Hydrodynamic Analysis is given below in Table 4
Table 4 Mass Model Properties of the Structure
Property Value Unit
Mass of structural Model 23.6 x 106 Kg
Buoyancy Volume 25.1x103 m3
Centre of Buoyancy in coordinate(x,y,z) (0, 0, -13.5) m
Centre of Gravity in coordinate (x,y,z) (0, 0, -10) m
Radius of Gyration (x,y,z) 30.9, 29.7,38.6 m
Roll-Pitch Centrifugal Moment (XYRAD) -5.67 x10-14 m2
Roll-YAW Centrifugal Moment (XZRAD) 0 m2
Pitch-YAW Centrifugal Moment(YZRAD) -4.63 x10-15 m2
The mass model of the structure as show belong in Figure 32 was created by HydroD using
“user defined” option of homogenous density panel model with input co-ordinate system and
“fill from buoyancy” tab
Figure 32 Mass model of the Drilling Unit
Fatigue Analysis of Offshore Drilling Unit 45
“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
The load-cases based on combination of wave direction and wave period analyzed for different
loading conditions has been mentioned as follows
Table 5 Load cases for Heading and Wave periods
Load
Case Heading Period
Load
Case Heading Period
Load
Case Heading Period
Load
Case Heading Period
2_01 0 0.5 3_01 45 0.5 4_01 90 0.5 5_01 135 0.5
2_02 0 1.5 3_02 45 1.5 4_02 90 1.5 5_02 135 1.5
2_03 0 2.5 3_03 45 2.5 4_03 90 2.5 5_03 135 2.5
2_04 0 3.5 3_04 45 3.5 4_04 90 3.5 5_04 135 3.5
2_05 0 4.5 3_05 45 4.5 4_05 90 4.5 5_05 135 4.5
2_06 0 5.5 3_06 45 5.5 4_06 90 5.5 5_06 135 5.5
2_07 0 6.5 3_07 45 6.5 4_07 90 6.5 5_07 135 6.5
2_08 0 7.5 3_08 45 7.5 4_08 90 7.5 5_08 135 7.5
2_09 0 8.5 3_09 45 8.5 4_09 90 8.5 5_09 135 8.5
2_10 0 9.5 3_10 45 9.5 4_10 90 9.5 5_10 135 9.5
2_11 0 10.5 3_11 45 10.5 4_11 90 10.5 5_11 135 10.5
2_12 0 11.5 3_12 45 11.5 4_12 90 11.5 5_12 135 11.5
2_13 0 12.5 3_13 45 12.5 4_13 90 12.5 5_13 135 12.5
2_14 0 13.5 3_14 45 13.5 4_14 90 13.5 5_14 135 13.5
2_15 0 14.5 3_15 45 14.5 4_15 90 14.5 5_15 135 14.5
2_16 0 15.5 3_16 45 15.5 4_16 90 15.5 5_16 135 15.5
2_17 0 16.5 3_17 45 16.5 4_17 90 16.5 5_17 135 16.5
2_18 0 17.5 3_18 45 17.5 4_18 90 17.5 5_18 135 17.5
2_19 0 18.5 3_19 45 18.5 4_19 90 18.5 5_19 135 18.5
2_20 0 19.5 3_20 45 19.5 4_20 90 19.5 5_20 135 19.5
2_21 0 20.5 3_21 45 20.5 4_21 90 20.5 5_21 135 20.5
2_22 0 21.5 3_22 45 21.5 4_22 90 21.5 5_22 135 21.5
2_23 0 22.5 3_23 45 22.5 4_23 90 22.5 5_23 135 22.5
2_24 0 23.5 3_24 45 23.5 4_24 90 23.5 5_24 135 23.5
2_25 0 24.5 3_25 45 24.5 4_25 90 24.5 5_25 135 24.5
2_26 0 25 3_26 45 25 4_26 90 25 5_26 135 25
P 46 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
Load Case Heading Period
Load Case
Heading Period Load Case
Heading Period Load Case
Heading Period
6_01 180 0.5 7_01 225 0.5 8_01 270 0.5 9_01 315 0.5
6_02 180 1.5 7_02 225 1.5 8_02 270 1.5 9_02 315 1.5
6_03 180 2.5 7_03 225 2.5 8_03 270 2.5 9_03 315 2.5
6_04 180 3.5 7_04 225 3.5 8_04 270 3.5 9_04 315 3.5
6_05 180 4.5 7_05 225 4.5 8_05 270 4.5 9_05 315 4.5
6_06 180 5.5 7_06 225 5.5 8_06 270 5.5 9_06 315 5.5
6_07 180 6.5 7_07 225 6.5 8_07 270 6.5 9_07 315 6.5
6_08 180 7.5 7_08 225 7.5 8_08 270 7.5 9_08 315 7.5
6_09 180 8.5 7_09 225 8.5 8_09 270 8.5 9_09 315 8.5
6_10 180 9.5 7_10 225 9.5 8_10 270 9.5 9_10 315 9.5
6_11 180 10.5 7_11 225 10.5 8_11 270 10.5 9_11 315 10.5
6_12 180 11.5 7_12 225 11.5 8_12 270 11.5 9_12 315 11.5
6_13 180 12.5 7_13 225 12.5 8_13 270 12.5 9_13 315 12.5
6_14 180 13.5 7_14 225 13.5 8_14 270 13.5 9_14 315 13.5
6_15 180 14.5 7_15 225 14.5 8_15 270 14.5 9_15 315 14.5
6_16 180 15.5 7_16 225 15.5 8_16 270 15.5 9_16 315 15.5
6_17 180 16.5 7_17 225 16.5 8_17 270 16.5 9_17 315 16.5
6_18 180 17.5 7_18 225 17.5 8_18 270 17.5 9_18 315 17.5
6_19 180 18.5 7_19 225 18.5 8_19 270 18.5 9_19 315 18.5
6_20 180 19.5 7_20 225 19.5 8_20 270 19.5 9_20 315 19.5
6_21 180 20.5 7_21 225 20.5 8_21 270 20.5 9_21 315 20.5
6_22 180 21.5 7_22 225 21.5 8_22 270 21.5 9_22 315 21.5
6_23 180 22.5 7_23 225 22.5 8_23 270 22.5 9_23 315 22.5
6_24 180 23.5 7_24 225 23.5 8_24 270 23.5 9_24 315 23.5
6_25 180 24.5 7_25 225 24.5 8_25 270 24.5 9_25 315 24.5
6_26 180 25 7_26 225 25 8_26 270 25 9_26 315 25
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“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
6.2 Global Motion Response Analysis:
The response of the structure was measured in terms of its Response Amplitude Operators
(RAOs) for the 6 degree of freedom which is presented with POSTRESP software below:
Figure 33 RAO for different wave directions at relative points (0, 0, and 35)
The RAO is shown above for a relative point (0, 0, and 35). There are two peaks, one at 21s
(amplitude 8.1) which comes from the heave resonance mainly and one at 24s (amplitude 2.4)
which comes from the roll resonance mainly. The worst wave direction is 270 and 45 degrees
for both peaks. RAO for Heave, Roll and Pitch are given below in Figure 34, Figure 35 and
Figure 36:
P 48 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
Figure 34 RAO of Heave
Figure 35 RAO of Roll
Fatigue Analysis of Offshore Drilling Unit 49
“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
Figure 36 RAO of Pitch
Since the critical wave periods are related to natural periods and viscous damping is important
for the vertical motions of a semi-submersible. So Wadam was rerun after introducing some
damping in heave, roll and pitch. 5% damping is given in all modes as shown in below Figure.
.
Figure 37 Damping Matrix
The new RAO is shown in Figure 38. There are still two peaks, one at 14s (amplitude 0.6)
which comes from the roll resonance and one at 24s (amplitude 1.6) which comes from the
heave resonance. But now the first peak is significantly larger.
P 50 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
Figure 38 RAO at relative point (0, 0, and 35) after addition of damping
The worst wave direction is 180 degrees for the largest peak and 270 degree for highest peak.
DNV-NA scatter diagram is used and short crested sea states is assumed.
From Postresp long term response is calculated for 270 degree heading as given in Table 6
Table 6 Long term response from Postresp
Heading 270 Year=1 Year=5 Year=10 Year=50 Year=100
RAO 7.95 8.93 9.36 10.4 10.8
Output from the HydroD Wadam was represented as a global motion response and
hydrodynamic loading on the drilling unit. Surface wave loads on the platform for various load-
cases based on excitation frequencies for different motions has shown below in Figure 39 to
Figure 44 with contour plots. From the figures it is clear that heave, pith and roll motions are
more dominant where other motions like Sway, yaw or surge motions are almost negligible.
Sway or yaw motions are negligible because of symmetry of the structure and also in deep
water sway motion is negligible.
Fatigue Analysis of Offshore Drilling Unit 51
“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
Figure 39 Surface wave loads at 180 degree heading and 0.053 Hz frequency (Pitch RAO)
Figure 40 Surface wave loads at 270 degree heading and 0.045 Hz frequency (Heave RAO)
P 52 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
Figure 41Surface wave loads at 270 degree heading and 0.042 Hz frequency (Roll RAO)
Figure 42 Surface wave loads at 180 degree heading and 0.033 Hz frequency (Surge RAO)
Fatigue Analysis of Offshore Drilling Unit 53
“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
Figure 43 Surface wave loads at 270 degree heading and 0.033 Hz frequency (Sway RAO)
Figure 44 Surface wave loads at 315 degree heading and 0.166 Hz frequency (YAW RAO)
P 54 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
7. GLOBAL STRUCTURAL STRENGTH ANALYSIS
The hydrodynamic load is transferred to structural model (Figure 45) for subsequent quasi-
static analysis of the structure. The rigid body motions of the model were restrained by means
of applying spring elements to provide the required balance of forces to the structural loading.
The load cases of the structure are listed below:
Self-weight of the structure
Equipment’s which are positioned symmetrically in four positons of the structure, each
of them are 15000Kg, 4m height, 3m length and 5m width
Hydrodynamic loads from WADAM analysis
Four mass points at top of the derrick where each mass point has a mass of 2.0E5 Kg
The local effect of the wind and current loads on the structure is considered negligible
compared to extreme wave loading of 100 year return period
Figure 45 Global structural model
The quasi- static structural analysis were done for different wave frequencies and headings.
Some von-misses stresses are plotted below with XTRACT software tool in Figure 46 and
Figure 47. The von Mises stresses are low, since the structure response from only one frequency
can be considered in a frequency domain analysis but the wave load is a sum of frequencies
that are in different phases relative to each other. Combined effects are considered in later
section during fatigue analysis.
Fatigue Analysis of Offshore Drilling Unit 55
“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
Figure 46 Von-Misses Stress at 45 degree wave heading and 0.1111 Hz excitation frequency
Figure 47 Von-Misses Stress on Column
P 56 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
8. GLOBAL FATIGUE ANALYSIS AND RESULT:
Stofat software tool is used for spectral fatigue analysis which is followed by frequency domain
hydrodynamic analysis from HydeoD Wadam and quasi-static structural analysis from Sestra
that was executed earlier. Harmonic waves of unit amplitude at different frequencies and
directions are passed through the structure and generate a set of stress transfer functions which
are read into Stofat through the Result Interface File and used in the long term stochastic fatigue
calculations. In spectral method, long term fatigue calculation is based directly on a scatter
diagram, response spectrum and SN-curves as input. SN curve is used to define the fatigue
characteristics of a material subjected to repeated cycle of stress of constant magnitude. The
wave climate is presented by a scatter diagram representing North Atlantic which provides the
frequency of occurrence of a given parameter pair (e.g. (HS, Tz)) as shown in Figure 48 below:
Figure 48 Scatter Diagram for the North Atlantic (Source: DNV-RP-C205)
Fatigue Analysis of Offshore Drilling Unit 57
“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
The SN-curve delivers the number of cycles required to produce failure for a given magnitude
of stress (Figure 49). DNVC-I SN-curve is used which is default for Stofat (Figure 50)
Figure 49 DNV-SN Curves (Stofat_UM)
Figure 50 DNVC-I SN curve plotted from STOFAT
P 58 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
A Bretschneider wave spectrum is used. Priority is given to worst usage factor. Usage factor is
above 0.80 and design fatigue life is set to 20 years. Cos2 is the wave-spreading function to
define short crested sea for fatigue analysis which is plotted from STOFAT below:
Figure 51 Wave Spreading function for short crested Sea
STOFAT obtains the principal stresses from SESTRA and calculates the accumulated partial
damage .The accumulated partial damage is weighted over sea states and 8 wave directions.
The wave directions that are considered are 0, 45 up to 360 degrees. The definition of the wave
direction, or heading angle, is presented in Fig. 52
Fatigue Analysis of Offshore Drilling Unit 59
“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
The locations of the most critical elements in terms of usage factors are presented in Figure 53.
The usage factor is defined as the design life - life in service - divided by the calculated fatigue
life. For example, if the usage factor is 1.0, it will result in failure after 20 years, or if the usage
factor is 0.5, it will result in failure after 40 years.
Figure 53 Maximum Usage Factor of the Structure
Beam 90°
Bow 135°
Following 0°
Quarter 45°
Quarter 315°
Beam 270°
Bow 225°
Structure
Figure 52 Definition of the wave direction (heading angle) in this investigation.
Head 180°
P 60 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
Figure 54 Fatigue Life of Global Structure
Fatigue life is shown in above Figure 54 based on element of the global structure. Fatigue life
for critical connections are presented below which are the average value of adjacent elements
of the connections.
Table 7 Fatigue life in Critical connections
Connections Fatigue Life (Years)
Deck to Column Above 50
Column to Pontoon Around 30
Column to Brace Above 50
Deck to Derrick Around 40 The fatigue-critical locations are presented in Table 7 for a fatigue analysis with equal
probability for all wave directions. It seems reasonable that the elements that have the maximum
usage factors and minimum fatigue life are located in the column to pontoon region for
combined loading conditions; column to pontoon connections is also the maximum stressed
region of the unit. The Appendix B present the elements with the maximum usage factors for
different wave directions and the calculated fatigue life for these elements.
Fatigue Analysis of Offshore Drilling Unit 61
“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
9. CONCLUSIONS AND RECOMMENDATIONS:
Global fatigue analysis of an offshore drilling unit with extreme climatic conditions was
presented in this study. First, a global model of the platform was done followed by
hydrodynamic analysis. A linear structural FE-analysis and fatigue analysis was performed for
the global model in order to localize the critical locations. The analyses showed that the critical
regions are located in the column to pontoon connections, column to brace connections and
deck to derrick connections. Among these locations, column to pontoon connections showed
the worst fatigue life.
A study on the influence of different wave directions was performed in order to find the most
critical wave direction. The worst wave direction is found at 270 and 180 degrees. The
maximum stress level due to wave induced loading were found to be occurring at around similar
wave frequency range (f= 0.041-0.047 Hz or T= 21-24 sec).
The motion response is one of the critical factor during drilling operation of the platform. Heave
is one of the most significant motion response for operations of drilling equipment’s. Heave
response was found maximum at 270 and 180 degree wave heading and peak response is at
around 8 seconds.
There are more analyses that could have been performed if there had been more time reserved
for the project. Here is some recommendations for future work:
Local sub-models can be created and analysis for local models can be performed as
stress ranges could locally become significant
More detailed local non- linear finite element analysis and consideration of mooring
lines & riser system can be done for more precise information regarding structural
strength.
Other sources of excitation for example; wind, current, engine and propeller response,
whipping, springing etc could be taken into account to get more accurate result.
P 62 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
The effect of the weld can be considered since offshore structures are commonly built
with welded plating. Tensile residual stresses from welding will emphasize the crack-
growth, which will decrease the fatigue life.
Fatigue Analysis of Offshore Drilling Unit 63
“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
REFERENCES
1. Guidelines to Assess High-Frequency Hull Girder Response of Container Ships by
DNV-GL, 2014
2. “Analysis and Design of Ship Structure”, Chapter 18, Philippe Rigo and Enrico
Rizzuto
3. “Probabilistic Fatigue of offshore structures”, G. Sigurdsson, University of Aalborg,
Sohngaardsholmsvej 51, DK-9000 Aalborg, Denmark
4. Global Response Analysis for Semisubmersible Offshore Platform, Niraj Kumar Singh,
Thesis, EMSHIP-2013
5. Global and Detailed Local Fatigue Assessment of a Container Vessel, Camilla Knifsund
& Andrea Tesanovic, Chalmers University of Technology, 2012
6. DNV-RP-C206, Fatigue Methodology of Offshore Ships, 2012
7. DNV-RP-C103, Column-Stabilized Units, April 2012
8. DNV-CN-30.7, Fatigue Assessment of Ship Structures APRIL 2014
9. DNVGL-RP-C203:Fatigue design of offshore steel structures, 2014
10. DNV Sesam GeniE user manual
11. DNV Sesam HydroD user manual
12. DNV Sesam Sestra user manual
13. DNV Sesam Xtract user manual
14. DNV Sesam Postresp user manual
15. DNV Sesam Stofat user manual
16. DNV-Mesh Guidance-GeniEv5.1, February 2010
17. DNV GeniE Tutorial
18. DNV HydroD Tutorial
19. http://www.boem.gov/2012-2017-Lease-Sale-Schedule/ -Picture for Components of
Offshore Rigs
20. http://www.brighthubengineering.com/marine-engines-machinery/30775-different-
types-of-offshore-production-platforms-for-oil-extraction/#- Picture of Fixed Platform
P 64 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
APPENDIX
Appendix A: Summary of Model Properties -------------------------------
ALL COORDINATES ARE GIVEN IN THE INPUT COORDINATE SYSTEM
THE RADII OF GYRATION AND CENTRIFUGAL MOMENTS OF THE MASS MATRIX
AND THE RESTORING COEFFICIENTS ARE GIVEN RELATIV TO THE MOTION
REFERENCE POINT
(ORIGIN OF THE GLOBAL COORDINATE SYSTEM).
UNITS DATA:
-----------
ACCELERATION OF GRAVITY G = 9.80665E+00 [L/T**2]
WATER DENSITY RHO= 1.02500E+03 [M/L**3]
GEOMETRY DATA:
--------------
CHARACTERISTIC LENGTH L = 8.06000E+01 [L]
VERTICAL COORDINATE OF STILL WATER LINE -ZLOC = 0.00000E+00 [L]
NUMBER OF NODES IN THE MORISON MODEL NMNOD = 45
NUMBER OF MORISON ELEMENTS NMELM = 47
NUMBER OF BASIC PANELS = 740
NUMBER OF SYMMETRY PLANES IN
THE PANEL MODEL = 2
TOTAL NUMBER OF PANELS = 2960
DISPLACED VOLUMES OF THE PANEL MODEL
VOL 1 = 2.48355E+04 [L**3]
VOL 2 = 2.48363E+04
VOL 3 = 2.48398E+04
Fatigue Analysis of Offshore Drilling Unit 65
“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
MASS PROPERTIES AND STRUCTURAL DATA:
------------------------------------
MASS OF THE STRUCTURE M = 2.57415E+07 [M]
WEIGHT OF THE STRUCTURE M*G = 2.52438E+08 [M*L/T**2]
CENTRE OF GRAVITY
XG = 8.32135E-16 [L]
YG = 1.44719E-16 [L]
ZG =-1.05366E+01 [L]
ROLL RADIUS OF GYRATION XRAD = 3.13273E+01 [L]
PITCH RADIUS OF GYRATION YRAD = 2.88244E+01 [L]
YAW RADIUS OF GYRATION ZRAD = 3.80055E+01 [L]
ROLL-PITCH CENTRIFUGAL MOMENT XYRAD =-5.78876E-14 [L**2]
ROLL-YAW CENTRIFUGAL MOMENT XZRAD = 0.00000E+00 [L**2]
PITCH-YAW CENTRIFUGAL MOMENT YZRAD = 2.31550E-15 [L**2]
HYDROSTATIC DATA:
-----------------
DISPLACED VOLUME VOL = 2.50991E+04 [L**3]
MASS OF DISPLACED VOLUME RHO*VOL = 2.57266E+07 [M]
WATER PLANE AREA WPLA = 5.16672E+02 [L**2]
CENTRE OF BUOYANCY
XCB = 3.64765E-09 [L]
YCB =-4.55957E-09 [L]
ZCB =-1.35398E+01 [L]
TRANSVERSE METACENTRIC HEIGHT GM4= 1.26292E+01 [L]
LONGITUDINAL METACENTRIC HEIGHT GM5= 1.26270E+01 [L]
HEAVE-HEAVE RESTORING COEFFICIENT C33= 5.19349E+06 [M/T**2]
HEAVE-ROLL RESTORING COEFFICIENT C34= 0.00000E+00 [M*L/T**2]
HEAVE-PITCH RESTORING COEFFICIENT C35= 0.00000E+00[M*L/T**2]
ROLL-ROLL RESTORING COEFFICIENT C44= 3.18623E+09 [M*L**2/T**2]
PITCH-PITCH RESTORING COEFFICIENT C55= 3.18569E+09 [M*L**2/T**2]
ROLL-PITCH RESTORING COEFFICIENT C45 = 0.00000E+00 [M*L**2/T**2
P 66 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
2.8 ENVIRONMENTAL DATA:
-----------------------
WATER DEPTH = 3.00000E+02 [L]
NUMBER OF WAVE LENGTHS = 30
NUMBER OF HEADING ANGLES = 8
WAVE DESCRIPTION:
WAVE WAVE WAVE WAVE ANG.
LENGTH NUMBER PERIOD FREQUENCY
1 1.56078E+00 4.02568E+00 1.00000E+00 6.28319E+00
2 6.24311E+00 1.00642E+00 2.00000E+00 3.14159E+00
3 1.40470E+01 4.47298E-01 3.00000E+00 2.09440E+00
4 2.49724E+01 2.51605E-01 4.00000E+00 1.57080E+00
5 3.90194E+01 1.61027E-01 5.00000E+00 1.25664E+00
6 5.61880E+01 1.11824E-01 6.00000E+00 1.04720E+00
7 7.64781E+01 8.21567E-02 7.00000E+00 8.97598E-01
8 9.98897E+01 6.29012E-02 8.00000E+00 7.85398E-01
9 1.26423E+02 4.96997E-02 9.00000E+00 6.98132E-01
10 1.56078E+02 4.02568E-02 1.00000E+01 6.28319E-01
11 1.88854E+02 3.32701E-02 1.10000E+01 5.71199E-01
12 2.24752E+02 2.79561E-02 1.20000E+01 5.23599E-01
13 2.63771E+02 2.38206E-02 1.30000E+01 4.83322E-01
14 3.05910E+02 2.05394E-02 1.40000E+01 4.48799E-01
15 3.51159E+02 1.78927E-02 1.50000E+01 4.18879E-01
16 3.99495E+02 1.57278E-02 1.60000E+01 3.92699E-01
17 4.50854E+02 1.39362E-02 1.70000E+01 3.69599E-01
18 5.05112E+02 1.24392E-02 1.80000E+01 3.49066E-01
19 5.62065E+02 1.11788E-02 1.90000E+01 3.30694E-01
20 6.21422E+02 1.01110E-02 2.00000E+01 3.14159E-01
21 6.82816E+02 9.20187E-03 2.10000E+01 2.99199E-01
22 7.45838E+02 8.42433E-03 2.20000E+01 2.85599E-01
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“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
23 8.10070E+02 7.75635E-03 2.30000E+01 2.73182E-01
24 8.75123E+02 7.17977E-03 2.40000E+01 2.61799E-01
25 9.40660E+02 6.67955E-03 2.50000E+01 2.51327E-01
26 1.00641E+03 6.24320E-03 2.60000E+01 2.41661E-01
27 1.07215E+03 5.86038E-03 2.70000E+01 2.32711E-01
28 1.13773E+03 5.52258E-03 2.80000E+01 2.24399E-01
29 1.20304E+03 5.22277E-03 2.90000E+01 2.16662E-01
30 1.26801E+03 4.95517E-03 3.00000E+01 2.09440E-01
HEADING ANGLES (ANGLE BETWEEN POS. X-AXIS AND DIRECTION
OF WAVE PROPAGATION):
IN DEGREES IN RADIANS
1 0.00000E+00 0.00000E+00
2 4.50000E+01 7.85398E-01
3 9.00000E+01 1.57080E+00
4 1.35000E+02 2.35619E+00
5 1.80000E+02 3.14159E+00
6 2.25000E+02 3.92699E+00
7 2.70000E+02 4.71239E+00
8 3.15000E+02 5.49779E+00
P 68 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
Appendix B: Element Fatigue Check Result
NOMENCLATURE:
Element Name of element
Stat = PASS or FAIL: *FAIL = UsageFactor > 1.0
UsageFact Accumulated damage (Usage factor)
ChkPnt Fatigue check point number of element
ChkPlc Check at: Stress/surface/corner/mid-plane/or membrane points
AccFatLif Design fatigue life/usage factor (year)
StrsCycle Total number of stress cycles
SNCurve SN curve name.
atSide -z side or +z side of shell element
ElType Element type
X-coord. X coordinate of fatigue check point
Y-coord. Y coordinate of fatigue check point
Z-coord. Z coordinate of fatigue check point
ElThck Element thickness
AxialScf Resulting Axial stress K-factor (SCF factor)
BendScf Resulting Bending stress K-factor (SCF factor)
ShearScf Resulting Shear stress K-factor (SCF factor)
WeibScale Scale parameter of Weibull distribution
WeibShape Shape parameter of Weibull distribution
StressRange Maximum Stress Range of principal stress
Coordinate reference system : Current superelement
Status on failure : *FAIL when UsageFactor > 1.0
Design fatigue life : 20.0 years
Fatigue calculation based on : Spectral moments of maximum principal stresses
STOCHASTIC ELEMENT fatigue check results
Run: FR1 Super element MODEL
Priority.....: Worst Usage Factor
Usage factor: Above 0.80
Element Stat Usage Fact ChkPnt ChkPlc AccFatLif StrsCycle SNCurve
Fatigue Analysis of Offshore Drilling Unit 69
“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
E1 Type X-coord Y-coord. Z-coord.
E1Thck AxialScf BendScf ShearScf
WeibScale WeibShape StressRange
1768 *FAIL 6.62E+00 10(+z) SurfPt 3.02E+00 7.01E+07 DNVC-I
FQUS24 -2.73E+01 -2.09E+01 -6.00E+00
0.04 1.5 1.5 1.5
3.90E+07 9.74E-01 6.84E+08
8916 *FAIL 6.48E+00 4 (-z) SurfPt 3.09E+00 7.06E+07 DNVC-I
FQUS24 2.74E+01 -2.09E+01 -6.00E+00
0.04 1.5 1.5 1.5
3.86E+07 9.72E-01 6.83E+08
1924 *FAIL 6.37E+00 9 (+z) SurfPt 3.14E+00 7.03E+07 DNVC-I
FQUS24 -2.73E+01 2.09E+01 -6.00E+00
0.04 1.5 1.5 1.5
3.85E+07 9.76E-01 6.72E+08
9078 *FAIL 5.94E+00 10(+z) SurfPt 3.37E+00 7.00E+07 DNVC-I
FQUS24 2.73E+01 2.09E+01 -6.00E+00
0.04 1.5 1.5 1.5
3.78E+07 9.74E-01 6.62E+08
9079 *FAIL 5.84E+00 6 (+z) SurfPt 3.42E+00 6.98E+07 DNVC-I
FQUS24 2.73E+01 2.09E+01 -6.00E+00
0.04 1.5 1.5 1.5
3.77E+07 9.76E-01 6.54E+08
1730 *FAIL 5.42E+00 10(+z) SurfPt 3.69E+00 7.05E+07 DNVC-I
FQUS24 -2.73E+01 -2.09E+01 -6.00E+00
0.04 1.5 1.5 1.5
3.65E+07 9.73E-01 6.43E+08
1937 *FAIL 5.39E+00 7 (+z) SurfPt 3.71E+00 7.04E+07 DNVC-I
FQUS24 -2.73E+01 2.09E+01 -6.00E+00
0.04 1.5 1.5 1.5
P 70 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
3.66E+07 9.79E-01 6.34E+08
8872 *FAIL 5.37E+00 4 (-z) SurfPt 3.73E+00 7.01E+07 DNVC-I
FQUS24 2.74E+01 -2.09E+01 -6.00E+00
0.04 1.5 1.5 1.5
3.66E+07 9.75E-01 6.40E+08
1050 *FAIL 5.14E+00 4 (-z) SurfPt 3.89E+00 7.01E+07 DNVC-I
FQUS24 -2.74E+01 -2.09E+01 -6.02E+00
0.04 1.5 1.5 1.5
3.60E+07 9.74E-01 6.31E+08
2599 *FAIL 5.01E+00 4 (-z) SurfPt 3.99E+00 7.02E+07 DNVC-I
FQUS24 -2.74E+01 -2.09E+01 -6.02E+00
0.04 1.5 1.5 1.5
3.57E+07 9.75E-01 6.27E+08
8250 *FAIL 4.98E+00 4 (-z) SurfPt 4.02E+00 7.03E+07 DNVC-I
FQUS24 2.74E+01 2.09E+01 -6.02E+00
0.04 1.5 1.5 1.5
3.57E+07 9.73E-01 6.28E+08
Element Stat Usage Fact ChkPnt ChkPlc AccFatLif StrsCycle SNCurve
E1 Type X-coord Y-coord. Z-coord.
E1Thck AxialScf BendScf ShearScf
WeibScale WeibShape StressRange
830 *FAIL 2.36E+00 6 (+z) SurfPt 8.49E+00 6.38E+07 DNVC-I
FQUS24 -3.43E+01 -2.54E+01 -1.30E+01
0.047 1.5 1.5 1.5
1.95E+07 7.67E-01 7.12E+08
7910 *FAIL 2.32E+00 10(+z) SurfPt 8.61E+00 6.25E+07 DNVC-I
FQUS24 2.04E+01 2.54E+01 -1.30E+01
0.047 1.5 1.5 1.5
2.18E+07 8.10E-01 6.56E+08
7888 *FAIL 2.23E+00 1 (-z) SurfPt 8.99E+00 7.03E+07 DNVC-I
FQUS24 2.25E+01 -2.07E+01 -1.14E+01
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“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
0.047 1.5 1.5 1.5
2.97E+07 1.02E+00 4.34E+08
2967 *FAIL 2.17E+00 1 (-z) SurfPt 9.20E+00 7.15E+07 DNVC-I
FQUS24 -2.25E+01 2.07E+01 -1.14E+01
0.047 1.5 1.5 1.5
2.76E+07 9.79E-01 4.58E+08
2950 *FAIL 2.07E+00 9 (+z) SurfPt 9.68E+00 6.32E+07 DNVC-I
FQUS24 -2.04E+01 2.34E+01 -1.30E+01
0.047 1.5 1.5 1.5
2.06E+07 8.00E-01 6.40E+08
7887 *FAIL 2.05E+00 4 (-z) SurfPt 9.76E+00 7.10E+07 DNVC-I
FQUS24 2.25E+01 -2.07E+01 -1.14E+01
0.047 1.5 1.5 1.5
2.89E+07 1.02E+00 4.22E+08
7870 *FAIL 1.94E+00 6 (+z) SurfPt 1.03E+01 6.48E+07 DNVC-I
FQUS24 2.04E+01 -2.54E+01 -1.30E+01
0.047 1.5 1.5 1.5
2.27E+07 8.59E-01 5.73E+08
2936 *FAIL 1.94E+00 9 (+z) SurfPt 1.03E+01 6.61E+07 DNVC-I
FQUS24 -2.04E+01 -2.34E+01 -1.30E+01
0.047 1.5 1.5 1.5
2.45E+07 9.08E-01 4.96E+08
2966 *FAIL 1.86E+00 9 (+z) SurfPt 1.07E+01 7.13E+07 DNVC-I
FQUS24 -2.25E+01 2.07E+01 -1.14E+01
0.047 1.5 1.5 1.5
2.58E+07 9.65E-01 4.51E+08
905 *FAIL 1.85E+00 6 (+z) SurfPt 1.08E+01 6.63E+07 DNVC-I
FQUS24 -3.43E+01 2.94E+01 -1.30E+01
0.047 1.5 1.5 1.5
1.93E+07 7.94E-01 6.18E+08
2924 *FAIL 1.84E+00 2 (-z) SurfPt 1.09E+01 7.03E+07 DNVC-I
FQUS24 -2.25E+01 -2.07E+01 -1.14E+01
0.047 1.5 1.5 1.5
2.81E+07 1.02E+00 4.14E+08
P 72 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
Element Stat Usage Fact ChkPnt ChkPlc AccFatLif StrsCycle SNCurve
E1 Type X-coord Y-coord. Z-coord.
E1Thck AxialScf BendScf ShearScf
WeibScale WeibShape StressRange
1768 *FAIL 6.62E+00 10(+z) SurfPt 3.02E+00 7.01E+07 DNVC-I
FQUS24 -2.73E+01 -2.09E+01 -6.00E+00
0.04 1.5 1.5 1.5
3.90E+07 9.74E-01 6.84E+08
8916 *FAIL 6.48E+00 4 (-z) SurfPt 3.09E+00 7.06E+07 DNVC-I
FQUS24 2.74E+01 -2.09E+01 -6.00E+00
0.04 1.5 1.5 1.5
3.86E+07 9.72E-01 6.83E+08
1924 *FAIL 6.37E+00 9 (+z) SurfPt 3.14E+00 7.03E+07 DNVC-I
FQUS24 -2.73E+01 2.09E+01 -6.00E+00
0.04 1.5 1.5 1.5
3.85E+07 9.76E-01 6.72E+08
9078 *FAIL 5.94E+00 10(+z) SurfPt 3.37E+00 7.00E+07 DNVC-I
FQUS24 2.73E+01 2.09E+01 -6.00E+00
0.04 1.5 1.5 1.5
3.78E+07 9.74E-01 6.62E+08
9079 *FAIL 5.84E+00 6 (+z) SurfPt 3.42E+00 6.98E+07 DNVC-I
FQUS24 2.73E+01 2.09E+01 -6.00E+00
0.04 1.5 1.5 1.5
3.77E+07 9.76E-01 6.54E+08
1730 *FAIL 5.42E+00 10(+z) SurfPt 3.69E+00 7.05E+07 DNVC-I
FQUS24 -2.73E+01 -2.09E+01 -6.00E+00
0.04 1.5 1.5 1.5
3.65E+07 9.73E-01 6.43E+08
1937 *FAIL 5.39E+00 7 (+z) SurfPt 3.71E+00 7.04E+07 DNVC-I
FQUS24 -2.73E+01 2.09E+01 -6.00E+00
0.04 1.5 1.5 1.5
3.66E+07 9.79E-01 6.34E+08
8872 *FAIL 5.37E+00 4 (-z) SurfPt 3.73E+00 7.01E+07 DNVC-I
FQUS24 2.74E+01 -2.09E+01 -6.00E+00
0.04 1.5 1.5 1.5
3.66E+07 9.75E-01 6.40E+08
Fatigue Analysis of Offshore Drilling Unit 73
“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
1050 *FAIL 5.14E+00 4 (-z) SurfPt 3.89E+00 7.01E+07 DNVC-I
FQUS24 -2.74E+01 -2.09E+01 -6.02E+00
0.04 1.5 1.5 1.5
3.60E+07 9.74E-01 6.31E+08
2599 *FAIL 5.01E+00 4 (-z) SurfPt 3.99E+00 7.02E+07 DNVC-I
FQUS24 -2.74E+01 -2.09E+01 -6.02E+00
0.04 1.5 1.5 1.5
3.57E+07 9.75E-01 6.27E+08
8250 *FAIL 4.98E+00 4 (-z) SurfPt 4.02E+00 7.03E+07 DNVC-I
FQUS24 2.74E+01 2.09E+01 -6.02E+00
0.04 1.5 1.5 1.5
3.57E+07 9.73E-01 6.28E+08
Element Stat Usage Fact ChkPnt ChkPlc AccFatLif StrsCycle SNCurve
E1 Type X-coord Y-coord. Z-coord.
E1Thck AxialScf BendScf ShearScf
WeibScale WeibShape StressRange
830 *FAIL 2.36E+00 6 (+z) SurfPt 8.49E+00 6.38E+07 DNVC-I
FQUS24 -3.43E+01 -2.54E+01 -1.30E+01
0.047 1.5 1.5 1.5
1.95E+07 7.67E-01 7.12E+08
7910 *FAIL 2.32E+00 10(+z) SurfPt 8.61E+00 6.25E+07 DNVC-I
FQUS24 2.04E+01 2.54E+01 -1.30E+01
0.047 1.5 1.5 1.5
2.18E+07 8.10E-01 6.56E+08
7888 *FAIL 2.23E+00 1 (-z) SurfPt 8.99E+00 7.03E+07 DNVC-I
FQUS24 2.25E+01 -2.07E+01 -1.14E+01
0.047 1.5 1.5 1.5
2.97E+07 1.02E+00 4.34E+08
2967 *FAIL 2.17E+00 1 (-z) SurfPt 9.20E+00 7.15E+07 DNVC-I
FQUS24 -2.25E+01 2.07E+01 -1.14E+01
0.047 1.5 1.5 1.5
2.76E+07 9.79E-01 4.58E+08
2950 *FAIL 2.07E+00 9 (+z) SurfPt 9.68E+00 6.32E+07 DNVC-I
FQUS24 -2.04E+01 2.34E+01 -1.30E+01
0.047 1.5 1.5 1.5
P 74 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
2.06E+07 8.00E-01 6.40E+08
7887 *FAIL 2.05E+00 4 (-z) SurfPt 9.76E+00 7.10E+07 DNVC-I
FQUS24 2.25E+01 -2.07E+01 -1.14E+01
0.047 1.5 1.5 1.5
2.89E+07 1.02E+00 4.22E+08
7870 *FAIL 1.94E+00 6 (+z) SurfPt 1.03E+01 6.48E+07 DNVC-I
FQUS24 2.04E+01 -2.54E+01 -1.30E+01
0.047 1.5 1.5 1.5
2.27E+07 8.59E-01 5.73E+08
2936 *FAIL 1.94E+00 9 (+z) SurfPt 1.03E+01 6.61E+07 DNVC-I
FQUS24 -2.04E+01 -2.34E+01 -1.30E+01
0.047 1.5 1.5 1.5
2.45E+07 9.08E-01 4.96E+08
2966 *FAIL 1.86E+00 9 (+z) SurfPt 1.07E+01 7.13E+07 DNVC-I
FQUS24 -2.25E+01 2.07E+01 -1.14E+01
0.047 1.5 1.5 1.5
2.58E+07 9.65E-01 4.51E+08
905 *FAIL 1.85E+00 6 (+z) SurfPt 1.08E+01 6.63E+07 DNVC-I
FQUS24 -3.43E+01 2.94E+01 -1.30E+01
0.047 1.5 1.5 1.5
1.93E+07 7.94E-01 6.18E+08
2924 *FAIL 1.84E+00 2 (-z) SurfPt 1.09E+01 7.03E+07 DNVC-I
FQUS24 -2.25E+01 -2.07E+01 -1.14E+01
0.047 1.5 1.5 1.5
2.81E+07 1.02E+00 4.14E+08
Element Stat Usage Fact ChkPnt ChkPlc AccFatLif StrsCycle SNCurve
E1 Type X-coord Y-coord. Z-coord.
E1Thck AxialScf BendScf ShearScf
WeibScale WeibShape StressRange
9968 *FAIL 1.84E+00 10(+z) SurfPt 1.09E+01 6.62E+07 DNVC-I
FQUS24 3.43E+01 -2.54E+01 -1.30E+01
0.047 1.5 1.5 1.5
2.40E+07 9.01E-01 5.19E+08
7907 *FAIL 1.80E+00 9 (+z) SurfPt 1.11E+01 6.31E+07 DNVC-I
FQUS24 2.04E+01 2.34E+01 -1.30E+01
Fatigue Analysis of Offshore Drilling Unit 75
“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
0.047 1.5 1.5 1.5
2.20E+07 8.55E-01 5.61E+08
829 *FAIL 1.78E+00 2 (-z) SurfPt 1.12E+01 6.42E+07 DNVC-I
FQUS24 -3.42E+01 -2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.77E+07 7.62E-01 6.58E+08
7895 *FAIL 1.77E+00 2 (-z) SurfPt 1.13E+01 6.81E+07 DNVC-I
FQUS24 2.25E+01 2.07E+01 -1.14E+01
0.047 1.5 1.5 1.5
2.77E+07 1.01E+00 4.18E+08
904 *FAIL 1.76E+00 2 (-z) SurfPt 1.14E+01 6.53E+07 DNVC-I
FQUS24 -3.42E+01 2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.88E+07 7.84E-01 6.28E+08
870 *FAIL 1.62E+00 10(+z) SurfPt 1.23E+01 6.45E+07 DNVC-I
FQUS24 -3.43E+01 2.54E+01 -1.30E+01
0.047 1.5 1.5 1.5
1.85E+07 7.84E-01 6.13E+08
9943 *FAIL 1.59E+00 10(+z) SurfPt 1.26E+01 6.83E+07 DNVC-I
FQUS24 3.43E+01 2.94E+01 -1.30E+01
0.047 1.5 1.5 1.5
1.95E+07 8.35E-01 5.34E+08
873 *FAIL 1.56E+00 2 (-z) SurfPt 1.28E+01 6.45E+07 DNVC-I
FQUS24 -3.42E+01 2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.82E+07 7.79E-01 6.15E+08
1230 *FAIL 1.52E+00 7 (+z) SurfPt 1.31E+01 6.27E+07 DNVC-I
FQUS24 -2.90E+01 2.07E+01 -9.48E+00
0.047 1.5 1.5 1.5
1.84E+07 7.86E-01 6.03E+08
895 *FAIL 1.52E+00 10(+z) SurfPt 1.31E+01 6.62E+07 DNVC-I
FQUS24 -3.43E+01 -2.94E+01 -1.30E+01
0.047 1.5 1.5 1.5
1.71E+07 7.80E-01 5.89E+08
898 *FAIL 1.52E+00 2 (-z) SurfPt 1.31E+01 6.51E+07 DNVC-I
FQUS24 -3.42E+01 -2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.69E+07 7.67E-01 6.12E+08
Element Stat Usage Fact ChkPnt ChkPlc AccFatLif StrsCycle SNCurve
P 76 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
E1 Type X-coord Y-coord. Z-coord.
E1Thck AxialScf BendScf ShearScf
WeibScale WeibShape StressRange
833 *FAIL 1.50E+00 1 (-z) SurfPt 1.33E+01 6.43E+07 DNVC-I
FQUS24 -3.42E+01 -2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.68E+07 7.61E-01 6.25E+08
2948 *FAIL 1.44E+00 2 (-z) SurfPt 1.39E+01 6.33E+07 DNVC-I
FQUS24 -2.06E+01 2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.79E+07 7.77E-01 6.02E+08
2914 *FAIL 1.44E+00 10(+z) SurfPt 1.39E+01 6.68E+07 DNVC-I
FQUS24 -2.04E+01 2.94E+01 -1.30E+01
0.047 1.5 1.5 1.5
1.72E+07 7.63E-01 6.06E+08
9946 *FAIL 1.43E+00 2 (-z) SurfPt 1.40E+01 6.74E+07 DNVC-I
FQUS24 3.42E+01 2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.86E+07 8.23E-01 5.33E+08
2964 *FAIL 1.43E+00 2 (-z) SurfPt 1.40E+01 6.90E+07 DNVC-I
FQUS24 -2.25E+01 2.07E+01 -1.14E+01
0.047 1.5 1.5 1.5
2.19E+07 9.13E-01 4.62E+08
908 *FAIL 1.40E+00 1 (-z) SurfPt 1.43E+01 6.52E+07 DNVC-I
FQUS24 -3.42E+01 2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.76E+07 7.83E-01 5.89E+08
9971 *FAIL 1.37E+00 2 (-z) SurfPt 1.46E+01 6.66E+07 DNVC-I
FQUS24 3.42E+01 -2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
2.17E+07 8.94E-01 4.78E+08
7871 *FAIL 1.36E+00 9 (+z) SurfPt 1.47E+01 6.65E+07 DNVC-I
FQUS24 2.04E+01 -2.34E+01 -1.30E+01
0.047 1.5 1.5 1.5
2.15E+07 8.92E-01 4.86E+08
872 *FAIL 1.35E+00 5 (-z) SurfPt 1.48E+01 6.46E+07 DNVC-I
FQUS24 -3.42E+01 2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.74E+07 7.79E-01 5.89E+08
9978 *FAIL 1.30E+00 6 (+z) SurfPt 1.54E+01 6.65E+07 DNVC-I
FQUS24 3.43E+01 2.54E+01 -1.30E+01
0.047 1.5 1.5 1.5
1.78E+07 8.14E-01 5.31E+08
7885 *FAIL 1.29E+00 2 (-z) SurfPt 1.55E+01 7.02E+07 DNVC-I
FQUS24 2.25E+01 -2.07E+01 -1.14E+01
0.047 1.5 1.5 1.5
2.54E+07 1.02E+00 3.77E+08
Fatigue Analysis of Offshore Drilling Unit 77
“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
Element Stat Usage Fact ChkPnt ChkPlc AccFatLif StrsCycle SNCurve
E1 Type X-coord Y-coord. Z-coord.
E1Thck AxialScf BendScf ShearScf
WeibScale WeibShape StressRange
835 *FAIL 1.27E+00 6 (+z) SurfPt 1.57E+01 6.38E+07 DNVC-I
FQUS24 -3.42E+01 -2.42E+01 -1.16E+01
0.047 1.5 1.5 1.5
1.61E+07 7.62E-01 5.96E+08
2942 *FAIL 1.27E+00 2 (-z) SurfPt 1.57E+01 6.41E+07 DNVC-I
FQUS24 -2.06E+01 -2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.72E+07 7.91E-01 5.53E+08
9977 *FAIL 1.27E+00 2 (-z) SurfPt 1.58E+01 6.67E+07 DNVC-I
FQUS24 3.42E+01 2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.76E+07 8.12E-01 5.28E+08
831 *FAIL 1.26E+00 9 (+z) SurfPt 1.59E+01 6.42E+07 DNVC-I
FQUS24 -3.44E+01 -2.34E+01 -1.30E+01
0.047 1.5 1.5 1.5
1.65E+07 7.76E-01 5.82E+08
9903 *FAIL 1.26E+00 6 (+z) SurfPt 1.59E+01 6.86E+07 DNVC-I
FQUS24 3.43E+01 -2.94E+01 -1.30E+01
0.047 1.5 1.5 1.5
2.20E+07 9.24E-01 4.34E+08
2459 *FAIL 1.25E+00 6 (+z) SurfPt 1.60E+01 6.35E+07 DNVC-I
FQUS24 -2.57E+01 2.05E+01 -1.12E+01
0.047 1.5 1.5 1.5
1.77E+07 8.00E-01 5.47E+08
897 *FAIL 1.24E+00 5 (-z) SurfPt 1.61E+01 6.50E+07 DNVC-I
FQUS24 -3.42E+01 -2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.59E+07 7.66E-01 5.80E+08
9902 *FAIL 1.23E+00 2 (-z) SurfPt 1.62E+01 6.76E+07 DNVC-I
FQUS24 3.42E+01 -2.74E+01 -1.13E+01
P 78 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
0.047 1.5 1.5 1.5
2.12E+07 9.04E-01 4.51E+08
1206 *FAIL 1.23E+00 7 (+z) SurfPt 1.62E+01 6.42E+07 DNVC-I
FQUS24 -2.90E+01 -3.41E+01 -9.48E+00
0.047 1.5 1.5 1.5
1.56E+07 7.61E-01 5.80E+08
1229 *FAIL 1.21E+00 7 (+z) SurfPt 1.66E+01 6.12E+07 DNVC-I
FQUS24 -2.90E+01 2.05E+01 -1.12E+01
0.047 1.5 1.5 1.5
1.69E+07 7.69E-01 5.91E+08
2874 *FAIL 1.19E+00 6 (+z) SurfPt 1.68E+01 6.56E+07 DNVC-I
FQUS24 -2.04E+01 -2.94E+01 -1.30E+01
0.047 1.5 1.5 1.5
1.51E+07 7.41E-01 6.13E+08
Element Stat Usage Fact ChkPnt ChkPlc AccFatLif StrsCycle SNCurve
E1 Type X-coord Y-coord. Z-coord.
E1Thck AxialScf BendScf ShearScf
WeibScale WeibShape StressRange
2952 *FAIL 1.17E+00 1 (-z) SurfPt 1.70E+01 6.35E+07 DNVC-I
FQUS24 -2.06E+01 2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.69E+07 7.76E-01 5.67E+08
9970 *FAIL 1.14E+00 5 (-z) SurfPt 1.76E+01 6.68E+07 DNVC-I
FQUS24 3.42E+01 -2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
2.05E+07 8.94E-01 4.52E+08
9945 *FAIL 1.13E+00 5 (-z) SurfPt 1.78E+01 6.73E+07 DNVC-I
FQUS24 3.42E+01 2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.73E+07 8.22E-01 5.00E+08
1205 *FAIL 1.10E+00 7 (+z) SurfPt 1.82E+01 6.30E+07 DNVC-I
FQUS24 -2.90E+01 -3.42E+01 -1.12E+01
0.047 1.5 1.5 1.5
1.47E+07 7.43E-01 5.90E+08
Fatigue Analysis of Offshore Drilling Unit 79
“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
9981 *FAIL 1.09E+00 1 (-z) SurfPt 1.83E+01 6.68E+07 DNVC-I
FQUS24 3.42E+01 2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.69E+07 8.12E-01 5.06E+08
1232 *FAIL 1.09E+00 9 (+z) SurfPt 1.83E+01 6.31E+07 DNVC-I
FQUS24 -2.90E+01 2.05E+01 -1.12E+01
0.047 1.5 1.5 1.5
1.66E+07 7.87E-01 5.42E+08
2928 *FAIL 1.08E+00 2 (-z) SurfPt 1.86E+01 7.03E+07 DNVC-I
FQUS24 -2.26E+01 -2.13E+01 -9.75E+00
0.047 1.5 1.5 1.5
2.40E+07 1.02E+00 3.60E+08
2917 *FAIL 1.07E+00 2 (-z) SurfPt 1.87E+01 6.52E+07 DNVC-I
FQUS24 -2.06E+01 2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.60E+07 7.67E-01 5.57E+08
910 *FAIL 1.07E+00 6 (+z) SurfPt 1.88E+01 6.54E+07 DNVC-I
FQUS24 -3.42E+01 3.06E+01 -1.16E+01
0.047 1.5 1.5 1.5
1.63E+07 7.86E-01 5.38E+08
2941 *FAIL 1.05E+00 5 (-z) SurfPt 1.90E+01 6.41E+07 DNVC-I
FQUS24 -2.06E+01 -2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.60E+07 7.84E-01 5.31E+08
866 *FAIL 1.03E+00 10(+z) SurfPt 1.94E+01 6.37E+07 DNVC-I
FQUS24 -3.42E+01 2.42E+01 -1.16E+01
0.047 1.5 1.5 1.5
1.61E+07 7.78E-01 5.48E+08
Element Stat Usage Fact ChkPnt ChkPlc AccFatLif StrsCycle SNCurve
E1 Type X-coord Y-coord. Z-coord.
E1Thck AxialScf BendScf ShearScf
WeibScale WeibShape StressRange
8368 *FAIL 1.02E+00 2 (-z) SurfPt 1.97E+01 7.28E+07 DNVC-I
FQUS24 2.57E+01 -2.09E+01 -7.73E+00
0.047 1.5 1.5 1.5
P 80 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
2.34E+07 1.02E+00 3.56E+08
2935 *FAIL 1.01E+00 10(+z) SurfPt 1.98E+01 6.40E+07 DNVC-I
FQUS24 -2.05E+01 -2.42E+01 -1.16E+01
0.047 1.5 1.5 1.5
1.67E+07 8.08E-01 4.98E+08
2954 *FAIL 1.00E+00 6 (+z) SurfPt 1.99E+01 6.28E+07 DNVC-I
FQUS24 -2.05E+01 2.42E+01 -1.16E+01
0.047 1.5 1.5 1.5
1.63E+07 7.83E-01 5.32E+08
2951 PASS 9.94E-01 6 (+z) SurfPt 2.01E+01 6.32E+07 DNVC-I
FQUS24 -2.04E+01 2.34E+01 -1.30E+01
0.047 1.5 1.5 1.5
1.65E+07 8.00E-01 5.15E+08
9906 PASS 9.94E-01 1 (-z) SurfPt 2.01E+01 6.75E+07 DNVC-I
FQUS24 3.42E+01 -2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.99E+07 9.02E-01 4.26E+08
5146 PASS 9.82E-01 6 (+z) SurfPt 2.04E+01 6.68E+07 DNVC-I
FQUS24 -5.61E+00 2.74E+01 -2.05E+01
0.038 1.5 1.5 1.5
2.33E+07 1.00E+00 3.70E+08
9964 PASS 9.75E-01 10(+z) SurfPt 2.05E+01 6.61E+07 DNVC-I
FQUS24 3.42E+01 -2.42E+01 -1.16E+01
0.047 1.5 1.5 1.5
1.94E+07 8.87E-01 4.42E+08
7913 PASS 9.75E-01 2 (-z) SurfPt 2.05E+01 6.32E+07 DNVC-I
FQUS24 2.06E+01 2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.56E+07 7.75E-01 5.46E+08
7899 PASS 9.73E-01 2 (-z) SurfPt 2.06E+01 6.91E+07 DNVC-I
FQUS24 2.26E+01 2.13E+01 -9.75E+00
0.047 1.5 1.5 1.5
2.34E+07 1.01E+00 3.52E+08
2873 PASS 9.70E-01 2 (-z) SurfPt 2.06E+01 6.45E+07 DNVC-I
FQUS24 -2.06E+01 -2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.47E+07 7.55E-01 5.57E+08
5846 PASS 9.69E-01 9 (+z) SurfPt 2.07E+01 6.67E+07 DNVC-I
FQUS24 5.61E+00 2.74E+01 -2.05E+01
0.038 1.5 1.5 1.5
2.32E+07 9.99E-01 3.69E+08
Fatigue Analysis of Offshore Drilling Unit 81
“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
Element Stat Usage Fact ChkPnt ChkPlc AccFatLif StrsCycle SNCurve
E1 Type X-coord Y-coord. Z-coord.
E1Thck AxialScf BendScf ShearScf
WeibScale WeibShape StressRange
4993 PASS 9.68E-01 7 (+z) SurfPt 2.07E+01 6.55E+07 DNVC-I
FQUS24 -5.61E+00 -2.74E+01 -2.05E+01
0.038 1.5 1.5 1.5
2.35E+07 1.00E+00 3.62E+08
5142 PASS 9.68E-01 9 (+z) SurfPt 2.07E+01 6.68E+07 DNVC-I
FQUS24 -5.61E+00 2.74E+01 -2.05E+01
0.038 1.5 1.5 1.5
2.33E+07 1.00E+00 3.68E+08
1228 PASS 9.61E-01 5 (-z) SurfPt 2.08E+01 6.24E+07 DNVC-I
FQUS24 -2.90E+01 2.05E+01 -1.12E+01
0.047 1.5 1.5 1.5
1.62E+07 7.89E-01 5.21E+08
5693 PASS 9.58E-01 10(+z) SurfPt 2.09E+01 6.53E+07 DNVC-I
FQUS24 5.61E+00 -2.74E+01 -2.05E+01
0.038 1.5 1.5 1.5
2.34E+07 1.00E+00 3.63E+08
5850 PASS 9.57E-01 6 (+z) SurfPt 2.09E+01 6.67E+07 DNVC-I
FQUS24 5.61E+00 2.74E+01 -2.05E+01
0.038 1.5 1.5 1.5
2.31E+07 9.99E-01 3.68E+08
1207 PASS 9.55E-01 7 (+z) SurfPt 2.10E+01 6.58E+07 DNVC-I
FQUS24 -2.90E+01 -3.39E+01 -7.73E+00
0.047 1.5 1.5 1.5
1.75E+07 8.48E-01 4.54E+08
4989 PASS 9.54E-01 10(+z) SurfPt 2.10E+01 6.55E+07 DNVC-I
FQUS24 -5.61E+00 -2.74E+01 -2.05E+01
0.038 1.5 1.5 1.5
2.34E+07 1.00E+00 3.61E+08
5697 PASS 9.44E-01 7 (+z) SurfPt 2.12E+01 6.53E+07 DNVC-I
FQUS24 5.61E+00 -2.74E+01 -2.05E+01
0.038 1.5 1.5 1.5
2.33E+07 1.00E+00 3.61E+08
P 82 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
906 PASS 9.44E-01 9 (+z) SurfPt 2.12E+01 6.73E+07 DNVC-I
FQUS24 -3.44E+01 3.14E+01 -1.30E+01
0.047 1.5 1.5 1.5
1.65E+07 8.19E-01 4.79E+08
2931 PASS 9.40E-01 10(+z) SurfPt 2.13E+01 6.60E+07 DNVC-I
FQUS24 -2.04E+01 -2.34E+01 -1.30E+01
0.047 1.5 1.5 1.5
1.98E+07 9.06E-01 4.04E+08
9965 PASS 8.98E-01 9 (+z) SurfPt 2.23E+01 6.59E+07 DNVC-I
FQUS24 3.44E+01 -2.34E+01 -1.30E+01
0.047 1.5 1.5 1.5
2.04E+07 9.22E-01 4.10E+08
Element Stat Usage Fact ChkPnt ChkPlc AccFatLif StrsCycle SNCurve
E1 Type X-coord Y-coord. Z-coord.
E1Thck AxialScf BendScf ShearScf
WeibScale WeibShape StressRange
2916 PASS 8.95E-01 5 (-z) SurfPt 2.23E+01 6.48E+07 DNVC-I
FQUS24 -2.06E+01 2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.53E+07 7.68E-01 5.29E+08
7902 PASS 8.67E-01 10(+z) SurfPt 2.31E+01 6.31E+07 DNVC-I
FQUS24 2.04E+01 2.34E+01 -1.30E+01
0.047 1.5 1.5 1.5
1.78E+07 8.56E-01 4.54E+08
9939 PASS 8.63E-01 10(+z) SurfPt 2.32E+01 6.76E+07 DNVC-I
FQUS24 3.42E+01 3.06E+01 -1.16E+01
0.047 1.5 1.5 1.5
1.60E+07 8.24E-01 4.59E+08
7869 PASS 8.58E-01 2 (-z) SurfPt 2.33E+01 6.43E+07 DNVC-I
FQUS24 2.06E+01 -2.74E+01 -1.13E+01
0.047 1.5 1.5 1.5
1.70E+07 8.29E-01 4.76E+08
9610 PASS 8.57E-01 4 (-z) SurfPt 2.33E+01 6.33E+07 DNVC-I
FQUS24 2.90E+01 2.05E+01 -1.12E+01
Fatigue Analysis of Offshore Drilling Unit 83
“EMSHIP” Erasmus Mundus Master Course, period of study September 2013 – February 2015
0.047 1.5 1.5 1.5
1.77E+07 8.54E-01 4.55E+08
914 PASS 8.53E-01 6 (+z) SurfPt 2.35E+01 6.52E+07 DNVC-I
FQUS24 -3.41E+01 2.93E+01 -9.76E+00
0.047 1.5 1.5 1.5
1.57E+07 8.02E-01 4.90E+08
7945 PASS 8.40E-01 6 (+z) SurfPt 2.38E+01 6.75E+07 DNVC-I
FQUS24 2.04E+01 2.94E+01 -1.30E+01
0.047 1.5 1.5 1.5
1.34E+07 7.29E-01 5.99E+08
891 PASS 8.40E-01 10(+z) SurfPt 2.38E+01 6.52E+07 DNVC-I
FQUS24 -3.42E+01 -3.06E+01 -1.16E+01
0.047 1.5 1.5 1.5
1.43E+07 7.72E-01 5.07E+08
8369 PASS 8.23E-01 10(+z) SurfPt 2.43E+01 6.85E+07 DNVC-I
FQUS24 2.57E+01 -2.05E+01 -1.12E+01
0.047 1.5 1.5 1.5
1.89E+07 9.06E-01 4.08E+08
Number of elements printed: 108
Number of elements failed: 80
P 84 Md Rezaul Karim
Master Thesis developed at West Pomeranian University of Technology, Szczecin
ACKNOWLEDGEMENTS
First of all I would like to thank Almighty Allah to give me strength and ability to finish the
thesis on time and for always being there for me.
Then I would like to express my heartfelt gratefulness to my supervisor Professor Maciej
Taczala from ZUT for giving me the chance to do the thesis on Fatigue Analysis of Offshore
Drilling Unit, especially for his confidence on me. He give me proper guidance and advice to
go through the work.
I would also like to thank Prof. Philippe Rigo for his excellent coordination of the EMSHIP
program and all of my Professors, faculty members and my friends from EMSHIP for their co-
operation throughout this 18 months period.
I am very grateful to all my colleagues from my internship company DNV-GL, Gdynia, Poland,
for their support, friendliness and hospitality during my three months stay. I would like to
thanks especially to Mr. Tomasz Msciwujewski, head of the section of Advisory Maritime and
Offshore for giving me this opportunity and access to all services that need to finish my thesis
work. Mr. Maciej, Ms Marzena, Ms Agnieszka and my friend Mr Tomek deserves my
wholehearted thanks for making my stay at DNV-GL Gdynia very special and memorable.
I would also like to thank my parents, their dreams made me bring here and give me strength
to finish my master’s program and also for their love, support and encouragement.
This thesis was developed in the frame of the European Master Course in “Integrated Advanced
Ship Design” named “EMSHIP” for “European Education in Advanced Ship Design”, Ref.:
159652-1-2009-1-BE-ERA MUNDUS-EMMC.