Project work,
TMR 4225
Marine Operations
By: Jon Eivind Skurtveit, Ole Gunnar Helgøy, Morten
Haukom, Camilla Stokvik and Ingrid Ødegård
TMR 4225 – Marine Operations
Project work
Preface
This report is a group project in the subject “TMR 4225 Marine Operations” the spring 2007.
The report is based on the curriculum in the subject. It counts 30% of the final grade.
The project focuses on the operational phases load out, towing and installation of a subsea
template. For one of the operational phases we have used MATLAB to execute calculations.
The information used to develop this report is based on the compendium and teaching
material in the course. We have also used a lot of supplement literature found on the internet
and from the library. The Lecturers and the assistant have answered questions and helped us
trough the process of writing the report. We would like to thank Finn Gunnar Nielsen, Tor
Einar Berg and Ken-Robert G. Jakobsen for all help and answers.
There have been some difficulties with understanding and sorting out the task information.
But with good cooperation within the group we solved the difficulties and moved on. The
group has worked well together.
Trondheim, april 07
_________________
_________________
Jon Eivind Skurtveit
Ole Gunnar Helgøy
_________________
_________________
Morten Haukom
Ingrid Ødegård
_________________
Camilla Stokvik
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TMR 4225 – Marine Operations
Summary
We have considered the case where a subsea template is transported on a barge to the Ormen
Lange field. We have focused our work on the operational phases load out, towing to site and
installation.
The Ormen Lange field is located in the in the Norwegian Sea. The field is situated on deep
water and faces challenging sea and wave conditions. These factors require that the operations
are carefully planned with regard to weather forecasts and statistical values. The sea bed
topography also has to be considered. In the case of Ormen Lange the sea floor can be
extremely rough. Mapping and survey operations are important and require great attention
when the template is being installed.
The template is constructed in Tønsberg and is then being rolled on to the barge. The weight
and large dimensions of the template makes the operation complicated. The next phase is the
towing of the barge to the installation site. Important aspects to consider in this phase are
mean towing force, effect of propeller race, directional stability and the dynamic loads in the
towing line. The installation process involves several sub operations. The sub operations we
have considered are the lift operation, water entry, immersion, landing and anchoring of the
template.
The vessels involved in the different operations have to be effective in performing their
mission. In addition, all have to be in accordance with rules and regulations and satisfy safety
requirements. Based on this the main vessels used have been decided.
Autonomous underwater vehicles (AUV) and remotely operated vehicles (ROV) can be used
to perform a fine-scaling geological mapping as a preparation to the installation phase. This is
important in planning the installation process.
It is important that the Det Norske Veritas (DNV) standards are followed in all parts of the
operations. In this consideration it is necessary to calculate and evaluate maximum wave
height allowed.
The coupled movements in the crane operation in the installation phase are considered in
greater detail. MATLAB is used as a tool in these calculations. A comparison of the
eigenperiods and the dynamic response from the coupled motions between the lifting of the
template in water and in air is performed. The eigenperiod in both cases indicates that
resonance is not likely to occur. This conclusion is based on a comparison of our results with
statistical wave data.
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TMR 4225 – Marine Operations
Index
PREFACE ............................................................................................................................................................... I
SUMMARY .......................................................................................................................................................... II
INDEX .................................................................................................................................................................. III
INDEX OF FIGURES......................................................................................................................................... IV
INDEX OF TABLES .......................................................................................................................................... IV
1
INTRODUCTION ....................................................................................................................................... 1
2
SCOPE OF WORK ..................................................................................................................................... 2
2.1
LOCATION ............................................................................................................................................. 2
2.2
WATER DEPTH ...................................................................................................................................... 3
2.3
ENVIRONMENT...................................................................................................................................... 3
2.3.1
Sea floor topography ....................................................................................................................... 3
2.3.2
Water temperature........................................................................................................................... 4
2.3.3
Wind, Weather and waves ............................................................................................................... 4
3
MAIN PHASES ........................................................................................................................................... 5
3.1
LOAD-OUT ............................................................................................................................................ 5
3.2
TOWING TO SITE.................................................................................................................................... 6
3.2.1
Towline ............................................................................................................................................ 6
3.2.2
Mean towing force and effect of propeller race .............................................................................. 6
3.2.3
Critical issues .................................................................................................................................. 7
3.3
INSTALLATION ...................................................................................................................................... 7
3.3.1
Crane operation .............................................................................................................................. 7
3.3.2
Water entry ...................................................................................................................................... 9
3.3.3
Immersion and landing at the bottom .............................................................................................. 9
3.3.4
Critical issues ................................................................................................................................ 11
4
VESSEL INVOLVED ............................................................................................................................... 12
4.1
4.2
4.3
4.4
4.5
5
TOR VIKING II (TUGBOAT) .................................................................................................................. 12
BOA BARGE 21 ................................................................................................................................... 12
SSCV THIALF (CRANE VESSEL) .......................................................................................................... 13
M/S GEOBAY( ROV-VESSEL) ............................................................................................................. 14
TRITON XL37 ROV ............................................................................................................................ 14
ROV AND AUV SUPPORT ..................................................................................................................... 16
5.1
5.2
MAPPING AND PREPARING THE SEAFLOOR .......................................................................................... 16
TEMPLATE INSTALLATION .................................................................................................................. 16
6
GANNT – CHART .................................................................................................................................... 18
7
USE OF THE DNV OFFSHORE STANDARD ...................................................................................... 20
8
DYNAMIC MODEL FOR CRANE VESSEL AND LOAD ................................................................... 22
8.1
CALCULATION OF EIGENPERIODS AND RESPONSES .............................................................................. 24
8.2
DYNAMIC RESPONSE ........................................................................................................................... 26
8.2.1
Template hanging in the air .......................................................................................................... 26
8.2.2
Template submerged ..................................................................................................................... 30
8.3
COMMENTS ......................................................................................................................................... 35
8.3.1
Results ........................................................................................................................................... 35
8.3.2
Improvements ................................................................................................................................ 35
8.3.3
Further work ................................................................................................................................. 35
9
FEASIBILITY OF THE OPERATION .................................................................................................. 36
10
KILDER ..................................................................................................................................................... 37
APPENDIX A: MODEL OF THE TEMPLATE, AND DEFINITIONS OF NOTATIONS ..........................A
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APPENDIX B: MATLAB ROUTINE “WATERRESPONSE.M” ...................................................................A
APPENDIX C: MATLAB ROUTINE “AIRRESPONSE.M” ...........................................................................A
APPENDIX D: WAVE STATISTICS ................................................................................................................. B
Index of figures
FIGURE 1: ILLUSTRATION OF TOWING ROUTE [MAP1] .............................................................................................. 2
FIGURE 2: A PICTURE SHOWING THE LOCATION OF ORMEN LANGE [MAP2] ............................................................ 2
FIGURE 3: ILLUSTRATION OF THE PLACING OF THE TEMPLATE ................................................................................. 3
FIGURE 4: AN ILLUSTRATION OF THE SEA BED TOPOGRAPHY ................................................................................... 4
FIGURE 5: LOAD OUT. THE TEMPLATE IS ROLLED ON THE BARGE............................................................................. 5
FIGURE 6: TOWING .................................................................................................................................................. 6
FIGURE 7: SSCV THIALF ......................................................................................................................................... 8
FIGURE 8: THE TEMPLATE RIGHT BEFORE LIFT-OFF .................................................................................................. 9
FIGURE 9: WATER ENTRY ........................................................................................................................................ 9
FIGURE 10: HYDRO ACOUSTIC TRANSPONDERS ...................................................................................................... 10
FIGURE 11: THE TEMPLATE IN DETAIL
FIGURE 12: THE SUCTION ANCHOR ...................................................... 10
FIGURE 13: CRITICAL ISSUES FOR CRANE LIFT ....................................................................................................... 11
FIGURE 14: TOR VIKING II ..................................................................................................................................... 12
FIGURE 15: BOA BARGE 21 .................................................................................................................................... 13
FIGURE 16: SSCV THIALF ..................................................................................................................................... 13
FIGURE 17: M/S GEOBAY ...................................................................................................................................... 14
FIGURE 18: TRINTON XL37 ROV .......................................................................................................................... 14
FIGURE 19: SEA FLOOR TOPOGRAPHY .................................................................................................................... 16
FIGURE 20: GANNT CHART..................................................................................................................................... 18
FIGURE 21: MASS MATRIX ..................................................................................................................................... 22
FIGURE 22: THE MOORING AND HYDROSTATIC STIFFNESS...................................................................................... 23
FIGURE 23: COUPLED VESSEL-TEMPLATE STIFFNESS.............................................................................................. 23
FIGURE 24: DYNAMIC RESPONSE IN DIRECTION 1 ................................................................................................... 26
FIGURE 25: DYNAMIC RESPONSE IN DIRECTION 2 ................................................................................................... 26
FIGURE 26: DYNAMIC RESPONSE IN DIRECTION 3 ................................................................................................... 27
FIGURE 27: DYNAMIC RESPONSE IN DIRECTION 4 ................................................................................................... 27
FIGURE 28: DYNAMIC RESPONSE IN DIRECTION 5 ................................................................................................... 28
FIGURE 29: DYNAMIC RESPONSE IN DIRECTION 6 ................................................................................................... 28
FIGURE 30: DYNAMIC RESPONSE IN DIRECTION 7 ................................................................................................... 29
FIGURE 31: DYNAMIC RESPONSE IN DIRECTION 8 ................................................................................................... 29
FIGURE 32: DYNAMIC RESPONSE IN DIRECTION 9 ................................................................................................... 30
FIGURE 33: DYNAMIC RESPONSE IN DIRECTION 1 ................................................................................................... 30
FIGURE 34: DYNAMIC RESPONSE IN DIRECTION 2 ................................................................................................... 31
FIGURE 35: DYNAMIC RESPONSE IN DIRECTION 3 ................................................................................................... 31
FIGURE 36: DYNAMIC RESPONSE IN DIRECTION 4 ................................................................................................... 32
FIGURE 37: DYNAMIC RESPONSE IN DIRECTION 5 ................................................................................................... 32
FIGURE 38: DYNAMIC RESPONSE IN DIRECTION 6 ................................................................................................... 33
FIGURE 39: DYNAMIC RESPONSE IN DIRECTION 7 ................................................................................................... 33
FIGURE 40: DYNAMIC RESPONSE IN DIRECTION 8 ................................................................................................... 34
FIGURE 41: DYNAMIC RESPONSE IN DIRECTION 9 ................................................................................................... 34
Index of tables
TABLE 1: RESPONSE IN AIR .................................................................................................................................... 24
TABLE 2: RESPONSE IN WATER .............................................................................................................................. 25
IV
Project work
TMR 4225 – Marine Operations
1 Introduction
Norway is one of the leading countries on subsea technology. The projects in the Norwegian
Sea and the North Sea continually move to larger sea depths and the sea bottom is more hilly
and tough. The development of subsea technology in the offshore industry is therefore
growing. Larger and more advanced systems are installed at the sea bottom.
In this report we will consider the transportation of a subsea template on a barge. We want to
make the installation realistic and have therefore chosen to consider a real case. We will
install our template at the Ormen Lange field in the Norwegian Sea.
The report focuses on three main phases, load-out, towing to site and installation. Sub phases
and critical issues for each of them will be described. We also look more detailed into the
installation phase where an analysis of the lifting operation will be performed. When the
template is lifted off the barge and lowered into the sea, high risks are involved in the
operation. The movements of the barge, template and crane vessel all have to be taken into
consideration.
The vessels we have used to perform different tasks in the operations will be presented with a
description of their work field. Remotely operated vehicles (ROV) are very effective in
assisting operations. ROVs can be used in several types of operations and perform different
tasks. Important work fields will also be described.
A schedule including the duration time for different tasks will be presented and the
information is represented in form of a Gannt diagram.
It is extremely important to be consistent with the rules and regulations established by the
classification companies. We will use offshore standard DNV-OS-HI101 in our discussion on
this.
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2 Scope of work
In this report we will use the Ormen Lange field as a reference. In the following subchapters
we will present relevant information on location and environment at the actual site.
2.1 Location
We want to transport our template to the Ormen Lange field, which is a gas field located 120
kilometres northwest of the Mørecoast, Norway [Hydro1]. The template will be produced in
Tønsberg, where the load-out operation is performed, and then towed on a barge from
Tønsberg to the Ormen Lange field. This is a distance of approximately 570 nautical miles.
Figure 1: Illustration of towing route [Map1]
Figure 2: A picture showing the location of Ormen Lange [Map2]
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2.2 Water depth
The water depth at the site varies from 850 to 1100 m [Hydro1][Hydro2][Hydro3]. This depth
sets requirements to the hydrodynamic pressure the template have to withstand. The template
consists of several structural parts that all have to be dimensioned for the pressure and forces
it is exposed to. This has to be taken in consideration when the template is designed. The
depth also has an effect on the complexity of the subsea operations. Large water depth cause
higher pressure, low temperatures and unpredictable currents.
Figure 3: Illustration of the placing of the template
2.3 Environment
2.3.1 Sea floor topography
The location where the template is placed permanently depends on the sea bed topography. It
is preferable that the ground is horizontal and free of large variations. At the Ormen Lange
field, the topography of the sea floor is irregular, hilly and challenging, therefore the sea bed
needs modification. Modifications can be removing of ground mass or filling of immersions
in the sea bed.
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Figure 4: An illustration of the sea bed topography
2.3.2 Water temperature
The Ormen Lange field is located in the Norwegian Sea. The Gulf Stream, a heated oceanic
current, moves from the Caribbean Sea to the Norwegian Sea [Golf]. The current brings
heated water and provides the region with a milder climate. Despite of this, the water
temperature near the sea bottom, at 800 to 1100 m depth, is down to zero degrees Celsius. We
can also find temperatures below zero [Water1][Water2]. The low temperatures combined
with high pressure can induce hydratization in the pipes on the template and in the pipes
connected to the template. That makes it necessary to take precautions, and this is often
preformed by injecting anti-freeze substances. The cold environment also effects the material
which the template is build of, and this has to be taken into consideration in the design phase.
2.3.3 Wind, Weather and waves
The execution of the operational phases, transporting and installing, of the template is
extremely weather dependent. The weather in the Norwegian Sea is very tough, and the wind
can be, and often is, very strong which induces large waves. This will affect the possibility to
carry out the operations. During the summer season the wind velocities and wave heights are
generally at their lowest, which can be seen from statistics. The weather interference is
therefore smallest at this time. Many operations are for this reason carried out in the summer.
Delays in the operations are very expensive and must be avoided if possible. It is important to
plan the operation with regard to weather forecasts so that stop because of the weather is not
likely to occur. In the Offshore Standard DNV-OSH101 section 3 we find requirements for
the environmental conditions such as wind, wave and current. We will follow these in the
planning and during the operations.
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3 Main phases
As mentioned, the main phases we are going to consider in this report are the load-out, towing
to site and installation phase. These phases consist of several smaller operations. The most
important aspects of these operations and critical issues for each phase are discussed in the
following sub chapters.
3.1 Load-out
Load-out is the operation where a structure is moved from land to the sea. There are different
ways of performing such an operation. A structure can be lifted from a quay onto a
ship/barge, or it can be rolled on to a barge. If the structure is self-floating it can be built in a
dry-dock and then towed out after water has been filled. When deciding how to perform the
load-out operation there are many important factors. However, crucial factors involve the
structure itself. Structures with a small weight and dimensions have relative small forces
involved which will simplify the operation. For small structures it is common to use crane
lifts in able to move the structure to a ship or a barge. For larger structures the load-out
operation is more difficult. The crane capacity is limited. Thus it is often more convenient to
execute the load-out operation without a crane involved. This can be done using a custom
made vehicle that rolls the structure onto a barge, or if it is floating, directly into the sea.
In our case we have a subsea template with length 44m, breadth 33m and height 15m and
weight 1150 ton. The template is constructed in Tønsberg at Grenland Group. The weight of
the template makes it a heavy lift and the crane capacity on the construction site cannot
handle the weight of the structure. Using a crane vessel is expensive, especially if delay
occurs. There may also be some difficulties according to the motion of the structure during
the lift operation. The template has a large mass and extension. As a result, the motion
response has to be limited. This can be difficult to maintain especially since the crane is not
on fixed ground. Another possibility is to roll the structure on the barge. This will cause a trim
moment on the barge and a huge ballast capacity is needed to handle the weight.
Figure 5: Load out. The template is rolled on the barge
From a risk viewpoint, the crane lift is much more exposed to accidents and the consequences
can be large. Intuitively the possibility of accident is larger for a crane operation than with a
roll-on operation, and the consequences are bigger. The economical aspect is also important to
consider. The cost of planning and execute a lifting operation is larger than for a roll-on
operation. Especially the hiring of a crane vessel is very expensive.
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Since the template has to be transported from the construction site to the quay, it is already on
a vehicle and thus the roll-on alternative is definitely easiest. From the discussion above we
have concluded that the roll-on alternative is the best load-out method in our case.
3.2 Towing to site
When the template has been constructed and placed on a barge it is ready to be towed to the
installation site. We estimate that the towing operation from Tønsberg to the Ormen Lange
field will take about four days. That means that we will have an average towing velocity of
about 6 knots.
Normally, different towing configurations are used during inshore and offshore tows. A
classical towing configuration for offshore towing of a barge is using a single tug. Towing
velocity, bollard pull and loads in the towing line are important factors to consider during
offshore tows. For inshore towing, maneuverability is the most important consideration. The
towing configuration can consist of more than one tug and shorter towing lines in order to
control and maneuver the barge.
Figure 6: Towing
In the following subchapters we have presented topics that are relevant to evaluate during a
towing operation.
3.2.1 Towline
The towline has to be chosen based on important parameters like breaking load, stiffness of
the line, weight, damping and abrasion and corrosion characteristics. Det Norske Veritas
(DNV) has established rules and regulations for minimum breaking strength of the towing
line. In addition, there are requirements set by DNV for minimum length. It is important that
we follow these rules in our case. It is extremely important to analyze the dynamic loads in
the towing lines. Damage to the towing lines can be critical in a towing situation. The line is
experiencing large loads and need to be dimensioned accordingly. Critical happenings in this
regard can be overloading, fatigue, local chafing and cutting by propeller.
3.2.2 Mean towing force and effect of propeller race
Another important factor is to consider is the mean towing force. Wind and waves will
increase the towing resistance and the available towing force will be reduced. The result is a
decrease in towing velocity. The available towing force will thus depend on the forces that act
on the tug. It is important to note that the mean force will depend on the relative importance
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between the forces on the tug and the barge. Wave drift forces also contribute as a resistant
force.
The forces that act on the barge may not have the same direction. This has to be considered in
the towing of the barge.
The interaction between the tug and the barge is important to evaluate in towing operations.
This is especially relevant to consider when the towing lines are short. The propeller race will
have an effect on the towed structure that will produce an additional towing force. Momentum
considerations can be used to estimate the additional forces. By calculating the difference in
the flux of momentum of two planes located before and after the water hits the structure, we
can make an estimation of the axial force that is working on the body. Model tests should be
preformed in order to evaluate the effect of the propeller race on the towed structure in a more
precise matter.
3.2.3 Critical issues
The climate and oceanographic conditions can cause critical situations in the towing phase.
The Ormen Lange field faces a lot of challenges with regard to the climate. Challenging sea
and wave conditions demand careful planning of the operation. Some parts of the template
might be especially vulnerable to these forces and has to be protected in special ways. Land
proximity and near-shore water depth also require great consideration in planning the
operation in able to avoid critical situations like stranding and collisions.
Directional stability is also important to evaluate in the towing phase. Directional stability is
the tendency of a moving body to align itself with the direction of motion. Difficult and
critical situations may occur if the barge lacks this stability. The barge will then move
uncontrolled and make sudden turns. The reason that the barge may experience loss in
direction stability is in many cases because of the length of the towline or the point where it is
attached.
In able to evaluate the tugs ability to tow the barge in the actual case, it is necessary to
understand the dynamics of the situation. Simple calculations can be preformed by illustrating
the tug and the barge by two masses which are influenced (acted upon) by time varying
accelerations, damping and spring coefficients. The towline can in this analysis be modeled
by a spring. The system that is described is very complex and in heavy sea the system will be
affected by large forces.
3.3 Installation
The installation process starts when the structure arrives at the field where it is supposed to be
installed. We can divide the whole process into several minor phases, and we will in the
following take a look at each of these phases.
3.3.1 Crane operation
Crane operations play an important role in many kinds of marine operations. Examples of
these operations are crane assisted installation of jacket structures, installation of deck
modules, installation of subsea equipment, and maintenance of subsea equipments. Crane
operations are normally divided into two subcategories, light lifts and heavy lifts.
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Lifts where the magnitude of the load is about 1-2% of the vessel displacement and less than a
few hundred tons can be classified as light lift operations. The motion characteristics of the
vessel can be assumed to be unaffected by the load, and heave compensation is possible for
these types of operations.
Heavy lifts is typically for loads over 1000tons. For such heavy lifts it is necessary to consider
the coupled effect between the vessel and the load system as there will be mutual interaction.
It is of great importance to avoid collision between the load and the lifting vessel, as this can
lead to damages on both parts. Normally, it is not possible to use heave compensation for such
huge loads.
Figure 7: SSCV Thialf
In our case, the Ormen Lange project, the weight of each template is 1150tons. The vessel
involved in the crane operations is “SSCV Thialf”. The crane vessel has a maximum capacity
of about 14200tons. This means that the weight should not cause any problems. The
dimensions of the templates should not cause problems either since the vessel is able to lift
such a weight if the lifting radius is less than 80m, though this depends on the weather
conditions.[Heerema]
The crane vessel is of great dimensions and can use its ballast system to keep the upper deck
stable even in strong winds and rough sea.[metoffice] Unfortunately this doesn’t mean that
the vessel can operate under almost any weather condition. As mentioned earlier there will be
coupled effects between the crane vessel and the load systems. This means that even if the
crane vessel is stable, the barge and the load can be highly affected by winds and waves.
Therefore it is of great importance to take weather forecasts and statistics in to consideration
when planning such a marine operation. The daily rate for a crane vessel is very high, and a
delay will cause huge and unnecessarily costs.
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Figure 8: The template right before lift-off
3.3.2 Water entry
A critical part of the installation process is when the template enters the water, also called
water entry. In this phase the structure will be exposed to forces caused by wind, waves and
currents. These forces may lead to uncontrolled motions such as wire snatch. The
hydrodynamic forces working on a body entering the water depends on the downward
velocity and the instantaneously submerged volume and added mass. Since the Ormen Lange
templates are of such great dimensions, 44[m] x 33[m] x 15[m], there is no doubt that great
forces will be acting in the water entry phase. When dealing with such great forces it is very
important that the preparations have been done carefully.
Figure 9: Water entry
3.3.3 Immersion and landing at the bottom
When the entire body has entered the water it has to be placed at the right location at the sea
bottom. In this phase the water depth and the currents play important roles. Large water
depths cause extreme challenges when it comes to landing in the accurate position. This
problem can be solved in different ways. One way is to use guidelines; another is to use
ultrasonic equipment.
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If guidelines are not being used, acoustic sound transponders placed on the sea floor can be
used for positioning of the template. The speed of sound in water is then used to determine the
templates position. This information is transferred to the computers on the surface. As showed
in the picture below there is communication between the surface vessel, the ROV and the
transponders on the sea floor. In our case, transponders are also present on the template. The
transponders are deployed by a ROV using information from to the sea floor mapping.
Figure 10: Hydro acoustic transponders
A critical issue is the speed of sound. This can influence the acoustic sound transponder for
positioning. Several aspects affect the speed of sound in water; the water temperature, the
concentration of salt and layer formation. As indicated in chapter 2, the Gulf Stream is
affecting the water temperature in the Norwegian sea. Because the temperatures in this area
are varying, the speed of sound is constantly changing. The communication between the
components must be calibrated correct.
The template is equipped with suction anchors. When they hit the sea floor the water inside
the cylindrical foundations flows out of a valve that is located on the top. To get the right
“suction effect” the valves closes and pumps located inside the foundation legs produce low
pressures in the cylinder. This form of anchoring will hold the template in exact position. This
is controlled by a ROV. The system is shown in the following figures.
Figure 11: The template in detail
Figure 12: The suction anchor
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3.3.4 Critical issues
The figure below demonstrates different phases of the crane operation. The mass is located in
five different positions in the figure. Several critical issues can be discussed for each phase.
Figure 13: Critical issues for crane lift
Phase number one represents the lift-off operation. This is when the template is lifted off the
barge. A critical issue related to this phase is the possibility of snatch loads. The load can also
start to slide horizontal which will cause problems in this phase. This problem can be solved
using “tugger lines”.
The second phase deals with the situation where the load has been lifted off the barge and is
in air. Problems in this phase are the pendulum movement and the possibility of collision. The
use of tugger lines can also be effective in this phase.
In phase number three in the figure we have the water entry. In this phase the template is
crossing the splash zone. Possible problems related to this phase can be dynamical forces
caused by waves. This can lead to yank and breakage of the winch and damage to the
template.
When the template is deeply submerged, as shown in phase number four, problems related to
vertical resonance can occur.
Landing the template at the bottom can cause severe damage to the template. This is a very
critical phase of the operation.
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TMR 4225 – Marine Operations
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4 Vessel involved
Several vessels are involved in the operations. In this chapter we have presented the vessels
we have used in our discussion. The vessels we have included are involved in the three main
phases we have considered; load out, towing and installation. The same vessels are in some
cases used in all three phases of the operation. It is important to emphasize that we are only
considering the operations that has to do with the operations in close connection to handling
of the template.
4.1 Tor Viking II (tugboat)
This is the tug that we use for towing the barge. Inshore and in narrow fjords it is necessary to
use an additional tugboat in the back of the tow. In these cases the importance of
manoeuvrability is increasing. In some cases the tug and barge has a large turning radius. The
use of another tugboat can in this case be very effective.
Figure 14: Tor Viking II
Information:
Length Over All (LOA):
Length between p.p.:
Breadth, moulded:
Depth, moulded:
Dead Weight:
Light Ship:
Gross:
83.70 metres
75.20 metres
18.00 metres
8.50 metres
2,528 tonnes
4,289 tonnes
3,382 tonnes
4.2 Boa Barge 21
We need a barge that can handle the templates dimensions of 44x33x15 m and its weight of
1150 tons. Even though the barge is only 31.5 m wide there will no problem because the legs
of the template is mounted with distance smaller than 31.5 m
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TMR 4225 – Marine Operations
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Figure 15: Boa Barge 21
Information:
Description: Deck cargo barge
Dimensions: 92 x 31.5 x 6.71m
Deadweight: 11 000 t
Pumping rate: 1 000 t/hr
Deck load: 25 t/m2
Built: 2000
4.3 SSCV Thialf (crane vessel)
The heavy-lift operation requires an enormous precision (±1m of design location and ±2
degree of design heading). Thialf and Heerema (owner company) has great experience with
heavy-lifts. Their co-operation with Sonardyne which is the developer of the acoustic sound
positioning system (skal være nevn under rov-bruk ) makes Thialf number one in the heavylift class. The template is lowered with cabels from Thialf and positioned with the help from
the sonar-sound-system. Special for Thialf is the enormous capacity of the ballast pumps, and
the use of tandem lift technology.
Figure 16: SSCV Thialf
Length overall:
Length of vessel:
Breadth:
Depth to workdeck:
Draught:
GRT:
NRT:
201.6 m
165.3 m
88.4 m
49.5 m
11.8-31.6 m
136,709 t
41,012 t
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4.4 M/S Geobay( ROV-vessel)
The Geoconsult ASA’s vessel M/S Geobay is used to assist in the placing of the sound
transponders on the sea floor. The transponders are placed on the sea floor with use of a ROV.
The M/S Geobay can be used with the ROV mention beneath.
Figure 17: M/S Geobay
Info:
LOA:
LBP:
Beam:
Draught:
Gross tonnage:
Net tonnage:
Service Speed:
85.45 m
78.0 m
15.6 m
6.91 m
3502 ton
1051 ton
11 knots
4.5 Triton XL37 ROV
We choose to use this flexible work class ROV. It can be operated in water depths up to
2500m, and has a 150 Hp system with 5 horizontal and 3 vertical thrusters. The ROV is used
to place the sound transponders on the seafloor, and have great light and cameras for deep
water filming.
Figure 18: Trinton XL37 ROV
Info:
Forward speed:
3 knots
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TMR 4225 – Marine Operations
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Lateral speed:
Height:
Width:
Length:
Weight (approx.):
Operating range:
2 knots
2.10 m
1.80 m
3.00 m
3.7 ton
4,000 m
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5 Rov and Auv Support
In the last few years there have been considerable changes in the oil/gas drilling market. A
large difference is that oilfields are found on constantly deeper depths. Marine operations in
connection to subsea installations at large water depths (i.e. OrmenLange at 850 m) require
complex equipment. Operations that used to be preformed by scuba divers, are now to a large
extent replaced by remotely operated vehicles (ROV’s) and autonomous underwater vehicle
(AUV’s).
5.1 Mapping and preparing the seafloor
It is important to map and establish a model of the seafloor in able to plan the installation
operation properly. In our case we use AUV’s as a support at an early phase of the operation.
Especially seafloor mapping is preformed by an AUV. Programmed AUV’s can be used to
scan the area at interest and get a 3-D picture of the sea floor. In these days it is possible to
make a full 3-D model of the installation with the correct sea floor dimension and curvatures.
The Ormen Lange field is located at a water depth of approximately 850 m. At large sea
depths the seafloor can be very hilly with peaks up to 30-50 meters high. As you can see from
the picture below it is important to make a detailed plan for both pipeline survey and
positioning of the template.
Figure 19: Sea floor topography
The template that is being installed has large dimensions (44[m] x 33 [m] x 15[m]). The
locations where the templates are installed have to be smooth and horizontal. It is therefore
necessary to prepare the seafloor for the installation of the templates. Special designed ROV’s
are used for these objectives, like Nexans “Spider dredging system (for pipe laying)”. ROV’s
are often used for placing equipments for positioning of the template on the sea floor. This has
to be done before the actual installation process begins.
5.2 Template installation
During the installation of the template at the sea floor, we can use a ROV for observation. The
ROV is equipped with hi-resolutions cameras (often more than one, with different wide angel
and focus) and special tool packages. The ROV have arms similar to human arms. The arms
can be controlled by the operator located on the surface.
For installations of smaller constructions, a ROV can be used for positioning of the object by
observation and communication to the surface. A ROV can also be used to push the object.
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Other components and pipelines are design to be mounted on to the template by a ROV. In
addition all valves are designed to be operated by a ROV.
All operation in respect to inspection and maintenance will be executed by ROV. The
template and the complex structure of line units are designed in accordance with the ROV’s
ability to operate and maintenance it.
The previously mentioned acoustic- sound-sonar system is also compatible with the ROV’s.
The ROV communicate with both the acoustic transponders and the surface vessel. ROVs are
also used in the pre-phase of the installation, when the transponder is calibrated and mounted
on the sea floor. ROV in co-operation with the surface vessel is very important for the
accuracy of the installation of the template. With a possible deviation of ±2 meter of design
location and ±2 degrees of design location, at a depth of 850 m requires an extreme degree of
accuracy.
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6 Gannt – Chart
Most of marine operations are high-cost operations. They often use large crane vessels and a
number of support and operation vessels. The daily costs are high and the tasks are often
sensitive for wind and waves. Based on this thorough and accurate planning are very
important. A key factor is estimating the completion time of operations which include waiting
on weather.
To start with, the total operation can be divided into sub operations. The sub operations are
usually dependent on each other. This means that if one sub operation stops because of the
weather conditions the total operation is put on hold. Some sub operations may be performed
in parts, and some sub operations are none reversible. If you start a non reversible operation
you have to finish the task within the weather window. It is also useful to determine if any of
the sub operations may be performed parallel to each other. The total duration for each sub
operation and weather waiting time have to be defined.
Important key parameters in the planning phase are significant wave height, wave peak
period, wave direction, wind speed and wind direction.
Norsk Hydro and Metrologisk Institutt have designed a simulation program, Marsim 1.1, for
presenting these data graphical. This system can be run both in a hindcast and forecast mode.
That means that Marsim is using wave and wind data from systemized observations (hindcast
mode), and 3-weeks weather/wave forecast (forecast mode).
In this project work we have made the Gannt-chart without the forcast/hindcast, but with
respect to the vessel and operations weather limits. We have estimated a rough timescale for
the total operation and the sub operations.
15 apr 2007
ID
Task Name
Start
Finish
22 apr 2007
Duration
18
1
Load Out
18.04.2007
18.04.2007
8h
2
Towing
18.04.2007
22.04.2007
96h
3
Positioning and preparation
22.04.2007
22.04.2007
6h
4
Crane Heavy Lift
22.04.2007
22.04.2007
3h
5
Installation on the sea floor
22.04.2007
22.04.2007
6h
19
20
21
22
23
Figure 20: Gannt chart
The chart gives the duration in hours. We have chosen to divide the operation in five tasks.
All of the tasks are linked to each other and there is no overlapping of the tasks. The durations
are based on information from the Ormen Lange project and our own logical assumptions.
18
24
25
26
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The load-out process is scheduled for one ordinary work day (8hours). This operation takes
place in sheltered waters and we assume the operation can be completed as long as the
weather is not extreme. This task is not very weather sensitive.
The towing phase is more critical with regard to the weather. Because of the large size of the
template, wind and waves can influence the towing. In this phase the barge cannot withstand
significant wave heights larger than 5m. [FinnG]
Before the lift-operation can take place all the vessels have to be in perfect position and all
equipment has to be prepared and ready for use. The duration is assumed to be 6 hours. This
phase is not directly weather dependent. The weather limits in this phase is the same as for the
crane lift. It is not necessary to start this task if the crane lift cannot be completed.
The crane lift is the most critical task and it is non reversible. You have a point of no return
when the template is elevated from the barge. The maximum significant wave height for this
operation is 2.5 meters [FinnG] and [Heerema]. It is very important to plan this task, because
of the restricted weather window. Use of weather forecasts is an important remedy in the
planning.
The installation of the template at the bottom has two critical issues regarding the weather.
They are water entry for the ROV and influences from currents on the ROV and its umbilical.
ROV’s can sometimes enter the water from a moonpool located below the ROV-vessel, or
being lowered into the water inside a cage. That will make the weather window wider for this
task. The currents close to the template can influence the ROV stability and steering. A
solution to this problem can be to select a ROV with several thrusters and more power.
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7 Use of the DNV Offshore Standard
To be sure that we have considered all relevant aspects when planning a marine operation we
can follow the DNV Offshore Standard DNV-OS-H101. Most aspects off marine operations,
precautions and security factors are included in the standard.
We can classify the operations into two groups:
Restricted operations, Section 4B 501: “Marine Operations with a reference
period (TR) less than 72 hours may be defined as weather restricted.”
Unrestricted operations, Section 4B 801: “Marine operations with an
operation reference period exceeding72 hours need normally to be defined as
unrestricted operations. Environmental criteria for these operations shall be
based on extreme value statistics.”
Categorizing of the operations in our case:
Restricted operations: Load-out, crane operation, water entry, immersion and
landing at the bottom.
Unrestricted operations: Towing
The standard covers all of these operations and is important for the whole marine operation.
In this report we take a closer look at the points in the standard that is relevant to the case we
are analysing. In our analysis we have focused on the crane operation. As mentioned earlier it
is important to evaluate the effects of wind and waves during lift and how it interrupts the
stability of the barge and crane vessel.
We have considered the following paragraphs in our analysis:
Section 2A203: “For operations passing a point where the operations can not be reversed, a
point of no return shall be defined. The first safe condition after passing a point of no return
shall be defined and considered in the planning.”
In our operation we consider it to be a point of no return when the template is lifted off the
barge and the barge is removed. At this point the operation can not be reversed. A safer
condition is when the template is fully submerged and at a depth where the largest surface
effects can be neglected.
Section 3B: Wind Conditions and Section 3C: Wave Conditions.
We have to map the weather in the area where the operation is to be executed. Wind and
waves are factors that decide if the operation is to be carried out. The lift operation has to be
planned according to this section.
Section 4C200 Weather forecast levels: This paragraph divides different operations into
forecasts levels. The categorisation for our operation phases will be:
Level B: Towing, installation, lifting
Level C: Load-out.
Section 4B600: Operational limiting criteria.
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We have to follow these paragraphs and decide the design value of the significant wave
height. We do not have enough information to calculate this value at this point, but we use the
wave statistics from the area and estimate a design value for the significant wave height
(Limiting operational criteria).
OPLIM= 2,5m
Section 4B701: Forecasted- and monitored operational limits: “Uncertainty in both
monitoring and forecasting of the environmental conditions shall be considered. It is
recommended that this is done by defining a forecasted (and if applicable, monitored at the
operation start) operational criteria – CO, defined as CO= α* OPLIM.”
We correct the significant wave height with the alpha factor in order to consider uncertainty in
the weather forecasts. The alpha factors can be found in the last appendices in the DNV
standard. We have in our crane vessel a monitoring system which applies to the DNV
standard for the monitoring, in section 4D300. And our crane lifting operation has duration of
3 hours. That gives:
α = 1.0
CO = 1.0 * 2,5m= 2,5m.
If the weather forecast announces a wave height of 2,5m or larger the operation will not be
preformed.
Section 5 Stability requirements: This chapter deals with the stability of the vessels involving
the operation.
Section 5D201: “Other vessels, semi submersibles, crane vessels etc, involved in marine
operations shall, for both intact and damaged conditions, comply with national or
international (IMO) stability regulations or codes”
The stability of the vessels involved in the operation has to be calculated before the operation
is started to make sure that the vessels can handle the load.
From the statistics we have found that the waves in the weather window we are considering
for the operation, the period of the waves lies between 4 and 13 seconds, more details can be
found in Appendix D. This means that if the response curve shows large motions in this area,
significant motions may occur, and extra precautions must be made.
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8 Dynamic model for crane vessel and load
We have decided to look more detailed into the installation phase, and the lifting operation of
the template. The template is lifted from the barge and then lowered to about 800 meters
below the surface. We want to compare the coupled motion of the vessel and the template
hanging in air versus the template submerged to the sea. This can be modeled as a coupled
mass- damping- spring system. The system has 12 degrees of freedom, but neglecting the
rotations of the load gives us 9 DOF. By solving the equation Mx  Bx  Cx  F for each
DOF, we can find the eigenperiods and eigenvalues for the system.
To solve the equation of motion, we need to estimate the mass-, damping- and restoring forces
for each DOF. That will require some detailed data about the crane vessel and template. The
mass matrix consists of mass and added mass in the translation directions and moments of
inertia and added mass in the rotation directions. Since we have few data about the crane
vessel, it is difficult to get a good estimate of the components in the matrix. Thus we need to
make some assumptions and simplifying the matrix. The coordinate system is placed with the
origin in the waterline, above the centre of gravity. We may assume the vessel to be
symmetric along the x-axis, which make the components A23  A13  0 .
Still there are some couples added mass contributions in the other directions that will affect
the motion of the vessel, but we choose to exclude these contributions. The coupled moments
of inertia are also excluded. Finally we get the following mass matrix:
0
0
0
mzG  A15
0
0
0
0 
 m  A11

m  A22
0
mzG
0
0
0
0
0 


m  A33
0
0
0
0
0
0 


I 44  A44
0
0
0
0
0 

M 
I 55  A55
0
0
0
0 


I 66  A66
0
0
0 


mL  A77
0
0 


mL  A88
0 


mL  A99 

Figure 21: Mass matrix
The definitions of the notations used are placed in appendix A.
The stiffness matrix of the system is a sum of three different contributions, where stiffness
and mooring on the vessel, and stiffness between the load and template are the parts. The
hydrostatic stiffness is a result of change in location and size of buoyancy. That gives
hydrostatic stiffness contribution inn heave-, roll- and pitch directions, since motion in these
directions will change buoyancy. Mooring will also have some contribution, but usually the
mooring stiffness is soft and will not influence on the resonance periods. If the vessel uses a
DP system, this can be modeled in the same way as a mooring system. It is also natural to
neglect mooring effects in vertical directions. With a DP-system this is evidently because the
thrusters don’t have a thrust component in the z-direction. Thus DP-system gives contribution
in surge, sway and yaw directions. The mooring and hydrostatic stiffness for our system may
be gives as:
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TMR 4225 – Marine Operations
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 Cm11 Cm12

Cm 22




Cv  







0
0
Ch 33
0
0
Ch 34
Ch 44
0
0
Ch 35
0
Ch 55
Cm16
Cm 26
0
Ch 46
Ch 56
Cm 66
0
0
0
0
0
0
0
0

0
0

0
0

0
0

0
0 
0
0
0
0
0
0
0
0
Figure 22: The mooring and hydrostatic stiffness
In addition to the hydrostatic and mooring a stiffness related to the coupling between the
template and vessel will occur. This stiffness may be written as:
w
l
 s










Cvt  














0
0
w
ls
0
AE
le
w
zt
ls
0

w
zt
ls
0
AE
yt
le
Cvl 44



AE
xt
le
w
yt
ls

w
ls
0
w
xt
ls
0
0
0
0
0
w
zt
ls
AE
xt yt
le

w
zt xt
ls
Cvl 55

w
zt yt
ls
Cvl 66


w
zt
ls
w
yt
ls
w
ls
w
ls
0

w
xt
ls
0
w
ls




0 

AE 


le 
AE 

yt 
le


AE
xt 
le


0 


0 


0 


AE 
le 
0
Figure 23: Coupled vessel-template stiffness
The total stiffness of the system is the sum of mooring and hydrostatic stiffness and the
coupled vessel-template stiffness.
When we should do the analysis with the load hanging in the air, we first had to change some
of the coefficient in the matrices. When the load is hanging in the air the added mass term can
be neglected because of the low density of air compared to the mass. Therefore we sat these
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TMR 4225 – Marine Operations
values equal to zero. In addition to this change we also had to change the values for stretch in
the wire. Out of water there will be no buoyancy force working on the load, so we had to set
the buoyancy force equal to zero too. Further we had to reduce the length and effective length
of the wire so that the length of the wire is shorter than the distance from the top of the crane
to the surface. The last thing we did was to set the forces that are working directly on the load
equal to zero. This is because of the assumption that there is light wind when the operation is
performed.
8.1 Calculation of eigenperiods and responses
With mass and stiffness matrixes established we can compute the undamped eigenfrequencies
and eigenvectors. The eigenfrequencies are given from, 0  M 1C ,
where M is the mass matrix and C is the stiffness matrix.
The eigenvectors can be solved from the equation:
 x  M 1Cx
The eigenvectors tells us which degree of freedom that gives us contribution for the given
eigenperiod. With a coupled system there will be many degrees of freedom that have a
contribution. For each eigenperiod we can identify the degree of freedom that has the main
contribution. In the case with the template hanging in the air, we get the following
eigenmodes:
Table 1: Response in air
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The case with the template hanging in the water gives the following eigenmodes:
Table 2: Response in water
For each eigenmode we have located the degree of freedom that gives the main contribution.
When comparing the two cases we see that the most of the eigenperiods doesn’t change much.
The greatest changes are in yaw-, load vertical-, load x- and load y-direction. This can be
explained by the change inn mass- and stiffness matrix, where the template has got a
contribution. If we look at eigenmode nr 9, we see that the motion has a connection to the
load y-direction as well as the yaw-direction, and results in large period when changing the
mass- and stiffness matrix.
The eigenperiods that belongs to the load-directions are motions that are almost pure freedom
of degree motions. That means that the eigenperiod of the motions are mainly dependent of
the change of stiffness and mass related to that direction.
When lowering the template below sea surface, the mass matrix gets a contribution from
added mass in all directions. In addition the coupled stiffness matrix will decrease due to
buoyancy of the template and a longer cable. This will result in larger periods, as the
eigenperiod is given by:
M
T  2
C
With the eigenperiods and eigenvectors established, we want to see what happens when
adding a force vector to the system. We have looked at a sea state that gives beam sea on the
crane vessel. The force is modelled as a harmonic load in the heave-, sway- and roll direction.
We have based the force on the potential theory, but in lack of vessel data it’s, the wave force
is simplified. In addition, forces on the template are ignored. This means that wind and wave
forces that may occur are neglected on the template. We have used the following force vector
for both cases:

F  Re  0 i * C22

C33 C33 *
B
2


0 0 0 0 0  * eit 


We may no solve the response for the system, given by:
    2 M  i B  C  F
1
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The responses are solved and plotted as a function of the wave period.
8.2 Dynamic response
Further we have plotted the responses inn all directions for case 1 and case 2.
For each plot the peak periods are located, and we have compared the peak periods with the
eigenperiods. Thus we can find the dominating motion that causes the responses for each
direction.
8.2.1 Template hanging in the air
Dynamic respons in direction 1
0.4
0.35
0.3
Respons
0.25
0.2
0.15
0.1
0.05
0
0
5
10
15
20
Periode
25
30
35
40
Figure 24: Dynamic response in direction 1
Peak periods:
Related Eigenmode:
Dominating mode of motion:
17,5 sec, 19,7 sec.
4, 6
pitch, heave
Dynamic respons in direction 2
3.5
3
Respons
2.5
2
1.5
1
0.5
0
0
10
20
30
40
50
Periode
60
70
80
90
100
Figure 25: Dynamic response in direction 2
Peak periods:
17,5 sec, 21,7 sec, 62,5 sec.
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Related Eigenmode:
Dominating mode of motion:
4, 8, 7
pitch, roll, sway
Dynamic respons in direction 3
12
10
Respons
8
6
4
2
0
0
10
20
30
Periode
40
50
60
Figure 26: Dynamic response in direction 3
Peak periods:
Related Eigenmode:
Dominating mode of motion:
19,7 sec.
6
heave
Dynamic respons in direction 4
0.14
0.12
Respons
0.1
0.08
0.06
0.04
0.02
0
0
10
20
30
40
50
60
70
Periode
Figure 27: Dynamic response in direction 4
Peak periods:
Related Eigenmode:
Dominating mode of motion:
19,1 sec, 21,7 sec
9,8
load y-direction, roll
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Dynamic respons in direction 5
0.04
0.035
0.03
Respons
0.025
0.02
0.015
0.01
0.005
0
0
5
10
15
20
25
Periode
30
35
40
45
50
Figure 28: Dynamic response in direction 5
Peak periods:
Related Eigenmode:
Dominating mode of motion:
-4
17,5 sec, 19,1 sec, 20,1 sec.
4, 9, 5
pitch, load y-direction, load x-direction
Dynamic respons in direction 6
x 10
5
Respons
4
3
2
1
0
0
10
20
30
40
50
60
70
Periode
Figure 29: Dynamic response in direction 6
Peak periods:
Related Eigenmode:
Dominating mode of motion:
5,3 sec, 19,1 sec, 21,7 sec.
4, 8, 7
yaw, load y-direction, roll
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Dynamic respons in direction 7
110
100
90
80
Respons
70
60
50
40
30
20
10
0
0
5
10
15
20
Periode
25
30
35
40
Figure 30: Dynamic response in direction 7
Peak periods:
Related Eigenmode:
Dominating mode of motion:
20,2 sec.
5
load x-direction
Dynamic respons in direction 8
100
Respons
80
60
40
20
0
0
10
20
30
40
50
60
70
Periode
Figure 31: Dynamic response in direction 8
Peak periods:
Related Eigenmode:
Dominating mode of motion:
19,1 sec, 21,7 sec, 62,5 sec.
9, 8, 7
load y-direction, roll, sway
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Dynamic respons in direction 9
11
10
9
8
Respons
7
6
5
4
3
2
1
0
0
10
20
30
Periode
40
50
60
Figure 32: Dynamic response in direction 9
Peak periods:
Related Eigenmode:
Dominating mode of motion:
17,5 sec, 19,7 sec.
4, 6
pitch, heave
8.2.2 Template submerged
Dynamic respons in direction 1
0.4
0.35
0.3
Respons
0.25
0.2
0.15
0.1
0.05
0
0
20
40
60
80
100
120
Periode
140
160
180
200
Figure 33: Dynamic response in direction 1
Peak periods:
Related Eigenmode:
Dominating mode of motion:
17,7 sec, 36 sec, 161 sec.
4, 8, 7
pitch, load y-direction, surge
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Dynamic respons in direction 2
4.5
4
3.5
Respons
3
2.5
2
1.5
1
0.5
0
0
10
20
30
40
50
Periode
60
70
80
90
100
Figure 34: Dynamic response in direction 2
Peak periods:
Related Eigenmode:
Dominating mode of motion:
20,6 sec, 36 sec, 62,5 sec.
6, 3, 7
roll, load x-direction, sway
Dynamic respons in direction 3
16
14
12
Respons
10
8
6
4
2
0
0
5
10
15
20
25
Periode
30
35
40
45
50
Figure 35: Dynamic response in direction 3
Peak periods:
Related Eigenmode:
Dominating mode of motion:
19,7 sec,
5
heave
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Dynamic respons in direction 4
0.25
0.2
Respons
0.15
0.1
0.05
0
0
10
20
30
40
50
60
70
Periode
Figure 36: Dynamic response in direction 4
Peak periods:
Related Eigenmode:
Dominating mode of motion:
20,6 sec, 36 sec.
6, 8
roll, load y-direction
Dynamic respons in direction 5
0.07
0.06
Respons
0.05
0.04
0.03
0.02
0.01
0
0
5
10
15
20
Periode
25
30
35
40
Figure 37: Dynamic response in direction 5
Peak periods:
Related Eigenmode:
Dominating mode of motion:
17,6 sec, 19,7 sec, 36 sec.
4, 5, 3
pitch, heave, load x-direction
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Dynamic respons in direction 6
0.1
0.09
0.08
0.07
Respons
0.06
0.05
0.04
0.03
0.02
0.01
0
0
100
200
300
400
500
600
Periode
700
800
900
1000
Figure 38: Dynamic response in direction 6
Peak periods:
Related Eigenmode:
Dominating mode of motion:
20,6 sec, 36 sec, 62,5 sec, 938,6 sec.
4, 8, 7, 9
roll, load y-direction, sway, yaw
Dynamic respons in direction 7
9
8
7
Respons
6
5
4
3
2
1
0
0
20
40
60
80
100
Periode
120
140
160
180
Figure 39: Dynamic response in direction 7
Peak periods:
Related Eigenmode:
Dominating mode of motion:
17,7 sec, 19,7 sec, 36 sec, 161,2 sec
4, 5, 3, 2
pitch, heave, load x-direction, surge
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Dynamic respons in direction 8
70
60
Respons
50
40
30
20
10
0
0
10
20
30
40
Periode
50
60
70
80
Figure 40: Dynamic response in direction 8
Peak periods:
Related Eigenmode:
Dominating mode of motion:
20,6 sec, 36 sec, 62,5 sec.
6, 8, 7
roll, load y-direction, sway
Dynamic respons in direction 9
12
10
Respons
8
6
4
2
0
0
5
10
15
20
25
Periode
30
35
40
45
50
Figure 41: Dynamic response in direction 9
Peak periods:
Related Eigenmode:
Dominating mode of motion:
17,7 sec, 19,7 sec.
4, 5
pitch, heave
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8.3 Comments
In the following sections we will discuss the results, possible improvements and further work.
8.3.1 Results
When developing the MATLAB routine we based the calculations on the matrices defined in
the lecture notes, [FinnG] These matrices are a bit simplified by assuming y=0 as a plane of
symmetry and neglect insignificant terms. From this we assume that the model will give us
good results if it is followed. In our case we defined all the terms, but when we should give
them values we made some simplifications.
Some of our simplifications are questionable, some of them might not be very accurate. Based
on this it is clear that we would not get results of scientific standard. Even tough the results
are not 100% correct we feel that the results give us a good indication of how the motions
between the load and the vessel are coupled. This is because when we calculated and plotted
the dynamic response for each DOF, we saw that the response curve had peaks at periods
which responded to the eigenperiod for motions that seems natural to have an impact on the
actual DOF. Even if the results give us an approximation of how the motions are coupled,
some of the values for the eigenperiods and the responses seem to be unrealistic, for example
the eigenperiod for load in water where the yaw motion is dominating. We assume that this
comes from the simplification we have made, and that further work with finding more
accurate values for the terms in the matrices, will give us better results.
When we looked at the wavestatistics (Appendix D) for the summer period, we save that most
of the registered waves had periods between 4 and 13 seconds. From the calculation of the
eigenperiods we found that it is only the yaw-dominated period for the template in air that lies
in this interval. From the response curve we saw that there were not any motions with
significant values in the same region, so from this we can say that wave periods should not
cause any problem.
8.3.2 Improvements
Improvements will be to find out if the neglecting of terms will give us satisfactory results.
We can also extend our work by finding more realistic values for the estimated terms. Many
of these terms are defined by very complicated formulas, and for some of them model tests
will be required for accurate results. Model testing is out of the question for our project due to
the time-demand required. In addition, the information we need are most likely restricted and
therefore not available. This leaves us with estimating the terms, and good estimations often
demand a certain amount of experience, which again demands a lot of time. Since this
analysis is just a part of the whole project, we decided to go on with the chosen values.
Although we know that the correctness of these values might be questionable.
8.3.3 Further work
When we have got sufficient results these can used to perform further calculations. By taking
wave data in consideration, we can for example calculate the probabilities for resonance of the
coupled system during the actual period in time.
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9 Feasibility of the operation
Since we have based our project on a real marine operation, the Ormen Lange project, there is
no doubt that such operations are feasible. The installations at the Ormen Lange field was
succesfull. There is no doubt that the Ormen Lange project has faced a lot of challenges. Two
years was used for planning the installation phase[Hydro2]. When it comes to our project and
our calculations, several improvements can be done. This has been commented in the previous
chapter.
The importance off planning the operations in great detail is indicated throughout our project.
The Ormen Lange project is a very good example of this.
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10 Kilder
Websites:
[Hydro1] http://www.hydro.com/ormenlange/en/about_ormen/facts_and_figures/index.html
[Hydro2] http://www.hydro.com/no/press_room/news/archive/2005_09/templates_no.html
[Hydro3] http://www.hydro.com/ormenlange/en/concepts_solutions/well_design/index.html
[Map1] http://www.hydro.com/ormenlange/no/about_ormen/ormen_map.html
[Map2] http://www.hydro.com/ormenlange/no/about_ormen/key_features/storegga_slide/
index.html
[Water1] http://www.hydro.com/ormenlange/library/attachments/massive_gas_no.pdf
[Water2] http://www.hydro.com/ormenlange/no/concepts_solutions/import_pipelines/
index.html
[Golf]http://no.wikipedia.org/wiki/Golfstr%C3%B8mmen
http://www.hydro.com/ormenlange/no/media_room/news/2005_03/ol_status_no.html
http://hydro.no/no/press_room/news/archive/2005_08/templates_recorddeep_no.html
http://www.grenlandgroup.com/CMS/CMSpublish.nsf/$all/F6DF9F14C3901B16C1256FDD0
0663656?open&qm=MainMenu,3,12,0
[Heerema] http://hmc.heerema.com/Default.aspx?tabid=437
http://www.vikingsupply.com/vess_tor_spec.asp
http://www.vikingsupply.com/barges.asp
http://hmc.heerema.com/Default.aspx?tabid=437
http://www.sonardyne.co.uk/News/PressReleases/2005/ormenlange.html
http://www.sonardyne.co.uk/News/Newsletters/subsea_newsletter_2004.pdf
http://geoasa.no/publish_files/PerryTritonXL37rev_03.2006.pdf
[metoffice]http://www.metoffice.gov.uk/research/nwp/publications/nwp_gazette/dec01/nwp.h
tml
Literature:
[FinnG] Lecture notes in marine operations by Finn Gunnar Nielsen. January 2007.
Vindatlas for Nordsjøen og Norskehavet- Jan Aske Børresen
Global wave statistics (complied and edited by British Maritime Technology limited),
Primary contributors: N. Hogben, N. M. C. Dacunha, G. F.Olliver, Published for British
Maritime Technology by Unwin Brothers Limited.
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Appendix A: Model of the template, and definitions of
notations
A model of the crane vessel with the template is showed below.
We have used the following notations when establishing the equations:
m:
V:
Mass of vessel
Displaced volume of the vessel
mL :
Mass of load
Aij :
Added mass of vessel
x G , yG , z G :
Centre of gravity of vessel coordinates
x B , yB , zB:
Centre of buoyancy of vessel coordinates
x t , yt , zt :
Top of crane coordinates
ls :
Length of hoisting wire (From centre of load to top of crane)
le :
Effective length of wire
VL :
Submerged volume of load
w=m L lg- gVL :
Submerged weight of the load
a ij:
Added mass of the load
AE:
I nn :
Stiffness of wire per unit length
Moments of inertia
Appendix B: MATLAB routine “waterresponse.m”
Please see attached files.
Appendix C: MATLAB routine “airresponse.m”
Please see attached files.
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Appendix D: Wave statistics
B