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Modular design of cross flow channel through structural optimization
Sagaya Punithasegaran Arrshan
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 École Centrale de Nantes
developed at University of Rostock 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. Robert Bronsart, University of Rostock, Rostock, Germany
Internship tutor: M.Sc. Tim Stockhausen, Lürssen Werft, Bremen, Germany
Reviewer: Prof. Pierre Ferrant,
École Centrale de Nantes, Nantes, France
Rostock, January 2019
Modular design of cross flow channel through structural optimization 1
“EMSHIP” Erasmus Mundus Master Course, period of study September 2017 – February 2019
Table of Contents DECLARATION OF AUTHORSHIP .................................................................................................... 3
ABSTRACT ............................................................................................................................................ 4
1. INTRODUCTION .......................................................................................................................... 5
1.1 Background & Motivation ...................................................................................................... 5
1.2 Tasks & Objectives ................................................................................................................. 6
2. CROSS FLOW CHANNEL............................................................................................................ 7
2.1 Literature Review: Sea chest & crossover .............................................................................. 7
2.2 Cross flow channel Structure .................................................................................................. 8
2.3 Present Production process ..................................................................................................... 9
2.3.1 Sub-Assembly ................................................................................................................. 9
2.3.2 Block-Assembly ............................................................................................................ 10
2.4 Problems encountered in present method ............................................................................. 11
2.5 Requirements of a Crossover ................................................................................................ 12
2.5.1 Functional Requirements .............................................................................................. 12
2.5.2 Operational Requirements ............................................................................................. 13
3. OPTIMIZATION .......................................................................................................................... 14
3.1 Different possible solutions .................................................................................................. 14
3.2 Integrated pipe in double-bottom .......................................................................................... 15
3.2.1 Selection of Pipe ........................................................................................................... 15
3.2.2 Crossover Pipe and fittings ........................................................................................... 17
3.3 Structural Modifications ....................................................................................................... 18
3.3.1 Girder openings & strength ........................................................................................... 18
3.3.2 Modification of the deck ............................................................................................... 20
3.3.3 Addition of floor plate and support ............................................................................... 21
3.3.4 Elimination of additional stiffening .............................................................................. 22
3.3.5 Other modifications....................................................................................................... 23
3.3.6 Final modified structure ................................................................................................ 23
3.4 Impact on general design ...................................................................................................... 25
3.4.1 Idea behind the FE model ............................................................................................. 25
3.4.2 Mesh .............................................................................................................................. 26
3.4.3 Constraints and Load condition .................................................................................... 27
3.4.4 Simulation and results ................................................................................................... 28
3.4.5 The necessity to increase the height of girders ............................................................. 30
3.4.6 Open-deck above the pipe ............................................................................................. 31
4. MODULAR DESIGN AND CONSTRUCTION ......................................................................... 32
4.1 Literature Review: Modular Construction ............................................................................ 32
2 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
4.2 General design aspects .......................................................................................................... 33
4.2.1 Tolerances ..................................................................................................................... 33
4.2.2 Size standards ................................................................................................................ 33
4.2.3 Accessibility or Reachability ........................................................................................ 34
4.2.4 Working position & conditions ..................................................................................... 34
4.2.5 Number of parts ............................................................................................................ 34
4.2.6 Better utilization of the facility ..................................................................................... 34
4.2.7 Special parts/components .............................................................................................. 35
4.2.8 Possibility of subcontracting ......................................................................................... 35
4.3 Modular design of the cross-flow channel ............................................................................ 37
4.4 Selection of suitable substructures ........................................................................................ 38
4.4.1 Crossover pipe .............................................................................................................. 38
4.4.2 Transverse Frames and floor plates............................................................................... 38
4.4.3 Longitudinal Girders ..................................................................................................... 38
4.4.4 Deck and Shell plates .................................................................................................... 38
4.4.5 Stiffeners, brackets and docking profiles ...................................................................... 39
4.5 Sub-assemblies ...................................................................................................................... 39
4.5.1 Crossover pipe .............................................................................................................. 39
4.5.2 Longitudinals ................................................................................................................ 40
4.5.3 Transvers frames and floor plates ................................................................................. 40
4.6 Construction of the module ................................................................................................... 41
5. Review of benefits and drawbacks ................................................................................................ 46
5.1 Optimized structure ............................................................................................................... 46
5.1.1 Functional benefits ........................................................................................................ 46
5.1.2 Operational Benefits ..................................................................................................... 47
5.1.3 Structural & Production related benefits ....................................................................... 48
5.1.4 Drawbacks or issues not resolved ................................................................................. 50
5.1.5 Cost estimation for overall comparison of production .................................................. 51
5.2 Modular construction ............................................................................................................ 52
5.2.1 Benefits achieved .......................................................................................................... 52
5.2.2 Drawbacks ..................................................................................................................... 54
5.2.3 Cost estimation of modular construction ...................................................................... 55
6. CONCLUTION ............................................................................................................................. 56
ACKNOWLEDGEMENTS .................................................................................................................. 57
REFERENCES ..................................................................................................................................... 58
Modular design of cross flow channel through structural optimization 3
“EMSHIP” Erasmus Mundus Master Course, period of study September 2017 – February 2019
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 University of Rostock.
Date: Signature:
4 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
ABSTRACT
The master thesis work involves in studying the modular design of complex double bottom
structures in prefabrication as an alternative to working in section construction based on the
geometry of a cross-flow channel with its possible optimization.
Presently, the complex double bottom structures such as cross flow channel and sea chests are
built at the block assembly from separate single structural groups in most of the shipbuilding
industries. The goal of this study will be to look into the modular design and construction of
the cross flow channel. Which means that the entire construction is pre-fabricated and mounted
as one module in the block assembly. The background to this is the theme of producing such
built-in parts (e.g. double-hull or stainless steel tanks, shaft strut connection, etc.), together
with the surrounding shipbuilding structure with simple interfaces for subsequent assembly in
the section or on the ship as modules. This is to achieve a more favourable position &
accessibility, shorter distances and relocation of work into the prefabrication to save costs in
the preparation and construction time on the sectional building sites.
Taking advantage of the modular construction, there is a need of optimizing the cross flow
channel in order to achieve certain functional and operational advantages such as to
eliminate/reduce air bubbles & air cushions in flow, to have reduced flow resistance and
avoiding mud/sludge formation or marine growth and most importantly to have better
accessibility for inspection and maintenance. The cross-flow channel needs to be optimized
accordingly and should be designed to be constructed as a module since the complexity of the
structure might increase.
Nevertheless, in this study, we will review the basic principles of modular design and
construction, which will lead to better understanding of the method. In the company’s point of
view, the aim is to use recognized advantages of the optimized crossover and the modular
design for the future implementation in the upcoming projects.
Modular design of cross flow channel through structural optimization 5
“EMSHIP” Erasmus Mundus Master Course, period of study September 2017 – February 2019
1. INTRODUCTION
1.1 Background & Motivation
As the name suggests, ‘Complex’ double bottom structures have difficult and complex process
of construction along different building sites of a shipyard. Usually, such structures are built at
the block assembly as a complete block before it is moved to the ship erection site. During the
construction of certain components or parts, this process can be extremely difficult due to the
very limited space available between components especially in the double bottom. The biggest
challenge would be to reach the right location and to have a good quality welding.
The motivation of this thesis is to study the modular construction of such complex double
bottom structures specifically based on a cross flow channel and to identify the possible
modules with built-in parts (profiles, tanks & etc.) with simple interfaces for block assembly
or on board assembly. The main goal is to find an easy or favourable working position for a
good quality of job and studying the possibility of saving time and expenses by relocating the
work into the prefabrication. The results could be used to identify different other complex
geometries that could possibly be pre-fabricated as modules. Hence, the criteria for modular
design in general will also be studied.
Since the work is mainly concentrated on the cross flow channel, there are certain issues or
requirements with the crossover that needed to be sorted out. Briefly, they are mainly regarding
the flow and maintenance of the crossover. Hence, this study will take the advantage of modular
construction and begin with an optimization of the structure for the cross flow channel, that
can demonstrate certain improvements.
6 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
1.2 Tasks & Objectives
The main task of this study is to find out which assemblies or substructures of the cross flow
channel that would be suitable for modular prefabrication and the criteria for such a decision.
In terms of optimizing the structure of the cross flow channel, the main objective is to analyse
the requirements for a cross-flow channel and to optimize the structure to cope with those. It
can be studied that if the modular structures be used to meet these requirements as the
optimization might also increase the complexity as discussed earlier.
Considering on which possibilities of a modular design in prefabrication exist at the Lürssen
shipyard, it should be figured out if the existing infrastructure suitable for the construction of
modules of the selected size of the subassembly in terms of cranes, space, means of transport
and working conditions. Then a comparison should be done between the conventional building
process and the modular construction to see if it gives further advantages such as space,
capacities, costs, time and quality.
Modular design of cross flow channel through structural optimization 7
“EMSHIP” Erasmus Mundus Master Course, period of study September 2017 – February 2019
2. CROSS FLOW CHANNEL
2.1 Literature Review: Sea chest & crossover
Having a quick brief about Sea chests, a sea chest is a rectangular recess close to the bottom of
the vessel from which the piping systems draw water for cooling of the Engine, Generator, fire
pumps or other uses. A sea chest acts in much the same way as distilling basin or well, offsetting
the effects of the vessel speed and providing an intake reservoir.
In large vessels usually there will be two sea chests one on the side and the other on the bottom
of the double bottom, which are called high and low sea chest respectively. The purpose of
having high sea chest is to avoid the suction of mud or harbour silt at port or shallow waters
and the low sea chest is to get the cleanest and best seawater head at sea state. They also serve
as a redundancy measure in an event of failure or damage of one of the sea chests. A typical
representation of a sea chest is as shown below in fig. (1).
Figure 1. Sea chest. Available from: http://navy.memorieshop.com/Design-Details/Reservoir.html
[Accessed 10 June 2018]
Usually termed as Crossover, it is a means of structure or piping System that connects the Low
and High Sea Chests of the vessel. Water will be taken from the crossover with the help of
suction pipes connected to it for different uses such as cooling for the diesel generator, main
condensers or supply water for the forward diesel fire pump etc.
8 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
2.2 Cross flow channel Structure
On the yachts built at Lürssen shipyard, the crossover is designed to be a part of the structure
of double bottom between two water-tight bulkheads rather than just a piping system, hence
the name ‘Cross flow channel’.
This type of a channel is designed due to the limited space available in the machinery room
where it is required to place Engines, Generators and other equipment along with plenty of
pipes running along the floor while the conventional piping system would interrupt the
machinery room arrangements otherwise.
Typically the cross flow channel is designed between 3-5 frame spacing in such a way that,
either half of the channel is under fore and aft machinery rooms so that the water can be taken
out easily from each of the rooms without the need of extended piping. The main channel,
which is under the engine room, usually has a wider channel without a transverse floor plating
but stiffened longitudinally on the shell and deck plate. Large cut-outs are provided on the
longitudinal girders in order to have the required flow without much resistance. The size of the
cut-outs required are determined by the flow requirement that needs to be supplied to the
machinery equipment. All the structural surfaces inside the channel (including profiles,
brackets & etc.) will be treated with anti-fouling coating as they will be in contact with the sea
water throughout their lifetime.
The seawater is sucked in through the sea chests and fed into the cross channel after passing
through filters. Water is taken out for various purposes through the suction pipes, which are
inserted into the channel through the tank deck plate. The important factor here is the flow rate
of the water through the cross flow channel rather than the volume capacity. The required flow
rate is determined by accumulating the required amount of water for each of the equipment.
Modular design of cross flow channel through structural optimization 9
“EMSHIP” Erasmus Mundus Master Course, period of study September 2017 – February 2019
2.3 Present Production process
At Lürssen shipyard, the production of the cross flow channel is done at the block assembly as
a part of the whole block. The construction is carried out from separate longitudinal structural
groups starting from the centre and moving outwards transversely. The different structural
groups can be seen below indicated in different colours in fig. (2).
Figure 2. Single structural groups for construction
2.3.1 Sub-Assembly
Sub-Assembly or Pre-Fabrication is where most of the parts and components, which are
comparatively smaller and consist a few number of structures are built. Mainly, each parts of
the longitudinal girders and transverse frames are welded with the respective stiffeners or
profiles it is meant to have. In this case, as the deck plates at the crossover region needs
additional stiffening, the welding of the stiffening profiles on the deck plates is prefabricated
as well.
The parts and profiles are cut to the required sizes, prepared with the weld preparation and
given with unique names before it reaches the facility. After each sub assembly is built, they
are given with another unique name of the sub-assembly, which will be used in further process.
In addition, some of the modules are completely constructed in the pre fabrication. Especially,
the low sea chest, which is part of this block and an important component associated with the
cross flow channel, is built as a complete module here.
10 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
The walls of the low sea chest will be weld with the stiffening profiles and brackets first and
the module of the sea chest box will be completed. Different other modules and the reason to
be pre-fabricated as a module will be explained in the following chapters.
2.3.2 Block-Assembly
The block assembly is where the complete block is built with the sub-assemblies and modules
that are prepared at the pre-fabrication. Placed on a customisable jig setup, the block is built
upside down. From the production point of view, building upside down has the main advantage
of welding downwards. Since the cross flow channel is built as a part of the block, let us have
a brief about the construction of this particular block in this chapter.
As the first step, the tank deck plates are placed on the jig and weld with themselves together.
Next, one longitudinal section at the centre line is built with the respective sub-assembly parts.
It begins with the Central girder being placed first and each part of the transverse frames
associated along with it to the length of the girder in one side is welded together. One section
is then completed after welding with the required brackets, collar plates or other profiles.
Similarly, the next girder is placed and the transverse profiles follows and the construction of
the longitudinal section on the other side is done. After the completion of the central sections,
the keel plate is placed and welded together. The same procedure of section based construction
is followed until the block is constructed with the longitudinal and transverse members and the
shell plate is welded finally. Then the construction workers and welding technicians have to
get inside the double bottom in order to weld the frames, girders and the with the shell plate.
Finally, the modules of the sea chest, engine mounts, block joints and other required brackets,
collar plates and profiles will be weld together with the block.
After the completion of the block, it will be transported to the on board assembly for block
erection. This is the typical process of building the cross flow channel, which is an integral part
of the block in almost all of the projects at Lürssen shipyard.
Modular design of cross flow channel through structural optimization 11
“EMSHIP” Erasmus Mundus Master Course, period of study September 2017 – February 2019
2.4 Problems encountered in present method
After studying the current method and discussing with a few experts in the production and
design facilities, certain issues or problems were addressed.
Accessibility and reachability
The most important and major concern is the accessibility to the work. During the construction
of this double bottom block, the workers have to go through manholes carrying all equipment
they require to work with. Reachability is another concern, taking welding as example, the
welding torch should be able to reach the point of welding and the worker needs to have clear
vision on it. Deformation of structure due to uncontrolled welding is high and straightening the
buckled plates are a tough job as it requires large equipment to be carried inside the double
bottom.
In addition, small human errors also gets amplified due to this accessibility problems. As an
example, if a worker forgets any of his essentials such as glass or gloves, he has to go back
through the groves outside and come back again. This is a big issue though not quite addressed.
Missing parts
Another major issue encountered is the quite a large amount of time wasted in searching for
the parts or components at the block assembly and eventually having need to fabricate the parts
again. This is due to the large number of components involved and transportation, storage and
handling are always an issue.
Unsafe working conditions
A typical Yacht built at Lürssen shipyard would have a double bottom of 1.5 m height
maximum at the centreline in the engine room and the usual frame spacing is 650 mm. Hence
the compartments are very small and working inside such congested space creates an unsafe
working environment for the workers.
There’s very low ventilation, no natural light and the workers dealing with large electric
equipment might pose a risk of safety in those conditions. It will also be difficult to escape
during an emergency.
12 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
Other issues
Apart from these main issues, it is required to find and fix the favourable position of welding
very earlier in the design stage and place the structure according to that, as the block cannot be
turned. Which means that, everything has to be planned earlier and there’s no room for changes.
In addition, the idle time of workers are large as they need to wait for a machine to cycle or
waiting for the preceding operator to finish their work. When some changes needs to be done,
this might increase further.
2.5 Requirements of a Crossover
Similar to the problems encountered in the present production process, there are also several
requirements for a crossover, which are unable to be achieved due to the complex structure and
difficult construction process. Since the modular design and construction should be applied
through the optimization of the cross flow channel, let us understand the requirements of the
crossover and how modular design can help in such improvements to be made.
The important requirements of a crossover can be categorised under functional and operational
requirements, which are discussed below.
2.5.1 Functional Requirements
The first and foremost importance goes to the functional characteristics in the crossover. The
flow velocity in the crossover is usually maintained between 0.5~1.1 m/s to have a certain flow
rate that can meet the need of water from different machinery. The flow rate required will be
calculated by summing up the entire water intake rate of each equipment and on an average it
is found to be around 2000 m3/h. It is required to have low flow resistance for the cooling water
and good flushing.
At Lürssen shipyard, since it is the double bottom structure, which is used as the cross flow
channel, the flow is maintained at 0.5 m/s to avoid resistance due to the high number of
structure and profiles inside the channel. However, having a lower flow velocity lets room for
marine growth and this will again increase the resistance to flow and reduce the flow rate of
water which is necessary to feed the machines connected to it.
Modular design of cross flow channel through structural optimization 13
“EMSHIP” Erasmus Mundus Master Course, period of study September 2017 – February 2019
Hence, in terms of functional requirements, it is necessary to have a higher flow rate to reduce
the risk of marine growth while keeping the resistance down. It is also important to avoid air
bubbles or air cushion in the crossover to make sure that the suction pipes intake only water
from the crossover and not air which may damage the machinery.
2.5.2 Operational Requirements
The next most important aspect is operation and maintenance. As experienced from many
different vessels in the past, it is found that nearly after a year or two of usage, the cross channel
structure gets deposited with mud/sludge and marine growth which resists the flow and
eventually block the flow inside the channel. This problem has been a major concern, as it is
again a strenuous job to get inside and clean the double bottom structure.
The main cause for this is the sharp corners and edges of the structure, which can easily get
deposited by sludge. As discussed in the previous chapter, having a low flow velocity is another
reason behind this. Hence, it is a major requirement to avoid sharp corners and edges to reduce
the sludge formation and which also can reduce the resistance to flow.
The channel should have enough space to be able to get accessed inside for inspection and
maintenance purposes, preferably there should be space for a person to get in if necessary.
Additionally, the cross flow channel should be suitable for anti-fouling or chemical/electrical
fouling protection or for cathodic protection. With the idea of optimising the cross flow
channel, it is also required to have as little surface as possible to avoid fouling of larger areas.
14 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
3. OPTIMIZATION
3.1 Different possible solutions
In the early stages of the thesis, different possible solutions were discussed regarding the
optimization of the cross flow channel. As discussed in the previous chapter, the major concern
is to reduce structures or profiles from the cross flow channel. Hence as a simple solution, it is
discussed to build the stiffening profiles to the outside of the cross flow channel. In addition,
to reduce the sharp corners, a set of curved cover plates can be placed between two
perpendicular plates. The concept is represented as follows in fig. (3).
Figure 3. Idea of profiles built outside and additional cover plates
However, it is not possible to eliminate all the structures or profiles from the inside of the cross
flow channel. Also the concept of cover plates wouldn’t make much sense since not all the
corners can be covered and it will also increase the difficulty of building it. Moreover, not a lot
of benefits be achieved and the advantage of modular construction cannot be utilized.
Nevertheless, from the idea of curved cover plates, a new solution is discussed, which is using
a large pipe as the crossover instead of the cross flow channel. We know that this will definitely
increase the complexity of the structure and the process of construction. However, it is where
modular construction can better play its part.
Hence, the final decision is to integrate a large pipe inside the double bottom, which can carry
along with certain advantages over the conventional cross flow channel. The design process
and the benefits of the new structures will be discussed in the further chapters.
Modular design of cross flow channel through structural optimization 15
“EMSHIP” Erasmus Mundus Master Course, period of study September 2017 – February 2019
3.2 Integrated pipe in double-bottom
As mentioned above, the idea is to integrate a large pipe in the double bottom, which can serve
as a crossover instead of the conventional double bottom cross flow channel. The pipe should
be large enough to achieve the required flow as well as to give access inside for inspection and
maintenance. The basic idea is that a pipe of diameter 800-900 mm would be suitable for this
particular application.
3.2.1 Selection of Pipe
The most important factor in the selection of pipe is the flow requirements of the machinery
and equipment to which the crossover supplies seawater. After analysing the flow rate
requirements of the vessels built in the past, we can obtain an average value of 1856.6 m3/h of
flow rate usually required by the machinery & equipment. As the flow rate required was higher
only at a few occasions, we will choose a flow rate of 2000 m3/h as an average requirement in
a general perspective.
However, higher and lower rates of flow can be achieved depending on the cross section and
the flow velocity in the pipe. Considering the fact that the pipe does not poses too many
structures or profiles inside, a higher flow velocity can be achieved which is about 1 m/s.
Hence, the size of the pipe should be selected according to the flow requirement and achieved
velocity. The cross section area required can be calculated from formula shown in Eq. (1).
(1)
For an average flow rate of 2000 m3/h and a water flow velocity of 1 m/s, we get the cross
section area necessary is 0.55 m2.
To have a minimum cross section area of 0.55 m2, a standard size pipe with an inner diameter
of 843.6 mm is selected. With a cross section area of 0.558 m2, this pipe is capable of achieving
2012.17 m3/h, which is a little above what we expected to have. However, it is possible to
increase the flow velocity up to 1.1 m/s and hence it is possible to reach up to 2213.39 m3/h
with this standard size pipe.
16 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
Selection of pipe thickness is important as the buckling stiffness at a point where a stress around
70-100 MPa is experienced. Most of the Yachts built at Lürssen shipyard are classified under
DNVGL classification and there are certain rules, which are considered while selecting
thickness of plates.
According to DNVGL-RU-YACHT Pt.3 Ch.4 Sec.4., the minimum thickness for plating
of detached tanks is 3.0 mm and for stainless steel, the minimum thickness can be
reduced to 2.5 mm.
According to DNVGL-RU-SHIP Pt.3 Ch.6 Sec.3., the net thickness of plating shall not
be taken less than:
𝑡 = 𝑎 + 𝑏 ∙ 𝐿2 ∙ √𝑘 (2)
Where a=4.5 and b=0.02 for Inner bottom spaces. The factor k may be taken as unity.
Hence, for a ship of an average 100m, the minimum thickness would be about 6.5 mm.
According to the DNVGL rules of Sea going ships, I-1-1 Sec.12, the minimum plate
thickness of all structures in tanks shall be not less than:
𝑡 = 5.5 + 0.02 ∙ 𝐿 (3)
Hence, for a ship of an average 100m, the minimum thickness would be about 7.5 mm.
Usually the minimum thickness rules for tank boundaries would cover around 90% of the
buckling cases. However, extra stiffening is still considered for extreme cases. Hence, the
double bottom structure is usually stiffened with 15mm thickness on all transversely stiffened
plates and will be more than sufficient at a point so deep in the double bottom.
Considering the extra-stiffened girders and to comply with the minimum thickness
requirements, the pipe thickness should be selected between 7-15 mm. Hence, an available
standard size of 10 mm thickness is selected for the chosen pipe. However, it is only an entry
point and further investigation on the strength is necessary to validate it. With 10 mm thickness,
the selected pipe will have an outer diameter of 864 mm.
Modular design of cross flow channel through structural optimization 17
“EMSHIP” Erasmus Mundus Master Course, period of study September 2017 – February 2019
3.2.2 Crossover Pipe and fittings
A standard pipe of 864 mm outer diameter and with 10 mm thickness, which will serve the
need, is selected as the crossover pipe. On either end of the pipe, to the top, an opening with a
connection and a flange is provided in order to be fixed with the outlet of the pump through a
filter of seawater coming from the sea chests. This will be the inlet of seawater into the
crossover pipe. Additionally, the top of the crossover pipe will be provided with number of
cut-outs for the suction pipes to be sent through.
The crossover pipe is fitted with blind flanges on both sides in order to give access inside
whenever it is necessary to inspect or for the purpose of maintenance. The pipe also can be
given with only one opening at one end while the other is permanently closed. But there might
be some obstructions in getting through the pipe as it will be installed with many other suction
pipes to the middle. Hence, both ends are given with openings to make sure to have easy access
inside the pipe. The crossover pipe and its fittings are modelled and are as shown in fig. (4).
Figure 4. Crossover pipe
It should be noted that, with 210.5 kg/m weight of this standard pipe, together with the flanges
and after given with cut-outs it will bring in additional weight of about 1.6 tons to the structure.
However, the weight of the ship is maintained with no increase with several structural
modification, which will be explained in the following chapter.
18 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
3.3 Structural Modifications
Integrating the pipe inside the double bottom is a task that needs a lot of considerations from
the structural point of view, especially strength is a major concern.
3.3.1 Girder openings & strength
The crossover pipe should be placed in transverse direction that it would interrupt the
longitudinal girders in the double bottom. Usually, the cut-outs on the girders are made in such
a way that the opening is about 60 % of the web height of the girder, taken as a rule of thumb.
As this optimization work is based on an example of one particular vessel, this vessel has a
certain dead rise angle and the longitudinal girders have different heights at different positions,
the highest being 1.5 m of the centreline girder and the lowest being 1.02 m where the pipe
interrupts.
According to our case, having a cut-out as large as 0.86 m will make the cut-out being at about
85% of the web height on the smallest girder which is not acceptable even though it makes
only 57% at the centreline girder. Hence, to fit the pipe transversely through the girders, and to
comply with the strength standards, the girders are raised by 220 mm to achieve the cut-out
being at least 70% of the web height at the shortest girder. However, all the girders that are
interrupted should be raised to have an equal level.
It is important that the continuity of the girder should not be interrupted and hence the girder
is raised for a length of two transvers frame spacing and the raised height is tapered down to
the level of the tank deck for a length of one frame spacing. The knuckled edge is provided
with edge blends. The modified structure of a girder can be seen in the fig. (5).
Modular design of cross flow channel through structural optimization 19
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Figure 5. Modified longitudinal girder dimensions
By modifying in such a way, we have obtained a decent percentage of size of opening on the
girder below which is permissible. The space between the shell and the bottom of cut-out of
the smallest girder is 105 mm while the minimum requirement is 100 mm. However, this is
only an entry point to the solution and it would certainly need further investigated in a detailed
FEA with potential optimization strategy.
Additionally, the raised part of the girder needs additional stiffening to prevent buckling, as it
is not supported by the deck plate anymore. A belt profile of 120×10 is used in this case bent
to have a knuckle to run along the raised part of the girder. Also, stiffeners of 50×8 are used on
either sides of the raised part of the girder at the bend point, connecting the belt and the tank
deck. The completely modified girder with all the added profiles can be seen in fig. (6).
Figure 6. A completely modified girder with additional stiffeners and belts
20 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
It should be noted that the raised girders do not interrupt the platform on top of the deck as it
is built 1 m above the tank deck. Since most of the pipes in the machinery room are placed in
longitudinal direction, there is very minimal disturbance, which can be adjusted easily.
3.3.2 Modification of the deck
The pipe used is quite large and is placed inside the double bottom in such a way that the top
of the pipe reaches almost the same level of the deck. Hence, it is not possible to have a flat
deck at this point as in the conventional cross flow channel. Since there will be many suction
pipes installed on the pipe, it is decided to have an open deck along the length of the pipe.
The deck plates are knuckled downwards at 40˚ angle just after the frames before the pipe and
are connected to the pipe having an opening of the deck for a certain area exposing the pipe.
The edges of the opening on the deck is provided with edge blends to reduce the effect of stress
concentration. The modified new deck arrangement is as shown in fig. (7).
Figure 7. Modified deck
The knuckled plates are placed below the flat deck plate 40 mm away from the frames in order
to leave space for the weld seam of the frame on deck plate and 20 mm inside to the edge of
the flat deck in order to weld them together. The arrangement is as shown below in fig. (8).
Modular design of cross flow channel through structural optimization 21
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Figure 8. Knuckled deck plate arrangement
3.3.3 Addition of floor plate and support
In the conventional cross flow channel, usually a floor plate will be eliminated to give smooth
flow of seawater in the channel. The lost strength will be compensated with additional
stiffening of the shell, deck and longitudinal girders with long profiles spanning at least two-
frame spacing on either side of the missing floor plate.
However, the optimized structure is not a cross flow channel or a tank anymore and to give the
shell, girders and the pipe a good support, a floor plate is added below the pipe along its length
where it was missing before. Along with the pipe being welded on top of the floor plate, this
structure resembles a perfect girder and hence it gives an advantage of being able to eliminate
all the additional stiffening done in the conventional cross flow channels. This will be discussed
in detail in the following chapters.
Additionally, an extra plate spanning two-frame spacing is placed longitudinally at the end of
the floor plate where the pipe terminates. The structures added additionally to support the
bottom shell, girders and pipe can be seen below in the following fig. (9).
22 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
Figure 9. Added floor plate and additional support
Both of these additional structures would bring half a ton added weight to the ship, which
however is compensated by the structures eliminated.
3.3.4 Elimination of additional stiffening
Due to the addition of the floor plate & support and the open deck design as mentioned in the
previous chapters, a large number of stiffening profiles and brackets are eliminated in the new
structure which were present initially due to the lack of support strength on the deck and the
shell plates.
The elimination of such a large number of structure brings us certain benefits. One of the most
important in terms of structure is that, it helps maintaining the weight of the block. That means,
about 1.7 tons of weight is been removed due to the elimination of these profiles. Other added
advantages will be explained in later chapters.
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3.3.5 Other modifications
There are certain other modifications carried out to have a much precisely detailed structure
concerning other issues that can arise. One of them is the modified and additional cut-out on
the transverse frames on either side of the crossover pipe. Initially, the part of the frames at
keel had one larger cut-out on each giving smooth an uninterrupted flow of seawater through
it. As the optimized structure is not a cross flow channel, such a large cut-out is not really
necessary. However, the additional longitudinal support added at the end of the pipe had
created a new compartment behind it which do not have an opening to give any access into it.
Hence the initial cut-out of 1050×800 is reduced to 850×700 and an additional cut-out is
provided on the same frame but on the other side which can give access to the new compartment
at the end of the crossover pipe.
Similarly, other larger cut-outs on the floor plates are also reduced in size of opening as it is
not necessary since the structure in not the cross flow channel anymore and there are no
chambers which requires access often.
Due to the elimination of certain profiles and brackets, the end cuts of certain profiles on the
transvers frames and longitudinal girders also had to be changed. Many of these profiles, which
initially had an ‘end connection with brackets’ are given with a ‘snipped’ end cut as the bracket
would have probably been eliminated.
3.3.6 Final modified structure
The final structure after all the above mentioned structural optimization is as shown in fig. (10)
Figure 10. Optimized cross flow channel – cut section
24 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
According to the modifications made and calculation of weight of all structures added and
removed, the final structure has an increased weight of about 1.5 tons in total. However, this is
later compensated by the weight of anti-fouling paint which is been reduced by about 85% due
to the reduction of the size of the cross flow channel, we will look in detail in later chapters.
The size and number of pipes depends on the equipped machinery and requirement. As an
example, the model below in figures 11-12 are shown with possibilities of installing a number
of suction pipes of different sizes.
Figure 11. Installation of suction pipes
Figure 12. Installation of suction pipes – section view
However, it should be noted that it is only an idea and it is very specific for this case. Different
vessels will have different equipment and capacities, sometimes more or sometimes lesser.
All of these modifications are based on one particular ship and it will differ for different ships.
For example, a vessel with much lower dead rise angle could be integrated with a larger and
longer pipe while possibly without the need to increase the girder height.
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3.4 Impact on general design
According to an expert of basic design at Lürssen shipyard, the cross flow channel is treated as
a permanently flooded compartment but not permanently opened to the sea. And since the
crossover pipe is a part of the double bottom and as long as it is placed below the tank deck, it
is not concerned with SOLAS regulations of damaged stability.
However, a simple FE model is used for comparison of the modified structure to the
conventional structure to identify the effects on the longitudinal girders using Siemens NX
advanced simulation tool. It should be noted that it is only a comparison between two structures
and not a complete assessment of the local strength of the modified structure.
3.4.1 Idea behind the FE model
In a conservative approach, a longitudinal girder under the engine room between two bulkheads
is chosen, as it is necessary to analyse the impact on the girder and it is placed at an area of
very high stresses. The shell and deck plates attached up to 1.5 m on either side of the girder
are also modelled along with all the transverse frames between the bulkheads. The exact
spacing of the girder will not be a concern as we are not interested in the absolute stress results.
FE models for both the new and the conventional structure are modelled side by side as shown
in fig. (13) to have an easy comparison with same conditions. The two models have no
connection between them and given with same constraints and load conditions but separately.
Figure 13. Models of conventional structure & modified structure
26 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
The basic idea is to create a simple model, which is heavily idealized since the goal is to
compare the two different structures. The girder can be considered as a beam fixed at both ends
with a uniformly distributed load. The clamping condition produces a lot of reaction forces on
longitudinal girders while actual stress is carried by the them and not by the transvers frames.
Only one girder is modelled since it is a first approximation and only for comparison.
3.4.2 Mesh
2D shell elements are used with consideration of typical properties of steel (Modulus of
Elasticity = 210,000 M/mm2 and Poison’s ratio = 0.3) which are inbuilt in the program. Models
are given with a mesh of element size of 150 mm each. This is considered as a reasonable
number of elements for a first approximation as we are interested in static stress. Too much
detail or a very fine mesh might lead to the calculation of Notch stress. It is also a better choice
in terms of time required for simulation. The more finer the mesh, the more time consuming
the simulation is. Below in fig. (29) we can see the model meshed as described above.
Figure 14. Mesh with 150 mm of element size
It is also important to avoid triangles in the mesh. Triangles are more stiffer than squares and
might lead to underestimation of stress values during calculations. However, the FEM tool used
is not meant particularly for shipbuilding and not an accurate solver. Hence, the model had to
be meshed with ‘allowed triangles’ to be able to get the results without errors, which otherwise
wouldn’t run the simulation at all for the element size given.
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3.4.3 Constraints and Load condition
As discussed above, the longitudinal girder can be considered as a beam fixed at both ends.
Hence, the horizontal edges at the ends are fixed in X and Z-axes while the vertical edge is
fixed in all directions, however all of those edges are left free to rotate along each axes. Another
constraint of fixed displacement only at Y direction is given to all of the edges of the transvers
frames, shell and bottom plates as well as for the edge of the pipe, keeping in mind that those
elements are continuing further in Y axis without a constraint until the next girder. This way,
it suppresses constraints in X and Z-axes, which is a perfect symmetry. It is a matter of
completeness and however, the rotations can be left free as it does not constitute much. Below
in fig. (15) we can see the constraints given at different edges of the models.
Figure 15. Constraints given on different edges
The load condition applied is a uniform static pressure of 100 kPa as shown in fig. (16), which
is considered to be a reasonable value of pressure to be acted on the double bottom. No special
sea condition is taken into account as it is only for the purpose of comparison.
Figure 16. Load condition
28 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
3.4.4 Simulation and results
The simulation is run using Siemens NX 9.0 Advanced simulation tool and the results are
obtained in terms of nodal displacement, rotation, elemental & nodal stress and Reaction force
& moment. However, we will have a brief on the displacement and the elemental stress as it is
the most important aspect to analyse. The obtained results are as follows.
Displacement
The nodal displacement obtained after simulation is show below in fig. (17).
Figure 17. Nodal displacement – Optimized structure vs Conventional structure
It can be noted that the displacement is minimal in both the cases. However, there seem to be
a slight improvement in the optimized structure considering the whole as a beam. This is due
to the addition of the floor plate which is missing in the conventional structure. The additional
stiffening in the conventional structure may serve the purpose but not as good as a floor plate.
Elemental Stress
This is the most important aspect that needs to be analysed, as the main concern is to identify
the impact on girders due to the structural modification. The following is the obtained von-
Mises stress distribution acting on the girders of both different structures shown in fig. (18).
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“EMSHIP” Erasmus Mundus Master Course, period of study September 2017 – February 2019
Figure 18. Elemental stress – Optimized structure (a) vs Conventional structure (b)
As it can be seen clearly from the figure that the stress acting on the optimized girder seemed
to be significantly lower than that of the conventional structure. The main reason for this is the
large square shaped cut-out in the conventional structure, which has very high stress
concentration levels at the edges of the cut-out. In the modified structure, we can see that the
stress concentration around the cut-out is pretty much evenly distributed and are less than half
in values compared to the other. This is due to the circular cut-out and additional support with
a floor plate and a pipe attached with it.
Hence, according to this simple FEM analysis, it is clear that the optimised structure has a good
and actually, much better behaviour to the application of static pressure compared to the
conventional structure. For the purpose of this thesis, we can conclude that the optimised
structure satisfies the need.
However, as mentioned in the beginning of the chapter, it should be noted that these results do
not justify that the modified structure complies with required structural strength criteria. It is
only a comparison and we can only conclude that the optimized structure might possibly be a
good solution, but still needs further investigation in this regard. It is also important to note that
the simulation tool used is not meant particularly for shipbuilding and hence it cannot guarantee
the results to be perfect for the given case. Also as mentioned earlier, this tool had used triangles
for errorless working but it might underestimate the actual stress impact.
Hence, in order to analyse the exact impact on the structure, a strength assessment of the entire
bottom grillage should be made with all the possible sea conditions and with the right FEM
tool, which is much more time consuming and out of the scope of this thesis work.
30 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
3.4.5 The necessity to increase the height of girders
This is an important aspect from the structural strength point of view. According to the experts
of basic design at Lürssen shipyard, the girder should be increased if the cut-out is too large.
As a rule of thumb, about 60% of the girder web height is allowed for a cut-out.
Hence, to justify the answer, an FEM simulation of such a model is done and the results are as
follows. It is been compared to the results from the simulation of the optimised structure which
is discussed in the previous chapter.
Figure 19. Nodal Displacement –New structure without increased girder vs Conventional structure
As you can see from the above fig. (19) that there is a slight increase in deformation at the
central part of the girder and the shell plates compared to the FEM analysis done in the previous
chapter although it is not so significant. However, the elemental stress is the important factor
to be analysed and is obtained as follows.
Figure 20. Elemental Stress – Optimized structure, with raised girder (a) vs without raised girder (b)
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“EMSHIP” Erasmus Mundus Master Course, period of study September 2017 – February 2019
In the above comparison shown in fig. (20), it can be clearly seen that the stress concentration
at the opening of the girder is significantly higher in the model without the raised girder.
Though it is only a comparison, it can still interpret that the girders are need to be increased in
height if the size of the cut-out is increased.
3.4.6 Open-deck above the pipe
To see this question from the structural strength point of view, another model is prepared
accordingly and an FEM simulation is carried out to see the outcome and are presented as
follows.
Figure 21. Optimized structure, with open deck (a) vs conventional flat deck (b)
Looking at the elemental stress as shown in fig. (21), we can see that the stress concentration
also has no significant difference. In this way, this model can also be chosen as the right
optimised structure. But the major consideration to use the ‘open deck’ concept is that the
requirement of “easy to build”.
Although the knuckled deck plate concept needs extra plate cutting, it can still be worth during
the construction process. This is because, the crossover pipe is large and is placed in such a
way that it is almost at the level of the deck. Welding the deck plate with the curved surface of
the pipe needs extra profiles and brackets to be placed in between them while there is very tiny
space available. And the welding job will be very congested at those points while reachability
is also another concern to be worried of. In addition, the open deck concept has another
advantage that, the suction pipes are installed directly to the crossover pipe, which can also be
pre-outfitted.
32 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
4. MODULAR DESIGN AND CONSTRUCTION
4.1 Literature Review: Modular Construction
Modular construction was obtained from the idea of the lean production, which is one of the
theories in ship industry. A Module is combination of sub-assemblies joined together that can
be transported from one facility and to be assembled in another. The meaning of modularization
differs from field of work, but the general idea is to divide large systems into smaller, self-
sufficient parts.
Looking at the origin of Modular construction, Henry Kaiser’s introduction of Group
technology for the Liberty ships (to attain benefits associated with production lines) lead to
development of modular assembly for shipbuilding business during WWII bringing about an
industrial revolution within the industry. This concept of modular construction had come up
due to the requirement of optimizing shipbuilding production process by reducing costs and
increasing competitiveness without investing in new facilities, machines and tools.
Figure 22. Concept of modularization
Modular construction is now a common method applied in shipbuilding industry. Modular or
prefabricated construction is a procedure that practices a prefabricated building process, which
are gathered on-site to create a stable or temporary prefabricated building. Modular space earns
lots of benefit of well-ordered fabrication surroundings together with the plan flexibility of
classic structure procedures to yield superior stable or impermanent prefabricated structures
for some request. The way these modules are combined makes a final unique design.
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Modularization allows complex structures to be manageable in production, allows parallel
working and can accommodate future uncertainty. Discretizing the complexity down to self-
sustainable building blocks, where each module has defined system borders and demands, the
engineer is able to manage large and complex systems in a structured way. Modularization
techniques can be applied to platform construction and systems design. Larger modules can be
built with more fit-out and testing undertaken on land earlier in the build process.
Compared to conventional construction, modular construction needs a high degree of
interaction among construction activities, with planning of many of these activities to occur
early in the project as shown in fig. (22). Modular construction redefines relationships among
activities that are usually independent in conventional construction. Unlike standard
construction, where most of the design, engineering and construction activities are carried out
in sequential order, activities for modular construction involve additional interdependency
since those works can be performed in parallel in the same time at various fabrication shops or
at various construction sites.
4.2 General design aspects
We know that every sub assembly is a module; even a block is nothing but a module. There is
still a reason to select a certain size and particular number of components while designing a
module, each having different individual aspects. In this chapter, we will have a brief on the
important general aspects to be considered during implementation of the modular design
concept.
4.2.1 Tolerances
Tolerances in block mounting would be a big concern as there will be quite large imperfections
on fitting large structures. Considering this, modules can be chosen to have as less interfaces
as possible to avoid these issues.
4.2.2 Size standards
Modules can also be chosen with the standard sizes of sheets, plates, pipes and other type of
available material. This way, it is possible to avoid extra work such as cutting or welding.
34 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
4.2.3 Accessibility or Reachability
The most important work done in construction sites will be welding. When the structure
becomes large with increasing complexity, a module can be chosen that should give easy access
to all the places that needs to be welded.
4.2.4 Working position & conditions
It is always recommended to avoid upside welding as much as possible. A module can be
considered when there are large number of components to be welded to the top. It can give the
advantage of turning around to fit the most convenient welding position. It is important to
maintain a safe working condition during welding, cutting or other works. A module can be
selected considering the congested working spaces in the complex structures.
4.2.5 Number of parts
Another important aspect is the number of components involved. Transportation, handling and
storage of quite a large number of components are always an issue and it more often leads to
missing parts and wastage of time corresponding to it. Eventually, the missing parts might have
to be fabricated again. Modules can be selected with lesser number of parts, which does not
require larger storage and handling while reducing the same from the block assembly.
4.2.6 Better utilization of the facility
As much as it is important to have a facility, that is capable of dealing with modular
construction, it is also important to make use of it for the largest extent. For example, cranes
can be utilized more with a bit larger modules while reducing the work load from the block
assembly. At Lürssen shipyard, the cranes at the prefabrication facility can easily handle
modules up to 25 tons. This could be another important factor to consider modular construction.
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4.2.7 Special parts/components
Some structures might integrated with special parts or components especially like larger pipes
and fittings. Modules can make it easier to construct with the surrounding structure with very
congested space around. Parts to be assembled closer to the shell can also be in this category.
Some components could belong to two or more different levels or blocks, which would make
sense to be built as a module.
4.2.8 Possibility of subcontracting
In addition, when modular design is standardized for a particular component, it can be sub-
contracted rather than building it by own. In addition, when special parts exist in structures, it
is beneficial to sub-contract it. While saving much time in our production facility, sub-
contracting might possibly be cheaper than building on our own.
Let us look at a few examples of modules, which are pre-fabricated at Lürssen shipyard and
the importance to do so.
Outside walls of the superstructure
The walls of the superstructure has a lot of small parts and components involved especially a
lot of stiffeners which are placed horizontally on a vertical wall. Hence, to have the most
convenient welding positions and to avoid handling of too many parts in the block assembly,
this part is built as a module. In addition, extra work can be avoided when the modules of the
walls are selected to the standard size plates available in the market.
Bulwark
The importance to do so is that the bulwark should be built along the curved shell on top and
it will be difficult to weld the profiles. There will also be problems of tolerances as the bulwark
is a long and large structure. With a module, the bulwark can be prefabricated with the most
convenient welding position with the possibility of turning around.
36 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
Sea chests
The low sea chests usually stand on top of the tank deck. It will be difficult to build it along
with the double bottom block as the block will be built upside down and it is much easier to
build the sea chest as a module separately with the necessary plates and stiffening included.
Meantime, a part of the high sea chest should be integrated in the double bottom, another side
being part of the bulkhead while it had to be welded with the shell also. This makes it a very
complex situation in terms of construction. Hence, the top part of the high sea chest is built as
a module with the required stiffeners, brackets etc. This can also help avoid issues of
alignments. After the double bottom block is completed and turned upright, both the high and
low sea chests can be laid down and mounted on top of the double bottom structure.
Engine/Machine foundations
In this particular case, it should be noted that the machinery to be mounted and hence its
foundation belongs to two blocks. To avoid the risk of imperfect alignment, these components
are built as modules.
Bow Thruster
A bow thruster is a very special component, which has to be placed on the bottom of the ship.
Since it has a very large opening that interrupts the girder, the shell of the thruster tunnel has
to be provided with extra stiffening as shown in fig. (23). Along with the motor, rotor blades
and all other machinery, the whole structure with additional stiffening is subcontracted as a
module. When the surrounding structure is built, the module of the thruster is placed and
mounted with the rest before the shell plates being weld.
Figure 23. Bow Thruster. Available from https://www.vethpropulsion.com/products/bow-
thrusters/tunnel-thruster/ [Accessed 26 December 2018]
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4.3 Modular design of the cross-flow channel
As we already have an optimised structure of the cross flow channel, now we will study the
modular design and construction process of this particular cross flow channel structure in the
following chapters.
We know that the complexity of the cross flow channel structure is been increased due to the
modifications made, especially the addition of a pipe inside the double bottom structure. This
certainly rises the need for a modular design in terms of construction of the structure. However,
we should keep in mind that the structure is optimized to utilise the advantages of modular
construction. Following are the major and important requirements for a module.
Considering important aspects such as tolerances, accessibility and working condition issues,
number of parts involved and most importantly special part in this case as there is a large pipe
being integrated in the double bottom, a modular design is made for the cross flow channel.
The final module is as shown below in fig. (24).
Figure 24. Module of Cross flow channel
The module includes a total number of 137 single parts and constitutes 8.5 tons total in weight.
Pre-outfitting and painting of anti-fouling and anti-corrosion might increase a half a ton more.
However, the pre-fabrication facility at Lürssen shipyard is more than capable of handling such
a large module.
38 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
4.4 Selection of suitable substructures
In this chapter, we will have a brief about different major components or substructures, which
are a part of the module and the main reason for such selection.
4.4.1 Crossover pipe
As obvious, the crossover pipe is the core of the cross flow channel. Hence, the crossover pipe,
which is already prepared with the required openings, fitted with flanges, holes for suction
pipes and possibly with the pipe fittings for the suction already been welded will be built as a
module with the surrounding structure.
4.4.2 Transverse Frames and floor plates
Since building the structure around the crossover pipe is the main challenge, it is important to
have both the adjacent transverse frames in the module. The floor plate added newly supporting
the pipe below is also selected to be in the module. However, the parts of frames to be built as
module are limited to the length of the crossover pipe.
4.4.3 Longitudinal Girders
As we know that the crossover pipe is in transverse direction, the longitudinal girders have to
be limited in length in order to fit in the module. Considering the adjacent transverse frames
and to keep the continuity of the longitudinal girders, they were limited to the length of 200
mm away from the transverse frames to the outside on either sides. It is necessary to have such
an allowance to deal with tolerances and this way, it will be also convenient to join the girders
with the remaining structure during mounting of the module. The parts of the girders are cut
into half allowing the crossover pipe to be placed from above which otherwise wouldn’t be
possible at all.
4.4.4 Deck and Shell plates
The modified deck plates and the shell plates up to the length of the pipe are selected to be built
as module. These parts are also limited to a length of 200 mm away from the transverse frames.
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“EMSHIP” Erasmus Mundus Master Course, period of study September 2017 – February 2019
4.4.5 Stiffeners, brackets and docking profiles
All the stiffeners, brackets and shear plates associate mostly with the transverse plating and as
well as the deck and shell plate are selected to be pre-built as sub assembly with the
corresponding structure before being mounted as a module. The docking profile are also cut
200 mm away from the transverse frames in order to be built with the module.
4.5 Sub-assemblies
Before the construction of the module being started, the sub structures are built in the pre-
fabrication, so to say, as smaller modules. This way, the number of parts handled will be
reduced further while moving into the construction of bigger a module.
4.5.1 Crossover pipe
Since the pipe we are using is of a standard size, it is bought and then prepared for the modular
construction as a smaller and much simpler module by providing with the required holes, cut-
outs, flanges and fittings as shown in fig. (25).
The holes and cut-outs required for the inlet of sea water and suction pipes are cut out of the
pipe and the necessary flanges are weld with it. It is also possible to party pre-outfit the pipe,
i.e., to weld the pipe fittings for the suction pipes at this stage as the pipe is freely accessible
without any obstructions.
Figure 25. Crossover Pipe sub-assembly
Once the pre-fabrication is over, the pipe can also be coated with the anti-fouling paint already
in this stage leaving only a little space where the girders will be weld, which can be painted
later.
40 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
4.5.2 Longitudinals
The upper half of the longitudinal are also pre-fabricated with the stiffening belt to be welded
on top of them. It can also be welded as one single parts after completion of the mounting of
the module to avoid a little extra cutting work. However, in this case we will consider the pre-
fabrication of the upper half of the longitudinal girders as shown in fig (26), which can also
help on providing a horizontal surface for convenient placing on the jigs during the construction
of the module.
Figure 26. Sub-assemblies of parts of longitudinal girders
4.5.3 Transvers frames and floor plates
The transverse frames consist of additional stiffening and they are pre-fabricated to become
single components before being built as a module. These are the most important groups of sub-
assemblies since they involve in many different single components with different size scales.
Plate stiffeners, corner brackets and shear plates are weld together with the corresponding floor
plate.
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4.6 Construction of the module
The sub-assemblies discussed in the previous chapter along with the remaining selected parts
are constructed together to form a module. In this chapter we will have a look at the
construction of the module in steps for better understanding the procedure.
Each important step is presented with step drawings, which can help the workers picture the
procedure immediately to give the basic idea of how it can be done. In the step drawings, parts
indicated in a transparent manner are the ones which are placed first or welded/joint in the
previous step and the parts indicated orange in colour are the ones which are welded in the
current step.
Step-1
The construction of the module is done upside down, starting with a jig, on which initially, the
sub assembly of the upper half of the longitudinal girders will be placed. Then the horizontal
parts of the deck plate will be weld together with the upper half of the longitudinals as hown
in fig. (27). Also, the upper half of the additional support given to the crossover pipe and a
stiffener will also be weld on the deck plates.
Figure 27. Step 1 – Module building
42 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
Step-2
Now the crossover pipe is placed on the semi-circular cut-outs on the girders and the point of
contacts on either side of the girders can be weld easily. Later the inclined parts of the deck
plate are placed and can be welded with the girder as shown below in fig. (28).
Figure 28. Step 2 – Module building
Step-3
The next step involves in welding of the lower half of the longitudinal girders and the newly
added transverse floor plates below the crossover pipe as shown in fig. (29). This way there is
more than enough room around the connection points to be weld. However, this step can be
done in different ways to fit the workers convenient, which means changing the order of parts
being weld.
Figure 29. Step 3 – Module building
Modular design of cross flow channel through structural optimization 43
“EMSHIP” Erasmus Mundus Master Course, period of study September 2017 – February 2019
Step-4
In this step, the rest of the sub-assemblies of the transverse frames are placed and welded with
the module as shown in fig. (30). While the outer edges can be welded very easily, the inner
edges can also be welded conveniently, as there is free access for the workers around the
module and the module can also be tilted or rotated if necessary.
Figure 30. Step 4 – Module building
However, both of these steps 3 & 4 could be done in a combined manner with different
sequences to obtain different convenience of the workers. As an example, a group of structure
including a lower half of longitudinal girder and all three transverse frames attached to it can
be welded first which will follow with the next set of parts progressing from one end of the
crossover pipe to the other.
44 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
Step-5
Before placing the shell plate, the docking profiles are placed and welded together with the
transverse frames and the shear plates as shown in fig. (31).
Figure 31. Step 5 – Module building
Step-6
The final step is to place the shell plate and welding it with the module and is as shown below
in fig. (32).
Figure 32. Step 6 – Module building
Modular design of cross flow channel through structural optimization 45
“EMSHIP” Erasmus Mundus Master Course, period of study September 2017 – February 2019
It must be noted that at certain points, it can still be difficult to get access for welding of the
shell plate, especially with the longitudinal girder. However, there are alternate options like
plug welding or slot welding for those areas with limited space. Following fig. (33) can give
better understanding of the method.
Figure 33. Plug welding (a) and Slot welding (b)
In the case of our module, a weld backing which is a small plate strip of about 30-40 mm wide
can be welded along the bottom of the girders, as it might not have problems of accessibility.
On top of these backings, the shell plate with holes can be plug welded or a slot of 5-6 mm
between two shell plates can be filled to have a slot weld as shown in fig. (34).
Figure 34. Slot welding with weld backing on girder
Out of these two methods, slot welding is preferable over plug welding due to the effects of
stress flow through the material. In plug welding, the stress will tend to flow through the base
material regardless of the weld fill while in case of slot welding, there is a complete fill with
the weld material and the stress will flow straight regardless of the presence of backing.
Though it might be necessary to have special welding techniques even during a modular
construction, the required work is minimal compared to the advantages of accessibility
achieved though the module. In this case, the maximum length of above-mentioned special
welding jobs, which might require is only about 1.3 m, which is the distance between 2 frames.
46 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
5. Review of benefits and drawbacks
5.1 Optimized structure
The optimized structure itself poses certain benefits and drawbacks as well, which are
discussed in this chapter.
5.1.1 Functional benefits
As we discussed in the earlier chapter, there were certain requirements related to the function
of the crossover, which need to be achieved during its optimization. The optimized structure
did achieve those requirements giving certain advantages over the conventional structure of the
cross flow channel.
Flow velocity
The flow velocity up to 1.1 m/s can be achieved in the crossover pipe as it does not poses sharp
corners or edges. However, the suction pipes inserted inside needs to be considered. With high
flow velocity, it is possibly to achieve the required flow rate with minimal flow area, which
means that a further larger cross flow channel is unnecessary. High flow velocity also reduces
the risk of marine growth.
Reduced resistance
The conventional cross flow channel used to have a flow velocity of 0.5 m/s due to the
resistance caused by large number of structures and profiles inside of it. Since the new structure
has only a crossover pipe, resistance to flow is reduced even at high speeds. It is important to
make sure the water flow is not interrupted and is flowing continuously in the crossover and
being supplied to different machinery.
Reduction of air bubbles
As the crossover pipe is free from profiles and structures, the amount of air bubbles and air
cushion are reduced. It is important to make sure that the machinery which intakes water from
the crossover takes only water and not trapped-in air, which can damage or reduce the
efficiency of the machinery.
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Flow rate
As we discussed earlier, the flow rate is the important consideration and not the volume of
water. In this case, with such a large crossover pipe, it is possible to supply about 2000 m3/h
while reducing the volume of water being carried by about 90%. This possess certain other
advantages, which are discussed in the following chapter.
5.1.2 Operational Benefits
Reduced mud/sludge formation and marine growth
One of the most important requirement of the optimization was to reduced the mud/sludge
formation and marine growth on the corners and edges of the structures which are exposed to
sea water. As the optimized structure has only a pipe in which the seawater flows through, this
problem is reduced due to the smooth and curved walls with no corners. Higher flow velocity
is another factor that can help reduce the marine growth in the pipe.
Although this issue is reduced, it cannot be completely eliminated as there will still be marine
deposits as a crossover is a closed confined space with flow of sea water, those of which are
perfect environment for marine growth. To further reduce this problem, antifouling is done on
the walls which are exposed to sea water.
Reduced surface to avoid anti-fouling
Anti-fouling can further prevent marine growth on the structure. Considering the conventional
cross flow channel, anti-fouling can be a difficult task to complete with a more expense, as the
structure is complex and confined for work.
The conventional cross flow channel has a very large surface area of around 285m2 with a large
number of profiles placed inside the cross flow channel. Each of these plates, profiles, brackets
and every single structure inside the channel has to be coated with anti-fouling paint, which is
expensive and needs to be coated with 8 layers usually. The painting job can also be hectic, as
it is required to go into the double bottom to do the work. Each layer needs to be given time
for curing and that will also waste so much of time.
48 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
In the optimized structure, only a pipe is been used as the crossover and it will be the only
component, which is exposed to seawater. Hence, it would be sufficient to coat the inner surface
of the pipe with anti-fouling paint, which is only about 18 m2. It will also be much easier in
painting as the surface is smooth and curved. However, the rest of the structure must be painted
with anti-corrosive paint, but which is not so expensive and is effective with only two layers
of coating. According to a simple cost estimation, which is explained in the following chapter,
the total painting time can be reduced by 30% while the total expenses related to anti-fouling
painting is reduced by 62%.
Easy inspection and maintenance
This is the most important benefit that is achieved through the optimization of the structure.
The crossover pipe has openings on both ends, which can give access from either side. The
pipe is large enough to allow an average person inside, enabling easy inspection of the
crossover and maintenance work if necessary.
In addition, the crossover only being the pipe, which does not poses sharp corners or edges
makes it easier for the maintenance work to be carried out.
5.1.3 Structural & Production related benefits
Elimination of many structures and profiles
Due to the addition of the floor plate below the pipe and the additional support, a large number
of stiffening profiles and brackets are eliminated in the new structure which were present
initially. This can be an advantage as the fabrication of all of these structures and the
construction of work in the block assembly is eliminated. The material, cutting jobs and very
difficult welding jobs associated to those parts can save a lot of time and money, which is
further investigated with the cost analysis discussed in the following chapters.
Reduced stress concentration
The stress concentration in the edges of the cut-out on the girder have been reduced by a big
margin since the squared-shaped cut-out is changed into a circular one and hence the stress is
more evenly distributed. In addition, the pipe and the floor plate below together act as a girder
and increase the strength at that point.
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Space saved in double bottom
The initial cross flow channel was structured between about 4-5 frame spaces and had about
40 m3 in volume. The new structure however is limited between 2 frame spaces reducing the
volume to about 10 m3. We know that space in double bottom is highly valuable, but it depends
on the type of ships. On a merchant ship for example, the benefit is much more bigger because
there will be more space for the goods whereas on a mega yacht it depends extremely on the
situation. Hence depending on the requirement, this can also be an added advantage.
However, since the cross flow channel is now reduced only to a pipe, the volume of water
carried is reduced from 40 m3 to 4m3, which is 90% reduction. This reduces enormously the
issues of corrosion, sludge formation and marine growth and subsequently the antifouling and
maintenance work associated.
Reduced weight of antifouling paint
As we discussed earlier, the area to be painted with anti-fouling paint has been reduced due to
the reduction of the cross flow channel into a crossover pipe. The standard anti-fouling and
anti-corrosion paint used has surface densities of 0.75 kg/m2 and 0.2 kg/m2 respectively.
Considering the conventional cross flow channel, the weight of the paint itself will constitute
about 1.7 tons to the structure while the optimized cross flow channel will have about 220 kg
only. This is one of the biggest benefits as it compensates the added weight due to the addition
of pipe, floor plate and other supports.
50 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
5.1.4 Drawbacks or issues not resolved
There are a few drawbacks and some issues which still needs further study and investigation.
Extra cutting and welding
Though there is an advantage of elimination of a large number of parts and the corresponding
jobs, there is again addition of similar work due to the modified shape the structure, especially
the deck plate. Initially it was a flat deck plate but now it has to be knuckled and opened above
the pipe, which requires additional cutting and welding jobs. The crossover pipe can be bought
as it is a standard one but it still requires additional fittings and other preparations.
Air bubbles/cushions will still exist
Although the pipe does not has any profiles to interrupt the flow, air bubbles/cushions will still
exist due to suction pipes installed inside the crossover pipe. Standard reducers can be fixed at
the edge of the suction pipes to reduce turbulence as a remedy, but cannot eliminate the it
completely. However, this needs further investigation in terms of flow which is out of the scope
of this thesis work.
Additional suction pipe connections
Suction pipes should be installed into the cross flow channel to intake water for different
purposes. As we discussed in the earlier chapters, the conventional cross flow channel is
designed and built in such a way that, both forward and aft engine rooms will have a part of
the cross flow channel under the deck. This serves the need of seawater taken from suction
pipes from both of the engine rooms.
The area open to suction pipes is reduced by a large margin with the new crossover pipe, as it
is not a channel under the double bottom anymore. And in the present optimized design, the
crossover pipe is placed under the forward engine room and additional flaps and connections
need to be installed in order to reach it from the aft engine room.
A principle of alternate engine room arrangement is proposed as a remedy. That means, the
engine room bulkhead can be placed on the axis of the crossover pipe and hence suction pipes
from both of the engine rooms can be installed without needing to extra piping through
bulkheads. This again needs further strength investigations and additional piping would still be
feasible economically.
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5.1.5 Cost estimation for overall comparison of production
A simple cost analysis is carried out to identify the potential benefit in terms of material and
construction due to the optimization. The comparison is done between the structures eliminated
and the structures added and the major aspects considered in the cost estimation are the material
and labour cost in production.
The cost model includes the material cost, labour cost associated to the working hours including
difficult and easiest welding positions according to the part being constructed, time and
expense for placing parts or components and overheads. In addition, the anti-fouling paint and
the labour associated in painting is studied during the cost analysis, which changes the
comparison dramatically.
We studied earlier that a large number of stiffening profiles were eliminated in the process of
optimization. This saves a big part of the expenses in terms of material as well as labour
involved. However, the addition of the large crossover pipe and the new modified deck
arrangement plays a big role in the increased expenses in the new structure. Moreover, we
reach to a point where the expenses are almost neutral considering only the modification made.
The majority of the expenses saved comes from the anti-fouling paint and the painting work
associated. As we discussed earlier, only the crossover pipe needs to be coated with anti-fouling
paint and the rest only requires anti-corrosion. But the anti-fouling paint is expensive and
usually needs to be coated with 8 layers while the anti-corrosion needs only 2 layers of coating.
This saves a large part of the expense as the area of the cross flow channel is now reduced from
285 m2 to 18 m2 area of the crossover pipe which is about 93% reduction. Hence, only 18 m2
needs to be painted with anti-fouling paint which is the expensive one. In addition, the painting
work would become much easier as the surface needs to be painted is a curved interior of a
pipe and the rest being reduced to 2 layers of coating. Finally, by doing the cost analysis
considering these aspects we get an estimated reduction of about 62% in the expenses related.
Finally, we can identify from the obtained estimation that about 100 working hours have been
saved and we have achieved about 30% reduction in the overall expenses of material and labour
with the optimized structure. This can be a good starting point as we reach to a conclusion that
the optimized structure possess profit in terms of material and production while the other
advantages we discussed in the previous chapters especially the maintenance work, which
continues for years to come cannot be estimated properly until it becomes practical.
52 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
5.2 Modular construction
In this chapter, we will review about the benefits achieved through the modular construction
method of the cross flow channel and as well as the issues unresolved or problems raised due
to method followed.
5.2.1 Benefits achieved
Accessibility, Reachability and working conditions
One of the biggest problems during block construction is the accessibility to the working place.
In case of this module, the problem of going through groves or manholes carrying all the
equipment is eliminated. Concerning the reachability issues, it is now easily possible to reach
the point of work due to working with a module though the new cross flow channel has much
more complex structure.
Additionally, the time wastages due to human errors can be reduced since the workers are not
working inside complex structures. Talking about the same example we spoke earlier,
forgetting equipment or essentials wouldn’t waste so much time as they can easily pick it up
again and come back to work.
Welding position
One of the most important advantage is that the welding can be done always downwards.
Usually when the preliminary welding is done, a specially trained welding team comes in to
do the complete welding of all the joints with plates and profiles. This work can be done with
the most convenient position since the module can be rotated at any required angle. The errors
during welding can be reduced and a good quality weld can be expected.
Number of components
The number of components involves in the module are limited now and the construction is
relocated to the pre fabrication. This means that the time & expenses of transporting each &
every part to the block assembly and their storage & maintenance will be eliminated.
Meanwhile in the pre fabrication, there’s no need for storage as the number of parts are limited
and in addition, there will be minimal problem of missing parts or wastage of time in finding
the right one.
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Safe working conditions
The working condition is quite safe as there is no issue of ventilation or any other risks since
the workers are not working inside a double bottom in this case and in case of emergency, it is
easy to escape the facility.
Less overall process time
Since the module, which is a part of the block is now being relocated to the pre-fabrication, it
is possible to work in parallel with the block assembly. Which means that the module can be
built in the prefabrication while the block is being assembled. This can save time in the block
assembly, as the module is built in the prefabrication in a much easier way. The idle time of
the workers can also be reduced by distributing the work. This way, the overall process time
can be saved as well as the cost associated to it.
Possible pre-outfitting
To increase the advantage of modular construction, it is also possible to pre-outfit the module
of the cross flow channel. We know that the large crossover pipe should be installed with many
other smaller suction pipes. Hence those pipes can be pre-outfitted, welded and painted earlier
before the block assembly which can again save a large amount of time and money in the
outfitting work to be done later with difficult conditions.
Other benefits
There are few other benefits achieved such as;
Straightening the plates from welding distortion would become easier.
A better utilization of the cranes, which are capable to deal with up to 25t of weight as
well as the availability in prefabrication facility.
As we spoke about anti-fouling earlier, the painting job can be done much more easily
before the mounting of the module.
54 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
5.2.2 Drawbacks
Although a number of benefits are achieved through the modular construction, there are certain
disadvantages compared to the conventional construction method.
Extra cutting
Now that a part of the block is being built as a module, several parts and components has to be
cut to separate them which otherwise would have been one single part. The longitudinal girders,
deck and shell plates are such important parts, which need extra cutting due to being part of the
module. These are additional work compared to the conventional method.
As a remedy, the production process could be designed in such a way that, the plates and
profiles of the rest of the block can be standard sized and not cut due to the module. This may
reduce the extra cutting job a little but it cannot be completely eliminated.
Module mounting
After the module is built, it has to be mounted with the block either at the block assembly or at
the ship erection site. This is again a difficult job with concerns of tolerance issues especially
with girders. The module need to be given with extra material on one or both sides and mounted
very carefully to avoid misalignments. To avoid or reduce this problem, the module of the
crossflow channel can be built, placed first and then the construction of the rest of the block
can be started around it. However, the module-mounting job will result in additional expenses
compared to the conventional method.
Module handling and transportation
The module while being built and after needs very careful handling especially with the cranes.
Since the module is large and almost 10 tons heavy, a careless lifting may pose a risk of
permanent deformation in the structure.
Along with careful handling, transportation of the module is also a concern as it might require
additional lifting gear. Transportation of this large module will be an additional expense, which
wasn’t the case in the conventional method.
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5.2.3 Cost estimation of modular construction
A simple cost analysis is done to find out the benefits and drawback of modular construction.
It includes the time and expenses saved due to working with the module as well as the
additional cutting and module mounting expenses. The estimation of total labour time in
construction is done with consideration of the easiest welding positions in the module and as
well as the difficulties in the module mounting job.
We can see from the obtained results that there is some time saved in mounting and welding of
profiles and plates in the module rather than doing the same in the block assembly. Precisely,
around 20 hours of work can be saved in welding and 13 hours in mounting due to working in
a module with respect to this cross flow channel structure. However, there is extra labour
necessary for the mounting of the module and it has been estimated with quite a large number
of labour hours compared to the time saved due to the module. This result in extra work of
about 120 hours with a significant expense corresponding to it.
We have discussed about advantages in overall process time but evaluation of total process
time can only be found precisely after the implementation of the method. In addition, unlike
the previous cost analysis, this one does not have a comparison since this modified structure
have not been constructed before.
56 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
6. CONCLUTION
In this thesis work, we have seen the modular design and construction of the cross flow channel
and its structural optimization by taking advantage of modular design. Modular construction
has always been the favourite option for the workers in production and during the study of this
thesis, it is very highly recommended by them to build this particular structure as a module.
The biggest advantage of modular design and construction, which we utilised in this thesis, is
that we will get the opportunity to modify and optimize the structure to obtain certain
requirements or benefits, which were initially excluded to avoid complications in construction.
Combined with the structural optimization, the modular design has achieved plenty of benefits
with possibilities for more. Especially, in terms of functional and operational benefits achieved
through structural optimization could lay a foundation to the continuous benefits in years to
come through the life of the vessel.
We learned that the modular design of this cross flow channel structure brings slightly extra
expenses according to the simple cost analysis, which can suggest that it might not be
economically feasible. But keeping in mind that it would be much more complicated the other
way, the potential problems which are already been identified could be studied further for
remedies. However, if we consider both the cost analysis of optimization and modular
construction, we arrive almost at a neutral position. But the important aspect to be noted is that
these cost analysis are only in terms of material and labour in construction and we already
learned that there’s much more benefits been identified regardless of material production.
As the world moves towards high tech ship building processes, modularization can
revolutionize the way ships are built. As we spoke earlier, we could go for more complex
geometries by taking advantage of modular design. A well-planned, zone-oriented modular
design process can shorten the duration time and bring down costs.
Finally we can conclude that the modular design and construction of the cross flow channel is
been studied with its possible structural optimization and we have identified the potential
benefits as well as drawbacks while the purpose of this study is justified through the results
obtained.
Modular design of cross flow channel through structural optimization 57
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ACKNOWLEDGEMENTS
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.
The thesis topic was proposed by the EMship – SAB industrial partner Fr. Lürssen Werft
GmbH & Co. KG and the complete work is carried out at the their facility in Bremen, Germany
during the period of 1st of July to 10th of November.
I gladly acknowledge with grateful thanks the help, information, comments and encouragement
afforded to me by the following personnel in the shipyard:
My supervisor Tim Stockhausen, Atanas Atanasov, Joschua Fleck, Philipp Becker, and the
department head Mr. Heiko Buchholz from structural design department.
Uwe Meggars from basic design department, Anastasia Stobert from nesting department, Jan
Becker from estimation department, Micheal Kropp from machinery department, Rafael
Herdzina from Piping department, Max Pitschke from design standards, Hagen Niekamp from
prefabrication, Pascal Czytrich from block erection and Mate Konya & Sebastian Koop from
IT support.
A special thanks to Nicole Schenk for arranging this internship and making it possible along
with Prof. Robert Bronsart of University of Rostock.
58 Arrshan Sagaya Punithasegaran
Master Thesis developed at University of Rostock, Rostock
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