A STUDY ON VERY LARGE FLOATING STRUCTURES

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A BRIEF STUDY ON : VERY LARGE FLOATING STRUCTURES (VLFS) 2014
GUIDED BY : PROF.DR.P.PAVAN KUMAR 1
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Abstract:
In this report, introduction to the world of very large floating
structures (VLFS) that have been gradually appearing in the waters
off developed coastal cities (and countries with coastlines). Their
presence is largely due to a severe shortage of land and the sky-
rocketing land costs in recent times. After providing a description of
a VLFS and highlighting its advantages (under certain conditions)
over the traditional land reclamation in creating space from the sea,
the authors bring to attention the early, the present and future
applications of VLFS.
The input design data, hydroelastic analysis and design
considerations for very large floating structures are discussed, albeit
in the most basic forms.

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CONTENT:TOPIC PAGE
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1 PURPOSE AND DEFINITIONS 3
2 INTRODUCTION 4-5
3 PROLOGUE 6-8
4 ADVANTAGES OF VLFS 9
5 APPLICATIONS OF VLFS 10-14
6 ANALYSIS AND DESIGN OF VLFS 15-16
7 DESIGN LOAD CONSIDERATIONS 16-18
8 UNIQUENESS OF VLFS 19-20
9 DESK STUDY 21-23
10 MATERIAL CONSIDERATIONS 24
11 TYPES OF FLOATING STRUCTURES 24-28
12 PERFORMANCE V/S ACCEPTENCE 29-35
13 LOW LYING AREAS 36
14 BIBLIOGRAPHY 37

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PURPOSE :
To provide design criteria for permanently moored floating buildings not
intended for navigational use and built on a floatation system.
DEFINITIONS :
ACCEPTABLE SOLUTION: means a solution which is deemed to
satisfy the performance criteria.
BUILDING WORK has the same meaning as the Building Act 1975.
FLOATING BUILDING means a permanently moored floating
building built on a flotation system and not intended for, or
useable in, navigation.
METACENTRE, in relation to a floating building, means the
intersection of the verticals through the centre of buoyancy of the
floating building when in equilibrium and when tilted.
METACENTRIC HEIGHT, in relation to a floating building, means
the distance between the centre of gravity and the metacentre.
FIRE AUTHORITY means the Fire Rescue Service.

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INTRODUCTION :
As population and urban development expand in
land-scare island countries (or countries with long coastlines), city planners and
engineers resort to land reclamation to ease the pressure on existing heavily-used
land and underground spaces. Using fill materials from seabed, hills, deep
underground excavations, and even construction debris, engineers are able to create
relatively vast and valuable land from the sea. Countries such as the Netherlands,
Singapore and Japan, have expanded their land areas significantly through aggressive
land reclamation programmes.
However, land reclamation has its limitation. It is suitable when the water depth is
shallow (less than 20 m). When the water depth is large and the seabed is extremely
soft, land reclamation is no longer cost effective or even feasible.
When faced with these natural conditions and environmental consequences, very
large floating structures may offer an attractive alternative solution for birthing land
from the sea. There are basically two types of very large floating structures (VLFSs),
namely the semisubmersible- type and the pontoon-type.
Semi-submersible type floating structures are raised above the sea level using
column tubes or ballast structural elements to minimize the effects of waves while
maintaining a constant buoyancy force. Thus they can reduce the waveinduced
motions and are therefore suitably deployed in high seas with large waves. Floating
oil drilling platforms used for drilling for and production of oil and gas are typical
examples of semi-submersible-type VLFSs. When these semi-submersibles are
attached to the seabed using vertical tethers with high pretension as provided by
additional buoyancy of the structure, they are referred to as tension-leg platforms.
In contrast, pontoon-type floating structures lie on the sea level like a giant plate
floating on water. Pontoon-type floating structures are suitable for use in only calm
waters, often inside a cove or a lagoon and near the shoreline. Large pontoon-type
floating structures have been termed Mega-Floats by Japanese engineers.

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As a general rule of thumb, Mega-Floats are floating structures with at
least one of its length dimensions greater than 60 m. a Mega-Float
system consists of a
(a) very large pontoon floating structure,
(b) mooring facility to keep the floating structure in place,
(c) an access bridge or floating road to get to the floating structure from shore,
(d) a breakwater (usually needed if the significant wave height is
greater than 4 m) for reducing wave forces impacting the floating structure.
Pontoon-type VLFSs are also known in the literature as mat-like VLFSs
because of their small draft in relation to the length dimensions. Very large
pontoon-type floating structure is often called Mega-Floats. As a rule, the
Mega-Float is a floating structure having at least one length dimension
greater than 60 meters. Horizontally large floating structures can be from
500 to 5000 meters in length and 100 to 1000 meters in width, while their
thickness can be of the order of about 2-10 meters.
Aircushion supported Mega-Floaters are mega floaters that are
supported by an air cushion

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WHAT ARE FLOATING STRUCTURES?
Very large floating structures (VLFSs) or, as some literature refers to them, very large
floating platforms (VLFPs) can be constructed to create floating
airports, bridges, breakwaters, piers and docks, storage facilities (for oil & natural gas),
wind and solar power plants, for military purposes, to create industrial space,
emergency bases, entertainment facilities (such as casinos), recreation parks, mobile
offshore structures and even for habitation. Currently, different concepts have been
proposed for building floating cities or huge living complexes.
PROLOGUE :
Japan is an island country with a total land area of 0.38 millionkm2. Of the land,
80% is mountainous and most human activities are concentrated on the plains
along the shoreline. Ocean space utilization has been a key issue for Japan. Until
the 20th century, reclamation of shallow waters has been the only technology
available to expand human activities onto the sea. Shipbuilding technology had
attracted the attention of architects in the late 1950s.
Architects had proposed the concept of ocean space utilization using a floating
structure. In the 1970s and 1980s, several concepts and designs of floating cities
were published. Following this trend, a floating airport was proposed for phase 1
construction of Kansai International Airport in 1973. The proposal was not
accepted but ever since, industry has started performing research on the very
large floating structure (VLFS) technology.
A major milestone was achieved by the formation of the Technological Research
Association of Megafloat (TRAM) in 1995. Megafloat is a concept of VLFS studied
by the association. The fundamental technologies of design and construction
were studied and established. Design guidelines were compiled that summarized
the research and a 4000-m airport was designed. Onsite experiments that used a
1000-m-long model were carried out to demonstrate the soundness of the
technology. A legal process of approval and the environmental impact was
investigated. In addition to this research by TRAM, additional projects were
planned.

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P‘OLOGUE CONTINUED ……
HISTORY : OF MEGAFLOAT RESEARCH IN JAPAN:
Shipbuilding technology had attracted the attention of Japanese
architects in the late 1950s, and there was movement in architecture and urban
design to utilize ocean space and expand human habitat onto the ocean [1]. The
floating city project started at the University of Hawaii in 1971. The Okinawa
International Ocean Exhibition was held in Japan in 1975. Aquapolis, was
constructed for this exhibition as a large semi-submersible unit of a floating city.
In the 1970s and 1980s, concepts and proposals of floating cities were published
A floating airport was proposed for both phase 1 and phase 2 construction of
Kansai International Airport in 1973 and 1994, the Kansai International Airport
and the concept of a floating structure proposed in 1973.
The proposal was not accepted but industry and academia had already started
research on this technology. The Japanese government decided to construct 10
national oil stockpiles, based on the lesson learned from the oil crises
experienced in 1973 and 1979.
Two of the 10 bases were selected to be on a floating base.
The Kamigoto oil stockpile was constructed at the Kamigoto island of Nagasaki in
1988 the Kamigoto oil stockpile. The oil stockpile consists of five floating oil
storage barges that measure 390m long, 97m wide, and 27.6m deep. The
Shirashima oil stockpile that has seven oil storage barges that measure 397m
long, 82m wide, and 25.1m deep, was constructed at Shirashima Island offshore
Fukuoka City in 1996.

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The TRAM was founded in 1995 and the research activities continued until 2001 [3–5].
Megafloat is a concept of VLFS studied by this association. The activities are divided into
two phases. The fundamental technologies of design and construction were investigated
and established. Design guidelines were compiled and legal aspects of Megafloat
construction in Japan was studied.
Onsite experiments that used both a 300-m-long phase 1 model and a 1000-m-long
phase 2 model were conducted to demonstrate the soundness of the technology. Take
off and landing experiments were conducted during phase 2. The association terminated
its formal activities in 2001, which were succeeded by the Shipbuilding Research Center
of Japa SRCJ , a d the Ship uilders’ Asso iatio of Japa pla ed a e ru a for the
Haneda International Airport. Some projects with small scale floating structures and
reused structures of phase 2 models were planned and put into practice.
History of VLFS in Japan :
1950s - Floating city concepts in architecture and urban design
1960s - Puppet dra a Hykkori Hyouta Ji a
1973– 1974 Proposal of floating airport for Kansai International Airport,
semi-submersible-type floating structure
1975 - Okinawa International Ocean Exhibition
1988- Kamigoto oil stockpile
390m97m27.6m5 units
1996 - Shirashima oil stockpile
397m82m25.1m8 units
1994 Proposal of floating runway for Kansai International Airport phase
2 construction,
pontoon-type floating structure
1995/5 Foundation of Technological Research Association of Megafloat
(TRAM)
1995–1996 TRAM phase1 experiment 300m60m
1997–2001 TRAM phase 2 experiment 1000m60–120m
Landing & take-off experiment
2001– R&D by shipbuilding research center

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ADVANTAGES OF VLFS :
These Mega-Floats have advantages over the traditional land reclamation
solution for space creation in the following respects:
• the are ost effe ti e he the ater depth is large ote that the ost of
imported sand for land reclamation in some countries has risen significantly
and it may come a time that sand may not be even available from
neighbouring countries),
• e iro e tal frie dl as the do ot da age the ari e e o-system, or silt-
up deep harbours or disrupt the tidal/ocean currents,
• the are eas a d fast to o stru t o po e ts a e ade at differe t
shipyards and then brought to the site for assembling) and therefore sea-space
can be speedily exploited.
• the a e easil re o ed if the sea spa e is eeded i future or e pa ded
(sincethey are of a modular form),
• the fa ilities a d stru tures o Mega-Floats are protected from seismic
shocks since they are inherently base isolated, they do not suffer from
differential settlement due to reclaimed soil consolidation,
• their positio s ith respe t to the ater surfa e are o sta t a d thus
facilitate small boats and ship to come alongside when used as piers and
berths.
• their lo atio i oastal aters pro ide s e i od of ater all arou d,
making themsuitable for developments associated with leisure and water sport
activities.
Breakwater Mooring Floating Structure Building Access

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Applications of VLFS
The first concept of VLFS that appeared in the modern world after the
industrial revolution was the Floating Island described by the 19th century French
novelist Jules Verne, one of the founders of science fiction. The first VLFS promoted
in earnest was the Armstrong Seadrome. It was proposed initially to enable airline
routes across the world's oceans (Armstrong, 1924). Its stability was demonstrated
in tank tests , and various other related platforms were promoted until Armstrong's
death in 1955 (Nelson, 2001).
Interest in utilising the space afforded by the seas surrounding a
nation, for purposes other than conventional shipping or ocean resource extraction,
has increased as coastal population densities have increased. Until the potential of
modern shipbuilding technology became apparent in the 1950s the only manner in
which this ocean space could be exploited on a large scale was through land
reclamation. This limited such exploitation to shallow regions of the continental
shelf. In 1950s architects were drawn to the idea of floating cities and such a
concept was demonstrated in part at the Okinawa International Ocean Exhibition in
1975 with a semi-submersible unit of such a city. In a similar manner, a floating
airport was proposed for the new Kansai International Airport in 1973. Since the
early 1970s the technology for very large floating structures has developed
continually, while changing societal needs have resulted in many different
applications of the technology being considered. For example, the 101.5 m x 60 m x
3 m floating fishing pier at Awaji Island.

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FLOATING ENTERTAINMENT FACILITIES:
As the waterfront and the sea appeal to the
general public, VLFSs have been constructed to house entertainment facilities with a
scenic 360 degrees view of the surrounding water body.
There is a very large Floating Island (130 m x 40 m x 5 m) at Onomichi, Hiroshima.
Designed to resemble the Parthenon of Greece, this amusement facility has a 3D
visual image theatre, an aquarium and a marina (see Fig. 7). Another floating
amusement facility is the Estrayer (128 m x 38 m), shaped like a ship, which is
moored at the leisure pier in Kure, Hiroshima Prefecture, Japan. The top deck is
used as an event plaza while its deck below houses a movie theatre, restaurants and
a game centre.
The first floating hotel in Australia was located at the Great Barrier Reef. It was built
in Singapore and is seven storey high, 90 m long and 27 m wide. In case of a
cyclone, one mooring end was disconnected and the wind would blow it around in a
circle after everyone has evacuated. The floating heliport, tennis courts and pool
may be disconnected and towed some distance from the hotel to ride out the
storm. After one year of operation, the hotel was towed to Ho-Chi-Minh, Vietnam.
It is now located in North Korea. Hong Kong boasts of having a famous floating
restaurant called Jumbo Restaurant.
In 1991, Japan built a floating restaurant (on a 24 m x 24 m x 3.2 m pontoon) in
Yokohoma. The pier, next to the restaurant, is also a floating structure. Very large
floating structures are also used as fishing piers.
For example, the 101.5 m x 60 m x 3 m floating fishing pier at Awaji Island.

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AIRPORTS
Proposals to use floating structures for take-off and landing of aircraft
ere first o sidered i the 9 s to e a le airli e routes a ross the orld’s
oceans. These concepts were investigated more seriously for military applications
by the US in the 1940s and a demonstration project was built and tested
successfully in 1943.
With vast improvements in technology having been made, a floating
airport was proposed for the new Kansai International Airport in Japan in 1973.
Although the initial phase was not built as a floating structure, interest in the
concept remains strong. This is perhaps the area of VLFS research that has received
the most attention, due in large part to the efforts of the Technological Research
Association of Mega-Float (TRAM) active in Japan from 1995 to 2001. This
association studied the fundamental design and construction needs for a floating
airport to be realised. Numerical analysis tools were developed alongside an
experimental programme that resulted in the construction of a 1000m technology
demonstrator. The regulatory regime and environmental impact of such structures
were also considered in depth and design guidelines produced. Although a floating
airport has yet to be approved for construction interest remains strong, as
evidenced by proposals for the extension to Haneda International Airport in Japan.

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MOBILE OFFSHORE BASE
In the post-Cold War era, with smaller-scale conflicts seen in geographically
disparate regions, the importance of strategic sealift is heightened. One solution
considered is that of a mobile offshore base (MOB), a very large floating structure
consisting of several elements that are maneuvered into position and then joined to
form a single base. From this base large fixed-wing aircraft and ocean-going ships
may support littoral combat operations from a secure position without reliance on
achieving political support in other nations. The US Navy supported a substantial
research effort throughout the 1990s to develop the design methodologies suitable
for this concept. This work focused on verifying suitable numerical methods and on
conducting experimental trials. A similar concept may be envisaged for a mobile
emergency rescue base to operate in support of humanitarian relief operations
worldwide. A fixed Sea Base Facility (SBF) was also considered as an alternative to
land reclamation for relocation of the US Marine Corps Station Futenma offshore
Okinawa, Japan.
OFFSHORE PORT FACILITIES
Just as a floating airport is an attractive proposition in regions where suitable land
close to urban centres is limited, so offshore port facilities are being considered.
Proposals have been produced for offshore container terminals to service large
ocean-going vessels and supply the immediate hinterland with feeder container
ships. It may also be beneficial to site termini for potentially hazardous vessels, such
as LNG carriers, offshore.
OFFSHORE STORAGE AND WASTE DISPOSAL
FACILITIES
The potential of a very large floating structure as a storage facility is demonstrated
i Japa here t o of the atio ’s te atio al oil sto kpile ases o sist of floati g
units, constructed in 1988 and 1996. In increasingly densely populated coastal
regions, the ability to site storage facilities (of any kind), together with waste
processing and treatment plants, out of sight of land is an attractive one and such a
facility may also incorporate power generation capability.

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MOBILE OFFSHORE BASE
ENERGY ISLANDS AND FOOD PRODUCTION
In an extension to merely generating power from waste disposal, an offshore facility
may be considered for siting a range of sustainable energy technologies. Depending
on the prevailing climate such a structure may include some, or all, of wind
turbines, wave power generators, tidal current turbines and ocean thermal energy
conversion units. Such a structure may also be a natural host to environmental
research activities and food production through aquaculture and marine biomass
plantations. Variations on this application of very large floating structure technology
are being actively considered in South Korea with plans to install a wind and current
turbine plant in the Yellow Sea within 5 years, together with proposed installations
from Japan, France, United Kingdom and USA.
HABITATS
As perhaps the original idea for a very large floating structure, it is perhaps
surprising that more plans for offshore floating cities have not been developed over
the years, although there are current proposals for offshore sports facilities and
theme parks in Japan and South Korea. However, with ever increasing pressure on
coastal zones from increasing urban populations and the threat of environmental
change, it is likely that such ideas will resurface in the coming years, taking
advantage of the technology already developed and providing impetus for future
research.

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ANALYSIS AND DESIGN OF VLFS:
The analysis and design of floating structures need to account for some special
Characteristics when compared to land-based structures namely:
• Horizontal forces due to waves are in general several times greater than the
(non-seismic) horizontal loads on land-based structures and the effect of such
loads depends upon how the structure is connected to the seafloor. It is
distinguished between a rigid and compliant connection. A rigid connection
virtually prevents the horizontal motion while a compliant mooring will allow
maximum horizontal motions of a floating structure of the order of the wave
amplitude.
• In framed, tower-like structures which are piled to the seafloor, the horizontal
wave forces produce extreme bending and overturning moments as the wave
forces act near the water surface. In this case the structure and the pile
system need to carry virtually all the vertical loads due to self-weight and
payload as well as the wave, wind and current loads.
• In a floating structure the static vertical self-weight and payloads are carried
by buoyancy. If a floating structure has got a compliant mooring system,
consisting for instance of catenary chain mooring lines, the horizontal wave
forces are balanced by inertia forces. Moreover, if the horizontal size of the
structure is larger than the wave length, the resultant horizontal forces will be
reduced due to the fact that wave forces on different structural parts will have
different phase (direction and size). The forces in the mooring system will then
be small relative to the total wave forces. The main purpose of the mooring
system is then to prevent drift-off due to steady current and wind forces as
well as possible steady and slow-drift wave forces which are usually more
than an order of magnitude less than the first order wave forces.
• A particular type of structural system, denoted tension-leg system, is
achieved if a highly pre-tensioned mooring system is applied. Additional
buoyancy is then required to ensure the pretension. If this mooring system
consists of vertical lines the system is still horizontally compliant but is
vertically quite stiff. Also, the mooring forces will increase due to the high
pretension and the vertical wave loading. If the mooring lines form an angle
with the vertical line, the horizontal stiffness and the forces increase.
However, a main disadvantage with this system is that it will be difficult to
design the system such that slack of leeward mooring lines are avoided. A
possible slack could be followed by a sudden increase in tension that involves
dynamic amplification and possible failure.

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• Sizing of the floating structure and its mooring system depends on its function
and also on the environmental conditions in terms of waves, current and
wind. The design may be dominated either by peak loading due to permanent
and variable loads or by fatigue strength due to cyclic wave loading. Moreover,
it is important to consider possible accidental events such as ship impacts and
ensure that the overall safety is not threatened by a possible progressive
failure induced by such damage.
• Unlike land-based constructions with their associated foundations poured in
place, very large floating structures are usually constructed at shore-based
building sites remote from the deepwater installation area and without
extensive preparation of the foundation. Each module must be capable of
floating so that they can be floated to the site and assembled in the sea.
• Owing to the corrosive sea environment, floating structures have to be
provided with a good corrosion protection system.
• Possible degradation due to corrosion or crack growth (fatigue) requires a
proper system for inspection, monitoring, maintenance and repair during use.
DESIGN LOAD CONSIDERATIONS :
In the design of VLFSs, the following loads must be considered:
Dead load, hydrostatic pressure (including buoyancy), live load, abnormal loads
(such as impact loads due to collision of ships with the floating structure), earth
pressure on mooring system such as dolphins, wind load, effects of waves
(including swell), effects of earthquakes (including dynamic water pressure), effects
of temperature change, effects of water current, effects of tidal change, effects of
seabed movement, effects of movements of bearings, snow load, effects of
tsunamis, effects of storm surges, ship waves, seaquake, brake load, erection load,
effects of drift ice and ice pressure, effects of drifting bodies, and effects of marine
growths (corrosion and friction).

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Design consideration of VLFS

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LOAD TYPES AND COMBINATIONS :
For each limit state that is relevant to a given structural
element/assembly, sub-system or system, all load types and load
combinations should be considered.
The following load types should be included in the design loop where
applicable:
a. Permanent or dead loads. Permanent loads include self-weight, weight of
connectors, fixed equipment, permanent ballast, etc.
b. Variable or live loads. Variable loads include weight of temporary/movable
equipment, people, cargo (dry and liquid), variable ballast (dry and liquid),
etc.
c. Frequent and Rare Environmental loads. Environmental loads can arise
from wind, current, waves and earthquakes. Frequent environmental load
represents annual maximum load, which is a random variable. Its nominal
value is its one year return period value. Rare environmental load represents
lifetime maximum load, which is a random variable; it is nominally its 100-
year return period value.
d. Operation loads. Operational loads include aircraft landing loads, crane
loads, berthing/docking loads, connection/ disconnection loads, etc.
e. Cyclic loads. Cyclic loads include repetitive components of environmental
and operational loads.
f. Accidental loads. Accidental loads include on-board explosions, fires, and
abrupt changes in buoyancy, inter-module collision, crash of aircraft,
grounding etc.
In addition, any load associated with construction, fabrication and installation
shall also be considered. Load combination schemes considered for the
structural design of the VLFS should include all significant sets of
simultaneously acting loads for each limit state under consideration.

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UNIQUENESS OF VLFS :
VLFS concepts such as MOB and Mega-Float are unique ocean structures
primarily because of unprecedented lengths and displacements that vary
between 103 and 104m and between 106 and 107 tons , respectively.
These values are at least one order magnitude longer and twice heavier
than existing floating structures. Profound challenges for engineers
follow from this. Different from a ship, which has evolved with
accumulation of experience and with progress in analysis technology, a
VLFS is an unprecedented floating structure not only in terms of size and
displacement but also in cost and design life, and 50 to 100 years,
respectively.
The following considerations characterize further the
uniqueness of VLFS.
(1) Large Size
VLFS is an unprecedented large and flexible floating structure.
Consequently, hydroelastic response becomes dominant and has
driven supporting research and development in global analytical
methods for VLFS. Global failure modes are key issues. To compensate
for lack of experience, a first principles approach has been a constant
theme. Evolutionary trial and error type development is not acceptable
because of huge socio-economic implications. It also follows that VLFS
technology must be averse to risk.
(2) Environment Condition
Physical environmental conditions in which a VLFS must operate may not
be simply considered spatially uniform in the sense that coherence of
environmental conditions such as wind, wave and current must be
considered. Conventional methods for describing environmental
conditions were in fact insufficient for the design of Mega-Float and
MOB.

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(3) Design and Analysis :
For purposes of global analysis, a ship is generally considered a
rigid structure and its response to wave loading is evaluated by solving a rigid
body hydrodynamics problem. A VLFS is considered an elastic structure
wherein interaction between elastic response and fluid response is considered.
Once external loading is resolved, internal force effects are evaluated in the
same manner as for a ship structure but accuracy is largely dependent on
modeling internal elastic and inertia forces at the local level. Many analysis
tools with different levels of modeling and complexities have been developed
for hydroelastic analysis in MOB project, Mega-Float project and related
researches. Innovative design methodology is desired in the presence of
uncertainty and risk engendered by VLFS. It is therefore considered reasonable
to pursue a probabilistic and risk based design approach.
(4) Connection at Sea :
A VLFS is assembled or constructed by joining base units
either with flexible or rigid connections. Mega-Float was constructed from
many pontoon base units welded together in largely protected waters at
sea. Control of thermal deformation and alignment of units were key issues
in the construction (Yamashita et al., 2003). In contrast to permanently
connecting base units with Mega-Float, base unit modules of MOB are
connected so as to provide for assembly/disassembly at sea. Strength and
fatigue of the intermodule connectors are key issues in the design of MOB
(5) Positioning
Station keeping of MOB is accomplished by DPS, and
positioning of Mega-Float is accomplished with dolphin moorings.
Reliability of the station keeping system is crucial to the operational
availability of MOB, and to the prevention of drifting, which is an
especially important global failure mode for Mega-Float. Mega-Float
mooring capacity and breakwater capacity are design tradeoffs, and
reliability with respect to seismic effects was extensively investigated

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THE FLOATING ECOPOLIS, otherwise known as the Lilypad, is a
model designed by Belgian architect Vincent Callebaut for future climatic
refugees. He proposed this model as a long-term solution to rising water level as
per the GIEC(Intergovernmental group on the evolution of the climate) forecast. It
is a self-sufficient amphibious city and satisfies the four challenges laid down by
the OECD (Organization for Economic Co-operation and Development in March
2008 namely, climate, biodiversity water and health
There are very few urban design solutions that address housing the
inevitable tide of displaced people that could arise as oceans swell under global
warming. Certainly none are as spectacular as this one. The Lilypad, by Vincent
Callebaut, is a concept for a completely self-sufficient floating city intended to
provide shelter for future climate change refugees. The intent of the concept itself
is laudable, but it is Calle aut’s phenomenal design that has captured our
imagination.
Biomimicry was clearly the inspiration behind the design. The
Lilypad, which was designed to look like a waterlily, is intended to be a zero
emission city afloat in the ocean. Through a number of technologies (solar,
wind, tidal, biomass), it is envisioned that the project would be able to not only
produ e it’s o e erg , ut e a le to process CO2 in the atmosphere and
absorb it into its titanium dioxide skin.
DESK STUDY

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Each of these floating cities are designed to hold approximately
around 50,000 people. A mixed terrain man-made landscape, provided by an
artificial lagoon and three ridges, create a diverse environment for the
inhabitants. Each Lilypad is intended to be either near a coast, or floating around
in the ocean, traveling from the equator to the northern seas, according to where
the gulf stream takes it.
DESIGN STAGES :
PLAN
ELEVATION
VIEW SECTION

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VIEWS:

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MATERIAL CONSIDERATIONS FOR
FLOATING BODY :
The materials used for the floating body may be steel, or concrete or
steel-concrete composite and the relevant specifications should be followed.
Since water-tightness of concrete is important to avoid or limit corrosion of the
reinforcement, either watertight concrete or offshore concrete should be used.
High-performance concrete containing fly ash and silica fume is most suitable for
floating structures. The effects of creep and shrinkage are considered only when
the pontoon are dry, and hence not considered once the pontoon are launched
in the sea. Steel used for floating structures shall satisfy the appropriate standard
specifications.
VARIOUS TYPES OF FLOATING STRUCTURES :
Type of design offshore platform subjects to water depth,
geology condition and cost effective solution. The various types of
offshore platform shown as below:
1. Fixed Steel Structure
2. Compliant Tower
3. Jack-up Platform
4. Concrete Gravity Base Structure
5. Tension Leg Platform (TLP)
6. Semi-submersible Vessel
7. Floating Production System
8. Spar Platform

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Fixed steel structures:
The traditional offshore structure consists of weld
steel, tubular framework or jacket to support the
topside facilities. Piles driven into the seafloor secure
the jacket. Modern design with bridge linked jackets
tending to favour a separate well head platform,
processing platform and accommodation platform due
to safety concern. The Fixed Steel Structures are
restricted to shallow water developments with water
deep about 1500 ft.
Compliant Tower :
Compliant towers are similar to fixed platforms in that
they have a steel tubular jacket that is used to support
the topside facilities. Unlike fixed platforms, compliant
towers yield to the water and wind movements in a
manner similar to floating structures. Like fixed platforms,
they are secured to the seafloor with piles. The jacket of a
compliant tower has smaller dimensions than those of a
fixed platform. Compliant towers are designed to sustain
significant lateral deflections and forces, and are typically
used in water depths ranging from 1,500 to 3,000 ft.
Jack-up Platform
The Jack-up Platform consists of a triangular shaped
(sometimes rectangular), box section barge fitted with
three (sometimes four) moveable legs which enable the
vessel to stand to the seabed in water depths of up to
approximately 120 m (400 ft).

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Concrete Gravity Base Structure :
The Concrete Gravity Base Structure have
been constructed using a base manufactured
from reinforced concrete. The design of base
includes void spaces or caissons to provided
the structure with a natural buoyancy which
will enable it to be floated to field
development location. Once on location the
void spaces are flooded on the seabed whilst
the topside modules are lifted into place. The
void spaces then used as storage
compartments for crude oil, or filled with
permanent iron ore ballast. The colossal
weight of concrete structures obviates the
need to install foundation piles, hence the
name gravity base structure.
Tension Leg Platform (TLP) :
A Tension Leg Platform (TLP) is a buoyant
platform held in place by a mooring system.
The TLP’s are si ilar to o e tio al fi ed
platforms except that the platform is
maintained on location through the use of
moorings held in tension by the buoyancy of
the hull. The mooring system is a set of
tension legs or tendons attached to the
platform and connected to a template or
foundation on the seafloor. The template is
held in place by piles driven into the
seafloor. This method dampens the vertical
motions of the platform, but allows for
horizontal movements. TLPs are used in
water depths from 1500 ft to 7000 ft.

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Semi-Submersible Vessel :
These platforms have twin hulls (columns
and pontoons) of sufficient buoyancy to
cause the structure to float, but of weight
sufficient to keep the structure upright.
Semi-submersible platforms can be
moved from place to place; can be
ballasted up or down by altering the
amount of flooding in buoyancy tanks;
they are generally anchored by
combinations of chain, wire rope and/or
polyester rope during drilling and/or
production operations, though they can
also be kept in place by the use of
dynamic positioning. Semi-submersibles
can be used in water depths from 200 to
10,000 feet.
Floating Production System :
Basically, Floating Production Systems are ideal solution for
•The field is small and marginal
•The field is isolated and an established pipeline infrastructure does not exist
•The field is located in very deep water where it would not be possible to install a
conventional fixed platform .
•A major advantage of FPSO lies in the fact that they can simply lift anchors and depart
to pastures new when oil production reaches a commercially unprofitable level.

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Spar Platform :
SPAR is a deep-draft floating caisson, which is a hollow cylindrical structure similar
to a very large buoy. Its four major systems are hull, moorings, topsides, and
risers. The spar relies on a traditional mooring system (that is, anchor-spread
mooring) to maintain its position. About 90 percent of the structure is underwater.
Historically, spars were used as marker buoys, for gathering oceanographic data,
and for oil storage. The spar design is now being used for drilling, production, or
both. The distinguishing feature of a spar is its deep-draft hull, which produces
very favourable motion characteristics compared to other floating concepts. Low
motions and a protected centre-well also provide an excellent configuration for
deepwater operations. Water depth capability has been stated by industry as
ranging up to 10,000 ft.
The upper section is compartmentalized around
a flooded centre-well containing the different type
of risers. This section provides the buoyancy for the
spar. The middle section is also flooded but can be
economically configured for oil storage.
The bottom section (keel) is compartmentalized to
provide buoyancy during transport and to contain
any field-installed, fixed ballast.
PROCESS

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PERFORMANCE VS ACCEPTANCE :

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LOW LYING AREAS : INDIA

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BIBLIOGRAPHY :
 Minimizing differential deflection in a pontoon-type,
very large floating structure via gill cells
 Technology in Sustainable Development -The floating City by
Jeroen Gout and Martijn van Loon
 VERY LARGE FLOATING STRUCTURES: APPLICATIONS, ANALYSIS
AND DESIGN by E. WATANABE, C.M. WANG, T. UTSUNOMIYA
and T. MOAN
 Overview of Megafloat: Concept, design criteria, analysis, and
design by Hideyuki Suzuki
 Wikipedia for extra information
 Google Search Engine
Presented by:
SAHANA J
10GAEA2027
VIII SEM, B-Arch UVCE

A STUDY ON VERY LARGE FLOATING STRUCTURES

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