PUBLIC INFORMATION SERIES


REPRESENTATIONAL PLANNING, ENGINEERING, ENVIRONMENTAL & TECHNOLOGY EXHIBITS
PRESENTATION 2015


VERY LARGE FLOATING STRUCTURES
[VLFS]
EXHIBITS

 


STUDY CREDIT

Very large floating structure(s) [VLFS] or, as some literature refers to them, very large floating platform(s) [VLFP]) 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.

VLFS for habitation could become reality sooner than one may expect. Currently, different concepts have been proposed for building floating cities or huge living complexes

Pontoon-type VLFS' 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.

San Diego International Offshore Airport VLFS Platform Studies TBNC OPLAT USA BP Graphics Credit.001

BUILT STRUCTURE

San Diego International Offshore Airport Platform VLFS  TBNC OPLAT Studies 2011San Diego Offshore International Airport Platform VLFS Studies BP TBNC OPLAT USA

VLFS SD California Offshore International Airport Platform Program TBNC 2011

 

Thunder Horse is the largest moored semisubmersible oil platform in the world, located in 1,920 metres [6,300 feet] of water in the Mississippi Canyon Block 778/822, Thunder Horse Oilfield, approximately one hundred fifty [150] miles [241 km] southeast of New Orleans, Louisiana in the Gulf of Mexico.

Construction cost was approximately one billion [ $ 1,000,000,000.] dollars US.

The facility is expected to operate for twenty-five [25] years producing approximately one billion [1,000,000,000] barrels of oil. At its peak, it is expected to process two hundred million [200mcf] cubic feet [5,700,000 m3] of natural gas and two hundred fifty thousand [250,000] barrels [40,000 m3] of oil equivalent per day.

The Thunder Horse Platform is owned by BP® [75%} and ExxonMobil® [25%], and operated by BP®.

The Hull Section was constructed by DSME in South Korea and was delivered in 2004 to Corpus Christi, Texas [birthplace of Tom Edgemon, CEO, OPLAT-USA] aboard MV Blue Marlin for site completion. Thunder Horse was completed at Kiewit Offshore services in nearby Ingleside, Texas, USA.

Daewoo's Shipbuilding and Marine Engineering Division Manufactured the Semisubmersible Hull and Drilling Rig for a floating production, drilling and Quarters [housing] {PDQ] Platform. Construction was completed at Okpo in Sou the Korea after Daewoo won a three hundred eighty million [$ 380,000,000.] dollar US contract for the work in November 2001.

The one hundred twenty thousand [120,000] deadweight ton hull was designed by GVA Consultants of Sweden, which Haliburton purchased from British Marine Technology.

The Thunder Horse hull is based on the four-leg semisubmersible design previously produced by GVA for the Visund Field in Norway.

In Morgan City, Louisiana J. Ray McDermott dedicated its complete facility site to build process topside modules for the Thunder Horse PDQ and for the three [3] spars for Altantis, Holstein and Mad Dog in a six hundred million [$ 600,000,000.] dollar US deal.

Some of the other major project contracts were awarded to Sulzer for pumps and to GE® [General Electric] for platform turbines. Kiewit Contractors, which previously provided construction managemental on the Hibernia gravity base structure, was responsible for heavy lift deck and hull integration on Thunder Horse while Heerema Marine Contractors installed the platform in 2005.

 

San Diego International Offshore Airport Platform Program Chevron City Platform Studies OPLAT by TBNC 2011
Posted October 21, 2010
Brett Clanton


Chevron Plans New Floating City

Chevron Corp. has approved a $7.5 billion project to develop two deep-water fields in the outer rim of the Gulf of Mexico, marking one of the oil and gas industry’s biggest investments ever in the U.S. offshore area and a big vote for the future of the region after the BP oil spill.

The decision on the Jack and St. Malo fields, which comes seven years after the first discovery there, sets in motion a sweeping effort to design and build a massive floating city about 280 miles southwest of New Orleans that is expected to produce its first barrels of crude oil in 2014.


It also represents a major step forward in a highly touted frontier region of the Gulf, which has been hailed as the biggest domestic discovery since Alaska’s Prudhoe Bay a generation ago.

But as Chevron’s project illustrates, there is nothing easy about operating in the remote area. Not only are the fields beneath 7,000 feet of water and as much as four additional miles below the sea floor, they are in ancient rock layers that are still not well understood by industry.

“This one, by and large, is going to be our biggest and most complex undertaking in our history in the U.S. Gulf of Mexico,” said Gary Luquette, the company’s chief of North American exploration and production, in an interview with the Houston Chronicle in advance of today’s official announcement.

To make the project feasible, Chevron and its partners are building a giant facility that will function as a single hub for the fields – located 25 miles apart – with the capacity to produce 170,000 barrels of crude oil per day and 42.5 million cubic feet of natural gas per day.

It will tie in production from three clusters of pumps and other equipment on the seafloor that will help suck oil and gas from the deep formations and send it to the platform above.

As such, it will closely resemble Shell’s Perdido hub, which in March became the first offshore facility to begin production in the ancient rock layers – deposited from 35 million to 65 million years ago – referred to by scientists as the Lower Tertiary trend.

 

 


TBNC Edgemon San Diego Region Offshore International Airport Platform VLFS Studies Royal utch Shell Group, Southern California USA
Updated May 22, 2011
http://oilleader.com


Shell eyes up deep-sea resources
with world’s first floating natural gas rig

Gas giant eschews Arctic oil rush to moor 500-metre, 600,000-tonne construction off Australian coast.

The world’s first floating natural gas platform is to be built by Royal Dutch Shell, opening up vast new areas of the deep seabed for gas exploration.

 

The massive platform, nearly half a kilometre long, will be the biggest floating offshore drilling structure in the world, weighing in at about 600,000 tonnes – equivalent to six aircraft carriers – and staffed by 110 people at a time. Five times more steel will be used in its construction than went into the Sydney Harbour Bridge. Shell would not say how much it is expected to cost, but the total cost of exploiting the company’s Australian off-shore oil fields, where it will be used, is likely to exceed $ 30bn.

It will take about five years to build, and is not expected to be fully operational before 2017.

Floating offshore gas platforms could be used to explore areas of the globe previously too remote for drilling. Companies are racing to discover offshore resources in deep water, as the world’s readily available stores of onshore and close-to-shore oil and gas have already been snapped up. Advances in technology and melting sea ice are also helping to allow oil and gas exploration in sensitive parts of the globe, such as the Arctic, where a scramble to claim the undersea resources is now under way.

Shell has no such plans yet, and will moor its new platform 200km out to sea off the coast of Australia at the Prelude gas field. The size of the Shell platform means it can only be used on large gas fields, as it would not be economically viable on smaller fields.

“Our innovative FLNG technology will allow us to develop offshore gasfields that otherwise would be too costly to develop,” said Malcolm Brinded, executive director, of Shell’s upstream international business. “Our decision to go ahead with this project is a true breakthrough for the LNG industry, giving it a significant boost to help meet the world’s growing demand for the cleanest-burning fossil fuel [and] help accelerate the development of gas resources.”

He said the company was seeking to develop more floating platform projects.

Ann Pickard, country chair of Shell in Australia, said the technology would be “a game-changer for the energy industry”.

Liquefied natural gas is a growing market as it is easier to transport. It is shrunk by about 600 times in the cooling process and can be transported before being turned back into a gas and used for power generation or heating, though it can also be used as a road fuel in specially adapted vehicles.

The floating platform, which Shell has now started to design in detail, will be built in South Korea. It will take gas from the Prelude field and liquefy it to -162C (-260F) on board, from where it will be removed by tankers and shipped to the rapidly growing LNG markets in Asia. Previously, gas had to be piped to onshore facilities to be liquefied.

The facility would be designed to withstand even the most severe cyclones, Shell said.

 

 

PROTOTYPICAL BALLAST COLUMN - SEMISUBMERSIBLE PLATFORM
REPRESENTATIONAL INTERIOR VIEW

San Diego Offshore International Airport Platform VLFS Ballast Systems Study OPLAT TBNC USA 2011
VLFS Ballast Interior View San Diego Offshore International Airport Platform TBNC OPLAT 2011 Studies

 

 

 

 


 

Representational Maritime Engineering Conceptual Studies

Jan van Kessel

Very Large Floating Structures, DELAT Mag.Van.Tech.DELFT, Huge Floating Structures OPLAT.USA Techincal Studies, Offshore Floating Airports, California USA TBNC-Edgemon Environmental Planners, Site Designers, Engineers, Tom Edgemon CA.CSLB

Visit Delta Publications @ Off Site Web Presence
www.delta.tudelft.nl

Imagine a runway at sea, a moored harbour or even a floating city.
PhD student Jan van Kessel calculated a way to make mega-floaters more resilient.


Jan van Kessel The Freedom Ship Maritime Engineering Image Credits OPLAT-USA Offshore International Airport Platform Program TBNC-Edgemon California USA Image Credit Edgemon Environmental Planners, Site Designers, Engineers, Construction Managers USA

The Freedom Ship is the most ambitious mega-floater thus far.
Image Credit: www.freedomship.com

Jan van Kessel Discussion

Like so many other technical novelties, mega-floaters or floating islands were first described by Jules Verne in his 1895 novel ‘L’ile à hélice’ (or ‘Propelled island’). Fast-forward a century and the same dream is now called 'Freedom Ship', whose website describes a floating city that dwarfs the Queen Mary. The structure would be 1.5 kilometres long, 250 metres wide and more than 100 metres high. It would house hotels, shopping malls and leisure facilities, all topped by a small landing strip.

Enough of dreams, for floating superstructures have already been built. The largest so far was a kilometre-long floating airstrip in Tokyo Bay. At 149 million dollars, it was a costly experiment to see how well a floating airstrip would perform. Experiments performed after its completion in 1999 showed that there were no significant differences between a land-based runway and a floating one. Quod erat demonstrandum. Afterwards, this structure was dismantled and parts of it are still in use as car parks, fishing piers, fair grounds and an information centre.

 

PhD student, Jan van Kessel (cum laude Maritime Engineering, 2004), thinks that thus far mega-floaters have been rather conventional. He points out that breakwaters have always sheltered large floating structures from the waves.  In his thesis, entitled ‘Aircushion supported Mega-Floaters’, he presents and calculates another form of floating entirely. Not an immense barge, but rather a bottomless box, floating on a ‘cushion’ of encapsulated air. Think of a shoebox without its lid, turned upside down and placed in the water.  Van Kessel shows that the forces on a floating shoebox structure are about half of those on a conventional closed barge. Besides, he argues, the use of aircushions to make things float offshore isn’t new. Forty years ago, gigantic oil storage tanks in Dubai were constructed on land, lifted by pressurised air and towed to their offshore locations, eventually sinking on the spot.

In his thesis Van Kessel develops a method to calculate the dynamic behaviour of mega-floaters in waves. His numerical model calculates how the waves pass under the floating structure and how the air pressure varies. He then compares the outcome of the calculations with tank tests using a bottomless barge measuring 2.5 by 0.7 metres, and concludes there is a fitting correspondence between theory and test. What’s more, the aircushion-supported barge performs better than a conventional closed box. The roll and pitch motions are smaller (the waves can pass more freely underneath the structure) and the wave-induced bending motions are halved.

Ships are assumed to be stiff by conventional hydromechanics, and incapable of being deformed by wave-induced forces. But mega-floaters are so large that one can no longer assume that the whole structure will retain its form. Van Kessel therefore repeated his calculations for a flexible barge - a box that could bend with the waves. With an impressive array of matrices, summations and numerical hydroelastic calculations, Van Kessel shows that aircushions reduce the vertical bending of the structure (in comparison with a closed structure), but they also move the spots of the highest bending from mid-ship towards stern and bow. The torsion of the (flexible) structure caused by incoming oblique waves may be too large, but – according to Van Kessel – that can easily be fixed by adapting the design.

Now let’s get practical. The most logical mega-floating structure needed in the near future is an offshore airstrip, Van Kessel argues. At 3800 metres, its runway would be as long as Schiphol’s longest runway. The most plausible place for this airstrip would be off the coast of Singapore, since it is a densely populated city-state that has little else to extend to other than the seas. Taking the local wave regime into consideration, Van Kessel shows once more that the bending moments on the structure in the open seas would be reduced by two thirds if the builders would simply leave out the bottom of the barge.

 

Very Large Floating Structures, DELAT Mag.Van.Tech.DELFT, Huge Floating Structures OPLAT.USA Techincal Studies, Offshore Floating Airports, California USA TBNC-Edgemon Environmental Planners, Site Designers, Engineers, Tom Edgemon CA.CSLB

Visit Delta Publications @ Off Site Web Presence
www.delta.tudelft.nl

 

Vessel Plate Steel San Diego Offshore International Airport Platform Program 2011

 

 

OPLAT INTERNATIONAL OFFSHORE AIRPORT PLATFORM TECHNICAL STUDIES  ·  VERY LARGE FLOATING STRUCTURES

Brief Study Excerpts

NUS OPLAT-USA VLFS Technical Studies. Oplat-Usa TBNC Edgemon Environmental Studies, Environmental Planning Tom Edgemon CSLB 274107 California International Offshore Airport Platform, Edgemon Construction Management AEIS 2016 Edgemon, Carlsbad, California

A TECHNICAL DISCUSSION

E. Watanabe, C.M. Wang, T. Utsunomiya and T. Moan

Department of Civil and Earth Resources Engineering,
Kyoto University , Kyoto 606-8501, Japan

Centre for Offshore Research and Engineering, Department of Civil Engineering
National University of Singapore,Kent Ridge 119260, Singapore

Centre for Ships and Ocean Structures,
The Norwegian University of Science and Technology, NO-7491
Trondheim, Norway

 

Abstract – In this report, structural and civil engineers are introduced 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 fr om 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 [vlfs] are discussed, albeit in the most basic forms.

 

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. Probably the first large scale and systematic land reclamation work was carried out by Kiyomori Taira off Kobe's coastal waters in the 12th Century. 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. Moreover, land reclamation destroys the marine habitat and may even lead to the disturbance of toxic sediments. 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 semi-submersible-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 wave-induced 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 floatistructures 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. 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, and (d) a breakwater [usually needed if the significant wave height is greater than 4 m] for reducing wave forces impacting the floating structure.

 

These Mega-Floats have advantages over the traditional land reclamation solution for space creation in the following respects:

ST.08.01

They are cost effective when the water depth is large [note that the cost 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].

ST.08.02

Environmental friendly as they do not damage the marine ecosystem, or silt-up deep harbours or disrupt the tidal / ocean currents.

ST.08.03

They are easy and fast to construct [components may be made at different shipyards and then brought to the site for assembling] and therefore sea-space can be speedily exploited.

ST.08.04

They can be easily removed [if the sea space is needed in future] or expanded [since they are of a modular form].

ST.08.05

The facilities and structures on Mega-Floats are protected from seismic shocks since they are inherently base isolated.

ST.08.06

They do not suffer from differential settlement due to reclaimed soil consolidation.

ST.08.07

Their positions with respect to the water surface are constant and thus facilitate small boats and ship to come alongside when used as piers and berths.

ST.08.08

Their location in coastal waters provide scenic body of water all around, making them suitable for developments associated with leisure and water sports.

 

 

NUS.14 Study Discussion 01:   FLOATING ENTERTAINMENT & DINING 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. 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 locate d 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.

Oplat-Usa NAU Techbical Studies Floating VLFS Resatuarants & man Made Islands, Proof of Concept Edgemon Environmental Planners, Site Designers, Engineers & Construction Managers, Tom Edgemon CSLB 274107 Carlsbad, California Offshore International Airport Platform USA

Study Exhibit NUS.14.01 TBNC OA.112.016
FLOATING ISLAND @ ONOMICHI
Hiroshima  ·  Japan

Study Exhibit NUS.14.01 TBNC OA.112.033
FLOATING RESTAURANT
Yokohama ·  Japan


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 Yokohama. 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.

 

 

NUS.14 Study Discussion 02: FLOATING LIQUID STORAGE FACILITIES

Very large floating structures have been use d for storing fuel. Constructed like flat tankers [box-shaped] parked side by side, they form an ideal oil storage facility, keeping the explosive, inflammable fluid from populated areas on land.

Japan has two major floating oil storage systems. One oil storage facility is located in Shirashima with a capacity of 5.6 million kilolitres while the other is at Kamigoto with a capacity of 4.4 million kilolitres.

 

NAU Technical Studies, Offshore VLFS [Very Large Floating Structures] Opal-Usa Offshore International Airport Platform San Diego Region, California USA Edgemon Environmental Planners, Site Designers, Engineers & Constructuion Managers, San Diego, California USA Edgemon CSLB 274107

Study Exhibit NUS.14.01 TBNC OA.112.053
SHIRASHIMA FLOATING OIL STORAGE BASE
Japan

Study Exhibit NUS.14.01 TBNC OA.112.060
KAMIGOTO FLOATING OIL STORAGE BASE
Nagasaki Prefecture  ·   Japan

Image Left  Credits Shirashima Oil Storage Co., Ltd.

 

 

NUS.14 Study Discussion 03: FLOATING EMERGENCY BASES

As floating structures are inherently base isolated from earthquakes, they are ideal for applications as floating emergency rescue  bases in earthquake prone countries. Japan has a number of such floating rescue bases parked in the Tokyo Bay, Ise Bay and Osaka Bay.

NUS Japan VLFS Technical Studies Opal-Usa 2014 Offshore International Airport Platform Program, Southern California USA TBNC-Edgemon Environmental Planners, Site Designers, Engineers, Construction Managers Tom Edgemon CSLB 274107

Study Exhibit NUS.14.01 TBNC OA.112.060
EMERGENCY RESCUE BASE
Tokyo Bay

Study Exhibit NUS.14.01 TBNC OA.112.064
EMERGENCY RESCUE BASE
Osaka Bay

 

NUS Japan VLFS Technical Studies Opat-Usa Offshore International Airport Platform Program, California USA TBNC-Edgemon Environmental Planners, Site Designers, Engineers& Construction Managers Tom Edgemon CSLB 274107 Opat AEIS 2015
Study Exhibit NUS.14.01 TBNC OA.64.010
EMERGENCY RESCUE BASES JAPAN

 

 

NUS.14 Study Discussion 04: FLOATING PRODUCTION & MANUFACTURING PLANTS

A floating structure consisting of two sections was constructed in 1978 in Brazil. One section of the structure is built for a pulp plant [230 m x 45 m x 14.5 m] while the other section is for a power plant [220 m x 45 m x 14.5 m]. It was towed to its site at Munguba as a floating structure but was installed in its location on piled foundations.

In 1979, Bangladesh purchased from Japan a 60.4 m x 46.6 m x 4 m floating power plant. The power plant is located at Khulna, Bangladesh.

In 1981, Saudi Arabia built a 70 m x 40 m x 20.5 m floating desalination plant and towed to its site where it was sunk into position and rests on the seabed.

In 1981, Argentina constructed a 89 m x 22.5 m x 6 m floating polyethylene plant at Bahia Blance.

In 1985, Jamaica acquired a 45 m x 30.4 m x 10 m floating power plant. This plant was built in Japanese shipyards and towed to Jamaica and moored by a dolphin-rubber fender system. Studies are already underway to use floating structures for wind farms, sewage treatment plant and power plant in Japan.

 

 

NUS.14 Study Discussion 05: FLOATING DOCKS, PIERS, BERTHS & CONTAINER TERMINALS

There are in existence many floating docks, piers and wharves. For example, the 124 m x 109 m floating dock in Texas Shipyard built by Bethlehem Marine Construction Group in 1985.

Floating structures are ideal for piers and wharves as the ships can come alongside them since their positions are constant with respect to the waterline. An example of a floating pier is the one located at Ujina Port, Hiroshima. The floating pier is 150 m x 30 m x 4m.

Vancouver, Canada has also a floating pier designed for car ferries. Car ferry piers must allow smooth loading and unloading of cars and the equal tidal rise and fall of the pier and ferries is indeed advantageous for this purpose. A floating type pier was also designed for berthing the 50,000 ton container ships at Valdez, Alaska . The floating structure was adopted due to the great water depth.

 

NAU Technical Studies VLFS Floating Piers Methodologies, Opalt-Usa Offshore International Airport Platform Near San Diego, California Oplat-Usa Tom Edgemon Environmental Planners, Site Designers, Engineers & Construction Managers Tom Edgemon CSLB 274107 California USA
Study Exhibit NUS.14.01 TBNC OA.112.012
FLOATING PIER
Ujina  ·   Japan

 

 

NUS.14 Study Discussion 06: FLOATING AIRPORTS & MOBILE OFFSHORE BASES

In circa 1920, Edward Armstrong proposed the concept of a seadrome [an aerodrome in the sea] as stepping stones for aircrafts flying across the oceans. At that time, the planes could not travel long distances and needed refueling. I

n 1943, US Navy Civil Engineers Corps constructed a floating airfield [1810 ft x 272 ft] consisting of 10,920 pontoons. It has a flight deck and a parking area. However, the enthusiasm for building these floating airfields was dampened by the extraordinary non-stop flight of Charles Lindbergh from New York to Paris in 1927.

In more recent times, a different sort of problem arose. Land costs in major cities have risen considerably and city planners are considering the possibility of using the coastal waters for urban developments including having floating airports. As the sea and the land near the water edge is usually flat, landings and take-offs of aircrafts are safer. In this respect, Canada has a floating heliport in a small bay in Vancouver. Moreover, this busy traffic heliport is built for convenience as well as noise attenuation.

Japan has made great progress by constructing a large airport in the sea. Kansai International Airport at Osaka is an example of an airport constructed in the sea, albeit on a reclaimed island. The first sizeable floating runway is the one-km long Mega-Float test model built in 1998 in the Tokyo bay. This floating runway was awarded the world's largest man-made floating island in the Guinness book of records in 1999. Studies on the test model include the investigation of facilities and equipment for floating airport, development of simulation technology of functions of airport, instruments for landing, landing and taking off tests on a floating runway, effects on the environment and verification of construction technologies of a floating airport.

The Mega-Float is a precursor to a 3.6-km floating runway which will augment Haneda airport facilities. The decision to proceed building this ultra-large floating Haneda runway will be known by the March 2005.

 

NUS Japan Technical Journal Studies, VLFS Offshore Airports, Oplat-Usa San Diego, California Regiona Offshore International Airport Platform Program, California USA TBNC-Edgemon Environmental Planners, Site Designers, Engineers & Construction Managers Tom Edgemon CSLB 274107 San Diego, California USA

Study Exhibit NUS.14.01 TBNC OA.112.011
MEGA-LOAT IN TOKYO BAY
Tokyo  ·  Japan

Study Exhibit NUS.14.01 TBNC OA.112.029
PROPOSED FLOATING RUNWAY @ HANEDA
Tokyo  ·  Japan

Image Left Credits SRCJ

The Office of Naval Research, US, has been conducting studies on the technical feasibility and costs of building a mobile offshore base. A mobile offshore base is a self-propelled, modular, floating platform that could be assembled into lengths on the order of one mile to provide logistic support of US military operations where fixed bases are not available. We may be seeing these huge mobile offshore bases in the oceans in the future.

 


NUS.14 Study Discussion 07: FLOATING CITIES

Perhaps in this 21st Century, floating cities may become a reality with the advancing technology in construction and the shortage of land. Architects and engineers have already made design sketches of how such floating cities could look like. Many artist impressions of some floating cities are being proposed by various Japanese corporations.

 

 

ANALYSIS AND DESIGN OF VERY LARGE FLOATING STRUCTURES
[VLFS]

 

NUS.14 Study Discussion 08: DESIGN & ENGINEERING CONSIDERATIONS FOR VERY LARGE FLOATING STRUCTURES [VLFS]

The analysis and design of floating structures need to account for some special characteristics [Clauss et al. 1992, Moan 2004] when compared to land-based structures, namely:

ST.12.01

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.

ST.12.02

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.

ST.12.03

In a floating structure the static vertical selfweight 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 magnitud e less than the first order wave forces.

ST.12.04

A particular type of structural system, denoted tension-leg system, is achieved if a highly pretensioned 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 for forces will increase due to the high pretension and the vertical wave loading. If the mooring lines form an angtical 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. For this reason such systems have never been implemented for offshore structures.

ST.12.05

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.

ST.12.06

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.

ST.12.07

Owing to the corrosive sea environment, floating structures have to be provided with a good corrosion protection system.

ST.12.08

Possible degradation due to corrosion or crack growth (fatigue) requires a proper system for inspection, monitoring, maintenance and repair during use.


 

NUS.14 Study Discussion 09: LOADS & LOADS EFFECT DESIGN ASSOCIATED WITH VLFS

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).

 

 

NUS.14 Study Discussion 10: BUOYANCY, WAVES, CURRENTS & WINDS ASSOCIATED WITH VLFS

The buoyancy is computed by the integration of hydrostatic pressure. The specific weight of seawater may be taken to be 10.09 kN/m
3 or 1.03 t/m 3 . In the design of very large pontoon floating structures, the change in water level due to tide, tsunami and storm surge may dominate the design loads when the structure is designed with a fixed vertical position relative to the seafloor. Since the point of action of buoyancy depends on the tide and water level, the most unfavourable case will be considered.

Surface water waves may be generated by wind, tidal bore, earthquakes or landslides. The focus here is an oscillatory wind-generated surface waves. Waves developed in an area may endure after the wind cease and propagate to another area; as swell with decaying intensity and slowly changing form. Long period swell travels a very long distance as long-crested waves.

Wind-generated waves consist of a large number of wavelets of different heights, periods and directions superimposed on one another. Although regular waves are not found in real seas they can closely model some swell conditions. They also provide the basic components in irregular waves and are commonly used to establish wave conditions for design. Regular waves are characterised by the wave period and height.

The kinematics and hydrodynamic pressure within a regular wave are described by the wave potential as described subsequently.

During a suitably short period of time [from half an hour to some hours] the sea surface elevation, is commonly assumed to be a zero-mean, stationary and ergodic Gaussian process [e.g. Kinsman, 1965]. The Gaussian process is completely specified in terms of the wave spectral density for long-crested waves.

In the time domain the wave elevation may be described by a sum of long-crested waves specified by linear theory, with different amplitudes, frequencies and phase angles which are uniformly distributed over time.

NUS Japan, Very Large Floating Structures VLFS Oplat-Usa Offshore International Airport Platform California USA, TBNC-Edgemon Environmental Planners, Site Designers, Engineers & Construction Managers Tom Edgemon CSLB 274107 San Diego, California USA

The Amplitude May be Expressed by the Wave Spectrum

According to the linear wave theory, the wave kinematics in irregular waves is obtained by superimposing the kinematics of the regular waves constituting the irregular sea. Various analytical formulations for the wave spectrum are applied as parameterized by the significant wave height and period as well as possible other parameters. The significant wave height [i.e. the average wave height of the highest one -third of all waves] and the peak period or significant wave period [i.e. the average wave period of the highest one-third of all waves] are used to define the wave spectrum.

In developing seas the JONSWAP spectrum [Hasselman et al., 1973] is recommended and frequently used. Based on hindcasting Nagai et al. [1990] established data for JONSWAP wave spectra for the Tokyo Bay.

For fully developed seas, the Pierson-Moskowitz spectrum is relevant. Wind sea and swell have different peak periods and a combined sea state may have a two-peaked spectrum, as proposed e.g. by Torsethaugen [1996]. It should be noted that much of the wave energy is concentrated in a narrow frequency band close to the peak(s) of the spectrum.

Moreover there is a significant difference in the spectral amplitudes for high frequencies, implied by different models. The variation of the sea state in a long-term period, i.e. of some years duration, can be described as a sequence of short-term sea states, each completely described by the spectral density. For a given analytical model of the spectrum [JONSWAP, Pierson-Moskowitz], the spectral parameters, etc. completely specify the sea state.

 

By expressing the magnitude of these parameters and direction in probabilistic measures, the long term process is described. For extra tropical regions, like the North Sea, the joint probability density of the parameters is applied towards this aim [see e.g. ISSC, 1973]. For tropical areas subjected to hurricanes, the long-term wave climate described by storms arriving in a sequence may be used [e.g. Jahns and Wheeler, 1972].

Data for the long-term model of the waves can be generated (i) by direct observation of wave condition; (II) hindcasting based on wind data. In addition to wave conditions, current and wind need to be characterized. Besides generating waves, the wind generates a surface current as well as contribute to wind loads. These effects of the wind depend on its velocity, direction and duration, the coastline topography and the depth of the sea. The design wind speed may be variable.

The current velocity, in general, is composed of two components, namely, wind driven and tide driven components. In addition, coastal and ocean currents may occur. Also, eddy currents, currents generated over steep slopes, currents caused by storm surge and internal waves, should be considered. Very little information about their surface velocity and velocity distribution is generally available and measurements are necessary.

The long-term model of wave, wind and current conditions form the basis for identifying the relevant environmental conditions for determining loads for design. In case of design for ultimate strength, the sea loads with an average occurrence period of, say, 100 years or an annual exceedance probability of 10-2 is relevant. The wave load pattern may be described by a relevant sea state or even a representative regular wave. When significant structural dynamics effects influence the wave load effects, design based on a sea state rather than a [calibrated] regular wave should be used. Load effects for fatigue analysis should be determined by considering all sea states that might be experienced by the structure.

 

 

NUS.14 Study Discussion 11: BASIC ASSUMPTIONS, EQUATIONS & BOUNDARY CONDITIONS FOR HYDROELASTIC ANALYSIS

The fluid-structure system and the coordinate system are expanded in Case Study TBNC.OPLAT.12, Revision 06. The origin of the coordinate system is on the undisturbed free surface. The axis is pointing upwards, and the sea-bed is assumed to be flat.

The VLFS has a maximum length of 2 in the x direction, a maximum width of 2 in the y direction, and a draft d in the z direction.

The problem at hand is to determine the response of the VLFS under the action of wave forces. In a basic hydroelastic analysis of pontoon-type VLFSs, the following assumptions are usually made:

ST.14.01

The VLFS is modeled as an elastic [isotropic/orthotropic] thin plate with free edges

ST.14.02

The fluid is incompressible, inviscid and its motion is irrotational so that a velocity potential exists.

ST.14.03

The amplitude of the incident wave and the motions of the VLFS are both small and only the vertical motion of the structure is considered [i.e. we constrained the plate from moving horizontally in the analysis].

ST.14.04

There are no gaps between the VL FS and the free fluid surface.

 

The analysis may be carried out in the frequency domain or in the time domain.

Most hydroelastic analyses are carried out in the frequency-domain, being the simpler of the two. However, for transient responses and for nonlinear equations of motion due to the effects of a mooring system or nonlinear wave [as in a severe wave condition], it is necessary to perform the analysis in the time-domain.

 

 

NUS.14 Study Discussion 12: FREQUENCY-DOMAIN ANALYSIS ASSOCIATED WITH VERY LARGE FLOATING STRUCTURES [VLFS]

Considering time-harmonic motions with the complex time dependence being applied to all first-order oscillatory quantities, where represents the imaginary unit, the time, the complex velocity potential is governed by the Laplace's equation in the fluid domain.

The velocity potential must satisfy the boundary conditions on the free surface, on the sea-bed, and on the wetted surfaces of the floating body, [bottom surface] and [side surface]:

ST.11.01

The vertical complex displacement of the plate, expanded discovery on file.

ST.11.02

The draft of the floating structure, expanded discovery on file.

ST.11.03

The gravitational acceleration, expanded discovery on file.

ST.11.04

The unit normal vector pointing from the fluid domain into the body. The radiation condition for the scattering and radiation potential is also applied at infinity, where is the radial coordinate measured from the centre of the VLFS, the wave number that obeys the dispersion relation for a finite water depth and the potential representing the undisturbed incident wave and it is given;
A:   is the amplitude of the incident wave [obtained from the wave spectrum for a given frequency or period]
B:   the angle of incident wave, assuming the VLFS as an elastic, isotropic, thin plate, the motion of the floating body is governed by the equation of a thin plate resting on a uniform elastic foundation.

ST.11.05

The floating body, with no constraints in the vertical direction along its edges, must satisfy the zero effective shear force and zero bending moment conditions for a free edge, with the normal and tangential directions and modal expansion method and the direct method

ST.11.06

In the modal expansion method the interaction problem of the fluid motion and the plate response [given by Eqs. (8) and (9)] is decoupled into a hydrodynamic problem in terms of the velocity potential and the mechanical problem of a freely vibrating plate with free where is the amplitude of the velocity and these amplitudes are the unknowns that are to be determined.

 

For the modal functions, researchers have used products of free-free beam modes [Maeda et al . 1995, Wu et al . 1995, 1996, 1997, Kashiwagi 1998a, Nagata et al. 1998, Utsunomiya et al. 1998, Ohmatsu 1998a]; B-spline functions [Lin and Takaki 1998], Green functions (Eatock Taylor and Ohkusu 2000), two-dimensional polynomial functions (Wang et al. 2001) and finite element solutions of freely vibrating plates [Takaki and Gu 1996a].

Based on the linear theory, the velocity potential can be expressed as the sum of the incident potential, the diffraction potential and radiation potential by using the same modal amplitudes [Newman 1994].

Apart from a circular fluid domain associated with a circular floating body where closed form solution for the velocity potential may be obtained [see Watanabe et al. 2003], numerical methods [such as the boundary element method] have to be employed for determining the velocity potential. After having obtained the velocity potential, the Galerkin's method [by which the governing equation of the plate is approximately satisfied] is then used to calculate the modal amplitudes.

The modal responses are summed up to obtain the total response. For more details of the hydroelastic analysis using the modal expansion method, readers may refer to the papers by Utsunomiya et al. [1998] and Watanabe et al . [2003].

In the direct method, the deflection of the VLFS is determined by directly solving the motion of equation without any help of eigenmodes. Mamidipudi and Webster and Webster [1994] pioneered this direct method for a VLFS. In their solution procedure, the potentials of diffraction and radiation problems were established first, and the deflection of VLFS was determined by solving the combined hydroelastic equation via the finite difference scheme.

Their method was modified by Yago and Endo [1996] who applied the pressure distribution method and the equation of motion was solved using the finite element method. Ohkusu and Namba [1996] proposed a different type of direct method which does away with the commonly used two-step modal expansion approach. Their approach is based on the idea that the thin plate is part of the water surface but with different physical characteristics than those of the free surface of the water. The problem is considered as a boundary value problem in hydrodynamics rather than the determination of the elastic response of the body to hydrodynamic action. This approach was used to analyze a similar problem of two dimensional ice floe dynamics by Meylan and Squire [1994].

Ohkusu and Namba [1998] treated the VLFS as a plate of infinite length and the velocity potential was solved directly from a combined hydroelastic 6th-order differential equation. The deflections are estimated from the resultant velocity potential. The advantage of this method is that a closed form solution may be obtained in the case of shallow waters. In Kashiwagi's direct method [1998b], the pressure distribution method was applied and the deflection was solved from the vibration equation of the structure. In order to achieve a high level of accuracy in very short wavelength regime as well as short computational times and fewer unknowns, he uses bi-cubic B-spline functions to represent the unknown pressure and a Galerkin method to satisfy the body boundary conditions. His method for obtaining accurate results in the short wavelength regime is a significant improvement over the numerical techniques proposed by other researchers [Yago 1995, Wang et al . 1997] who have who have also employed the pressure distribution method.

In sum, the principal difference between the modal superposition method and the direct method lies in the treatment of the radiation motion for determining the radiation pressure. For example, we observed that Takaki and Gu [1996a, 1996b] used the shape function of dry eigen-modes of a plate with free edges while Yago and Endo [1996] employed the shape function of a constant panel for the unknown pressure. The shortcoming of the constant panel method is that it is very difficult to deal with short incident waves that are important in VLFS analysis. In order to cater for the short wave case, Lin and Takaki [1998] proposed the method be based on high-order B-spline panels.

Recently, acceleration techniques for the hydrodynamic analysis using free-surface Green's function method have been developed, and applied very successfully for thy successfully for the hydroelastic analysis of VLFSs [Kring et al . 2000, Utsunomiya et al. 2001a, 2001b., 2003].

 

NUS.14 Study Discussion 13:   TIME-DOMAIN ANALYSIS ASSOCIATED WITH VERY LARGE FLOATING STRUCTURES [VLFS]

The commonly-used approaches for the time-domain analysis of VLFS are the direct time integration method [Watanabe and Utsunomiya 1996, Watanabe et al. 1998] and the method that uses the Fourier transform [Miao et al. 1996, Endo et al. 1998, Ohmatsu 1998b, Endo 2000, Kashiwagi 2000].

In the direct time integration method, the equations of motion are discretized for both the structure and the fluid domain. In the Fourier transform method, we first obtain the frequency domain solutions for the fluid domain and then Fourier transform the results for substitution into the differential equations for elastic motions. The equations are then solved directly in the time domain analysis by using the finite element method or other suitable computational methods.

 

 NUS.14 Study Discussion 14: LOCAL STRUCTURAL ANALYSIS ASSOCIATED WITH VERY LARGE FLOATING STRUCTURES [VLFS]

In this paper we have focused on the global analysis of a pontoon type VLFS. To accomplish structural design the load effects in the various components of the structure, such as stiffened panels of deck and bottom and bulkheads, girders, stiffeners and plates are required. A particular challenge is associated with determining load effects for fatigue design checks, for which local [hot spot] stresses are required. In general a hierarchy of finite element models would be used for this purpose.

 

NUS.14 Study Discussion 15: DESIGN CONSIDERATIONS FOR FLOATING BODY [VLFS]

The design of the floating structure must meet the operating conditions, strength and serviceability requirements, safety requirements, durability, visually pleasing to the environment and cost-effective. An appropriate design service life is prescribed depending on the importance of the structure and the return period of natural loads. Its service life is generally expected to be as long as 50 to 100 years with preferably a low maintenance cost.


NUS.14 Study Discussion 16: MATERIALS APPLICABLE TO VERY LARGE FLOATING STRUCTURES [VLFS]

The materials used for the floating body maybe steel, or concrete or steel-concrete composite and the relevant specifications should be followed. Since watertightness 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, an d hence not considered once the pontoon are launched in the sea. Steel used for floating structures shall satisfy the appropriate standard specifications [such as the Technological Standard and Commentary of Port and Harbour Facilities 1999].

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NUS.14 Study Discussion 17: CONFIGURATIONS ASSOCIATED WITH VERY LARGE FLOATING STRUCTURES [VLFS]

As mentioned above, the main configurations of VLFS are the pontoon or barge and the semi-submersible type structures. Various special features may be envisaged for the pontoon type. For instance it may be connected to a submerged plate and skirt like structures which reduces motions [Ohta et al. 1999], or it might be attached to a floating breakwater to reduce wave excitation on the VLFS itself. Yet another feature could be the design of the edges of the pontoon type VLFS. By proper choice of edge layout the propagation of the incident waves into the main part of the structure is reduced by efficient scattering or reflection of the incident waves on the weather side.

Finally, possible use of air-cushion to reduce excitation of vertical motions should be mentioned [Ikoma et al. 2003].

Some of these innovative design features are promising, but commonly there are disadvantages as well, and they need to be assessed.

 

 

NUS.14 Study Discussion 18: DESIGN CRITERIA ASSOCIATED WITH VERY LARGE FLOATING STRUCTURES [VLFS]

Adequate performance of offshore structures is ensured by designing them to comply with serviceability and safety requirements for a service life of 100 years or more. Serviceability criteria are introduced to ensure that the structure fulfils the function required, and are specified by the owner. Typical serviceability requirements relate to motions and structural deformations. Motion characteristics might not only include displacements, velocities and accelerations.

It is noted that criteria in terms of the third order time derivative of the displacement are also considered for floating bridges.

Safety requirements are imposed to avoid ultimate consequences such as fatalities, environmental damage or property damage. Depending upon the regulatory regime, separate acceptance criteria for these consequences are established. Property damage is measured in economic terms. But, fatalities and pollution obviously have economic implications. While fatalities caused by structural failures would be related to a major structural damage, smaller damage may result in property damage which is expensive to repair e.g. for an underwater structure.

An important design issue regarding safety of personnel is evacuation and rescue. An effective safety measure in this connection could be to provide a safe place where people can survive on board after an accident some time before safe escape can be made

In principle the global failure modes of floating structures include capsizing, sinking, global structural failure and drift-off. A broad risk analysis approach needs to be carried out to identify possible accident scenarios and their likelihood. However, overall stability of floating structures is considered in terms of overturning moment by wind only, and uprighting moment due to hydrostatics of the inclined body. However, due to the large horizontal dimensions of VLFS, stability of the intact VLFS structure is not a problem. Even damage to a few compartments does not seem to impose a stability problem. Sinking could be caused by [excessive] flooding or structural failure. Hence, global failure of the structure and mooring system are, therefore, major failure modes.

 

 

NUS.14 Study Discussion 19: MODERN SAFETY CRITERIA FOR MARINE STRUCTURES

ULS and FLS criteria for structural components have been developed for the relevant failure modes dependent upon geometry and load conditions. The relevant criteria follow the same principles as established for ships and especially for offshore structures, which are based on first principles.

However, the implicit safety level aimed at should be carefully considered in view of the potential consequences of failure. The safety level implied by ULS and FLS requirements is determined by the chosen definition of characteristic values of loads and strength and the safety factors in ULS criteria and safety margin in FLS.

The fatigue life of the structure is estimated by comparing the long-term cyclic loading in a structural detail with the resistance of that detail to fatigue damage. The main design approach for determining fatigue damage is based on the S-N data. This approach uses an S-N curve which gives the number of cycles to failure for a specific structural detail or material as a function of constant stress range, based on experimental results. The long-term stress distribution is used to calculate the cumulative fatigue damage ratio.

The failure at stress range is given by the appropriate SN curve. The allowable damage is often taken to be 1.0 for ships, while for offshore structures it varies between 1.0 and 0.1. It can be shown that with an allowable of 1.0, the probability of fatigue failure in the service life of the structure will be 10% [Moan, 2004]. This estimate has been validated for offshore structures and ships by service experiences. With a large number of welded joints fully utilized according to this criterion, many fatigue cracks should be expected in a structure with thousands of welded joints. On the other hand, the definition of fatigue failure implicit in SN curves is typically through thickness crack.

Hence, in monocoque structures made of stiffened steel panels, there will be a significant period of crack growth before the cracks really become critical from a strength point of view. From a safety point of view, a fatigue criterion with D= 1.0 would be acceptable, but the maintenance and repair efforts implied may imply so large expenditure that a more restrictive fatigue design criterion would be more optimal based on cost-benefit considerations.

 

 

NUS.14 Study Discussion 20: ACCIDENTAL COLLAPSE LIMIT STATE [ALS] ASSOCIATED WITH VLFS

Safety requirements are motivated by the design philosophy that "small damage, which inevitably occur, should not cause disproportionate consequences". Since the purpose of this criterion is to prevent progressive development of failure, the criterion was initially denoted Progressive Limit State criterion.

A quantitative ALS criterion was introduced for offshore structures in Norway in 1984 [e.g. NORSOK N-001 2000]. The initial damage according to the NORSOK N-001 should correspond to events which are exceeded with an annual probability of 10-4, e.g. due to ship impacts or fires, as identified by risk analyses. The [local] damage, or permanent deformations or rupture of components need to be estimated by accounting for nonlinear effects. Relevant initial damage for the mooring system should also be assessed. For floating offshore structures, it is required that one of the mooring lines has failed.

Obviously for application of such a criterion to VLFSs, the probability level that defines the initial damage condition should be judged in view of the target safety level aimed at. For VLFSs, the relevant damage due to ship impact would involve structural damage and loss of buoyancy due to possible flooding. The structure and mooring system are required to survive the various damage conditions as mentioned above without global failure.

Compliance with this requirement for the hull can in some cases be demonstrated by removing the damaged parts, and then accomplishing a conventional ULS design check, based on a global linear analysis and component design checks using truly ultimate strength formulations. However, such methods may be very conservative and more accurate nonlinear analysis methods should be applied.

 

 

NUS.14 Study Discussion 21: CORROSIONS & CATHODIC PROTECTION ASSOCIATED WITH VLFS

The corrosion protection system includes coatings, cathodic protection, corrosion allowance and corrosion monitoring. Overprotection which may cause hydrogen embrittlement should be avoided. In areas where marine organisms are active, antifouling coatings may be considered to reduce marine growth.

The steel should be protected from corrosion using a corrosion protection system that is in accordance to specifications such as NACE Standard RP-01-76. Care should be given to parts just beneath the mean low water level [MLWL] where severe local corrosion occurs. For such parts, cathodic protection is generally applied while coating methods are applied for parts shallower than the depth of 1 m below the low water level [LWL]. The coating methods include painting, titanium-clad lining, stainless steel lining, thermal spraying with zinc, aluminium and aluminium alloy.

Further discussion is associated with the Standard Values of the Rate of Corrosion and the Distribution of Corrosion according to depth of water and seabed.

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The splash zone is the most severe with regard to corrosive environment and its upper limit zone is determined according to the installation of the structure.

The ebb and flow zone corresponds to the next most severe environment but this zone does not exist for floating structures since they conform to the changing water level. Special attention should be given to the region immediately below LWL. In the seawater zone , the environment becomes milder but marine growths and water current may some times accelerate the corrosion. The environment in the soil layer beneath the seabed is even milder, although it depends on the salt density and the degree of contamination.

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NUS.14 Study Discussion 22: DESIGN CONSIDERATIONS FOR MOORING SYSTEMS ASSOCIATED WITH VLFS

The mooring system must be well designed as it ensures that the very large floating structure is kept in position so that the facilities installed on the floating structure can be reliably operated and to prevent the structure from drifting away under critical sea conditions and storms. A freely drifting very large floating structure may lead to not only damage to the surrounding facilities but also the loss of human life if it collides with ships. Note that there are a number of mooring system s such as the dolphin-guideframe system, mooring by cable and chain, tension leg method and pier/quay wall method.

The design procedure for a mooring system may take the following steps:

We first select the mooring method, the shock absorbing material, the quantity and layout of devices to meet the environmental conditions and the operating conditions and requirements.

The layout of the mooring dolphins for example is such that the horizontal displacement of the floating structure is adequately controlled and the mooring forces are appropriately distributed.

The behaviour of the floating structure under various loading conditions is examined.

The layout and quantity of the devices are adjusted so that the displacement of floating structure and the mooring forces do not exceed the allowable values.

Finally, devices such as dolphins and guide frames are designed by applying the design load based on the calculated mooring forces.

 

 

CONCLUDING REMARKS

The definition, applications, analysis and design of very large floating structures have been presented. For details of analysis and design on pontoon-type VLFS, the reader may refer to a large body of references given in a recent literature survey paper by Watanabe et al. [2004].


It is hoped that this report will create an awareness and interest in structural and civil engineers on the subject of very large floating structures and to exploit their special characteristics in conditions that are favourable for their applications.

 

ACKNOWLEDGEMENTS

The second author gratefully acknowledges the support by JSPS that makes the research collaboration possible between the Structural Mechanics Laboratory of Kyoto University and the Centre for Offshore Research and Engineering of the National University of Singapore

 

Oplat-Usa Offshore International Airport Platform Program Technical Studies Credit University of Singapor - TBNC-Edgemon Environmental Planners, Site Designers, Engineers & Construction Managers Tom Edgemon CSLB 274107 San Diego, California USA

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By
Steve Chapple, Special to the U-T, Noon September 21, 2013

Floating an idea: airport on the water

Noted ocean scientist Walter Munk thinks it's the solution to future problem

Oplat-Usa Walter Munk, Phd.San Diego Offshore International Airport Platform Program, TBNC-Edgemon Environmental Planners, Site Designers, Engineers & Construction Managers San Diego, California Tom Edgemon CA.CSLB 274107 Carlsbad, CaliforniaImage Credit
John R. McCutchen    ·    2010 U-T Archive

What happens when San Diego outgrows its new $1 billion expansion of Lindbergh Field?

Walter Munk of the Scripps Institution of Oceanography at UC San Diego has been floating practical and visionary ideas for a long time.


WALTER H. MUNK, Ph.D.

 

Some 17 million passengers used Lindbergh in 2012. Noise, safety and environmental concerns become ever more vexing as the airport is surrounded by the high-rise city that San Diego is becoming.

Land is expensive. The Marines appear to have no interest in sharing space at Miramar for a new civilian airfield. It’s a long drive to the desert, if the county were to build one there.

But the ocean is wide open, and it’s right here. Why not build the world’s first major floating airport?

This is the practical and visionary idea being “floated” by Dr. Walter Munk, who holds the Secretary of the Navy/Chief of Naval Operations Chair at the Scripps Institution of Oceanography at UC San Diego. Munk is widely considered the dean of world ocean scientists.

At age 95, Munk has been floating practical and visionary ideas for a long time. His forecasts of surf dynamics helped guide the Allies in amphibious landings throughout the Pacific, in North Africa and in Gen. Dwight Eisenhower’s decision to postpone the D-Day invasion during World War II.

Munk solved the mystery of why one side of the moon always faces the earth in its rotation, showed that Alaska’s waves (and in the summer San Diego’s) mostly start in Antarctica, pioneered advanced acoustical techniques to provide information about how the deep sea works, and discovered the ways winds shape currents, encapsulated in his phrase “wind-driven gyres.”

To Munk, the idea of a floating airport for San Diego would be inexpensive compared with terrestrial alternatives, and it would help to brand San Diego as the great ocean metropolis of the future. It would be cool, iconic and great fun. A tourist attraction, even. He adds that San Diego and Tijuana could do it together.

“It would be nice to change something before everyone else does it, and it could become San Diego’s trademark,” he says in his soft Austrian accent, as we sit sipping chardonnay with guacamole and chips at his small estate overlooking Black’s Beach. “There are several dozen coastal cities in the world that are having problems accommodating their airports with expanding use and growing populations. Let’s be the first.”

What would “Dr. Munk’s Floating Airport” look like?

(Of course, Munk insists the idea is not “his,” so much as a proposal by himself and two esteemed colleagues. One is Frieder Seible, the former dean of the Jacobs School of Engineering at UC San Diego and an expert in expanding airports, such as San Francisco International, into the sea. The other was marine explorer Fred Spiess, a former director of the Scripps Institution of Oceanography and developer of novel ocean vessels, who died in 2006.)

First, the runways would be about twice as long, which would cut down on taxiing time, and save money. “You see,” says Munk, “when you land, you would end up stopping at an entrance tunnel and when you take off you would leave from there so you wouldn’t have to go to the end of the field. Now, when you land, you come in and stop right at the terminal, but taking off you have to taxi for 10 minutes.”

The entire platform would be supported some 20 to 25 feet off the waves on columns he calls spars, giant versions of the spar buoy.

Munk knows much about creating stable ocean platforms from his relationship with Spiess, who helped to create the Floating Instrument Platform, or “FLIP.” The famous 355-foot research vessel anchored in Point Loma flips from horizontal to vertical to allow data to be collected on whale sounds or temperature gradients hundreds of feet below the surface. He believes an entire airport would move very little, even in a storm, so pilots would not notice.

How would people get to the airport? In boats? No, suggests Munk. “There would be high-speed transportation tubes built on the ocean floor, much like San Francisco’s BART system,” he says. The tube would “come up” to the floating platform. All ticketing and baggage collection would be done at the current airport, which Munk likes because it’s downtown. You don’t have to drive far. “Narita, Tokyo’s airport, already does this.”

In fact, Munk points out that Narita was almost the world’s first floating airport. A major model was even built. But planners decided at the last minute to build it on fill, which led to problems with settling. A real floating airport “remains to be done by some city with a little bit of guts.”

He means us.

But what about fog? San Diego is a city famous for its marine layer, and that’s just the coast. “There is a fog problem at Lindbergh Field already,” Munk says. “But I have been told that within a very few years all landing and takeoffs will be instrumental.” With the growth in sensor technology, as well, fog is not the problem it once was.

A floating airport would solve the problem of noise pollution, since it would be a mile or so from land. Noise is a major problem at Lindbergh, so far as neighbors are concerned, and to Munk’s way of thinking, reducing noise increases nearby property values as well as makes the experience of San Diego’s “wonderful” open-air theaters much more pleasant.

Best of all, Munk says, the floating airport could be built today. We already know how to do it. The Navy did pilot studies for other locations long ago. San Diego has world-class engineering schools. The talent is here. It would just take some practical vision — and a little bit of guts.

Pity if China, Brazil or — God forbid — Los Angeles steals the idea.

 

Researchers Cy Bates, Elizabeth Li and Subin Ryoo contributed to this column.
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OPLAT-USA Offshore International irport Platform Program San Diego, California  TBNC Edgemon Environmental Planners, Site Designers, Engineers & Construction Managers Tom Edgemon CA.CSLB 274107 San Diego, California USA Edgemon
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RESEARCH TOPICS

 Earth through Space and Time    ·    Energy and the Environment    ·   Global Change    ·     Global Environmental Monitoring
Ice and Climate    ·    Sound and Light in the Sea     ·     Waves and Circulation

WALTER H. MUNK, Ph.D
Emeritus

wmunk at ucsd.edu

Institute of Geophysics and Planetary Physics
Scripps Institution of Oceanography
UC San Diego
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VLFS San Diego Offshore International Airport Vessel Plate Steal Componets Study

 

 

San Diego Offshore International Airport x Disney Wonder Length Comparative Studies 2011

 

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