Very large floating structures (VLFSs) or very large floating platforms (VLFPs) are artificial islands, which may be constructed to create floating airports, bridges, breakwaters, piers and docks, storage facilities (for oil and 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, several different concepts have been proposed for building floating cities or huge living complexes.[1] Some units have been constructed and are presently in operation.[2]
Floating structures offer several advantages over more permanent structures which might extend from the shore into open water:
they do not damage the marine eco-system;
they do not cause silt deposition in deep harbors;
they do not disrupt the ocean currents;
they are easy to construct, since much of the construction is completed onshore;
VLFSs differ from watercraft in that most or all of the usable area is the top surface instead of the internal (hold) areas. Thus a useful VLFS will cover significant area. It can be constructed by joining the necessary number of floating units together. The design of the floating structure must comport with safety and strength requirements, operating conditions, etc. Steel, concrete (prestressed or reinforced hybrid) or steel-concrete composite materials may be used to build the floating structure. The motion of the floating structure due to wind or wave action must be substantially neutralized, to ensure the safety of people and facilities on a VLFS, and to allow useful activities. VLFSs must be securely moored to the ocean bed.[3]
The semi-submersible-type VLFS has a raised platform above sea level using column tubes; it is more suitable for deployment in high seas with large waves. In open sea, where the waves are relatively large, the semi-submersible VLFS minimizes the effects of waves while maintaining a constant buoyant force. Semi-submersible types are used for petroleum exploration in deep waters. They are fixed in place by column tubes, piles, or other bracing systems.
The pontoon-type VLFS platform rests on the water surface and is intended for deployment in calm waters such as a cove, a lagoon or a harbor. Its basic element is a simple box structure; it usually offers high stability, low manufacturing cost and easy maintenance and repair. The pontoon type is supported by its buoyancy on the sea surface. The pontoon type is flexible compared to other kinds of offshore structures, so that the elastic deformations are more important than their rigid body motions. Thus, hydroelastic analysis is uppermost in designing the pontoon-type VLFS. Together with the motion of the floating structure, the response of the structure to water waves and the impact on the entire fluid domain have to be studied.
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 structures are often called ‘mega-floats'. As a rule, the mega-float is a floating structure having at least one length dimension greater than 60 metres (200 ft) Horizontally large floating structures can be from 500 to 5,000 metres (1,600 to 16,400 ft) in length and 100 to 1,000 metres (330 to 3,280 ft) in width, with typical thickness of 2 to 10 metres (6.6 to 32.8 ft).
Applications
Many large floating structures have been conceptualized, including a golf course,[4]
a farm,[5] and habitable long-term living complexes (seasteading).
Some large floating structures that have been built include floating airports and floating landing platforms for returning rockets.
Floating airport
A Mega-Floatfloating airport prototype was constructed in Tokyo Bay from 1998 to 1999.[6] It was one kilometer in length and was primarily intended as a test vehicle, to research the loadings and responses of such installations.[7] This project was substituted as a study project to provide more definite information about a proposed floating runway at Kansai International Airport, which was not built (an artificial island was instead constructed to support the runway). However the choice to build an airport on two islands composed of sand landfill has resulted in the Kansai Airport sinking several centimeters per year. (https://www.smithsonianmag.com/air-space-magazine/how-to-save-a-sinking-airport-180968985/)
On 8 April 2016, the first stage of the rocket that launched the DragonCRS-8 spacecraft, successfully landed on the drone ship named Of Course I Still Love You, the first successful landing of a rocket booster on a floating platform.[14]
A concept has been patented for a floating automotive parking barge with angled sides to deflect wind shear.[16]
Floating LNG production facility
The Shell floating LNG plant was constructed to process and liquify offshore natural gas into liquified natural gas for transport and storage.[17][18] The Shell project was scheduled to begin processing gas in 2016.[19] In December 2018, Shell announced that the wells have been opened and the plant was ready to begin the initial phase of production.[20] In June 2019, it reached a significant milestone, shipping its first liquefied natural gas cargo to customers in Asia.[18]
^Japan constructed the Mega-Float (a floating runway in Tokyo bay); Japan also has floating fuel storage bases at Shirashima and Kamigoto Islands, and floating ferry piers at Ujina port (Hiroshima). Several very long floating bridges are currently in use; three are located near Seattle, Washington USA. The Floating Bridge, Dubai, over the Dubai Creek, is 300 meters long. Singapore built the world’s largest floating performance stage at the Marina Bay, and is currently installing a mega floating fuel storage facility off Pulau Sebarok. South Korea is currently installing three floating islands on the Han River, to be used for convention centers, and another project at Seoul will function as hotel/convention center/customs site/quay. Science Direct, Very Large Floating Structures, p. 63
^Areas being studied in Mega-Float include the hydroelastic behavior of the unit, the mooring system response and durability, the connector system and its welded joints, the anti-corrosion system, the unit's effect on the surrounding sea waves which impact the nearby shoreline, and the unit's effect on the bay's prevailing currents, water quality, and marine ecosystems.
^Kelly, Ross (19 June 2014). "GDF Suez, Santos Halt Innovative LNG Plan in Australia: Companies Say Offshore Conversion Project Not Commercially Viable". Wall Street Journal. Retrieved 30 December 2014. The decision highlights the risks confronting Australian gas-export projects as they grapple with high costs and competition from North America and Russia, which are vying to provide Asian utilities with cleaner-burning fuels. Confidence in "floating" liquefied natural gas may also be diminishing—two years before a Royal Dutch Shell PLC-owned vessel is due to begin processing gas for the first time.
