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A STUDY ON VERY LARGE FLOATING STRUCTURES

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.



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.

Very large floating structure
Very large floating structures (VLFSs) or very large floating platforms (VLFPs) are manmade islands, which may 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, several different concepts have been proposed for building floating cities or huge living complexes. Some units have been constructed and are presently in operation.
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;
installation is rapid;
they are immune to seismic shock.

Floating structures have enabled drilling and production in the deepest waters of the Gulf of Mexico and elsewhere in the world. The proper design of these platforms is essential for the survival of the risers and the safety of the people that operate the platforms.

This course provides an introduction to the fundamentals involved in floating structure design: hydrostatics and stability, hull structure, global design and sizing, mooring, global responses and an overview of structure fabrication, transportation and installation methods. The scope of specific platforms include: semi-submersibles, tension-leg-platforms (TLPs), spars, and FPSO (ship-shaped). The content is based largely upon application of Rule and Recommended Practice-based methods. The use of “first principles” in the design is discussed as well.

You Will Learn To:
- Identify the functions and salient design drivers of different floating structures
- Configure floating structures and moorings to meet their function, safely
- Identify the methods for design and analysis of floating structures
- Recognize applicable Industry Standards, the role of Classification Societies, and application of the Rules, particularly, to hull stability, structure, and mooring design

Outline
Please click HERE to view the course outline.

Who Should Attend
This course is intended for naval architects, civil and mechanical engineers interested in learning more about the methods for design and analysis of floating offshore platforms, specifically production and drilling platforms. The course would be particularly useful for engineers working on or planning on working on deepwater projects involving risers, moorings and floating structures. Some background knowledge of basic fluid mechanics and strength of materials is necessary.