The increasing demand for natural gas is encouraging the development of novel floating units’ designs, capable of processing large quantities of hydrocarbon. These units called FLNG (Floating Liquefied Natural Gas) are facilities that produce, process and store liquefied natural gas (LNG) offshore. Once the topside and tanks of a FLNG are larger and more complex than the regular FPSO vessels, a design process considering these particularities must be used.

Once just few FLNG units are under construction and under design and not yet in operation, the information on the design first stages is poor. It is difficult to obtain a first hull sizing without taking in account the complexity mentioned above.

Thus, a set-based approach that works with sets of possible solutions that are analyzed and compared using a merit function in order to select the best and feasible solutions was used.

However, to produce a sufficiently large family of solutions, which includes most of the solution space, either the solution descriptions or the models must be simplified. From the computational point of view, the analyses of a family of design solutions basically relies on an initial parameterization of the object and a set of mathematical models that, as a group, will be referred as synthesis model. Additionally, some restrains are also applied to eliminate unfeasible solutions. The output of the synthesis model is a set of performance quantities that will be used to rank the solutions.

This design approach is particularly useful to deal with project trade-offs and to optimize multiple characteristics. Optimal solutions belongs to a surface (or a hyper surface) called Pareto boundary. This paper aims to achieve a platform design capable of producing, storing and offloading liquefied natural gas. It must safely survive under environmental conditions of Santos Basin in São Paulo, Brazil. In the same way, the design should guarantee the shortest downtime as well as keep costs, of acquisition and operation, as low as possible. Each of these characteristics must be quantified to allow a ranking of the generated solutions through an objective function.

Capacities, production rates, equipments, load distribution, environmental actions, stability, sea keeping and structural design estimates are the major areas to consider and will be related to one or more mathematical models, constraint and objective functions. The work will present a general overview of each model separately and how they work together, as well as examples of solutions and analyses depending on the input values.

It must be clear that this approach is applicable just in the early stages of design to obtain the first hull sizing. After that it is necessary to fall back on the traditional iteration process to rely in a feasible design.

This content is only available via PDF.
You do not currently have access to this content.