Methodology for the design of LNG terminals in a nearshore environment
Author Frédérick Jaouën, Olaf Waals, Martijn de Jong, Arne van der Hout, Marios Christou
Title Methodology for the design of LNG terminals in a nearshore environment
Conference/Journal OMAE ASME 35th International Conference on Ocean, Offshore and Arctic Engineering, Busan, South Korea, 2016
Paper no. 54724
Month June
Year 2016


 

Abstract
Nowadays, more and more nearshore LNG terminals are being
built as it offers easy access to vessels coming from deep water
and mitigates the risk by isolating regasification units from the
cities. However, designing these terminals can be challenging
in shallow water, as it is exposed to low-frequency waves which
can excite the moored vessels at their natural periods. By lack
of knowledge and adequate numerical simulation techniques,
the effect of these low-frequency waves on the motions of
moored vessels are unfortunately often ignored in the design.
This is likely to result in an underestimation of the vessel
motions and terminal downtime. In this paper, a methodology
for the design of terminals in a nearshore wave climate is
presented. The methodology consists of six steps which guide
the engineer from the definition of the deep-water sea states to
the calculation of the vessel motions and terminal downtime. In
an initial stage, computational efficient tools are used, with the
limitation that several approximations need to be made. In a
later stage, more detailed but expensive methods are applied.
The objective of this paper is to show how the developed
methodology can give insight in the expected downtime due to
the low-frequency waves in any nearshore mooring location. As
an example, the methodology is applied on a fictive but
realistic case, for which the motion response of a LNG carrier
moored to a jetty on a sloping bottom is calculated. From seven
years of deep-water sea states, the terminal downtime is
estimated. The application of the methodology to the design
case confirms that the terminal downtime can be significantly
underestimated if shallow water effects are not taken into
account. So the influence of the water depth, bathymetry, wave
directionality and low-frequency waves on the vessel motions
should be investigated with care. However, the results obtained
in the design case also show that the spectral shape of the lowfrequency
waves predicted by the wave models are sensitive to
the tuning of numerical parameters. Tuning the wave models
against model tests or full scale data is therefore highly
recommended, because the motion response of a low-damped
moored vessel can be dominated by the amount of lowfrequency
free wave energy at its natural periods.

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