3.5.2.2 Determination of the critical sea state
In this section, a simplified model of the boom and mooring
system is used for determining the most critical sea
state. Using the more extensive boom model would result
in long computation times.
Boom and mooring
The 1,000 m long boom is connected to the sea bottom
by means of two mooring lines. The chosen water depth
is 200 m; the lines’ horizontal offset with respect to the
boom end is 200 m as well. The polypropylene mooring
line material is buoyant, which can be seen in Figure 3.53,
1 The sea state with highest fluctuation of sea surface clearance. and the mooring line shows a reverse catenary.
Figure 3.53 Side view of boom and mooring model configuration
in Orcaflex
Environmental conditions
Multiple sea state simulations were run containing a current
and a dominant significant wave height and period.
The current was kept constant for all simulations while
the combination of wave height and period was changed
for each simulation.
As a result of acquired environmental data, presented in
Chapter 2, the input for current speed was set at 0.15 m/s
and it was directed perpendicular to the boom. Later in
the study, it was found that the current speed is 0.29 m/s;
the effect of this is elaborated on in Figure 3.54.
Since the sea surface is in fact a summation of different
wave components, the sea state is described by a spectrum
representation. Each combination of wave height
and period is represented in a JONSWAP spectrum. The
wave direction was modeled both perpendicular and parallel
to the boom. The full range of sea states is shown in
Table 3.11.