3.7.4 Mooring Configurat ion Des ign Considerations
When evaluating mooring system strength, the maximum
design condition and maximum operating condition are
used.
Maximum design condition is the most severe weather
condition. For permanent mooring, structures are designed
to survive at 100-year return period storm conditions.
This is the condition for a storm occurring once
every 100 years at that location. This statistical sea state
is extrapolated from long term in situ measurements.
As the term announces, the maximum operating condition
is the limit for operation. In the case of The Array, this
means that for more severe weather conditions plastic
collection cannot continue.
Wind
For the final design of permanent moorings, fluctuating
wind should be modeled. This is usually based on
the one-hour average velocity, plus a time-varying component
calculated from a suitable empirical wind gust
spectrum.
Waves
In situ measurements allow for accurate determination
of the wave height versus wave period relationships. The
period can significantly affect the wave drift forces and
Array motions. Therefore a range of wave periods should
be examined. Fatigue analysis uses the long-term joint
distribution (often presented as scatter plot).
Current
Most common categories of currents are tidal currents,
circulation currents (loop/eddy), storm-generated currents
and soliton currents.
In certain geographic areas, current force can be the governing
design load. The selection of appropriate current
profile requires careful consideration.