Risk and design conditions for offshore structures - the biggest waves in the biggest storms?
P.H. Taylor
University of Oxford
Any offshore structure must survive all the waves that occur during
its operational life. This talk will discuss two related problems in
offshore engineering:
How large can a wave get in a given storm?
The statistical properties of most waves in real storms are well
understood at least for engineering design - (Rayleigh statistics with
local non-linear corrections). However, the largest waves are the
rarest and the most non-linear. Do the available statistical models fit
the far tail of the distribution for wave height (or crest elevation),
or is there new and interesting physics to be explored? After all,
uni-directional wave motion on deep water can support solitons -
inherently non-linear localised wave groups. Numerical simulations show
that there is some carry-over of 1-D soliton-type behaviour for more
realistic directionally spread wave groups.
How severe do storms get in the open ocean?
Large winter depressions produce massive storms in open areas such as
the North Atlantic and northern North Sea. What type of long-term
statistical models should be used to estimate the 100-year or
10,000-year storm based on perhaps a few decades of data? Recent work
shows that a simple model can be used to extrapolate existing data sets
out to very long return periods. Although there is significant decade
to decade variability in storm severity (which itself might be locally
predictable), there are important features of the wave climate
extrapolations that appear to be very robust.
