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Trondheim Tekniske Fagskole
The “Design Wave Philosophy’’***** Calculation of the design wave *****Wave forces on semi-submersible platformsWave forces and bending moments in FPSO-shipsPlatform movements in large wavesExamples of heavy weather damageWhat is a Rogue Wave ?Why, where and when ?Shall we design against Rogue and Freak Waves ?What can a platform master do against Rogue and Freak Waves ?Remote-sensing of sea conditionsSearch And Rescue and emergency operationsDecision making in an emergency
Calculation of the design wave
Trondheim Tekniske Fagskole
Calculation of the design wave
Trondheim Tekniske Fagskole
Calculation of the design wave
• Data collection• Extrapolation to extremes• Examples
Trondheim Tekniske Fagskole
Data sources
buoy - satellite - hindcast model
Trondheim Tekniske Fagskole
Data sources
Field measurements:• costly• short duration• local validity• often only synthetic
parameters• reasonably good…
Trondheim Tekniske Fagskole
Data sources
…but should one trust them at all times ?
Trondheim Tekniske Fagskole
Data sources
…but should one trust them at all times ?
Trondheim Tekniske Fagskole
Data sources
Satellite • only significant wave height• no wave direction• very unreliable period
estimates• sparse sampling both in time
and space• yet available almost anywhere
Trondheim Tekniske Fagskole
Data sources
hindcast models• costly• better calibrated in common
conditions than in extreme ones
• good length databases• no individual wave data
Trondheim Tekniske Fagskole
Data sources
Reconciliation problems when merging buoy - satellite - hindcast model
Trondheim Tekniske Fagskole
Calculation of the design wave
• Data collection
• Extrapolation to extremes• Examples
Trondheim Tekniske Fagskole
Database:
20 years of data available from Frigg QP platform in the North Sea
Trondheim Tekniske Fagskole
Database:
1979-1989: mostly 3-hourly measurements, many time-series available.
1991-1999: mostly 20-minute statistics, only reduced parameters
Trondheim Tekniske Fagskole
Calculation of the design wave
Empirical distribution and duration it represents
Trondheim Tekniske Fagskole
Calculation of the design wave
Fitted parametric model
Trondheim Tekniske Fagskole
Calculation of the design wave
Approximated model for maximum over observation duration
Trondheim Tekniske Fagskole
Calculation of the design wave
Extrapolation to planned duration
Trondheim Tekniske Fagskole
Calculation of the design wave
• Data collection• Extrapolation to extremes
• Example• The Port-Louis case
Trondheim Tekniske Fagskole
The Port-Louis case
Trondheim Tekniske Fagskole
The Port-Louis case
Build a wharf for a coal power generation facility
Trondheim Tekniske Fagskole
The Port-Louis case
Hs less than 1 m more than 99.7% of the time, yet once in a while...
Trondheim Tekniske Fagskole
The Port-Louis case
Trondheim Tekniske Fagskole
The Port-Louis case
6 in 40 years, and Port Louis was sheltered on some of them
Trondheim Tekniske Fagskole
The Port-Louis case
Variables not “i.i.d.” => 2 options:• cheap one, consider a nearby more exposed location and define risk attenuation from that location• expensive one, run hindcast again sending synthetic hurricanes into the area