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