Calculation of the design wave The Design Wave

Calculation of the design wave The “Design Wave Philosophy’’ ***** Calculation of the design wave ***** Wave forces on semi-submersible platforms Wave forces and bending moments in FPSO-ships Platform movements in large waves Examples of heavy weather damage What 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 conditions Search And Rescue and emergency operations Decision making in an emergency 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 • Examples Trondheim Tekniske Fagskole to extremes

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 Trondheim Tekniske Fagskole