A5 – Stochastic modelling of the combination of unsteady conditions and condition parameters

For Offshore Wind Turbines (OWT) primarily environmental conditions dominate the loads alongside dead loads and operating loads. Especially wind, wave and currents but also temperature or earthquake loads are highly relevant for the design of offshore support structures. Concurrently OWT are characterised by highly dynamic loads, changing load scenarios and reactive components. Besides a detailed description of the partly new environmental scenarios and their scatter (SP A01, SP A03), the realistic combination of the mentioned loads substantially influences the reliability and economic efficiency of Offshore Megastructures.

In SP A05 an empirically based stochastic combination method for Offshore Megastructures and other reactive support structures (e.g. support structures with tuned mass dampers), should be developed. Although the method is developed for the use with Offshore Megastructures, the combination method is independent from the support structure and its dynamic behaviour. Moreover, this combination method should realistically consider changes in time- and direction-variant environmental parameters and their combinations over the lifetime (e. g. adjustments in the turbine control or the over lifetime changing hydrodynamics, see A03). The main innovation of the subproject is the development of a combination method, which not only considers the simultaneous occurrence of environmental load parameters, but for the first time also incorporates the occurring load directions.

For a safe design of Offshore Megastructures, combinations of environmental conditions must also be taken into account that are not characterised by one extreme single load and for which the environmental conditions and their combination change over the lifespan. The to be developed combination method therefore should be extended by a time dependent description of the changes in the environmental conditions, occurring as a result of increasing extreme weather events, as well as, changed hydrodynamic impacts (e.g. morphological rearrangement processes on the seabed on long time scales). Based on the complex combination approach for time- and direction-variant random variables, a reduced combination method for integration in the digital twin and in practical design concepts should be developed.

[1] Hildebrandt, A.; Schmidt, B.; Marx, S. (2019): Wind-wave misalignment and a combination method for direction-dependent extreme incidents, Ocean Engineering Volume 180, 15 May 2019, pp. 10-22