PO030

Provision of State-of-the-art MetOcean Design Conditions for the Dutch Offshore Wind Farms

Maziar Golestani 1, Frank van Erp2
1DHI, Hørosholm, Denmark, 2Rijksdienst voor Ondernemend Nederland, Ultrecht, The Netherlands

Abstract

High quality and reliable Metocean data are fundamental to the success of any marine project such as design, operation and maintenance of offshore wind farms. Consistent and reliable metocean data can result in a more cost efficient design in offshore wind farm projects in Europe.
In this talk, the Dutch's Government's approach in providing developers with high quality metocean data is discussed. The new approach ensures having access to consistent and reliable metocean data all along the Dutch coast Wind Farm Zones, which can be easily accessible. Using advanced numerical models and analysis methods, comprehensive metocean data sets have been provided with a user-friendly interface which will provide all necessary information for design purposes at any given point within the defined project area. The metocean data is based on more than 37 years of state-of-the-art modelling and have been validated against various measurements in the North Sea and English Channel. Advanced analysis methods were applied on the data to provide normal and extreme metocean conditions within the Dutch North Sea. This sophisticated database will serve as a basis for design, operation and maintenance of the Hollandse Kust (zuid) and (noord) and a few future wind farms in the Netherlands.
Some of the modelling results will be presented in this talk together with differences with other metocean studies. The new updated design values which will serve as the basis in the Dutch waters will be briefly discussed. This data will be used in development of more than 2100MW of offshore wind power.

Method

Long-term high-resolution hydrodynamic and wave modelling were performed covering the North Sea and English Channel for the period 1979-2016. The MIKE Powered by DHI software package was utilized for modelling. Latest improvement in wave modelling such as the effect of atmospheric stability, air-sea density ratio and effects of surface currents on the wave growth were incorporated into the wave model. The hydrodynamic model took advantage of Data Assimilation techniques. The models were calibrated/validated against various measurements in the North Sea, English Channel and at a few of Dutch offshore wind farms. After analysing the data using advanced methods, the results at any given point within the Dutch water were populated into a user-friendly and fit-for-purpose database software based on MIKE IPO solutions.

Results

Comparisons with the long-term measurements indicated the high quality of the modelling results. Furthermore, the new and advanced numerical and analysis methods resulted in re-defining the common design values in the Dutch waters. The new design parameters will help the Dutch Government to lower the costs of construction and eventually provide a more sustainable solution in regards with energy provision to the Dutch market.
The user-friendly database which contains all the modelling data in addition to design parameters, enables the developers to get easy access to reliable and high-resolution data for their purposes (tender/design) in a matter of minutes. As the database has been certified by DNV-GL, there will be no need for further metocean studies in relation with the design of future offshore wind farms.

Conclusions

Taking the atmospheric stability effects together with the changes in air-sea density ratio were considered important in accurate modelling of sea states. Applying the right CAP on wind friction and correction of wave celerity for surface current speeds were also found to influence the more extreme sea states. Assimilating the water level at specific locations helped to improve reproducing the complicated hydrodynamics of the study area significantly.
The database solution which is based on +37 years of modelling data and modern analysis methods has provided a cost effective solution to the Dutch Government to develop the future offshore wind farms.

Objectives

The objective of the talk is to present some of the results (with relation to design- for example extreme wave height maps) within the Dutch water and share the experiences with other parties who will be responsible in developing future offshore wind farms. The new improvements in numerical modelling which resulted in accurate modelling of sea states will be presented in order to encourage using such methods within the industry.
The database approach will help the authorities to pursue cost-effective solution for the design of offshore wind farms. Furthermore, it helps the industry to have easy access to high quality and consistent metocean data which has already been certified and is ready to be used in design.