Wave behaviour

Recording rollers and breakers using Doppler measurement to investigate space-time changes in the sea swell field within the range of offshore structures

Helmholtz-Zentrum Geesthacht - Zentrum für Material- und Küstenforschung GmbH
Dr. Friedwart Ziemer

The radar measurement of wave combs is aimed at clarifying the behaviour of large, steep waves at sea. The new process was developed by scientists from the Helmholtz-Zentrums Geesthacht – Centre for Materials and Coastal Research and is being tested for the first time as a permanent operation on the FINO3 research platform.

Information on large steep waves – so-called breakers – is of great interest for the constructors and operators of offshore wind turbine installations. For example, it is as yet unknown, how the breakers impact wind turbine installations and to what extent the installations themselves generate breakers. To obtain these figures the Helmholtz-Zentrum Geesthacht - Centre for Materials and Coastal Research operates a Doppler radar approximately 50 m above sea level on the FINO3 lattice tower.

In particular the frequency of large breakers and the force generated by the steep waves is not only of interest to the researchers but also to the operators of offshore wind turbines or oil platforms. This would mean that the stability of the turbines in particular would be more predictable.

The FINO3 location, the "Dan Tysk” sandbank, lies about 80 km west of Sylt – where up to 80 windmills will stand in a few years time. Every mill has an influence on the fluid dynamics and generates turbulence in its tow or even periodic movements, which influence other structures. This can lead to unwanted or even dangerous oscillations. In the case of waves this leads to interference.

This means that in a harmless wave field without a fleet of windmills these interferences can generate individual high waves, which may become critical. The wave researchers of the Helmholtz-Zentrum Geesthacht - Centre for Materials and Coastal Research want to observe just that - i.e. waves that have their behaviour changed by the structure.