Lead Session Chair:
Stephan Barth, Managing Director, ForWind - Center for Wind Energy Research, Germany
Andreas Manjock (1) F P Jose Azcona (2) Frank Sandner (3)
(1) DNV GL, Hamburg, Germany (2) CENER, Pamplona, Spain (3) University of Stuttgart, Stuttgart, Germany
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Presenter's biographyBiographies are supplied directly by presenters at OFFSHORE 2015 and are published here unedited
Andreas Manjock is in wind energy since over two decades. His master thesis at TU-Berlin was already dealing about a large offshore wind turbine. In the 1990's he gets familiar with rotor blade design and production during his engagement for a blade manufacturer. In 2001 he joined Germanischer Llyd, now DNV GL, as a load calculation expert. He is specialised on load assumptions for bottom mounted and floating offshore wind turbines. Currently he has the role as deputy head of the section “Offshore Loads and Site Conditions” at DNV GL Renewables Certification in Hamburg.
Tank testing of Rotor thrust modeling of floating wind turbines
Floating Wind Turbines (FWT) are seen a promising foundation concept for the exploration of deep water areas where bottom mounted foundation concepts such as monopile and jacket design reach their economical limits. Especially in countries like Norway, Spain, Scotland, US, Japan and Korea which have steep coast lines, FWT are able to harvest the stable and profitable wind resource at water depth above 60m. As opposed to a fixed structure, FWT are merely attached to the seafloor by the mooring lines.
The numerical simulation tools for calculating motion and dynamics of FWT are still under development. Many existing codes of the offshore and oil & gas industry provide approved and validated routines describing the dynamics and loading from waves and currents to floating structures. But they lack a sufficient consideration of the wind loaded part of a FWT caused by turbulent wind, complex rotor aerodynamics and an own control system on top of the structure. This introduces a fully non-linear loading source to the entire system.
Main body of abstract
In order to model correctly the global system behavior towards environmental impacts from wind and waves overall and structural system dynamics need to be properly scaled. This can be achieved by maintaining a constant Froude number. These constant non dimensional quantities lead to specific model scale factors that are used in the design process of the experimental model. The correct design of experimental FWT models is a difficult procedure due to the interaction of the regarded system with two different environments, wind and waves, which ask for counteracting scaling procedures. Two methods for modelling aerodynamic thrust force (and torque) have been applied in a test campaign:
A real-time controlled fan can be used to produce a given thrust force aligned with the correct Froude-scaled force. The introduced “Software-in-the-Loop” approach enables to apply varying rotor thrust at the tower top of FWT model representing realistic aerodynamic damping. Turbine control behaviour from previous simulations can be applied as well as wind gust loading. Another very advanced solution is to design a specific test rotor for low Reynolds numbers, which keeps roughly the tip-speed ratio and the Froude-number.
This study is dealing with the experimental scale testing of a semisubmersible design type focusing on the relevant parameters for rotor thrust modelling. Therefore this study compares the different approaches of rotor thrust modeling with the so called “Software-in-the-loop” controlled thrust generator and the low Reynolds number blade design approach.
The results of the study will be supported by tank tests planned within the EU Seventh Framework Programme Innwind (ENERGY.2012.2.3.1 “Innovative wind conversion systems (10-20MW) for offshore applications”).