Abstract
To obtain fundamental knowledge on the elastic response characteristics of a light-weight floating support structure of a FOWT (floating offshore wind turbine) with guywire supported tower, basic load transmission mechanism was investigated. Static analysis with elastic frame model, numerical analysis and wave tank experiment with elastically and dynamically similar segmented backbone model were conducted to clarify the dynamic elastic response characteristics of the structure. In the numerical analysis, analysis code of a rotor-floater-mooring-control coupled response NK-UTWind developed in University of Tokyo is used. It is clarified that when the rigidity of the frame structural part is low compared with guywire, the load is mainly borne by guywire under pitch motion. It was found that the tension fluctuation of guywire becomes large at wave period of 6 s when the inertial force due to pitch motion is large, and at wave period of 18–20 s when inclination of tower is larger the tension fluctuation also becomes large due to the overturning moment.
Highlights
Concerning floating offshore wind turbines, demonstration of technological feasibility by domestic technology is under way in Japan, and floating offshore wind turbines of real scale are operated in real sea
The assumed floating support structure is a light-weight FOWT with guywire supported tower moored by single point mooring system and yaw mechanism is abolished [4], but since the shape is complicated, such as the inclination of the tower with different length of guywires, a generalized model was designed extracting general features of the guywire supported structure
For the calculation of the aerodynamic load acting on the rotor, wind turbine analysis code FAST [6, 10] based on the blade element momentum theory (BEM) developed by NREL is used
Summary
Concerning floating offshore wind turbines, demonstration of technological feasibility by domestic technology is under way in Japan, and floating offshore wind turbines of real scale are operated in real sea. This type is a light-weight semi-submersible type floating structure and requirement for tower strength which is stringent in conventional design is much relieved by the use of guywire in particular at the base of the tower While this floating type is expected to be considerably lighter, elastic response due to wind and waves may be increased due to a decrease in rigidity, and this may have an effect on the mooring system. There is a two-step solution method that separately evaluates the rigid body motion and structural response In the another method, a one-step solution method, a floating offshore wind turbine is modeled as an elastic body, and the structural response is solved simultaneously with the rigid body motion movement.
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