Offshore wind energy is one of the most promising renewable energy resources and an increasing interest arises to develop floating vertical axis wind turbines (VAWTs), which have the potential to reduce the cost of energy. Assessment of the performance of floating VAWTs requires sophisticated fully coupled aerohydro-servo-elastic simulation tools, which are currently limited. This paper aims to develop a fully integrated simulation tool for floating VAWTs. Based on the actuator cylinder (AC) flow model, aerodynamic modeling of floating VAWTs is established with consideration of the effects of turbulence, dynamic inflow and dynamic stall. The developed aerodynamic code is then coupled with the code SIMO-RIFLEX to achieve a fully coupled tool, i.e. SIMO-RIFLEX-AC, which can account for the aerodynamic, hydrodynamics, structural dynamics and controller dynamics with high fidelity. A series of code-to-code comparisons with the codes HAWC2 and SIMO-RIFLEX-DMS are carried out using a landbased VAWT and a semi VAWT, and reveal that the present code can predict the aerodynamic loads and dynamic responses accurately. Moreover, the code SIMO-RIFLEX-AC can predict more accurate responses than the code SIMO-
The Norwegian Public Road Administration (NPRA) is currently developing the E39 ferry-free project, in which several floating bridges will be built across deep and wide fjords. In this study, we consider the floating bridge that was an early concept for crossing the Bjørnafjorden with a width of about 4600 m and with a depth of more than 500 m. The floating bridge concept is a complex endanchored curve bridge, consisting of a cable-stayed high bridge part and a low bridge part supported by 19 pontoons. It has a number of eigen-modes, which can be excited by wave loads. Wave loads and their effects should thus be properly modeled and assessed. Therefore, the effect of hydrodynamic load modeling are investigated in homogeneous wave conditions, including varying water depth at the ends of the bridge, viscous drag force on pontoons, short-crestedness and second order wave loads. It is found that the varying water depth has negligible effect, while the other features are important to consider. Second order difference-frequency wave loads contribute significantly to sway motion, axial force and strong axis bending moments along the bridge. However, these effects can be reduced by viscous drag forces, which implies that an appropriate model of viscous drag force effect on the pontoons is important. short-crested
Recently, interest in the development of floating vertical axis wind turbines (FVAWTs) has been increasing, since FVAWTs might prove to be one of the optimal configurations in deep waters. In this study, a FVAWT with a 5 MW Darrieus rotor was used as the reference wind turbine and was mounted on three different floating support structures: the OC3 spar buoy, the OC4 semi-submersible, and a tension leg platform (TLP). Fully coupled nonlinear time domain simulations using the code SIMO-RIFLEX-DMS were conducted. A series of load cases with turbulent wind and irregular waves was carried out to investigate the dynamic responses of these three FVAWT concepts by estimating the generator power production, the platform motions, the tower base bending moments, and the mooring line loads. For the spar, semi-submersible, and TLP FVAWT concepts, twice-per-revolution (2P) effects resulting from the 2P aerodynamic loads are prominent in the dynamic responses of these concepts. Because of the compliant catenary mooring systems, the spar and the semisubmersible can help to mitigate the 2P effects on structural loads and mooring line tensions as compared to the TLP concept, at the cost of larger platform motions. The TLP is not a good substructure for a vertical axis wind turbine unless the cyclic variation of aerodynamic loads is significantly reduced.
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