a b s t r a c tTension leg platform wind turbines (TLPWTs) represent one potential method for accessing offshore wind resources in moderately deep water. Although numerous TLPWT designs have been studied and presented in the literature, there is little consensus regarding optimal design, and little information about the effect of various design variables on structural response. In this study, a wide range of parametric single-column TLPWT designs are analyzed in four different wind-wave conditions using the Simo, Riflex, and AeroDyn tools in a coupled analysis to evaluate platform motions and structural loads on the turbine components and tendons. The results indicate that there is a trade-off between performance in storm conditions, which improves with larger displacement, and cost, which increases approximately linearly with displacement. Motions perpendicular to the incoming wind and waves, especially in the parked configuration, may be critical for TLPWT designs with small displacement. Careful choice of natural period, diameter at the water line, ballast, pretension, and pontoon radius can be used to improve the TLPWT performance in different environmental conditions and water depths.
This article presents a method for performing Real-Time Hybrid Model testing (ReaTHM testing) of a floating wind turbine (FWT). The advantage of this method compared to the physical modelling of the wind in an ocean basin, is that it solves the Froude-Reynolds scaling conflict, which is a key issue in FWT testing. ReaTHM testing allows for more accurate testing also in transient conditions, or degraded conditions, which are not feasible yet with physical wind. The originality of the presented method lies in the fact that all aerodynamic load components of importance for the structure were identified and applied on the physical model, while in previous similar projects, only the aerodynamic thrust force was applied on the physical model. The way of applying the loads is also new. The article starts with a short review (mostly references) of ReaTHM testing when applied to other fields than marine technology. It then describes the design of the hybrid setup, its qualification, and discusses possible error sources and their quantification. The second part of the article [1] focuses on the performance of a braceless semisubmersible FWT, tested with the developed method. The third part [2] describes how the experimental data was used to calibrate a numerical model of the FWT.
Phase I of the OC6 project is focused on examining why offshore wind design tools underpredict the response (loads/motion) of the OC5-DeepCwind semisubmersible at its surge and pitch natural frequencies. Previous investigations showed that the underprediction was primarily related to nonlinear hydrodynamic loading, so two new validation campaigns were performed to separately examine the different hydrodynamic load components. In this paper, we validate a variety of tools against this new test data, focusing on the ability to accurately model the low-frequency loads on a semisubmersible floater when held fixed under wave excitation and when forced to oscillate in the surge direction. However, it is observed that models providing better load predictions in these two scenarios do not necessarily produce a more accurate motion response in a moored configuration.
The global dynamic response of floating wind turbines is commonly simulated using aero‐hydro‐servo‐elastic tools that consider numerically generated wind files as input. Based on the guidelines given in existing standards, two methods of generating such wind files are typically used: the Mann uniform shear model and the Kaimal spectral and exponential coherence model. Both models consider the Kaimal spectrum with similar frequency characteristics: The main difference between the approaches is related to the spatial coherence. The present work examines the consequences of using the two different wind file generation methods for estimating the global responses of representative spar, semi‐submersible, and tension leg platform (TLP) 5 MW wind turbines. Predictions of the standard deviation of low‐frequency responses in operational conditions, including motions at the natural frequency in surge and pitch as well as quasi‐static (spar, TLP) and resonant (semi‐submersible) motions in yaw, are seen to differ up to 30% to 40% depending on the wind field model. The differences in motion responses have important consequences for the design of the mooring system components. Proper orthogonal decomposition (POD) techniques are used to qualitatively explain the differing spatial coherence of the wind field. Simulations including a limited number of POD modes in the wind field highlight the importance of the low‐frequency, energy‐rich modes, suggesting that this type of visualization can be a useful tool.
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