Abstract
In this study, the typical ocean environment was simulated with the aim to investigate the dynamic response under various environmental conditions of a Tension Leg Platform (TLP) type floating offshore wind turbine system. By applying Froude scaling, a scale model with a scale of 1:200 was designed and model experiments were carried out in a lab-scale wave flume that generated regular periodic waves by means of a piston-type wave generator while a wave absorber dissipated wave energy on the other side of the channel. The model was designed and manufactured based on the standard prototype of the National Renewable Energy Laboratory (NREL) 5 MW offshore wind turbine. In the first half of the study, the motion and structural responses for operational wave conditions of the North Sea near Scotland were considered to investigate the performance of a traditional TLP floating wind turbine compared with that of a newly designed TLP with added mooring lines. The new mooring lines were attached with the objective of increasing the horizontal stiffness of the system and thereby reducing the dominant motion of the TLP platform (i.e., the surge motion). The results of surge translational motions were obtained both in the frequency domain, using the response amplitude operator (RAO), and in the time domain, using the omega arithmetic method for the relative velocity. The results obtained show that our suggested concept improves the stability of the platform and reduces the overall motion of the system in all degrees-of-freedom. Moreover, the modified design was verified to enable operation in extreme wave conditions based on real data for a 100-year return period of the Northern Sea of California. The loads applied by the waves on the structure were also measured experimentally using modified Morison equation—the formula most frequently used to estimate wave-induced forces on offshore floating structures. The corresponding results obtained show that the wave loads applied on the new design TLP had less amplitude than the initial model and confirmed the significant contribution of the mooring lines in improving the performance of the system.
Highlights
Offshore wind turbines generate more electricity than their onshore counterparts owing to higher wind speeds occasioned by the low surface roughness of the ocean
Wayman and Scalavonous [2] conducted comparative static and dynamic analyses of a Tension Leg Platform (TLP) FOWT and a shallow drafted barge FOWT to explore the effects of water depth, wind speed, and combined wind–wave conditions on system performance
A new tension leg platform conceptual design for offshore wind turbines was proposed with the objective of reducing the dominant surge motion of this kind of platform
Summary
Offshore wind turbines generate more electricity than their onshore counterparts owing to higher wind speeds occasioned by the low surface roughness of the ocean. Energy Laboratory (NREL) 5 MW offshore wind turbine, which is considered the baseline wind turbine This model has been mounted on various types of floating platforms and studies conducted on each structure. Wayman and Scalavonous [2] conducted comparative static and dynamic analyses of a Tension Leg Platform (TLP) FOWT and a shallow drafted barge FOWT to explore the effects of water depth, wind speed, and combined wind–wave conditions on system performance. In their study, they evaluated the response amplitude operator (RAO) standard deviation of the system in order to define the natural frequency at each degree of freedom. Naqvi [4] performed experiments using a 1:100 scale TLP and spar buoy derived from the NREL prototype to study the motion and tension in the cables in response to regular waves and operational wind speed
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