Abstract
The catenary mooring system is a well recognized station keeping method. However, there could be economical and environmental benefits of reducing the footprint. In the last decades, more focus has been given to synthetic mooring lines and different mooring layouts to optimize the levelized cost of energy (LCOE) for offshore renevable energy converters such as wave energy converters. Therefore, this work presents a parametric study of two important parameters, namely the mooring line angle and line pretension, for a taut mooring configuration focusing on the dynamic response when applied to the TetraSpar floating foundation compared to a catenary mooring system. The work is based on experimental results conducted in the wave basin at Aalborg University (AAU) and compared to analytical stiffness calculations. In addition, a numerical model was tuned based on the main dynamics to achieve the tension response. The results showed satisfying dynamic behavior where the angle and pretension mainly influenced the surge and yaw natural periods. The motion response showed similar behavior between the chosen parameters, and larger pitch amplitudes were found compared to the catenary system.
Highlights
The wind energy sector has over the past decades shown a continuous reduction in costs [1], and both the onshore and offshore wind turbines provide a commercially viable alternative to conventional CO2-emitting power generation in northwestern Europe and along the North American east coast.In Europe, the rapid expansion of new sites is massively dominated by bottom-fixed turbines at water depths between 20 and 40 m [2], despite the fact that 80% of the total wind resource is located at sites of +60 m of water [1]
More focus has been given to synthetic mooring lines and different mooring layouts to optimize the levelized cost of energy (LCOE) for offshore renevable energy converters such as wave energy converters
This work presents a parametric study of two important parameters, namely the mooring line angle and line pretension, for a taut mooring configuration focusing on the dynamic response when applied to the TetraSpar floating foundation compared to a catenary mooring system
Summary
The wind energy sector has over the past decades shown a continuous reduction in costs [1], and both the onshore and offshore wind turbines provide a commercially viable alternative to conventional CO2-emitting power generation in northwestern Europe and along the North American east coast.In Europe, the rapid expansion of new sites is massively dominated by bottom-fixed turbines at water depths between 20 and 40 m [2], despite the fact that 80% of the total wind resource is located at sites of +60 m of water [1]. The catenary mooring has been the main choice in the design of the spar type floating offshore wind turbines. The relation between the anchor and the mooring line is a key point for catenary mooring, where a significant part of the chain lays horizontally along the seabed to prevent vertical anchor loads This length is, a considerable contribution to the total footprint, as the prevention of vertical lift is designed based on ultimate limit state (ULS) load cases. The footprint is defined as the radius from the FOWT center to the anchor points With this in mind, some negative aspects for the catenary mooring system exists, including the design, environment and material costs: 1. The intended restoring response could be changed
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