Parametric Study of a Taut Compliant Mooring System for a FOWT Compared to a Catenary Mooring

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.

Impacts of water depth increase on offshore floating wind turbine dynamics

“…A lumped-mass model (Hall and Goupee, 2015) is used for the dynamic response of the mooring line and realised through the MoorDyn Module of FAST (Hall, 2017). Numerical modelling of mooring line considered hydrodynamic loadings (Morison et al, 1950) and a linear stiffness representation (Bach-Gansmo et al, 2020). For slack mooring chains with a certain component on the seabed, it is important to model the dynamic interactions between the horizontal mooring line and the seabed.…”

A Comparative Investigation of Prevalent Hydrodynamic Modelling Approaches for Floating Offshore Wind Turbine Foundations: A TetraSpar Case Study

“…The latter has been particularly focused on the dynamic response of the concept. Several experimental campaigns have tested the coupled hydro-and aerodynamic response [12][13][14], while numerical models have been used to test various design aspects and response of the FOWT foundation [15][16][17].…”

Modeling the TetraSpar Floating Offshore Wind Turbine Foundation as a Flexible Structure in OrcaFlex and OpenFAST

“…In summer 2021, a 3.6 MW demonstrator completed manufacturing in Denmark and was installed off the Norwegian coast [8]. During the design phase of the concept, several experimental test campaigns and studies were conducted [10][11][12], while the final design highly relied on numerical modeling [13][14][15]. Naturally, this resembles the procedure applied by most other FOWT developers and designers of offshore structures and is recommended by most design standards such as DNVGL-OS-E301 [16], DNVGL-RP-C205 [17], IEC TS 61400-3-2:2019 [18], and DNVGL-ST-0119 [19].…”