Incidence of spectrum estimation methods on the fatigue life assessment of mooring lines for floating offshore wind turbines

Spar-type floating offshore wind turbines commonly vibrate excessively when under the coupling impact of wind and wave. The wind turbine vibration can be controlled by developing its mooring system. Thus, this study proposes a novel mooring system for the spar-type floating offshore wind turbine. The proposed mooring system has six mooring lines, which are divided into three groups, with two mooring lines in the same group being connected to the same fairlead. Subsequently, the effects of the included angle between the two mooring lines on the mooring-system’s performance are investigated. Then, these six mooring lines are connected to six independent fairleads for comparison. FAST is utilized to calculate wind turbine dynamic response. Wind turbine surge, pitch, and yaw movements are presented and analyzed in time and frequency domains to quantitatively evaluate the performances of the proposed mooring systems. Compared with the mooring system with six fairleads, the mooring system with three fairleads performed better. When the included angle was 40°, surge, pitch, and yaw movement amplitudes of the wind turbine reduced by 39.51%, 6.8%, and 12.34%, respectively, when under regular waves; they reduced by 56.08%, 25.00%, and 47.5%, respectively, when under irregular waves. Thus, the mooring system with three fairleads and 40° included angle is recommended.

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Hydro-Servo-Aero-Elastic Analysis of Floating Offshore Wind Turbines

Fluids ◽

10.3390/fluids5040200 ◽

2020 ◽

Vol 5 (4) ◽

pp. 200

Author(s):

Dimitris I. Manolas ◽

Vasilis A. Riziotis ◽

George P. Papadakis ◽

Spyros G. Voutsinas

Keyword(s):

Structural Dynamics ◽

Wind Turbines ◽

Computational Cost ◽

Physical Models ◽

Offshore Wind ◽

Mooring Lines ◽

Rotor Aerodynamics ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines ◽

Free Wake

A fully coupled hydro-servo-aero-elastic simulator for the analysis of floating offshore wind turbines (FOWTs) is presented. All physical aspects are addressed, and the corresponding equations are concurrently solved within the same computational framework, taking into account the wind and wave excitations, the aerodynamic response of the rotor, the hydrodynamic response of the floater, the structural dynamics of the turbine-floater-mooring lines assembly and finally the control system of the wind turbine. The components of the complex multi-physics system of a FOWT interact with each other in an implicitly coupled manner leading to a holistic type of modeling. Different modeling options, of varying fidelity and computational cost, are made available with respect to rotor aerodynamics, hydrodynamic loading of the floater and mooring system dynamics that allow for timely routine certification simulations, but also for computationally intense simulations of less conventional operating states. Structural dynamics is based on nonlinear multibody analysis that allows reproducing the large rigid body motions undergone by the FOWT, as well as large deflections and rotations of the highly flexible blades. The paper includes the description of the main physical models, of the interaction and solution strategy and representative results. Verification is carried out by comparing with other state-of-art tools that participated in the Offshore Code Comparison Collaboration Continuation (OC4) IEA Annex, while the advanced simulation capabilities are demonstrated in the case of half-wake interaction of floating wind turbines by employing the free-wake aerodynamic method.

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Evaluation of a Hybrid Representation to Model the Wind Turbine, Platform and Mooring Lines in the Analysis of Floating Offshore Wind Turbines

10.1115/1.0001206v ◽

2021 ◽

Author(s):

Eloi Daniel de Araujo Neto ◽

William Rodriguez ◽

Fabr\xedcio Nogueira Corr\xeaa ◽

Beatriz De Souza Leite Pires De Lima ◽

Breno Pinheiro Jacob ◽

...

Keyword(s):

Wind Turbine ◽

Wind Turbines ◽

Offshore Wind ◽

Mooring Lines ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines

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Fatigue Assessment of Moorings for Floating Offshore Wind Turbines by Advanced Spectral Analysis Methods

Journal of Marine Science and Engineering ◽

10.3390/jmse10010037 ◽

2021 ◽

Vol 10 (1) ◽

pp. 37

Author(s):

Vincenzo Piscopo ◽

Antonio Scamardella ◽

Giovanni Battista Rossi ◽

Francesco Crenna ◽

Marta Berardengo

Keyword(s):

Spectral Analysis ◽

Wind Turbine ◽

Wind Turbines ◽

Time Domain ◽

Offshore Wind ◽

Stress Process ◽

Mooring Lines ◽

Offshore Wind Turbines ◽

Analysis Methods ◽

Floating Offshore Wind Turbines

The fatigue assessment of mooring lines for floating offshore wind turbines represents a challenging issue not only for the reliable design of the stationkeeping system but also for the economic impact on the installation and maintenance costs over the entire lifetime of the offshore wind farm. After a brief review about the state-of-art, the nonlinear time-domain hydrodynamic model of floating offshore wind turbines moored by chain cables is discussed. Subsequently, the assessment of the fatigue damage in the mooring lines is outlined, focusing on the combined-spectrum approach. The relevant fatigue parameters, due to the low- and wave-frequency components of the stress process, are estimated by two different methods. The former is based on the time-domain analysis of the filtered stress process time history. The latter, instead, is based on the spectral analysis of the stress process by two advanced methods, namely the Welch and Thomson ones. Subsequently, a benchmark study is performed, assuming as reference floating offshore wind turbine the OC4-DeepCWind semisubmersible platform, equipped with the 5 MW NREL wind turbine. The cumulative fatigue damage is determined for eight load conditions, including both power production and parked wind turbine situations. A comparative analysis between time-domain and spectral analysis methods is also performed. Current results clearly show that the endorsement of advanced spectral analysis methods can be helpful to improve the reliability of the fatigue life assessment of mooring lines.

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DESIGN OF A 3D PHYSICAL AND NUMERICAL EXPERIMENT ON FLOATING OFF-SHORE WIND TURBINES

Coastal Engineering Proceedings ◽

10.9753/icce.v33.structures.67 ◽

2012 ◽

Vol 1 (33) ◽

pp. 67 ◽

Cited By ~ 7

Author(s):

Giuseppe Roberto Tomasicchio ◽

Elvira Armenio ◽

Felice D'Alessandro ◽

Nuno Fonseca ◽

Spyros A. Mavrakos ◽

...

Keyword(s):

Wind Turbines ◽

Preliminary Test ◽

Offshore Wind ◽

Mooring Lines ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines ◽

Wave Basin ◽

Particle Hydrodynamics ◽

Smoothed Particle ◽

Smoothed Particle Hydrodynamics Method

The knowledge of the behavior of floating offshore wind turbines (W/T) under wave and/or wind action remains one of the most difficult challenges in offshore engineering which is mostly due to the highly non-linear response of the structure. The present study describes the design process of a 3D physical experiment to investigate the behavior of the most promising structure technology of floating W/T: spar buoy (SB) and tension leg platform (TLP) under different meteo conditions. In order to properly design the two W/T models, the following topics have been analyzed: mooring lines, mass distribution, appropriate scaling factor and data relative to the geometrical characteristics, wave basin dimensions and wind and waves conditions. In addition, the Smoothed Particle Hydrodynamics method (SPH) (Monaghan 1994) has been considered to simulate the 3D behavior of a floating offshore W/T. In particular, the SPH, calibrated and verified on the basis of the experimental observations, may represent a reliable tool for preliminary test of changes in the floater geometry.

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Investigation of Hydrodynamic Forces for Floating Offshore Wind Turbines on Spar Buoys and Tension Leg Platforms with the Mooring Systems in Waves

Applied Sciences ◽

10.3390/app9030608 ◽

2019 ◽

Vol 9 (3) ◽

pp. 608 ◽

Cited By ~ 1

Author(s):

Yu-Hsien Lin ◽

Shin-Hung Kao ◽

Cheng-Hao Yang

Keyword(s):

Wind Turbines ◽

Time Domain ◽

Simulation System ◽

Offshore Wind ◽

Modular System ◽

Mooring System ◽

Mooring Lines ◽

Offshore Wind Turbines ◽

Motion Responses ◽

Floating Offshore Wind Turbines

This study aims to develop a modularized simulation system to estimate dynamic responses of floating Offshore Wind Turbines (OWTs) based on the concepts of spar buoy and Tension Leg Platform (TLP) corresponding with two typical mooring lines. The modular system consists of the hydrodynamic simulator based the Cummins time domain equation, the Boundary Element Method (BEM) solver based on the 3D source distribution method, and an open-source visualization software ParaView to analyze the interaction between floating OWTs and waves. In order to realize the effects of mooring loads on the floating OWTs, the stiffness and damping matrices are applied to the quasi-static mooring system. The Response Amplitude Operators (RAOs) are compared between our predicted results and other published data to verify the modularized simulation system and understand the influence of mooring load on the motion responses in regular or irregular waves. It is also demonstrated that the quasi-static mooring system is applicable to different types of mooring lines as well as determining real-time motion responses. Eventually, wave load components at the resonance frequencies of different motion modes for selected floating OWTs would be present in the time domain.

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Wave hydrodynamic forces over mooring lines on floating offshore wind turbines

Ocean Engineering ◽

10.1016/j.oceaneng.2019.106730 ◽

2020 ◽

Vol 195 ◽

pp. 106730

Author(s):

Pau Trubat ◽

Climent Molins ◽

Xavi Gironella

Keyword(s):

Wind Turbines ◽

Hydrodynamic Forces ◽

Offshore Wind ◽

Mooring Lines ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines

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Importance of Control Strategies on Fatigue Life of Floating Wind Turbines

Volume 5: Ocean Space Utilization; Polar and Arctic Sciences and Technology; The Robert Dean Symposium on Coastal and Ocean Engineering; Special Symposium on Offshore Renewable Energy ◽

10.1115/omae2007-29277 ◽

2007 ◽

Cited By ~ 23

Author(s):

Bjo̸rn Skaare ◽

Tor David Hanson ◽

Finn Gunnar Nielsen

Keyword(s):

Fatigue Life ◽

Wind Turbine ◽

Wind Turbines ◽

Control Strategy ◽

Control Strategies ◽

Offshore Wind ◽

Offshore Wind Turbines ◽

Pitch Control ◽

Floating Wind Turbine ◽

Floating Offshore Wind Turbines

Exploitation of wind energy at deep-waters locations requires floating wind turbine foundations. Several floating wind turbine foundation concepts are reported in the literature, and a common challenge is to make a low cost foundation with acceptable motion characteristics. In order to analyze the fatigue life of floating offshore wind turbines, the coupled action of wind, waves, current and blade pitch control strategy must be considered. State-of-the-art computer programs for motion analysis of moored offshore bodies, Simo-Riflex from Sintef Marintek, are coupled to a state-of-the-art aero-elastic computer program for wind turbines, Hawc2 from Riso̸ National Laboratory. The wave loads on the body may include wave diffraction and radiation loads as well as viscous forces. The mooring lines are modelled using cable finite elements with inertia and drag forces. The wind load on the rotor is based on common rotor aerodynamics including corrections for skew inflow and relative motion caused by large displacement and large tilt and yaw rotations of the rotor. Conventional wind turbine control strategies lead to wind-induced loads that may amplify or damp the motions of the floating wind turbine. The first case is a result of the blade pitch control strategy above rated wind speed for the wind turbine, and can result in large resonant motions that will reduce the fatigue life of the floating wind turbine significantly. The latter case implies energy extraction from the waves. This paper addresses the importance of control strategies on fatigue life for a given floating offshore wind turbine. A fatigue life time comparison between a conventional blade pitch control strategy and an estimator based blade pitch control strategy show that the fatigue life of floating offshore wind turbines can be significantly increased by use of alternative blade pitch control strategies.

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Fibre Spring Mooring Solution for Mooring Floating Offshore Wind Turbines in Shallow Water

10.1115/omae2021-62892 ◽

2021 ◽

Author(s):

Paul McEvoy ◽

Seojin Kim ◽

Malak Haynes

Keyword(s):

Shallow Water ◽

Wind Turbines ◽

Wind Farm ◽

Significant Proportion ◽

Wind Farms ◽

Offshore Wind ◽

Mooring Lines ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines ◽

Electrical Cables

Abstract Mooring of Floating Offshore Wind Turbines (FOWT) in shallow water sites (30–80m) is challenging. These sites account for a significant proportion of the nearer to shore potential wind farm locations, and are desirable as they are closer to existing infrastructure and easier to access. Mooring large floating structures in very shallow waters however results in very long heavy mooring lines designed to minimize platform surge and protect the electrical cables. This paper presents an innovative Fibre Spring Mooring (FSM) solution which combines a high modulus, non-stretch, lightweight rope with a compliant nonlinear polymer spring offering a complete semi-taut mooring system which can be connected directly between the platform and the seabed. The paper will present Orcaflex simulation results of a 12MW barge type FOWT platform, moored using a semi-taut FSM mooring at three chosen North Sea locations close to existing wind farms, of 30m, 40m and 50m water depths. Different FSM configurations, with different line lengths, footprint, and ratio of fibre to spring are considered.

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