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

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.

Harmonizing the Mooring System Reliability of Multiline Anchor Wind Farms

ASCE-ASME J Risk and Uncert in Engrg Sys Part B Mech Engrg ◽

10.1115/1.4052423 ◽

2021 ◽

Vol 7 (4) ◽

Author(s):

Spencer T. Hallowell ◽

Sanjay R. Arwade ◽

Brian D. Diaz ◽

Charles P. Aubeny ◽

Casey M. Fontana ◽

...

Keyword(s):

Wind Turbines ◽

System Reliability ◽

Wind Farm ◽

Wind Farms ◽

Offshore Wind ◽

Line System ◽

Offshore Wind Turbines ◽

Anchor System ◽

Additional Safety

Abstract One of many barriers to the deployment of floating offshore wind turbines is the high cost of vessel time needed for soil investigations and anchor installation. A multiline anchor system is proposed in which multiple floating offshore wind turbines (FOWTs) are connected to a single caisson. The connection of multiple FOWTs to a single anchor introduces interconnectedness throughout the wind farm. Previous work by the authors has shown that this interconnectedness reduces the reliability of the FOWT below an acceptable level when exposed to survival loading conditions. To combat the reduction in system reliability an overstrength factor (OSF) is applied to the anchors functioning as an additional safety factor. For a 100 turbine wind farm, single-line system reliabilities can be achieved using the multiline system with an OSF of 1.10, a 10% increase in multiline anchor safety factors for all anchors in a farm.

The Effect of Yaw Error on the Mooring Systems of Floating Offshore Wind Turbines in Extreme Weather Conditions

Volume 10: Ocean Renewable Energy ◽

10.1115/omae2018-77225 ◽

2018 ◽

Author(s):

Evelyn R. Hunsberger ◽

Spencer T. Hallowell ◽

Casey M. Fontana ◽

Sanjay R. Arwade

Keyword(s):

Wind Speed ◽

Wind Turbines ◽

Wind Farm ◽

Turbine Blades ◽

Wind Farms ◽

Offshore Wind ◽

Single Line ◽

Direct Result ◽

Offshore Wind Turbines ◽

As floating offshore wind turbines (FOWTs) become the most viable option for wind farms in deeper waters, it is important to investigate their dynamic response in inclement conditions when failures, such as yaw misalignment, are more likely to occur. This research uses hour-long simulations in FAST, software developed by The National Renewable Energy Lab (NREL), to analyze the effect of yaw error on anchor tensions and platform displacements in both a traditional single-line wind farm geometry, where each anchor is connected to one turbine, and an optimum multiline anchor geometry, where each anchor is connected to three turbines. NREL’s 5 MW reference turbine on a semi-submersible base is analyzed using six realizations of each combination of co-directional wind and waves, wind speed and yaw error; resulting in 2,484 simulations in total. The variability in platform displacements and mooring forces increases as wind speed increases, and as yaw errors approach critical values. The angle of incidence of the co-directional wind and waves dictates which anchor experiences the most tension for both the single-line and multiline concepts. In the multiline geometry, the greatest increases in anchor tension occurs when the downwind turbine has yaw error. Yaw error increases the maximum anchor tension by up to 43% in the single-line geometry and up to 37% in the multiline geometry. In the multiline geometry, yaw error causes the direction of the resultant anchor force to vary by up to 20°. These changes in anchor tension magnitudes and directions are governed by the platform displacements, and are a direct result of the differences in the tangential and normal coefficients of drag of the turbine blades. When designing floating offshore wind farms, the influence of yaw error on loading magnitudes and directions are to be considered when determining the necessary capacities and calculating the corresponding reliabilities for wind turbine components.

Proposal and Performance Study of a Novel Mooring System with Six Mooring Lines for Spar-Type Offshore Wind Turbines

Applied Sciences ◽

10.3390/app112411665 ◽

2021 ◽

Vol 11 (24) ◽

pp. 11665

Author(s):

Shi Liu ◽

Yi Yang ◽

Chao Wang ◽

Yuangang Tu

Keyword(s):

Wind Turbine ◽

Wind Turbines ◽

Offshore Wind ◽

Irregular Waves ◽

Offshore Wind Turbine ◽

Mooring System ◽

Mooring Lines ◽

Included Angle ◽

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.

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

10.1109/metrosea52177.2021.9611621 ◽

2021 ◽

Author(s):

Vincenzo Piscopo ◽

Antonio Scamardella ◽

Giovanni Battista Rossi ◽

Francesco Crenna ◽

Marta Berardengo

Keyword(s):

Fatigue Life ◽

Wind Turbines ◽

Life Assessment ◽

Offshore Wind ◽

Estimation Methods ◽

Spectrum Estimation ◽

Mooring Lines ◽

Offshore Wind Turbines ◽

Fatigue Life Assessment ◽

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 ◽

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.

Floating Performance of a Composite Bucket Foundation with an Offshore Wind Tower during Transportation

Energies ◽

10.3390/en13040882 ◽

2020 ◽

Vol 13 (4) ◽

pp. 882 ◽

Cited By ~ 1

Author(s):

Hongyan Ding ◽

Zuntao Feng ◽

Puyang Zhang ◽

Conghuan Le ◽

Yaohua Guo

Keyword(s):

Wind Turbine ◽

Wind Turbines ◽

Wind Farm ◽

Wind Farms ◽

Interaction Force ◽

Offshore Wind ◽

Construction Technique ◽

Bucket Foundation ◽

Offshore Wind Turbines ◽

One Step

The composite bucket foundation (CBF) for offshore wind turbines is the basis for a one-step integrated transportation and installation technique, which can be adapted to the construction and development needs of offshore wind farms due to its special structural form. To transport and install bucket foundations together with the upper portion of offshore wind turbines, a non-self-propelled integrated transportation and installation vessel was designed. In this paper, as the first stage of applying the proposed one-step integrated construction technique, the floating behavior during the transportation of CBF with a wind turbine tower for the Xiangshui wind farm in the Jiangsu province was monitored. The influences of speed, wave height, and wind on the floating behavior of the structure were studied. The results show that the roll and pitch angles remain close to level during the process of lifting and towing the wind turbine structure. In addition, the safety of the aircushion structure of the CBF was verified by analyzing the measurement results for the interaction force and the depth of the liquid within the bucket. The results of the three-DOF (degree of freedom) acceleration monitoring on the top of the test tower indicate that the wind turbine could meet the specified acceleration value limits during towing.

Numerical Study of a Proposed Semi-Submersible Floating Platform with Different Numbers of Offset Columns Based on the DeepCwind Prototype for Improving the Wave-Resistance Ability

Applied Sciences ◽

10.3390/app9061255 ◽

2019 ◽

Vol 9 (6) ◽

pp. 1255

Author(s):

Zhenqing Liu ◽

Yicheng Fan ◽

Wei Wang ◽

Guowei Qian

Keyword(s):

Wind Turbines ◽

Numerical Study ◽

Wind Farms ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Floating Platform ◽

Offshore Wind Turbines ◽

Irregular Wave ◽

Decay Test ◽

DeepCwind semi-submersible floating offshore wind turbines have been widely examined, and in some countries this type of floating offshore wind turbine has been adopted in the construction of floating wind farms. However, the DeepCwind semi-submersible floating offshore wind turbines still experience large surge motion that limits their operational time. Therefore, in this study, a semi-submersible floating platform with different numbers of offset columns, but with the same total weight, based on the DeepCwind prototype is proposed. From the free-decay test, it was found that the number of the floating columns will affect the natural frequency of the platform. Furthermore, the regular wave test in the time domain and the irregular wave test in the frequency domain show that increasing the number of the floating columns will reduce the surge motion greatly, while the effects in the heave and pitch motions are not obvious.

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 ◽

Efficient Multiline Anchor Systems for Floating Offshore Wind Turbines

Volume 6: Ocean Space Utilization; Ocean Renewable Energy ◽

10.1115/omae2016-54476 ◽

2016 ◽

Cited By ~ 3

Author(s):

Casey M. Fontana ◽

Sanjay R. Arwade ◽

Don J. DeGroot ◽

Andrew T. Myers ◽

Melissa Landon ◽

...

Keyword(s):

Dynamic Simulation ◽

Wind Turbines ◽

Wind Farm ◽

Offshore Wind ◽

Wave Loading ◽

Peak Demand ◽

Offshore Wind Turbines ◽

Anchor Systems ◽

Floating Platforms

A mooring and anchoring concept for floating offshore wind turbines is introduced in which each anchor moors multiple floating platforms. Several possible geometries are identified and it is shown that the number of anchors for a wind farm can be reduced by factors of at least 3. Dynamic simulation of turbine dynamics for one of the candidate geometries and for two directions of wind and wave loading allows estimation of multiline anchor forces the preview the types of loads that a multiline anchor will need to resist. Preliminary findings indicate that the peak demand on the anchor may be reduced by as much as 30% but that anchors used in such a system will need to be able to resist multi-directional loading.

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 ◽

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.