Numerical Analysis of a Catenary Mooring System Attached by Clump Masses for Improving the Wave-Resistance Ability of a Spar Buoy-Type Floating Offshore Wind Turbine

The International Energy Agency (IEA), under the auspices of their Offshore Code Comparison Collaboration (OC3) initiative, has completed high-level design OC-3 Hywind system. In this system the wind turbine is supported by a spar buoy platform, showing good wave-resistance performance. However, there are still large values in the motion of surge degree of freedom (DOF). Addition of clump masses on the mooring lines is an effective way of reducing the surge motion. However, the optimization of the locations where the clump masses are added is still not clear. In this study, therefore, an in-house developed code is verified by comparing the results of the original OC3 model with those by FAST. The improvement of the performance of this modified platform as a function of the location of the clump masses has been examined under three regular waves and three irregular waves. In the findings of these examination, it was apparent that attaching clump masses with only one-tenth of the mass of the total mooring-line effectively reduces the wave-induced response. Moreover, there is an obvious improvement as the depth of the location where the clump masses mounted is increased.

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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 ◽

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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Alternative Mooring Systems for a Very Large Offshore Wind Turbine Supported by a Semisubmersible Floating Platform

Journal of Solar Energy Engineering ◽

10.1115/1.4039984 ◽

2018 ◽

Vol 140 (5) ◽

Cited By ~ 2

Author(s):

Jinsong Liu ◽

Lance Manuel

Keyword(s):

Wind Turbine ◽

Integrated System ◽

Offshore Wind ◽

Mooring Line ◽

Offshore Wind Turbine ◽

System Response ◽

Mooring System ◽

Floating Platform ◽

Mooring Lines ◽

Wind Speeds

As offshore wind turbines supported on floating platforms extend to deep waters, the various effects involved in the dynamics, especially those resulting from the influence of moorings, become significant when predicting the overall integrated system response. The combined influence of waves and wind affect motions of the structure and induce tensile forces in mooring lines. The investigation of the system response under misaligned wind-wave conditions and the selection of appropriate mooring systems to minimize the turbine, tower, and mooring system loads is the subject of this study. We estimate the 50-year return response of a semisubmersible platform supporting a 13.2 MW wind turbine as well as mooring line forces when the system is exposed to four different wave headings with various environmental conditions (wind speeds and wave heights). Three different mooring system patterns are presented that include 3 or 6 mooring lines with different interline angles. Performance comparisons of the integrated systems may be used to define an optimal system for the selected large wind turbine.

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Development and Verification of an Aero-Hydro-Servo-Elastic Coupled Model of Dynamics for FOWT, Based on the MoWiT Library

Energies ◽

10.3390/en13081974 ◽

2020 ◽

Vol 13 (8) ◽

pp. 1974

Author(s):

Mareike Leimeister ◽

Athanasios Kolios ◽

Maurizio Collu

Keyword(s):

Wind Turbine ◽

International Energy Agency ◽

Coupled Model ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

System Behavior ◽

Energy Agency ◽

Realistic Representation ◽

Non Linear System ◽

Fully Coupled

The complexity of floating offshore wind turbine (FOWT) systems, with their coupled motions, aero-hydro-servo-elastic dynamics, as well as non-linear system behavior and components, makes modeling and simulation indispensable. To ensure the correct implementation of the multi-physics, the engineering models and codes have to be verified and, subsequently, validated for proving the realistic representation of the real system behavior. Within the IEA (International Energy Agency) Wind Task 23 Subtask 2 offshore code-to-code comparisons have been performed. Based on these studies, using the OC3 phase IV spar-buoy FOWT system, the Modelica for Wind Turbines (MoWiT) library, developed at Fraunhofer IWES, is verified. MoWiT is capable of fully-coupled aero-hydro-servo-elastic simulations of wind turbine systems, onshore, offshore bottom-fixed, or even offshore floating. The hierarchical programing and multibody approach in the object-oriented and equation-based modeling language Modelica have the advantage (over some other simulation tools) of component-based modeling and, hence, easily modifying the implemented system model. The code-to-code comparisons with the results from the OC3 studies show, apart from expected differences due to required assumptions in consequence of missing data and incomplete information, good agreement and, consequently, substantiate the capability of MoWiT for fully-coupled aero-hydro-servo-elastic simulations of FOWT systems.

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Dynamic Response for a Submerged Floating Offshore Wind Turbine with Different Mooring Configurations

Journal of Marine Science and Engineering ◽

10.3390/jmse7040115 ◽

2019 ◽

Vol 7 (4) ◽

pp. 115 ◽

Cited By ~ 5

Author(s):

Yane Li ◽

Conghuan Le ◽

Hongyan Ding ◽

Puyang Zhang ◽

Jian Zhang

Keyword(s):

Dynamic Response ◽

Wind Turbine ◽

Dynamic Responses ◽

Offshore Wind ◽

Mooring Line ◽

Offshore Wind Turbine ◽

Intermediate Water ◽

Mooring System ◽

Mooring Lines ◽

Floating Offshore Wind Turbine

The paper discusses the effects of mooring configurations on the dynamic response of a submerged floating offshore wind turbine (SFOWT) for intermediate water depths. A coupled dynamic model of a wind turbine-tower-floating platform-mooring system is established, and the dynamic response of the platform, tensions in mooring lines, and bending moment at the tower base and blade root under four different mooring configurations are checked. A well-stabilized configuration (i.e., four vertical lines and 12 diagonal lines with an inclination angle of 30°) is selected to study the coupled dynamic responses of SFOWT with broken mooring lines, and in order to keep the safety of SFOWT under extreme sea-states, the pretension of the vertical mooring line has to increase from 1800–2780 kN. Results show that the optimized mooring system can provide larger restoring force, and the SFOWT has a smaller movement response under extreme sea-states; when the mooring lines in the upwind wave direction are broken, an increased motion response of the platform will be caused. However, there is no slack in the remaining mooring lines, and the SFOWT still has enough stability.

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Proposal of a Novel Semi-Submersible Floating Wind Turbine Platform Composed of Inclined Columns and Multi-Segmented Mooring Lines

Energies ◽

10.3390/en12091809 ◽

2019 ◽

Vol 12 (9) ◽

pp. 1809 ◽

Cited By ~ 1

Author(s):

Zhenqing Liu ◽

Qingsong Zhou ◽

Yuangang Tu ◽

Wei Wang ◽

Xugang Hua

Keyword(s):

Wind Turbine ◽

Offshore Wind ◽

Mooring Line ◽

Offshore Wind Turbine ◽

Analysis Tool ◽

Mooring Lines ◽

Offshore Area ◽

Floating Wind Turbine ◽

Inclined Angle ◽

Heave Motion

The semi-submersible floating offshore wind turbine has been studied in detail due to its good stability. However, the occurrence of typhoons are very frequent in China’s offshore area, putting forward a higher requirement for the stability of the floating wind turbine system. By changing the connection mode of the mooring line as well as the structural form of the platform based on the original OC4 model, two groups of models were examined by an in-house developed code named as the Analysis Tool of Floating Wind Turbine (AFWT). The influence of the arrangement of the mooring lines and the inclination angle of the upper columns on the motion response were clarified. It was found that the surge motion of the platform would be obviously decreased by decreasing the length of the upper segments of the mooring lines, while the heave motion of the platform would be significantly decreased as increasing the inclined angle of the columns. Therefore, a new model integrating the optimized multi-segmented mooring lines and the optimized inclined columns was proposed. The examinations showed that compared with the response motions of the original OC4 semi-submersible model, the proposed model could reduce both the surge and heave motions of the platform effectively.

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Offshore Code Comparison Collaboration Continuation Within IEA Wind Task 30: Phase II Results Regarding a Floating Semisubmersible Wind System

Volume 9B: Ocean Renewable Energy ◽

10.1115/omae2014-24040 ◽

2014 ◽

Cited By ~ 19

Author(s):

Amy Robertson ◽

Jason Jonkman ◽

Fabian Vorpahl ◽

Wojciech Popko ◽

Jacob Qvist ◽

...

Keyword(s):

Wind Turbine ◽

International Energy Agency ◽

Lessons Learned ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Energy Agency ◽

Code Comparison ◽

Mooring Dynamics ◽

Offshore Floating Wind Turbine ◽

Incident Waves

Offshore wind turbines are designed and analyzed using comprehensive simulation tools (or codes) that account for the coupled dynamics of the wind inflow, aerodynamics, elasticity, and controls of the turbine, along with the incident waves, sea current, hydrodynamics, mooring dynamics, and foundation dynamics of the support structure. This paper describes the latest findings of the code-to-code verification activities of the Offshore Code Comparison Collaboration Continuation project, which operates under the International Energy Agency Wind Task 30. In the latest phase of the project, participants used an assortment of simulation codes to model the coupled dynamic response of a 5-MW wind turbine installed on a floating semisubmersible in 200 m of water. Code predictions were compared from load case simulations selected to test different model features. The comparisons have resulted in a greater understanding of offshore floating wind turbine dynamics and modeling techniques, and better knowledge of the validity of various approximations. The lessons learned from this exercise have improved the participants’ codes, thus improving the standard of offshore wind turbine modeling.

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The Influence of the Mooring System on the Motions and Stability of a Semi-Submersible Floating Wind Turbine

Volume 9: Ocean Renewable Energy ◽

10.1115/omae2015-41947 ◽

2015 ◽

Cited By ~ 1

Author(s):

Fons Huijs

Keyword(s):

Wind Turbine ◽

Low Frequency ◽

Considerable Effect ◽

Offshore Wind ◽

Mooring Line ◽

Offshore Wind Turbine ◽

Mooring System ◽

Mooring Lines ◽

System A ◽

Turbine Design

One of the main aspects of a floating offshore wind turbine design is its mooring system, which can strongly influence the floater stability and motions. This is illustrated by considering two catenary mooring systems for the same semi-submersible. The main difference between the two systems is the position of the connection points of the mooring lines on the floater, the so-called fairleads. The philosophy is that the design can be improved by shifting the fairleads to the highest feasible level. For both mooring systems, the floater motions and stability are assessed. Stability curves are derived, taking both the effect of hydrostatics and the mooring system into account. Floater motions are analyzed using both uncoupled frequency domain calculations and coupled aero-hydro-servo-elastic time domain simulations. The mooring system is found to have a considerable effect on the floating stability. The effect on the motions is less profound for the considered mooring systems and limited to the low frequency range. Mooring line tensions are however significantly affected by the fairlead position. It is concluded that, with a well-designed mooring system, a smaller and thus less expensive floater can be used while still meeting the requirements in terms of stability and maximum motions. In addition, the mooring lines may be lighter as well.

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Snap Loads on Mooring Lines of a Floating Offshore Wind Turbine Structure

Volume 9A: Ocean Renewable Energy ◽

10.1115/omae2014-23587 ◽

2014 ◽

Cited By ~ 1

Author(s):

Wei-ting Hsu ◽

Krish P. Thiagarajan ◽

Matthew Hall ◽

Michael MacNicoll ◽

Richard Akers

Keyword(s):

Wind Turbine ◽

Impact Load ◽

Offshore Wind ◽

Mooring Line ◽

Offshore Wind Turbine ◽

Special Focus ◽

Mooring Lines ◽

Floating Offshore Wind Turbine ◽

Marine Applications

There are a number of design challenges facing mooring systems of floating offshore wind turbine (FOWT) platforms in an offshore environment. Some unique aspects of the FOWT industry should be considered when examining applicability of established offshore mooring practices. Important among these are: economy and cost effectiveness; light weight minimal platforms; and water depths ranging from 50–300 m. A lighter displacement platform in shallow water, supported by lines with light to moderate pre-tension can result in a higher probability of slack line events and hence snap loads during re-engagement. Such loads can result in shock on the line material and considerably reduce the fatigue life. Such events have the potential to occur in various sea states, and not necessarily limited to extreme conditions. These conditions will be dependent on structure resonant motions, which are influenced by wind loads and moments, wave conditions and mooring line properties. Model tests of typical concepts for FOWT reported in literature have shown occasional slack line episodes. This paper is a review of literature on snap load occurrence in marine applications, including lifting and lowering operations, ROV and diving bell operations. This paper presents a case study of a FOWT. Special focus is on mooring systems which are affected by impact load conditions. Criteria are reviewed and consequences are documented.

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DeepCwind Semi-Submersible Floating Offshore Wind Turbine Platform with Nonlinear Multi-Segment Catenary Mooring Line and Intermediate Buoy

10.22541/au.161519883.34994214/v1 ◽

2021 ◽

Author(s):

mohammad motallebi ◽

Hassan Ghassemi

Keyword(s):

Adverse Effects ◽

Wind Turbine ◽

Water Depth ◽

Offshore Wind ◽

Correct Selection ◽

Mooring Line ◽

Offshore Wind Turbine ◽

Mooring Lines ◽

Floating Offshore Wind Turbine ◽

Selection Of

In this paper, with the purpose of improving the mechanical behavior of DeepCwind semi-submersible floating offshore wind turbine (FOWT) platform mooring lines, nonlinear catenary cables of platform are divided into multi-segments and intermediate buoy. The mathematical formulations of the dynamic equation acted on the cable with buoys are described. Present study is employed to the OC4-DeepCwind semi-submersible FOWT platform. It is designed for 200-meter water depth with mooring lines consist of three catenary steel chain cables that have an angle of 120 degrees to each other. The dynamic response of multi-segment catenary mooring line with different buoys radiuses and different positions along the cables were investigated. The full-scale platform was modeled in ANSYS-AQWA software and the simulations are performed in harsh offshore. The tension, strain, anchor uplift, cable uplift for different buoy radiuses and its position along cable are presented and discussed. Moreover, platform motions at three directions (surge, heave and pitch) are also analyzed. It is concluded that by correct selection of the buoy volume and position along cable, the tension of the cable may be reduced up to 45%. By incorrect selection of the buoy, the results will cause adverse effects.

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Multipoint high-fidelity CFD-based aerodynamic shape optimization of a 10 MW wind turbine

Wind Energy Science ◽

10.5194/wes-4-163-2019 ◽

2019 ◽

Vol 4 (2) ◽

pp. 163-192 ◽

Cited By ~ 12

Author(s):

Mads H. Aa. Madsen ◽

Frederik Zahle ◽

Niels N. Sørensen ◽

Joaquim R. R. A. Martins

Keyword(s):

Shape Optimization ◽

Wind Turbine ◽

International Energy Agency ◽

Operating Conditions ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

High Fidelity ◽

Energy Agency ◽

Cross Sectional

Abstract. The wind energy industry relies heavily on computational fluid dynamics (CFD) to analyze new turbine designs. To utilize CFD earlier in the design process, where lower-fidelity methods such as blade element momentum (BEM) are more common, requires the development of new tools. Tools that utilize numerical optimization are particularly valuable because they reduce the reliance on design by trial and error. We present the first comprehensive 3-D CFD adjoint-based shape optimization of a modern 10 MW offshore wind turbine. The optimization problem is aligned with a case study from International Energy Agency (IEA) Wind Task 37, making it possible to compare our findings with the BEM results from this case study and therefore allowing us to determine the value of design optimization based on high-fidelity models. The comparison shows that the overall design trends suggested by the two models do agree, and that it is particularly valuable to consult the high-fidelity model in areas such as root and tip where BEM is inaccurate. In addition, we compare two different CFD solvers to quantify the effect of modeling compressibility and to estimate the accuracy of the chosen grid resolution and order of convergence of the solver. Meshes up to 14×106 cells are used in the optimization whereby flow details are resolved. The present work shows that it is now possible to successfully optimize modern wind turbines aerodynamically under normal operating conditions using Reynolds-averaged Navier–Stokes (RANS) models. The key benefit of a 3-D RANS approach is that it is possible to optimize the blade planform and cross-sectional shape simultaneously, thus tailoring the shape to the actual 3-D flow over the rotor. This work does not address evaluation of extreme loads used for structural sizing, where BEM-based methods have proven very accurate, and therefore will likely remain the method of choice.

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