An Experimental Study of Snap Loads on a Vertical Hanging Cable System

2019 ◽  
Author(s):  
Wei-Ting Hsu ◽  
Tzu-Ching Chuang ◽  
Wen-Yang Hsu ◽  
Krish Sharman ◽  
Ray-Yeng Yang
Keyword(s):  
Drag Force ◽  
Excitation Amplitude ◽  
Offshore Wind ◽  
Theoretical Development ◽  
Mooring Line ◽  
Offshore Wind Turbine ◽  
Hydrodynamic Drag ◽  
Cable Model ◽  
Mooring Lines ◽  
Line System

Abstract Sudden snap events on mooring lines and hanging cables can cause spikes in tension, resulting in reduced safety factors during extreme events. For example, the mooring system of a floating offshore wind turbine (FOWT) can be exposed to wave-induced motions making the former vulnerable to snap type impact. Suitable criteria to define snap events are still largely unclear, making current design practices overly conservative. To understand the underlying physics of snap loads on a mooring line system, this paper presents a theoretical development and an experimental parametric study of snap events. The effects of the nonlinearity of bilinear line stiffness and hydrodynamic drag force, as well as the weight of payload on snap events are investigated using the vertical hanging cable model. This cable model includes two springs in series and a payload. The bilinear spring model is designed to create nonlinear dynamic tension. A total of 108 tests were conducted in the wave tank of Tainan Hydraulic Laboratory. The excitation amplitude ranges from 0.01 to 0.04m; excitation time period ranges from 0.5 to 2s; the weight of payload ranges from 6.13 to 18.95N. The tests carried out in water are compared to those conducted in air. It is seen that the hydrodynamic drag force together with the small pretension could result in larger normalized tension ranges.

scholarly journals Mooring Line Damping Estimation for a Floating Wind Turbine

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Dongsheng Qiao ◽  
Jinping Ou
Keyword(s):  
Wind Turbine ◽  
Estimation Method ◽  
Excitation Amplitude ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Scale Model ◽  
Mooring Line ◽  
Offshore Wind Turbine ◽  
Floating Wind Turbine ◽  
Excitation Period

The dynamic responses of mooring line serve important functions in the station keeping of a floating wind turbine (FWT). Mooring line damping significantly influences the global motions of a FWT. This study investigates the estimation of mooring line damping on the basis of the National Renewable Energy Laboratory 5 MW offshore wind turbine model that is mounted on the ITI Energy barge. A numerical estimation method is derived from the energy absorption of a mooring line resulting from FWT motion. The method is validated by performing a 1/80 scale model test. Different parameter changes are analyzed for mooring line damping induced by horizontal and vertical motions. These parameters include excitation amplitude, excitation period, and drag coefficient. Results suggest that mooring line damping must be carefully considered in the FWT design.

scholarly journals 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

2019 ◽  
Vol 9 (6) ◽  
pp. 1075 ◽  
Author(s):  
Zhenqing Liu ◽  
Yuangang Tu ◽  
Wei Wang ◽  
Guowei Qian
Keyword(s):  
Wind Turbine ◽  
International Energy Agency ◽  
Wave Resistance ◽  
Offshore Wind ◽  
Irregular Waves ◽  
Mooring Line ◽  
Offshore Wind Turbine ◽  
Induced Response ◽  
Mooring Lines ◽  
Energy Agency

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.

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

2018 ◽  
Vol 140 (5) ◽  
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.

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

2019 ◽  
Vol 7 (4) ◽  
pp. 115 ◽  
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.

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

Energies ◽  
2019 ◽  
Vol 12 (9) ◽  
pp. 1809 ◽  
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.

scholarly journals Influence of Clumps-Weighted Moorings on a Spar Buoy Offshore Wind Turbine

Energies ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 6407
Author(s):  
Niccolo Bruschi ◽  
Giulio Ferri ◽  
Enzo Marino ◽  
Claudio Borri
Keyword(s):  
Line Tension ◽  
Optimal Choice ◽  
Offshore Wind ◽  
Mooring Line ◽  
Offshore Wind Turbine ◽  
National Renewable Energy Laboratory ◽  
Mooring Lines ◽  
Offshore Wind Turbines ◽  
Open Issue ◽  
Response Amplitude Operators

The spar buoy platform for offshore wind turbines is the most utilized type and the OC3 Hywind system design is largely used in research. This system is usually moored with three catenary cables with 120° between each other. Adding clump weights to the mooring lines has an influence on the platform response and on the mooring line tension. However, the optimal choice for their position and weight is still an open issue, especially considering the multitude of sea states the platform can be exposed to. In this study, therefore, an analysis on the influence of two such variables on the platform response and on the mooring line tension is presented. FAST by the National Renewable Energy Laboratory (NREL) is used to perform time domain simulations and Response Amplitude Operators are adopted as the main indicators of the clump weights effects. Results show that the clump weight mass is not as influential as the position, which turns out to be optimal, especially for the Surge degree of freedom, when closest to the platform.

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

2015 ◽  
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.

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

2014 ◽  
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.

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

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.

scholarly journals Seakeeping Tests of a FOWT in Wind and Waves: An Analysis of Dynamic Coupling Effects and Their Impact on the Predictions of Pitch Motion Response

2021 ◽  
Vol 9 (2) ◽  
pp. 179
Author(s):  
Giovanni Amaral ◽  
Pedro Mello ◽  
Lucas do Carmo ◽  
Izabela Alberto ◽  
Edgard Malta ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Dynamic Coupling ◽  
Coupling Effects ◽  
Mooring Lines ◽  
Scaled Model ◽  
Wave Basin ◽  
Domain Models ◽  
Catenary System

The present work highlights some of the dynamic couplings observed in a series of tests performed in a wave basin with a scaled-model of a Floating Offshore Wind Turbine (FOWT) with semi-submersible substructure. The model was moored by means of a conventional chain catenary system and an actively controlled fan was used for emulating the thrust loads during the tests. A set of wave tests was performed for concomitant effects of not aligned wave and wind. The experimental measurements illustrate the main coupling effects involved and how they affect the FOWT motions in waves, especially when the floater presents a non-negligible tilt angle. In addition, a frequency domain numerical analysis was performed in order to evaluate its ability to capture these effects properly. The influence of different modes of fan response, floater trim angles (changeable with ballast compensation) and variations in the mooring stiffness with the offsets were investigated in the analysis. Results attest that significant changes in the FOWT responses may indeed arise from coupling effects, thus indicating that caution must be taken when simplifying the hydrodynamic frequency-domain models often used as a basis for the simulation of FOWTs in waves and in optimization procedures for the design of the floater and mooring lines.

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