Fracture mechanics-based mooring system fatigue analysis for a spar-based floating offshore wind turbine

2021 ◽  
Vol 223 ◽  
pp. 108618
Author(s):  
Xifeng Gao ◽  
Xiaoyong Liu ◽  
Xutian Xue ◽  
Nian-Zhong Chen
Keyword(s):  
Fracture Mechanics ◽  
Wind Turbine ◽  
Fatigue Analysis ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Mooring System ◽  
Floating Offshore Wind Turbine

Mooring system fatigue analysis of a floating offshore wind turbine

2020 ◽  
Vol 195 ◽  
pp. 106670
Author(s):  
Carlos Barrera ◽  
Tommaso Battistella ◽  
Raúl Guanche ◽  
Iñigo J. Losada
Keyword(s):  
Wind Turbine ◽  
Fatigue Analysis ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Mooring System ◽  
Floating Offshore Wind Turbine

Fatigue Analysis for Mooring System of a Spar-Type Floating Offshore Wind Turbine

2020 ◽  
Author(s):  
Xutian Xue ◽  
Xiaoyong Liu ◽  
Nian-Zhong Chen ◽  
Xifeng Gao
Keyword(s):  
Wind Turbine ◽  
Fatigue Analysis ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Safety Factors ◽  
Mooring Lines ◽  
Hydrodynamic Analysis ◽  
Floating Offshore Wind Turbine ◽  
Different Diameters ◽  
Rainflow Counting

Abstract This paper aims to perform a time-domain mooring fatigue analysis for a Spar-type floating offshore wind turbine operated in the South China Sea. Tension ranges of mooring lines are achieved from a hydrodynamic analysis where the effects of wind, wave and current are considered. A rainflow counting method is used to calculate the number of mooring tension cycles with corresponding ranges. The fatigue lives of mooring lines are then predicted by Palmgren-Miner’s rule according to T-N & S-N curves. A comparison of fatigue lives predicted by T-N & S-N curves-based approaches with/without considering safety factors is made. The results show that the T-N curves-based approach is more conservative than the S-N curves-based approach if safety factors are not considered in the two approaches, while the fatigue lives predicted by both approaches are in general comparable when the safety factors suggested by API and DNVGL are applied in the two approaches. A comparative study of three kinds of R4 grade studless mooring chains with different diameters (2.5-inch, 4-inch, 5-inch) is also conducted and the results show that the design with the 2.5-inch chain does not meet the fatigue requirements.

Dynamic Responses of a Spar Type Floating Offshore Wind Turbine With Failed Moorings

2020 ◽  
Author(s):  
Yajun Ren ◽  
Vengatesan Venugopal
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Mooring System ◽  
Floating Offshore Wind Turbine ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Platform Motions

Abstract The complex dynamic characteristics of Floating Offshore Wind Turbines (FOWTs) have raised wider consideration, as they are likely to experience harsher environments and higher instabilities than the bottom fixed offshore wind turbines. Safer design of a mooring system is critical for floating offshore wind turbine structures for station keeping. Failure of mooring lines may lead to further destruction, such as significant changes to the platform’s location and possible collisions with a neighbouring platform and eventually complete loss of the turbine structure may occur. The present study focuses on the dynamic responses of the National Renewable Energy Laboratory (NREL)’s OC3-Hywind spar type floating platform with a NREL offshore 5-MW baseline wind turbine under failed mooring conditions using the fully coupled numerical simulation tool FAST. The platform motions in surge, heave and pitch under multiple scenarios are calculated in time-domain. The results describing the FOWT motions in the form of response amplitude operators (RAOs) and spectral densities are presented and discussed in detail. The results indicate that the loss of the mooring system firstly leads to longdistance drift and changes in platform motions. The natural frequencies and the energy contents of the platform motion, the RAOs of the floating structures are affected by the mooring failure to different degrees.

Development of Floating Offshore Wind Turbine and the Mooring System

2013 ◽  
Vol 790 ◽  
pp. 634-637
Author(s):  
Xue Liang Zhao ◽  
Wei Ming Gong
Keyword(s):  
Wind Turbine ◽  
Research Work ◽  
Experimental Tests ◽  
Offshore Wind ◽  
Future Research ◽  
Offshore Wind Turbine ◽  
Mooring System ◽  
Floating Offshore Wind Turbine ◽  
Energy Demands

The offshore wind turbine, especially the floating offshore wind turbine in the deep sea is a perspective technology in the context of increasing energy demands. Mooring system, as an important unit of the floating offshore wind turbine is emphasized. The methods of in-situ test and the laboratory experimental tests are reviewed. Some new testing methods are discussed. The most commonly used anchor systems are explored. The paper aims to present some future research work that is important for the development of the floating offshore wind turbine technology.

Coupled Numerical Analysis of a Concept TLB Type Floating Offshore Wind Turbine

2019 ◽  
Author(s):  
Iman Ramzanpoor ◽  
Martin Nuernberg ◽  
Longbin Tao
Keyword(s):  
Wind Turbine ◽  
Renewable Energy Sources ◽  
Second Order ◽  
Offshore Wind ◽  
Design Stage ◽  
Offshore Wind Turbine ◽  
Clear Understanding ◽  
Mooring System ◽  
Floating Platform ◽  
Floating Offshore Wind Turbine

Abstract The main drivers for the continued decarbonisation of the global energy market are renewable energy sources. Moreover, the leading technological solutions to achieve this are offshore wind turbines. As installed capacity has been increasing rapidly and shallow water near shore sites are exhausted, projects will need to be developed further from shore and often in deeper waters, which will pose greater technical challenges and constrain efforts to reduce costs. Current floating platform solutions such as the spar and semi-submersible rely on large amounts of ballast and complex structural designs with active stabilisation systems for stability of the floating offshore wind turbine platform (FOWT). The primary focus of this study is to present a design concept and mooring arrangement for an alternative floating platform solution that places emphasis on the mooring system to achieve stability for a FOWT. The tension leg buoy (TLB) is designed to support future 10MW offshore wind turbine generators. This paper presents the numerical methodology used for a coupled hydro-elastic analysis of the floater and mooring system under combined wind, wave and current effects. A concept TLB design is presented and its platform motion and mooring line tension characteristics are analysed for a three-hour time domain simulation representing operating and survival conditions in the northern North Sea with water depths of 110 metres. The importance of wave drift forces and the other non-linear excitation forces in the concept design stage are evaluated by comparing the motion and tension responses of three different numerical simulation cases with increasing numerical complexity. The preliminary TLB system design demonstrated satisfactory motion response for the operation of a FOWT and survival in a 100-year storm condition. The results show that accounting for second-order effect is vital in terms of having a clear understanding of the full behaviour of the system and the detailed response characteristics in operational and survival conditions. Extreme loads are significantly reduced when accounting for the second-order effects. This can be a key aspect to not overdesign the system and consequently achieve significant cost savings.

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.

Fatigue Analysis at the Tower of a 12MW Floating Offshore Wind Turbine

2018 ◽  
Author(s):  
Junbae Kim ◽  
Hyeonjeong Ahn ◽  
Byoungcheon Seo ◽  
Hyunkyoung Shin
Keyword(s):  
Fatigue Life ◽  
Wind Turbine ◽  
Fatigue Analysis ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Strength Analysis ◽  
Cycle Number ◽  
Floating Offshore Wind Turbine ◽  
Design Life ◽  
Safety Margins

The initial design of a 12-MW floating offshore wind turbine (FOWT) was made by the University of Ulsan (UOU) based on the 5-MW offshore wind turbine of the National Renewable Energy Laboratory (NREL) using the law of similarity. The tower design was checked through the eigenfrequency and fatigue strength analysis according to the GL guideline of tower design conditions. The direct expansion of the 5 MW wind turbine support structure caused a resonance problem of the tower of the 12-MW UOU FOWT and the tower length was adjusted to avoid the 3P resonance. Wind turbines are required to have a design life of more than 20 years and shall be designed to endure both ultimate and fatigue loads experienced during the design life. The platform pitch motion of FOWTs due to combined wave and wind loading may result severely in both fore-aft forces and moments at the base of the tower. In this study, we used the simplified fatigue analysis, which is generally applied when considering safety margins by stress to predict the fatigue life of tower. In order to calculate the fatigue load, the Markov matrix was constructed by using the cycle counting method to determine range, average value, and cycle number of loads from peak and valley values of actual load histories simulated by FAST v8 of the tower base. The predicted fatigue life at the tower base was follow by S/N curves for welded steel structures and it was calculated by the Palmgren-Miner’s rule.

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