The Effect of Turbulence Model on the Response of a Large Floating Wind Turbine

2017 ◽  
Author(s):  
Lene Eliassen ◽  
Erin E. Bachynski
Keyword(s):  
Wind Speed ◽  
Wind Turbine ◽  
Fatigue Damage ◽  
Turbulence Model ◽  
Wind Turbines ◽  
Low Frequency ◽  
Turbulence Models ◽  
Line Tension ◽  
Offshore Wind ◽  
Mooring Line

The wind turbine design standards advise choosing one of two recommended turbulence models for load simulations of offshore wind turbines. The difference in fatigue loads for the two turbulence models is relatively small for bottom-fixed wind turbines, but some floating wind turbines show a higher sensitivity to the chosen turbulence model. In this study, the motions and mooring line fatigue damage of two semi-submersible floating wind turbines are investigated for three different wind speeds: 8 m/s, 14 m/s and 20 m/s, and three different wave states for each wind speed. For both concepts, the CSC 5 MW and the CSC 10 MW, the low-frequency surge response is important for the mooring line tension, and the simulations using the Kaimal turbulence model give the largest variation in tension at the surge eigenfrequency. However, using the Mann turbulence model in the load simulations give a higher response in the range of the blade passing frequency (3P). The CSC 10 MW has a higher aerodynamic thrust relative to the CSC 5 MW, and will therefore have a larger surge response at the lower frequencies than the CSC 5 MW. At the lowest wind speed, where the variation in mooring line tension at surge eigenfrequency is high, the fatigue damage is larger if the Kaimal turbulence model is applied to the load simulations. However, at the highest wind speed, using the Mann turbulence model in the simulations, give a higher mooring line fatigue damage.

scholarly journals On mooring line tension and fatigue prediction for offshore vertical axis wind turbines: A comparison of lumped mass and quasi-static approaches

2018 ◽  
Vol 42 (2) ◽  
pp. 97-107 ◽  
Author(s):  
D Cevasco ◽  
M Collu ◽  
CM Rizzo ◽  
M Hall
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Line Tension ◽  
Vertical Axis ◽  
Offshore Wind ◽  
Mooring Line ◽  
Offshore Wind Turbine ◽  
Vertical Axis Wind Turbine ◽  
Lumped Mass ◽  
Vertical Axis Wind Turbines

Despite several potential advantages, relatively few studies and design support tools have been developed for floating vertical axis wind turbines. Due to the substantial aerodynamics differences, the analyses of vertical axis wind turbine on floating structures cannot be easily extended from what have been already done for horizontal axis wind turbines. Therefore, the main aim of the present work is to compare the dynamic response of the floating offshore wind turbine system adopting two different mooring dynamics approaches. Two versions of the in-house aero-hydro-mooring coupled model of dynamics for floating vertical axis wind turbine (FloVAWT) have been used, employing a mooring quasi-static model, which solves the equations using an energetic approach, and a modified version of floating vertical axis wind turbine, which instead couples with the lumped mass mooring line model MoorDyn. The results, in terms of mooring line tension, fatigue and response in frequency have been obtained and analysed, based on a 5 MW Darrieus type rotor supported by the OC4-DeepCwind semisubmersible.

Numerical Simulation of Dynamics of a Spar Type Floating Wind Turbine and Comparison With Laboratory Measurements

2016 ◽  
Author(s):  
Hyunseong Min ◽  
Cheng Peng ◽  
Fei Duan ◽  
Zhiqiang Hu ◽  
Jun Zhang
Keyword(s):  
Numerical Simulation ◽  
Wind Speed ◽  
Numerical Simulations ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Deep Water ◽  
Offshore Wind ◽  
Wind Loads ◽  
Floating Offshore Wind Turbines ◽  
The Cost

Wind turbines are popular for harnessing wind energy. Floating offshore wind turbines (FOWT) installed in relatively deep water may have advantages over their on-land or shallow-water cousins because winds over deep water are usually steadier and stronger. As the size of wind turbines becomes larger and larger for reducing the cost per kilowatt, it could bring installation and operation risks in the deep water due to the lack of track records. Thus, together with laboratory tests, numerical simulations of dynamics of FOWT are desirable to reduce the probability of failure. In this study, COUPLE-FAST was initially employed for the numerical simulations of the OC3-HYWIND, a spar type platform equipped with the 5-MW baseline wind turbine proposed by National Renewable Energy Laboratory (NREL). The model tests were conducted at the Deepwater Offshore Basin in Shanghai Jiao Tong University (SJTU) with a 1:50 Froude scaling [1]. In comparison of the simulation using COUPLE-FAST with the corresponding measurements, it was found that the predicted motions were in general significantly smaller than the related measurements. The main reason is that the wind loads predicted by FAST were well below the related measurements. Large discrepancies are expected because the prototype and laboratory wind loads do not follow Froude number similarity although the wind speed was increased (or decreased) in the tests such that the mean surge wind force matched that predicted by FAST at the nominal wind speed (Froude similarity) in the cases of a land wind turbine [1]. Therefore, an alternative numerical simulation was made by directly inputting the measured wind loads to COUPLE instead of the ones predicted by FAST. The related simulated results are much improved and in satisfactory agreement with the measurements.

Dynamic Modeling of Deepwater Offshore Wind Turbine Structures in Gulf of Mexico Storm Conditions

2006 ◽  
Author(s):  
Thomas Zambrano ◽  
Tyler MacCready ◽  
Taras Kiceniuk ◽  
Dominique G. Roddier ◽  
Christian A. Cermelli
Keyword(s):  
Gulf Of Mexico ◽  
Wind Turbine ◽  
Wind Waves ◽  
Line Tension ◽  
Offshore Wind ◽  
Mooring Line ◽  
Offshore Wind Turbine ◽  
Wave Forces ◽  
Offshore Structure ◽  
Force Coefficient

A Fourier spectrum based model of Gulf of Mexico storm conditions is applied to a 6 degree of freedom analytic simulation of a moored, floating offshore structure fitted with three rotary wind turbines. The resulting heave, surge, and sway motions are calculated using a Newtonian Runge-Kutta method. The angular motions of pitch, roll, and yaw are also calculated in this time-domain progression. The forces due to wind, waves, and mooring line tension are predicted as a function of time over a 4000 second interval. The WAMIT program is used to develop the wave forces on the platform. A constant force coefficient is used to estimate wind turbine loads. A TIMEFLOAT computer code calculates the motion of the system based on the various forces on the structure and the system’s inertia.

Wind/Wave Misalignment Effects on Mooring Line Tensions for a Spar Buoy Wind Turbine

2018 ◽  
Author(s):  
Luigia Riefolo ◽  
Fernando del Jesus ◽  
Raúl Guanche García ◽  
Giuseppe Roberto Tomasicchio ◽  
Daniela Pantusa
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Wind Wave ◽  
Offshore Wind ◽  
Mooring Line ◽  
Ultimate Limit State ◽  
International Electrotechnical Commission ◽  
Wave Loads ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines

The design methodology for mooring systems for a spar buoy wind turbine considers the influence of extreme events and wind/wave misalignments occurring in its lifetime. Therefore, the variety of wind and wave directions affects over the seakeeping and as a result the evaluation of the maxima loads acting on the spar-buoy wind turbine. In the present paper, the importance of wind/wave misalignments on the dynamic response of spar-type floating wind turbine [1] is investigated. Based on standards, International Electrotechnical Commission IEC and Det Norske Veritas DNV the design of position moorings should be carried out under extreme wind/wave loads, taking into account their misalignments with respect to the structure. In particular, DNV standard, in ‘Position mooring’ recommendations, specifies in the load cases definition, if site specific data is not available, to consider non-collinear environment to have wave towards the unit’s bow (0°) and wind 30° relative to the waves. In IEC standards, the misalignment of the wind and wave directions shall be considered to design offshore wind turbines and calculate the loads acting on the support structure. Ultimate Limit State (ULS) analyses of the OC3-Hywind spar buoy wind turbine are conducted through FAST code, a certified nonlinear aero-hydro-servo-elastic simulation tool by the National Renewable Energy Laboratory’s (NREL’s). This software was developed for use in the International Energy Agency (IEA) Offshore Code Comparison Collaborative (OC3) project, and supports NREL’s offshore 5-MW baseline turbine. In order to assess the effects of misaligned wind and wave, different wind directions are chosen, maintaining the wave loads perpendicular to the structure. Stochastic, full-fields, turbulence simulator Turbsim is used to simulate the 1-h turbulent wind field. The scope of the work is to investigate the effects of wind/wave misalignments on the station-keeping system of spar buoy wind turbine. Results are presented in terms of global maxima determined through mean up-crossing with moving average, which, then, are modelled by a Weibull distribution. Finally, extreme values are estimated depending on global maxima and fitted on Gumbel distribution. The Most Probable Maximum value of mooring line tensions is found to be influenced by the wind/wave misalignments. The present paper is organized as follows. Section ‘Introduction’, based on a literature study, gives useful information on the previous studies conducted on the wind/wave misalignments effects of floating offshore wind turbines. Section ‘Methodology’ describes the applied methodology and presents the spar buoy wind turbine, the used numerical model and the selected environmental conditions. Results and the corresponding discussion are given in Section ‘Results and discussion’ for each load case corresponding to the codirectional and misaligned wind and wave loads. Results are presented and discussed in time and frequency domains. Finally, in Section ‘Conclusion’ some conclusions are drawn.

Low Cycle Fatigue Analysis of Offshore Wind Turbines Subjected to Hurricane

2017 ◽  
Author(s):  
Gholamreza Amirinia ◽  
Sungmoon Jung
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Low Cycle Fatigue ◽  
Turbulence Models ◽  
Offshore Wind ◽  
Cycle Fatigue ◽  
Offshore Wind Turbines ◽  
Hurricane Wind ◽  
New Formulation ◽  
Spectrum Model

The main objective of this paper is to investigate the effects of hurricanes on low cycle fatigue of tower and blades in offshore wind turbines. For this purpose, first, recent observations on hurricane turbulence models were discussed. Second, the buffeting wind loads on the wind turbine structure were introduced. A new formulation was used to address unsteady wind forces on the tower. This new formulation was later used to modify NREL-FAST (Fatigue, Aerodynamics, Structures, and Turbulence) for the analysis. In the next step, according to importance of recent findings about hurricanes, hurricane wind and wave fields were simulated based on the Saffir-Simpson hurricane wind scale. Then, to investigate the effects of various turbulence models on the wind turbine structures, the modified NREL-FAST was used to analyze structure-wind-wave-soil interaction of the NREL-5 MW monopile wind turbine. Finally, the low cycle fatigue analysis was presented and discussed. Results for various hurricane turbulence models showed that by using quasi-steady analysis of the tower, the spectrum Model A and Model B resulted in average 53% lower and 12% higher damage index compared to the conventional Kaimal spectrum model respectively; however, by considering unsteady formulation on the tower, spectrum Model A and Model B resulted in average 96% and 24% lower blade root damage indices compared to the conventional Kaimal spectrum model respectively.

scholarly journals Analysis of Dynamic Characteristics of an Ultra-Large Semi-Submersible Floating Wind Turbine

2019 ◽  
Vol 7 (6) ◽  
pp. 169 ◽  
Author(s):  
Zhixin Zhao ◽  
Xin Li ◽  
Wenhua Wang ◽  
Wei Shi
Keyword(s):  
Wind Turbine ◽  
Structural Dynamics ◽  
Dynamic Characteristics ◽  
Line Tension ◽  
Offshore Wind ◽  
Mooring Line ◽  
Offshore Wind Turbine ◽  
Static And Dynamic Analysis ◽  
Motion Responses ◽  
The Difference

An initial design of the platform for the moderate water depth (100 m) is performed by upscaling of an existing 5 MW braceless semi-submersible platform design to support the DTU (Danish University of Science and Technology) 10 MW wind turbine. To investigate the dynamic characteristics of the ultra-large semi-submersible floating offshore wind turbine (FOWT), an aero-hydro-servo-elastic numerical modeling is applied to carry out the fully coupled time-domain simulation analysis. The motion responses of the ultra-large semi-submersible FOWT are presented and discussed for selected environmental conditions. Based on the quasi-static and dynamic analysis methods, the influence of the dynamic effects of the mooring lines on the platform motion responses and mooring line tension responses are discussed. Subsequently, the difference in the motion responses and structural dynamics of the DTU 10 MW and NREL (National Renewable Energy Laboratory) 5 MW FOWT is studied due to the difference in turbine properties. The simulation results reveal that the excitation of the low-frequency wind loads on the surge and pitch motions, the tower-base fore-aft bending moments and the mooring line tension response becomes more prominent when the size of the wind turbine increases, but the excitation action of the 3P effect on the structural dynamics of the 5 MW FOWT is more obvious than those of the 10 MW FOWT.

Fatigue Damage to the Spar-Type Offshore Floating Wind Turbine Under Blade Pitch Controller Faults

2014 ◽  
Author(s):  
Mahmoud Etemaddar ◽  
Elaheh Vahidian ◽  
Otto Skjåstad
Keyword(s):  
Wind Turbine ◽  
Fatigue Damage ◽  
Wind Turbines ◽  
Pitch Angle ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Composite Blade ◽  
Floating Wind Turbine ◽  
Offshore Floating Wind Turbine ◽  
Blade Pitch Angle

The safety and reliability margin of offshore floating wind turbines need to be higher than that of onshore wind turbines due to larger environmental loads and higher operational and maintenance costs for offshore wind turbines compared to onshore wind turbines. However rotor cyclic loads coupled with 6 DOFs motions of the substructure, amplifies the fatigue damage in offshore floating wind turbines. In general a lower fatigue design factor is used for offshore wind turbines compared to that of the stationary oil and gas platforms. This is because the consequence of a failure in offshore wind turbines in general is lower than that of the offshore oil and gas platforms. In offshore floating wind turbines a sub-system fault in the electrical system and blade pitch angle controller also induces additional fatigue loading on the wind turbine structure. In this paper effect of selected controller system faults on the fatigue damage of an offshore floating wind turbine is investigated, in a case which fault is not detected by a fault detection system due to a failure in the fault detection system or operator decided to continue operation under fault condition. Two fault cases in the blade pitch angle controller of the NREL 5MW offshore floating wind turbine are modeled and simulated. These faults include: bias error in the blade pitch angle rotary encoder and valve blockage or line disconnection in the blade pitch angle actuator. The short-term fatigue damage due to these faults on the composite blade root, steel low-speed shaft, tower bottom and hub are calculated and compared with the fatigue damage under normal operational conditions considering same environmental conditions for both cases. This comparison shows that how risky is to work under the fault conditions which could be useful for wind turbine operators. The servo-hydro-aeroelastic code HAWC2 is used to simulate the time domain responses of the spar-type offshore floating wind turbine under normal and faulty operational conditions. The rain-flow cycle counting method is used to calculate the load cycles under normal operational and fault conditions. The short term fatigue damage to the composite blade root and steel structures are calculated for 6-hour reference period. The bi-linear Goodman diagram and a linear SN curve are used to estimate the fatigue damage to the composite blade root and the steel structures respectively. Moreover the fatigue damage for different mean wind speeds, sea states and fault amplitudes are calculated to figure out the region of wind speeds operation with the highest risk of damage.

scholarly journals Control Algorithm for Parallel Connected Offshore Wind Turbine Generators

Energies ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4670
Author(s):  
Emir Omerdic ◽  
Jakub Osmic ◽  
Cathal O’Donnell ◽  
Edin Omerdic
Keyword(s):  
Wind Turbine ◽  
Wind Power ◽  
Wind Turbines ◽  
Control Algorithm ◽  
Low Frequency ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Power Extraction ◽  
Turbine Generators ◽  
Wind Turbine Generators

A control algorithm for Parallel Connected Offshore Wind Turbines with permanent magnet synchronous Generators (PCOWTG) is presented in this paper. The algorithm estimates the optimal collective speed of turbines based on the estimated mechanical power of wind turbines without direct measurement of wind speed. In the proposed topology of the wind farm, direct-drive Wind Turbine Generators (WTG) is connected to variable low-frequency AC Collection Grids (ACCG) without the use of individual power converters. The ACCG is connected to a variable low-frequency offshore AC transmission grid using a step-up transformer. In order to achieve optimum wind power extraction, the collective speed of the WTGs is controlled by a single onshore Back to Back converter (B2B). The voltage control system of the B2B converter adjusts voltage by keeping a constant Volt/Hz ratio, ensuring constant magnetic flux of electromagnetic devices regardless of changing system frequency. With the use of PI pitch compensators, wind power extraction for each wind turbine is limited within rated WTG power limits. Lack of load damping in offshore wind parks can result in oscillatory instability of PCOWTG. In this paper, damping torque is increased using P pitch controllers at each WTG that work in parallel with PI pitch compensators.

scholarly journals Fatigue Assessment of Monopile Supported Offshore Wind Turbine under Non-Gaussian Wind Field

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Bing Li ◽  
Kang Rong ◽  
Haifeng Cheng ◽  
Yongxin Wu
Keyword(s):  
Fatigue Life ◽  
Wind Turbine ◽  
Fatigue Damage ◽  
Wind Turbines ◽  
Wind Field ◽  
Pile Foundation ◽  
Offshore Wind ◽  
Wind Fields ◽  
Offshore Wind Turbines ◽  
Non Gaussian

The vibration of offshore wind turbines caused by external loads is significant, which will cause fatigue damage to offshore wind turbines. Wind load is the main load during the operation period of the wind turbine, and available studies have shown that the external wind field often exhibits certain non-Gaussian characteristics. This article aims to obtain the fatigue assessment of the monopile foundation of the wind turbine under the non-Gaussian wind fields. A 5 MW wind turbine is selected in this article, and OpenFAST is applied to simulate the wind load. By comparing the Mises stress time histories of the pile foundation at a different depth, the fatigue analysis of the critical spots of the pile foundation is obtained. In the analysis of fatigue damage, the rain flow counting method is adopted, and the two-segment S-N curve is selected to analyze the fatigue life of the critical spots. The results show that, by taking the non-Gaussian characteristic of the wind field into account, the fatigue life of the monopile foundation decreases. Therefore, attention should be paid to the influence of non-Gaussian characteristics of wind fields on the fatigue life of monopile-supported wind turbines.

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.

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