scholarly journals A study on fully nonlinear wave load effects on floating wind turbine

2019 ◽  
Vol 88 ◽  
pp. 216-240 ◽  
Author(s):  
Kun Xu ◽  
Yanlin Shao ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Wind Turbine ◽  
Nonlinear Wave ◽  
Wave Load ◽  
Fully Nonlinear ◽  
Floating Wind Turbine ◽  
Load Effects

scholarly journals Analysis of Load Reduction of Floating Wind Turbines Using Passive Tuned Mass Dampers

2021 ◽  
Vol 9 (9) ◽  
pp. 1340-1345
Author(s):  
Aabas Ahmad
Keyword(s):  
Standard Deviation ◽  
Wind Turbine ◽  
Tuned Mass Damper ◽  
Mass Ratio ◽  
Longitudinal Displacement ◽  
Wave Load ◽  
Tuned Mass Dampers ◽  
Floating Wind Turbine ◽  
Mass Damper ◽  
Offshore Floating Wind Turbine

Abstract: An efficient method for restraining the large vibration displacements and loads of offshore floating wind turbines under harsh marine environment is proposed by putting tuned mass dampers in the cabin. A dynamics model for a barge-type offshore floating wind turbine with a fore–aft tuned mass damper is established based on Lagrange’s equations; the nonlinear least squares Leven berg–Marquardt algorithm is employed to identify the parameters of the wind turbine; different parameter optimization methods are adopted to optimize tuned mass damper parameters by considering the standard deviation of the tower top longitudinal displacement as the objective function. Aiming at five typical combined wind and wave load cases under normal running state of the wind turbine, the dynamic responses of the wind turbine with/without tuned mass damper are simulated and the suppression effect of the tuned mass damper is investigated over the wide range of load cases. The results show that when the wind turbine vibrates in the state of damped free vibration, the standard deviation of the tower top longitudinal displacement is decreased approximately 60% in 100 s by the optimized tuned mass damper with the optimum tuned mass damper mass ratio 1.8%. The standard deviation suppression rates of the longitudinal displacements and loads in the tower and blades increase with the tuned mass damper mass ratio when the wind turbine vibrates under the combined wind and wave load cases. When the mass ratio changes from 0.5% to 2%, the maximum suppression rates vary from 20% to 50% correspondingly, which effectively reduce vibration responses of the offshore floating wind turbine. The results of this article preliminarily verify the feasibilities of using a tuned mass damper for restraining vibration of the barge-type offshore floating wind turbine

Dynamic Response of Spar Wind Turbine Moored by Dynamic Catenaries Under Random Wind and Wave Loads

2019 ◽  
Author(s):  
Yilun Li ◽  
Shuangxi Guo ◽  
Yue Kong ◽  
Weimin Chen ◽  
Min Li
Keyword(s):  
Dynamic Response ◽  
Wind Turbine ◽  
Integrated System ◽  
Mooring Line ◽  
Offshore Wind Turbine ◽  
Response Analysis ◽  
Flexible Beam ◽  
Wave Loads ◽  
Wave Load ◽  
Floating Wind Turbine

Abstract As offshore wind turbine is developed toward larger water depth, the dynamics coming from structural and fluid inertia and damping effects of the mooring-line gets more obvious, that makes the response analysis of the large floating wind turbine under wind&wave load more challenging. In this study, the dynamic response of a spar floating wind turbine under random wind and wave loads is examined by the modified FEM simulations. Here an integrated system including flexible multi-bodies such as blades, tower, spar and mooring-lines is considered while the catenary dynamics is involved. The dynamic restoring performance of the catenary mooring-line is analyzed based on the vector equations of 3D curved flexible beam and its numerical simulations. Then the structural responses, e.g. the top tension, structural displacements and stress of the tower and the blade, undergoing random wind&wave loads, are examined. Morevoer, the influences of the catenary dynamics on its restoring performance and the hysteresis behavior are presented. Our numerical results show: the dynamics of mooring-line may significantly increase the top tension, and, particularly, the snap tension could be more than 3 times larger than the quasi-static one. Moreover, the structural response under random wind&wave load gets smaller mainly because of the hysteresis effect coming from the mooring-line dynamics. The floating body displacement at surge frequency is around 20% smaller, and the tower root stress at bending frequency is about 30% smaller than the quasi-static values respectively.

Spectral analysis of nonlinear wave load effects on offshore platforms

1982 ◽  
Vol 4 (1) ◽  
pp. 29-36 ◽  
Author(s):  
Ragnar Sigbjörnsson ◽  
Morten Mörch
Keyword(s):  
Spectral Analysis ◽  
Nonlinear Wave ◽  
Offshore Platforms ◽  
Wave Load ◽  
Load Effects

Model-Inversion Feedforward Control for Wave Load Reduction in Floating Wind Turbines

2021 ◽  
Author(s):  
Alessandro Fontanella ◽  
Marco Belloli
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Control Strategy ◽  
Feedforward Control ◽  
Operating Conditions ◽  
Offshore Wind ◽  
Linear Wave ◽  
Wave Load ◽  
Floating Wind Turbine ◽  
Floating Offshore Wind Turbines

Abstract This paper develops a novel feedforward control strategy for reducing structural loads caused by waves in floating offshore wind turbines. The proposed control strategy is based on the inversion of a linear model of the floating wind turbine, and a real-time forecast of the wave obtained from an upstream measurement is utilized to compute a collective pitch control action. Two feedforward controllers are considered: one is designed to cancel the rotor speed oscillations and one to lower the towertop fore-aft shear force. The feedforward control strategies are implemented in a 10MW floating wind turbine, complementing the standard feedback controller for generator speed regulation. Numerical simulations are carried out in FAST, in four operating conditions with realistic wind and waves, proving the proposed feedforward controller effectively mitigates the structural loads caused by waves. In detail, the feedforward action reduces the loads spectra in the frequency range where linear wave is active. The best performance is realized higher winds (the FA force is reduced up to 25% in 22 m/s wind), where the wave excitation is the strongest.

Effect of Second-Order and Fully Nonlinear Wave Kinematics on a Tension-Leg-Platform Wind Turbine in Extreme Wave Conditions

2017 ◽  
Author(s):  
Antonio Pegalajar-Jurado ◽  
Michael Borg ◽  
Amy Robertson ◽  
Jason Jonkman ◽  
Henrik Bredmose
Keyword(s):  
Wind Turbine ◽  
Nonlinear Wave ◽  
Second Order ◽  
Surface Elevation ◽  
Tension Leg Platform ◽  
Fully Nonlinear ◽  
Wave Kinematics ◽  
Wave Basin ◽  
Definition Of ◽  
The Impact

In this study, we assess the impact of different wave kinematics models on the dynamic response of a tension-leg-platform wind turbine. Aero-hydro-elastic simulations of the floating wind turbine are carried out employing linear, second-order, and fully nonlinear kinematics using the Morison equation for the hydrodynamic forcing. The wave kinematics are computed from either theoretical or measured signals of free-surface elevation. The numerical results from each model are compared to results from wave basin tests on a scaled prototype. The comparison shows that sub and superharmonic responses can be introduced by second-order and fully nonlinear wave kinematics. The response at the wave frequency range is better reproduced when kinematics are generated from the measured surface elevation. In the future, the numerical response may be further improved by replacing the global, constant damping coefficients in the model by a more detailed, customizable definition of the user-defined numerical damping.

scholarly journals Model Test of the STC Concept in Survival Modes

2014 ◽  
Author(s):  
Ling Wan ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Wind Turbine ◽  
Model Test ◽  
Extreme Conditions ◽  
Regular Wave ◽  
Wave Load ◽  
Large Wave ◽  
Irregular Wave ◽  
Floating Wind Turbine ◽  
The Mean ◽  
Wave Conditions

The STC (Spar Torus Combination) concept combines a Spar floating wind turbine and a torus-shaped heaving-body wave energy converter (WEC). Numerical simulation has shown positive synergy between the WEC and the Spar floating wind turbine in operational conditions. However, in extreme wind and wave conditions, it is challenging to maintain structural integrity, especially for the WEC. To ensure survivability of this concept in extreme conditions, three survival modes have been proposed. To investigate the performance of the STC in extreme conditions, model tests with a scale factor of 1:50 were carried out in the towing tank of MARINTEK, Norway. Two survival modes were tested. In both modes, the Torus WEC was fixed to the Spar. In the first mode, the Torus WEC is at the mean water surface, while in the second mode, the Torus WEC is fully submerged to a specified position. In the tests, 6 D.O.F rigid body motions, mooring line tensions, forces in 3 directions (X, Y and Z) between the Spar and Torus were measured, wind velocity and wind force were also measured by a sensor in front of the model and a load cell installed on the wind disc. In this paper, the model test set-up for the two survival modes are described, and then decay tests, regular wave tests and the statistical tests for wind only, irregular wave only and irregular wave plus wind are presented, compared and analyzed. In the mean water level survival mode, the Torus had a small draft and large water plane area, so slamming and green water were observed as expected. In addition, Mathieu instability phenomena were observed during the regular wave test. In some large wave conditions in the fully submerged mode, no severe wave load occurred. All the results are presented in model scale unless specified, for direct comparison with numerical simulations later.

Dynamic Load Analysis of the Tower Structure of a Floating Wind Turbine Under Random Wind and Wave Excitation by Detuning Blade Pitch Controller Proportional Gains

2020 ◽  
Author(s):  
Zhao Shilun
Keyword(s):  
Wind Turbine ◽  
Dynamic Load ◽  
Gain Coefficient ◽  
Sea State ◽  
Wind Speeds ◽  
Floating Wind Turbine ◽  
Tower Structure ◽  
Load Effects ◽  
Motion Performance ◽  
Base Connections

Abstract This paper carried out coupled non-linear aero-hydro-servo-elastic simulations of a semisubmersible floating wind turbine under normal and severe sea states at various wind speeds. The NREL 5MW turbine was modeled by the SIMO-RIFLEX module in SESAM with hydrodynamic gathered by the WADAM code. A taut leg mooring system with redundancy was applied to account for the relatively shallow water site in the South China Sea. By detuning KP, the proportional gain coefficient of the blade-pitch controller, the platform motions and dynamic load effects on tower structure were investigated. It was found that the reduction of KP mitigates the load effects on tower top and base connections in certain load conditions. The motion performance of the platform was improved to some extent. The generator power output, as well as the fluctuation, were analyzed. Finally, suggestion on detailed blade pitch gains tuning according to specific wind speed and sea state was given.

Irregular Nonlinear Wave Simulation and Associated Loads on Offshore Wind Turbines

2013 ◽  
Author(s):  
E. Marino ◽  
H. Nguyen ◽  
C. Lugni ◽  
L. Manuel ◽  
C. Borri
Keyword(s):  
Wind Turbine ◽  
Nonlinear Wave ◽  
Wind Turbines ◽  
Design Guidelines ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Modeling ◽  
Linear Solution ◽  
Fully Nonlinear ◽  
Offshore Wind Turbines

The accuracy of predicted loads on offshore wind turbines depends on the mathematical models employed to describe the combined action of the wind and waves. Using a global simulation framework that employs a domain-decomposition strategy for computational efficiency, this study investigates the effects of nonlinear waves on computed loads on the support structure (monopile) and the rotor-nacelle assembly of a bottom-supported offshore wind turbine. The fully nonlinear (FNL) numerical wave solver is invoked only on sub-domains where nonlinearities are detected; thus, only locally in space and time, a linear solution (and associated Morison hydrodynamics) is replaced by the FNL one. An efficient carefully tuned linear-nonlinear transition scheme makes it possible to run long simulations such that effects from weakly nonlinear up to fully nonlinear events, such as imminent breaking waves, can be accounted for. The unsteady nonlinear free-surface problem governing the propagation of gravity waves is formulated using potential theory and a higher-order boundary element method (HOBEM) is used to discretize Laplace’s equation. The FNL solver is employed and associated hydrodynamic loads are simulated in conjunction with aerodynamic loads on the rotor of a 5-MW wind turbine using the NREL open-source software, FAST. We assess load statistics associated with a single severe sea state. Such load statistics are needed in evaluating relevant load cases specified in offshore wind turbine design guidelines; in this context, the influence of nonlinear wave modeling and its selection over alternative linear or linearized wave modeling is compared. Ultimately, a study such as this one will seek to evaluate long-term loads using the FNL solver in computations directed towards reliability-based design of offshore wind turbines where a range of sea states will need to be evaluated.

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