Stochastic Linearization of the Morison Equation Applied to an Offshore Wind Turbine

2015 ◽  
Author(s):  
Charaf Ouled Housseine ◽  
Charles Monroy ◽  
Guillaume de Hauteclocque
Keyword(s):  
Wind Turbine ◽  
Wave Field ◽  
Frequency Domain ◽  
Wave Model ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Morison Equation ◽  
Incoming Wave ◽  
Irregular Wave ◽  
Seakeeping Analysis

This paper aims at comparing different implementations of the Morison equation for seakeeping analysis in frequency domain. For more consistency, different wave models are considered and the total wave field (incoming wave, the diffracted and the radiated wave field) is included in the Morison equation. A state-of-the-art of theMorison equation and the drag force linearized forms are presented. The implementation procedure, based on an iterative frequency domain scheme, is developed for the regular and the irregular wave cases. Seakeeping analysis of an offshore wind turbine is considered as an application case. A comparison between numerical simulations and measured responses is presented. For the floater’s numerical model, skirts damping effect and hydrodynamic loads applied on cylindrical bracings are modeled using the Morison equation. The drag and inertia coefficients are considered constant for all sea states and calibrated using the experimental results. Response amplitude operators (RAOs) and short-termstatistics of motions show a good agreement between experimental and numerical results. The influence of different calculation parameters including the wave model (regular/irregular) and the wave fields (incident/total) are investigated.

On the Modeling of Nonlinear Waves for Prediction of Long-Term Offshore Wind Turbine Loads

2008 ◽  
Author(s):  
P. Agarwal ◽  
L. Manuel
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Return Period ◽  
Wave Model ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Offshore Wind Turbines ◽  
Irregular Wave ◽  
Inflow Turbulence

In the design of wind turbines—onshore or offshore—the prediction of extreme loads associated with a target return period requires statistical extrapolation from available loads data. The data required for such extrapolation are obtained by stochastic time-domain simulation of the inflow turbulence, the incident waves, and the turbine response. Prediction of accurate loads depends on assumptions made in the simulation models employed. While for the wind, inflow turbulence models are relatively well established, for wave input, the current practice is to model irregular (random) waves using a linear wave theory. Such a wave model does not adequately represent waves in shallow waters where most offshore wind turbines are being sited. As an alternative to this less realistic wave model, the present study investigates the use of irregular nonlinear (second-order) waves for estimating loads on an offshore wind turbine, with a focus on the fore-aft tower bending moment at the mudline. We use a 5MW utility-scale wind turbine model for the simulations. Using, first, simpler linear irregular wave modeling assumptions, we establish long-term loads and identify governing environmental conditions (i.e., the wind speed and wave height) that are associated with the 20-year return period load derived using the inverse first-order reliability method. We present the nonlinear irregular wave model next and incorporate it into an integrated wind-wave-response simulation analysis program for offshore wind turbines. We compute turbine loads for the governing environmental conditions identified with the linear model and also for an extreme environmental state. We show that computed loads are generally larger with the nonlinear wave modeling assumptions; this establishes the importance of using such refined nonlinear wave models in stochastic simulation of the response of offshore wind turbines.

On the Modeling of Nonlinear Waves for Prediction of Long-Term Offshore Wind Turbine Loads

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
P. Agarwal ◽  
L. Manuel
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Return Period ◽  
Wave Model ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Offshore Wind Turbines ◽  
Irregular Wave ◽  
Inflow Turbulence

In the design of wind turbines—onshore or offshore—the prediction of extreme loads associated with a target return period requires statistical extrapolation from available loads data. The data required for such extrapolation are obtained by stochastic time-domain simulation of the inflow turbulence, the incident waves, and the turbine response. Prediction of accurate loads depends on assumptions made in the simulation models employed. While for the wind, inflow turbulence models are relatively well established; for wave input, the current practice is to model irregular (random) waves using a linear wave theory. Such a wave model does not adequately represent waves in shallow waters where most offshore wind turbines are being sited. As an alternative to this less realistic wave model, the present study investigates the use of irregular nonlinear (second-order) waves for estimating loads on an offshore wind turbine with a focus on the fore-aft tower bending moment at the mudline. We use a 5 MW utility-scale wind turbine model for the simulations. Using, first, simpler linear irregular wave modeling assumptions, we establish long-term loads and identify governing environmental conditions (i.e., the wind speed and wave height) that are associated with the 20-year return period load derived using the inverse first-order reliability method. We present the nonlinear irregular wave model next and incorporate it into an integrated wind-wave response simulation analysis program for offshore wind turbines. We compute turbine loads for the governing environmental conditions identified with the linear model and also for an extreme environmental state. We show that computed loads are generally larger with the nonlinear wave modeling assumptions; this establishes the importance of using such refined nonlinear wave models in stochastic simulation of the response of offshore wind turbines.

scholarly journals Spoke Dimension on the Motion Performance of a Floating Wind Turbine with Tension-Leg Platform

2016 ◽  
Vol 2016 ◽  
pp. 1-16
Author(s):  
H. F. Wang ◽  
Y. H. Fan
Keyword(s):  
Wind Turbine ◽  
Good Choice ◽  
Offshore Wind ◽  
Experimental Result ◽  
Offshore Wind Turbine ◽  
Tension Leg Platform ◽  
Irregular Wave ◽  
Wind Turbine System ◽  
Floating Offshore Wind Turbines ◽  
Tower Structure

The tension-leg platform (TLP) supporting structure is a good choice for floating offshore wind turbines because TLP has superior motion dynamics. This study investigates the effects of TLP spoke dimensions on the motion of a floating offshore wind turbine system (FOWT). Spoke dimension and offshore floating TLP were subjected to irregular wave and wind excitation to evaluate the motion of the FOWT. This research has been divided into two parts: (1) Five models were designed based on different spoke dimensions, and aerohydroservo-elastic coupled analyses were conducted on the models using the finite element method. (2) Considering the coupled effects of the dynamic response of a top wind turbine, a supporting-tower structure, a mooring system, and two models on a reduced scale of 1 : 80 were constructed and experimentally tested under different conditions. Numerical and experimental results demonstrate that the spoke dimensions have a significant effect on the motion of FOWT and the experimental result that spoke dimension can reduce surge platform movement to improve turbine performance.

Experimental Study on the Wave Loads on Monopile and Jacket Type Support of Offshore Wind Turbines

2018 ◽  
Author(s):  
Jing Zhang ◽  
Qin Liu ◽  
Xing Hua Shi ◽  
C. Guedes Soares
Keyword(s):  
Experimental Study ◽  
Wind Turbine ◽  
Nonlinear Wave ◽  
Wave Force ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Forces ◽  
Wave Loads ◽  
Morison Equation ◽  
Offshore Wind Turbines

As the offshore fixed wind turbine developed, more ones will be installed in the sea field with the depth 15–50 meters. Wave force will be one of the main forces that dominate the design of the wind turbine base, which is calculated using the Morison equation traditionally. This method can predict the wave forces for the small cylinders if the drag and inertia coefficients are obtained accurately. This paper will give a series scaled tests of monopile and jacket type base of the offshore wind turbine in tank to study the nonlinear wave loads.

Study on the Dynamic Characteristic for Spar Type Floating Foundation of Offshore Wind Turbine

2012 ◽  
Vol 170-173 ◽  
pp. 2316-2321
Author(s):  
Ruo Yu Zhang ◽  
Chao He Chen ◽  
You Gang Tang
Keyword(s):  
Wind Turbine ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Constant Current ◽  
Offshore Wind Turbine ◽  
Analysis Model ◽  
Mooring Lines ◽  
Irregular Wave ◽  
Floating Foundation ◽  
Ocean Environment

In this paper, the dynamic behaviors are studied for Spar type floating foundation of a 3kW in the 10m deep water considering the coupled wind turbine-tower-floating foundation and mooring lines and ocean environment load effects. The paper focus on the key issues of design of floating foundation, such as coupling dynamic analysis model and calculating method. The finite element models are established and dynamic responses of floating wind turbine system under different combinations of turbulent wind, constant current and irregular wave are calculated in frequency and time domain with SESAM software. The motion performance and lines’ tension are investigated, and some valuable conclusions are drawn. The results show that the Spar type floating foundation and mooring system can work in the ocean environment which significant wave height less than 2m, the designed large water-entrapment plate can minimized the motion of floating foundation obviously.

A Review of Hydrodynamic Effects on Bottom-Fixed Offshore Wind Turbines

2009 ◽  
Author(s):  
Karl O. Merz ◽  
Geir Moe ◽  
Ove T. Gudmestad
Keyword(s):  
Free Surface ◽  
Drag Coefficient ◽  
Wind Turbine ◽  
Separated Flow ◽  
Offshore Wind ◽  
Structural Vibration ◽  
Offshore Wind Turbine ◽  
Morison Equation ◽  
Drift Motion ◽  
Empirical Coefficients

Recent and historical literature regarding hydrodynamics has been reviewed, with offshore wind turbine support structures in mind. Under conditions of separated flow, several relevant phenomena have been noted which are not covered by the commonly-used Morison equation: 1. damping of structural vibration or slow-drift motion; 2. the interaction of structural vibration and vortex shedding; 3. loads near the free-surface; and, 4. burst motions, caused by impulse-like loading from steep waves. References have been given to books and articles that describe the phenomena in more detail. A form of the Morison equation is proposed which has separate empirical coefficients for each of the velocity and acceleration terms. The coefficients can be determined from existing test data with use of least-squares error minimization. A simplified form of the equation provides a means to obtain conservative bias on both the applied load (bias towards a high drag coefficient) and damping (bias towards a low drag coefficient). Further investigation into free-surface and burst motion (ringing) phenomena is recommended, considering a slender wind turbine monotower in 20 to 50 m water depth.

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