scholarly journals Offshore Wind Turbine Nonlinear Wave Loads and Their Statistics

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Paul D. Sclavounos ◽  
Yu Zhang ◽  
Yu Ma ◽  
David F. Larson
Keyword(s):  
Nonlinear Wave ◽  
Machine Learning Algorithms ◽  
Offshore Wind ◽  
Support Vector ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Wave Load ◽  
Support Structure ◽  
Nonlinear Load ◽  
Floating Offshore Wind Turbines

The development of an analytical model for the prediction of the stochastic nonlinear wave loads on the support structure of bottom mounted and floating offshore wind turbines is presented. Explicit expressions are derived for the time-domain nonlinear exciting forces in a sea state with significant wave height comparable to the diameter of the support structure based on the fluid impulse theory (FIT). The method is validated against experimental measurements with good agreement. The higher order moments of the nonlinear load are evaluated from simulated force records and the derivation of analytical expressions for the nonlinear load statistics for their efficient use in design is addressed. The identification of the inertia and drag coefficients of a generalized nonlinear wave load model trained against experiments using support vector machine learning algorithms is discussed.

scholarly journals Offshore Wind Turbine Nonlinear Wave Loads and Their Statistics

2017 ◽  
Author(s):  
Paul D. Sclavounos ◽  
Yu Zhang ◽  
Yu Ma ◽  
David F. Larson
Keyword(s):  
Nonlinear Wave ◽  
Machine Learning Algorithms ◽  
Offshore Wind ◽  
Support Vector ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Wave Load ◽  
Support Structure ◽  
Nonlinear Load ◽  
Floating Offshore Wind Turbines

The development is presented of an analytical model for the prediction of the stochastic nonlinear wave loads on the support structure of bottom mounted and floating offshore wind turbines. Explicit expressions are derived for the time-domain nonlinear exciting forces in a seastate with significant wave height comparable to the diameter of the support structure based on the fluid impulse theory. The method is validated against experimental measurements with good agreement. The higher order moments of the nonlinear load are evaluated from simulated force records and the derivation of analytical expressions for the nonlinear load statistics for their efficient use in design is addressed. The identification of the inertia and drag coefficients of a generalized nonlinear wave load model trained against experiments using Support Vector Machine learning algorithms is discussed.

scholarly journals Nonlinear Wave Loads on Offshore Wind Turbines: Extreme Statistics and Fatigue

2019 ◽  
Author(s):  
Yu Zhang ◽  
Paul D. Sclavounos
Keyword(s):  
Nonlinear Wave ◽  
Wind Turbines ◽  
Offshore Wind ◽  
Wave Loads ◽  
Extreme Statistics ◽  
Support Structure ◽  
Nonlinear Load ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
The Time Domain

Abstract The development is presented of an analytical model for the prediction of the stochastic nonlinear wave loads on the support structure of bottom mounted and floating offshore wind turbines. Explicit expressions are derived for the time-domain and frequency-domain nonlinear exciting forces in a seastate with significant wave height comparable to the diameter of the support structure based on the fluid impulse theory. The higher order moments of the nonlinear load are evaluated from simulated force records and the derivation of analytical expressions for the nonlinear load statistics for their efficient use in design is addressed.

scholarly journals Nonlinear Wave Loads on Offshore Wind Turbines: Extreme Statistics and Fatigue

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Yu Zhang ◽  
Paul D. Sclavounos
Keyword(s):  
Nonlinear Wave ◽  
Wind Turbines ◽  
Offshore Wind ◽  
Wave Loads ◽  
Extreme Statistics ◽  
Support Structure ◽  
Nonlinear Load ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
The Time Domain

Abstract The development is presented of an analytical model for the prediction of the stochastic nonlinear wave loads on the support structure of bottom-mounted and floating offshore wind turbines. Explicit expressions are derived for the time-domain and frequency-domain nonlinear exciting forces in a seastate with a significant wave height comparable to the diameter of the support structure based on the fluid impulse theory. The higher-order moments of the nonlinear load are evaluated from simulated force records, and the derivation of analytical expressions for the nonlinear load statistics for their efficient use in design is addressed.

scholarly journals The Effect of the Second-Order Wave Loads on Drift Motion of a Semi-Submersible Floating Offshore Wind Turbine

2020 ◽  
Vol 8 (11) ◽  
pp. 859
Author(s):  
Thanh-Dam Pham ◽  
Hyunkyoung Shin
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Second Order ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Hydrodynamic Loads ◽  
Drift Motion ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines

Floating offshore wind turbines (FOWTs) have been installed in Europe and Japan with relatively modern technology. The installation of floating wind farms in deep water is recommended because the wind speed is stronger and more stable. The design of the FOWT must ensure it is able to withstand complex environmental conditions including wind, wave, current, and performance of the wind turbine. It needs simulation tools with fully integrated hydrodynamic-servo-elastic modeling capabilities for the floating offshore wind turbines. Most of the numerical simulation approaches consider only first-order hydrodynamic loads; however, the second-order hydrodynamic loads have an effect on a floating platform which is moored by a catenary mooring system. At the difference-frequencies of the incident wave components, the drift motion of a FOWT system is able to have large oscillation around its natural frequency. This paper presents the effects of second-order wave loads to the drift motion of a semi-submersible type. This work also aimed to validate the hydrodynamic model of Ulsan University (UOU) in-house codes through numerical simulations and model tests. The NREL FAST code was used for the fully coupled simulation, and in-house codes of UOU generates hydrodynamic coefficients as the input for the FAST code. The model test was performed in the water tank of UOU.

Key Contributors to Lifetime Accumulated Fatigue Damage in an Offshore Wind Turbine Support Structure

2017 ◽  
Author(s):  
Emil Smilden ◽  
Erin E. Bachynski ◽  
Asgeir J. Sørensen
Keyword(s):  
Wind Turbine ◽  
Fatigue Damage ◽  
Control Strategies ◽  
Time Domain Analysis ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Support Structure ◽  
Wear And Tear ◽  
Collateral Effects

A simulation study is performed to identify the key contributors to lifetime accumulated fatigue damage in the support-structure of a 10 MW offshore wind turbine placed on a monopile foundation in 30 m water depth. The relative contributions to fatigue damage from wind loads, wave loads, and wind/wave misalignment are investigated through time-domain analysis combined with long-term variations in environmental conditions. Results show that wave loads are the dominating cause of fatigue damage in the support structure, and that environmental condtions associated with misalignment angle > 45° are insignificant with regard to the lifetime accumulated fatigue damage. Further, the results are used to investigate the potential of event-based use of control strategies developed to reduce fatigue loads through active load mitigation. Investigations show that a large reduction in lifetime accumulated fatigue damage is possible, enabling load mitigation only in certain situations, thus limiting collateral effects such as increased power fluctuations, and wear and tear of pitch actuators and drive-train components.

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.

Design Requirements for Floating Offshore Wind Turbines

2013 ◽  
Author(s):  
Xiaohong Chen ◽  
Qing Yu
Keyword(s):  
Wind Turbine ◽  
Case Studies ◽  
Wind Turbines ◽  
Offshore Wind ◽  
Design Parameters ◽  
Offshore Wind Turbine ◽  
Support Structure ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Design Requirements

This paper presents the research in support of the development of design requirements for floating offshore wind turbines (FOWTs). An overview of technical challenges in the design of FOWTs is discussed, followed by a summary of the case studies using representative FOWT concepts. Three design concepts, including a Spar-type, a TLP-type and a Semisubmersible-type floating support structure carrying a 5-MW offshore wind turbine, are selected for the case studies. Both operational and extreme storm conditions on the US Outer Continental Shelf (OCS) are considered. A state-of-the-art simulation technique is employed to perform fully coupled aero-hydro-servo-elastic analysis using the integrated FOWT model. This technique can take into account dynamic interactions among the turbine Rotor-Nacelle Assembly (RNA), turbine control system, floating support structure and stationkeeping system. The relative importance of various design parameters and their impact on the development of design criteria are evaluated through parametric analyses. The paper also introduces the design requirements put forward in the recently published ABS Guide for Building and Classing Floating Offshore Wind Turbine Installations (ABS, 2013).

Validation and Development of Improved Methods for the Calculation of Wave Loads on XXL Monopiles

2018 ◽  
Author(s):  
Mareike Leimeister ◽  
Bastian Dose
Keyword(s):  
State Of The Art ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Wave Load ◽  
Wind Turbine System ◽  
Engineering Models ◽  
Dynamics Simulations ◽  
Diffraction Effects ◽  
Wave Induced

With the offshore wind industry aiming to deploy deeper water sites (> 30 m) while still utilizing monopiles, support structures with larger diameters are required. For the design and assessment of so-called XXL monopiles, wave-induced forces, which become more dominant with increasing diameter, have to be determined accurately. Thus, this study focuses on the identification of differences between state-of-the-art theories for wave load calculations with engineering models and the forces exerted on large monopiles from high-precision numerical reference methods. Within the framework of the research project TANDEM (Towards an Advanced Design of Large Monopiles) a 7 m diameter monopile is designed to support Fraunhofer’s IWT-7.5-164. This offshore wind turbine system is used as reference to determine wave-induced loads based on the MacCamy-Fuchs approach, implemented in models in Modelica. Different waves, defined in a simulation matrix, are investigated to elaborate the significance of diffraction effects, as well as the relevance of non-linear effects. The results are compared to CFD (Computational Fluid Dynamics) simulations. Deviations in the wave-induced forces are analyzed, taking into account the different capabilities of the applied tools, trends in the applicability of the engineering model are elaborated, and suggestions for improvement of the code based on state-of-the-art theories are given.

scholarly journals Optimization of Floating Offshore Wind Turbine Platforms With a Self-Tuning Controller

2017 ◽  
Author(s):  
Frank Lemmer ◽  
Kolja Müller ◽  
Wei Yu ◽  
David Schlipf ◽  
Po Wen Cheng
Keyword(s):  
Wind Turbine ◽  
Offshore Wind ◽  
Design Parameters ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Offshore Wind Turbines ◽  
Material Costs ◽  
Floating Offshore Wind Turbines ◽  
Self Tuning ◽  
Cost Efficient

The dynamic response of floating offshore wind turbines is complex and requires numerous design iterations in order to converge at a cost-efficient hull shape with reduced responses to wind and waves. In this article, a framework is presented, which allows the optimization of design parameters with respect to user-defined criteria such as load reduction and material costs. The optimization uses a simplified nonlinear model of the floating wind turbine and a self-tuning model-based controller. The results are shown for a concrete three-column semi-submersible and a 10 MW wind turbine, for which a reduction of the fluctuating wind and wave loads is possible through the optimization. However, this happens at increased material costs for the platform due to voluminous heave plates or increased column spacing.

scholarly journals Uncertainty Assessment of CFD Investigation of the Nonlinear Difference-Frequency Wave Loads on a Semisubmersible FOWT Platform

2020 ◽  
Vol 13 (1) ◽  
pp. 64
Author(s):  
Lu Wang ◽  
Amy Robertson ◽  
Jason Jonkman ◽  
Yi-Hsiang Yu
Keyword(s):  
Low Frequency ◽  
Uncertainty Assessment ◽  
Difference Frequency ◽  
Offshore Wind ◽  
Wave Loads ◽  
Wave Excitation ◽  
Wave Load ◽  
Frequency Wave ◽  
Floating Offshore Wind Turbines ◽  
Frequency Excitation

Current mid-fidelity modeling approaches for floating offshore wind turbines (FOWTs) have been found to underpredict the nonlinear, low-frequency wave excitation and the response of semisubmersible FOWTs. To examine the cause of this underprediction, the OC6 project is using computational fluid dynamics (CFD) tools to investigate the wave loads on the OC5-DeepCwind semisubmersible, with a focus on the nonlinear difference-frequency excitation. This paper focuses on assessing the uncertainty of the CFD predictions from simulations of the semisubmersible in a fixed condition under bichromatic wave loading and on establishing confidence in the results for use in improving mid-fidelity models. The uncertainty for the nonlinear wave excitation is found to be acceptable but larger than that for the wave-frequency excitation, with the spatial discretization error being the dominant contributor. Further, unwanted free waves at the difference frequency have been identified in the CFD solution. A wave-splitting and wave load-correction procedure are presented to remove the contamination from the free waves in the results. A preliminary comparison to second-order potential-flow theory shows that the CFD model predicted significantly higher difference-frequency wave excitations, especially in surge, suggesting that the CFD results can be used to better calibrate the mid-fidelity tools.

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