New perspectives in offshore wind energy.

Renewable energy provides a solution for complex current and future social and environmental problems whereas offshore industry has a large potential for providing renewable energy for future. Currently, offshore technology making use of wind for energy generation purpose becomes a hot spot with highly advanced research and development going on on one side and complex and critical problems present and difficult to solve on the other. This paper is trying to study problems related to the quantification of the hydrodynamic and aerodynamic loads for the design of offshore wind turbine support structures in the offshore wind farm. Both the hydrodynamic and aerodynamic conditions in the offshore site are extremely complex resulting in the difficulty of reasonable determination for the external loads on the wind turbine support structures. However, due to the increasing global demands for future energy solution, the design, analysis and optimization of offshore wind turbine is nevertheless an important issue. The paper first gives an introduction of the offshore wind farm and the complexity of the offshore environment. Wave load is explored with introduction of existing wave load models, comparison of their characteristics while the focus is placed on the nonlinear wave load by means of the Stokes higher order wave theory. Properties of a single regular wave based on methods of linear wave theory and Stokes higher order wave theory are compared which lead to differences in the results of wave load models when these two different methods are used. Wind load model is introduced briefly, followed by the introduction of current methods for determination or approximation of combined wave and wind load and also recommendations for practice. Park effect of the wind load and wave load is also introduced at limited depth in the latter stage as a direction for future research. Conclusion and recommendations based on all the above are therefore given at the last section of the paper.

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.

Impact of climate change on the design of multi-megawatt spar floating wind turbines

Assessing code-based design wind loads for offshore wind turbines in China against typhoons

Extreme load extrapolation and long-term fatigue assessment of offshore wind turbine tower based on monitoring data

Design and construction of offshore wind turbines (OWT) in near-fault sites is more in demand worldwide. However, very limited studies are available that assess the effects of near-field ground motions on the response of OWTs. This paper describes a numerical study on the response of OWTs to pulse-like near-field earthquakes in liquefiable soils by performing a series of advanced fully coupled nonlinear dynamic analyses using FLAC-3D. The simple anisotropic sand (SANISAND) constitutive model was adopted for soil to consider liquefaction. Two types of foundations commonly used for OWTs, namely the monopile and suction bucket were modeled. One of the characteristics of near-field ground motions is containing a significant vertical component, which is mostly in the range of high frequencies. Meanwhile, OWTs can be sensitive to vertical ground motion in terms of having a high natural frequency in the vertical direction. Therefore, focusing on the frequency content of input seismic motion, a comparison was made between the response of OWT structures to horizontal and vertical components of earthquakes in the far-field and near-field conditions. The mechanisms behind the obtained results were elaborated, and some suggestions were made for the design of OWTs under near-field conditions. According to the results, liquefaction and tilt are the major potential risks associated with the near-field earthquakes in the horizontal direction. However, in the vertical direction, the excessive amplification of acceleration and upthrow of the rotor-nacelle-assembly (RNA), are the major issues to be considered. Under near-field conditions, a suction bucket foundation can be a better option in terms of lower amplification factor of vertical acceleration, although its aspect ratio should be selected with special care to the rotation response.

Fatigue life analysis of monopile-supported offshore wind turbines based on hyperplastic ratcheting model

Multi-objective parameter optimization of large-scale offshore wind Turbine's tower based on data-driven model with deep learning and machine learning methods

Evaluation of dynamic responses under extreme environmental conditions is important for the structural design of offshore wind turbines. Previously, a modified environmental contour method has been proposed to estimate extreme responses. In the method, the joint distribution of environmental variables near the cut-out wind speed is used to derive the critical environmental conditions for a specified return period, and the turbulence intensity (TI) of wind is assumed to be a deterministic value. To address more realistic wind conditions, this paper considers the turbulence intensity as a stochastic variable and investigates the impact on the modified environmental contour. Aerodynamic simulations are run over a range of mean wind speeds at the hub height from 9–25 m/s and turbulence levels between 9%–15%. Dynamic responses of a monopile offshore wind turbine under extreme conditions were studied, and the importance of considering the uncertainties associated with wind turbulence is highlighted. A case of evaluating the extreme response for 50-year environmental contour is given as an example of including TI as an extra variant in environmental contour method. The result is compared with traditional method in which TI is set as a constant of 15%. It shows that taking TI into consideration based on probabilistic method produces a lower extreme response prediction.

Analysis of the design of experiments of offshore wind turbine fatigue reliability design with Kriging surfaces

This paper comprehensively analyses advancements in wind turbine design and offshore wind energy integration, emphasizing technological innovations, economic viability, and environmental impacts. It explores significant progress in wind energy, driven by technological advancements and supported by economic and environmental considerations. The methodology includes an extensive review of recent literature, policy frameworks, and case studies to assess wind energy's current state and future prospects. Key findings reveal that innovations such as larger turbine designs, floating wind turbines, and advanced materials have significantly enhanced turbine efficiency and reliability, resulting in increased energy capture and reduced costs. The study highlights a substantial reduction in the levelized cost of energy (LCOE) for both onshore and offshore wind projects, making wind energy increasingly competitive with traditional fossil fuels. Supportive government policies and innovative financing mechanisms have been crucial in attracting investment and facilitating growth in the sector. Despite these advancements, wind energy presents challenges such as wildlife impacts and noise pollution, which require careful management. The study emphasizes the necessity for comprehensive environmental impact assessments and mitigation measures. Additionally, social acceptance and public perception are identified as critical factors for the successful implementation of wind energy projects. In conclusion, wind energy is a viable and sustainable solution to the global energy challenge. Recommendations include continued investment in research and development, streamlined regulatory processes, and the integration of wind energy with other renewable sources to enhance grid stability. Keywords: Wind Turbine Design, Offshore Wind Energy, Technological Innovations, Economic Viability, Environmental Impacts, Renewable Energy.

Structural Design and Analysis of Offshore Wind Turbines from a System Point of View

Chapter17 - Seismic design and analysis of offshore wind turbines

The need for different numerical models with varying degrees of simplification for the conceptual design of a floating offshore wind turbine is the focus of this paper. While parts on the component level can be designed apart from the others the overall dynamics on the system level have to be assessed from the beginning. Starting with very simple models and identifying the significant contributions to the system behavior while going step by step to more detailed ones makes a successful dimensioning possible. The significant effect of the blade pitch controller on the system dynamics is analysed and preliminarily designed with a simple 1-degree of freedom (dof) model. Further on the section forces at tower base and the distributed platform loads are calculated with a 9-dof multibody system with simplified aerodynamics and Morison equation allowing a pre-dimensioning of the structure.

The development of offshore wind power has become a pressing energy issue, driven by the need to find new electrical power sources and to reduce the use of fossil fuels. Offshore wind farms can harness tremendous wind resources without annoying citizens and with a comparatively low environmental impact. They are thus becoming a central pillar of a carbon free energy system. However offshore turbines and wind farms are costly to install and maintain, making reliability and cost-effectiveness key issues. This work covers reliability of offshore wind farms as a whole, starting from weather and wind conditions, dealing with wind turbine technology, farm layout, monitoring, safety and maintenance. The thoroughly revised second edition additionally covers turbines of up to 10 MW, turbine design changes, turbine converters, HVDC converter stations and DC links, offshore sub-sea collector and export cables, and the structures supporting large offshore wind farms. Offshore Wind Power is essential reading for scientists, engineers, technicians and advanced students interested or engaged in the design of wind turbines, drivetrain technology and power mechatronics, in academia and industry.