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This article presents an innovative structural system for offshore wind turbines supported on monopiles. The novelty of this system lies in its enhancement of the lateral stiffness of the tubular tower through the incorporation of an outrigger system, widely employed in high-rise buildings. This novel system is modeled as a Timoshenko beam-column element under both static and dynamic loading scenarios, incorporating geometric nonlinearity and accounting for the effect of soil-structure interaction. A comprehensive numerical analysis was conducted to evaluate the system's behavior under various static and dynamic load cases, utilizing soil data from the Red Sea region of Egypt. A modal analysis is also incorporated to investigate the eigenmodes of the proposed system. This study offers valuable insights for designers and researchers, providing guidelines and diagrams for the implementation of the proposed system. [ABSTRACT FROM AUTHOR]

Floating ice loading is a severe natural hazard for offshore wind turbines (OWTs) operating in cold sea regions. The long-term ice-induced vibration resulting from winter drift ice presents a significant threat to the fatigue reliability of OWTs. Machine learning not only exhibits robust data-driven capabilities but also efficiently handles complex relationships among multiple factors. Through effective learning and utilization of diverse features, a comprehensive assessment of the fatigue reliability of structures becomes achievable, consequently resulting in increased efficiency, accuracy, and adaptability of the assessment. This study conducts ice-induced vibration simulations on a 5-MW monopile OWT. Employing orthogonal experimental methods, the study investigates the influence of three critical ice parameters, i.e., ice thickness, ice velocity, and ice crushing strength, on the fatigue damage caused by ice loading on OWTs. Additionally, it explores the effects of ice loading exceedance probability on extreme fatigue damage values of OWTs under combined ice and wind loadings. Furthermore, a surrogate model based on support vector machine (SVM) is developed to effectively capture the intricate mapping relationship between fatigue damage and various random environmental parameters. By conducting a comprehensive evaluation that considers the probabilistic characteristics of ice loading, wind loading, and the S-N curve, this study assesses the fatigue reliability under combined ice and wind. Moreover, this study analyzes the impact of operational duration during winter drift ice on the fatigue reliability index of OWTs. The findings of this study can provide a theoretical basis for devising operational strategies for OWTs operating in icy sea regions. [ABSTRACT FROM AUTHOR]

Offshore wind energy is characterized by its clean and renewable nature, leading to rapid growth in the industry. However, the incidence of ship collisions with offshore wind turbines has also risen with the increasing number of offshore wind farms, particularly in commercial shipping lanes. To gain a thorough understanding of dynamic response between wind turbines and vessels, this paper extensively reviews studies related to wind turbine–ship collisions over the past 2 decades to cover four key aspects: (i) the fundamental requirements and background of collision analysis study, (ii) the analysis of dynamic response and collision characteristics of the fixed-bottom and floating offshore wind turbines (OWTs) subjected to ship collision forces, (iii) the influence of key collision factors that include impact positions, initial ship kinetic energy, and soil–structure interaction on the structural response for the wind turbines, and (iv) a discussion of protection measures to mitigate the collision damage to the substructure. The limitations in the existing studies are discussed, and future research directions are suggested. [ABSTRACT FROM AUTHOR]

AbstractScour occurs inevitably around monopiles of offshore wind turbines (OWTs), negatively impacting the operation of the turbines. For the purpose of ensuring the long-term safety and stability of the foundations, solidified soil which provides higher scour resistance can be used to remediate scour considering its technical convenience. In this study, flume tests were conducted under unidirectional flow conditions to investigate the dynamic remediation of the local scour hole, which was applied to different scour development processes, using solidified soil. Various remediation schemes were simulated by controlling the design elevation of the solidified soil layers to investigate their performance under different conditions. Meanwhile, the phenomenon and characteristics of edge scour during remediation were also analyzed. Results show that different remediation elevations and initiation would lead to varying degrees of edge scour. Early remediation costs less solidified soil but results in severe edge scour, while late remediation needs more materials and experiences milder edge scour. In addition, an evaluation method assessing solidified soil remediation was established. This method was utilized to evaluate the comprehensive benefit and edge scour risk for different remediation schemes. [ABSTRACT FROM AUTHOR]

This study investigates the impact of soil–structure interaction (SSI) and foundation–soil–foundation interaction (FSFI) on the dynamic behaviour of jacket substructures founded on buckets for offshore wind turbines. A parametric analysis was conducted, focusing on critical load cases for conservative foundation design. Different load configurations were examined: collinear wind and wave (fluid–structure interaction) loads, along with misaligned configurations at 45° and 90°, to assess the impact of different loading directions. The dynamic response was evaluated through key structural parameters, including axial forces, shear forces, bending moments, and stresses on the jacket. Simulations employed the National Renewable Energy Laboratory (NREL) 5MW offshore wind turbine mounted on the OC4 project jacket founded on suction buckets. An additional optimised jacket design was also studied for comparison. An OpenFAST model incorporating SSI and FSFI considering a homogeneous soil profile was employed for the dynamic analysis. The results highlight the significant role of the FSFI on the dynamic behaviour of multi-supported jacket substructure, affecting the natural frequency, acceleration responses, and internal forces. [ABSTRACT FROM AUTHOR]

Offshore wind turbines (OWTs) often operate in complex marine environments, where they are not only subjected to wind and wave loads, but also adversely affected by scour. Therefore, it is of great significance to explore the effect of scour on the dynamic responses of OWTs under external loads to ensure structural safety, improve performance, and extend service life. In this study, a comprehensive numerical model of a 5-MW OWT, including tower, monopile, and soil-structure interaction (SSI) systems, is established by using ABAQUS platform. Aerodynamic loads is generated using blade element momentum, while wave loads is generated using the P-M spectral. The depth of scour is obtained based on on-site measured data. A comparative analysis is conducted between fixed foundations and SSI systems when conducting dynamic response analysis of OWTs under wave loads. Subsequently, the effect of scour on dynamic responses of OWTs under aerodynamic and wave loads is investigated. Results demonstrate that SSI can significantly influence the natural frequency and dynamic responses of the OWT. Therefore, it is essential to thoroughly consider SSI when evaluating the dynamic response of the OWT with local scour. The tower-top displacement and acceleration of the OWT with show a significant increasing trend compared to the non-scoured OWT. An increase in scour depth leads to higher maximum stress and stress amplitude in the steel monopile, which could potentially cause fatigue issues and should be given due attention. [ABSTRACT FROM AUTHOR]

Data‐driven assistant for the design of offshore jacket substructures As the power output of offshore wind turbines increases, more and more influencing factors in the different life phases of the support structure become relevant to improve feasibility, economic viability, and provability. Conventional design methods for offshore wind turbines are complex and expensive. Conventional conceptual designs often rely on the expertise and intuition of engineers, creating a risk of bias due to insufficient design information at the beginning of a project. To minimize this risk, this paper develops a data‐driven method to simplify conceptual support structure design. The method is realized by analyzing a self‐generated global database of existing wind farms. As an example, the data‐driven method is implemented and evaluated for the conceptual design of offshore jacket substructures. It shows that the rated power of the turbine and the water depth of the wind farm should be considered as two structural parameters for the conceptual design of jacket structures for offshore wind turbines. Thus, the process is simplified and made more economical. The result forms the basis for the overall offshore wind turbine's detailed design and structural implementation. [ABSTRACT FROM AUTHOR]

The deployment of offshore wind turbines (WTs) is gaining momentum worldwide, offering significant potential for clean energy generation. However, the maintenance and longevity of offshore WT structures present complex challenges, particularly concerning corrosion protection coatings and their environmental impacts. This paper discusses the key design criteria, protective mechanisms, and application methods of coating systems for offshore WTs, emphasizing the need for durable solutions to withstand harsh marine conditions. Additionally, the study examines the chemical emissions originating from offshore wind farms, including corrosion products and plastics, and their potential ecological impacts. While there is a lack of comprehensive scientific studies on the environmental effects of deepwater, floating offshore wind farms, this paper aims to shed light on these issues and their implications for marine ecosystems and human health. By synthesizing existing literature on analogous situations, the discussion provides insights into the environmental footprints of offshore wind power and underscores the importance of prudent decision-making in advancing future offshore wind projects. [ABSTRACT FROM AUTHOR]

The research related to subsea inspection, and the prediction of corrosion is a challenging task, and the progress in this area is continuously generating exciting new developments that may be used in subsea inspection. Wall thickness monitoring is an important tool to control and predict corrosion, such as on platforms for the infrastructure of floating offshore wind power production. This study shows the results obtained in marine environments. For this experiment, a steel plate equipped with ultrasound transducers was placed in seawater to corrode naturally. The sensor test setup consisted of 15 ultrasound transducers and 1 temperature sensor, which were installed in the cassette. The data acquisition system was based on a standard industrial computer with software written in Python and MATLAB. The ultrasound signals were collected at regular intervals and processed to calculate the instantaneous wall thickness. The progress of corrosion was evaluated by trend plots of wall thickness versus time, and the change in shape of the ultrasonic back wall reflection waveform measured by each sensor. [ABSTRACT FROM AUTHOR]

The evidence of soil nonuniformity has been reported in several site investigation reports and is well-confirmed for any soil in general. However, studies related to the spatial soil variability of offshore ground are somewhat limited, and current design practices for monopile foundations also overlook the uncertainty of the offshore ground. This paper presents the probabilistic evaluation of the serviceability limit state of monopile foundations considering the spatial variability of offshore ground. The nonuniformity of the ground is modeled utilizing the site-specific undrained shear strength (su) as a stochastic variable, using a spatially correlated Gaussian random field. A hardening soil constitutive model is utilized in 3D finite element analysis of offshore ground, with a focus on parameter calibration. The reliability of the serviceability limit state is assessed based on the allowable load on the pile head. The stochastic behavior of the maximum bending moment and maximum shear force along the depth of the monopile is also investigated. Besides, the paper also highlights the importance of incorporating ground nonuniformity during the design process of a monopile foundation. [ABSTRACT FROM AUTHOR]

Integrating renewable energy sources (RESs), such as offshore wind turbines (OWTs), into the power grid demands advanced control strategies to enhance efficiency and stability. Consequently, a Deep Fractional-order Wind turbine eXpert control system (DeepFWX) model is developed, representing a hybrid proportional/integral (PI) fractional-order (FO) model predictive random forest alternating current (AC) bus voltage controller designed explicitly for OWTs. DeepFWX aims to address the challenges associated with offshore wind energy systems, focusing on achieving the smooth tracking and state estimation of the AC bus voltage. Extensive comparative analyses were performed against other state-of-the-art intelligent models to assess the effectiveness of DeepFWX. Key performance indicators (KPIs) such as MAE, MAPE, RMSE, RMSPE, and R2 were considered. Superior performance across all the evaluated metrics was demonstrated by DeepFWX, as it achieved MAE of [15.03, 0.58], MAPE of [0.09, 0.14], RMSE of [70.39, 5.64], RMSPE of [0.34, 0.85], as well as the R2 of [0.99, 0.99] for the systems states [X1, X2]. The proposed hybrid approach anticipates the capabilities of FO modeling, predictive control, and random forest intelligent algorithms to achieve the precise control of AC bus voltage, thereby enhancing the overall stability and performance of OWTs in the evolving sector of renewable energy integration. [ABSTRACT FROM AUTHOR]

Damages to multilayer organic coating systems due to impact loads can deteriorate the corrosion protection performance of the coatings under offshore exposure. The contribution is concerned with statistical investigations into the effects of load-based and coating-based factors on the protection performance of impinged coating systems for offshore wind power structures. Accelerated cyclic laboratory tests were performed on damaged multilayer coating systems, and the results were statistically analysed. Results of analysis of variance revealed that the effects on the integral corrosion protection performance of the coatings (anticorrosive effect, AE) were dominated by the factor 'load intensity' (impact energy). This factor could explain 34% of all effects. It also was the only significant factor. The load-based factor 'damage area' affected the coating delamination and was extremely significant, but it did not affect the AE. Coating-based factors, namely 'coating system', 'total dry film thickness' and 'pull-off strength', did not deliver effects to AE and were statistically insignificant. The factor 'coating system' was statistically insignificant for delamination and for AE. 'Unknown' effects, not considered in this study, delivered the highest contributions to the regression models (50% to 68%), indicating that additional parameters/factors of the coating systems must be considered when developing impact-resistant coatings. [ABSTRACT FROM AUTHOR]

Cyclic lateral loads on monopile foundations of offshore wind turbines induce vibrations that affect the clear-water scour process around the foundations. Previous experimental studies showed that the current-induced equilibrium scour depths at vibrating monopiles may be less than those at static monopile foundations. However, this observation may not be comprehensive when applied to the cases of clear-water scour around vibrating monopile foundations subjected to different flow intensities. This paper presents an experimental study that investigated the clear-water scour mechanism at vibrating monopile foundations and obtained new findings. The experimental results indicate that the scour process is influenced by three major factors: vibration-induced sediment subsidence, vibration-induced sediment refill, and current-induced erosion. Based on the three major influencing factors and experimental data, a dimensionless equation for equilibrium clear-water scour depth at vibrating monopile foundations was derived. Furthermore, a regime transition flow intensity is defined, at which the equilibrium scour depth remains constant regardless of any changes in the vibration amplitudes. Two distinct scour trends under low and high flow intensities were identified. The two different trends were found to be induced by different dominant factors. The vibration-induced subsidence effect dominates in the low flow intensity regime, whereas the vibration-induced sediment refill effect dominates in the high flow intensity regime. The new findings of this paper help to understand the characterization of clear-water scour process around vibrating monopile foundations. Practical Applications: Monopile foundations of offshore wind turbines experience cyclic lateral vibration caused by winds and waves. The cyclic lateral vibration of monopile foundations potentially can affect the current-induced scour process around the foundations. The experimental results of this study revealed that the scour depth around vibrating monopile foundations under clear-water scour conditions is influenced by a coupling effect of flow intensities and vibration amplitudes and frequencies. The findings emphasize the influence of vibration on the scour process around monopile foundations of offshore wind turbines. These results provide valuable insights to optimize the design and manufacturing processes of monopile foundations. Moreover, the findings contribute to the development of more-effective scour protection measures in offshore wind engineering. [ABSTRACT FROM AUTHOR]

Offshore wind power is a crucial clean energy source for coastal countries and advances blue economies. Accurate spatial mapping of offshore wind turbines supports energy assessment and the sustainable development of marine resources. Offshore wind power has developed rapidly in China, but the spatiotemporal distribution characteristics of offshore wind turbines and farms remain poorly understood. Extracting nearshore small targets from Sentinel-1 synthetic aperture radar images remain challenging due to noise from the rough sea surface background and the diverse substrate types in offshore wind turbine (OWT) distributions. Here, to address these issues, we first created a dataset of China’s offshore wind turbines (COWTs) that contained typical substrate types (e.g. seawater and tidal flats). Then, a deep learning model integrating an attention mechanism and receptive fields was used to accurately detect COWTs. The well-trained model was used to detect the changes in COWTs from 2015 to 2022. Our model detected an increase in the number of offshore wind farms in China from 7 to 114 (clusters counted as an offshore wind farm), while COWTs increased from 305 to 6451 from 2015 to 2022. The Taiwan Strait exhibited the highest wind speeds, yet the Jiangsu and Guangdong regions had the most installed turbines. Over 90% of COWTs were located in areas with offshore wind energy resources less than 500 W/m3, indicating a mismatch between COWT installation and wind resource distribution. This study demonstrated temporal and geographical generalizability, which is promising for global wind power detection. Our analysis of spatiotemporal variation in COWTs facilitates informed decision-making for future field establishment and sustainable marine planning.

Offshore wind energy is characterized by its clean and renewable nature, leading to rapid growth in the industry. However, the incidence of ship collisions with offshore wind turbines has also risen with the increasing number of offshore wind farms, particularly in commercial shipping lanes. To gain a thorough understanding of dynamic response between wind turbines and vessels, this paper extensively reviews studies related to wind turbine–ship collisions over the past 2 decades to cover four key aspects: (i) the fundamental requirements and background of collision analysis study, (ii) the analysis of dynamic response and collision characteristics of the fixed-bottom and floating offshore wind turbines (OWTs) subjected to ship collision forces, (iii) the influence of key collision factors that include impact positions, initial ship kinetic energy, and soil–structure interaction on the structural response for the wind turbines, and (iv) a discussion of protection measures to mitigate the collision damage to the substructure. The limitations in the existing studies are discussed, and future research directions are suggested.

Due to its high energy intensity and the associated high welding depth, electron beam welding is particularly suitable for welding steel plates with high wall thicknesses. These are used, for example, in offshore wind power systems. However, due to the cooling conditions, the required cold toughness for offshore applications is often not achieved. The aim is to develop S355 ML steels – within the EN10025 4 standard – for welding monopiles for wind turbines. For this purpose, three parameters with different energy input are developed on three steels. The tests are carried out on plates with a wall thickness of 80 mm, whereby a full penetration weld must be achieved. The resulting top and bottom bead of the welds meet the standard DIN EN ISO 13919‐1. The parameters have an energy per unit length of 9.5 kJ mm−1 to 15.5 kJ mm−1. The resulting weld seams have an average width of 5.5 mm to 7.5 mm, and burn‐off of the manganese alloy element is observed, particularly on the top side of the seam. In addition, T8/5 times close to the weld seam of 11 s to 27 s are estimated using a simulation. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Wind energy is highly volatile, and large-scale wind power grid integration significantly impacts grid stability. Accurate forecasting of wind turbine power can improve wind power consumption and ensure the economy of the power grid. This paper proposes a multistep forecasting method for offshore wind turbine power based on a multi-timescale input and an improved transformer. First, the wind speed sequence is decomposed by the VMD method to extract adequate timing information and remove the noise, after which the decomposition signals are merged with the rest of the timing features, and the dataset is split according to different timescales. A GRU receives the short-timescale inputs, and the Improved Transformer captures the timing relationship of the long-timescale inputs. Finally, a CNN is used to extract the information of each time point at the output of each branch, and the fully connected layer outputs multistep forecasting results. Experiments were conducted on operation data from four wind turbines located within the offshore wind farm but not near the edge. The results show that the proposed method achieved average errors of 0.0522 in MAE, 0.0084 in MSE, and 0.0907 in RMSE on a four-step forecast. This outperformed comparison methods LSTM, CNN-LSTM, LSTM-Attention, and Informer. The proposed method demonstrates superior forecasting performance and accuracy for multistep offshore wind turbine power forecasting. [ABSTRACT FROM AUTHOR]

The present study aims to examine the suitability of two commonly used assumptions that simplify modelling metocean conditions for designing offshore wind turbines in the South China Sea (SCS). The first assumption assumes that joint N-year extreme wind and wave events can be independently estimated and subsequently combined. The second one assumes peak wind and waves can be modelled as occurring simultaneously during a tropical cyclone (TC) event. To better understand the potential TC activity, a set of 10000 years synthetic TC events are generated. The wind field model and the Mike 21 spectral wave model are employed to model the TC-induced hazards. Subsequently, the effect of the assumptions is evaluated by analyzing the peak structural response of both monopile and semisubmersible offshore wind turbines during TC events. The results demonstrate that the examined assumptions are generally accurate. By assessing the implications of these assumptions, valuable insights are obtained, which can inform and improve the modelling of TC-induced hazards in the SCS region. [ABSTRACT FROM AUTHOR]

To improve the power generation efficiency of offshore wind turbines and address the problem of high fire monitoring and warning costs, we propose a data-driven fire warning method based on transfer learning for wind turbines in this paper. This paper processes wind turbine operation data in a SCADA system. It uses an extreme gradient-boosting tree (XGBoost) algorithm to build an offshore wind turbine unit fire warning model with a multiparameter prediction function. This paper selects some parameters from the dataset as input variables for the model, with average cabin temperature, average outdoor temperature, average cabin humidity, and average atmospheric humidity as output variables. This paper analyzes the distribution information of input and output variables and their correlation, analyzes the predicted difference, and then provides an early warning for wind turbine fires. This paper uses this fire warning model to transfer learning to different models of offshore wind turbines in the same wind farm to achieve fire warning. The experimental results show that the prediction performance of the multiparameter is accurate, with an average MAPE of 0.016 and an average RMSE of 0.795. It is better than the average MAPE (0.051) and the average RMSE (2.020) of the prediction performance of a backpropagation (BP) neural network, as well as the average MAPE (0.030) and the average RMSE (1.301) of the prediction performance of random forest. The transfer learning model has good prediction performance, with an average MAPE of 0.022 and an average RMSE of 1.469. [ABSTRACT FROM AUTHOR]

Simplified methods are often used for load estimations during the initial design of the foundations of offshore wind turbines (OWTs). However, the reliability of simplified methods for designing different OWTs needs to be studied. This paper provides a comparative study to evaluate the reliability of simplified approaches. The foundation loads are calculated for OWTs at the mudline level using a simplified approach and OpenFAST simulations and compared. Three OWTs, NREL 5 MW, DTU 10 MW, and IEA 15 MW, are used as reference models. An Extreme Turbulence Model wind load at a rated wind speed, combined with a 50-year Extreme Wave Height (EWH) and Extreme Operating Gust (EOG) wind load and a 1-year maximum wave height are used as the load combinations in this study. In addition, the extreme loads are calculated using both approaches for various metocean data from five different wind farms. Further, the pile penetration lengths calculated using the mudline loads via two methods are compared. The results show that the simplified method provides conservative results for the estimated loads compared to the OpenFAST results, where the extent of conservativism is studied. For example, the bending moment and shear force at the mudline using the simplified approach are 23% to 69% and 32% to 53% higher compared to the OpenFAST results, respectively. In addition, the results show that the simplified approach can be effectively used during the initial phases of monopile foundation design by using factors such as 1.5 and 2 for the shear force and bending moment, respectively. [ABSTRACT FROM AUTHOR]

In this paper, a numerical formulation was developed to generate the consistent mass matrix for Timoshenko tapered beam-column element for geometrically nonlinear transient analysis. The basis of the suggested solution is the exact shape functions and their derivatives, which describe the non-uniformity of the element properties. To illustrate the variations in section properties along the tapered element length, the section properties were presented as exponential functions with tapering indices. The model can simulate elements with various solid and hollow cross-sections. The suggested formulation is integrated into a Visual Basic program to perform the analysis, along with numerous examples to verify its precision and effectiveness. As a practical application of the proposed formulation, a structural system was proposed for offshore wind turbines with high elevations, and a geometrical nonlinear dynamic analysis was conducted. The results demonstrated the proposed model's ability to perform this type of complex calculation with minimal computational effort. [ABSTRACT FROM AUTHOR]

This paper presents an optimization tool for jacket structures to support Offshore Wind Turbines (OWTs). The tool incorporates several combinations of optimization algorithms and constraint-handling techniques (CHTs): Genetic Algorithm; Differential Evolution (DE); Tournament Selection Method; Multiple Constraint Ranking (MCR); Adaptive Penalty Method, and Helper-and-Equivalent Optimization. The objective function regards the minimization of the jacket weight; the design variables are the diameter and thickness of the tubular members. The constraints are related to natural frequencies and Ultimate Limit State criteria. The candidate solutions are evaluated by full nonlinear time-domain Finite Element coupled analyses. To assess the optimization algorithms and CHTs, a case study is presented for the standardized OWT/jacket structure from the Offshore Code Comparison Collaboration Continuation project. First, a numerical model is built and validated, in terms of masses, natural frequencies, and vibration modes; then, this model is employed to run the optimization tool for all combinations of optimization algorithms and CHTs. The results indicate that, while all methods lead to feasible optimal solutions that comply with the constraints and present considerable weight reductions, the best performer is the combination of the DE algorithm with the MCR constraint-handling technique. [ABSTRACT FROM AUTHOR]

This paper reviews latest developments of substructures for offshore wind turbines focusing on investigations and applications of hybrid foundations. Model tests and numerical analyses were used to simulate the loading of hybrid piles in sand. The results of pile-soil interaction were investigated to confirm the changes in soil stiffness around the hybrid monopile head. The mechanism and factors affecting the change in lateral stiffness of the hybrid foundation were explained by analysing p–y curves for M+H loading conditions in sand. Based on this research, a new shape of p–y curves for hybrid monopiles was established and a method for determining key parameters was proposed. The effectiveness of new p–y curves was verified by comparing back-calculated results with those from numerical simulations. The conducted tests confirmed that the hybrid monopile displacement is 30–50% smaller when compared to a standard monopile with similar dimensions. The gained experiences can be useful for designers and researchers to enhance the design of foundations for offshore wind turbines.

This research paper conducts an extensive exploration of onshore, offshore, and floating offshore wind turbines, pivotal components in the landscape of sustainable energy generation. The study thoroughly investigates various wind energy systems, shedding light on their distinct attributes, advantages, and limitations. The examination of onshore wind turbines encompasses aspects such as installation procedures, size considerations, wind dynamics, accessibility challenges, and visual impact assessments. Similarly, the analysis of offshore wind turbines covers considerations such as location selection, installation complexities, size variations, wind conditions, environmental impacts, and visual aesthetics. The paper also delves into the emerging technology of floating offshore wind turbines, highlighting their unique features, advantages, and technological advancements. A thorough comparative examination is conducted to assess the economic, environmental, and social aspects of onshore, offshore, and floating offshore wind turbines. The research paper concludes by offering insights into policy considerations, addressing research gaps, and outlining prospects for the seamless integration and advancement of these diverse wind energy systems. This comprehensive review aspires to contribute to the existing knowledge base in sustainable energy generation, fostering informed decision-making for a greener and more sustainable future.

This study investigates the impact of soil–structure interaction (SSI) and foundation–soil–foundation interaction (FSFI) on the dynamic behaviour of jacket substructures founded on buckets for offshore wind turbines. A parametric analysis was conducted, focusing on critical load cases for conservative foundation design. Different load configurations were examined: collinear wind and wave (fluid–structure interaction) loads, along with misaligned configurations at 45° and 90°, to assess the impact of different loading directions. The dynamic response was evaluated through key structural parameters, including axial forces, shear forces, bending moments, and stresses on the jacket. Simulations employed the National Renewable Energy Laboratory (NREL) 5MW offshore wind turbine mounted on the OC4 project jacket founded on suction buckets. An additional optimised jacket design was also studied for comparison. An OpenFAST model incorporating SSI and FSFI considering a homogeneous soil profile was employed for the dynamic analysis. The results highlight the significant role of the FSFI on the dynamic behaviour of multi-supported jacket substructure, affecting the natural frequency, acceleration responses, and internal forces.

AbstractThe monopile-supported offshore wind turbines are located in a complex marine environment, bearing various long-term cyclic loads such as wind loads, waves, and currents. To explore the weakening of soil-structure interaction under long-term lateral load for the pile foundation, a series of model tests were conducted in the laboratory under normal gravity conditions, and the evolving trends for the weakening coefficients of varying soil depths and pile diameters were analyzed, leading to the proposal of a new expression for the weakening coefficient considering the governing factors in soil-structure interaction. The new formula for the weakening coefficient proposed in this paper is validated through the experimental results of this study and other references. Through a numerical example, affirming the viability of the soil stiffness attenuation model based on the finite element analysis method and revealing the weakening law of foundations for different cycling processes. This research contributes valuable insights for designing and analyzing offshore turbine foundations, particularly in the context of weakening phenomena. [ABSTRACT FROM AUTHOR]

The foundation of an offshore wind turbine (OWT) accounts for up to 20% of the total cost; therefore, investigations into reliable and efficient foundations are important for the offshore wind energy industry. This article describes an innovative winged caisson foundation for OWTs, which adapts the conventional caisson foundation to produce higher overturning capacities. The behaviour of this proposed novel foundation in the sand was investigated through experimental and numerical modelling using a series of 1 g tests (1/70th scale), centrifuge model tests (70 g ), and finite element (FE) simulations. Models with various wing sizes installed in different sand densities were tested in the laboratory by applying an overturning load. In this article, the moment–rotation performance of the foundation under monotonic loading is compared against that of conventional caissons to assess the potential benefits of adding wings to caisson foundations. Results show that there is a significant increase in overturning capacity provided by the novel foundation. FE models were first validated against experimental results, then, used to conduct a parametric study to better understand the behaviour of the winged caissons beyond the scaled model tests. In addition, the FE models were used to evaluate the drained response of the proposed foundation under combined loading. [ABSTRACT FROM AUTHOR]

Background: The estimation of the natural frequency is a key step in the design of an offshore wind turbine (OWT). In the literature, the natural frequency can be evaluated through two steps, the first one is the estimation of the fixed base natural frequency using formulas from the literature, and the second one is the estimation of the foundation system effect. These formulas are efficient for simple shapes of OWTs but become hard to use for recent OWTs. Method: The finite element method and the Fourier series have been used to develop a computer code under the name of "TurbiSoft" to compute the natural frequency of the OWT with the foundation system. Each of the linear, the quadratic volume elements, and the joint element was employed in TurbiSoft to model the whole system to examine the influence of the element type, the soil profile, and the interaction soil–pile state on the natural frequency. Results: The outcomes of TurbiSoft for several OWTs were compared with the measured frequencies to define the range error of each parameter. The results show that the quadratic elements are more suitable for the natural frequency calculation. Also, this study demonstrates that the natural frequency value is strongly related to the interaction soil–pile state, and is slightly affected by the soil profile variation. [ABSTRACT FROM AUTHOR]

This paper reviews latest developments of substructures for offshore wind turbines focusing on investigations and applications of hybrid foundations. Model tests and numerical analyses were used to simulate the loading of hybrid piles in sand. The results of pile-soil interaction were investigated to confirm the changes in soil stiffness around the hybrid monopile head. The mechanism and factors affecting the change in lateral stiffness of the hybrid foundation were explained by analysing p-y curves for M+H loading conditions in sand. Based on this research, a new shape of p-y curves for hybrid monopiles was established and a method for determining key parameters was proposed. The effectiveness of new p-y curves was verified by comparing back-calculated results with those from numerical simulations. The conducted tests confirmed that the hybrid monopile displacement is 30-50% smaller when compared to a standard monopile with similar dimensions. The gained experiences can be useful for designers and researchers to enhance the design of foundations for offshore wind turbines. [ABSTRACT FROM AUTHOR]

This paper explores the utilization of the excess capacity of monopiles supporting offshore wind turbines (OWTs) by deploying hybrid and colocated wave and current marine energy concepts. However, there is a lack of guidance in literature and standards relating to the evaluation of natural frequency and foundation damping for monopile-supported wind turbines in shared anchoring configurations. The work presented here represents one of the first studies quantifying the dynamic characteristics of simulated colocated and hybrid energy systems sharing the anchoring capacity of OWT monopiles. A 3D finite-elements numerical model is developed and used to perform dynamic simulations of the OWT monopile. The hybrid system is modeled as a marine hydrokinetic device represented by an annulus plate installed around the monopile perimeter, providing additional mass participating in system damping and vibration while inducing additional loading due to drag forces on its perimeter. For a colocated system, tension forces from the mooring lines of a wave hydrokinetic device are first computed by ANSYS-AQWA then these forces are applied to the monopile in the 3D numerical model. The dynamic analyses are first performed to calibrate the numerical model parameters using data from three existing OWT projects (i.e., Burbo Bank, Walney 1, and Gunfleet Sands). Results from a parametric study varying diameter and length of the monopile, demonstrated the effect of the added mass in the hybrid configuration, as well as the influence of the tension forces of the mooring lines in the colocated configuration on the natural frequency and foundation damping. Results indicate that the simulated hybrid and colocated systems do not alter the natural frequency of the system; however, the foundation damping of the hybrid system is approximately 1.5 to 2 times higher than that of the monopile supporting only the wind turbine tower. Results also demonstrated the minimum obtained natural frequency (f1,dmin) for a combination of diameter, length, and relative densities (i.e., DP = 5 m, LP = 38 m, and DR = 25%–100%) is higher than the minimum frequency of the dynamic loading caused by the passing blades (f3P,min = 0.25 Hz) while the maximum obtained natural frequency (f1,dmax) is lower than the maximum frequency of the 3P dynamic load (f3P,max = 0.65 Hz). As such, for the cases analyzed herein, f1,d falls within the frequency range of the 3P dynamic load, and the system operates in-between the two frequency zones of soft–stiff and stiff–stiff. To ensure operational natural frequency within the soft–stiff zone in these cases, reducing the dimensions of the tower would be necessary. [ABSTRACT FROM AUTHOR]

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Due to its special working conditions, offshore wind turbine will bear large direct and indirect loads under the combined action of air flow and wave flow. In this paper, a variable pitch system composed of variablepitch motorand variable pitch bearing is improved, and the characteristics of system's bending moment, torque, vibration and other physical quantities under the action of multiple physical loads are verified, and the mechanical response characteristics of floating wind turbine under the control of unified variable pitch and independent variable pitch are studied under the running conditions at sea. The results show that mechanical structure of uniform pitch is compared with that of independent pitch, the independent variable pitch structure can effectively reduce the mean oscillation value of wind turbine tower in the parallel direction of air flow by optimizing control strategy, and reduce the thrust at the hub of wind turbine and the bending moment at the root of tower, but increase the vibration frequency and fatigue load of offshore wind turbine tower along parallel direction of air flow. Reduce the fatigue life of equipment. The research results can be used as a reference to reduce the variable pitch control and vibration suppression of offshore wind turbines and improve the reliability of wind turbines.

Integrating renewable energy sources (RESs), such as offshore wind turbines (OWTs), into the power grid demands advanced control strategies to enhance efficiency and stability. Consequently, a Deep Fractional-order Wind turbine eXpert control system (DeepFWX) model is developed, representing a hybrid proportional/integral (PI) fractional-order (FO) model predictive random forest alternating current (AC) bus voltage controller designed explicitly for OWTs. DeepFWX aims to address the challenges associated with offshore wind energy systems, focusing on achieving the smooth tracking and state estimation of the AC bus voltage. Extensive comparative analyses were performed against other state-of-the-art intelligent models to assess the effectiveness of DeepFWX. Key performance indicators (KPIs) such as MAE, MAPE, RMSE, RMSPE, and R2 were considered. Superior performance across all the evaluated metrics was demonstrated by DeepFWX, as it achieved MAE of [15.03, 0.58], MAPE of [0.09, 0.14], RMSE of [70.39, 5.64], RMSPE of [0.34, 0.85], as well as the R2 of [0.99, 0.99] for the systems states [X1, X2]. The proposed hybrid approach anticipates the capabilities of FO modeling, predictive control, and random forest intelligent algorithms to achieve the precise control of AC bus voltage, thereby enhancing the overall stability and performance of OWTs in the evolving sector of renewable energy integration.

[Introduction] Monopile foundation is currently the most widely used support structure for offshore wind farms. For offshore wind farms in the medium water depth area such as Dafeng, Binhai and Sheyang in China, the design waves are very close to the wave breaking limit. Compared with the traveling wave, the focused waves can form an impact force on the pile column in a short time, which is larger than the conventional wave force, and undermines the operational performance and fatigue life of the offshore wind turbines. [Method] In this paper, NREL 5 MW monopile wind turbine model tests were carried out to investigate the hydrodynamic response of large offshore wind turbines to highly nonlinear waves and other harsh waves in combination with the marine environmental conditions of China's eastern coastal wind farms, focusing on exploring the test techniques for monopile wind turbines, and the mechanism of interaction between focused waves and monopiles under the action of focused waves. [Result] The results show that, the horizontal wave force on the pile foundation, which is significantly transient, will suddenly increase when the focused waves act on the monopile foundation, and receive the reverse impact force at the trough of focused wave fluctuation. [Conclusion] The results are of high theoretical value and have engineering prospect for the safe operation of monopile foundation.

At present, monopile-supported offshore wind turbines (MOWTs) are widely used in offshore wind farms. The influence of blade flexibility on the dynamic behaviors of MOWTs excited by waves and earthquakes was investigated in this study. Numerical analysis models were established for 5 MW and 10 MW MOWTs, incorporating flexible and rigid blade configurations. The modes and natural frequencies of the full system were compared between these two numerical models, and their dynamic responses were evaluated under wave-only and earthquake-only excitations. It was revealed that the influence of blade flexibility on the first- and second-order modes of the system can be neglected. The dynamic response of these MOWTs under wave excitation can be predicted by the rigid blade model, where the maximum relative difference is less than 5%. However, higher-order modes of the system are significantly affected by the blade flexibility. Under high-frequency excitations, these higher-order modes of the system are remarkably stimulated. Additionally, a large relative difference, exceeding 50%, is detected when the rigid blade model is used to predict the seismic response of the two MOWTs. Consequently, the blade flexibility should be adequately modeled when predicting the dynamic response of OWTs. [ABSTRACT FROM AUTHOR]

With the ongoing global drive towards renewable energy, several potential offshore wind energy lease areas worldwide have come into focus. This study aims to estimate the extreme wind and wave conditions across several newly designated offshore wind lease sites spanning six continents that are crucial for risk assessment and the design of offshore wind turbines. Firstly, the raw data of wind speeds and wave heights prevailing in these different lease areas were obtained. Following this, an in-depth extreme value analysis was performed over different return periods. Two principal methodologies were applied for this comparative study: the block-maxima and the peaks-over-threshold (POT) approaches. Various statistical techniques, including the Gumbel method of moments, Gumbel maximum likelihood, Gumbel least-squares, and the three-parameter GEV, were employed under the block-maxima approach to obtain the distribution parameters. The threshold for the POT approach was defined using the mean residual life method, and the distribution parameters were obtained using the maximum likelihood method. The Gumbel least-squares method emerged as the most conservative estimator of extreme values in the majority of cases, while the POT approach generally yielded lower extreme values compared to the block-maxima approach. However, the results from the POT approach showed large variations based on the selected threshold. This comprehensive study's findings will provide valuable input for the efficient planning, design, and construction of future offshore wind farms. [ABSTRACT FROM AUTHOR]