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Design of Foundations for Offshore Wind Turbines
As the demand for \"green\" energy increases the offshore wind power industry is expanding at a rapid pace around the world. This book is a comprehensive reference which covers the design of foundations for offshore wind turbines, and includes examples and case studies. It provides an overview of a wind farm and a wind turbine structure, and examines the different types of loads on the offshore wind turbine structure. Foundation design considerations and the necessary calculations are also covered. The geotechnical site investigation and soil behavior/soil structure interaction are discussed, and the final chapter takes a case study of a wind turbine and demonstrates how to carry out step by step calculations.
eBook
OFFSHORE SEABED PILE FOUNDATION ANALYSIS: SOIL-PILE INTERACTION AND LOAD CONDITIONS, AND DESIGN RECOMMENDATIONS
Offshore pile foundations are essential for supporting structures, such as wind turbines, oil platforms, and bridges. Important factors influencing soil-pile interactions and assessing the impact of various environmental loads, including axial, lateral, and moment loads. This study begins with a comprehensive review of the analytical and numerical methods used for pile analysis. This research aims to analyze the behavior of piles in the offshore seabed environment, taking into account various factors, such as soil-pile interactions, environmental load conditions, and the design of a sturdy pile foundation. This research method exploits the importance of accurate modelling to ensure the stability and longevity of offshore structures. The strength and performance of offshore structures, such as wind turbines, oil platforms, and bridges, are highly dependent on the integrity of the pile foundations. This research will provide a detailed analysis of piles in offshore seabed environments, emphasizing the importance of soil-pile interactions, varying loading conditions, and robust pile designs. These findings underscore the need for an integrated approach that combines geotechnical data, advanced modelling, and ongoing monitoring to ensure the stability and longevity of offshore pile foundations. This research produces a foundational analysis of pile behavior in offshore environments, considering factors such as soil-pile interactions, environmental load conditions, and variations in pile diameter. Piles with a diameter of 1.067 m demonstrate the highest axial and lateral capacities, making them ideal for more extreme environmental load conditions, such as strong ocean currents and high wind loads.
Journal Article
Studies on cyclic behavior of tripod suction bucket foundation system supporting offshore wind turbine using centrifuge model test
To be competitive in offshore wind energy production, safe and economical foundation design is essential. In recent years, tripod suction bucket foundations have been considered as an alternative to conventional foundations owing to their unique features suitable for offshore construction environments, economic installation, and high overturning resistance. However, it is difficult to accurately predict the behavior of tripod foundation because the load acting on the tripod is complex in HVM (i.e., horizontal, vertical, and moment loads) and the response varies depending on the size and direction of the load. Moreover, it is harder to analyze because the effects of cyclic loads must be considered in an offshore environment. This study, therefore, has investigated the behavior of the tripod suction bucket foundation under cyclic loadings. To analyze the complex responses of the tripod foundation in detail, the overall behavior of the tripod foundation system was observed based on the compression–pullout behavior of a single bucket. Moment–rotation responses, the cyclic stiffness, and permanent displacements of the tripod foundation are evaluated by analyzing the vertical behavior of the single‐bucket foundations as well as the rotational behavior of the tripod foundation. A number of centrifuge model tests were carried out with different loading conditions (i.e., loading amplitudes and directions). It was confirmed that the cyclic behavior of the tripod bucket foundation is significantly affected by loading amplitudes and directions. Furthermore, this study emphasized the importance of considering load characteristics when designing the tripod foundation.
Journal Article
Concrete Support Structures for Offshore Wind Turbines: Current Status, Challenges, and Future Trends
Today’s offshore wind turbine support structures market is largely dominated by steel structures, since steel monopiles account for the vast majority of installations in the last decade and new types of multi-leg steel structures have been developed in recent years. However, as wind turbines become bigger, and potential sites for offshore wind farms are located in ever deeper waters and ever further from the shore, the conditions for the design, transport, and installation of support structures are changing. In light of these facts, this paper identifies and categorizes the challenges and future trends related to the use of concrete for support structures of future offshore wind projects. To do so, recent advances and technologies still under development for both bottom-fixed and floating concrete support structures have been reviewed. It was found that these new developments meet the challenges associated with the use of concrete support structures, as they will allow the production costs to be lowered and transport and installation to be facilitated. New technologies for concrete support structures used at medium and great water depths are also being developed and are expected to become more common in future offshore wind installations. Therefore, the new developments identified in this paper show the likelihood of an increase in the use of concrete support structures in future offshore wind farms. These developments also indicate that the complexity of future support structures will increase due to the development of hybrid structures combining steel and concrete. These evolutions call for new knowledge and technical know-how in order to allow reliable structures to be built and risk-free offshore installation to be executed.
Journal Article
Influence of Foundation–Soil–Foundation Interaction on the Dynamic Response of Offshore Wind Turbine Jackets Founded on Buckets
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.
Journal Article
An Overview on Structural Health Monitoring and Fault Diagnosis of Offshore Wind Turbine Support Structures
The service environment of offshore wind turbine (OWT) support structures is harsh, and it is extremely difficult to replace these structures during their operational lifespan, making their failure a catastrophic event. The structural health monitoring (SHM) of OWT support structures is a crucial aspect of operational maintenance for OWT support structures, aiming to mitigate significant financial losses. This paper systematically summarizes the current monitoring methods and technologies for OWT support structures, including towers and foundations. Through the review of monitoring content and the evolution of monitoring techniques for supporting structures, it delves deeper into the challenges faced by wind turbine monitoring and highlights potential avenues for future development. Then, the current damage identification techniques for OWT towers and foundations are analyzed, exploring various methods including model-based, vibration-based, artificial intelligence and hybrid fault diagnosis methods. The article also examines the advantages and disadvantages of each approach and outlines potential future directions for research and development in this field. Furthermore, it delves into the current damage identification techniques for OWT towers and foundations, discussing prevalent challenges and future directions in this domain. This status review can provide reference and guidance for the monitoring design of OWT support structures, and provide support for the fault diagnosis of OWT support structures.
Journal Article
Centrifuge modelling of submarine landslides due to static liquefaction
Sand erosion and scouring caused by waves and marine currents result in gradual increase of local seabed inclination and formation of slopes around hydraulic structures and offshore foundations. During this process, shear stresses in the soil body increase monotonically which may lead to static liquefaction and damage of the adjacent offshore infrastructure. This paper presents the details of a newly developed static liquefaction triggering actuator to be used at an enhanced gravity condition in a geotechnical centrifuge. This actuator simulates the steeping process of submarine sand layers due to scouring and enables the investigation of failure mechanisms in submerged slopes. The details of the centrifuge test set-up designed and constructed to simulate the process of triggering static liquefaction in loose sand layers are presented. Furthermore, the performance of the novel integrated model preparation facility using sand fluidization is explained. The set-up was used to conduct several centrifuge tests at four different slope steepening rates to investigate the slope steepening rate effects. Moreover, the effect of viscosity of the submerging pore fluid on the behaviour of the slopes at the onset of failure is investigated. The Coriolis effect on loose saturated sand samples during increase of g-level is examined as well. Results show that the built-up of pore pressure due to local shear deformations can be detected and considered as one of the triggering mechanisms of this kind of submarine slope instabilities.
Journal Article
Uplift Performance of Suction Foundations in Sandy Soils for Offshore Platforms
Suction foundations are widely used in the construction of offshore platforms. Their uplift resistance in sandy soil strata is crucial for evaluating the stability of offshore platforms. A scaled-down experimental device was developed to investigate the pull-out performance of suction-type foundations in sandy soil. The relationship between the pull-out performance of suction-type foundations under the influence of different factors (e.g. different uplift directions) and the uplift speed was discussed. The ABAQUS finite element explicit dynamic analysis method was used to study the influence of different drainage conditions, loading speeds, loading angles, and loading methods on the stress change, deformation, and bearing performance of the surrounding soil during the design stage of the suction foundation. The comprehensive testing and numerical analysis results revealed the pull-out performance of suction foundations in sandy soils. The results showed that the uplift performance of the suction foundation is affected by the uplift angle and speed. At low uplift angles, increasing the uplift speed can improve the ultimate bearing capacity of the suction foundation, while at high uplift angles, a lower uplift speed can help improve its uplift resistance. At the same time, the ultimate bearing capacity of the complete drainage simulation is generally higher, which can provide a more conservative safety estimate for engineering design.
Journal Article
Development of a Quantitative Survey Method for Pelagic Fish Aggregations Around an Offshore Wind Farm Using Multibeam Sonar
Offshore wind farms are rapidly expanding worldwide, and the submerged structures supporting wind turbines have the potential to function as artificial reefs for marine organisms. Quantitative visualization of fish aggregations around these foundations can provide valuable information for promoting collaboration between fisheries and offshore wind energy development. This study explored the use of multibeam sonar to detect spatial distributions and estimate the biomass of pelagic fish aggregations around the foundations of offshore wind power facilities. Fish distribution was extracted from multibeam water column image data using an automated sequence of filtering steps, ending with a spatial filter designed to remove common noise artifacts in multibeam sonar data. The resulting fish aggregations were visualized in three dimensions, revealing a tendency to cluster leeward of turbine and observation tower foundations, and fish biomass was successfully estimated from beam backscatter strength. The developed method can be applied to other offshore wind farms to demonstrate the role of turbine foundations as artificial reefs for fish.
Journal Article