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Performance and Bearing Behavior of Foundations for Offshore Wind Turbines

Yang, Xu, Yang
http://rave.ohiolink.edu/etdc/view?acc_num=case1525707653847882

Abstract Details

2018, Doctor of Philosophy, Case Western Reserve University, Civil Engineering.
Offshore wind energy is one of the primary renewable sources of energy. The ongoing development of the capacity and distance to shore of offshore wind turbines (OWTs) lead to more severe loading conditions. The substructures for OWTs are required to be capable of withstanding the combined loads with vertical loads from the weight of upper structures, and relatively high lateral loads and resultant moments induced by waves, winds, ice and currents. Two types of innovative foundations: the suction bucket foundation and monopile-friction wheel foundation are investigated in this dissertation via centrifuge modellings and finite element (FE) analyses. Suction bucket foundations are a promising foundation option for offshore wind turbines. To assess the lateral-moment loading capacity of bucket foundations, a group of 3-D finite element (FE) simulations with different bucket dimensions in sand and clay is carried out based on the centrifuge model tests. The numerical methods are validated by comparisons with the results of centrifuge tests, and assessed by sensitivity analyses regarding the influences of soil properties and soil-foundation interface parameters. The interaction between the bucket and surrounding soil is illustrated in order to demonstrate the bearing behavior and failure mechanism of the bucket foundation. It is shown that in the ultimate state, the maximum passive earth pressure acting on the external skirt in the loading direction is approximately 4 times larger than that on the internal skirt. Furthermore, parametric studies on the L/D ratios (L is the skirt length and D is the bucket diameter) and loading eccentricity are conducted and discussed. Consequently, a modified calculation method is proposed to predict the ultimate lateral-moment loading capacity of bucket foundations in sand. The method is validated by field and laboratory test data. The monopile-friction wheel foundation integrates a wheel to a monopile to improve the lateral performance. Two types of wheels, the solid wheel and gravel wheel, are discussed in this part. A series of tests on the monopile, hybrid foundations with solid wheels of different diameters and thicknesses, and single solid wheel foundation were conducted. The results show that the lateral bearing capacity and stiffness increase significantly by adding a solid wheel to the monopile, and the improvement is related to the diameter and thickness of the wheel. An extensive experimental research regarding to the influential factors such as the embedment of the wheel and the vertical load is also presented. By means of FEM, the load transfer mechanism, interaction between the foundation and soil, and the bending moment in the pile are illustrated to study how the solid wheel contributes to the performance of the foundation system. Moreover, the effects of load eccentricity and vertical load are investigated by FEM analyses. The gravel wheel is a ring frame filled with large particles to potentially utilize the gravel or crushed stones in offshore areas. The results of centrifuge tests and FEM analyses demonstrate that the lateral loading capacity of the monopile increases when combined with a gravel wheel, and the improvement depends on the diameter and thickness of the wheel. By means of FEM, the interaction between the pile and surrounding soils and gravel fill are illustrated to interpret the effect of the gravel wheel on the hybrid system. Furthermore, an equivalent layer method adopting the conventional p-y curves is suggested to predict the lateral response of the hybrid foundation. This method is validated by comparisons with the centrifuge tests results. Finally, a case study of the monopile-gravel wheel foundation indicates that the gravel wheel is less efficient in configurations where the ultimate capacity of the hybrid system is dictated by the bending capacity of structures rather than the strengths of soils.
Xiangwu Zeng (Advisor)
Adel Saada (Committee Member)
Xiong Yu (Committee Member)
Longhua Zhao (Committee Member)
124 p.
Civil Engineering

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Citations

  • Yang, Yang, X. (2018). Performance and Bearing Behavior of Foundations for Offshore Wind Turbines [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1525707653847882

    APA Style (7th edition)

  • Yang, Yang, Xu. Performance and Bearing Behavior of Foundations for Offshore Wind Turbines. 2018. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1525707653847882.

    MLA Style (8th edition)

  • Yang, Yang, Xu. "Performance and Bearing Behavior of Foundations for Offshore Wind Turbines." Doctoral dissertation, Case Western Reserve University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1525707653847882

    Chicago Manual of Style (17th edition)

case1525707653847882
492
© 2018, some rights reserved.Creative Commons License Performance and Bearing Behavior of Foundations for Offshore Wind Turbines by Xu Yang Yang is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.