Advanced Numerical Modelling of Offshore Wind Turbine (OWT) Foundations in Sand

本研究项目旨在研究海上风力发电机基础在砂土中的性能，特别是在砂土（或粉质砂土）中的单桩基础。数值分析在预测单桩基础的行为方面起着至关重要的作用，特别是在无法通过实验手段精确复制的情况下。在这种条件下估计的行为可以用来优化当前的方法在实际设计中。通过数值分析，可以复制多个现实条件，提供更明确和详细的趋势。本项目属于EPSRC工程设计研究领域。在这项研究中，将使用先进的三维有限元（FE）模拟和耦合流体力学分析进行调查。作为初步研究，探索的案例将包括简单的风浪动力载荷。然后，流体力学分析进一步扩展到动力和风荷载的组合。在这些不同的实际动力荷载类型的复杂相互作用下，对单桩（大直径钢管）的结构响应和岩土土响应进行了比较和研究。土的孔隙水压力积累和消散等水力学特性将是本研究的重点。对于砂质土，加载条件通常模拟为排水。然而，在中间层（如粉质砂）中，快速循环加载可能导致部分排水行为。从岩土数值分析的角度出发，对目前用于单桩模拟的土本构模型在循环荷载和部分排水响应下的性能进行测试。这里的一个目标是在应用水力学分析时验证已知土壤模型（在上述加载条件下）的现有能力。目前，可以肯定的是，没有一个本构模型能够完整准确地反映一系列荷载条件和排水响应（在OWT中）的基础响应。通过了解现有土本构模型（在单桩基础研究中）的局限性，本研究希望在现有模型的基础上进行完善和构建。本研究的另一个目的是确定循环荷载和部分排水条件下已知本构模型的局限性和性能。这些“精炼”模型的目标/目的是：1)捕捉部分排水和循环加载条件下的适当流体力学行为；2)对执业工程师来说简单实用。另一个可能的目标是测试这些“精炼”的土壤模型，并评估其性能的程度。最后，初步的有限元分析将使用商业化的软件进行，希望建立一个新的软件，结合新的和改进的土壤模型，部分排水条件和循环载荷。

This research project aims to investigate the behaviour of offshore wind turbine foundations in sand, in particular monopile foundation of an OWT in sand (or silty sand). Numerical analysis has played a crucial role in predicting behaviours of monopile foundations, especially in conditions that cannot be replicated accurately by experimental means. Estimated behaviours in such conditions can then be used to optimise current approaches in practical design. With numerical analysis, multiple realistic conditions can be replicated, providing more explicit and detailed trends. This project falls within the EPSRC engineering design research area. In this study, investigations will be carried using advanced 3D finite element (FE) simulations with coupled hydromechanical analysis. As a preliminary study, cases explored will include simple dynamic loadings from wind and wave. Hydromechanical analyses are then further extended to a combination of both dynamic and wind loading. Under the complex interplay of these different realistic dynamic loading types, the structural response of a monopile (large-diameter steel pipe) and geotechnical soil response are compared and examined. Hydromechanical behaviours of soil like pore water pressure accumulation and dissipation will be a major focus in this study. For sandy soils, loading conditions are usually modelled as drained. However, in intermediate layers (like silty sand), fast cyclic loading may result in partially drained behaviours. From the perspective of geotechnical numerical analysis, current soil constitutive models used in the modelling of monopiles in OWT will be tested for their behaviours under cyclic loadings and partially drained responses. One objective here is to validate the existing capabilities of known soil models (under the loading conditions mentioned above) when hydromechanical analysis is applied. At the current moment, it is definite that no one constitutive model is able to capture a complete and accurate foundation response for a range of loading conditions and drainage responses (in OWT). By understanding the limitations of existing soil constitutive models (in the study of monopile foundation), this study hopes to refine and build upon the current models. Another objective of this study is to identify the current of limitations and performance of known constitutive models under cyclic loadings and partially drained conditions. The objective/aim for these "refined" models would be to 1) Capture the proper hydromechanical behaviours under partially drained and cyclic loading conditions 2) Easy and practical applicability for practicing engineers. Another possible objective would be to test these "refined" soil models and evaluate the extent of its performance. Lastly, preliminary FE analyses will be carried out using commercialised software, in hopes of building a novel software incorporating new and refined soil models for partially drained conditions and cyclic loadings.