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

本研究项目旨在调查海上风力涡轮机基础在砂中的行为，特别是在砂（或粉砂）中的OWT的可弯曲基础。数值分析在预测地基变形方面发挥了至关重要的作用，特别是在无法通过实验手段准确复制的条件下。在这种条件下的估计行为，然后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。该项目属于EPSRC工程设计研究领域的福尔斯。在这项研究中，调查将进行先进的三维有限元（FE）模拟耦合流体力学分析。作为初步研究，探讨的情况下，将包括简单的动态载荷风和波浪。流体力学分析，然后进一步扩展到动态和风荷载的组合。在这些不同的实际动力荷载类型的复杂的相互作用下，比较和研究了一个管道（大直径钢管）的结构响应和岩土响应。土的流体力学行为，如孔隙水压力的积累和消散将是本研究的主要重点。对于桑迪，荷载条件通常模拟为排水。然而，在中间层（如粉砂），快速循环荷载可能导致部分排水行为。从岩土工程数值分析的角度来看，目前的土壤本构模型中使用的OWT中的碎石的建模将测试其在循环荷载和部分排水响应下的行为。这里的一个目标是验证现有的能力，已知的土壤模型（在上述负载条件下）时，应用流体力学分析。目前，可以肯定的是，没有一个本构模型能够捕捉到一系列荷载条件和排水响应（在OWT中）的完整和准确的基础响应。通过了解现有的土壤本构模型的局限性（在软土地基的研究），本研究希望完善和建立在现有的模型。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的本构模型的局限性和性能。这些“改进”模型的目标/目的是：1）在部分排水和循环荷载条件下捕获适当的水力力学行为2）对实践工程师的简单实用性。另一个可能的目标是测试这些“改进的”土壤模型，并评估其性能的程度。最后，将使用商业化软件进行初步的有限元分析，希望建立一个新的软件，将新的和完善的土壤模型，部分排水条件和循环荷载。

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.