Coupled micromechanical modelling for the analysis and prevention of erosion in hydraulic and offshore infrastructures

本项目的范围涉及与土木工程基础设施（如防洪堤坝和海上风电场基础）具有重大社会经济意义的失败有关的水流侵蚀地质材料。我们的目标是澄清这些系统在流体流动的压力下的潜在机制，直到在固体介质中最终产生局部位错，导致材料损失，最终导致整个结构的机械不稳定。为此，我们希望通过开发有效的大尺度耦合模拟模型，直接再现流体相与固体颗粒结合组合之间的相互作用，弥合颗粒尺度上的微观力学现象与工程问题的宏观力学应用之间的差距。为此，我们将结合流体和固体相的相关模拟技术（分别为晶格玻尔兹曼方法和离散元方法）。我们设想在不同尺度上逐步发展具有代表性的模型，首先在中尺度上再现我们实验室测试的小型装置中的局部现象，然后在尺寸和复杂性上增加，直到工程问题的实际规模。该模型应具有颗粒间黏聚和瞬态材料损伤的固体接触方案，这是可能控制岩土系统宏观力学破坏模式的关键因素。开发阶段的一个关键任务将是通过图形处理器和集群使我们的算法适应并行计算。第一个应用领域应是对诸如河堤等水利工程的侵蚀进行评估。在这方面，我们将开发典型可蚀性评估情景的详细微观力学模型，并分析所得参数对土壤颗粒特性和岩土特性的依赖关系。然后，验证的情景将被放大，以模拟实际堤防侵蚀问题中的局部真实对应。与此同时，第二个应用领域涉及海上风力涡轮机的基础结构。对不同冲刷情况的详细评估将为优化基础设计提供依据，并有助于降低风电场发展的成本。此外，由于其与海洋土壤和孔隙水的双重相互作用在很大程度上尚未解决，因此在海上领域有前景的创新基础，如吸力桶，仍然没有很好地建立起来。吸水机构的稳定性以及桶在安装过程中局部液压故障（管道）的可能性是这里要解决的关键问题。从微观力学角度处理这些现象的预期模型的发展将提供迄今为止离岸实践中所缺失的答案。

The scope of this project concerns the water-flow erosion of geomaterials in relation to the failure of civil engineering infrastructures with large socio-economic relevance such as flood protection dykes and offshore wind-farm foundations. We aim to clarify the underlying mechanisms by which such systems are stressed by a fluid flow until a local dislocation is finally generated within the solid medium, leading to a material loss and eventually to the mechanical instability of the whole structure.For this, we want to bridge the gap between the micromechanical phenomena at the grain scale and the macromechanical application for engineering problems by developing efficient large-scale coupled simulation models that reproduce directly the interactions between a fluid phase and the bonded assembly of solid particles. To this end, we will couple relevant simulation techniques for the fluid and solid phases (the Lattice Boltzmann Method and the Discrete Element Method, respectively).We envisage a progressive development of representative models at different scales, at first on a meso-scale to reproduce local phenomena in small setups of our laboratory tests, and then increasing in size and complexity up to the real scale of the engineering problems. The models shall feature a solid contact scheme for intergranular cohesion and transient material damage, which are key elements that may govern the macromechanical failure modes of geotechnical systems. A key task at the development stage will be the adaption of our algorithms for parallel computation by means of graphical processors and clusters.A first field of application shall be the assessment of erosion in hydraulic constructions such as a river levee. In this respect, we will develop detailed micromechanical models of typical erodibility assessment scenarios and analyse the dependencies of the resulting parameters on the granular properties and geotechnical characterizations of the soil. The validated scenarios shall then be upscaled to simulate locally their real-scale counterparts within a practical levee erosion problem.In parallel, the second field of application concerns the foundation structures for offshore wind-turbines. A detailed assessment of different scouring scenarios shall provide a basis for optimized foundation designs and help reduce the costs of windfarm developments. Besides, promising innovative foundations in the offshore field, such as the Suction Buckets, are still not well established due to largely unresolved questions concerning their dual interaction to both the marine soil and the pore water. The stability of the suction mechanism as well as the possibility of a localized hydraulic failure (piping) of the buckets during their installation are key questions that will be addressed here. The development of the intended models dealing with such phenomena from a micromechanical perspective shall provide answers which have been missing in the offshore practice so far.