3D Finite Element Analysis of Ultimate Capacity of Suction Caissons under Multi-line Loading

开发海洋能源对美国当前的可再生能源和能源独立战略具有重要意义。 岩土工程现场调查和基础设计是海上开发的关键方面，而且往往成本高昂，但也存在与动态海洋环境和异质海底地质的设计力相关的风险和不确定性。 因此，岩土工程问题一直是一些欧洲海上风电场延迟和成本超支的关键因素。 本研究旨在通过推进用于多设备开发的新型集成基础系统，减少与潮汐、波浪、洋流和深水风等浮动技术基础系统的设计和施工相关的海上可再生能源开发障碍。 这种新颖的系统由一个相互连接的吸力沉箱网络组成，这些吸力沉箱是大直径、空心圆柱体、封闭帽、桩型基础，因其通过内部负压安装而得名（即，在从海底和海底盖之间形成的差距抽水的过程中产生的吸力）。 当在互连网络中用于摩尔多个设备的系泊时，吸力式沉箱有可能通过减少安装基础的总数来显著降低开发成本。本研究的目标是发展必要的基本工程知识，将粘性土壤中的海上吸力式沉箱从单锚系泊变为多锚系泊。 本研究将发展三维数值模式，以预测吸力式沉箱在拉紧正交多线荷载作用下之极限承载力及变形。 将使用已发表的文献和主要研究者先前进行的单调和循环荷载下多线沉箱行为的物理建模研究结果对模型进行校准/确认。 将进一步开发该模型，以研究垂直荷载连接点、管线数量和径向连接角以及荷载倾斜度相对于沉箱高度对预测承载力的影响。 这项研究工作将导致数值建模和分析工具，将允许继续调查多线加载吸力沉箱的能力，为各种海上应用。

Development of ocean energy sources is significant to the current U.S. renewable energy and energy independence strategy. Geotechnical site investigation and foundation design are critical, and often costly, aspects of offshore development, however are subject to risks and uncertainties associated with design forces from the dynamic ocean environment and heterogeneous seafloor geology. Consequently, geotechnical issues have been a key factor in delays and cost overruns for some European offshore wind farms. This research seeks to reduce barriers to offshore renewable energy development associated with design and construction of foundation systems for floating technologies such as tidal, wave, ocean current, and deep water wind through advancement of a novel integrated foundation system for multi-device developments. This novel system is comprised of a network of interconnected suction caissons, which are large diameter, hollow cylinder, closed cap, pile-type foundations named for their installation by internal underpressure (i.e., suction) developed during pumping of water from the gap formed between the seafloor and cap. When used in an interconnected network to moor multiple devices, suction caissons have the potential to significantly alleviate development costs by reducing the total number of installed foundations.This goal of this research is develop the basic engineering knowledge necessary to transform the use of offshore suction caissons in clay soils from single to networked, multi-line mooring anchors. This research will lead to development of three dimensional numerical models used to predict ultimate capacity and deformation of a suction caisson under taut, orthogonal multi-line loading. The models will be calibrated/validated using both published literature and results from a physical modeling study of multi-line caisson behavior under monotonic and cyclic loading previously conducted by the principal investigator. The model will be further developed to investigate the effects of vertical load attachment point, number of lines and radial attachment angles, and load inclination with respect to caisson height on predicted capacity. This research effort will result in numerical modeling and analysis tools that will allow for continued investigation of multi-line loaded suction caisson capacity for a variety of offshore applications.