Abstract The floating platform with taut or semi-taut mooring systems is the main option for oil and gas exploitations in deep sea. However, it has been reported that the reciprocating motion of the mooring line tends to induce the seabed trench near the anchor, which consequently reduces the anchor capacity. In this paper, two parts of work have been carried out to enhance the understanding of the seabed trench. Firstly, the dimensions of reported trenches in the field as well as their formation conditions are summarized, and four feature points are proposed to describe the trench profile. Secondly, a numerical method considering mooring line dynamics to predict the final trench profiles is proposed, which contains two simulation modules, i.e. mooring line dynamics and seabed trenching. The method is verified using the data from the field and centrifuge tests. The influences of the mooring line tension and soil strength on trench profiles are comprehensively investigated further. The results show that obvious trenches are likely to form when the amplitude of mooring line tension variation is large and the soil shear strength is low. The main impact of the formed trenches is that the loading direction at the pad-eye tends to be horizontal.

中文翻译：

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系泊锚附近的海底挖沟：历史案例和数值研究

摘要 带拉紧或半拉紧系泊系统的浮动平台是深海油气开采的主要选择。然而，据报道，系泊绳的往复运动往往会在锚附近引起海床沟槽，从而降低锚的承载力。本文开展了两部分工作，以加深对海底海沟的认识。首先，总结了现场报道的沟槽尺寸及其形成条件，并提出了四个特征点来描述沟槽轮廓。其次，提出了一种考虑系泊线动力学的数值方法来预测最终的海沟剖面，该方法包含两个模拟模块，即系泊线动力学和海底挖沟。该方法使用来自现场和离心机测试的数据进行验证。进一步综合研究了系泊线张力和土壤强度对沟渠剖面的影响。结果表明，当系泊线张力变化幅度较大且土体抗剪强度较低时，容易形成明显的沟渠。形成的沟槽的主要影响是垫眼处的加载方向趋于水平。