Effect of strain rate and strain softening on embedment depth of a torpedo anchor in clay
Effect of strain rate and strain softening on embedment depth of a torpedo anchor in clay
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DOI：
10.1016/j.oceaneng.2015.07.067
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发表时间：
2015-11
影响因子：
5
通讯作者：
Youngho Kim;M. Hossain;Dong Wang
中科院分区：
文献类型：
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作者：
Youngho Kim;M. Hossain;Dong Wang
鱼雷锚（直径约1米）从离海床50-100米的高度释放，撞击沉积物时的速度高达35米/秒。因此，这种动态安装在周围土壤中引起的应变率明显高于与其他海上基础和锚固系统安装相关的应变率。高应变率提高了动员不排水抗剪强度相比，在现场应变计或实验室测试。本文报道了鱼雷锚在应变软化，率依赖性软粘土动态安装的结果，量化的效果相对于理想的Tresca材料的结果。采用欧拉-拉格朗日耦合方法对结构进行了三维动态大变形有限元分析。对简单的理想弹塑性Tresca土模型进行了修正，使剪切强度具有应变软化和应变率相关性。参数分析进行了不同的应变率参数，敏感性和延性的土壤，土壤不排水剪切强度。总体而言，嵌入深度的速率依赖，应变软化粘土低于理想的Tresca材料。增加应变率依赖性的土壤导致显着减少嵌入深度，只有部分补偿脆性。主要结果以设计图表的形式呈现，用简单的表达式拟合以估计鱼雷锚的嵌入深度。
Torpedo anchors (of diameter ~1 m) are released from a height of 50–100 m from the seabed, achieving velocities up to 35 m/s at impacting the sediment. The strain rates induced in the surrounding soil by this dynamic installation is therefore significantly higher than those associated with installation of other offshore foundations and anchoring systems. The high strain rates enhance the mobilised undrained shear strength compared to that measured by in-situ penetrometer or laboratory tests. This paper reports the results from dynamic installation of a torpedo anchor in strain softening, rate dependent soft clays, quantifying the effects relative to results for ideal Tresca material. The three-dimensional dynamic large deformation finite element (LDFE) analyses were carried out using the coupled Eulerian–Lagrangian approach. The simple elastic-perfectly plastic Tresca soil model was modified to allow strain softening and strain rate dependency of the shear strength. Parametric analyses were undertaken varying the strain rate parameter, the sensitivity and ductility of the soil, and the soil undrained shear strength. Overall, embedment depth for rate dependent, strain softening clays lay below that for ideal Tresca material. Increased strain rate dependency of the soil led to marked reduction in embedment depth, only partly compensated by brittleness. Key results have been presented in the form of design charts, fitted by simple expressions to estimate the embedment depth of a torpedo anchor.