块石和混凝土排垫保护下海底管道落锚撞击变形响应研究

以往的海底管道落锚撞击防护数值模拟主要为单一保护层模型，这里则针对块石+混凝土排垫复合方案建立模型并开展防护性能研究。基于ABAQUS建立有限元数值模型，模拟了落锚、海底管道、海床土体、块石层和混凝土排垫组成的复杂系统相互作用，研究了管道壁厚、内压，落锚质量和撞击速度等因素对管道应变极值和管体凹陷变形的影响。与单纯块石层保护方案相比，采用的块石+混凝土排垫方案具有更优良的防护效果。研究结果表明：在撞击点处，管道的轴向应变和环向应变均达到最大值，且随着与撞击点距离的增加沿管道轴向逐渐减小；撞击结束后，管道上仍然残留一定的塑性应变。随着管道壁厚的增加，管道的最大应变和凹陷深度也随之减小；随着内压的增加，管道上最大拉伸应变变大，而最大压缩应变和凹陷深度减小。随着落锚速度或者质量的增加，管道上最大应变和凹痕深度均变大；在相同动能情况下，管道上的最大应变和凹陷值基本相同，也表明落锚动能是影响管道变形响应的控制因素。本文研究成果可为海底管道防护方案设计提供科学依据。

Deformation response of a submarine pipeline with rock berm + concrete mattress protection subjected to impact by a dropping anchor

In the previous studies, a single protective layer for a submarine pipeline hit by a dropping anchor was often simulated. In this study, the performance of a complex protective scheme, rock berm + concrete mattress, under the impact of a dropping anchor is numerically investigated. The complex system composed of anchor, pipeline, soil seabed, rock berm and concrete mattress is simulated with the finite element software ABAQUS. The effects of wall thickness, internal pressure, mass of anchor and falling speed on the maximum strain and deformation dent of the pipeline are investigated. Compared with the pure rock berm, the rock berm + concrete mattress adopted in the present study can provide better protection. At the location of impact, both the axial strain and circumferential strain of the pipeline reach the maximum values, then decrease along the axial pipeline from the dropping point. There is still a residual plastic strain after the impact. With the increase of the wall thickness, the maximum strain and dent depth of the pipeline decrease. With the increase of the internal pressure, the maximum tensile strain increases, while the maximum compressive strain and dent depth decrease. With the increase of the mass of anchor and falling speed, the maximum strain and dent depth of the pipeline increase. The maximum strain and dent depth of the pipeline almost keep constant when the kinetic energy is fixed, indicating that the kinetic energy of falling anchor is the main governing factor for the deformation response of the pipeline. The present numerical results can provide technical support for the design of protection of submarine pipelines.