﻿ 基于粘聚单元的层冰-海洋平台碰撞数值模拟
 舰船科学技术  2023, Vol. 45 Issue (19): 99-103    DOI: 10.3404/j.issn.1672-7649.2023.19.018 PDF

Numerical simulation of layer ice-offshore platform collision based on cohesive element method
ZHANG Jian, WANG Xiang, JI He-gang, LI Yin-song
School of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang 212100, China
Abstract: In order to study the anti-icing performance of the offshore platform, the finite element model of the collision between layer ice and semi-submersible offshore platform is constructed by using the cohesive element model for numerical simulation. The ice force and structural energy absorption changes during the collision process are analyzed. Subsequently, the sensitivity analysis of cohesive element parameters (the effect of fracture energy release rate and traction-separation law curve) on ice force is studied. The results show that the deviation between the ice force calculated by the cohesive element method and the one calculated by the empirical formula is only 2.2%, which verifies the accuracy of the cohesive element method in simulating the collision process between layer ice and marine structures. The outer plate of the column is the main energy consuming component of the platform during the collision, and the energy absorption accounts for 82.67%. The ice force value increases with the increase of fracture energy release rate, but the influence of different forms of TSL curve on the ice force value is very limited.
Key words: cohesive element method     semi-submersible offshore platform     collision     ice force
0 引　言

1 有限元模型的构建 1.1 半潜式海洋平台有限元模型

 图 1 半潜式海洋平台有限元模型 Fig. 1 Finite element model of semi-submersible offshore platform
1.2 基于粘聚单元的层冰模型

 图 2 牵引力-位移准则曲线 Fig. 2 Traction-separation law curve

 图 3 冰体单元与粘聚单元有限元模型 Fig. 3 Ice element and cohesive element finite element models

 ${\sigma _r} = \left[1 + {\left(\frac{{\mathop \varepsilon \limits^ \cdot }}{C}\right)^{1/P}}\right]\left[{\sigma _0} + {f_h}\left(\varepsilon _{eff}^{Pla}\right)\right]。$ (1)

 ${G}_{I}^{c}=\frac{1}{2}{T}_{I}^{\mathrm{max}}(\left|{\lambda }_{2}-{\lambda }_{1}\right|+{u}_{I}^{c})。$ (2)

1.3 数值模拟设置

 图 4 层冰与半潜式平台碰撞有限元模型 Fig. 4 Finite element model of collision between layer ice and semi-submersible platform
2 数值模拟结果分析 2.1 冰力经验公式

 $F = mDh{\sigma _c} 。$ (3)

2.2 冰力分析

 图 5 数值模拟冰力值时历曲线 Fig. 5 Time history curve of numerical simulation of ice force value

 图 6 t=5 s时层冰模型变形示意图 Fig. 6 Deformation diagram of layer ice model at t=5 s

2.3 结构吸能分析

 图 7 数值模拟计算的立柱各构件吸能变化 Fig. 7 Energy absorption change of each component of the column calculated by numerical simulation

3 粘聚单元参数敏感性分析 3.1 不同断裂能量释放率的冰力对比

 图 8 不同断裂能量释放率的冰力时历曲线 Fig. 8 Time history curves of ice force with different fracture energy release rates

3.2 不同形式TSL曲线下的冰力对比

TSL曲线作为粘聚单元的本构关系式，研究其不同形式对数值结果的影响很有必要。将各曲线与横坐标围成的面积调整至相同，以保证断裂能大小一致。保持其余设置一致，通过数值模拟研究不同TSL曲线形式对冰力的影响。数值模拟得到的各曲线冰力时历曲线见图9，对比结果见表5

 图 9 不同TSL曲线形式的冰力时历曲线 Fig. 9 Time history curves of Ice force with different TSL curve forms

4 结　语

1）对比数值模拟与经验公式计算得到的冰力值，发现两者偏差仅为2.2%，较为接近，验证了采用粘聚单元法进行数值模拟计算的准确性。数值模拟发现粘聚单元法可较好地模拟层冰与海洋结构物的碰撞过程、层冰裂纹的形成与展开以及碎冰的堆积过程，同时研究发现层冰破坏模式主要是局部挤压破坏。

2）通过数值模拟得到碰撞区域立柱各构件吸能变化情况，发现外板吸能最大，占比82.67%，外板T型材次之，横向框架最小，说明立柱外板是层冰-海洋平台碰撞过程中主要的受力耗能构件。

3）通过研究粘聚单元参数对冰力的影响可发现，一定范围内，在保持其他参数一致的情况下，冰力值随着断裂能量释放率的增大而增大，但不同形式的TSL曲线对数值计算的冰力值带来的影响十分有限。

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