Optimization and verification of mesh size for air shock wave from large distance and near ground explosion
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摘要: 建筑结构上爆炸荷载的确定是进行结构动态响应和损伤破坏分析以及结构抗爆设计和加固的前提。考虑到空气爆炸冲击波远距离传播数值模拟计算效率和精度以及软硬件能力的平衡问题，通过确定和优化网格尺寸，从而为大型复杂街区爆炸冲击波荷载的数值模拟网格尺寸选取提供合理建议。针对汽车炸弹和弹药库等典型近地面爆炸场景，首先，使用AUTODYN软件分别开展比例距离为0.2～5.0 m/kg1/3和0.2～39.0 m/kg1/3的空中爆炸自由场和地面爆炸入射场超压和冲量的单一尺寸网格敏感性分析，并考虑软硬件对单元网格数量的限制，给出依赖比例距离的渐变网格尺寸建议。其次，基于映射算法和建议的渐变尺寸网格对地面爆炸入射场超压和冲量进行数值模拟，提出了比例距离大于10.0 m/kg1/3的峰值超压误差修正方法，并得到UFC 3-340-02规范的验证。最后，基于足尺房屋爆炸荷载分布试验共71个测点的超压和冲量时程数据，对提出的优化网格尺寸的计算精度和效率进行了验证。Abstract: The determination of the blast loading on building structures is a prerequisite for the analyses of dynamic response and damage mode, as well as the blast-resistant design and the structural reinforcement. In determining the blast loadings on building structures with the upgraded computing hardware and software, the low-cost and high-safety numerical simulation methods have increasingly attracted the attention of researchers. In order to improve the computing efficiency and accuracy, and to balance the capacities of both the hardware and the software, by adopting the simplified calculation method, i.e., using symmetry (1D-2D-3D extension) and remapping method, the optimized sets of mesh sizes for the numerical simulation of blast wave propagating for a long distance in large complex block are proposed. Firstly, aiming at the typical near-ground explosion scenarios, e.g., car bombs and ammunition depots, the sensitivity analyses of single-size mesh based on incident wave of air and ground explosions at the scaled distances of 0.2−5.0 m/kg1/3 and 0.2−39.0 m/kg1/3 are carried out, respectively. Secondly, considering the limitations of the software and hardware, a set of gradient mesh sizes against the scaled distances is recommended. Furthermore, based on the remapping technique and the suggested gradient mesh sizes, the incident overpressure and impulse of ground explosion are numerically calculated, and an improved method for correcting the peak overpressure with the scaled distances larger than 10.0 m/kg1/3 is proposed, which is then verified by UFC 3-340-02. Finally, the computing accuracy and efficiency of the proposed optimized mesh sizes are verified by comparing the simulated and experimental overpressures and impulses (71 gauges) in the field explosion test on a full-scaled building. Besides, the applicability of the proposed gradient mesh size in simple reflection field is verified, which provides a reference for the subsequent proportional amplification application of gradient mesh size and the simulation application of blast loadings in more complex reflection environment.
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Key words:
- near ground explosion /
- blast wave propagation /
- mesh size /
- overpressure
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图 1 典型远距离近地面爆炸场景示意图
Figure 1. Schematic diagram of a typical long-distance near-ground explosion scenario
图 3 空中爆炸自由场峰值超压对比
Figure 3. Comparisons of peak overpressures in the free field of air explosion
图 4 空中爆炸自由场最大冲量对比
Figure 4. Comparisons of the maximum impulses in the free field of air explosion
图 7 基于渐变网格的峰值超压结果对比
Figure 7. Comparisons of peak overpressures based on gradient mesh sizes
图 8 基于渐变网格的最大冲量结果对比
Figure 8. Comparisons of the maximum impulses based on gradient mesh sizes
图 13 冲击波传播途径中测点峰值超压及最大冲量
Figure 13. Peak overpressures and maximum impulses at gauges in the path of blast wave propagation
图 14 V2各截面测点反射峰值超压对比
Figure 14. Comparisons of reflected peak overpressures in V2 test
图 15 V2各截面测点反射最大冲量对比
Figure 15. Comparisons of the maximum reflected impulses in V2 test
图 16 V2反射超压时程曲线对比
Figure 16. Comparisons of reflected overpressure-time histories in V2 test
图 17 V3各截面测点反射峰值超压对比
Figure 17. Comparisons of reflected peak overpressures in V3 test
图 18 V3各截面测点反射最大冲量对比
Figure 18. Comparisons of the maximum reflected impulses in V3 test
图 19 V3反射超压时程曲线对比
Figure 19. Comparisons of reflected overpressure-time histories in V3 test
表 1 空中爆炸自由场单一网格尺寸建议
Table 1. Recommended mesh sizes of the free field of air explosion
比例距离/（m·kg−1/3） <0.4 0.4～0.6 0.6～4.0 4～5 ≥5 网格尺寸/mm 2 5 10 25 50 
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表 2 地面爆炸入射场网格尺寸和比例距离对应关系
Table 2. Relationship between mesh sizes and scaled distances for ground explosion
网格尺寸/mm 1 2 5 10 20 50 100 200 500 比例距离范围/（m·kg−1/3） 0.2～1.0 0.2～1.4 0.2～4.0 0.2～4.0 1～15 1～39 1～39 1～39 1～39 测点间距/（m·kg−1/3） 0.1 0.2 0.2 0.2 1.0 1.0 1.0 1.0 1.0
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表 3 地面爆炸入射场计算单一网格尺寸建议
Table 3. Recommended mesh sizes for ground explosion
比例距离范围/(m·kg-1/3) ≤0.4 0.4～0.6 0.6～1.0 1～2 2～5 ≥5 网格尺寸/mm 2 5 10 20 50 100
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表 4 网格尺寸和比例距离范围对应关系
Table 4. Relationship between mesh sizes and the scaled distance
比例距离范围/（m·kg−1/3） 0～0.1 0.1～0.2 0.2～0.5 0.5～1.0 1～2 2～5 5～10 10～20 20～50 网格尺寸/mm 1 2 5 10 20 50 100 200 500
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表 5 第二阶段各比例距离范围模型数据
Table 5. Model data of the second stage at different scaled distances
比例距离范围/
（m·kg−1/3）网格尺寸/
mm模型对称轴
长度/mm模型地面
长度/mm网格数量 0.183～0.5 5 2 400 1 800 172 800 0.5～1.0 10 4 100 3 500 143 500 1～2 20 7 600 7 000 133 000 ≥2 50 21 600 21 000 181 440
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