INPUT METHOD OF SEISMIC WAVE IN IRREGULAR TERRAIN BASED ON WAVE FIELD SEPARATION
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摘要: 不规则地形条件下斜入射地震波场求解难度较大,以往的方法在计算精度和适用范围方面仍有不足。该文结合解析推导和有限元模拟,提出了一种基于波场分离技术的不规则地形条件下地震波输入方法,将地震P波和SV波在不同边界下进行波场分离:垂直入射时在侧面边界上分离为自由波场和散射波场,底部边界上分离为入射波场和边界外行场;斜入射时将输入侧对面的边界改为分离成入射波场和边界外行场;并充分考虑局部地形条件的影响,还基于改进的波动方法以便捷地输入节点力。同时对比了多组不同地震入射角度下规则场地和不规则场地的振动反应。结果表明:该方法在多类地形条件下计算精度与效率均较高,适用范围广且易于推广至复杂场地条件,并发现地震波入射角度和局部场地条件对地表位移响应影响较大。该研究可为不规则地形条件下的振动响应分析提供有效的手段。Abstract: Solving the oblique incident seismic wave field under irregular terrain conditions is challenging, and previous methods are limited in calculation accuracy and application range. A ground motion input method was proposed for irregular terrains based on wave field separation by combining analytical derivation and finite element simulation. Seismic P waves and SV waves are separated under different boundary conditions. When incident vertically, they are decomposed into free wave field and scattered wave field at the side boundary, and incident wave field and boundary outer field at the bottom boundary. For oblique incidence, the seismic wave at the opposite boundary of the input side is separated into incident wave field and outer boundary field. In this paper, the influence of local topographic conditions was fully considered, and the improved wave method was used to input nodal force conveniently. Besides, the vibration responses of regular and irregular terrains under different incidence angles were analyzed. The results show that the method has high computational accuracy and efficiency under multiple topographic conditions and can be applied to complex site conditions. Moreover, the incident angle and local site conditions are found to have significant effects on surface displacement response. The study can provide an effective way for response analysis under irregular terrain conditions.
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Key words:
- site response /
- irregular terrain /
- seismic wave input /
- seismic wave field separation /
- incident angle
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表 1 场地模型参数
Table 1. Model parameters of the site
场地模型 密度/
(kg·m−3)泊松比 弹性模量/
GPaSV波波速/
(m·s−1)P波波速/
(m·s−1)阶梯型场地 2000 0.25 0.2000 200 346 V字河谷型场地 1500 0.25 0.3375 300 520 梯形河谷型场地 1500 0.25 0.3375 300 520 表 2 两种方法的结果对比
Table 2. Comparison of the two methods
入射
角度/(°)远置边界方法 本文方法 模型网
格数计算时长/
min结果文件
大小/GB模型网
格数计算时长/
min结果文件
大小/GBθP=0 43 550 29 2.84 4550 4.2 0.38 θP=30 89 700 56 5.72 3700 4.5 0.32 θSV=0 43 550 28 2.84 4550 4.1 0.38 θSV=15 90 000 56 5.74 4500 4.6 0.37 表 3 P波入射时不同地形条件下自由表面A1点位移
Table 3. Displacement of A1 under different terrain conditions when P waves incident
入射
角度/(°)横向位移幅值 竖向位移幅值 规则地形/m 阶梯型/m 相差/(%) 规则地形/m 阶梯型/m 相差/(%) 0 0.00 0.17 −100.00 2.00 2.07 −3.35 15 0.59 0.84 −29.50 1.92 2.50 −23.34 30 1.12 1.28 −12.39 1.69 1.96 −13.86 45 1.52 2.26 −32.67 1.36 1.36 0.14 60 1.73 2.48 −30.25 1.00 0.85 18.05 75 1.60 2.25 −28.82 0.65 0.52 25.71 90 0.73 0.97 −24.90 0.52 0.27 89.50 表 4 SV波入射时不同地形条件下自由表面A1点位移
Table 4. Displacement of A1 under different terrain conditions when SV waves incident
入射
角度/(°)横向位移幅值 竖向位移幅值 规则地形/m 阶梯型/m 相差/(%) 规则地形/m 阶梯型/m 相差/(%) 0 2.00 1.98 0.86 0.00 −0.12 −99.98 5 1.99 1.96 1.46 −0.16 −0.15 7.55 10 1.95 1.90 2.75 −0.31 −0.20 51.98 15 1.89 1.81 4.59 −0.45 −0.26 70.47 20 1.81 1.77 2.36 −0.58 −0.40 46.42 25 1.71 1.70 0.37 −0.70 −0.51 35.32 30 1.59 1.72 −7.10 −0.79 −0.68 16.66 -
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