Seismic response analysis method of offshore site based on the seismic wave input technique of hybrid wave field
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摘要: 基于人工边界子结构模型，提出一种利用混合波场实现近海场地中地震P波和SV波垂直输入的方法。该方法中用于波动输入的混合波场由计算模型两侧截断边界的自由波场和底面边界的入射波场构成，避免了不规则近海场地的自由波场求解。同时采用基于声流体单元的流固耦合算法模拟场地-海水动力相互作用，利用流体介质人工边界和黏弹性人工边界单元模拟无限流、固介质的辐射阻尼，建立了近海场地动力相互作用分析模型。将该模型与基于混合波场的地震波动输入方法相结合，提出了近海场地地震反应时域整体分析方法。数值算例表明，本文的计算模型和分析方法可以较为准确地实现地震波在近海场地中的输入问题，对于近海场地及海洋工程的地震反应分析具有良好的适用性。Abstract: The seismic response analysis of offshore site is the foundation for the seismic safety evaluation of ocean engineering. Seismic wave input is a key part of site seismic response analysis. However, the slope of the offshore site inclines to the ocean, which interacts with the seawater directly, leading to natural difficulties in solving the free wave field and thus provides a challenge to the existing seismic wave input methods based on the free wave fields. In this study, we adopted and improved the seismic wave input method based on the substructure of artificial boundaries, and constructed a hybrid input wave field with the free wave field on two lateral boundaries and the incident wave field on the bottom boundary of the calculation model. On that basis, an offshore site seismic wave input method for vertically incident P and SV waves is proposed. The proposed method avoids calculating the free wave field of irregular offshore sites, therefore it can simplify the seismic response analysis of offshore engineering considering characteristics of offshore site and the soil-structure interaction. Meanwhile, the fluid-structure coupling algorithm based on the acoustic fluid element is used to simulate the dynamic interaction between the offshore site and the seawater, and the fluid dynamic artificial boundary and the uniform viscoelastic artificial boundary element are used to simulate the radiation damping of the infinite fluid and solid medium. On that basis, the dynamic interaction model of offshore site is established. Combine this model with the proposed seismic wave input method based on the hybrid wave field, thereby an overall time-domain analysis method for the seismic response of offshore sites is established. Numerical examples show that the analysis method and numerical model proposed in this study can accurately realize the input of seismic waves in offshore sites, and have good applicability for seismic response analysis of offshore engineering.
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图 2 流体介质动力人工边界示意图
Figure 2. Schematic diagram of dynamic artificial boundaries of fluid medium
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图 3 基于混合波场的近海场地地震动输入方法
Figure 3. Seismic wave input method of offshore site based on hybrid wave field
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图 4 基于混合波场的近海场地地震波动输入方法实现步骤
（a） 利用子结构模型求解等效地震荷载；（b） 在近海场地模型中施加等效地震荷载
Figure 4. Implementation steps of seismic wave input method of offshore site based on hybrid wave field
（a） Solving equivalent seismic loads through the substructure model；（b） Applying equivalent seismic loads on the offshore site model
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图 7 SV波入射下近海场地的水平（a）和垂直（b）位移波形
Figure 7. Displacement waveforms in horizontal （a） and vertical （b） directions on offshore site under incident SV wave
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图 8 SV波入射下近海场地位移峰值放大系数的空间分布
Figure 8. Spatial distributions of peak displacement amplification coefficient on offshore site under incident SV wave
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图 9 P波入射下近海场地的水平（a）和垂直（b）位移波形
Figure 9. Displacement waveforms in horizontal （a） and vertical （b） directions on offshore site under incident P wave
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图 10 P波入射下近海场地位移峰值放大系数的空间分布
Figure 10. Spatial distributions of peak displacement amplification coefficient on offshore site under incident P wave
表 1 介质材料参数
Table 1 Material parameters of media
流体介质 固体介质 密度ρF
/（kg·m−3）声速cF
/（m·s−1）密度ρ
/（kg·m−3）剪切波波速cS
/（m·s−1）泊松比γ 1000 1435.27 2 000 200 0.25 
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