地震-波浪耦合作用下考虑相位差影响的深水桥墩动力响应分析

跨海深水桥墩往往受到不可忽视的波浪作用，在设计时需考虑波浪力。在地震作用下，桥墩附近海域的波浪场受到地震动水压力的干扰，波浪作用也受到影响，桥墩的动力响应需考虑两者的耦合作用。另一方面，地震起振时，墩底处地震波的相位可简单视为0，而桥墩处的波浪相位可能在0~2π之间变化，地震与波浪之间的相位差将直接影响波浪作用的大小，进而影响地震-波浪耦合作用。为了研究地震-波浪对深水桥墩的动力耦合作用，并考虑相位差对桥墩动力响应的影响，采用有限元分析软件ADINA建立的组合桥墩的精细化模型及桥墩附近水体的势流体单元模型，以模拟流固耦合作用；分别进行了地震单独作用下、波浪单独作用下以及地震-波浪耦合作用下桥墩的动力响应分析，并考虑了地震动、波高及地震与波浪之间相位差的不同。研究结果表明：地震与波浪间的耦合作用不能忽略，其对桥墩上总动水压力的影响在15%左右；地震与波浪之间的相位差对桥墩动力响应影响显著，当相位差在0~2π之间变化时，最大响应幅值变化接近54%；最不利相位差的取值与地震频率、桥墩水下基频和结构形式密切相关。利用MATLAB软件，提出了最不利相位差的计算方法及其适用条件；提出了耦合作用折算系数，以简化最大动力响应幅值的计算，推动实际工程应用。

Dynamic Response Analysis of Deep-water Piers Under Coupled Earthquake-wave Action Considering Phase Difference

Cross-sea deep-water piers are often subjected to wave action. Because this cannot be ignored, wave force should be considered in deep-water pier design. During an earthquake, the wave field near piers is disturbed by the dynamic water pressure, and the wave action is also affected. Therefore, coupling interaction between an earthquake and wave should be considered in dynamic response analysis. However, when an earthquake begins, the phase of the seismic excitation at the bottom of piers can be simply regarded as 0, whereas the phase of the wave on the surface of piers may vary from 0 to 2π. The phase difference between the earthquake and wave will directly affect the magnitude of wave action and in turn affect the coupled earthquake-wave action. Therefore, studying the dynamic coupling effect of earthquakes and waves on deep-water piers and considering the influence of phase difference on the dynamic responses of piers are of great significance. In this study, a refined model of composite piers and potential fluid element model of water bodies near piers were established using the finite element analysis software ADINA to simulate fluid-structure interaction. The dynamic responses of piers under independent earthquake action, independent wave action, and coupled earthquake-wave action were analyzed, and the differences in ground motion, wave height, and phase difference between the earthquake and wave were considered. Results show that the coupling interaction between an earthquake and wave must not be ignored and its influence on total hydrodynamic pressure is approximately 15%. The phase difference between an earthquake and wave has a significant effect on the dynamic responses of piers. When the phase difference varies between 0 and 2π, the maximum response amplitude varies nearly 54%. The most unfavorable phase difference is closely related to the frequency of earthquake excitation, natural frequency under water, and pier structural type. A method for identifying the most unfavorable phase difference using MATLAB software and a simplified method for calculating the maximum coupled dynamic responses of piers using a coupling coefficient were proposed, which allow for convenient application to actual engineering design.