基于流固耦合模型的U型渡槽模态分析及验证

为提高渡槽结构工作模态特征的准确度，结合附加质量法原理和流固耦合（fluid solid interaction，FSI）系统理论，以景电工程输水渡槽为研究对象，建立不同形式的固-液耦合模型，对其进行工作模态数值分析，并将数值分析结果与采用小波阈值-经验模态分解联合滤波的希尔伯特-黄变换法（hilbert-huang transform，HHT）实测提取的频率值进行对比。结果表明：考虑FSI系统耦合模型的结果与HHT辨识结果吻合的较好，最大误差值为4.59%，比附加质量模型最大误差小5.97百分点，同阶次频率误差均比附加质量模型小，且弥补了附加质量模型出现的模态缺失现象。可见考虑FSI系统耦合模型的计算结果在模拟阶数和精度方面都优于附加质量模型，能准确反映渡槽结构的工作特性，可用在渡槽结构动力特性分析中，亦可作为后续渡槽结构损伤诊断研究的基准有限元模型。

Modal analysis and validation of U-shaped aqueducts based on fluid solid interaction model

The key point to analyze dynamic characteristic of aqueduct is the coupling effect caused by the interaction between water and aqueduct. In order to simulate the coupling effect effectively and improve the accuracy of working modal characteristics, Jingdian project in Gansu (103.45-104.04o E, 37.26-37.36oN) was selected as the research object. Added masses model and fluid solid interaction (FSI) system coupling model were built under different forms of water coupling. First, different coupling models were calculated and analyzed under the conditions of different water levels by using different modal extraction methods based on different solving principles,obtaining graphics of principal frequency and vibration shapes of aqueduct structure. Then the same span aqueduct was tested to get the dynamic displacement response under operational excitation conditions, and the tested response signals were de-noised by wavelet threshold and empirical mode decomposition (EMD) to extract effective vibration information. Thus the structural natural frequency could be identified by hilbert–huang transform (HHT) modal parameter identification method. Finally, the modal frequency in normal water level condition of added mass model and the FSI system coupling model was compared with frequency measured by HHT method. The results showed that the calculation results of different coupling models had a certain degree of decline compared with the results under the anhydrous condition, and the largest amplitude of fundamental frequency was 15.03%. So the interaction of water and aqueduct had a greater impact on natural frequency of aqueduct structure and could not be ignored in structural dynamic characteristics analysis. The frequency error percentage between added mass coupling modal calculation results and identification results was 3.23%-10.56%, while the simulation results of the FSI system coupling model suited well with the HHT identification results, and the effective frequency error ranged from 0.18%to 4.59%. The maximum frequency error of FSI system coupling model was 5.97%smaller than the added masses model. What’s more, the frequency error of same order was smaller than the added massed model, and it could offset the modal lack of the added massed model. The comparison results of finite element simulation and modal identification showed that the HHT modal identification method was able to extract the modal parameters of the aqueduct, which had high identification precision. Coupling model of FSI system considering the coupling effect of solid-liquid was superior to added masses model in simulation order and precision and could reflect the real characteristics of aqueduct more comprehensively and accurately. Meanwhile, the FSI system coupling model could be applied in the dynamic characteristics analysis of other kinds of aqueduct and could also provide guidance for the selection of dynamic model while evaluating health condition of aqueduct structure.