基于拉格朗日方法建立考虑流固耦合效应的模态方程，利用ANSYS软件建立包含土层自由场地、桩基承台场地模型，刚性地基空罐、满罐、以及考虑土结相互作用的空罐和满罐等六个数值模型，得到工程场地的自振频率以及土体对罐体系统动力特性的影响。研究了各种模型自振频率和振型参与系数随阶数的分布情况。结果表明，桩基承台的存在使得场地第一阶振动频率有所增大。罐内液体的晃动频率不受土结相互作用的影响。考虑土结相互作用之后，出现了液体对流晃动频率、土-罐-液整体振动频率和罐液耦联振动频率等低、中、高三个振动频率，且前两阶频率罐液耦联振动频率有所减小，也更为密集。应考虑土结相互作用的影响，否则将会高估罐液耦联振动频率。最后运用子结构理论对考虑土结相互作用引起动力特性变化进行了解释，并给出了动力计算中考虑土结相互作用时罐液体系瑞利阻尼系数的选取建议。研究结论可为考虑土结相互作用储罐的地震响应分析提供参考。
Abstract
Based on Lagrange method, a modal equation of a storage tank considering fluid-solid coupled effect was established. 6 numerical models including soil free site, pile foundation platform model, rigid foundation empty tank, rigid foundation full tank as well as empty tank and full tank considering soil-structure interaction (SSI) were established with software ANSYS. Natural frequencies of the site and influences of soil-structure interaction on dynamic characteristics of a tank system were obtained using computation results of 6 numerical models. The distribution of natural frequencies and each modal shape’s participation coefficients of various models were studied. The results showed that the existence of pile foundation platform makes the site’s first order natural frequency increase; SSI does not affect the slosh frequency of liquid in tank; after considering SSI, 3 types vibration frequencies including liquid convective sloshing frequencies, soil-tank-liquid whole vibration frequencies and tank-liquid coupled vibration frequencies appear, the first two order tank-liquid coupled vibration frequencies decrease and are more dense; SSI effect should be considered otherwise tank-liquid coupled vibration frequencies are over-estimated. Finally, the sub-structure theory was used to explain changes of dynamic characteristics of a tank system due to considering SSI, the suggestion for choosing Rayleigh damping coefficient of a tank-liquid system considering SSI was given in dynamic calculation. The study conclusions provided a reference for seismic response analysis of storage tank systems considering SSI.
关键词
储罐 /
模态分析 /
动力特性 /
土结相互作用 /
罐液耦合
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Key words
storage tank /
modal analysis /
dynamic characteristics /
SSI /
tank-liquid coupled vibration
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