地震动频谱特性对罐液体系地震响应的影响分析

基于拉格朗日方法建立考虑流固耦合效应的位移格式的运动方程,运用ANSYS建立立式拱顶储罐的三维有限元模型,分别选取短周期成分丰富(S1)、普通地震波(S2)和长周期成分丰富(S3)的三条天然地震波,分析了地震波频谱特性对液体晃动、罐底剪力、弯矩以及罐壁响应等结果的影响。研究表明,罐液体系自振频率存在两个明显频段,即液体晃动低频率段(长周期)和罐液耦联振动高频率段(短周期)。罐液体系的动力响应对地震波频谱特性的影响较为敏感。S3地震波卓越周期最接近罐液晃动周期,引起液面大幅度晃动,较其他增长4倍。罐液耦联振动对轴向应力响应影响最大,S1地震波卓越周期最接近罐液耦联振动周期,其引起罐底轴向压应力超过规范许用应力,出现明显"象足"屈曲变形。罐底剪力和弯矩受耦联振动影响最大,而液体晃动对其影响较小,地震激励仅引起液体表面少量单元产生对流运动。

The Effect of Earthquake Frequency Characteristics on the Seismic Behavior of Tank-liquid System

Based on the Lagrangian approximation method, the motion equation of the displacement scheme considering the liquid-structure interaction is established, and a three-dimensional (3-D) finite element model of the vertical tank is constructed by using ANSYS. There natural seismic waves with rich short-period content (S1), rich moderate-period content (S2) and rich long-period content (S3) are selected as inputs, and the effect of seismic wave spectrum characteristics on the simulated results of liquid sloshing, shear force and bending moment of the base, and tank wall stresses are analyzed. The results show that there are two obvious frequency bands in the natural frequency of the tank-liquid system, i.e., the low frequency band (long period) of liquid convective motion, and the high frequency (short period) of coupling vibration of the tank-liquid system. The predominant period of the S3 seismic wave is closest to that of the liquid convective motion, therefore induces obvious liquid sloshing, which is 4 times higher than that under the other two seismic waves. The effect of tank-liquid coupling vibration on the axial stress response is the greatest. The predominant period of the S1 seismic wave is closest to the tank-coupled vibration period, therefore induces the largest axial compressive stress of the tank, which has exceeded the allowable stress and results in significant "elephant-foot" buckling deformation. The shear force and bending moment of the tank base are most vulnerable to the influence of the tank-liquid coupling vibration, and the effect of liquid sloshing is very small. The seismic excitation only causes a convective motion of small amount of elements near the liquid surface. It is concluded that the dynamic behaviour of the fluid-tank system is highly sensitive to frequency characteristics of the earthquake record.