大跨悬索桥时域颤振有限元精细化分析

Refined finite element analysis of time-domain flutter for long-span suspension bridges

为准确揭示大跨悬索桥的颤振稳定性能,采用了平均风荷载与气动自激力一体化的气动力模型,并基于ANSYS有限元软件实现了桥梁的时域颤振分析,评估了平均风效应、几何非线性以及时域计算采取的时间步长对桥梁颤振及后颤振性能的影响。基于上述研究思路,针对某大跨悬索桥的节段模型与全桥模型分别进行了时域颤振分析。数值结果表明:平均风效应会对桥梁的颤振稳定性能产生显著的影响,忽略主梁的平均升力与升力矩将会高估桥梁的颤振稳定性能;主梁的平均阻力促使结构运动的振幅在起始的一段时间内有所增大,但最终逐渐衰减至零;时域计算设置的时间步长不宜偏大,较大的时间步长将使桥梁的颤振临界风速明显偏大;几何非线性效应对桥梁颤振临界风速的影响甚微,但会显著影响桥梁颤振后结构的运动状态,即考虑非线性效应后桥梁的颤振最终演变成限幅的软颤振。

For the sake of investigating the flutter stability performance of suspension bridges accurately,an aerodynamic force model in which mean wind loads and self-excited forces were integrated was adopted.Based on ANSYS finite element software,time-domain flutter analysis for a long-span suspension bridge with a main-span of 1660 m was conducted,the effect of mean wind loads,geometric nonlinearity and the time step taken for the time domain calculation on the flutter and post-flutter performance of bridges were evaluated.According to the presented method,time-domain flutter analysis for the sectional and whole bridge model of a long-span suspension bridge was performed respectively to characterize flutter performance.Numerical results show that the mean wind effects have significant influence on flutter performance of long-span suspension bridges.Neglecting the mean lift and lift moment would overestimate the critical wind speed of flutter greatly.The mean wind drag would cause that the vibration amplitude increases in the initial period of motion,but eventually attenuates to zero.The time step set in time-domain simulation must be reasonable,larger time step would result in a larger critical wind speed of flutter.Furthermore,geometric nonlinearities have inappreciable influence on the flutter threshold,but significant influence on the motion state of post flutter.As we all know,the linear theory of flutter reveals that bridges will experience a terrible divergence when wind speeds exceed the critical value,but a soft flutter with smaller amplitude is the final motion state when geometric nonlinearities are involved in the flutter analysis.