基于模态综合和移频方法的中频段模态计算

Mid-frequency range modes computation based on component mode synthesis and frequency shifting

采用基于特征约束模态降阶的模态综合方法计算结构中频段振动特性时,针对低阶特征约束模态不能截断的问题,引入了移频方法对子结构动力学方程进行变换,并推导了移频后低阶特征约束模态与系统中频段模态的关系,结果表明:采用移频方法后,低阶特征约束模态可以截断。采用该方法计算了某白车身有限元模型160～190Hz频段内的振动特性,结果表明:采用移频方法后,保留的特征约束模态阶数较少,系统振动特性的计算时间较短,说明该方法有助于提高复杂结构中频段振动特性的计算效率。

The component mode synthesis method was used to compute structural mid-frequency range modes, and the characteristic constraint mode was used for reducing interface DOFs. The frequency shifting technique was induced to cut off lower frequency characteristic constraint modes. The influence of lower frequency characteristic constraint modes on structural mid-frequency range modes was studied. The results showed that before frequency shifting, the lower frequency characteristic constraint modes have an important influence on the mid-frequency range modes of a system, the former can not be cut off; but after frequency shifting, the former can be cut off. The frequency shifting technique was used to compute a prototype vehicle modes in a frequency range of 250 -300 Hz. The results showed that the lower frequency characteristic constraint modes can be cut off after frequency shifting, the computation needs less time; it means this technique can improve the computational efficiency for mid-frequency range modes of a complex structure.