柔性体的前几阶频率为负？

anjingzhang

柔性体的前几阶频率为负？这是怎么回事？

johnson_liao

Most of mechanical system satisties positive definite or semi positive definite.
So natural frequency is greater than zero or equal zero.
But It isn`t always right.

The following case can have negative values in natural frequency.

[A - ]X = 0



1. The matrix A doesn`t satisfy positive definite or semi positive definite.
2. When The Matrix A transforms one space into another space to solve equation of motion, the changed matrix A can include error.
    So Natural frequency can be negative value.
3. If the first frequency except 6 rigid body frequency has high frequency , the 6 rigid body frequency can have negative value in natural frequency nearby zero.
4. If the mechanical system has residual stress , it can have large negative value in natural frequency

JL

luckyli

把前几阶模态失效，不用管是正得还是负得