关于模态综合法的注记

本文以两端固定直角梁为例，探讨模态综合法应用于计算高阶固有频率。单纯使用前2阶约束振型为假设振型时，可能出现频率遗漏而不能计算第2阶固有频率。
假设振型同时取前2阶模态振型和前2阶约束振型，可以计算前3阶固有频率；假设振型取前4阶模态振型和前4阶约束振型，可以计算前5阶固有频率，相对误差小于5%。

A NOTE ON THE METHOD OF MODE SYNTHESIS

A right-angle beam with fixed both ends is treated as an example to investigate the application of the mode synthesis method for calculation of higher-order natural frequencies. If the first 2 constrained mode shapes serve as the assumed mode shapes, some frequencies may miss and thus the second-order natural frequency cannot be calculated.
If the assumed mode shapes include both the first 2 modal shapes and the first 2 constrained mode shapes, the first 3 natural frequencies can be calculated; and the assumed mode shapes include both the first 4 modal modes and the first 4 constrained mode shapes, the first 5 order natural frequencies can be calculated with the relative errors less than 5%.