Introduction

Modal analysis computes the vibration characteristics of a structure and often is the first step to a more detailed dynamic analysis such as a random vibration or transient simulation. A modal analysis assumes undamped, free vibration to compute natural frequencies and mode shapes of a structure, which shows how a structure will vibrate for a specific natural frequency.

Identifying natural frequencies and mode shapes allows engineers to avoid exciting structural resonances by modifying designs to change the stiffness and/or the mass of the structure to shift the natural frequency away from the frequency of a dynamic excitation. As a rule, increasing the stiffness or reducing the mass will tend to increase the natural frequency, whereas reducing the stiffness or increasing the mass will tend to reduce the natural frequency.