Modal analysis is a commonly used tool in design in an effort to reduce or avoid vibration in machine designs.

A dynamic loading on a machine will introduce vibrations. The excessive vibrations will cause noise, lead to fatigue damage of the components. Vibrations in a vehicle will make passengers uncomfortable and lead to tiredness.

Every structure has its own natural frequencies. When the excitation of a vibration on a machine coincide with a natural frequency of the system, the structure resonance with the excitation force which lead to excessive sometimes violent vibrations, which may lead to damage of the structure.

Modal analysis is used to identify natural frequencies and their vibration modes. Engineers are often required to design the system which do not have natural frequencies near the frequency of a excitation loads. Using an iterative process with modal analysis, the relevant component structure can be varied to shift the natural frequency higher or lower.

With Natural Frequency Analysis, mode shapes associated with the natural frequencies can be used to decide the suitable location of support and evaluate the significance of a particular vibration mode.

Animations can be produced to provide valuable insight into how the structure will behave when excited.

Rotordynamics analysis is special form of modal analysis. It is important when designing or troubleshooting rotating systems. Stress stiffening due to centrifugal force and gyroscopic effect can be considered in rotordynamics analysis. By modelling the rotating geometry and its dynamic characteristics, such as stiffness and damping, the critical speeds can be predicted. Design adjustments can then be made to avoid continuous running at those speeds.

Modal analysis is also a pre-requisite of harmonic response analysis and some further shock / vibration analysis, such as shock spectrum analysis and power density spectrum analysis (PSD) for random vibration.