Modal Analysis

What Is Modal Analysis?

Modal analysis is a technique used to study the dynamic behavior of structures and systems. It helps engineers understand the natural modes of vibration and response to external forces. This technique enables engineers to make systems safer, more efficient, and more comfortable.

Engineers often use experimental modal analysis to measure the dynamic response of a structure they’re designing. Modal testing involves exciting the structure with known input signals and measuring its response using sensors. One experimental technique is impact testing, in which a structure is excited by an impact hammer and the resulting vibrations are captured by accelerometers. The collected data is then processed to extract the natural frequencies of the system.

  On the left, a flexible wing aircraft with a 3-meter wingspan. On the right, Bode plots of the experimental modal analysis.

MATLAB plot for two frequency-response functions of a flexible flying wing aircraft. The peaks visible in the frequency-response diagram identify some of the natural frequencies of the wing structure.

With MATLAB®, you can perform experimental modal analysis by estimating frequency-response function, natural frequencies, damping ratios, and mode shapes.

In modal analysis, natural frequencies represent the frequencies at which a structure or system naturally vibrates when disturbed. Mode shapes describe the spatial distribution of displacements and deformations associated with these natural frequencies. Signal Processing Toolbox™ provides functions for determining frequency responses and mode shapes from experimental data.

Industrial Applications of Modal Analysis

Modal analysis is a key part of the development process for many products and industries:

  • Aerospace: Studying the interaction between aerodynamic forces and structural dynamics helps ensure stability and avoid flutter and other phenomena. Ongoing analysis of components can predict and detect issues, increasing reliability and safety.
  • Automotive: Reducing noise, vibration, and harshness improves ride feel, vehicle comfort, and passenger experience.
  • Construction: Natural phenomena such as wind and human activity such as walking and driving can excite large structures, such as bridges and skyscrapers, to the point of failure. Designing structures with proper damping is essential to their safety.
  • Consumer appliances: Proper vibration control keeps machines from moving and creating excessive noise.

See also: signal processing, System Identification Toolbox™, frequency response

Signal Processing Onramp

An interactive introduction to practical signal processing methods for spectral analysis.