What is modal analysis?

Modal analysis is the procedure of determining a structure's dynamic characteristics; namely, resonant frequencies, damping values, and the associated pattern of structural deformation called mode shapes.

This analysis is performed while the test article is not running. A series of frequency response functions are measured at various geometric locations using either an instrumented impact hammer or an electro-dynamic shaker to supply an input force. Responses are measured in the X, Y, and Z directions with motion sensors, typically accelerometers. A frequency response function is the response per unit force over the frequency range of interest.

Modal analysis software curve fits these data into a matrix and determines the unique mode shape associated with each of the resonances. Animated mode shapes are then shown on a computer screen.

Testing data can be further input to structural modification software to investigate the effectiveness of potential corrective actions prior to actually implementing such a modification.

If vibration troubleshooting reveals that the problem is due to forced vibration rather than resonant enhancement, an operating deflection shape analysis is performed. This analysis is mathematically similar to modal analysis and also results in the display of animated structural deformation.

STC provides modal analysis services. Please contact us today for more information.