What does "Modal Analysis" mean?

In Experimental Modal Analysis (EMA), beneath the resonance frequencies and damping coefficients, also the geometric shapes of the movements corresponding to the resonance frequencies are determined. Each resonance frequency is uniquely related to a certain geometric form of movement, the so-called Mode Shape. A mode shape together with the respective resonance frequency is called a Mode. Knowledge about the critical frequencies in the component's frequency response together with the related mode shapes is the basis for constructive measures in order to change the vibration behaviour in a desired way. Also it can be determined to what extent a certain resonance is responsible for noise generation. If a physical prototype of a device is already available, Experimental Modal Analysis is in most cases at far more cost-efficient and much faster than a dynamical finite element calculation. Furthermore, as the results are based on measurements they are highly trustworthy.

How does that work?

Experimental Modal Analysis is an extension to vibration testing: A device is excited with a well-defined and suitable excitation signal covering the frequency range of interest. At the points of a measurement grid, which represents the geometry of the device under test, the frequency response functions are recorded in one or more directions. By evaluating the complete set of frequency responses, the mode shapes can be determined. They are visualized using the mesurement grid. The two pictures above show the preparation of an airship rotorblade for an EMA. One can clearly see the reflection pads for the laser-vibrometer at the corners of the measurement grids.